JP2822754B2 - Method and apparatus for removing noise from SQUID magnetometer output - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting quantum interference device (SQUID; Supercon
SQ with inductive Quantum Interference Device)
The present invention relates to a method and an apparatus for removing noise caused by vibration of a refrigerator from a fluxmeter output when the UID magnetometer is cooled by the refrigerator.

[0002]

2. Description of the Related Art Conventionally, a superconducting quantum interference device utilizing the Josephson effect has been known as one of superconducting devices. By connecting a magnetic flux input circuit with a superconducting pickup coil to this superconducting quantum interference device, it is possible to measure extremely weak magnetic flux such as a magnetic field accompanying a minute current flowing in a living body or a magnetic field from a minute magnetic body in the body. The obtained SQUID magnetometer can be obtained.

When the SQUID magnetometer is cooled to a cryogenic level, that is, a temperature at which the superconducting quantum interference device and the superconducting coil transition to a superconducting state, cryogenic liquid helium is stored in a cryostat (cryostat), There is a method of immersing a SQUID magnetometer in the liquid helium to cool it. In this case, usually, a cooler of a refrigerator for generating cold is inserted into the low-temperature holding container, and the helium gas evaporated in the container is condensed and liquefied by the refrigerator.

In this method, since the SQUID magnetometer is immersed in liquid helium, the whole SQUID magnetometer can be cooled stably and in a short time. However, on the other hand, since helium in the low-temperature holding container is interposed for cooling the SQUID magnetometer, the cooling system becomes large and the operability deteriorates. From this, the above S
Attention has been paid to a method of cooling by bringing a QUID magnetometer into direct contact with a cooler of a refrigerator in such a manner that heat can be transferred (for example, Japanese Patent Application Laid-Open No. HEI 2 (1990) -210).
-302680).

[0005]

However, in that case,
The refrigerator has a portion that vibrates during operation, and it is difficult to completely eliminate the vibration. For this reason, there has been a problem that noise due to vibration of the refrigerator is mixed into the output signal of the magnetometer, and the inherent signal detection of the magnetometer becomes inaccurate.

This problem can be solved by making the signal system of the magnetometer two channels, performing normal measurement on the other hand, measuring noise due to vibration of the refrigerator on the other channel at the same time, and comparing the two. . However, this method has a problem that the number of channels of the signal system is increased.

[0007] In addition, it is also possible to measure the noise due to the vibration of the refrigerator after performing a normal measurement while keeping the number of signal channels as one, and compare the two. Therefore, it is unavoidable that the vibration characteristics of the refrigerator change, and accurate detection is difficult.

[0008] The present invention has been made in view of the above points, and an object thereof is to detect noise due to vibration of a refrigerator based on the output signal itself of the SQUID magnetometer and remove the noise. With a simple system configuration without the need for anti-vibration measures for the refrigerator or complicated hardware and software,
It is an object of the present invention to remove noise caused by vibration of a refrigerator from an output signal of a SQUID magnetometer.

[0009]

In order to achieve the above object, the present invention focuses on the fact that noise due to vibration of a refrigerator has periodicity, and outputs an output signal of a magnetic flux meter to the vibration cycle of the refrigerator. The template of periodic noise was created by averaging every minute, and this template was subtracted from the output signal of the magnetometer.

That is, according to the first aspect of the present invention, as shown in FIGS. 1 and 2, a superconducting quantum interference device (31) and a magnetic flux input circuit (32) which are brought into a superconducting state at a cryogenic level are provided. SQ in which the interference element (31) and the magnetic flux input circuit (32) are cooled by the cryogenic refrigerator (A)
SQ for obtaining a desired signal by removing the periodic noise due to the vibration of the refrigerator (A) from the output signal of the UID magnetometer (B)
As a method of removing noise from the output of the UID magnetometer, the output signal of the SQUID magnetometer (B) is added and averaged for each basic cycle of the noise caused by the vibration of the refrigerator (A), and the cycle from which the signal and other noises are removed is obtained. In this method, a template of sexual noise is generated, and the template is subtracted from the output signal of the magnetometer (B) to obtain a target signal.

