JP7364485B2 - Magnetic field measurement device, magnetic field measurement method, and magnetic field measurement program - Google Patents

Description

The present invention relates to a magnetic field measuring device, a magnetic field measuring method, and a magnetic field measuring program.

Conventionally, a magnetic field measurement device is known that measures the magnetic field emitted from the head or chest of a subject using a sensor platform board in which a plurality of tunnel magneto-resistance (TMR) elements are arranged in an array ( For example, see Patent Document 1).
[Prior art documents]
[Patent document]
[Patent Document 1] Japanese Patent Application Publication No. 2012-152514

In conventional magnetic field measuring devices, a pair of magnetic sensing elements are stacked in the magnetic field detection direction, and while the magnitude of the measurement result between the pair of magnetic sensing elements is the same in response to a disturbance magnetic field, the magnetic field to be measured is In contrast, the magnetic field to be measured was measured by suppressing the disturbance magnetic field based on the principle that the magnitude of the measurement result between a pair of magnetic detection elements is different. However, it is possible to measure magnetic fields with higher precision, for example by measuring the weak biomagnetic field (referred to as "magnetocardia") generated by the electrical activity of the heart to more precisely examine the state of the heart. desired.

In order to solve the above problems, a first aspect of the present invention provides a magnetic field measuring device. The magnetic field measurement device has a curved surface shape curved in at least one direction, and each device includes a magnetic sensor, an output section that outputs an output signal, and an input magnetic field detected by the magnetic sensor with a size corresponding to the output signal. It is configured by arranging multiple magnetic sensor cells three-dimensionally at lattice points included in a curved surface shape, and has a magnetic field generating section that generates a feedback magnetic field that reduces A magnetic sensor array may be provided. The magnetic field measurement device may include a measurement data acquisition unit that acquires measurement data measured by the magnetic sensor array. The magnetic field measuring device converts the spatial distribution of the input magnetic field indicated by the measurement data into a vector having as each signal component a signal output by each magnetic sensor when a magnetic field with a spatial distribution of an orthonormal function is detected by a magnetic sensor array. A signal space separation unit may be provided that separates the signals using the signals as basis vectors. The magnetic field measuring device calculates the sensor error in the magnetic sensor based on the separation error when the spatial distribution of the calibration magnetic field generated from the magnetic field generation unit of at least one of the plurality of magnetic sensor cells is separated into signals. It may include a calibration section that performs calibration.

The output section may output an output signal according to a feedback current that the magnetic field generation section sends to generate the feedback magnetic field.

Each of the magnetic sensors includes a magnetoresistive element and two magnetic convergence plates arranged at both ends of the magnetoresistive element, and the magnetoresistive element may be arranged at a position sandwiched between the two magnetic convergence plates.

The magnetic field generation unit may include a feedback coil wound along the axial direction of the magnetic field to be detected by the magnetic sensor so as to surround the magnetoresistive element and the two magnetic convergence plates.

The calibration unit may calibrate sensor errors in the magnetic sensor based on respective separation errors when at least one magnetic sensor cell is sequentially switched.

The magnetic sensor array is configured by arranging a plurality of magnetic sensor cells three-dimensionally in an arc shape when viewed in cross section, and the calibration unit sequentially switches at least one magnetic sensor cell across the plurality of magnetic sensor cells forming an inner arc. The sensor error in the magnetic sensor may be calibrated based on the respective separation error in the magnetic sensor.

At least one magnetic sensor cell may further include a switching unit that switches whether the magnetic field generation unit generates a feedback magnetic field or a calibration magnetic field.

When separating the spatial distribution of the calibration magnetic field into signals, the signal space separation unit may use a position where a magnetic field generation unit included in at least one magnetic sensor cell is arranged as an origin of coordinates in calculation.

The calibration unit may calibrate sensor errors by changing basis vectors.

The calibration unit may optimize the basis vectors to minimize the separation error.

The magnetic field measuring device may further include a synchronous detection unit that detects the calibration magnetic field, which is an alternating magnetic field, using a signal having a frequency of the alternating magnetic field.

The frequency of the alternating magnetic field may be higher than the frequency band of the magnetic field to be measured.

In a second aspect of the present invention, a magnetic field measurement method is provided. The magnetic field measurement method has a curved surface shape curved in at least one direction, each of which includes a magnetic sensor, an output section that outputs an output signal, and a magnetic field that outputs an input magnetic field detected by the magnetic sensor with a size corresponding to the output signal. It is configured by arranging a plurality of magnetic sensor cells having a magnetic field generating section that generates a feedback magnetic field to reduce the magnetic field in three dimensions so as to be arranged at lattice points included in a curved surface shape, and is capable of detecting input magnetic fields in three axial directions. The method may include acquiring measurement data measured by the magnetic sensor array. The magnetic field measurement method calculates the spatial distribution of the input magnetic field indicated by the measurement data using a vector whose signal components are the signals output by each magnetic sensor when a magnetic sensor array detects a magnetic field with a spatial distribution of an orthonormal function. The method may include signal separation using signals as basis vectors. The magnetic field measurement method may include generating a calibration magnetic field from a magnetic field generating section included in at least one magnetic sensor cell among the plurality of magnetic sensor cells. The magnetic field measurement method may include calibrating a sensor error in the magnetic sensor based on a separation error when the spatial distribution of the calibration magnetic field is separated into signals.

In a third aspect of the present invention, a magnetic field measurement program is provided. The magnetic field measurement program may be executed by a computer. The magnetic field measurement program includes a computer having a curved surface shape curved in at least one direction, each having a magnetic sensor, an output part that outputs an output signal, and a size corresponding to the output signal detected by the magnetic sensor. It is configured by arranging a plurality of magnetic sensor cells three-dimensionally so as to be arranged at lattice points included in a curved surface shape, and has a magnetic field generating section that generates a feedback magnetic field that reduces an input magnetic field, and generates an input magnetic field in three axial directions. It may function as a measurement data acquisition unit that acquires measurement data measured by a detectable magnetic sensor array. The magnetic field measurement program causes the computer to calculate the spatial distribution of the input magnetic field indicated by the measurement data, and calculate the signals output by each magnetic sensor when the magnetic sensor array detects a magnetic field with a spatial distribution of an orthonormal function, for each signal component. It may function as a signal space separation unit that separates signals using a vector signal having as a basis vector. The magnetic field measurement program causes a computer to detect signals in a magnetic sensor based on a separation error when the spatial distribution of a calibration magnetic field generated from a magnetic field generation unit of at least one of a plurality of magnetic sensor cells is separated. It may function as a calibration section that calibrates sensor errors.

In a fourth aspect of the present invention, a magnetic field measuring device is provided. Each of the magnetic field measurement devices includes a magnetic sensor, an output section that outputs an output signal, and a magnetic field generation section that generates a feedback magnetic field that reduces the input magnetic field detected by the magnetic sensor and has a size according to the output signal. A magnetic sensor array may be provided, which is configured by arranging a plurality of magnetic sensor cells in three dimensions and is capable of detecting input magnetic fields in three axial directions. The magnetic field measurement device may include a measurement data acquisition unit that acquires measurement data measured by the magnetic sensor array. The magnetic field measuring device converts the spatial distribution of the input magnetic field indicated by the measurement data into a vector having as each signal component a signal output by each magnetic sensor when a magnetic field with a spatial distribution of an orthonormal function is detected by a magnetic sensor array. A signal space separation unit may be provided that separates the signals using the signals as basis vectors. The magnetic field measuring device calculates the sensor error in the magnetic sensor based on the separation error when the spatial distribution of the calibration magnetic field generated from the magnetic field generation unit of at least one of the plurality of magnetic sensor cells is separated into signals. It may include a calibration section that performs calibration.

Note that the above summary of the invention does not list all the necessary features of the invention. Furthermore, subcombinations of these features may also constitute inventions.

1 shows a configuration of a magnetic field measuring device 10 according to this embodiment. 1 shows a configuration of a magnetic sensor unit 110 according to this embodiment. The configuration of a magnetic sensor cell 220 in a magnetic sensor array 210 according to this embodiment is shown. An example of input/output characteristics of a magnetic sensor having a magnetoresistive element according to the present embodiment is shown. A configuration example of a sensor unit 300 according to the present embodiment is shown. An example of input/output characteristics of the sensor section 300 according to the present embodiment is shown. A configuration example of a magnetic sensor 520 according to this embodiment is shown. The magnetic flux distribution when a feedback magnetic field is generated in the magnetic sensor 520 according to this embodiment is shown. An example of the arrangement of a plurality of magnetic sensor cells 220 in the magnetic sensor array 210 according to the present embodiment is shown. The structure of the sensor part 300inside which the inner magnetic sensor cell 220 in the magnetic sensor array 210 based on this embodiment has is shown. The configuration of a magnetic sensor array 210, a sensor data collection section 230, and a sensor data processing section 1100 according to this embodiment is shown. 10 shows a flow in which the magnetic field measuring device 10 according to the present embodiment separates signals of the spatial distribution of a magnetic field. A signal space separation operation using an ideal basis vector [A B] _Ideal is illustrated geometrically when the magnetic sensor array 210 is ideally made. A signal space separation operation using an ideal basis vector [A B] _Ideal is geometrically illustrated when the magnetic sensor array 210 is made with a sensor error. 10 shows a flow in which the magnetic field measuring device 10 according to the present embodiment acquires a sensor array signal Φ(i, j, 1) for calibration. 3 shows a flow in which the magnetic field measuring device 10 according to the present embodiment performs calibration. A signal space separation operation using the calibrated basis vector [A B] _Calib is geometrically illustrated when the magnetic sensor array 210 is made with a sensor error. 22 illustrates an example computer 2200 in which aspects of the invention may be implemented, in whole or in part.

Hereinafter, the present invention will be described through embodiments of the invention, but the following embodiments do not limit the invention according to the claims. Furthermore, not all combinations of features described in the embodiments are essential to the solution of the invention.

FIG. 1 shows the configuration of a magnetic field measuring device 10 according to this embodiment. When measuring a target magnetic field using a magnetic sensor, the magnetic field measurement device 10 generates a calibration magnetic field from a magnetic field generation unit included in at least one of the plurality of magnetic sensor cells in the magnetic sensor array, and Calibration Errors in the magnetic sensor are calibrated based on the results of measuring the magnetic field. In this embodiment, an example will be described in which the magnetic field measuring device 10 is a magnetocardial measuring device that measures magnetocardial magnetism, which is a magnetic field generated by the electrical activity of a human heart. However, it is not limited to this. The magnetic field measuring device 10 may be used to measure the magnetocardial field of a living body other than a human, or may be used to measure a biomagnetic field other than the magnetocardial field, such as a brain magnetic field. Further, the magnetic field measuring device 10 may be used for magnetic flaw detection inspection for detecting flaws on the surface and surface of steel materials and welded parts.

The magnetic field measuring device 10 includes a main body section 100 and an information processing section 150. The main body section 100 is a component for sensing the subject's magnetocardial field, and includes a magnetic sensor unit 110, a head 120, a drive section 125, a base section 130, and a pole section 140.

The magnetic sensor unit 110 is placed at a position facing the heart in the subject's chest during magnetocardial measurement, and senses the subject's magnetism. The head 120 supports the magnetic sensor unit 110 and makes the magnetic sensor unit 110 face the subject when measuring cardiac magnetism. The drive unit 125 is provided between the magnetic sensor unit 110 and the head 120, and changes the orientation of the magnetic sensor unit 110 with respect to the head 120 when performing calibration. The drive unit 125 according to the present embodiment includes a first actuator that can rotate the magnetic sensor unit 110 360 degrees around the Z-axis in the figure, and an axis perpendicular to the Z-axis (in the state in the figure, the X-axis ), and the azimuth and zenith angle of the magnetic sensor unit 110 are changed using these actuators. As shown as a drive unit 125 in the figure, the drive unit 125 has a Y-shape when viewed from the Y-axis direction in the figure, and the second actuator moves the magnetic sensor unit 110 360 degrees around the X-axis in the figure. It can be rotated.

The base portion 130 is a base that supports other components, and in this embodiment serves as a platform on which a subject stands during magnetocardial measurement. The pole section 140 supports the head 120 at the level of the subject's chest. The pole section 140 may be expandable and retractable in the vertical direction to adjust the height of the magnetic sensor unit 110 to the height of the subject's chest.

