JP2021113801A - Magnetic field measurement device, magnetic field measurement method, and magnetic field measurement program - Google Patents

Abstract

To provide a magnetic field measurement device including a calibration magnetic field generating device.SOLUTION: Measurement data measured by a magnetic sensor array formed by arranging plurality of magnetic sensor cells each including a magnetic sensor having a magnetoresistive element and a magnetic convergence plate so as to form a plane covering at least part of a measurement object is obtained. On the basis of the position and magnetic sensitivity of each magnetic sensor, spatial distribution of a magnetic field indicated by the measurement data is signal-separated. Calibration magnetic field is generated in a cross-sectional view, outside a measurement space where the plurality of magnetic sensor cells are not arranged, of a closed space composed of the smallest convex polygon including all of the plurality of magnetic sensor cells, in a position above a straight line drawable from the measurement space without via the plurality of magnetic sensor cells. Sensor error of the magnetic sensor is calibrated based on separation error when the spatial distribution of the calibration magnetic field is signal-separated.SELECTED DRAWING: Figure 1

Description

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

Conventionally, a magnetic field measuring device for measuring a magnetic field emitted from a subject's head or chest using a sensor platform board in which a plurality of tunnel magneto-resistance (TMR) elements are arranged in an array is known ( For example, see Patent Document 1).
[Prior art literature]
[Patent Document]
[Patent Document 1] Japanese Unexamined Patent Publication No. 2012-152514

In the first aspect of the present invention, a magnetic field measuring device is provided. The magnetic field measuring device is a magnetic sensor configured by arranging a plurality of magnetic sensor cells each having a magnetic sensor including a magnetoresistive element and a magnetic focusing plate so as to form a surface covering at least a part of a measurement object. It may have an array. The magnetic field measuring device may include a measurement data acquisition unit that acquires measurement data measured by the magnetic sensor array. The magnetic field measuring device may include a signal space separating unit that signals and separates the spatial distribution of the magnetic field indicated by the measurement data based on the position and magnetic sensitivity of each magnetic sensor. The magnetic field measuring device is a plurality of magnetic sensor cells from the measurement space outside the measurement space in which the plurality of magnetic sensor cells are not arranged in the closed space composed of the smallest convex polygons including all the plurality of magnetic sensor cells in the cross-sectional view. A calibration magnetic field generating unit that generates a calibration magnetic field may be provided at a position on a straight line that can be pulled without passing through. The magnetic field measuring device may include a calibration unit that calibrates the sensor error in the magnetic sensor based on the separation error when the spatial distribution of the calibration magnetic field is signal-separated.

The magnetic sensor array is configured by arranging a plurality of magnetic sensor cells in a three-dimensional shape in a circular arc in cross section, and connects the center of a plane composed of strings connecting both end points of the arc with the center of a calibration magnetic field generator. The angle formed by the straight line and the straight line connecting the contact point between the arc and the chord on the same cross section as the center of the plane and the center of the calibration magnetic field generation portion may be larger than 6 degrees.

Each of the plurality of magnetic sensor cells outputs a magnetic field generator that generates a feedback magnetic field that reduces the input magnetic field detected by the magnetic sensor, and an output signal that corresponds to the feedback current that the magnetic field generator flows to generate the feedback magnetic field. It may further have an output unit.

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

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

The calibration magnetic field generator may have at least three or more calibration coils, each of which generates a calibration magnetic field in different axial directions.

The different axial directions may be axial directions that are orthogonal to each other.

In separating the spatial distribution of the calibration magnetic field, the signal space separation unit may use the position where the calibration magnetic field generation unit is arranged as the origin of the coordinates in the calculation.

The signal space separation unit may signal-separate the spatial distribution of the magnetic field based on the orthonormal function and the basis vector calculated from the position and magnetic sensitivity of each magnetic sensor.

The calibrator may calibrate the sensor error by changing the basis vector.

The calibrator may optimize the basis vector to minimize separation error.

A synchronous detection unit that detects a calibration magnetic field, which is an AC magnetic field, using a signal having a frequency of the AC magnetic field may be further provided.

The frequency of the AC magnetic field may be higher than 80 Hz and lower than the cutoff frequency of the attenuation characteristic of the magnetic field by the magnetic focusing plate.

In the second aspect of the present invention, a magnetic field measurement method is provided. The magnetic field measurement method is a magnetic sensor configured by arranging a plurality of magnetic sensor cells each having a magnetic sensor including a magnetoresistive element and a magnetic focusing plate so as to form a surface covering at least a part of a measurement object. It may be provided to acquire the measurement data measured by the array. The magnetic field measurement method may include signal separation of the spatial distribution of the magnetic field indicated by the measurement data based on the position and magnetic sensitivity of each magnetic sensor. The magnetic field measurement method is a method of measuring a plurality of magnetic sensor cells from the measurement space outside the measurement space in which a plurality of magnetic sensor cells are not arranged in a closed space composed of the smallest convex polygons including all the plurality of magnetic sensor cells in a cross-sectional view. It may be provided to generate a calibration magnetic field at a position on a straight line that can be pulled without going through. The magnetic field measurement method may include calibrating the sensor error in the magnetic sensor based on the separation error when the spatial distribution of the calibration magnetic field is signal separated.

In the third aspect of the present invention, a magnetic field measurement program is provided. The magnetic field measurement program may be executed by a computer. The magnetic field measurement program is configured by arranging a computer by arranging a plurality of magnetic sensor cells each having a magnetic sensor including a magnetoresistive element and a magnetic focusing plate so as to form a surface covering at least a part of a measurement object. It may function as a measurement data acquisition unit that acquires measurement data measured by a magnetic sensor array. The magnetic field measurement program may allow the computer to function as a signal space separator that signals the spatial distribution of the magnetic field indicated by the measurement data based on the position and magnetic sensitivity of each magnetic sensor. The magnetic field measurement program allows the computer to be mounted on a computer from the measurement space outside the measurement space in which a plurality of magnetic sensor cells are not arranged in a closed space composed of the smallest convex polygons including all the multiple magnetic sensor cells in a cross-sectional view. It may function as a calibration magnetic field generator that generates a calibration magnetic field at a position on a straight line that can be pulled without going through the magnetic sensor cell of the above. The magnetic field measurement program may allow the computer to function as a calibrator that calibrates the sensor error in the magnetic sensor based on the separation error when the spatial distribution of the calibration magnetic field is signal separated.