Further, according to the invention of claim 4, as shown in FIG. 1, a superconducting quantum interference device (31) and a magnetic flux input circuit (32) which enter a superconducting state at a cryogenic level are provided. 31) and the magnetic flux input circuit (32) removes the periodic noise due to the vibration of the refrigerator (A) from the output signal of the SQUID magnetometer (B) cooled by the cryogenic refrigerator (A), and is a target signal. SKU to get
As a noise elimination device for the output of the ID magnetometer, a cycle in which the output signal of the SQUID magnetometer (B) is added and averaged for each basic cycle of the noise caused by the vibration of the refrigerator (A), and the signal and other noises are removed. Noise template generating means (46) for generating a template of sexual noise, and subtracting the noise template generated by the noise template generating means (46) from the output signal of the magnetometer (B) to obtain a target signal. And a periodic noise removing means (47) (adder or subtractor).

According to the second aspect of the present invention, the SQ of the first aspect is used to compensate for fluctuations in noise due to vibration of the refrigerator.
In the method of removing noise from the output of the UID magnetometer, the signals are phase-matched when adding the output signals of the magnetometer (B).

According to a fifth aspect of the present invention, similarly, in the noise removing apparatus of the SQUID magnetometer output according to the fourth aspect, the noise template generating means (46) is configured to add the output signal of the magnetometer (B). It is configured to perform signal phase matching.

According to the third aspect of the present invention, the SQUID of the first aspect is provided.
In the method for removing noise from the output of the D magnetometer, if the target signal can be added and averaged, the average of the output signal at the time of generation of the periodic noise template is reduced in order to reduce the influence of the target signal included in the noise template. The data obtained by subtracting the target signal of (1) is used.

According to a sixth aspect of the present invention, similarly, in the noise elimination device of the SQUID magnetometer output according to the fourth aspect, when the target signal can be added and averaged, the SQUID magnetometer is generated before the noise template is generated. It is configured to subtract the averaging waveform of the target signal from the output.

[0016]

According to the above construction, the SQ of the first aspect is
By adding and averaging the output signal of the UID magnetometer (B) for each vibration cycle of the refrigerator (A), signals and other noises are removed, and periodic noise caused only by the vibration of the refrigerator (A) is removed. A template is generated. Thereafter, when this template is subtracted from the output signal of the original magnetometer (B), a target signal is obtained. In this way, the output signal of the magnetometer (B) is processed to form a noise template, and the noise template is used to remove noise from the output signal of the magnetometer (B). The noise due to the vibration of the refrigerator (A) can be removed from the output signal of the magnetometer (B) without requiring any countermeasures against vibration, and the target signal can be accurately obtained. In addition, a single system is required for the signal system, and the number of measurements is one.

According to the fourth aspect of the present invention, the noise template generating means (46) adds and averages the output signals of the SQUID magnetometer (B) for each oscillation cycle of the refrigerator (A),
A template of the periodic noise due to the vibration of the refrigerator (A) is generated, and the template is subtracted from the original output signal of the magnetometer (B) by the periodic noise removing means (47).
The desired signal is obtained. In this case, the same operation and effect as the first aspect can be obtained.

According to the second or fifth aspect of the present invention, the phase of the signals is adjusted when the output signals of the magnetometer (B) are added. Therefore, even if the vibration cycle of the refrigerator (A) fluctuates, the refrigerator ( The noise due to the vibration in A) can be accurately matched with the period of the template, and more accurate noise can be removed.

According to the third or sixth aspect of the present invention, when the target signal included in the magnetometer (B) can be added and averaged, the addition of the target signal from the magnetometer output signal before generating the noise template is performed. By subtracting the average waveform,
The effect of the target signal included in the noise template can be further suppressed. As a result, the waveform distortion included in the waveform obtained by the noise removal according to the first or fourth aspect of the invention can be suppressed to a small level.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 3 shows a configuration of a SQUID magnetometer and its peripheral devices according to an embodiment of the present invention.
The D magnetometer is used to detect a magnetocardiogram of the human body (a type of biomagnetism emitted from the heart). In the figure,
(1) is a support on which a subject (M) for detecting a magnetocardiogram is mounted, and is installed inside an electromagnetically shielded room (R) (or a magnetically shielded room). A receiving table (2) is installed below the supporting table (1), and a closed vacuum vessel (3) is fixed on the receiving table (2) by lowering its lower end into the receiving table (2). Have been. The inside of the vacuum vessel (3) is kept in a vacuum state, and a SQUID magnetometer (B) is housed at the upper end of the inside. (A) is a binary circuit helium refrigerator that cools the SQUID magnetometer (B) to an operable cryogenic level.