The information processing section 150 is a component for processing data measured by the main body section 100 and outputting the data by displaying, printing, or the like. The information processing unit 150 may be a computer such as a PC (personal computer), a tablet computer, a smartphone, a workstation, a server computer, or a general-purpose computer, or may be a computer system in which a plurality of computers are connected. Alternatively, the information processing unit 150 may be a dedicated computer designed for information processing of magnetic field measurements, or may be dedicated hardware realized by a dedicated circuit.

FIG. 2 shows the configuration of the magnetic sensor unit 110 according to this embodiment. The magnetic sensor unit 110 includes a magnetic sensor array 210 and a sensor data collection section 230. The magnetic sensor array 210 has a plurality of magnetic sensor cells 220 and can detect input magnetic fields in three axial directions. This figure shows a magnetic sensor array 210 having a plurality of magnetic sensor cells 220 in each of the X, Y, and Z directions (for example, 8 in the X direction, 8 in the Y direction, and 2 in the Z direction, 128 in total). The case is shown in which magnetic sensor cells 220) are arranged.

The sensor data collection unit 230 is electrically connected to the plurality of magnetic sensor cells 220 included in the magnetic sensor array 210 (not shown), collects sensor data (detection signals) from the plurality of magnetic sensor cells 220, and collects information. It is supplied to the processing section 150.

FIG. 3 shows the configuration of the magnetic sensor cells 220 in the magnetic sensor array 210 according to this embodiment. Each of the plurality of magnetic sensor cells 220 has at least one sensor section 300 each having a magnetoresistive element. In this figure, an example is shown in which each of the plurality of magnetic sensor cells 220 has three sensor sections 300x to 300z (collectively referred to as "sensor sections 300") and can detect input magnetic fields in three axial directions. Shown as However, each of the plurality of magnetic sensor cells 220 is not limited to having the three sensor sections 300x to 300z, and as long as at least a portion of the magnetic sensor array 210 can detect input magnetic fields in three axial directions. good. At this time, as will be described later, when each spherical harmonic is spatially sampled by the magnetic sensor array 210, it is necessary to detect the dependence on the spatial frequency related to the angular momentum in the magnetic field. Therefore, it is preferable that each sensor section 300 in the magnetic sensor array 210 is arranged as evenly as possible at least in the azimuth angle direction and the zenith angle direction. For the same reason, the magnetically sensitive axes of each sensor in the magnetic sensor array 210 are preferably arranged as evenly as possible at least in the azimuth angle direction and the zenith angle direction. The sensor unit 300x is arranged along the X-axis direction and can detect a magnetic field in the X-axis direction. Further, the sensor unit 300y is arranged along the Y-axis direction and can detect a magnetic field in the Y-axis direction. Further, the sensor unit 300z is arranged along the Z-axis direction and can detect a magnetic field in the Z-axis direction. As shown in the enlarged view indicated by the dashed line in this figure, in this embodiment, each sensor section 300 has magnetic convergence plates arranged at both ends of the magnetoresistive element. Therefore, each sensor unit 300 samples the spatial distribution of the magnetic field using a magnetoresistive element placed in a narrow position sandwiched between magnetic convergence plates, thereby clarifying the sampling point in space in each axial direction. be able to. Details of the configuration of each sensor section 300 will be described later.

The plurality of magnetic sensor cells 220 are arranged at equal intervals of Δx along the X-axis direction, Δy along the Y-axis direction, and Δz along the Z-axis direction. The position of each magnetic sensor cell 220 in the magnetic sensor array 210 is represented by a set [i, j, k] of a position i in the X direction, a position j in the Y direction, and a position k in the Z direction. Here, i is an integer satisfying 1≦i≦Nx (Nx indicates the number of magnetic sensor cells 220 arranged in the X direction), and j is an integer satisfying 1≦j≦Ny (Ny is an integer satisfying 1≦j≦Ny). (indicates the number of magnetic sensor cells 220 arranged in the Z direction), k is an integer satisfying 1≦k≦Nz (Nz indicates the number of magnetic sensor cells 220 arranged in the Z direction). In addition, in the above description, the case where the plurality of magnetic sensor cells 220 are arranged at equal intervals along each axis direction is shown as an example. However, it is not limited to this. The plurality of magnetic sensor cells 220 may be arranged at different intervals in at least one of the X-axis direction, the Y-axis direction, and the Z-axis direction, for example.

In this figure, the three axial directions of the magnetic fields detected by the sensor sections 300x, 300y, and 300z are the same as the three-dimensional direction in which the magnetic sensor cells 220 are arranged. This makes it easy to understand each component of the distribution of the measured magnetic field. Furthermore, the three sensor sections 300x, 300y, and 300z are provided within each magnetic sensor cell 220 so that they do not overlap with each other when viewed from each of the three-dimensional directions in which the magnetic sensor cells 220 are arranged, and are provided between the three sensor sections 300. It is preferable that one end is provided on the gap side, and the other end extends in each of the three axial directions so as to be away from the gap. As an example, in this figure, a gap is provided at the lower left corner of the magnetic sensor cell 220 when viewed from the front, and the sensor sections 300x, 300y, and 300z are provided such that one end is in contact with the gap, and the other end is in contact with the gap. An example is shown in which they are arranged to extend in the X-axis, Y-axis, and Z-axis directions so as to be away from the gap. In this figure, sensor sections 300x, 300y, and 300z are arranged along three mutually perpendicular sides from one corner of a cubic magnetic sensor cell 220, and a gap is provided at the one corner. However, the three axial directions of the magnetic field to be detected and the three-dimensional direction in which the magnetic sensor cells 220 are arranged may be different. For example, instead of the X-axis, Y-axis, and Z-axis as the three axial directions of the magnetic field to be detected, the r-axis, θ-axis, and φ-axis of a polar coordinate system may be used. Moreover, as the three-dimensional direction in which the magnetic sensor cells 220 are arranged, the r-axis, theta-axis, and the phi-axis of a polar coordinate system may be used instead of the x-axis, y-axis, and z-axis. When the three-axis directions of the magnetic field to be detected are different from the three-dimensional direction in which the magnetic sensor cells 220 are arranged, there are no restrictions on the arrangement of the sensor section 300 within the magnetic sensor cell 220 or the arrangement direction of the magnetic sensor cells 220, and the magnetic field is The degree of freedom in designing the sensor array 210 can be increased. Furthermore, the sensor sections 300x, 300y, and 300z may be provided at the corners of the magnetic sensor cell 220 without providing gaps. In this case, the magnetic sensor cell 220 can be configured to be small, and therefore the magnetic sensor array 210 having such a plurality of magnetic sensor cells 220 can be downsized.

FIG. 4 shows an example of input/output characteristics of a magnetic sensor having a magnetoresistive element according to this embodiment. In this figure, the horizontal axis indicates the magnitude B of the input magnetic field input to the magnetic sensor, and the vertical axis indicates the magnitude V_xMR0 of the detection signal of the magnetic sensor. The magnetic sensor includes, for example, a giant magneto-resistance (GMR) element or a tunnel magneto-resistance (TMR) element, and detects the magnitude of a magnetic field in a predetermined uniaxial direction. .

Such a magnetic sensor has high magnetic sensitivity, which is the slope of the detection signal V_xMR0 with respect to the input magnetic field B, and can detect a minute magnetic field of about 10 pT. On the other hand, in the magnetic sensor, the detection signal V_xMR0 is saturated when the absolute value of the input magnetic field B is about 1 μT, for example, and the range in which the linearity of the input/output characteristics is good is narrow. Therefore, by adding a closed loop that generates a feedback magnetic field to such a magnetic sensor, the linearity of the magnetic sensor can be improved. Such a magnetic sensor will be explained next.

FIG. 5 shows a configuration example of the sensor section 300 according to this embodiment. The sensor section 300 is provided inside each of the plurality of magnetic sensor cells 220 and includes a magnetic sensor 520, a magnetic field generation section 530, and an output section 540. Note that a part of the sensor unit 300, such as the amplifier circuit 532, may be provided not on the magnetic sensor cell 220 side but on the sensor data collection unit 230 side.

The magnetic sensor 520 includes a magnetoresistive element such as a GMR element or a TMR element, similar to the magnetic sensor described in FIG. 4 . Furthermore, each of the magnetic sensors 520 includes a magnetoresistive element and two magnetic convergence plates arranged at both ends of the magnetoresistive element, and the magnetoresistive element is arranged at a position sandwiched between the two magnetic convergence plates. . When the positive direction of the magnetic sensing axis is the +X direction, the magnetic resistance element of the magnetic sensor 520 increases in resistance when a magnetic field in the +X direction is input, and decreases in resistance when a magnetic field in the -X direction is input. It may be formed to do so. That is, by observing changes in the resistance value of the magnetoresistive element included in the magnetic sensor 520, the magnitude of the magnetic field B input to the magnetic sensor 520 can be detected. For example, if the magnetic sensitivity of the magnetic sensor 520 is S, the detection result for the input magnetic field B of the magnetic sensor 520 can be calculated as S×B. Note that the magnetic sensor 520 is connected to, for example, a power source, and outputs a voltage drop corresponding to a change in resistance value as a detection result of an input magnetic field. Details of the configuration of the magnetic sensor 520 will be described later.

The magnetic field generating section 530 generates a feedback magnetic field that reduces the input magnetic field detected by the magnetic sensor 520, with a magnitude corresponding to the output signal output by the output section 540, and supplies it to the magnetic sensor 520. For example, the magnetic field generation unit 530 operates to generate a feedback magnetic field B_FB having a direction opposite to the magnetic field B input to the magnetic sensor 520 and having substantially the same absolute value as the input magnetic field, thereby canceling the input magnetic field. Magnetic field generation section 530 includes an amplifier circuit 532 and a feedback coil 534.

The amplifier circuit 532 outputs a current according to the detection result of the input magnetic field of the magnetic sensor 520 as a feedback current I_FB. When the magnetoresistive element included in the magnetic sensor 520 is configured by a bridge circuit including at least one magnetoresistive element, the output of the bridge circuit is connected to the input terminal pair of the amplifier circuit 532, respectively. Then, the amplifier circuit 532 outputs a current according to the output of the bridge circuit as a feedback current I_FB. The amplifier circuit 532 includes, for example, a transconductance amplifier, and outputs a feedback current I_FB according to the output voltage of the magnetic sensor 520. For example, if the voltage/current conversion coefficient of the amplifier circuit 532 is G, the feedback current I_FB can be calculated as G×S×B.

Feedback coil 534 generates feedback magnetic field B_FB according to feedback current I_FB. The feedback coil 534 is wound along the axial direction of the magnetic field to be detected by the magnetic sensor 520 so as to surround the magnetoresistive element of the magnetic sensor 520 and the two magnetic convergence plates arranged at both ends of the magnetoresistive element. ing. Feedback coil 534 preferably generates a uniform feedback magnetic field B_FB across magnetic sensor 520. For example, if the coil coefficient of the feedback coil 534 is β, the feedback magnetic field B_FB can be calculated as β×I_FB. Here, since the feedback magnetic field B_FB is generated in a direction that cancels the input magnetic field B, the magnetic field input to the magnetic sensor 520 is reduced to BB_FB. Therefore, the feedback current I_FB is expressed as follows.

When formula (1) is solved for the feedback current I_FB, the value of the feedback current I_FB in the steady state of the sensor section 300 can be calculated. Assuming that the magnetic sensitivity S of the magnetic sensor 520 and the voltage/current conversion coefficient G of the amplifier circuit 532 are sufficiently large, the following equation is calculated from equation (1).

The output section 540 outputs an output signal V_xMR according to the feedback current I_FB that the magnetic field generation section 530 sends to generate the feedback magnetic field B_FB. The output unit 540 includes, for example, a resistive element having a resistance value R, and outputs a voltage drop caused by the feedback current I_FB flowing through the resistive element as an output signal V_xMR. In this case, the output signal V_xMR is calculated from equation (2) as shown in the following equation.

As described above, since the sensor unit 300 generates a feedback magnetic field that reduces the magnetic field input from the outside, it substantially reduces the magnetic field input to the magnetic sensor 520. As a result, the sensor section 300 uses, for example, a magnetoresistive element as the magnetic sensor 520, which is nonlinear and has the characteristics of a narrow operating magnetic field range as shown in FIG. , it is possible to prevent the detection signal V_xMR from becoming saturated. The input/output characteristics of such a sensor section 300 will be explained next.