In the fourth aspect of the present invention, a magnetic field measuring device is provided. The magnetic field measuring device is a magnetic sensor configured by arranging a plurality of magnetic sensor cells each having a magnetic sensor including a magnetoresistive element and a magnetic focusing plate so as to form a surface covering at least a part of a measurement object. It may have an array. The magnetic field measuring device may include a measurement data acquisition unit that acquires measurement data measured by a group of magnetic sensor cells that is at least a part of the plurality of magnetic sensor cells in the magnetic sensor array. The magnetic field measuring device may include a signal space separating unit that signals and separates the spatial distribution of the magnetic field indicated by the measurement data based on the position and magnetic sensitivity of each magnetic sensor in the magnetic sensor cell group. The magnetic field measuring device may include a calibration magnetic field generating unit that generates a calibration magnetic field at a plurality of different positions. The magnetic field measuring device is based on the separation error when the spatial distribution of the calibration magnetic field generated at the first position is signal-separated, and the sensor error in the magnetic sensor of the first magnetic sensor cell group among the plurality of magnetic sensor cells. Based on the separation error when the spatial distribution of the calibration magnetic field generated at the second position is signal-separated, the sensor error in the magnetic sensor of the second magnetic sensor cell group among the plurality of magnetic sensor cells is calculated. It may be provided with a calibration unit for calibration.

A fifth aspect of the present invention provides a magnetic field measurement method. The magnetic field measurement method is a magnetic sensor configured by arranging a plurality of magnetic sensor cells each having a magnetic sensor including a magnetic resistance element and a magnetic focusing plate so as to form a surface covering at least a part of a measurement object. It may be provided to acquire the measurement data measured by the magnetic sensor cell group which is at least a part of the plurality of magnetic sensor cells in the array. The magnetic field measurement method may include signal separation of the spatial distribution of the magnetic field indicated by the measurement data based on the position and magnetic sensitivity of each magnetic sensor in the magnetic sensor cell group. The magnetic field measurement method may include generating a calibration magnetic field at a plurality of different positions. The magnetic field measurement method is based on the separation error when the spatial distribution of the calibration magnetic field generated at the first position is signal-separated, and the sensor error in the magnetic sensor of the first magnetic sensor cell group among the plurality of magnetic sensor cells. Based on the separation error when the spatial distribution of the calibration magnetic field generated at the second position is signal-separated, the sensor error in the magnetic sensor of the second magnetic sensor cell group among the plurality of magnetic sensor cells is calculated. May be prepared to calibrate.

In the sixth aspect of the present invention, a magnetic field measurement program is provided. The magnetic field measurement program may be executed by a computer. The magnetic field measurement program is composed of a computer in which a plurality of magnetic sensor cells each having a magnetic sensor including a magnetoresistive element and a magnetic focusing plate are arranged so as to form a surface covering at least a part of a measurement object. It may function as a measurement data acquisition unit that acquires measurement data measured by a group of magnetic sensor cells that is at least a part of the plurality of magnetic sensor cells in the magnetic sensor array. The magnetic field measurement program may allow the computer to function as a signal space separator that signals the spatial distribution of the magnetic field indicated by the measurement data based on the position and magnetic sensitivity of each magnetic sensor in the magnetic sensor cell group. The magnetic field measurement program may allow the computer to function as a calibration magnetic field generator that generates a calibration magnetic field at a plurality of different positions. The magnetic field measurement program is a magnetic sensor of the first magnetic sensor cell group among a plurality of magnetic sensor cells based on the separation error when the computer signals the spatial distribution of the calibration magnetic field generated at the first position. In the magnetic sensor of the second magnetic sensor cell group among the plurality of magnetic sensor cells, based on the separation error in the case where the sensor error in the above is calibrated and the spatial distribution of the calibration magnetic field generated at the second position is signal-separated. It may function as a calibration unit for calibrating the sensor error.

The outline of the above invention does not list all the necessary features of the present invention. Sub-combinations of these feature groups can also be inventions.

The configuration of the magnetic field measuring device 10 according to this embodiment is shown. The configuration of the magnetic sensor unit 110 according to this embodiment is shown. The configuration of the magnetic sensor cell 220 in the magnetic sensor array 210 according to the present embodiment is shown. An example of the input / output characteristics of the magnetic sensor having the magnetoresistive element according to the present embodiment is shown. A configuration example of the sensor unit 300 according to this embodiment is shown. An example of the input / output characteristics of the sensor unit 300 according to the present embodiment is shown. A configuration example of the magnetic sensor 520 according to this embodiment is shown. The magnetic flux distribution when a feedback magnetic field is generated in the magnetic sensor 520 according to the present embodiment is shown. An arrangement example of a plurality of magnetic sensor cells 220 in the magnetic sensor array 210 according to the present embodiment is shown. The preferable arrangement position of the calibration magnetic field generation part 144 at the time of calibration is shown. The configuration of the calibration magnetic field generation unit 144, the magnetic sensor array 210, the sensor data collection unit 230, and the sensor data processing unit 1100 according to the present embodiment is shown. The flow in which the magnetic field measuring device 10 according to this embodiment signals separates the spatial distribution of the magnetic field is shown. When the magnetic sensor array 210 is ideally constructed, the signal space separation operation using _{the ideal basis vector [AB] Ideal is geometrically shown.} When the magnetic sensor array 210 is made with sensor error, the signal space separation operation using _{the ideal basis vector [AB] Ideal is geometrically shown.} The flow in which the magnetic field measuring apparatus 10 according to this embodiment acquires the sensor array signal Φ (n) for calibration is shown. The flow in which the magnetic field measuring apparatus 10 according to this embodiment calibrates is shown. When the magnetic sensor array 210 is made with sensor error, the signal space separation operation using _{the calibrated basis vector [AB] Calib is geometrically shown.} Another example of a preferable arrangement position of the calibration magnetic field generating unit 144 at the time of calibration is shown. Another arrangement example of the calibration magnetic field generation part 144 at the time of calibration is shown. The relative positional relationship between the magnetic sensor array 210 and the calibration magnetic field generator 144 is shown. The simulation result of the sensor error when the calibration magnetic field generation part 144 is separated from the magnetic sensor array 210 is shown. An example of the division calibration for the first magnetic sensor cell group 2210 is shown. An example of the division calibration for the second magnetic sensor cell group 2310 is shown. It shows how an eddy current is generated in the magnetic sensor 520 including the magnetic focusing plates 720 and 730. The gain characteristics of the magnetic field due to the eddy current 2410 are shown. An example of a computer 9900 in which a plurality of aspects of the present invention may be embodied in whole or in part is shown.