The vacuum vessel (3) has an expander (5) and a J in a pre-cooling refrigeration circuit (4) constituting a part of the refrigerator (A).
-The expansion unit (11) of the T circuit (10) is attached. The pre-cooling refrigeration circuit (4) is constituted by a GM (Gifford McMahon) cycle refrigerator, and compresses and expands helium gas in order to pre-cool helium gas in the JT circuit (10). Yes, a pre-cooling compressor (not shown) and the expander (5) are connected in a closed circuit. The expander (5) is attached to the bottom wall of the vacuum vessel (3) in a state where vibration is insulated. The expander (5) includes a casing (6) fixedly arranged on the lower surface of the bottom wall of the vacuum vessel (3), and a two-stage cylinder (7) connected to an upper part of the casing (6). The casing (6) has a high-pressure gas inlet (6a) connected to the discharge side of the pre-cooling compressor and a low-pressure gas outlet (6b) connected to the suction side. The cylinder (7) extends upward through the bottom wall of the vacuum vessel (3) in an airtight manner, and has an upper end with a diameter of 55-6.
A first heat station (8) maintained at a temperature level of 0K, and a second heat station (8) maintained at the upper end of the small diameter portion at a temperature level of 15-20K lower than the first heat station (8). 9) are formed respectively.

Although not shown, a displacer (replacer) is formed in the cylinder (7) to define an expansion chamber in the cylinder (7) at a position corresponding to the heat stations (8) and (9). Are reciprocally fitted. On the other hand, in the casing (6), the valve is opened each time it rotates, and the helium gas flowing from the high-pressure gas inlet (6a) is supplied to the expansion chamber in the cylinder (7) or expanded in the expansion chamber. Helium gas is supplied to the low pressure gas outlet (6
b) a rotary valve that switches to discharge from
A valve motor for driving the rotary valve is fitted. Then, the high-pressure helium gas is Simon-expanded in the expansion chamber in the cylinder (7) by opening a rotary valve in the expander (5), and a cryogenic level of cold is generated due to a temperature drop accompanying the expansion. At the first and second heat stations (8) and (9) in the cylinder (7). Therefore, high-pressure helium gas discharged from the pre-cooling compressor is supplied to the expander (5), and the temperatures of the heat stations (8) and (9) are reduced by adiabatic expansion in the expander (5). , J-T circuit (10), a pre-cooler (15), (16), which will be described later, is pre-cooled, and the expanded low-pressure helium gas is returned to the compressor to be re-compressed. ) Is configured.

On the other hand, the JT circuit (10) has a capacity of about 4K.
A JT compressor (not shown) for compressing helium gas and compressing helium gas to generate Joule-Thomson expansion in order to generate a cryogenic level of refrigeration; The expansion unit (11) for expanding the gas by Joule-Thomson. This expansion unit (11) is a first JT heat exchanger (12) that penetrates the bottom wall of the vacuum vessel (3) in an airtight manner.
The first and second JT heat exchangers (12) have second and third JT heat exchangers (13) and (14) disposed inside the vacuum vessel (3). Is connected. Each of the above J-
The T heat exchangers (12) to (14) exchange heat with each other between the helium gas passing through the primary side and the secondary side, respectively, and the primary side of the first JT heat exchanger (12). Is J
-Connected to the discharge side of the T compressor. The primary sides of the first and second JT heat exchangers (12) and (13) are connected to the heat exchanger (8) disposed around the first heat station (8) of the expander (5). The first precooler (1
5). Similarly, each primary side of the second and third JT heat exchangers (13) and (14)
The heat exchanger (9) of the expander (5) is connected via a second precooler (16) composed of a heat exchanger arranged on the outer periphery. Further, the third JT heat exchanger (1)
The primary side of 4) is provided with a cooler (1) through a J-T valve (17) for expanding high-pressure helium gas by Joule-Thomson.
8). The opening of the JT valve (17) is adjusted by an operation rod (not shown) from outside the vacuum vessel (3). The cooler (18) is composed of a coiled pipe wound around the outer periphery of the cold receiving portion (19a) on the lower surface of the cold receiving plate (19). With this structure, the cold receiving plate (19) is used to cool the cooler (18). And is kept at about the same temperature of about 4K stage. The cooling plate (1
The SQUID magnetometer (B) is integrally mounted on the upper surface of 9) so as to be able to conduct heat.