FIG. 6 shows an example of input/output characteristics of the sensor section 300 according to this embodiment. In this figure, the horizontal axis indicates the magnitude B of the input magnetic field input to the sensor section 300, and the vertical axis indicates the magnitude V_xMR of the detection signal of the sensor section 300. The sensor unit 300 has high magnetic sensitivity and can detect a minute magnetic field of about 10 pT. Further, the sensor unit 300 can maintain good linearity of the detection signal V_xMR even if the absolute value of the input magnetic field B exceeds 100 μT, for example.

That is, in the sensor unit 300 according to the present embodiment, the detection result for the input magnetic field B has linearity within a predetermined range of the input magnetic field B, for example, where the absolute value of the input magnetic field B is several hundred μT or less. It is configured as follows. By using such a sensor unit 300, weak magnetic signals such as magnetocardial signals can be easily detected.

FIG. 7 shows a configuration example of the magnetic sensor 520 according to this embodiment. In this figure, magnetic sensor 520 includes a magnetoresistive element 710 and magnetic convergence plates 720 and 730 arranged at both ends of magnetoresistive element 710. Magnetic convergence plates 720 and 730 are arranged at both ends of magnetoresistive element 710 so that magnetoresistive element 710 is sandwiched therebetween. In this figure, the magnetic convergence plate 720 is provided on the negative side of the magnetoresistive element 710 along the magnetically sensitive axis, and the magnetic convergent plate 730 is provided on the positive side of the magnetoresistive element 710 along the magnetically sensitive axis. There is. Note that here, the magnetically sensitive axis may be along the direction of magnetization fixed in the magnetization fixed layer forming the magnetoresistive element 710. Furthermore, when a magnetic field is input from the negative side to the positive side of the magnetically sensitive axis, the resistance of the magnetoresistive element 710 may increase or decrease. The magnetic convergence plates 720 and 730 are made of a material with high magnetic permeability, such as permalloy. When the magnetic sensor 520 is configured as shown in this figure, the feedback coil 534 surrounds the cross section of the magnetoresistive element 710 and the magnetic convergence plates 720 and 730 arranged at both ends of the magnetoresistive element 710. The magnetic sensor 520 is wound along the axial direction of the magnetic field to be detected. Further, when one magnetic sensor 520 includes a plurality of magnetoresistive elements 710, the magnetic sensor 520 may have a plurality of sets including a magnetoresistive element and magnetic convergence plates arranged at both ends thereof. In that case, the feedback coil 534 may be wound so that one coil surrounds a set including a magnetoresistive element and magnetic convergence plates arranged at both ends thereof.

In such a magnetic sensor 520, when a magnetic field is input from the negative side to the positive side of the magnetically sensitive axis, the magnetic convergence plates 720 and 730 formed of a material with high magnetic permeability are magnetized, so that as shown in this figure, A magnetic flux distribution as shown by the broken line occurs. Then, the magnetic flux generated by magnetizing the magnetic convergence plates 720 and 730 passes through the position of the magnetoresistive element 710 sandwiched between the two magnetic convergence plates 720 and 730. Therefore, the magnetic flux density at the location of magnetoresistive element 710 can be significantly increased by arranging magnetic convergence plates 720 and 730. Furthermore, as shown in this figure, sampling points in space can be made clear by sampling the spatial distribution of the magnetic field using a magnetoresistive element 710 placed in a narrow position sandwiched between magnetic convergence plates 720 and 730. Can be done.

FIG. 8 shows a magnetic flux distribution when a feedback magnetic field is generated in the magnetic sensor 520 according to this embodiment. In FIG. 8, members having the same functions and configurations as those in FIG. 7 are denoted by the same reference numerals, and description thereof will be omitted except for differences. In the magnetic sensor 520 according to the present embodiment, when a feedback current is supplied to the feedback coil 534, the feedback coil 534 generates a feedback magnetic field, thereby generating a magnetic flux distribution as shown by the dashed line in the figure. The magnetic flux generated by this feedback magnetic field is spatially distributed so as to cancel the spatial distribution of the magnetic field input to the magnetoresistive element 710 and magnetically amplified by the magnetic convergence plates 720 and 730. Therefore, when magnetic convergence plates 720 and 730 are arranged at both ends of the magnetoresistive element 710 as shown in this figure, the magnetic sensor 520 accurately adjusts the magnetic field distribution at the position of the magnetoresistive element 710 using a feedback magnetic field. Therefore, it is possible to realize a sensor with high linearity between the input magnetic field and the output voltage.

FIG. 9 shows an example of the arrangement of a plurality of magnetic sensor cells 220 in the magnetic sensor array 210 according to this embodiment. In FIGS. 2 and 3, the case where the magnetic sensor array 210 is planar is shown as an example. However, as shown in this figure, the magnetic sensor array 210 may have a curved surface shape curved in at least one direction. A plurality of magnetic sensor cells 220 may be arranged three-dimensionally at grid points included in the curved shape. As an example, the magnetic sensor array 210 may be configured by arranging a plurality of magnetic sensor cells 220 three-dimensionally in an arc shape when viewed in cross section. Note that, from now on, a case where the magnetic sensor array 210 has a curved shape will be described as an example, but the present invention is not limited to this. The magnetic sensor array 210 does not have to have a curved shape as shown in this figure, and may have a planar shape, for example, as shown in FIGS. 2 and 3.

The plurality of magnetic sensor cells 220 may be arranged in an arc shape in a cross-sectional view along the chest of the object to be measured, centering on the center of gravity of the object to be measured. At this time, each magnetic sensor cell 220 is arranged at a lattice point included in a curved surface shape in a three-dimensional lattice space. Note that the lattice points herein are lattice-shaped points provided at equal intervals at predetermined intervals in each of the X direction, the Y direction, and the Z direction. As an example, each magnetic sensor cell 220 is arranged along a curved surface having a convexity in a direction orthogonal to one direction when viewed from any one of the X direction, the Y direction, and the Z direction. This figure shows an example in which each magnetic sensor cell 220 is arranged along a curved surface having a convexity in the positive direction of the Z axis when viewed from the Y direction. The magnetic sensor array 210 is arranged, for example, in the negative direction of the Z-axis as much as possible within a range where each vertex of each magnetic sensor cell 220 does not exceed a predetermined curved surface having a convexity in the positive direction of the Z-axis. By arranging each magnetic sensor cell 220 at a lattice point in a three-dimensional lattice space, a curved surface shape having a convexity in the positive direction of the Z-axis may be formed.

More specifically, in the cross-sectional view of this figure, a plurality of magnetic sensor cells 220 on the inside (Z-axis negative side), that is, magnetic sensor cells 220[1,j,1] to 220[8,j,1] are denoted by the reference numeral 910. They are arranged along a circular arc indicated by a dashed line 915 so as to form a part of the inscribed circle of the magnetic sensor array 210 indicated by . Further, a plurality of outer magnetic sensor cells 220 (on the Z-axis positive side), that is, magnetic sensor cells 220 [1, j, 2] to 220 [8, j, 2], are located at the circumference of the magnetic sensor array 210 indicated by reference numeral 920. They are arranged along a circular arc indicated by a chain double-dashed line 925 so as to form a part of a circle.

Thereby, the magnetic sensor array 210 can have sensor sections arranged not only in one direction facing the heart but also in multiple directions, and can sense cardiac magnetism from multiple directions. Further, in the magnetic sensor array 210 according to the present embodiment, the magnetic sensor cells 220 are formed in a rectangular parallelepiped shape, for example, so that the shape of the magnetic sensor array 210 can be easily changed. That is, the magnetic sensor array 210 according to this embodiment can take various shapes that can be configured by arranging the magnetic sensor cells 220 at lattice points, and has a high degree of freedom in design. Therefore, as shown in this figure, the magnetic sensor array 210 can easily form a curved shape in a three-dimensional space by arranging a plurality of magnetic sensor cells 220 at lattice points included in the curved shape in a three-dimensional space. can do. The magnetic field measuring device 10 arranges the magnetic sensor array 210 so that the chest of the object to be measured is located at the center of the curved surface, that is, the heart, which is the source of the magnetic field to be measured, is located at the center of the curved surface. to measure the magnetic field. As a result, the magnetic field measuring device 10 performs signal spatial separation (described later) using measurement data measured at a position close to the heart, which is the source of the magnetic field to be measured, to accurately separate the magnetic field to be measured from the disturbance magnetic field. can do. In this case, it is preferable that the curvature of the curved surface of the magnetic sensor array 210 be approximately equal to the curvature around the chest of the object to be measured, since this allows the magnetic field to be measured closer to the heart, which is the source of the magnetic field to be measured.

FIG. 10 shows the configuration of a sensor section 300inside included in the inner magnetic sensor cell 220 in the magnetic sensor array 210 according to this embodiment. In FIG. 10, members having the same functions and configurations as those in FIG. 5 are denoted by the same reference numerals, and description thereof will be omitted except for differences. As shown in this figure, inner magnetic sensor cells 220 in the magnetic sensor array 210, that is, a plurality of magnetic sensor cells 220[1,j,1] to 220[8,j] forming an inner circular arc 915 of the magnetic sensor array 210. , 1] further includes a switching section 1010.

The switching unit 1010 switches whether the magnetic field generating unit 530 generates a feedback magnetic field or a calibration magnetic field. That is, at least one magnetic sensor cell 220 among the plurality of magnetic sensor cells 220 in the magnetic sensor array 210 further includes a switching unit 1010 that switches whether the magnetic field generation unit 530 generates a feedback magnetic field or a calibration magnetic field. . More specifically, the switching unit 1010 is configured by a switch, and one end of the switch is connected to one end of the feedback coil 534. Then, the switching unit 1010 switches between inputting the output of the amplifier circuit 532 to one end of the feedback coil 534 and inputting an alternating current according to the frequency of a calibration clock signal to be described later. When the switching unit 1010 switches to input an alternating current according to the frequency of the calibration clock signal to one end of the feedback coil 534, the magnetic field generation unit 530 causes the feedback coil 534 to generate a calibration magnetic field. .

Such a calibration magnetic field may be an alternating magnetic field. As an example, the calibration magnetic field may be a sine wave of frequency f0, or a sine wave of multiple frequencies (e.g., frequency f0, frequency f1 (>frequency f0), frequency f2 (>frequency f1), etc.). It may be the sum of waves. The magnetic field, which is one of the magnetic fields to be measured by the magnetic field measuring device 10, has no DC component. Therefore, the magnetic field measuring device 10 only calibrates the magnetic sensor using a calibration magnetic field that is an alternating magnetic field, and is capable of dealing with the DC offset of the magnetic sensor and offset drift at very low frequencies (for example, 0.1 Hz or less). There is no need to calibrate the magnetic sensor.

Here, generally, the higher the frequency, the smaller the environmental magnetic field is. For example, the environmental magnetic field is on the order of several tens of pT in a band higher than 50 Hz, which is the same as the peak of cardiac magnetism, which is one of the magnetic fields measured by the magnetic field measuring device 10 according to the present embodiment. level. Therefore, the magnetic field generation unit 530 preferably generates an alternating magnetic field with a frequency higher than 50 Hz (frequency f0>50 Hz) as the calibration magnetic field. That is, since most of the signal frequencies of magnetocardiography are lower than 20 Hz, the frequency of the alternating current magnetic field as the calibration magnetic field may be higher than the frequency band of the magnetic field to be measured.

Further, in general, the frequency of commercial power supply is, for example, 50 Hz or 60 Hz. Therefore, power supply noise exists when the frequency of these commercial power sources is multiplied. Therefore, it is preferable that the magnetic field generation unit 530 uses a frequency higher than the frequency of the magnetic field to be measured and that avoids multiplication of the frequency of the commercial power source as the frequency of the alternating magnetic field. As an example, the magnetic field generation unit 530 may use a frequency higher than 50 Hz and avoid integral multiples of 50 Hz or 60 Hz as the frequency of the calibration magnetic field. As a result, the environmental magnetic field can be suppressed to the order of tens of pT, so it is sufficient for the magnetic field generation unit 530 to generate a weak calibration magnetic field of about several tens of nT, for example, to the extent that environmental noise can be ignored. That is, by using such a frequency as the frequency of the alternating magnetic field, the magnetic field measuring device 10 does not need to generate a strong magnetic field as the calibration magnetic field.

