JP6964859B2 - Magnetic material position search system and position search method - Google Patents

Description

The present application relates to a position search system and a position search method for searching the position of a magnetic material by detecting a change in the magnetic flux density of a magnetic field.

In recent years, hyperthermia (hyperthermia), which has fewer side effects than chemotherapy and is a means for treating malignant tumors with less invasiveness than surgical therapy, has attracted attention. Hyperthermia is a therapy that heats tumor tissue using microwaves or high-frequency current as an energy source, and utilizes the fact that an antitumor effect occurs when the tumor tissue is continuously heated to 40 ° C to 45 ° C. be.

In Patent Document 1, a temperature-sensitive magnetic material is placed in a measured portion such as inside the body, and a magnetic field is generated from a place away from the temperature-sensitive magnetic material to induce and heat the temperature-sensitive magnetic material to add the measured portion. The method of heating is described.

International Publication No. 2009/088062

In the method of Patent Document 1, since the position of the temperature-sensitive magnetic material arranged in the measured portion cannot be appropriately grasped, the temperature-sensitive magnetic material may be deviated from the central axis of the magnetic field generation source. When a magnetic field is generated while the temperature-sensitive magnetic material is off the central axis of the magnetic field generation source, the magnetic flux density (magnetic flux vector) of the magnetic field applied to the temperature-sensitive magnetic material decreases, and the heat generation efficiency of the temperature-sensitive magnetic material decreases. May decrease. In addition, there is a risk that the SN ratio of the signal for detecting the temperature of the temperature-sensitive magnetic material may decrease.

Therefore, in the present application, a position search system and a position search method for searching the position of a magnetic material are disclosed.

As a result of diligent studies, the present inventors have found that it is possible to search for the position of a magnetic material by generating a magnetic field and detecting a change in the magnetic flux density of the magnetic field.

In the present application, based on the above findings, as one of the means for solving the above problems,
A system for searching the position of a magnetic material, which comprises a magnetic field generation source for generating a magnetic field and at least one magnetic sensor capable of detecting a change in the magnetic flux density of the magnetic field, and the magnetic material exists. By moving the magnetic sensor together with the magnetic field generation source while applying the magnetic field, scanning is performed so that the magnetic sensor detects a change in the magnetic flux density, and the magnetic sensor performs scanning during the scanning. A position search system that searches for the position where the magnetic material exists in the region based on the detected change in magnetic flux density.
To disclose.

The "change in the magnetic flux density of the magnetic field" means a change in the magnetic flux density of the magnetic field depending on the magnetic permeability of the magnetic material.
The “region in which the magnetic material can exist” means a region in which the magnetic sensor can detect a change in the magnetic flux density of the magnetic field depending on the magnetic permeability of the magnetic material.

The position system includes three or more of the magnetic sensors, the magnetic sensor outputs a change in the magnetic flux density as a change in voltage, and two magnetics arbitrarily selected from the three or more magnetic sensors. The difference between the voltages output from the sensors is in the range of 5 μV or less, and the average value of the voltages output from the two magnetic sensors and the voltage output from the magnetic sensors other than the two magnetic sensors. It is preferable to specify the position B in which the difference between the two is in the range of 5 μV or less.

The position search system identifies a position A in which the difference between the voltages output from the two magnetic sensors arbitrarily selected from the three or more magnetic sensors is in the range of 5 μV or less, and from the position A, the position A is described. It is preferable to specify the position B by performing the scanning while maintaining the difference between the voltages output from the two magnetic sensors in the range of 5 μV or less.

The position search system transfers the region to the three or more magnetic sensors by moving the magnetic sensor together with the magnetic field generation source while applying a magnetic field so that the locus of the central axis of the magnetic field generation source is closed. Two or more trials for scanning are performed, and based on the voltage output from the magnetic sensor, the trial in which the central axis of the magnetic field generation source is closest to the magnetic material is determined, and on the trajectory of the closest trial. Alternatively, it is preferable to further perform the scanning from the position where the central axis exists inside the locus to specify the position A.

The "central axis of the magnetic field generation source" means the central axis of the magnetic field generated from the magnetic field generation source, and when the magnetic field generation source is a coil, it is the central axis of the coil.

It is preferable to move the magnetic field generation source and the magnetic sensor so that the locus in the trial is circular.
Further, it is preferable to exclude the trial in which at least one of the voltages output from the three or more magnetic sensors is 0 V or less.

The position search system extracts the maximum value of the voltages output from each of the three or more magnetic sensors for each trial, compares the extracted maximum values, and compares the extracted maximum values with the smallest maximum value (the smallest maximum value (). It is _preferable to extract V max_min), compare the _{V max_min} extracted for each trial, and determine the trial with the largest _{V max_min as the closest trial.}

The position search system performs the scanning from the position B in a direction parallel to the central axis, and from the relationship between the average value of the voltages output from the three or more magnetic sensors and the moving distance of the magnetic sensors. , It is preferable to search for the position of the magnetic material.

It is preferable that the three or more magnetic sensors are arranged at positions on the plane which are substantially equidistant from the central axis on the plane orthogonal to the central axis. The term "substantially equidistant" means that the difference in distance between the central axis and each magnetic sensor on a plane orthogonal to the central axis is within the range of 1/10 of the size of the magnetic material. show. The size of the magnetic material here represents the largest length of the magnetic material, but when the magnetic material is a granular powder, it is not the particle size of the magnetic material but the largest in the range in which the magnetic material is distributed. Represents a large length.
Further, it is preferable that the three or more magnetic sensors are arranged at equal intervals on the circumference centered on the central axis.