Further, the cooler (18) passes through the secondary sides of the third and second JT heat exchangers (14) and (13), and the first JT heat exchanger (12). ) Is connected to the secondary side of the first JT heat exchanger (12).
-Connected to the suction side of the T compressor. Therefore, JT
In the circuit (10), the helium gas is compressed to a high pressure by the JT compressor and supplied to the vacuum vessel (3) side, and the helium gas is supplied to the first to third JT heat exchangers of the vacuum vessel (3). (12)-
In (14), heat is exchanged with the low-temperature and low-pressure helium gas returning to the compressor side, and the first and second precoolers (1) are exchanged.
5) and (16), the first and second expanders (5) respectively.
After cooling by heat exchange with the heat stations (8) and (9), it is expanded by Joule-Thomson by the J-T valve (17) and helium in a gas-liquid mixed state of about 1 atm and about 4K by the cooler (18) Then, the cooling plate (19) and the SQUID magnetometer (B) in contact therewith are cooled and kept at a cryogenic level of about 4K by the latent heat of vaporization of helium. First
The third to third JT heat exchangers (12) to (14) are configured to be sucked into the JT compressor through the respective secondary sides and recompressed.

The SQUID magnetometer (B) is a superconducting quantum interference device (31) which is in a superconducting state at a cryogenic level.
And a magnetic flux input circuit (32) connected to the superconducting quantum interference device (31), wherein the superconducting quantum interference device (31) is mounted on the upper surface of the cooling plate (19) so as to be able to conduct heat. Fixed. On the other hand, a magnetic flux input circuit (32)
Has a pickup coil (33) composed of a superconducting wire wound in a loop around a cylindrical bobbin (34), and the pickup coil (33) has, for example, a total of four loops, of which upper and lower loops are provided. And two central loops are connected in series at regular intervals so that currents alternately flow in opposite directions. That is, the SQUID magnetometer (B) constitutes a gradiometer that measures a magnetic field gradient with the pickup coil (33) wound around four loops.

On the upper surface of the cooling plate (19), a heat transfer bracket (20) is provided with a superconducting quantum interference device (3).
1) is mounted so as to cover it from above, and the bobbin (34) is erected on the upper surface of the bracket (20). The bobbin (34) has a length of about 200 to 300 mm, extends upward in an upper bulge (3a) formed in the center of the upper wall of the vacuum vessel (3), and has a pickup coil (33) on its upper part. ) Is wound around the bobbin (34) to cool the pickup coil (33) below its superconducting transition temperature.

The bulge (3a) of the vacuum vessel (3)
The upper end faces the opening (1a) at the center of the support (1), and the magnetocardiogram of the subject (M) on the upper surface of the support (1) is measured through the opening (1a).

In FIG. 3, reference numeral (21) denotes the inside of the vacuum vessel (3) so as to cover the cooling plate (19), the superconducting quantum interference device (31), the bracket (20), the lower part of the bobbin (34), and the like. The radiation shield arranged at the upper part contacts the first heat station (8) in the expander of the pre-cooling refrigeration circuit (32) and is maintained at about 80K.

The output signal of the superconducting quantum interference device (31) of the SQUID magnetometer (B) is output from the FLL controller (4).
1), optical isolation amplifier (42), anti-
It is input to a computer (45) via an alias filter (43) and an AD converter (44). The procedure for processing the output signal of the magnetometer (B) in the computer (45) will be described with reference to the flowchart shown in FIG.

First, consider the measurement data (D) composed of a target signal and periodic noise (noise comprising a fundamental frequency component and its harmonic components). If the target signal is a signal that can be averaged, such as a cardiac magnetic wave or an induced brain magnetic wave, the process proceeds from step S0 after the start to step S1. On the other hand, in the case of NO where averaging cannot be performed, such as an arrhythmia wave or a spontaneous brain wave, step S
From 0, the measurement data (D) is set to the target data (D ') in step S3, and then the process proceeds to step S4.

In step S1, the measurement data (D)
, A waveform synchronized with a target signal is used as a trigger (when the signal is sufficiently large compared to noise, the data (D) itself is used as a trigger), and an averaged waveform (Sa) of the signal is obtained.
Get.