Furthermore, when performing calibration using such an alternating magnetic field, it is necessary to suppress the generation of eddy currents. Therefore, the housing of the feedback coil 534 that generates the calibration magnetic field is preferably formed of a resin material or the like with low electrical conductivity. Furthermore, the casing housing the magnetic sensor array 210 that similarly measures the calibration magnetic field may also be formed of a resin material or the like with low electrical conductivity.

FIG. 11 shows the configuration of the magnetic sensor array 210, sensor data collection section 230, and sensor data processing section 1100 according to this embodiment.

The magnetic sensor array 210 is composed of a plurality of magnetic sensor cells 220 each having at least one sensor section 300, and the magnetic sensor array 210 as a whole can detect input magnetic fields in three axial directions. In this figure, an example is shown in which the magnetic sensor array 210 has M sensor units 300[1] to 300[M].

When performing calibration, the magnetic sensor array 210 receives an alternating current according to the frequency of the calibration clock signal, and selects at least one magnetic sensor cell 220 of the plurality of magnetic sensor cells 220 in the magnetic sensor array 210. A calibration magnetic field is generated from a magnetic field generation unit 530 included in the calibration magnetic field. More specifically, the magnetic sensor array 210 includes at least one magnetic sensor cell 220 that generates a calibration magnetic field from the magnetic field generation unit 530, and a plurality of magnetic sensor cells 220 [1, j, 1] to 220 that form an inner circular arc 915. 220 [8, j, 1] one by one, and adds an alternating current according to the frequency of the calibration clock signal to the feedback coil 534 of the sensor unit 300inside of the corresponding magnetic sensor cell 220, and 534, an alternating current magnetic field is sequentially generated according to the frequency of the clock signal. That is, a calibration magnetic field is generated from the magnetic field generating section 530 included in at least one sensor section 300 among the plurality of sensor sections 300 in the magnetic sensor array 210.

The sensor data collection unit 230 includes a plurality of AD converters 232 and a clock generator 234. The plurality of AD converters 232 are provided corresponding to each of the plurality of sensor sections 300[1] to 300[M], and the analog detection signals (V_xMR in FIG. 6) output by the corresponding sensor sections 300 are provided. are converted into digital measurement data V[1] to V[M], respectively.

The clock generator 234 generates a sampling clock and supplies a common sampling clock to each of the plurality of AD converters 232. Each of the plurality of AD converters 232 performs AD conversion in response to a common sampling clock supplied from the clock generator 234. Therefore, all of the plurality of AD converters 232 that perform AD conversion on the outputs of the plurality of sensor sections 300[1] to 300[M] provided at different positions operate synchronously. Thereby, the plurality of AD converters 232 can simultaneously sample the detection results of the plurality of sensor sections 300[1] to 300[M] provided in different spaces.

The sensor data processing section 1100 includes a plurality of measurement data acquisition sections 1120, a plurality of synchronous detection sections 1130, and a plurality of data output sections 1140, which are provided corresponding to each of the plurality of sensor sections 300[1] to 300[M]. , a basis vector storage section 1150, a signal space separation section 1160, a calibration clock generation section 1170, an error calculation section 1180, and a calibration section 1190.

The measurement data acquisition section 1120 is connected to each of the plurality of AD converters 232 connected to the corresponding sensor section 300, and the measurement data acquisition section 1120 is connected to each of the plurality of AD converters 232 connected to the corresponding sensor section 300. The measured data V[1] to V[M] are obtained respectively. Specifically, the measurement data acquisition unit 1120 may be configured using a flip-flop or the like that latches and acquires the digital measurement data V converted into digital data by the AD converter 232 at a predetermined timing T. The measurement data acquisition unit 1120 supplies the acquired measurement data V to the synchronous detection unit 1130.

When measuring the magnetic field to be measured, the synchronous detection section 1130 supplies the measurement data V supplied from the measurement data acquisition section 1120 as is to the data output section 1140. On the other hand, when performing calibration, the synchronous detection unit 1130 detects a calibration magnetic field, which is an alternating magnetic field, using a signal of the frequency of the alternating magnetic field. As an example, the synchronous detection unit 1130 synchronously detects the calibration magnetic field in accordance with a calibration clock signal. In synchronous detection, the synchronous detection unit 1130 detects each measurement data V[1] to V[M] based on the relationship between the phase of a clock signal for calibration and the phase of each measurement data V[1] to V[M], for example. You may decide whether the sign is positive or negative. Then, the synchronous detection unit 1130 extracts a frequency component (including signal strength and sign) synchronized with the calibration magnetic field, which is an alternating magnetic field, from the measurement data V supplied from the measurement data acquisition unit 1120, and Measured data V related to frequency components is supplied to the data output section 1140. Here, such synchronous detection may be performed on software or may be performed on hardware. In addition, in the above description, an example was given in which the synchronous detection unit 1130 performs synchronous detection to extract frequency components synchronized with the calibration magnetic field. A frequency component synchronized with the calibration magnetic field may be extracted using a band-pass filter or the like.

The data output unit 1140 generates a sensor array signal in which the measurement data V[1] to V[M] supplied from each of the plurality of synchronous detection units 1130 is converted into each sensor signal component Φ[1] to Φ[M]. Φ is supplied to the signal space separation unit 1160.

The basis vector storage section 1150 stores basis vectors necessary for the signal space separation section 1160 to separate the sensor array signal Φ, and supplies the basis vectors to the signal space separation section 1160. Note that the basis vector storage section 1150 sequentially updates the stored basis vectors to the basis vectors changed by the calibration section 1190. This will be discussed later.

The signal space separation unit 1160 converts the spatial distribution of the input magnetic field indicated by the measurement data V[1] to V[M] supplied as each component of the sensor array signal Φ from the data output unit 1140 into a spatial distribution of an orthonormal function. When the magnetic sensor array 210 detects a magnetic field having a magnetic field, the signals are separated using a vector signal having, as each signal component, a signal output by each of the plurality of magnetic sensors 520 as a base vector. At this time, the signal space separation unit 1160 acquires basis vectors necessary for signal separation from the basis vector storage unit 1150. Then, the signal space separation unit 1160 uses the basis vectors acquired from the basis vector storage unit 1150 to calculate the spatial distribution of the magnetic field indicated by the measurement data V[1] to V[M] in the measurement target magnetic field (signal source space signal) and a disturbance magnetic field (disturbance spatial signal), suppress the disturbance magnetic field, calculate the magnetic field to be measured, and output it. This will also be discussed later.

When performing calibration, the calibration clock generating section 1170 generates a clock signal for generating an alternating current calibration magnetic field and an alternating current according to the frequency of the clock signal. Then, the calibration clock generation section 1170 supplies the generated clock signal to each of the magnetic sensor array 210 and the plurality of synchronous detection sections 1130. Accordingly, the magnetic sensor array 210 includes at least one magnetic sensor cell 220 that generates a calibration magnetic field from the magnetic field generation unit 530, and a plurality of magnetic sensor cells 220 [1, j, 1] to 220 that form an inner circular arc 915. 220 [8, j, 1] one by one, and the feedback coil 534 of the sensor section 300inside of the corresponding magnetic sensor cell 220 sequentially generates an alternating current magnetic field according to the frequency of the clock signal. In addition, the plurality of synchronous detection units 1130 each detect an AC calibration magnetic field generated by a magnetic field generation unit 530 included in at least one magnetic sensor cell, according to the clock signal. In addition, in the above description, the case where the calibration clock generation section 1170 is provided inside the sensor data processing section 1100 is shown as an example, but the calibration clock generation section 1170 is, for example, provided in the sensor data collection section. It may be configured inside 230.

When performing calibration, the error calculation unit 1180 allows the signal space separation unit 1160 to calculate the spatial distribution of the calibration magnetic field generated from the magnetic field generation unit 530 of at least one of the plurality of magnetic sensor cells 220. Calculate the separation error when the signals are separated. The error calculation unit 1180 then supplies the calculated separation error to the calibration unit 1190.

The calibration unit 1190 calculates the magnetic sensor 520 based on the separation error when the spatial distribution of the calibration magnetic field generated from the magnetic field generation unit 530 of at least one of the plurality of magnetic sensor cells 220 is separated into signals. Calibrate the sensor error in. More specifically, the calibration unit 1190 replaces at least one magnetic sensor cell 220 that generates a calibration magnetic field from the magnetic field generation unit 530 with a plurality of magnetic sensor cells 220 [1, j, 1] to 220 forming an inner circular arc 915. The sensor error in the magnetic sensor 520 is calibrated based on the respective separation errors when sequentially switching over [8,j,1]. At this time, the calibration unit 1190 calibrates the sensor error by changing the base vector used by the signal space separation unit 1160. The calibration unit 1190 then supplies information regarding the changed basis vectors to the basis vector storage unit 1150. In response, the basis vector storage unit 1150 updates the stored basis vectors. This will be explained in detail using mathematical formulas.

FIG. 12 shows a flow in which the magnetic field measuring device 10 according to this embodiment separates signals of the spatial distribution of a magnetic field. In step 1210, basis vector storage section 1150 stores the basis vectors. As an example, the basis vector storage unit 1150 uses, as the initial basis vector, a signal vector that is predetermined based on a simulation result assuming that the magnetic sensor array 210 is ideally created without any errors in each sensor. You can remember it. Furthermore, as described later, when the sensor error is calibrated by the calibration unit 1190, the base vector storage unit 1150 may store a changed updated base vector.

Next, in step 1220, the signal space separation unit 1160 obtains the sensor array signal Φ measured by the magnetic sensor array 210, that is, the measurement data V[1] to V[M] from the data output unit 1140.

Further, in step 1230, the signal space separation unit 1160 obtains from the basis vector storage unit 1150 the signal vector that the basis vector storage unit 1150 stored as a basis vector in step 1210. Note that in this flow, either step 1220 or step 1230 may be performed first.

In step 1240, the signal space separation unit 1160 calculates the spatial distribution of the magnetic field indicated by the measurement data V[1] to V[M] obtained in step 1220 by using the signal vector obtained in step 1230 as a basis vector. Expand the series. Then, the signal space separation unit 1160 separates the spatial distribution of the magnetic field into a measurement target magnetic field and a disturbance magnetic field from the vector obtained by series expansion. That is, the signal space separation unit 1160 determines the spatial distribution of the input magnetic field indicated by the measurement data V[1] to V[M] when the magnetic sensor array 210 detects a magnetic field having a spatial distribution of an orthonormal function. A vector signal having signals output from each of the sensors 520 as each signal component is used as a base vector to separate the signals. Here, the orthonormal function may be a spherical harmonic function. Further, in signal separation, the signal space separation unit 1160 calculates coefficients of basis vectors by the method of least squares.

Then, in step 1250, the signal space separation unit 1160 suppresses the disturbance magnetic field and calculates and outputs only the magnetic field to be measured based on the result of signal separation in step 1240, and ends the process. This will be explained in detail below.

Regarding the position where each sensor constituting the magnetic sensor array 210 is arranged, when the current i(r) = 0 at the position of the position vector r representing the position from the coordinate origin, the static magnetic field B(r) is Using the potential V(r) that satisfies the equation Δ·V(r)=0, it is determined as a spatial gradient of the potential V(r) as shown in the following equation. Here, Δ is the Laplacian, μ is the magnetic permeability, and ∇ is an operator representing vector differential operation.

The solution to Laplace's equation generally has a solution in the form of a series expansion using the spherical harmonic function Y _l,m (θ, φ), which is an orthonormal function system, so the potential V(r) is expressed as It can be expressed as Here, |r| is the absolute value of the position vector r (distance from the coordinate origin), θ and φ are the two argument angles in spherical coordinates, l is the azimuthal quantum number, and m is the magnetic quantum number , α and β are multipolar moments, and Lin and Lout are the numbers of series for the space in front of and behind the magnetic sensor array 210, respectively, when viewed from the object to be measured. The azimuthal quantum number l takes a positive integer, and the magnetic quantum number m takes an integer from -l to +l. That is, for example, when l is 1, m is -1, 0, and 1; for example, when l is 2, m is -2, -1, 0, 1, and 2. Note that since there is no single magnetic pole in a magnetic field, the azimuth quantum number l starts from 1 instead of 0 in (Equation 5). The first term in (Equation 5) is a term that is inversely proportional to the distance from the coordinate origin, and indicates the potential that exists in the space in front of the magnetic sensor array 210 when viewed from the measured object. Further, the second term in (Equation 5) is a term proportional to the distance from the coordinate origin, and indicates the potential that exists in the space behind the magnetic sensor array 210 when viewed from the measured object.