Hereinafter, the present invention will be described through embodiments of the invention, but the following embodiments do not limit the inventions that fall within the scope of the claims. Also, not all combinations of features described in the embodiments are essential to the means of solving the invention.

FIG. 1 shows the configuration of the magnetic field measuring device 10 according to the present embodiment. The magnetic field measuring device 10 generates a calibration magnetic field when measuring a target magnetic field using a magnetic sensor, and calibrates an error in the magnetic sensor based on the measurement result of the calibration magnetic field. In the present embodiment, a case where the magnetic field measuring device 10 is a magnetocardiographic measuring device that measures a magnetocardiogram, which is a magnetic field generated by the electrical activity of the human heart, will be described as an example. However, it is not limited to this. The magnetic field measuring device 10 may be used for measuring the magnetocardiography of a living body other than a human being, or may be used for measuring a biomagnetic field other than the magnetocardiography such as a cerebral magnetic field. Further, the magnetic field measuring device 10 may be used for a magnetic particle inspection for detecting scratches on the surface and surface of a steel material or a welded portion.

The magnetic field measuring device 10 includes a main body unit 100 and an information processing unit 150. The main body 100 is a component for sensing the magnetic field of the subject, and calibrates the magnetic sensor unit 110, the head 120, the drive unit 125, the base unit 130, the pole unit 140, the support unit 142, and the like. It has a magnetic field generating unit 144.

The magnetic sensor unit 110 is arranged at a position toward the heart in the chest of the subject at the time of magnetocardiography measurement, and senses the magnetocardiography of the subject. The head 120 supports the magnetic sensor unit 110 and makes the magnetic sensor unit 110 face the subject when measuring the magnetocardiography. Further, the head 120 may be expandable and contractible in the Z-axis direction, and extends to make the magnetic sensor unit 110 face the calibration magnetic field generating unit 144 when performing calibration. The drive unit 125 is provided between the magnetic sensor unit 110 and the head 120, and changes the orientation of the magnetic sensor unit 110 with respect to the head 120 when performing calibration. The drive unit 125 according to the present embodiment has a first actuator capable of rotating the magnetic sensor unit 110 360 degrees around the Z axis in the drawing, and an axis perpendicular to the Z axis (X axis in the state in the drawing). ) Is included, and the second actuator that rotates the magnetic sensor unit 110 is included, and the azimuth angle and the zenith angle of the magnetic sensor unit 110 are changed by using these. As shown as the drive unit 125 in the figure, the drive unit 125 has a Y-shape when viewed from the Y-axis direction in the figure, and the second actuator has the magnetic sensor unit 110 360 degrees around the X-axis center in the figure. Can be rotated.

The base portion 130 is a base that supports other parts, and in the present embodiment, is a base on which the subject rides during magnetocardiography measurement. The pole portion 140 supports the head 120 at the height of the subject's chest. The pole portion 140 may be stretchable in the vertical direction so as to adjust the height of the magnetic sensor unit 110 to the height of the chest of the subject.

The support unit 142 supports the calibration magnetic field generation unit 144 so as to have the same height as the magnetic sensor unit 110 at the time of calibration. In the above description, a case where the head 120 is extended to face the magnetic sensor unit 110 with the calibration magnetic field generating unit 144 when performing calibration is shown as an example. However, it is not limited to this. The support unit 142 moves in the Z-axis direction so that the calibration magnetic field generating unit 144 can move between the calibration position facing the magnetic sensor unit 110 and the retracted position retracted from the calibration position. It may be possible.

The calibration magnetic field generator 144 generates a calibration magnetic field at the time of calibration. Such a calibration magnetic field may be an AC magnetic field. As an example, the calibration magnetic field may be a sine wave of frequency f0, or a sine wave of multiple frequencies (eg, frequency f0, frequency f1 (> frequency f0), frequency f2 (> frequency f1), etc.). It may be the sum of waves. Magnetocardiography, which is one of the magnetic fields to be measured by the magnetic field measuring device 10, has no DC component. Therefore, the magnetic field measuring device 10 only calibrates the magnetic sensor using a calibration magnetic field which is an AC magnetic field, and is subject to DC offset of the magnetic sensor and offset drift of a very low frequency (for example, 0.1 Hz or less). There is no need to calibrate the magnetic sensor.

Here, in general, the environmental magnetic field is smaller at higher frequencies. For example, the environmental magnetic field is on the order of several tens of pT in a band higher than 50 Hz, which is the same as the peak of magnetocardiography, which is one of the magnetic fields to be measured by the magnetic field measuring device 10 according to the present embodiment. It is a level. Therefore, the calibration magnetic field generator 144 may generate an AC magnetic field having a frequency higher than 50 Hz (frequency f0> 50 Hz) as the calibration magnetic field. That is, since the signal frequency of the core magnetism is mostly lower than 20 Hz, the frequency of the AC magnetic field as the calibration magnetic field may be higher than the frequency band of the magnetic field to be measured.

Further, in general, as the frequency of the commercial power supply, for example, 50 Hz or 60 Hz is used. Therefore, power supply noise exists in the multiplication of the frequencies of these commercial power supplies. Therefore, the calibration magnetic field generator 144 may use a frequency higher than the frequency of the magnetic field to be measured and avoiding multiplication of the frequency of the commercial power supply as the frequency of the AC magnetic field. As an example, the calibration magnetic field generator 144 may use a frequency higher than 50 Hz and avoiding an integral multiple of 50 Hz or 60 Hz. As a result, the environmental magnetic field can be suppressed to the order of several tens of pT. Therefore, it is sufficient for the calibration magnetic field generator 144 to generate a weak calibration magnetic field of about several tens of nT, for example, to the extent that environmental noise can be ignored. be. That is, by using such a frequency as the frequency of the AC magnetic field, the magnetic field measuring device 10 does not need to generate a strong magnetic field as the calibration magnetic field.