Next, in step S2, in order to remove the influence of the signal from the data (D) and obtain a waveform (D ') mainly composed of noise, the above-mentioned averaging is performed from the signal portion of the data (D). Each of the waveforms (Sa) is subtracted. This subtraction may cause a discontinuous portion in the obtained data (D '). However, the DC component may be removed from the waveform (Sa) to be subtracted, or the values and gradients at both ends may converge to zero. The discontinuity can be prevented from occurring by multiplying the window function as follows.

Thereafter, in step S4, in order to obtain a waveform as close as possible to the noise waveform included at an arbitrary position (n) of the data length (p) of the data (D) (= sampling frequency / basic frequency of noise). Then, the following processing is performed. In other words, when the route from step S0 to step S1 is passed, the data (D) is obtained, and otherwise, the waveform (D ') obtained in step S2 is shifted back and forth from the same time interval (n). The average noise waveform (Na) is obtained by adding and averaging (k) section and data length (p).

Then, in step S5, by subtracting this from the same section (n) of the data (D), noise can be removed from any section (n) of the data (D).

In step S6, steps S4 and S5 are applied to all sections of the data (D) to obtain a waveform (D ") containing almost no noise.

In steps S4 and S5, if the noise includes some frequency fluctuations, the cross-correlation with the section (n) of the data (D ') is calculated for each section during the averaging of the noise. By calculating, the variation can be considered. In addition, when the noise source is the vibration of the refrigerator (A), the deviation of the noise adjacent to one cycle of the fundamental frequency is usually 0.1.
% Or less, it is not necessary to calculate the cross-correlation over the entire section. It is sufficient to calculate the section corresponding to about 1% of one cycle of the fundamental frequency of noise, and only a small processing time is required. do not do.

When a route is taken from step S0 to step S4 via step S3, step S4
Must be sufficiently large. This is because when steps S1 and S2 are omitted, the influence of the signal contained in the average noise waveform (Na) is inversely proportional to (2k + 1).

In this embodiment, in step S4, the output signal of the SQUID magnetometer (B) is output to the refrigerator (A).
A noise template generating means (46) is configured to generate an average of periodic noise from which a target signal and other noises have been removed by performing averaging while performing phase adjustment for each fundamental frequency of the vibration.

In steps S5 and S6, the target signal is obtained by subtracting the noise template generated by the noise template generating means (46) from the output signal of the magnetometer (B) while performing phase matching. A periodic noise removing means (47) is obtained.

Next, the operation of the above embodiment will be described. When the SQUID magnetometer (B) is cooled with the operation of the helium refrigerator (A) and the temperature of the SQUID magnetometer (B) drops to a cryogenic level of about 4K, the SQUID magnetometer (B) is cooled.
The ID magnetometer (B) is activated.

That is, first, when the compressors of the pre-cooling refrigeration circuit (4) and the JT circuit (10) are started and the helium refrigerator (A) is in a steady operation state, the expansion in the pre-cooling refrigeration circuit (4) is performed. The high-pressure helium gas supplied from the pre-cooling compressor expands in the machine (5), and the first heat station (8) of the cylinder (7) reaches a temperature level of 55 to 60K due to a temperature drop accompanying the expansion of the gas. And the second heat station (9) is cooled to a temperature level of 15-20K, respectively.

On the other hand, at the same time, the JT circuit (10)
In this example, the high-pressure helium gas discharged from the compressor is supplied to the vacuum vessel (3), and the high-pressure helium gas supplied to the vacuum vessel (3) is supplied to the first JT heat exchanger (1).
It enters the primary side of 2), where it exchanges heat with the low-pressure helium gas on the secondary side, which returns to the compressor side.
K, and then 55 to 6 of the expander (5).
It enters the first precooler (15) on the outer periphery of the first heat station (8) cooled to 0K and is cooled to about 55K. This cooled gas is supplied to the second JT heat exchanger (1).
The second heat station which enters the primary side of 3), is similarly cooled to about 20K by heat exchange with the low-pressure helium gas on the secondary side, and is then cooled to 15 to 20K of the expander (5). (9) Approximately 1 after entering the second precooler (16)
Cool down to 5K. Further, the gas enters the primary side of the third JT heat exchanger (14) and is cooled to about 5K by heat exchange with the low pressure helium gas on the secondary side, after which the JT is cooled.
-To the T-valve (17). In this JT valve (17), the high-pressure helium gas is throttled and expanded by Joule-Thomson,
Atmospheric pressure, approx. 4K gas-liquid helium becomes J-T
It is supplied to a cooler (18) downstream of the valve (17). Then, in the cooler (18), the cooling plate (19) is cooled by the latent heat of vaporization of the liquid portion of the helium in the gas-liquid mixed state. When the cooling plate (19) is cooled, the superconducting quantum interference device (31), the bobbin (34), and the magnetic flux of the SQUID magnetometer (B) in contact with the cooling plate (19) so as to be able to conduct heat. The pickup coil (33) of the input circuit (32) is also cooled.