Therefore, according to (Equation 4) and (Equation 5), the static magnetic field B(r) can be expressed by the following equation. Here, the first term in (Equation 6) is a magnetic field source that exists in the space in front of the magnetic sensor array 210 when viewed from the measured object, that is, for example, a magnetocardiogram (measurement target magnetic field) generated by the electrical activity of the heart. It shows. Moreover, the second term in (Equation 6) indicates the disturbance magnetic field generated by the magnetic field source existing in the space behind the magnetic sensor array 210 when viewed from the object to be measured.

When the solution to Laplace's equation is expressed in the form of a series expansion using spherical harmonics, the general solution becomes an infinite series, but the SNR (signal to noise ratio, i.e., the disturbance magnetic field and It is sufficient to obtain the ratio of the magnetic field signal to be measured to the sensor noise, and it is said that it is actually sufficient to express it as a series of about 10 terms. Furthermore, it is said that the series for signal space separation in a magnetoencephalograph may be approximately Lin=8 and Lout=3. Therefore, in this embodiment as well, the case where Lin=8 and Lout=3 will be described as an example. However, the values of Lin and Lout are not limited to these, and may be any numerical values that are sufficient to sufficiently suppress the disturbance magnetic field and calculate only the magnetic field to be measured.

Here, the sensor array signal Φ is composed of an M-dimensional vector, and each signal component of the vector is a magnetic field vector B (r[m] ) and the magnetic sensitivity vector S[m] of each magnetic sensor 520. Therefore, for each magnetic sensor 520, the magnetic sensitivity vector S _Ideal [m] = (S _Ideal [m], x, S _Ideal [m], y, S _Ideal [m], z) as each designed. When the sensor array signal Φ Ideal is held at the designed position, the ideal sensor array signal Φ _Ideal is expressed by the following equation.

In other words, each sensor is ideal without any sensor error (magnetic sensitivity error due to other axis sensitivity or main axis sensitivity of each sensor, position error due to deviation in placement position of each sensor during assembly of magnetic sensor array 210, etc.). The signal component Φ _Ideal [m] is expressed by the following equation.

Therefore, in an ideal case where there is no sensor error in each magnetic sensor 520, the base vectors a _{Ideal l,m} and b _{Ideal l,m} are defined as in the following equations.

Here, in an ideal case where there is no sensor error in each magnetic sensor 520, A _Ideal , B _Ideal , Xin, and Xout are defined as follows. That is, when A _Ideal is an integer from l=1 to L=Lin, and for each l an integer from m=-l to l, each vector a _Ideal is arranged in a column in order, resulting in a total of Lin・(Lin+2) columns. is defined as a vector of In addition, B _Ideal is a total of Lout・(Lout+2) columns in which each vector b _Ideal is arranged in a column in order from l=1 to L=Lout, and each l takes an integer from m=-l to l. is defined as a vector of In addition, Xin is the total Lin・Define it as a vector with (Lin+2) rows. In addition, Xout is the total of Lout・(Lout+2 ) is defined as a vector of rows.

Then, the sensor array signal Φ _Ideal of the ideal magnetic sensor array 210 can be expressed in the form of an inner product of the ideal basis vector matrix [A B] _Ideal and the vertical vector X, as shown in the following equation. Here, the ideal basis vector matrix [A B] _Ideal indicates a basis vector, and is acquired from the basis vector storage section 1150 by the signal space separation section 1160 in step 1230, for example. Further, the vertical vector X indicates a coefficient related to the basis vector.

In step 1240, the signal space separation unit 1160 uses the following equation to determine a vertical vector that satisfies Φ _Ideal = [A B] _Ideal ·X by least squares approximation, based on the model equation obtained in (Equation 11). The vector ^X _Ideal (here, "^X _ideal " indicates the left side in (Equation 12) and means the hat (estimated value) of X _Ideal ) is determined.

Therefore, the signal space separation unit 1160 can express the sensor array signal Φ _Ideal of the ideal magnetic sensor array 210 as an M-dimensional vector of the least squares solution using the following equation. This allows the signal space separation unit 1160 to solve the spatial distribution of the magnetic field in step 1240.

Then, in step 1250, the signal space separation unit 1160 uses the vertical vector determined in step 1240 to reduce ^Xout·B _Ideal and remove the disturbance magnetic field component, that is, the second term component in (Equation 6). Output the suppressed results. By outputting only ^Xin·A _Ideal as a result, the signal space separation unit 1160 suppresses the disturbance magnetic field component and outputs only the magnetic field component to be measured, that is, the first term component in (Equation 6). It's okay. That is, the signal space separation unit 1160 separates the signal space into a disturbance magnetic field component and a measurement target magnetic field component.

As a result, according to the magnetic field measuring device 10 according to the present embodiment, the measurement data V[1 ]~V[M] can be signal-separated into a measurement target magnetic field and a disturbance magnetic field. Further, the magnetic field measurement device 10 suppresses the disturbance magnetic field component and outputs only the magnetic field component to be measured, so that the magnetic field to be measured can be measured with higher precision. Furthermore, since each of the plurality of sensor sections 300 has a magnetic convergence plate, it is possible to increase the magnetic sensitivity of the sensor section 300 and to clarify the spatial sampling point, thereby further increasing compatibility with signal space separation technology. can.

FIG. 13 geometrically illustrates a signal space separation operation using an ideal basis vector [A B] _Ideal when the magnetic sensor array 210 is ideally made. Reference numeral 1310 indicates the sensor array signal Φ _Ideal of the ideal magnetic sensor array 210. Reference numeral 1320 indicates a linear subspace Span{A _Ideal } spanned by the ideal basis vector A _Ideal . Reference numeral 1330 indicates a linear subspace Span{B _Ideal } spanned by the ideal basis vector B _Ideal . Reference numeral 1340 indicates a linear subspace spanned by an ideal basis vector [A B] _Ideal that is a linear sum of the linear subspace Span {A _Ideal } and the linear subspace Span {B _Ideal }. Reference numeral 1350 indicates an M-dimensional vector of the least squares solution. As shown in this figure, when the magnetic sensor array 210 is ideally made, that is, made without any sensor error, the sensor array signal Φ _Ideal of the ideal magnetic sensor array 210 is It exists in the linear subspace spanned by the basis vector [A B] _Ideal . In other words, the equation (11) is established with high accuracy, and the signal space separation unit 1160 accurately separates the signal space into the target magnetic field component and the disturbance magnetic field component for the magnetic field detected by the magnetic sensor array 210. have been able to do so.

However, the actual sensor signal component Φ _Uncalibb [m] from each sensor unit 300 is a magnetic sensitivity vector S _Uncalibb [m] = (S _Uncalibb [m], x, S _Uncalib [m], y, S _Uncalib [m], z). That is, the magnetic sensor array 210 assumes the magnetic sensitivity vector S _Ideal [m] = (S _Ideal [m], x, S _Ideal [m], y, S _Ideal [m], z) for each magnetic sensor 520. However, in reality, the unknown magnetic sensitivity vector S _Uncalibi [m] = (S _Uncalibib [m], x, S _Uncalibib [m], y, S _Uncalibib [m], z) ).

That is, each sensor signal component Φ _Uncalibb [m] having a magnetic sensitivity error is expressed by the following equation.

In this way, for the sensor array signal Φ _Uncalibb measured by the magnetic sensor array 210 completed with a magnetic sensitivity error, using the assumed ideal basis vector [A B] _Ideal , the following equation is calculated. Suppose we set up

In this case, even if the vertical vector ^X _Uncalibb is determined by the following equation based on the model equation obtained in (Equation 15), the solution to the equation will be inaccurate.

In this case, as an M-dimensional vector of the least squares solution, the sensor array signal Φ _Uncalib of the magnetic sensor array 210 having a magnetic sensitivity error is expressed by the following equation.

FIG. 14 geometrically shows a signal space separation operation using an ideal basis vector [A B] _Ideal in a case where the magnetic sensor array 210 is made with a sensor error. In FIG. 14, members having the same functions and configurations as those in FIG. 13 are denoted by the same reference numerals, and description thereof will be omitted except for differences. Reference numeral 1410 indicates the sensor array signal Φ _Uncalibb of the magnetic sensor array 210 with sensor error. Reference numeral 1450 indicates an M-dimensional vector of the least squares solution. As shown in this figure, if the magnetic sensor array 210 has a sensor error, the sensor array signal Φ _Uncalibb does not exist in the linear subspace spanned by the ideal basis vector [A B] _Ideal . .

At this time, there is a separation error between the sensor array signal Φ _Uncalibb indicated by 1410 and the least squares solution M-dimensional vector ^Φ _Uncalibb indicated by 1450, that is, an error vector ε indicated by 1460. Then, an error angle γ shown at 1470 is generated. Here, the error vector ε and the error angle γ are expressed by the following equations.

As described above, due to the sensor error of the actual magnetic sensor array 210, the error vector ε in the signal space separation calculation is generated as a finite vector (not a zero vector). Therefore, the equation (15) is not established with high precision, and the solution to the equation (16) becomes inaccurate. That is, the signal space separation unit 1160 cannot accurately perform signal space separation into a target magnetic field component and a disturbance magnetic field component for the magnetic field detected by the magnetic sensor array 210.

Therefore, the magnetic field measuring device 10 according to the present embodiment calibrates the sensor error in the magnetic sensor 520 so as to reduce the separation error when such signal space separation calculation is performed.

FIG. 15 shows a flow in which the magnetic field measuring device 10 according to this embodiment acquires the sensor array signal Φ(i, j, 1) for calibration. Here, i indicates the position of the magnetic sensor cell 220 in the X direction in the magnetic sensor array 210, and is an integer that satisfies 1≦i≦Nx (however, Nx indicates the number of magnetic sensor cells 220 arranged in the X direction). It is. Further, j indicates the position of the magnetic sensor cell 220 in the Y direction in the magnetic sensor array 210, and is an integer satisfying 1≦j≦Ny (where Ny indicates the number of magnetic sensor cells 220 arranged in the Y direction). be. Further, k indicates the position of the magnetic sensor cell 220 in the magnetic sensor array 210 in the Z direction, and in this flow, z is fixed to 1. In addition, in the explanation of this flow and the flow of FIG. 16 described later, M/2 sensor units 300 included in a plurality of magnetic sensor cells 220 forming an inner circular arc 915 among M sensor units 300 are sequentially calibrated. An example will be shown in which a magnetic field is generated and the remaining M-1 sensor sections 300 that do not generate a magnetic field perform measurements. However, the number of sensor units 300 that generate the calibration magnetic field is not limited to this number, and can be realized from one depending on the parameter to be calibrated (for example, calibration of one component of position coordinates, etc.). In addition, the number of sensors that measure the magnetic field can be changed depending on the calibration parameters and the dimension of the basis vector, ranging from the few required to form the basis vector to M-1 sensors that do not generate a magnetic field. It can be a number. Further, even if measurement is performed using M-1 sensor sections 300 that do not generate a magnetic field, the number of sensor sections 300 to be calibrated for sensor error may be less than M-1. For example, sensor errors may be calibrated for M/2 sensor units 300 that do not generate a calibration magnetic field.

In step 1510, the magnetic field measuring device 10 initializes the cell address. As an example, the magnetic field measuring device 10 assigns 1 to i, 1 to j, and 1 to k. That is, the magnetic field measuring device 10 designates the magnetic sensor cell 220 [1, 1, 1] as the first magnetic sensor cell 220 that generates the calibration magnetic field.