The calibration magnetic field generator 144 may each have a plurality of calibration coils that generate a calibration magnetic field. Then, the calibration magnetic field generator 144 receives an alternating current corresponding to the frequency of the clock signal for calibration, which will be described later, and adds an alternating current corresponding to the frequency of the clock signal to each of the plurality of calibration coils. An AC magnetic field corresponding to the frequency of the clock signal may be generated from each of the plurality of calibration coils. For example, the calibration magnetic field generator 144 may have at least three or more calibration coils, each of which generates a calibration magnetic field in different axial directions. Then, these different axial directions may be axial directions orthogonal to each other. As an example, the calibration magnetic field generator 144 has a plurality of three-axis calibration coils that generate a calibration magnetic field in the three-axis directions (for example, the X-axis direction, the Y-axis direction, and the Z-axis direction) that are orthogonal to each other. You may have. As a result, the magnetic field measuring device 10 calibrates the magnetic sensor using a plurality of calibration magnetic fields in which magnetic fields of three axes, each of which is primary and independent, are generated from different positions, so that the accuracy of calibration can be further improved. Can be done.

Further, when calibration is performed using such an alternating magnetic field, it is necessary to suppress the generation of eddy current. Therefore, the housing of the calibration coil that generates the calibration magnetic field is preferably formed of a resin material having low electrical conductivity or the like.

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

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

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

FIG. 3 shows the configuration of the magnetic sensor cell 220 in the magnetic sensor array 210 according to the present embodiment. Each of the plurality of magnetic sensor cells 220 has at least one sensor unit 300, each of which has a magnetoresistive element. In this figure, an example is a case where each of the plurality of magnetic sensor cells 220 has three sensor units 300x to z (collectively referred to as “sensor unit 300”), and the input magnetic field can be detected in the three axial directions. Shown as. However, none of the plurality of magnetic sensor cells 220 is limited to having three sensor units 300x to z, and if at least a part of the magnetic sensor array 210 can detect an input magnetic field in the three axial directions. good. At this time, as will be described later, when each spherical harmonic is spatially sampled by the magnetic sensor array 210, it is necessary to detect the dependence on the spatial frequency related to the angular momentum in the magnetic field. Therefore, it is preferable that the positions of the sensor units 300 in the magnetic sensor array 210 are arranged as evenly as possible at least in the azimuth angle direction and the zenith angle direction. For the same reason, it is preferable that the magnetic sensing axes of the sensors in the magnetic sensor array 210 are arranged at least as evenly as possible in the azimuth direction and the zenith angle direction. The sensor unit 300x is arranged along the X-axis direction and can detect the magnetic field in the X-axis direction. Further, the sensor unit 300y is arranged along the Y-axis direction and can detect the magnetic field in the Y-axis direction. Further, the sensor unit 300z is arranged along the Z-axis direction and can detect the magnetic field in the Z-axis direction. As shown by the enlarged view shown by the alternate long and short dash line in this figure, in the present embodiment, each sensor unit 300 has magnetic convergence plates arranged at both ends of the magnetoresistive element. Therefore, each sensor unit 300 clarifies the sampling points in space in each axial direction by sampling the spatial distribution of the magnetic field using the magnetoresistive element arranged at a narrow position sandwiched between the magnetic focusing plates. be able to. Details of the configuration of each sensor unit 300 will be described later.

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

In this figure, the three-axis directions of the magnetic fields detected by the sensor units 300x, 300y, and 300z and the three-dimensional directions in which the magnetic sensor cells 220 are arranged are the same directions. This makes it easy to grasp each component of the distribution of the measured magnetic field. However, the three-axis direction of the magnetic field to be detected and the three-dimensional direction in which the magnetic sensor cells 220 are arranged may be different. For example, instead of the X-axis, Y-axis, and Z-axis, the r-axis, θ-axis, and φ-axis of the polar coordinate system may be used as the three-axis directions of the magnetic field to be detected. Further, as the three-dimensional direction in which the magnetic sensor cells 220 are arranged, the r-axis, θ-axis, and φ-axis of the polar coordinate system may be used instead of the X-axis, Y-axis, and Z-axis. When the three-axis direction of the magnetic field to be detected and the three-dimensional direction in which the magnetic sensor cells 220 are arranged are different, the magnetism is not restricted by the arrangement of the sensor unit 300 in the magnetic sensor cell 220 or the arrangement direction of the magnetic sensor cells 220. The degree of freedom in designing the sensor array 210 can be increased. In this case, the magnetic sensor cell 220 can be made smaller, and therefore, the magnetic sensor array 210 having such a plurality of magnetic sensor cells 220 can be made smaller.

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

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

FIG. 5 shows a configuration example of the sensor unit 300 according to the present embodiment. The sensor unit 300 is provided inside each of the plurality of magnetic sensor cells 220, and includes a magnetic sensor 520, a magnetic field generation unit 530, and an output unit 540. A part of the sensor unit 300, for example, an amplifier circuit 532 or the like may be provided on the sensor data collection unit 230 side instead of the magnetic sensor cell 220 side.

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

The magnetic field generation unit 530 generates a feedback magnetic field having a size corresponding to the output signal output by the output unit 540 and reduces the input magnetic field detected by the magnetic sensor 520, and gives the feedback magnetic field to the magnetic sensor 520. The magnetic field generation unit 530, for example, generates a feedback magnetic field B_FB whose absolute value is substantially the same as the input magnetic field in the direction opposite to the magnetic field B input to the magnetic sensor 520, and operates so as to cancel the input magnetic field. The magnetic field generation unit 530 includes an amplifier circuit 532 and a feedback coil 534.

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

The feedback coil 534 generates a feedback magnetic field B_FB corresponding to the feedback current I_FB. The feedback coil 534 is wound along the axial direction of the magnetic field to be detected by the magnetic sensor 520 so as to surround the magnetoresistive element of the magnetic sensor 520 and the two magnetic focusing plates arranged at both ends of the magnetoresistive element. ing. It is desirable that the feedback coil 534 generate a uniform feedback magnetic field B_FB throughout the magnetic sensor 520. For example, assuming that the coil coefficient of the feedback coil 534 is β, the feedback magnetic field B_FB can be calculated as β × I_FB. Here, since the feedback magnetic field B_FB is generated in a direction that cancels the input magnetic field B, the magnetic field input to the magnetic sensor 520 is reduced to BB_FB. Therefore, the feedback current I_FB is expressed by the following equation.