Then, the evaporated low-pressure helium gas is supplied from the cooler (18) to the second JT heat exchanger (14).
Returning to the next side, in the meantime, a saturated gas of about 4K is obtained, and this helium gas is supplied to the second and first JT heat exchangers (13),
Finally, while cooling the high-pressure helium gas on the primary side through the secondary side of (12), the temperature finally rises to about 300 K (room temperature), and then returns to the suction side of the compressor. Thus, one cycle of the pre-cooling refrigeration circuit (4) and the JT circuit (10) is completed, and thereafter, the same cycle is repeated to perform the refrigeration operation of the refrigerator (A). The continuation of such refrigeration operation lowers the temperature of the SQUID magnetometer (B) toward the cryogenic level (operating temperature level), and after reaching the cryogenic level, the SQUID magnetometer (B) changes to the operating state. Become.

In this embodiment, a process for obtaining a target magnetocardiogram signal by eliminating noise due to the vibration of the refrigerator (A) from the output signal data (D) of the SQUID magnetometer (B) is shown in FIG. It will be explained by. First, waveform 1 is data (D) including a magnetocardiogram signal and noise due to vibration of the refrigerator (A). Since the magnetocardiogram signal is an addition average, the process proceeds from step S0 to step S1 in the flowchart of FIG. 2, and data (D) is added and averaged for the magnetocardiogram to obtain waveform 2 (addition average waveform (Sa)).

Next, the waveform 2 is subtracted from the waveform 1 (see step S2 in the flow chart) to obtain a waveform 3 (data (D ')) containing almost no noise including the magnetocardiographic signal.

Noise template (Na) as close as possible to the noise waveform contained in any part (c) of data length (p) (= sampling frequency / basic frequency of noise) of waveform 1
In order to obtain the noise, an average of the noise is performed by 2 (= k) sections around the same section (c) at the same time of the waveform 3 (data (D ′)), and the waveform 4 (average noise waveform (Na)) Get) At this time, in order to consider the frequency variation of noise, the cross-correlation between the section (c) and each of the sections (a), (b), (d), and (e) is about 1% of the data length (p). The averaging is performed while taking.

By subtracting waveform 4 (average noise waveform (Na)) from section (c) of waveform 1 (data (D)), noise from section (c) of waveform 1 (data (D)) is obtained. Can be removed. By applying this to all sections, a waveform 5 (a waveform (D ″) containing almost no noise) is obtained.

Accordingly, a noise template is created by processing the output signal data of the magnetometer (B), and noise due to the vibration of the refrigerator (A) is removed from the output signal of the magnetometer (B) using the noise template. Therefore, even if there is vibration in the refrigerator (A), noise due to the vibration of the refrigerator (A) can be removed from the output signal of the magnetic flux meter (B) without taking measures to prevent the vibration, and the desired magnetocardiogram can be obtained. The signal can be obtained accurately. In addition, a single system is required for the signal system, and the number of measurements is one.

Further, when adding the output signals of the magnetometer (B) and subtracting the noise template from the output signals of the magnetometer (B), the phases of the signals are adjusted so that the period between the signal and the noise can be accurately determined. Therefore, more accurate detection can be performed.

It should be noted that the present invention is not limited to the SQUA
Of course, it can be applied to an ID magnetometer.

[0051]

As described above, according to the present invention, the SQUID cooled by the cryogenic refrigerator is provided.
In the magnetometer, the output signal is added and averaged for each vibration cycle of the refrigerator to create a template of the periodic noise by the refrigerator, and the template is subtracted from the original output signal of the magnetometer to remove the noise. Therefore, even if there is vibration in the refrigerator, the noise caused by the vibration of the refrigerator can be removed from the output signal of the magnetometer with a simple system configuration without the need for anti-vibration measures or complicated hardware and software. The signal can be obtained accurately.