In step 1520, the magnetic field measuring device 10 generates a signal from the magnetic field generation unit 530 of the magnetic sensor cell 220 [i, j, 1], for example, in the step 1520 following step 1510, the magnetic sensor cell [1, 1, 1]. Generate a calibration magnetic field. That is, the magnetic field measuring device 10 switches the switching section 1010 in the sensor section 300 of the magnetic sensor cell 220 [i, j, 1] to the calibration mode, and outputs the clock signal supplied from the calibration clock generating section 1170 to one end of the feedback coil 534. An alternating current corresponding to the frequency of the calibration clock signal is input. Then, the magnetic field measurement device 10 generates an alternating current magnetic field according to the frequency of the clock signal from the feedback coil 534 included in the magnetic sensor cell 220 [i, j, 1]. At this time, the calibration magnetic field generated by the feedback coil 534 included in the magnetic sensor cell 220[i,j,1] becomes close to the magnetic field generated from the magnetic dipole. The calibration magnetic field generated by the feedback coil 534 included in the magnetic sensor cell 220 [i, j, 1] corresponds to the component of the first term in (Equation 6). At this time, by generating a relatively strong AC magnetic field from the feedback coil 534, it is possible to ignore the second term component in (Equation 6), that is, the influence of the disturbance magnetic field during calibration.

In step 1530, the magnetic field measuring device 10 obtains the sensor array signal Φ(i, j, 1) when a calibration magnetic field is generated from the feedback coil 534 included in the magnetic sensor cell 220 [i, j, 1]. . More specifically, when the calibration magnetic field is generated from the feedback coil 534 included in the magnetic sensor cell 220 [i, j, 1], the measurement data acquisition unit 1120 generates the calibration magnetic field from the plurality of sensor units 300 [ included in the magnetic sensor array 210]. 1] to 300[M], except for the sensor unit 300[P] that generated the calibration magnetic field (here, P is an integer satisfying 1≦P≦M), (M-1) pieces. Measurement data V[1] to V[M] measured by the sensor unit 300 are respectively acquired. Then, the synchronous detection section 1130 receives the calibration clock signal supplied from the calibration clock generation section 1170, and synchronously detects the calibration magnetic field in accordance with the clock signal. Then, the synchronous detection unit 1130 extracts a frequency component synchronized with the calibration magnetic field, which is an alternating current magnetic field, from the measurement data V[1] to V[M], and measures the measurement data V[1] related to the extracted frequency component. ] to V[M] are respectively supplied to the data output section 1140. Then, the data output unit 1140 uses the measurement data V[1] to V[M] supplied from the synchronous detection unit 1130 to generate a calibration magnetic field from the feedback coil 534 included in the magnetic sensor cell 220[i,j,1]. In the case where the calibration magnetic field is generated, each sensor signal component Φ[1 ] to Φ[M] (excluding Φ[P]), the sensor array signal Φ(i, j, 1) for calibration is supplied to the signal space separation unit 1160. Thereby, the signal space separation unit 1160 generates the sensor array signal Φ(i, j, 1) for calibration when a calibration magnetic field is generated from the feedback coil 534 included in the magnetic sensor cell 220 [i, j, 1]. get.

In step 1540, the magnetic field measuring device 10 determines whether i is equal to Nx. That is, the magnetic field measuring device 10 determines whether a calibration magnetic field is generated from the magnetic field generating sections 530 of all the magnetic sensor cells 220 arranged in the X direction. When it is determined that i is equal to Nx, that is, when it is determined that the calibration magnetic field has been generated from the magnetic field generation units 530 of all the magnetic sensor cells 220 arranged in the X direction, the magnetic field measuring device 10 performs processing. Proceed to step 1560.

On the other hand, if it is determined in step 1540 that i is not equal to Nx, that is, it is determined that the calibration magnetic field is not generated from the magnetic field generation units 530 of all the magnetic sensor cells 220 arranged in the X direction. In this case, the magnetic field measuring device 10 increments i to i=i+1 in step 1550, returns the process to step 1520, and continues the flow.

In step 1560, the magnetic field measuring device 10 determines whether j is equal to Ny. That is, the magnetic field measuring device 10 determines whether a calibration magnetic field is generated from the magnetic field generation units 530 of all the magnetic sensor cells 220 arranged in the Y direction. When it is determined that j is equal to Ny, that is, when it is determined that the calibration magnetic field has been generated from the magnetic field generation units 530 of all the magnetic sensor cells 220 arranged in the Y direction, the magnetic field measuring device 10 The flow for acquiring the sensor array signal Φ(i, j, 1) for the application ends.

On the other hand, in step 1560, if it is determined that j is not equal to Ny, that is, it is determined that the calibration magnetic field is not generated from the magnetic field generation units 530 of all the magnetic sensor cells 220 arranged in the Y direction. In this case, the magnetic field measuring device 10 increments j to set j=j+1 in step 1570, returns the process to step 1520, and continues the flow.

Thereby, the magnetic field measurement device 10 is included in the plurality of magnetic sensor cells 220 from i=1 to i=Nx and from j=1 to j=Ny, k=1, that is, forming the inner circular arc 915. When a calibration magnetic field is generated from the magnetic field generation units 530 of M/2 sensor units 300, array signals Φ(i, j, 1) for calibration are respectively acquired.

FIG. 16 shows a flow in which the magnetic field measuring device 10 according to this embodiment performs calibration. In this flow, an example will be shown in which sensor errors are calibrated for M/2 sensor units 300 that do not generate a calibration magnetic field. In step 1610, the magnetic field measuring device 10 assigns 1 to C. Here, C means the number of times the calibration is executed, and is an integer from 1 to MAX_COUNT, which is the upper limit of the number of times the calibration is executed.

In step 1620, the magnetic field measuring device 10 calculates a separation error. More specifically, the signal space separation unit 1160 performs signal space separation on the calibration sensor array signal Φ(i, j, 1) for 1≦i≦Nx and 1≦j≦Ny. conduct. At this time, in step 1620 following step 1610, the signal space separation unit 1160 determines the solution of the equation shown in (16) from the equation shown in (15). In this case, the signal space separation unit 1160 separates the spatial distribution of the calibration magnetic field from the signal at a position where the magnetic field generation unit 530 of at least one magnetic sensor cell 220 that generates the calibration magnetic field from the magnetic field generation unit 530 is arranged. Let be the origin of the coordinates in the calculation. That is, in signal separation of the sensor array signal Φ(1,1,1), the signal space separation unit 1160 calculates the position where the magnetic field generation unit 530 of the magnetic sensor cell 220[1,1,1] is placed. Let the origin of the coordinates be at . Similarly, when separating the sensor array signal Φ(i, j, 1), the signal space separation unit 1160 determines the position where the magnetic field generation unit 530 of the magnetic sensor cell 220 [i, j, 1] is located. For example, the center position of the feedback coil 534 of the magnetic field generation unit 530 is set as the origin of coordinates in the calculation. In this way, when the calibration magnetic field is generated from the magnetic field generation unit 530(n) of the n-th (n is an integer from 1 to M/2) magnetic sensor cell 220, the signal space separation unit 1160 generates the magnetic field. When the calibration magnetic field is generated from the unit 530(n), the sensor array signal Φ(n) (equal to Φ(i, j, 1)).Then, the magnetic field from the n-th magnetic field generating unit 530(n) is measured. When performing the signal space separation calculation and the calculation of the error ε for the sensor array signal Φ (abbreviated as Φ(n)), the coordinates in the signal space separation calculation are Calculation is performed while sequentially matching the origin. Thereby, the magnetic field measuring device 10 can greatly simplify the calibration of each magnetic sensor 520 in the sensor unit 300 included in the magnetic sensor array 210, and can accelerate the convergence of calibration parameters. Then, based on (Equation 18), the error calculation unit 1180 calculates a plurality of numbers forming the inner arc 915 from i=1 to i=Nx, from j=1 to j=Ny, and k=1. When a calibration magnetic field is generated from the magnetic field generating sections 530 of M/2 sensor sections 300 included in the magnetic sensor cell 220, the separation error is an error vector ε(n) and an error angle γ(n ), respectively.

In step 1630, the magnetic field measuring device 10 determines whether the separation error exceeds a predetermined threshold. For example, the magnetic field measuring device 10 determines whether the sum of squares of M/2 separation errors exceeds a predetermined threshold. That is, the magnetic field measurement device 10 has the M included in the plurality of magnetic sensor cells 220 forming the inner circular arc 915 from i=1 to i=Nx, from j=1 to j=Ny, and k=1. /at least one of the sum of squares of error vector ε(n) and the sum of squares of error angle γ(n) when a calibration magnetic field is generated from the magnetic field generation unit 530 of two sensor units 300. It is determined whether one of the two exceeds a predetermined threshold. If it is determined that the separation error does not exceed the threshold, the magnetic field measuring device 10 terminates the process, assuming that the calibration has been completed.

On the other hand, if it is determined in step 1630 that the separation error exceeds the predetermined threshold, the magnetic field measuring device 10 calibrates the sensor error in step 1640. That is, for example, when a calibration magnetic field is generated from the magnetic field generating sections 530 included in the first to M/2th sensor sections 300, the magnetic field measuring device 10 Using M/2 sensor array signals Φ(1) to Φ(M/2) excluding sensor signal components from , sensor errors are calibrated for the M/2 sensor units 300. For example, the calibration unit 1190 sets M/2+1≦m≦M so that at least one of the separation error as the objective function, that is, the error vector ε(n) and the error angle γ(n), becomes zero. , optimize the magnetic sensitivity vector S _Calib [m]. At this time, the calibration unit 1190 may use, for example, a computer science method such as Stochastic annealing. Here, the basis vector after calibration is expressed as in the following equation (described as an M-dimensional vector for simplicity). In this way, the calibration unit 1190 changes the basis vector so as to minimize the separation error by optimizing the magnetic sensitivity vector S _Calib [m].

In step 1650, the magnetic field measuring device 10 determines whether C is equal to MAX_COUNT. That is, the magnetic field measuring device 10 determines whether the number of times calibration is performed is the upper limit number of times.

If C is equal to MAX_COUNT, that is, if the number of times the calibration is executed is the upper limit number of times, the magnetic field measuring device 10 times out the execution of the calibration in step 1660 and ends the process. At this time, the magnetic field measuring device 10 may, for example, notify that the calibration has timed out.

On the other hand, if C is not equal to MAX_COUNT, in step 1670, the magnetic field measurement device 10 increments C to set C=C+1, initializes n to set n=1, returns the process to step 1620, and continues the flow. do. Note that in step 1620 following step 1670, the signal space separation unit 1160 may determine the solution to the equation using the following equation instead of (Equation 16).

Further, the signal space separation unit 1160 may determine the hat Φ _Calib of the sensor array signal of the magnetic sensor array 210 having a sensor error as a least squares solution vector using the following equation.

Then, the signal space separation unit 1160 may calculate the separation error between the sensor array signal Φ _Calib and the least squares solution vector Φ _Calib using a method similar to (Equation 18).

As described above, according to the magnetic field measuring device 10 according to the present embodiment, when calibrating the magnetic sensor array 210, the magnetic field generation of at least one magnetic sensor cell 220 among the plurality of magnetic sensor cells 220 in the magnetic sensor array 210 is performed. A calibration magnetic field is generated from section 530. That is, a calibration magnetic field is generated from the magnetic field generating section 530 included in at least one sensor section 300 among the plurality of sensor sections 300 in the magnetic sensor array 210. Therefore, the magnetic field measuring device 10 does not need to separately provide a device (such as a coil) for generating a calibration magnetic field in addition to the magnetic sensor array 210. Further, according to the magnetic field measurement device 10 according to the present embodiment, at least one magnetic sensor cell 220 that generates a calibration magnetic field from the magnetic field generation unit 530 is replaced with a plurality of magnetic sensor cells 220 [1, j . Therefore, the magnetic field measuring device 10 can reduce the distance between the coil that generates the calibration magnetic field and the magnetic sensor 520 that is the target of calibration, and the calibration magnetic field input to the magnetic sensor 520 can be relatively can be made stronger. Thereby, the magnetic field measuring device 10 can improve the SNR in the calibration calculation. In addition, the magnetic field measurement device 10 generates a calibration magnetic field from each of the magnetic field generation units 530 included in all the plurality of magnetic sensor cells 220 forming the inner circular arc 915, so that it is used to calibrate the magnetic sensor array 210. As the calibration magnetic field, it is possible to generate a magnetic dipole magnetic field that is less biased with respect to the position in the magnetic sensor array 210 and the direction of the magnetic field.