In the position search system, it is preferable that the magnetic field generation source and the magnetic sensor are coils.

The position search system preferably includes a lock-in amplifier that detects a signal from the magnetic sensor and a resistor that inputs a reference signal to the lock-in amplifier.

It is preferable that the magnetic material is a temperature-sensitive magnetic material having an arbitrary Curie point.

In the present application, based on the above findings, as one of the means for solving the above problems,
A method of searching for the position of a magnetic material, in which a magnetic flux density of the magnetic field is changed in the magnetic sensor by moving the magnetic sensor together with a magnetic field generation source while applying a magnetic field in a region where the magnetic material can exist. A position search method for searching for a position in the region where the magnetic material exists based on a change in the magnetic flux density detected by the magnetic sensor during the scan.
To disclose.

According to the magnetic body position search system and the position search method of the present disclosure, it is possible to specify the range in which the magnetic material exists even for the magnetic material that cannot be searched visually.

It is an external perspective view explaining the position system 10. It is a figure which observed the position system 10 from above. It is a figure which observed the magnetic field application detection means 3 from the direction of III of FIG. It is a figure which shows and explains the relative movement of a magnetic body 100 when specifying a position A and a position B based on the closest trial. It is a figure explaining the position system which concerns on Example. This is a result showing the relationship between the relative orbital angle and the pickup voltage in the trial when the distance between the central axis O and the center Z is 0 mm. This is a result showing the relationship between the relative orbital angle and the pickup voltage in the trial when the distance between the central axis O and the center Z is 10 mm. This is a result showing the relationship between the relative orbital angle and the pickup voltage in the trial when the distance between the central axis O and the center Z is 30 mm. This is a result showing the relationship between the relative orbital angle and the pickup voltage in the trial when the distance between the central axis O and the center Z is 50 mm. When the magnetic material is arranged at a position 10 mm upward in the vertical direction from the xy plane, the position of the central axis X when the central axis X of the magnetic material moves relative to the x-axis (-10 mm to 10 mm). This is a result showing the relationship with the pickup voltage. When the magnetic material is arranged at a position 20 mm upward in the vertical direction from the xy plane, the position of the central axis X when the central axis X of the magnetic material moves relative to the x-axis (-10 mm to 10 mm). This is a result showing the relationship with the pickup voltage. This is a result showing the relationship between the position of the central axis X and the pickup voltage when the central axis X of the magnetic material moves relative (-10 mm to 55 mm) on the x-axis. This is a result showing the relationship between the distance between the magnetic field application detecting means and the magnetic material and the pickup voltage when the magnetic field detecting means is moved from the position B in a direction parallel to the central axis O of the drive coil.

In the present application, a scan is performed in which a magnetic sensor is made to detect a change in the magnetic flux density of the magnetic field by moving the magnetic sensor together with the magnetic field generation source while applying a magnetic field in a region where a magnetic material can exist. Disclosed is a position search system and a position search method for searching a position where a magnetic material exists in the region based on a change in the magnetic flux density detected by a magnetic sensor.
Here, the "change in the magnetic flux density of the magnetic field" means a change in the magnetic flux density of the magnetic field depending on the magnetic permeability of the magnetic material. The “region in which a magnetic material can exist” means a region in which a magnetic sensor can detect a change in the magnetic flux density of a magnetic field depending on the magnetic permeability of the magnetic material.

Hereinafter, a mode in which a drive coil is used as the magnetic field generation source and a pickup coil is used as the magnetic sensor will be described, but the position search system and the position search method of the present disclosure are not limited to this.
Further, in the following forms, the drive coil and the pickup coil are provided in the magnetic field application detection unit.

1. 1. Magnetic material position search system 10
FIG. 1 shows how the position search system 10 searches for the position of the magnetic material 100. The position search system 10 applies a magnetic field including a drive coil 1 (magnetic field generation source) for generating a magnetic field and three pickup coils 2 (magnetic sensors) capable of detecting changes in the magnetic flux density of the magnetic field. The detection means 3 is provided.

1.1. Magnetic material 100
The magnetic material 100 is not particularly limited as long as it is a material capable of being magnetized, but is preferably a ferromagnetic material. Specific examples thereof include ferromagnets containing magnetic materials such as iron, cobalt, and nickel. Further, as the ferromagnet, it is preferable to use a temperature-sensitive magnetic material in which the Curie point can be arbitrarily set.
The temperature-sensitive magnetic material is a magnetic material containing a magnetic material whose Curie point can be arbitrarily set by changing the composition ratio, adding additives, heat treatment, or the like. Specific examples of the magnetic material used for the temperature-sensitive magnetic material include Ni-Zn-based ferrite and Mn-Cu-Zn-based ferrite. When used for measuring the temperature of the affected area when performing hyperthermia (hyperthermia), it is preferable to select a magnetic material capable of setting the Curie point to about 43 degrees. Specific examples of such a magnetic material include Ni—Zn-based ferrite and Mn—Cu—Zn-based ferrite.
Further, when searching for the position of the temperature-sensitive magnetic material using the position search system 10, it is preferable that the temperature of the temperature-sensitive magnetic material is a temperature equal to or lower than the Curie point. This is because the magnetic permeability of the temperature-sensitive magnetic material sharply decreases when the temperature is equal to or higher than the Curie point.

1.2. Magnetic field application detecting means 3
The magnetic field application detecting means 3 includes a drive coil 1 (magnetic field generation source) and a pickup coil 2 (magnetic sensor).