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

The output unit 540 outputs an output signal V_xMR corresponding to the feedback current I_FB that the magnetic field generation unit 530 flows to generate the feedback magnetic field B_FB. The output unit 540 has, for example, a resistance element having a resistance value R, and outputs a voltage drop caused by a feedback current I_FB flowing through the resistance element as an output signal V_xMR. In this case, the output signal V_xMR is calculated from the equation (Equation 2) as follows.

As described above, since the sensor unit 300 generates a feedback magnetic field that reduces the magnetic field input from the outside, the magnetic field that is substantially input to the magnetic sensor 520 is reduced. As a result, the sensor unit 300 uses, for example, a magnetoresistive element having the non-linearity shown in FIG. 4 as the magnetic sensor 520 and having a narrow operating magnetic field range, even if the absolute value of the input magnetic field B exceeds 1 μT. , It is possible to prevent the detection signal V_xMR from being saturated. The input / output characteristics of such a sensor unit 300 will be described below.

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

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

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

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

FIG. 8 shows the magnetic flux distribution when a feedback magnetic field is generated in the magnetic sensor 520 according to the present embodiment. In FIG. 8, the members having the same functions and configurations as those in FIG. 7 are designated by the same reference numerals, and the description thereof will be omitted except for the following differences. In the magnetic sensor 520 according to the present embodiment, when a feedback current is supplied to the feedback coil 534, the feedback coil 534 generates a feedback magnetic field, so that a magnetic flux distribution as shown by a single point chain line in this figure is generated. The magnetic flux generated by this feedback magnetic field is spatially distributed so as to cancel the spatial distribution of the magnetic field that is input to the magnetic resistance element 710 and magnetically amplified by the magnetic focusing plates 720 and 730. Therefore, when the magnetic focusing plates 720 and 730 are arranged at both ends of the magnetic resistance element 710, the magnetic sensor 520 accurately determines the magnetic field distribution at the position of the magnetic resistance element 710 by the feedback magnetic field. Since it can be canceled, a sensor with high linearity between the input magnetic field and the output voltage can be realized.

FIG. 9 shows an arrangement example of a plurality of magnetic sensor cells 220 in the magnetic sensor array 210 according to the present embodiment. In FIGS. 2 and 3, for convenience of explanation, the magnetic sensor array 210 is shown to be flat. However, in practice, the magnetic sensor array 210 may have a curved surface shape that is curved in at least one direction, as shown in this figure. Then, a plurality of magnetic sensor cells 220 may be arranged three-dimensionally so as to be arranged at lattice points included in the curved surface shape. As an example, the magnetic sensor array 210 may be configured by arranging a plurality of magnetic sensor cells 220 three-dimensionally in a cross-sectional view arc shape.

That is, the plurality of magnetic sensor cells 220 may be arranged in an arc shape in a cross-sectional view so as to be centered on the center of gravity of the body to be measured and along the chest of the body to be measured. At this time, each magnetic sensor cell 220 is arranged at each lattice point included in the curved surface shape in the three-dimensional lattice space. Here, the grid points are grid-like points provided at equal intervals in the X direction, the Y direction, and the Z direction at predetermined intervals. As an example, each magnetic sensor cell 220 is arranged along a curved surface having a protrusion in a direction orthogonal to one direction when viewed from any one of the X direction, the Y direction, and the Z direction. In this figure, an example is shown in which each magnetic sensor cell 220 is arranged along a curved surface having a protrusion in the positive direction of the Z axis when viewed from the Y direction. Then, for example, the magnetic sensor array 210 is arranged in the negative direction of the Z axis as much as possible within a range in which each apex of each magnetic sensor cell 220 does not exceed a predetermined curved surface having a convex in the positive direction of the Z axis. As described above, by arranging each magnetic sensor cell 220 at each lattice point in the three-dimensional lattice space, a curved surface shape having a convex shape in the positive direction of the Z axis may be formed.

More specifically, in the cross-sectional view of this figure, a plurality of inner (Z-axis minus side) magnetic sensor cells 220, that is, magnetic sensor cells 220 [1, j, 1] to 220 [8, j, 1] are designated by reference numeral 910. It is arranged outside the arc indicated by the alternate long and short dash line of reference numeral 915 so as to be arranged outside the inscribed circle of the magnetic sensor array 210 shown by. Further, a plurality of magnetic sensor cells 220 on the outside (Z-axis plus side), that is, magnetic sensor cells 220 [1, j, 2] to 220 [8, j, 2] are circumscribed of the magnetic sensor array 210 indicated by reference numeral 920. It is arranged inside the arc indicated by the alternate long and short dash line of reference numeral 925 so as to be arranged inside the circle. The centers of these inscribed circles and circumscribed circles are common and coincide with the coordinate origins in the signal separation calculation described later.

As a result, the magnetic sensor array 210 can arrange the sensor unit not only in one direction facing the heart but also in multiple directions, and can sense the magnetism from multiple directions. Further, in the magnetic sensor array 210 according to the present embodiment, since the magnetic sensor cell 220 is formed in a rectangular parallelepiped shape as an example, the shape of the magnetic sensor array 210 can be easily changed. That is, the magnetic sensor array 210 according to the present embodiment can take various shapes that can be configured by arranging the magnetic sensor cells 220 at lattice points, and has a high degree of freedom in design. Therefore, as shown in this figure, the magnetic sensor array 210 easily forms a curved surface shape in a three-dimensional space by arranging a plurality of magnetic sensor cells 220 at lattice points included in the curved surface shape in the three-dimensional space. can do. Then, the magnetic field measuring device 10 arranges the magnetic sensor array 210 so that the chest of the object to be measured is located on the center side of the curved surface, that is, the heart, which is the magnetic field source to be measured, is located on the center side of the curved surface. And measure the magnetic field. As a result, the magnetic field measuring device 10 separates the measurement target magnetic field and the disturbance magnetic field with high accuracy by separating the signal space using the measurement data measured at a position close to the heart, which is the measurement target magnetic field source (described later). can do. At this time, it is preferable that the curvature of the curved surface of the magnetic sensor array 210 is substantially equal to the curvature around the chest of the object to be measured because the magnetic field can be measured at a position closer to the heart, which is the magnetic field source to be measured.