In the above description, the magnetic field measuring device 10 sequentially generates the magnetic field generating units 530 of M/2 sensor units 300 included in the plurality of magnetic sensor cells 220 forming the inner arc 915 of the magnetic sensor array 210. Although the case where the calibration magnetic field is generated by switching is shown as an example, the present invention is not limited to this. The magnetic field measuring device 10 generates a calibration magnetic field by sequentially switching between the magnetic sensor cells 220 located inside the magnetic sensor array 210 and M/2 sensor sections 300 included in the magnetic sensor cells 220 located outside. It's okay. That is, the magnetic field measurement device 10 may generate the calibration magnetic field by sequentially switching the magnetic field generation units 530 included in all the magnetic sensor cells 220 in the magnetic sensor array 210. In addition, when generating a calibration magnetic field by sequentially switching the magnetic field generation units 530 included in the magnetic sensor cell 220 located inside the magnetic sensor array 210, as described above, the component of the second term in (Equation 6) at the time of calibration can be ignored. On the other hand, when generating a calibration magnetic field by sequentially switching a plurality of magnetic sensor cells 220 forming an outer arc 925 of the magnetic sensor array 210, the component of the first term in (Equation 6) can be ignored during calibration. .

In that case, the magnetic field measurement device 10 generates a calibration magnetic field according to the number of calibration parameters and the number of dimensions of the basis vector, as described above, while sequentially switching the magnetic field generation units 530 included in all the magnetic sensor cells 220. The sensor error may be calibrated for all M sensor units 300 by sequentially calibrating the sensor error for (M-1) sensor units 300 excluding the sensor unit 300[P].

Instead, the magnetic field measuring device 10 performs calibration while sequentially switching the magnetic sensor cells 220[1,j,1] to 220[8,j,1] having M/2 sensor units 300 located inside. Even if a magnetic field is generated and sensor errors are sequentially calibrated only for the sensor units 300 of M/2 magnetic sensor cells 220 [1, j, 2] to 220 [8, j, 2] located outside. good. Similarly, the magnetic field measuring device 10 applies a calibration magnetic field while sequentially switching the magnetic sensor cells 220[1,j,2] to 220[8,j,2] having M/2 sensor units 300 located on the outside. The sensor errors may be sequentially calibrated only for the sensor units 300 of the M/2 magnetic sensor cells 220[1,j,1] to 220[8,j,1] located inside. That is, the sensor errors of both the sensor sections 300 of the M/2 magnetic sensor cells 220 located on the inside and the sensor sections 300 of the M/2 magnetic sensor cells 220 located on the outside may be divided and calibrated.

Furthermore, in the above description, the magnetic field measuring device 10 classifies and controls the plurality of magnetic sensor cells 220 in the magnetic sensor array 210 into an inner magnetic sensor cell 220 group and an outer magnetic sensor cell 220 group, as an example. However, it is not limited to this. For example, the magnetic field measuring device 10 divides the plurality of magnetic sensor cells 220 in the magnetic sensor array 210 into a group of magnetic sensor cells 220 [1, j, 1] to 220 [4, j, 2] on the left side and a group of magnetic sensor cells 220 [4, j, 2] on the right side when viewed from the measured object. The magnetic sensor cells 220 [5, j, 1] to 220 [8, j, 2] may be divided into groups and controlled in the same manner as above. That is, the magnetic field measuring device 10 generates a calibration magnetic field while sequentially switching the magnetic sensor cells 220 [1, j, 1] to 220 [4, j, 2] having M/2 sensor units 300 located on the left side. Then, sensor errors may be successively calibrated only for the sensor units 300 of the M/2 magnetic sensor cells 220[5,j,1] to 220[8,j,2] located on the right side. Similarly, the magnetic field measuring device 10 applies the calibration magnetic field while sequentially switching the magnetic sensor cells 220 [5, j, 1] to 220 [8, j, 2] having M/2 sensor units 300 located on the right side. The sensor error may be sequentially calibrated only for the sensor units 300 of the M/2 magnetic sensor cells 220[1,j,1] to 220[4,j,2] located on the left side.

In this way, the magnetic field measuring device 10 classifies the plurality of magnetic sensor cells 220 in the magnetic sensor array 210 into the first magnetic sensor cell 220 group and the second magnetic sensor cell 220 group, and the first magnetic sensor cell 220 group. A calibration magnetic field is generated while sequentially switching the magnetic sensor cells 220, and sensor errors are sequentially calibrated for the sensor units 300 in the second group of magnetic sensor cells 220, and the magnetic sensor cells 220 of the second group of magnetic sensor cells 220 are sequentially switched. At the same time, a calibration magnetic field may be generated to sequentially calibrate sensor errors targeting the sensor units 300 in the first magnetic sensor cell 220 group.

In addition, the magnetic field measurement device 10 generates a calibration magnetic field while sequentially switching the magnetic sensor cells 220 of one magnetic sensor cell 220 group, and sequentially calibrates sensor errors for the sensor units 300 of the other magnetic sensor cell 220 group. , it is not necessary to generate a calibration magnetic field from all the magnetic sensor cells 220 in one group of magnetic sensor cells 220. That is, the magnetic field measuring device 10 generates a calibration magnetic field while sequentially switching some of the magnetic sensor cells 220 in the first magnetic sensor cell 220 group, and targets the sensor section 300 in the second magnetic sensor cell 220 group to detect sensor errors. may be calibrated sequentially. Similarly, the magnetic field measuring device 10 generates a calibration magnetic field while sequentially switching some of the magnetic sensor cells 220 in the second magnetic sensor cell 220 group, and targets the sensor section 300 in the first magnetic sensor cell 220 group. Errors may be calibrated sequentially.

Furthermore, in the above description, the case where the magnetic field measuring device 10 classifies the plurality of magnetic sensor cells 220 in the magnetic sensor array 210 into two groups is shown as an example, but the present invention is not limited to this. For example, the magnetic field measuring device 10 may classify the plurality of magnetic sensor cells 220 in the magnetic sensor array 210 into three groups. For example, the magnetic field measuring device 10 divides the plurality of magnetic sensor cells 220 in the magnetic sensor array 210 into a first group of magnetic sensor cells 220 located on the left side when viewed from the measured object, and a second group of magnetic sensor cells located on the right side when viewed from the measured object. and a third magnetic sensor cell 220 group located between the first magnetic sensor cell 220 group and the second magnetic sensor cell 220 group. Then, the magnetic field measuring device 10 generates a calibration magnetic field while sequentially switching the magnetic sensor cells 220 of the first magnetic sensor cell 220 group, and generates a calibration magnetic field to generate a calibration magnetic field for the sensor units 300 in the second magnetic sensor cell 220 group and the third magnetic sensor cell 220 group. The sensor error may be sequentially calibrated for . Similarly, the magnetic field measuring device 10 generates a calibration magnetic field while sequentially switching the magnetic sensor cells 220 of the second magnetic sensor cell 220 group, and generates a calibration magnetic field in the sensor units of the first magnetic sensor cell 220 group and the third magnetic sensor cell 220 group. 300 may be sequentially calibrated for sensor error. That is, the magnetic field measuring device 10 generates a calibration magnetic field while sequentially switching the sensor unit 300 in the third magnetic sensor cell 220 group to the magnetic sensor cell 220 in the first magnetic sensor cell 220 group, and In both the case where the calibration magnetic field is generated while sequentially switching the magnetic sensor cells 220 of the sensor cell 220 group, overlapping calibration targets may be used.

FIG. 17 geometrically shows a signal space separation operation using the calibrated basis vector [A B] _Calib in the case where the magnetic sensor array 210 is made with a sensor error. In FIG. 17, members having the same functions and configurations as those in FIG. 14 are denoted by the same reference numerals, and description thereof will be omitted below except for differences. The magnetic field measuring device 10 updates the base vector according to the flow shown in FIG. 16 . Here, reference numeral 1720 indicates a linear subspace Span{A _Calib } spanned by the basis vector A _Calib after calibration. Reference numeral 1730 indicates a linear subspace Span{B _Calib } spanned by the basis vector B _Calib after calibration. Reference numeral 1740 indicates a linear subspace spanned by a basis vector [A B] _Calib that is a linear sum of the linear subspace Span {A _Calib } and the linear subspace Span {B _Calib }. Reference numeral 1750 indicates an M-dimensional vector of the least squares solution. As shown in this figure, the sensor array signal Φ _Uncalibb of the magnetic sensor array 210 having a sensor error exists in a linear subspace spanned by the calibrated basis vector [A B] _Calib . In other words, the signal space separation unit 1160 optimizes the basis vectors so as to minimize the separation error, thereby dividing the signal space distribution into the target magnetic field component and the disturbance magnetic field component for the magnetic field detected by the magnetic sensor array 210. can be done accurately.

In addition, in the above description, an example is given of a case where the magnetic field measuring device 10 changes the basis vector so as to minimize the separation error by optimizing the magnetic sensitivity vector S _Calib [m] as a calibration parameter. It was shown as However, as described above, in addition to the magnetic sensitivity error of each sensor, the sensor error may include a position error due to a shift in the arrangement position of each sensor during assembly of the magnetic sensor array 210. Therefore, the magnetic field measurement device 10 uses the position information of the magnetic sensors 520 of the M sensor units 300 as a calibration parameter, instead of or in addition to the magnetic sensitivity vector S _Calib [m], here, the signal space separation The basis vector may be changed to minimize the separation error by optimizing the position information in the calculation coordinate system, that is, the radius r, the zenith angle θ, and the azimuth angle φ. That is, the base vector may be changed using r, θ, and φ in (Equation 19) as calibration parameters. Note that the magnetic field measuring device 10 can also calibrate such position errors using the same method as the calibration of magnetic sensitivity errors. Further, the magnetic field measuring device 10 may perform calculations to simultaneously optimize the magnetic sensitivity error calibration and the position error calibration.

Furthermore, in the above description, an example is given in which the magnetic field measuring device 10 measures the magnetic field to be measured after performing calibration. However, for example, if the frequency of the alternating magnetic field as the calibration magnetic field is higher than the frequency band of the magnetic field to be measured, the magnetic field measuring device 10 may perform calibration and measurement of the magnetic field to be measured at the same time. good. In this case, the magnetic field measuring device 10 may frequency-separate the calibration magnetic field signal and the measurement target magnetic field signal using an LPF, an HPF, or the like.

Various embodiments of the invention may be described with reference to flowcharts and block diagrams, where the blocks represent (1) a stage in a process at which an operation is performed, or (2) a device responsible for performing the operation. may represent a section of Certain steps and sections may be implemented by dedicated circuitry, programmable circuitry provided with computer-readable instructions stored on a computer-readable medium, and/or a processor provided with computer-readable instructions stored on a computer-readable medium. It's fine. Specialized circuits may include digital and/or analog hardware circuits, and may include integrated circuits (ICs) and/or discrete circuits. Programmable circuits include logic AND, logic OR, logic may include reconfigurable hardware circuits, including, for example.

A computer-readable medium may include any tangible device capable of storing instructions for execution by a suitable device, such that the computer-readable medium having instructions stored thereon is illustrated in a flowchart or block diagram. An article of manufacture will be provided that includes instructions that can be executed to create a means for performing the operations. Examples of computer readable media may include electronic storage media, magnetic storage media, optical storage media, electromagnetic storage media, semiconductor storage media, and the like. More specific examples of computer readable media include floppy disks, diskettes, hard disks, random access memory (RAM), read only memory (ROM), erasable programmable read only memory (EPROM or flash memory), Electrically Erasable Programmable Read Only Memory (EEPROM), Static Random Access Memory (SRAM), Compact Disc Read Only Memory (CD-ROM), Digital Versatile Disk (DVD), Blu-ray (RTM) Disc, Memory Stick, Integrated Circuit cards etc. may be included.

Computer-readable instructions include assembler instructions, instruction set architecture (ISA) instructions, machine instructions, machine-dependent instructions, microcode, firmware instructions, state configuration data, or object-oriented programming such as Smalltalk, JAVA, C++, etc. language, and either source code or object code written in any combination of one or more programming languages, including traditional procedural programming languages such as the "C" programming language or similar programming languages. good.

Computer-readable instructions may be implemented on a processor or programmable circuit of a general purpose computer, special purpose computer, or other programmable data processing device, either locally or over a wide area network (WAN), such as a local area network (LAN), the Internet, etc. ), computer-readable instructions may be executed to create a means for performing the operations specified in the flowchart or block diagrams. Examples of processors include computer processors, processing units, microprocessors, digital signal processors, controllers, microcontrollers, and the like.