1.2.1. Drive coil 1
The drive coil 1 is a coil capable of passing alternating current. By using a coil capable of passing alternating current, it is possible to improve the durability of the entire position search system 10 and reduce the cost. Further, there is an advantage that the cross-axis effect generated in the semiconductor element can be completely removed.
The coil is preferably formed of a litz wire (a conductor obtained by twisting 100 thin wires obtained by coating and insulating a copper wire (for example, a copper wire having a diameter of 0.08 mm) with enamel or the like). By using the litz wire, the resistance value does not increase due to the skin effect when a high frequency current is passed, and the heat generated by the coil itself can be cooled.
The outer diameter, inner diameter, thickness, and number of turns of the coil can be appropriately set as needed. Note that increasing the inner diameter of the coil or increasing the number of turns can increase the inductance of the coil, so that the magnitude of the magnetic flux density can be increased even at a position away from the central axis of the coil. , Requires a large power supply. When used for hyperthermia (hyperthermia), the thinner the coil, the easier it is to handle.

1.2.2. Pickup coil 2
The pickup coil 2 is a coil, and a change in the detected magnetic flux density can be output as a change in voltage.
The coil is preferably formed from litz wire. By using the litz wire, the resistance value does not increase due to the skin effect when a high frequency current is passed, and the heat generated by the coil itself can be cooled. Further, by reducing the cross-sectional area of the copper wire used for the litz wire as illustrated above, it is possible to suppress the generation of eddy current due to the high frequency magnetic field and reduce the influence of the pickup coil itself disturbing the magnetic field.
The outer diameter, inner diameter, thickness, and number of turns of the coil can be appropriately set as needed. If the inner diameter of the coil is small, the output voltage will decrease, but the spatial resolution for detecting distortion (change) in the magnetic flux density will improve. On the other hand, if the inner diameter of the coil is large, the output voltage is improved, but the spatial resolution for detecting the distortion (change) of the magnetic flux density is lowered. The thinner the coil, the easier it is to place the coil in the position search system.

Further, in the magnetic field application detecting means 3 shown in FIG. 1, the pickup coil 2 is composed of three pickup coils 2a, 2b, and 2c (hereinafter, the "pickup coil 2" is the pickup coils 2a, 2b, and 2c. It may refer to the one including all.).
When the number of pickup coils is three, the range in which the magnetic body 100 exists in the region where the magnetic body 100 can exist can be specified up to the central axis of the drive coil 1, and the position of the magnetic body 100 can be specified. Is easy to estimate.

FIG. 2 is a view of the magnetic field application detecting means 3 observed from above. Here, the xy plane is a plane orthogonal to the central axis O of the drive coil and in contact with the upper surface of the pickup coil 2.

As shown in FIG. 2, it is preferable that the pickup coil 2 is arranged at a position on the plane which is substantially equidistant from the central axis O on the plane orthogonal to the central axis O. This means that all the pickup coils 2 are included on a plane orthogonal to the central axis O, and the distances from the central axis O on the plane to the pickup coils 2 are approximately equidistant. It is more preferable that the center of the pickup coil 2 is included in a plane orthogonal to the central axis O. Further, it is more preferable that the distances from the central axis O to the pickup coil 2 are equidistant. As a result, the magnetic field of the drive coil 1 applied to the pickup coil 2 becomes uniform, so that the position search accuracy of the magnetic body 100 is improved.
Here, "substantially equidistant" means that the difference in distance between the central axis O and each pickup coil on a plane orthogonal to the central axis O is within the range of 1/10 of the size of the magnetic material. Represents that. The size of the magnetic material here represents the longest length of the magnetic material, but when the magnetic material is a granular powder, it is not the particle size of the magnetic material but the range in which the magnetic material is distributed. Represents the largest length in.

FIG. 3 is a side view of the magnetic field application detecting means 3 observed from the direction shown in FIG. 2III.
As shown in FIG. 3, a plane orthogonal to the central axis O of the drive coil 1 and in contact with the upper surface of the drive coil 1 and orthogonal to the central axis O of the drive coil 1 and on the upper surface of the pickup coil 2. The distance h from the contact plane (xy plane) is preferably 5 mm or more and 15 mm or less, and more preferably 8 mm or more and 12 mm or less.
By arranging the drive coil 1 and the pickup coil 2 so that the distance h is included in the above range, the sensitivity for detecting the change in the magnetic flux density of the pickup coil 2 can be improved, and the region where the magnetic body 100 can exist can be expanded. .. That is, even if the magnetic body 100 and the pickup coil 2 are separated to some extent, the change in the magnetic flux density of the magnetic field depending on the magnetic permeability of the magnetic body 100 can be detected by the pickup coil 2.

Further, it is preferable that the pickup coils 2 are arranged at equal intervals on the circumference centered on the central axis O. As a result, the range in which the change in the magnetic flux density when the magnetic field application detecting means 3 is scanned is maximized. Further, under the condition that the central axis O coincides with the central axis of the magnetic material, the voltages output from the pickup coils 2 become equal to each other, so that the position search algorithm of the magnetic material becomes simple. In FIG. 1, the smaller of the angles formed by the central axis O and the two pickup coils 2 is arranged so as to be 120 °, respectively.

The distance of the drive coil 1 of the pickup coil 2 from the central axis O can be appropriately set according to the usage conditions, but the shorter the distance, the larger the change in the magnetic flux density can be detected.
Here, the distance of the drive coil 1 of the pickup coil 2 from the central axis O represents the shortest distance from the central axis O.
Further, as shown in FIGS. 1 and 2, it is preferable that the pickup coil 2 is arranged inside the drive coil 1.