FIG. 10 shows a preferable arrangement position of the calibration magnetic field generating unit 144 at the time of calibration. As described above, the magnetic field measuring device 10 makes the magnetic sensor unit 110 face the calibration magnetic field generating unit 144 when performing calibration. At this time, the calibration magnetic field generating unit 144 is arranged on the side facing the object to be measured when viewed from the magnetic sensor array 210. That is, the calibration magnetic field generator 144 is located on the Z-axis minus side of the plurality of magnetic sensor cells 220 [1, j, 1] to 220 [8, j, 1] inside the magnetic sensor array 210 (Z-axis minus side). Is placed in.

Here, the outside of the circle circumscribing the magnetic sensor array 210 represented by reference numeral 920 is the disturbance magnetic field source space. Further, the sensor space is inside the circle circumscribing the magnetic sensor array 210 indicated by reference numeral 920 and outside the circle inscribed in the magnetic sensor array 210 indicated by reference numeral 910. Further, the inside of the circle inscribed in the magnetic sensor array 210 indicated by reference numeral 910 is the signal source space.

The magnetic field measuring device 10 may arrange the calibration magnetic field generating unit 144 in the signal source space when performing calibration. In particular, the calibration magnetic field generating unit 144 may be arranged inside the region surrounded by the arc 915 and the string 917 connecting both end points of the arc 915. As described above, the calibration magnetic field generating unit 144 may be arranged in the region indicated by the dots in this figure. Further, at this time, the calibration magnetic field generating unit 144 may be arranged adjacent to the plurality of inner magnetic sensor cells 220 [1, j, 1] to 220 [8, j, 1] forming the arc 915. .. By arranging the calibration magnetic field generator 144 at such a position, the magnetic field measuring device 10 can apply a relatively strong calibration magnetic field from the signal source space to the magnetic sensor 520 when performing calibration. Therefore, the magnetic sensor 520 can be calibrated even in an environmental magnetic field, ignoring the influence of the disturbance magnetic field.

FIG. 11 shows the configurations of the calibration magnetic field generation unit 144, the magnetic sensor array 210, the sensor data collection unit 230, and the sensor data processing unit 1100 according to the present embodiment.

The calibration magnetic field generating unit 144 is arranged on the side facing the object to be measured as viewed from the magnetic sensor array 210, preferably at a position indicated by a dot in FIG. 10 when performing calibration. As described above, the calibration magnetic field generating unit 144 may have a plurality of calibration coils, each of which generates a calibration magnetic field. Then, the calibration magnetic field generator 144 receives an alternating current corresponding to the frequency of the clock signal for calibration, and adds an alternating current corresponding to the frequency of the clock signal to each of the plurality of calibration coils to obtain a plurality of alternating currents. An AC magnetic field corresponding to the frequency of the clock signal is generated from each of the calibration coils.

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

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

The clock generator 234 generates a sampling clock and supplies a common sampling clock to each of the plurality of AD converters 232. Then, each of the plurality of AD converters 232 performs AD conversion according to the common sampling clock supplied from the clock generator 234. Therefore, all of the plurality of AD converters 232 for AD-converting the outputs of the plurality of sensor units 300 [1] to 300 [M] provided at different positions perform synchronous operation. As a result, the plurality of AD converters 232 can simultaneously sample the detection results of the plurality of sensor units 300 [1] to 300 [M] provided in different spaces.

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

The measurement data acquisition unit 1120 is connected to each of the plurality of AD converters 232 connected to the corresponding sensor unit 300, and is measured by the plurality of sensor units 300 [1] to 300 [M] included in the magnetic sensor array 210. The measured measurement data V [1] to V [M] are acquired respectively. Specifically, the measurement data acquisition unit 1120 may be configured by using a flip-flop or the like that latches and acquires the digital measurement data V converted to digital by the AD converter 232 at a predetermined timing T. The measurement data acquisition unit 1120 supplies the acquired measurement data V to the synchronous detection unit 1130.

When measuring the measurement target magnetic field, the synchronous detection unit 1130 supplies the measurement data V supplied from the measurement data acquisition unit 1120 to the data output unit 1140 as it is. On the other hand, when performing calibration, the synchronous detection unit 1130 detects the calibration magnetic field, which is an AC magnetic field, using a signal having a frequency of the AC magnetic field. As an example, the synchronous detection unit 1130 synchronously detects the calibration magnetic field according to the clock signal for calibration. Then, the synchronous detection unit 1130 extracts a frequency component synchronized with the calibration magnetic field, which is an AC magnetic field, from the measurement data V supplied from the measurement data acquisition unit 1120, and obtains the measurement data V related to the extracted frequency component. It is supplied to the data output unit 1140. Here, such synchronous detection may be performed on software or hardware. Further, in the above description, the case where the synchronous detection unit 1130 performs synchronous detection and extracts the frequency component synchronized with the calibration magnetic field is shown as an example, but the frequency separation by FFT (the frequency component synchronized with the calibration magnetic field is used as an example. A frequency component synchronized with the calibration magnetic field may be extracted by a band path filter) or the like.

The data output unit 1140 sets the measurement data V [1] to V [M] supplied from each of the plurality of synchronous detection units 1130 as the sensor signal components Φ [1] to Φ [M], and sets the sensor array signal. Φ is supplied to the signal space separation unit 1160.

The basis vector storage unit 1150 stores the basis vector required for the signal space separation unit 1160 to signal-separate the sensor array signal Φ, and supplies this to the signal space separation unit 1160. The basis vector storage unit 1150 sequentially updates the stored basis vector to the basis vector changed by the calibration unit 1190. This will be described later.