FIG. 18 illustrates an example computer 2200 in which aspects of the invention may be implemented, in whole or in part. A program installed on computer 2200 may cause computer 2200 to function as an operation or one or more sections of an apparatus according to an embodiment of the present invention, or to perform one or more operations associated with an apparatus according to an embodiment of the present invention. Sections and/or computer 2200 may be caused to perform a process or a step of a process according to an embodiment of the invention. Such programs may be executed by CPU 2212 to cause computer 2200 to perform certain operations associated with some or all of the blocks in the flowcharts and block diagrams described herein.

Computer 2200 according to this embodiment includes a CPU 2212, RAM 2214, graphics controller 2216, and display device 2218, which are interconnected by host controller 2210. Computer 2200 also includes input/output units, such as a communication interface 2222, a hard disk drive 2224, a DVD-ROM drive 2226, and an IC card drive, which are connected to the host controller 2210 via an input/output controller 2220. There is. The computer also includes legacy input/output units, such as ROM 2230 and keyboard 2242, which are connected to input/output controller 2220 via input/output chip 2240.

CPU 2212 operates according to programs stored in ROM 2230 and RAM 2214, thereby controlling each unit. Graphics controller 2216 obtains image data generated by CPU 2212, such as in a frame buffer provided in RAM 2214 or itself, and causes the image data to be displayed on display device 2218.

Communication interface 2222 communicates with other electronic devices via a network. Hard disk drive 2224 stores programs and data used by CPU 2212 within computer 2200. DVD-ROM drive 2226 reads programs or data from DVD-ROM 2201 and provides the programs or data to hard disk drive 2224 via RAM 2214. The IC card drive reads programs and data from and/or writes programs and data to the IC card.

ROM 2230 stores therein programs that are dependent on the computer 2200 hardware, such as a boot program that is executed by the computer 2200 upon activation. Input/output chip 2240 may also connect various input/output units to input/output controller 2220 via parallel ports, serial ports, keyboard ports, mouse ports, and the like.

A program is provided by a computer readable medium such as a DVD-ROM 2201 or an IC card. The program is read from a computer readable medium, installed on hard disk drive 2224, RAM 2214, or ROM 2230, which are also examples of computer readable media, and executed by CPU 2212. The information processing described in these programs is read by the computer 2200 and provides coordination between the programs and the various types of hardware resources described above. An apparatus or method may be configured to implement the manipulation or processing of information according to the use of computer 2200.

For example, when communication is performed between the computer 2200 and an external device, the CPU 2212 executes a communication program loaded into the RAM 2214 and sends communication processing to the communication interface 2222 based on the processing written in the communication program. You can give orders. The communication interface 2222 reads transmission data stored in a transmission buffer processing area provided in a recording medium such as a RAM 2214, a hard disk drive 2224, a DVD-ROM 2201, or an IC card under the control of the CPU 2212, and transmits the read transmission data. Data is transmitted to the network, or received data received from the network is written to a reception buffer processing area provided on the recording medium.

Further, the CPU 2212 causes the RAM 2214 to read all or a necessary part of a file or database stored in an external recording medium such as a hard disk drive 2224, a DVD-ROM drive 2226 (DVD-ROM 2201), an IC card, etc. Various types of processing may be performed on data on RAM 2214. The CPU 2212 then writes back the processed data to the external recording medium.

Various types of information, such as various types of programs, data, tables, and databases, may be stored on a recording medium and subjected to information processing. The CPU 2212 performs various types of operations, information processing, conditional determination, conditional branching, unconditional branching, and information retrieval on the data read from the RAM 2214 as described elsewhere in this disclosure and specified by the instruction sequence of the program. Various types of processing may be performed, including /substitutions, etc., and the results are written back to RAM 2214. Further, the CPU 2212 may search for information in a file in a recording medium, a database, or the like. For example, if a plurality of entries are stored in the recording medium, each having an attribute value of a first attribute associated with an attribute value of a second attribute, the CPU 2212 search the plurality of entries for an entry that matches the condition, read the attribute value of the second attribute stored in the entry, and thereby associate it with the first attribute that satisfies the predetermined condition. The attribute value of the second attribute may be acquired.

The programs or software modules described above may be stored on computer readable media on or near computer 2200. Also, a recording medium such as a hard disk or RAM provided in a server system connected to a dedicated communication network or the Internet can be used as a computer-readable medium, thereby providing the program to the computer 2200 via the network. do.

Although the present invention has been described above using the embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments. It will be apparent to those skilled in the art that various changes or improvements can be made to the embodiments described above. It is clear from the claims that such modifications or improvements may be included within the technical scope of the present invention.

The order of execution of each process, such as the operation, procedure, step, and stage in the apparatus, system, program, and method shown in the claims, specification, and drawings, is specifically defined as "before" or "before". It should be noted that they can be implemented in any order unless the output of the previous process is used in the subsequent process. Even if the claims, specifications, and operational flows in the drawings are explained using "first," "next," etc. for convenience, this does not mean that it is essential to carry out the operations in this order. It's not a thing.

10 Magnetic field measuring device 100 Main unit 110 Magnetic sensor unit 120 Head 125 Drive unit 130 Base unit 140 Pole unit 150 Information processing unit 210 Magnetic sensor array 220 Magnetic sensor cell 230 Sensor data collection unit 232 AD converter 234 Clock generator 300 Sensor unit 520 Magnetic sensor 530 Magnetic field generation section 532 Amplification circuit 534 Feedback coil 540 Output section 710 Magnetoresistive elements 720, 730 Magnetic convergence plate 1010 Switching section 1100 Sensor data processing section 1120 Measured data acquisition section 1130 Synchronous detection section 1140 Data output section 1150 Base vector storage Section 1160 Signal space separation section 1170 Calibration clock generation section 1180 Error calculation section 1190 Calibration section 2200 Computer 2201 DVD-ROM
2210 Host controller 2212 CPU
2214 RAM
2216 Graphic controller 2218 Display device 2220 Input/output controller 2222 Communication interface 2224 Hard disk drive 2226 DVD-ROM drive 2230 ROM
2240 Input/output chip 2242 Keyboard

Claims (15)

Each has a curved surface shape curved in at least one direction, each of which includes a magnetic sensor, an output section that outputs an output signal, and a size that corresponds to the output signal to reduce the input magnetic field detected by the magnetic sensor. A magnetic field generator configured by arranging a plurality of magnetic sensor cells having a magnetic field generating section that generates a feedback magnetic field in three dimensions so as to be arranged at lattice points included in the curved surface shape, and capable of detecting input magnetic fields in three axial directions. sensor array,
a measurement data acquisition unit that acquires measurement data measured by the magnetic sensor array;
A vector signal having, as each signal component, a signal output by each of the magnetic sensors when the magnetic sensor array detects a magnetic field having a spatial distribution of an orthonormal function of the spatial distribution of the input magnetic field indicated by the measurement data. a signal space separation unit that separates signals using the basis vector;
A sensor error in the magnetic sensor is calibrated based on a separation error when a spatial distribution of a calibration magnetic field generated from the magnetic field generation unit of at least one of the plurality of magnetic sensor cells is separated into signals. A magnetic field measurement device comprising a calibration section and. The magnetic field measurement device according to claim 1, wherein the output section outputs the output signal according to a feedback current that the magnetic field generation section sends to generate the feedback magnetic field. Each of the magnetic sensors includes a magnetic resistance element and two magnetic convergence plates arranged at both ends of the magnetic resistance element, and the magnetic resistance element is arranged at a position sandwiched between the two magnetic convergence plates. The magnetic field measuring device according to claim 2. 4. The magnetic field generation unit includes a feedback coil wound along the axial direction of the magnetic field to be detected by the magnetic sensor so as to surround the magnetoresistive element and the two magnetic convergence plates. The magnetic field measurement device described. The magnetic field according to any one of claims 1 to 4, wherein the calibration unit calibrates a sensor error in the magnetic sensor based on each of the separation errors when the at least one magnetic sensor cell is sequentially switched. Measuring device. The magnetic sensor array is configured by arranging the plurality of magnetic sensor cells three-dimensionally in an arc shape when viewed in cross section,
The calibration unit calibrates a sensor error in the magnetic sensor based on each of the separation errors when the at least one magnetic sensor cell is sequentially switched over a plurality of magnetic sensor cells forming an inner circular arc. 5. The magnetic field measuring device according to 5. The at least one magnetic sensor cell further includes a switching unit that switches whether the magnetic field generation unit generates the feedback magnetic field or the calibration magnetic field. Magnetic field measurement device. 1 . The signal space separation unit, in signal separation of the spatial distribution of the calibration magnetic field, uses a position where the magnetic field generation unit of the at least one magnetic sensor cell is arranged as an origin of coordinates in calculation. 8. The magnetic field measuring device according to any one of 7 to 7. The magnetic field measurement device according to any one of claims 1 to 8, wherein the calibration unit calibrates the sensor error by changing the base vector. The magnetic field measuring device according to claim 9, wherein the calibration unit optimizes the basis vector so as to minimize the separation error. The magnetic field measuring device according to any one of claims 1 to 10, further comprising a synchronous detection unit that detects the calibration magnetic field, which is an alternating magnetic field, using a signal having a frequency of the alternating magnetic field. The magnetic field measuring device according to claim 11, wherein the frequency of the alternating magnetic field is higher than the frequency band of the magnetic field to be measured. Each has a curved surface shape curved in at least one direction, and each includes a magnetic sensor, an output section that outputs an output signal, and a feedback that reduces the input magnetic field detected by the magnetic sensor, with a size corresponding to the output signal. A magnetic sensor configured by arranging a plurality of magnetic sensor cells having a magnetic field generation unit that generates a magnetic field in three dimensions so as to be arranged at lattice points included in the curved surface shape, and capable of detecting input magnetic fields in three axial directions. obtaining measurement data measured by the array;
A vector signal having, as each signal component, a signal output by each of the magnetic sensors when the magnetic sensor array detects a magnetic field having a spatial distribution of an orthonormal function of the spatial distribution of the input magnetic field indicated by the measurement data. to separate the signals using as the basis vector,
Generating a calibration magnetic field from the magnetic field generation unit included in at least one magnetic sensor cell of the plurality of magnetic sensor cells;
A method for measuring a magnetic field, comprising: calibrating a sensor error in the magnetic sensor based on a separation error when the spatial distribution of the calibration magnetic field is separated into signals. executed by a computer to cause said computer to:
Each has a curved surface shape curved in at least one direction, and each includes a magnetic sensor, an output section that outputs an output signal, and a feedback that reduces the input magnetic field detected by the magnetic sensor, with a size corresponding to the output signal. A magnetic sensor configured by arranging a plurality of magnetic sensor cells having a magnetic field generation unit that generates a magnetic field in three dimensions so as to be arranged at lattice points included in the curved surface shape, and capable of detecting input magnetic fields in three axial directions. a measurement data acquisition unit that acquires measurement data measured by the array;
A vector signal having, as each signal component, a signal output by each of the magnetic sensors when the magnetic sensor array detects a magnetic field having a spatial distribution of an orthonormal function of the spatial distribution of the input magnetic field indicated by the measurement data. a signal space separation unit that separates signals using the basis vector;
A sensor error in the magnetic sensor is calibrated based on a separation error when a spatial distribution of a calibration magnetic field generated from the magnetic field generation unit of at least one of the plurality of magnetic sensor cells is separated into signals. A magnetic field measurement program that functions as a calibration section. A plurality of magnetic field generators each having a magnetic sensor, an output section that outputs an output signal, and a magnetic field generation section that generates a feedback magnetic field having a size according to the output signal and that reduces an input magnetic field detected by the magnetic sensor. A magnetic sensor array configured by three-dimensionally arranging magnetic sensor cells and capable of detecting input magnetic fields in three axial directions;
a measurement data acquisition unit that acquires measurement data measured by the magnetic sensor array;
A vector signal having, as each signal component, a signal output by each of the magnetic sensors when the magnetic sensor array detects a magnetic field having a spatial distribution of an orthonormal function of the spatial distribution of the input magnetic field indicated by the measurement data. a signal space separation unit that separates signals using the basis vector;
A sensor error in the magnetic sensor is calibrated based on a separation error when a spatial distribution of a calibration magnetic field generated from the magnetic field generation unit of at least one of the plurality of magnetic sensor cells is separated into signals. A magnetic field measurement device comprising a calibration section and.

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