Further, it is preferable that the pickup coil 2 is fixed in a posture in which an induced electromotive force is not generated in the pickup coil 2 in a state where it is not affected by the magnetic material 100. Specifically, as shown in FIGS. 1 to 3, it is preferable that the surface including the outer periphery of the pickup coil 2 is fixed in a direction parallel to the applied magnetic field, and the pickup coil 2 is preferably fixed. It is more preferable that the central axis of the drive coil and the central axis O of the drive coil are orthogonal to each other.

1.3. Search for magnetic body 100 The position search system 10 causes the pickup coil 2 to change the magnetic flux density of the magnetic field by moving the pickup coil 2 together with the drive coil 1 while applying a magnetic field in the region where the magnetic body 100 can exist. Scanning to be detected (hereinafter, may be referred to as "scanning by a magnetic field application detecting means") is performed, and the magnetic material 100 in the above region is based on the change in the magnetic flux density detected by the pickup coil 2 during the scanning. One of the features is to search for the position where is present.
The preferred embodiment will be described below.

In the position search system 10, the pickup coil 2 outputs a change in magnetic flux density as a change in voltage, and the voltage output from two pickup coils arbitrarily selected from the three pickup coils 2 (hereinafter, "pickup"). The difference between (sometimes referred to as “voltage”) is in the range of 5 μV or less, and the average value of the pickup voltages output from the above two pickup coils 2 and the pickup coils 2 other than the above two pickup coils 2 are output. It is preferable to specify the position B in which the difference from the pickup voltage is in the range of 5 μV or less.
Thereby, the range in which the magnetic body 100 exists in the magnetic body existing region can be specified up to the central axis of the drive coil 1.
The difference in voltage output from the two pickup coils 2 arbitrarily selected from the three pickup coils 2 is more preferably 3 μV or less, further preferably 1 μV or less, and 0.5 μV or less. Is particularly preferable, and 0 V is most preferable. The closer the difference is to 0V, the higher the accuracy of searching for the position of the magnetic material. Further, the difference between the average value of the pickup voltages output from the two pickup coils 2 and the pickup voltages output from the pickup coils 2 other than the two pickup coils 2 is more preferably 3 μV or less, and more preferably 1 μV or less. Is more preferable, 0.5 μV or less is particularly preferable, and 0 V is most preferable. The closer the difference is to 0V, the higher the accuracy of searching for the position of the magnetic material.

At position B, a position A in which the difference between the pickup voltages output from the two pickup coils 2 arbitrarily selected from the three pickup coils 2 is within a range of 5 μV or less is specified, and from the position A, the above two pickup coils 2 are specified. It is preferable to specify by scanning with the magnetic field application detecting means while maintaining the difference of the pickup voltage output from the above in the range of 5 μV or less.
As a result, the position B can be easily specified.
The difference between the pickup voltages output from the two pickup coils 2 is more preferably 3 μV or less, further preferably 1 μV or less, particularly preferably 0.5 μV or less, and 0 V. Is the most preferable. The closer the difference is to 0V, the higher the accuracy of searching for the position of the magnetic material.
Further, from the relationship between the two pickup coils 2 and the position A, the region where the magnetic material 100 can exist is referred to as a plane equidistant from the two pickup coils 2 including the position A (hereinafter, referred to as "xz plane"). It may be possible to identify up to the above. Therefore, it can be said that the movement from the position A to the position B is moving in the direction parallel to the xz plane.

Further, the position A is a region where the magnetic body 100 can exist by moving the pickup coil 2 together with the drive coil 1 while applying a magnetic field so that the locus of the central axis O of the drive coil 1 is closed. Is performed twice or more, and based on the pickup voltage output from the pickup coil 2, the trial in which the central axis O of the drive coil 1 is closest to the magnetic body 100 is determined, and the locus of the closest trial is determined. It is preferable to specify by further scanning with the magnetic field application detecting means from the position where the central axis O exists on the upper side or the inner side of the locus.
As a result, the position A can be easily specified.

It is preferable to move the drive coil 1 and the pickup coil 2 so that the locus in the above trial is circular. Thereby, it is possible to determine the trial in which the center of the locus of the central axis O and the magnetic material 100 are closest to each other. The circular radius can be set as appropriate, but is preferably less than half the distance from the central axis O of the drive coil 1 to the pickup coil 2. For example, it is 5 mm or more and 10 mm or less. This improves the accuracy of determining the closest trial.

It is preferable to exclude trials in which at least one of the pickup voltages output from the pickup coil 2 is 0 V or less. This improves the accuracy of determining the closest trial.
It is preferable that the trajectories in the above trial do not overlap with each other. This makes it possible to scan a wide range with a small number of trials.

Further, in the determination of the closest trial, the maximum value of the pickup voltages output from each of the three pickup coils 2 is extracted for each trial, and the extracted maximum values are compared to obtain the smallest maximum value. It is _preferable to extract (V max_min), compare the _{extracted V max_min} for each trial, and determine the trial with the largest _{V max_min as the closest trial.}
This improves the accuracy of determining the closest trial.

This will be described with reference to FIG.
The smallest circle surrounding the central axis O in FIG. 2 is a magnetic material seen from the central axis O (magnetic field application detecting means 3) in the xy plane when the above trial is performed so that the locus of the central axis O is circular. It represents the relative orbit of the central axis X of 100.
The reason for using the relative orbit is for convenience to facilitate the illustration.