According to the second or fifth aspect of the present invention, when the output signals of the magnetometers are added and when the noise template is subtracted from the output signals of the magnetometers, the phases of the signals are adjusted. Even if the oscillation period fluctuates, the period of the signal and the period of the noise can be accurately matched, and more accurate noise removal can be performed.

According to the third or sixth aspect of the present invention, when the target signal included in the magnetometer (B) can be averaged, the target signal is output from the magnetometer output signal before generating the noise template. By subtracting the averaging waveform, the effect of the target signal included in the noise template can be further suppressed, and as a result,
Alternatively, the waveform distortion included in the waveform obtained by the noise removal according to the fourth aspect can be suppressed to a small value.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of the present invention.

FIG. 2 is a flowchart illustrating a signal processing procedure performed by a computer in the embodiment of the present invention.

FIG. 3 is a diagram schematically showing a cryogenic refrigerator, a SQUID magnetometer, and a signal system thereof in the embodiment.

FIG. 4 is a characteristic diagram showing waveforms of an actual processing procedure when a section k is set to 2 in the embodiment.

[Explanation of symbols]

 (A) Helium refrigerator (3) Vacuum container (4) Pre-cooling refrigeration circuit (5) Expander (10) JT circuit (17) JT valve (18) Cooler (19) Cooling plate (B) SQUID magnetometer (31) Superconducting quantum interference device (32) Magnetic flux input circuit (45) Computer (46) Noise template generating means (47) Periodic noise removing means

Claims (6)

(57) [Claims] 1. A superconducting quantum interference device (31) and a magnetic flux input circuit (32) which enter a superconducting state at a cryogenic level, wherein the superconducting quantum interference device (31) and the magnetic flux input circuit (32) are cryogenic refrigerators. SKU cooled by (A)
SQUI for removing a periodic noise due to the vibration of the refrigerator (A) from an output signal of the ID magnetometer (B) to obtain a target signal
A method of removing noise from an output of an ID magnetometer, wherein an output signal of the SQUID magnetometer (B) is added and averaged for each fundamental period of noise due to vibration of the refrigerator (A), thereby removing a signal and other noise. And generating a desired signal by subtracting the noise template from the output signal of the magnetometer (B).
A method for removing noise from the output of the D magnetometer. 2. The method for removing noise from the output of a SQUID magnetometer according to claim 1, wherein the phase of the signal is adjusted when the output signals of the magnetometer (B) are added. Method. 3. The method for removing noise from an output of a SQUID magnetometer according to claim 1, wherein, when a target signal can be averaged, data obtained by subtracting the average target signal from the output signal when a template of periodic noise is generated. SQUID characterized by using
How to remove noise from the magnetometer output. 4. A cryogenic refrigerator comprising a superconducting quantum interference device (31) and a magnetic flux input circuit (32) which are brought into a superconducting state at a cryogenic level, wherein said superconducting quantum interference device (31) and magnetic flux input circuit (32) are provided. SKU cooled by (A)
A SQUID magnetometer output noise eliminator for removing a periodic noise due to the vibration of the refrigerator (A) from an output signal of the ID magnetometer (B) to obtain a target signal, comprising: a SQUID magnetometer ( A noise template generating means (46) for adding and averaging the output signal of B) for each basic period of noise due to the vibration of the refrigerator (A) to generate a template of periodic noise from which signals and other noises are removed. And a periodic noise removing means (4) for subtracting the noise template generated by the noise template generating means (46) from the output signal of the magnetometer (B) to obtain a target signal.
7) A noise eliminator for SQUID magnetometer output, comprising: 5. The noise removing device for SQUID magnetometer output according to claim 4, wherein the noise template generating means (46) is configured to perform signal phase matching when adding the output signals of the magnetometer (B). A noise eliminator for SQUID magnetometer output. 6. A noise removing device for an SQUID magnetometer output according to claim 4, wherein, when a target signal can be added and averaged, adding the target signal from the SQUID magnetometer output before generating a noise template. An SQUID magnetometer output noise eliminator configured to subtract an average waveform.