The signal space separation unit 1160 sets the spatial distribution of the input magnetic field indicated by the measurement data V [1] to V [M] supplied as each component of the sensor array signal Φ from the data output unit 1140 to the spatial distribution of the normal orthogonal function. When a magnetic field having a magnetic field is detected by the magnetic sensor array 210, a vector signal having a signal output from each of the plurality of magnetic sensors 520 as each signal component is used as a base vector for signal separation. At this time, the signal space separation unit 1160 acquires the basis vector required for signal separation from the basis vector storage unit 1150. Then, the signal space separation unit 1160 uses the base vector acquired from the base vector storage unit 1150 to obtain the spatial distribution of the magnetic field indicated by the measurement data V [1] to V [M], and obtains the measurement target magnetic field (signal source space). The signal is separated into a disturbance magnetic field (disturbance space signal), the disturbance magnetic field is suppressed, the measurement target magnetic field is calculated, and this is output. This will also be described later.

When performing calibration, the calibration clock generation unit 1170 generates a clock signal for generating an AC calibration magnetic field and an AC current corresponding to the frequency of the clock signal. Then, the calibration clock generation unit 1170 supplies the generated clock signal to the plurality of synchronous detection units 1130, and also supplies the calibration magnetic field generation unit 144 with an alternating current corresponding to the frequency of the clock signal. In response to this, the calibration magnetic field generator 144 applies an alternating current corresponding to the frequency of the clock signal to each of the plurality of calibration coils, and responds to the frequency of the clock signal from each of the plurality of calibration coils. Generates an alternating magnetic field. Further, the plurality of synchronous detection units 1130 each detect the AC calibration magnetic field generated by the calibration magnetic field generation unit 144 according to the clock signal. In the above description, the case where the calibration clock generation unit 1170 is provided inside the sensor data processing unit 1100 is shown as an example, but the calibration clock generation unit 1170 generates, for example, the calibration magnetic field. It may be configured inside the portion 144.

The error calculation unit 1180 calculates the separation error when the signal space separation unit 1160 separates the spatial distribution of the calibration magnetic field when performing calibration. Then, the error calculation unit 1180 supplies the calculated separation error to the calibration unit 1190.

The calibration unit 1190 calibrates the sensor error in the magnetic sensor 520 based on the separation error when the spatial distribution of the calibration magnetic field is signal-separated. At this time, the calibration unit 1190 calibrates the sensor error by changing the basis vector used by the signal space separation unit 1160. Then, the calibration unit 1190 supplies the information regarding the changed basis vector to the basis vector storage unit 1150. In response to this, the basis vector storage unit 1150 updates the basal vector to be stored. This will be described in detail using mathematical formulas.

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

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

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

In step 1240, the signal space separation unit 1160 uses the spatial distribution of the magnetic field indicated by the measurement data V [1] to V [M] acquired in step 1220 as the basis vector using the signal vector acquired in step 1230. Expand the series. Then, the signal space separation unit 1160 separates the spatial distribution of the magnetic field into the measurement target magnetic field and the disturbance magnetic field from the vector obtained by the series expansion. That is, the signal space separation unit 1160 is magnetic when the magnetic field having the spatial distribution of the normal orthogonal function is detected by the magnetic sensor array 210 for the spatial distribution of the input magnetic field indicated by the measurement data V [1] to V [M]. A vector signal having a signal output by each of the sensors 520 as each signal component is used as a base vector for signal separation. That is, based on the position and magnetic sensitivity of each magnetic sensor 520, in particular, the basis vector is calculated from the orthonormal function and the position and magnetic sensitivity of each magnetic sensor 520, and the spatial distribution of the magnetic field indicated by the measurement data is signal-separated. Here, the orthonormal function may be a spherical harmonic. Further, the signal space separation unit 1160 calculates the coefficient of the basis vector by the method of least squares when separating signals.

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

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

Since the solution of Laplace's equation generally _{has a solution in the form of series expansion using spherical harmonics Y l, m} (θ, φ), which is a normal orthogonal function system, the potential V (r) is given by the following equation. Can be represented by. Here, | r | is the absolute value of the position vector r (distance from the coordinate origin), θ and φ are two deviation angles in spherical coordinates, l is the azimuthal quantum number, and m is the magnetic quantum number. Α and β are multipolar moments, and Lin and Lout are the number of coordinates for the space in front of the magnetic sensor array 210 and the space in the back, respectively, when viewed from the object to be measured. The azimuthal quantum number l takes a positive integer, and the magnetic quantum number m takes an integer from −l to + l. That is, for example, when l is 1, m is -1, 0, and 1, and when l is 2, for example, m is -2, -1, 0, 1, and 2. Since there is no monopole in the magnetic field, the azimuthal quantum number l starts from 1 instead of 0 in (Equation 5). The first term in (Equation 5) is a term that is inversely proportional to the distance from the coordinate origin, and indicates the potential existing in the space in front of the magnetic sensor array 210 when viewed from the object to be measured. The second term in (Equation 5) is a term proportional to the distance from the coordinate origin, and indicates the potential existing in the space behind the magnetic sensor array 210 when viewed from the object to be measured.

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

When the solution of the Laplace equation is expressed in the form of a series expansion using spherical harmonics, the general solution is an infinite series, but the SNR (signal-to-noise ratio, that is, the disturbance magnetic field and It suffices if the ratio of the magnetic field signal to be measured to the sensor noise) can be obtained, and it is said that it is actually sufficient to express it in a series of about 10 terms. Further, it is said that the series of signal space separation in the magnetoencephalograph may be about Lin = 8 and Lout = 3. Therefore, also in this embodiment, the case of Lin = 8 and Lout = 3 will be described as an example. However, the values of Lin and Lout are not limited to this, and may be any numerical value sufficient to sufficiently suppress the disturbance magnetic field and calculate only the magnetic field to be measured.

Here, the sensor array signal Φ is composed of an M-dimensional vector, and each signal component of the vector is a magnetic field vector B (r [m]) in the position vector r [m] in which the magnetic sensor 520 of each sensor unit 300 is arranged. ) And the inner product of the magnetic sensitivity vector S [m] of each magnetic sensor 520. Therefore, for each magnetic sensor 520, the magnetic sensitivity vector S _Ideal [m] = (S _Ideal [m], x, S _Ideal [m], y, S _Ideal [m], z) as designed for each magnetic sensor 520. When held and placed in the designed position, the ideal sensor array signal Φ _Ideal is expressed by:

That is, each ideal sensor has no sensor error (magnetic sensitivity error due to other axis sensitivity or spindle sensitivity of each sensor, position error due to displacement of each sensor during assembly of the magnetic sensor array 210, etc.). The signal component Φ _Ideal [m] is expressed by the following equation.