The inventors focused on the pickup coil 2b (the farthest pickup coil) having the longest distance to the center Z of the relative orbit among the three pickup coils 2.
(1) The pickup voltage at the position where the central axis X is closest to the farthest pickup coil 2b (X ₁ ) is the maximum, and the pickup voltage at the farthest position (X ₂ ) is the minimum.
(2) As the farthest pickup coil 2b approaches the central axis X (the closer the central axis O approaches the center Z of the relative orbit), the maximum value of the pickup voltage output from the farthest pickup coil 2b increases.
It was considered that the closest trial could be determined by comparing the maximum value of the pickup voltage of the farthest pickup coil for each trial.

Further, here, an example of a method of specifying the position A and the position B based on the closest trial will be described with reference to FIG. FIG. 4 shows the movement (relative movement) of the magnetic body 100 as seen from the central axis O of the drive coil 1 on the xy plane. Further, the yz plane of FIG. 4 is a plane orthogonal to the xy plane and the xz plane. Therefore, the magnetic material 100 moves relative to the xyz space including these planes. The magnetic body 100 before movement shown in FIG. 4 is relative to the magnetic body 100 when the central axis O of the drive coil 1 is located on the closed locus or inside the locus in the closest trial. It represents the position.

First, the magnetic material 100 moves relative to each other along the direction (1) parallel to the y-axis, and moves to the relative position A'where the difference between the pickup voltages output from the two pickup coils 2 is within a range of 5 μV or less. .. At this time, the actual magnetic field application detecting means 3 exists at the position A. Then, while maintaining that the difference between the pickup voltages output from the two pickup coils 2 is within the range of 5 μV or less, the magnetic material 100 moves relative to each other along the direction (2) parallel to the x-axis. The difference between the average value of the pickup voltages output from the two pickup coils 2 and the pickup voltage output from the other pickup coil 2 moves to the relative position B'within a range of 5 μV or less. At this time, the actual magnetic field application detecting means 3 exists at the position B.
The relative movement of the magnetic body 100 for specifying the relative position A'and the relative position B'(movement of the magnetic field application detecting means 3) is not limited to the method shown in FIG. 4, and for example, the magnetism shown in FIG. The relative position A'may be specified by relatively moving the body 100 in a direction including all of the x, y, and z components, a direction parallel to the xy plane, or a direction parallel to the x-axis, and from the relative position A'. When specifying the relative position B', it may be relatively moved in a direction parallel to the xz plane.

Further, the position search system 10 scans from the position B in a direction parallel to the central axis O of the drive coil 1 by the magnetic field application detecting means 3, and the average value of the pickup voltages output from the three pickup coils 2 and the pickup coil. The position of the magnetic material 100 can be searched from the relationship with the moving distance of 2.
From the above relationship, the distance between the magnetic field application detecting means 3 (pickup coil 2) and the magnetic body 100 can be estimated, which makes it possible to estimate the position where the magnetic body 100 exists.
If the relationship between the distance between the magnetic material 100 and the magnetic field application detecting means 3 (pickup coil 2) and the pickup voltage is measured in advance, the accuracy of estimating the position where the magnetic material 100 exists is further improved.

Although one embodiment of the position search system of the present disclosure has been described above, the position search system of the present disclosure is not limited to this.

In the above embodiment, the drive coil is used as the magnetic field generation source, but the magnetic field generation source that can be used in the position search system is not limited to this, and any magnetic field can be generated. Specific examples include superconducting coils and permanent magnets.

In the above embodiment, the pickup coil is used as the magnetic sensor, but the magnetic sensor that can be used in the position search system is not limited to this, and it is sufficient that the change in the magnetic flux density can be detected. Specific examples include Hall elements, magnetoresistive elements, flux gate sensors, Faraday elements, superconducting quantum interference elements, and the like. However, it is preferable that the change in magnetic flux density detected by the magnetic sensor can be output as a change in voltage.
Further, although three magnetic sensors are used in the above embodiment, the number of magnetic sensors that can be used in the position search system is not limited to this, and the position where the magnetic body exists in the region where the magnetic material can exist is not limited to this. It suffices if it is possible to search for, and at least one is sufficient. When the number of magnetic sensors is two, it is possible to specify the position where the magnetic material exists in the region where the magnetic material can exist even on a plane equidistant from the two magnetic sensors. When the number of magnetic sensors is four or more, the position of the magnetic material can be searched with higher accuracy than when the number of magnetic sensors is three.

The position search system preferably further includes a lock-in amplifier that detects a signal from a magnetic sensor and a resistor that inputs a reference signal to the lock-in amplifier. As a result, the detection error of the change in the magnetic flux density can be reduced.

Further, the means for causing the magnetic sensor to detect the change in the magnetic flux density by moving the magnetic sensor together with the magnetic field generation source while applying the magnetic field in the region where the magnetic material can exist is not particularly limited. For example, a magnetic field generation source and a magnetic sensor are connected to a robot arm, and the robot arm is operated by a controller to obtain position information of a magnetic field application detecting means obtained from the controller, information on changes in magnetic flux density obtained from the magnetic sensor, and the like. Examples thereof include a form in which the scanning is controlled by processing by a computer.

2. Position Search Method Next, a position search method for a magnetic material using the position search system 10 will be described.

The position search method of the present disclosure is a method of searching the position of a magnetic material, and moves a pickup coil (magnetic sensor) together with a drive coil (magnetic flux generation source) in a region where the magnetic material can exist while applying a magnetic field. By causing the pickup coil to perform scanning to detect a change in the magnetic flux density of the magnetic field, and based on the change in the magnetic flux density detected by the pickup coil during the scanning, a position in the above region where the magnetic material exists. Is to search for.

As for the preferred form of the position search method, any of the methods corresponding to the functions described in the position search system 10 can be applied.

As described above, according to the position search system and the position search method of the present disclosure, the position where the magnetic material exists can be searched. Therefore, for example, when performing hyperthermia, the range in which the temperature-sensitive magnetic material injected into the body exists can be searched in advance, and the heat generation efficiency of the induction heating of the temperature-sensitive magnetic material by applying a magnetic field thereafter is improved. In addition, it is possible to improve the SN ratio of the signal for detecting the temperature of the temperature-sensitive magnetic material. In addition to hyperthermia, it can also be applied to search for land mines and precious metal products buried in the ground.

Hereinafter, the position search system and the position search method will be described based on the examples, but the position search system and the position search method of the present disclosure are not limited to this.

(Position search system)
FIG. 5 shows a schematic diagram of the position search system according to the embodiment. The position search system according to the embodiment includes a magnetic field application detecting means including a drive coil and three pickup coils 1, 2, and 3. In addition, a function generator (NF Circuit Design Block Co., Ltd., WF1944A) and a bipolar amplifier. (NF Circuit Design Block Co., Ltd., BP4610) and three lock-in amplifiers 1, 2 and 3 (Ametek. Inc., Signal Recovery) that detect signals from pickup coils 1, 2 and 3, respectively. 7265 type DSP), 0.5Ω non-inductive resistance that inputs a reference signal to the lock-in amplifier, and a robot arm for moving the magnetic field application detection means (Yasukawa Electric Co., Ltd., MOTOMAN-SIA 10F, positioning accuracy error 0) .1 mm) and a control computer equipped with a controller to control the robot arm, and a measurement for processing the position information of the magnetic field application detecting means obtained from the control computer and the information on the change in magnetic flux density obtained from the magnetic sensor. It is equipped with a computer and is connected as shown in FIG.
Further, as the magnetic material to be searched, one in which 1 g of the temperature-sensitive magnetic material is dispersed in 1 g of ion-exchanged water is used.

The drive coil uses a litz wire (a conductor wire obtained by twisting 100 thin wires of 0.08 mm diameter copper wire coated with enamel to form one), and has an outer diameter of 118 mm, an inner diameter of 76 mm, and a thickness of 9 mm. A coil having 20 turns was used and arranged so that the central axis was vertical.
The pickup coils 1, 2 and 3 have an outer diameter of 12.5 mm and are made of a litz wire (a conductor wire obtained by twisting 100 thin wires in which a copper wire having a diameter of 0.08 mm is coated with enamel and insulating it into one wire). A coil having an inner diameter of 10 mm, a thickness of 5 mm, and a number of turns of 10 turns was used.
Further, the drive coil and the pickup coil are arranged according to FIGS. 1 to 3. The distances from the central axis O of the drive coil to the pickup coil are 21.8 mm, respectively. The distance between the plane orthogonal to the central axis O of the drive coil and in contact with the upper surface of the drive coil and the plane (xy plane) orthogonal to the central axis O of the drive coil and in contact with the upper surface of the pickup coil is 11 mm. be.
The definition of the xy plane is the same as in one embodiment described above.

The high-frequency AC power supply generates a sine wave AC of 2560 Hz with a function generator, amplifies it to 8 App by a bipolar amplifier, and applies it to the drive coil, whereby a magnetic field is generated around the drive coil.
The three lock-in amplifiers synchronously detect and measure the pickup voltage output from the pickup coil connected to each of them. In addition, in order to detect the change in the magnetic flux density of the magnetic field applied from the drive coil, the pickup coil uses the offset function of the lock-in amplifier with the magnetic field applied from the drive coil without installing a magnetic material in advance. Then, the three pickup voltages are standardized (calibrated) to 0V.
The measurement computer is connected to each lock-in amplifier by a GPIB interface, and is connected to the control computer by a LAN cable. Then, the real-time voltage waveform of the pickup voltage is displayed by the automatic measurement program created by LabVIEW 2012 (National Instruments), and the position information of the magnetic field application detecting means received from the control computer and the information of the pickup voltage are associated with each other for measurement. Save to computer.
The control computer can accurately move the robot arm by the automatic control program developed using VC ++ 2008.

The temperature-sensitive magnetic material has a composition ratio of Fe ₂ O ₃ : CuO: ZnO: MgO = 49: 7: 30: 14 (mol%), and its surface is coated with gold (Japanese Patent Laid-Open No. 2011-251042). Made based on the issue). The particle size of the temperature-sensitive magnetic material is a powder of 50 μm or more and 150 μm or less. The Curie point is 43 ° C.

Using the position search system with such a configuration, the following experiment was conducted to search for the position of the magnetic material.

[Magnetic material position search experiment]
In this experiment, when a vertical straight line passing through the center of the magnetic material (the center of the container containing the magnetic material dispersed in pure water) is defined as the central axis X of the magnetic material, the central axis O of the drive coil is the central axis X. This is to search for the position of the magnetic material when it deviates from. This experiment was performed at a sufficiently low magnetic flux density so that the magnetic material would not be induced and heated by the magnetic flux density of the applied magnetic field. Further, the magnetic flux density of 10 mm above the central axis O of the drive coil in the xy plane in the vertical direction was 0.576 mT in the state where the magnetic material was not installed.

<Judgment of the closest trial>
(Experimental operation)
An attempt was made to fix the magnetic material at a position 20 mm above the xy plane in the vertical direction and rotate the magnetic field application detecting means in a circle with a radius of 5 mm in a direction parallel to the plane orthogonal to the central axis O.
The position of the circular rotation is the central axis O when the locus of the central axis X seen from the central axis O (magnetic field application detecting means) on the xy plane when the magnetic field application detecting means is rotated in a circle is taken as a relative orbit. The distance from the center Z of the relative orbit was 0 mm, 10 mm, 30 mm, and 50 mm.

(result)
The results of each trial in which the distances between the center axis O of the drive coil and the center Z of the relative orbit are 0 mm, 10 mm, 30 mm, and 50 mm are shown in FIGS. 6 to 9. In FIGS. 6 to 9, the angle of the circle in the relative orbit (clockwise is defined as the + direction) is defined as the horizontal axis. The state in which the central axis X of the magnetic material is on the white point in the enlarged view of the relative orbit shown in FIG. 6 is defined as 0 °. The same applies to the 0 ° position in FIGS. 7 to 9. Further, Vp1, Vp2, and Vp3 in the figure represent the pickup voltages of the pickup coils 1, 2, and 3, respectively.

From FIGS. 6 to 9, when the magnetic field application detecting means is rotated in a circle, the relative positions of the magnetic material and each pickup coil change periodically, so that each pickup voltage also changes periodically. I was able to confirm that.

Focusing on the pickup voltage 1 of the pickup coil 1 arranged at the position closest to the center Z of the relative orbit , in FIGS. 6, 7, and 9 , the magnetic material on the relative orbit is the closest to the pickup coil 1. It was found that the absolute value of the pickup voltage 1 at the closest position was the largest, and in FIG. 8 , the absolute value of the pickup voltage 1 at the position where the magnetic material on the relative orbit was farthest from the pickup coil 1 was the largest. ..
On the other hand, when the pickup coils (hereinafter, sometimes referred to as "farthest pickup coils") 2 and 3 arranged at the position farthest from the center Z of the relative orbit are closest to the magnetic material on the relative orbit. Focusing on the pickup voltages 2 and 3 (maximum values of the pickup voltages 2 and 3), it was found that the pickup voltage tends to decrease as the center Z of the relative orbit moves away from the central axis O.
From this, it is considered that the trial in which the central axis O is closest to the magnetic material (center Z of the relative orbit) can be determined by comparing the maximum values of the farthest pickup coils in each trial.

Here, when determining the trial in which the central axis O of the drive coil is closest to the magnetic material, the maximum values of the three pickup voltages in one trial are compared, and the smallest maximum value (V _{max_min} ) is determined. Considering that the output pickup coil is the farthest pickup coil, from FIG. 6, since the maximum values of the pickup voltages 1, 2 and 3 are the same, all of the pickup coils 1, 2 and 3 are used. Judged as the farthest pickup coil. From FIG. 7, since the maximum value of the pickup voltages 2 and 3 is smaller than the maximum value of the pickup voltage 1, it is determined that the pickup coils 2 and 3 are the farthest pickup coils.
On the other hand, from FIGS. 8 and 9, since the maximum value of the pickup voltage 1 is smaller than the maximum value of the pickup voltages 2 and 3, the pickup coil 1 is determined to be the farthest pickup coil.

As described above, the trial farthest pickup coil in FIGS. 8 and 9 is determined differently from the actual farthest pickup coil. However, the determination of the trial in which the central axis O is closest to the magnetic material is _{to compare the smallest maximum value (V max_min} ) of each trial and determine the trial having the largest value as the closest trial. _Therefore , when the V max_min of each trial judged from FIGS. 6 to 9 is compared, it can be determined that the trial of FIG. 6 is the closest trial.
As will be described later, in order to improve the accuracy of the determination of the closest trial, at least one of the pickup voltages output from the pickup coil is 0 V or less (trials according to FIGS. 8 and 9) are excluded. The closest trial may be determined.

Focusing on the maximum value of the pickup voltage 1 of the pickup coil 1 closest to the center Z of the relative orbit, and comparing the maximum value of the pickup voltage 1 for each trial, the trial according to FIG. 7 is the central axis O of the drive coil. Is determined as the trial closest to the magnetic material (center Z of the relative orbit).

<Search for position A where the difference between the two pickup voltages is within a predetermined range>
From the results of FIG. 6, the difference between the pickup voltages 2 and 3 was 0.48 μV when the angle was 0 °, 0.48 μV when the angle was 180 °, and 0.44 μV when the angle was 360 °. .. Here, the position of the magnetic material when the difference between the pickup voltages 2 and 3 is included in the range of 5 μV or less can be set as the relative position A'(the closer the difference is to 0 V, the more preferable). Therefore, here, any of the positions of the magnetic materials having angles of 0 °, 180 °, and 360 ° can be set as relative positions A'. The position of the magnetic field application detecting means at this time is the position A.
Further, from the pickup coils 2 and 3 and the position A, it can be seen that the magnetic material exists on a plane (xz plane) equidistant from the pickup coils 2 and 3 including the position A.

<Search for position B where the difference between the average value of the two pickup voltages and the other pickup voltages is within a predetermined range>
(Experimental operation)
Scanning was performed by the magnetic field application detecting means so that the magnetic material relatively moves between -10 mm and 10 mm on the x-axis where the xy plane and the xz plane overlap. The results are shown in FIGS. 10 and 11 together with the relative orbit of the central axis X. Note that 0 mm in FIGS. 10 and 11 is a position where the central axis O of the drive coil and the central axis X of the magnetic material overlap.

(result)
FIG. 10 shows the central axis in the relative orbit when the magnetic material is fixed at a position 10 mm upward in the vertical direction from the xy plane, and FIG. 11 shows the central axis in the relative orbit when the magnetic material is fixed at a position 20 mm upward in the vertical direction from the xy plane. The relationship between the position of X and the pickup voltage is shown.
From FIGS. 10 and 11, it was found that when the magnetic field application detecting means was scanned so that the central axis X moved relative to the x-axis, the pickup voltages 2 and 3 were substantially the same. Further, it was confirmed that the closer the central axis X is to the central axis O (x = 0), the more the three pickup voltages tend to match.
Further, when the average values of the pickup voltages 2 and 3 at 0 mm in FIGS. 10 and 11 and the difference between the average value and the pickup voltage 1 were calculated, they were 2.49 μV and 1.24 μV, respectively. Here, the position of the magnetic material when the difference between the average value of the pickup voltages 2 and 3 and the pickup voltage 1 is within a range of 5 μV or less can be set as the relative position B'(the closer the difference is to 0 V, the more preferable). .. Therefore, here, in both cases of FIGS. 10 and 11, the position of the magnetic material whose angle is 0 ° can be set as the relative position B'. The position of the magnetic field application detecting means at this time is the position B.

<Examination of changes in pickup voltage with respect to the position of the magnetic material>
Using the results of 0 °, 180 °, and FIG. 11 of FIGS. 6 to 9, the position of the central axis X in the relative orbit when the magnetic material moves relative to the x-axis between -10 mm and 55 mm. The relationship with the pickup voltage is shown in FIG.
The pick-up coil 1 shown in FIG. 12 is a range on the x-axis of the pickup coil 1 as viewed from the side surface (y-axis direction) of the magnetic field application detecting means at a position where the central axis X overlaps the central axis O (0 mm in FIG. 12). Is shown.

From FIG. 12, when the central axis X is located in the region (a), the number of magnetic flux densities interlinking increases as it approaches the pickup coil 1, but when it is located in the region (b), the chain increases as it approaches the pickup coil 1. It was confirmed that the number of intersecting magnetic flux densities decreased, and as shown in the region (c), when passing through the pickup coil 1, the direction of the magnetic flux densities interlinking with the pickup coil 1 was reversed and became 0 V or less. can.
Therefore, in the trial performed when determining the closest trial, the trial in which the pickup voltage is 0 V or less indicates that the magnetic material is located outside the pickup coil, so that at least one of the pickup voltages is 0 V or less. It is considered that the accuracy is improved by determining the closest trial except for the above trial.

<Estimation of the distance between the magnetic field application detecting means and the magnetic material>
(Experimental operation)
Scanning was performed by the magnetic field application detecting means by moving the magnetic field application detecting means in a direction parallel to the central axis of the drive coil from the position where the magnetic material exists at the relative position B'.

(result)
FIG. 13 shows the relationship between the distance between the magnetic field application detecting means and the magnetic material (distance from the xy plane to the magnetic material) and the pickup voltage.
From FIG. 13, it was confirmed that the three pickup voltages were almost the same, and that the pickup voltage decreased as the magnetic field application detecting means moved away from the magnetic material. Further, when the average value of the three pickup voltages at an arbitrary distance was calculated and the relationship between the average value and the distance was approximately index-approximate, a high coefficient of determination (R ² = 0.998) was obtained.
Therefore, it was found that the distance between the magnetic field application detecting means and the magnetic material can be estimated from the relationship between the average value of the three pickup voltages and the distance between the magnetic field application detecting means and the magnetic material. It was also found that the position of the magnetic material can be estimated from this relationship.

Claims (5)

A system that searches for the position of a magnetic material
A magnetic field generation source for generating a magnetic field and three or more magnetic sensors capable of detecting changes in the magnetic flux density of the magnetic field are provided.
The three or more magnetic sensors are arranged at positions on the plane that are approximately equidistant from the central axis on a plane orthogonal to the central axis of the magnetic field generation source.
The three or more magnetic sensors are arranged at equal intervals on the circumference centered on the central axis.
By moving the magnetic sensor together with the magnetic field generation source while applying the magnetic field in a region where the magnetic material can exist, scanning is performed so that the magnetic sensor detects a change in the magnetic flux density.
Based on the change in the magnetic flux density detected by the magnetic sensor during the scanning, the position where the magnetic material exists in the region is searched for.
Location search system. The position search system according to claim 1, wherein the magnetic field generation source and the magnetic sensor are coils. The position search system according to claim 1 or 2 , further comprising a lock-in amplifier that detects a signal from the magnetic sensor and a resistor that inputs a reference signal to the lock-in amplifier. The position search system according to any one of claims 1 to 3 , wherein the magnetic material is a temperature-sensitive magnetic material having an arbitrary Curie point. It is a method of searching for the position of a magnetic material.
A magnetic field generation source for generating a magnetic field and three or more magnetic sensors capable of detecting changes in the magnetic flux density of the magnetic field are provided.
The three or more magnetic sensors are arranged at positions on the plane that are approximately equidistant from the central axis on a plane orthogonal to the central axis of the magnetic field generation source.
The three or more magnetic sensors are arranged at equal intervals on the circumference centered on the central axis.
By moving the magnetic sensor together with the magnetic field generation source while applying the magnetic field in the region where the magnetic material can exist, scanning is performed so that the magnetic sensor detects a change in the magnetic flux density of the magnetic field.
Based on the change in the magnetic flux density detected by the magnetic sensor during the scanning, the position where the magnetic material exists in the region is searched for.
Location search method.

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