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

Here, in an ideal case where there is no sensor error in each magnetic sensor 520, A _Ideal , B _Ideal , Xin, and Xout are defined as follows, respectively. That _is, the _{A Ideal,} from l = 1 to l = Lin, each vector _{a Ideal} when taking integer from m = -l to l in each l were sequentially arranged in columns, a total of Lin · (Lin + 2) column Defined as a vector of. _Further, the _{B Ideal,} from l = 1 to l = Lout, each vector _{b Ideal} when taking integer from m = -l to l in each l were sequentially arranged in columns, a total of Lout · (Lout + 2) column Defined as a vector of. Further, Xin is transposed from a vector in which each multipolar moment α when an integer from m = −l to l is taken in each l from l = 1 to l = Lin is transposed. It is defined as a vector of (Lin + 2) rows. Further, Xout is transposed from a vector in which each multipolar moment β when an integer from m = −l to l is taken in each l from l = 1 to l = Lout is transposed, for a total of Lout · (Lout + 2). ) Defined as a row vector.

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

_{In step 1240, the signal space separation unit 1160 satisfies Φ Ideal} = [ _{AB] Ideal} X with a minimum square approximation using the following equation based on the model equation obtained in this (Equation 11). Determine the vector ^ X _Ideal (where "^ X _ideal " indicates the left side of (Equation 12) and means the hat (estimated value) of _{X Ideal).}

_{Therefore, the signal space separation unit 1160 can express the hat ^ Φ Ideal} of the sensor array signal of the ideal magnetic sensor array 210 as an M-dimensional vector of the minimum squared solution by the following equation. As a result, the signal space separation unit 1160 can solve the spatial distribution of the magnetic field in step 1240.

Then, in step 1250, the signal space separation unit 1160 _{reduces the ^ Xout · B Ideal} by using the vertical vector determined in step 1240 to reduce the disturbance magnetic field component, that is, the component of the second term in (Equation 6). Output the suppressed result. The signal space separation unit 1160 _{suppresses the disturbance magnetic field component by outputting only ^ Xin · A Ideal} as a result, and outputs only the measurement target magnetic field component, that is, the component of the first term in (Equation 6). You may.

As a result, according to the magnetic field measuring device 10 according to the present embodiment, the measurement data V [1] measured using the magnetic sensor array 210 having a plurality of magnetic sensor cells 220 and capable of detecting the input magnetic field in the three axial directions. ] ~ V [M], the spatial distribution of the magnetic field can be signal-separated into the measurement target magnetic field and the disturbance magnetic field. Further, since the magnetic field measuring device 10 suppresses the disturbance magnetic field component and outputs only the measurement target magnetic field component, the measurement target magnetic field can be measured with higher accuracy. Further, since each of the plurality of sensor units 300 has a magnetic focusing plate, the magnetic sensitivity of the sensor unit 300 can be enhanced, the spatial sampling point can be clarified, and the affinity with the signal space separation technology can be further enhanced. can.

FIG. 13 geometrically shows a signal space separation operation using _{the ideal basis vector [AB} ] Ideal when the magnetic sensor array 210 is ideally made. Reference numeral 1310 indicates the sensor array signal Φ _Ideal of the ideal magnetic sensor array 210. Reference numeral 1320 indicates a linear subspace Span {A _Ideal } stretched by the ideal basis vector A _Ideal. Reference numeral 1330 indicates a linear subspace Span {B _Ideal } stretched by the ideal basis vector B _Ideal. Reference numeral 1340 indicates a linear subspace stretched by _{an ideal basis vector [AB} ] ideal that is a linear sum of the linear _{subspace Span {A Ideal} } and the linear subspace Span {B _Ideal}. Reference numeral 1350 indicates an M-dimensional vector of a minimum squared solution. As shown in this figure, if the magnetic sensor array 210 is ideally made, i.e. without sensor error, the sensor array signal Φ _Ideal of the ideal magnetic sensor array 210 is ideal. It exists in a linear subspace stretched by the base vector [ _{AB] Ideal.} That is, the equation (Equation 11) is established with high accuracy, and the signal space separation unit 1160 accurately separates the signal space into the target magnetic field component and the disturbance magnetic field component with respect to the magnetic field detected by the magnetic sensor array 210. Can be done.

However, the actual sensor signal component Φ _{Uncalib [m] from each sensor unit 300 is a magnetic sensitivity vector S Uncalib} [m] = (S _Uncalib [m], x, S) including the magnetic sensitivity error of each magnetic sensor 520. _{It is expressed using Uncalib} [m], y, S _Uncalib [m], z). That is, the magnetic sensor array 210 _{assumes a magnetic sensitivity vector S Ideal} [m] = (S _Ideal [m], x, S _Ideal [m], y, S _Ideal [m], z) for each magnetic sensor 520. However, in reality, the unknown magnetic sensitivity vector S _Uncalib [m] = (S _Uncalib [m], x, S _Uncalib [m], y, S _Uncalib [m], z. ) Is completed.

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

_{In this way, for the sensor array signal Φ Uncalib} measured by the magnetic sensor array 210 created with the magnetic sensitivity error, the equation of the following equation is used using the assumed ideal basis vector [ _{AB] Ideal.} Suppose you want to set up.

_{Then, even if the vertical vector ^ X Uncalib} is determined by the following equation based on the model equation obtained in (Equation 15), the solution of the equation is inaccurate.

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

FIG. 14 geometrically shows a signal space separation operation using _{the ideal basis vector [AB} ] Ideal when the magnetic sensor array 210 is made with sensor error. In FIG. 14, members having the same functions and configurations as those in FIG. 13 are designated by the same reference numerals, and the description thereof will be omitted except for the following differences. _Reference numeral 1410 indicates a sensor array signal Φ Uncalib of the magnetic sensor array 210 having a sensor error. Reference numeral 1450 indicates an M-dimensional vector of a minimum squared solution. As shown in this figure, when the magnetic sensor array 210 has a sensor error, the sensor array signal Φ _Uncalib does not exist in the linear subspace stretched by the ideal basis vector [ _{AB] Ideal.} ..

At this time, a separation error, that is, an error vector ε represented by the reference numeral 1460, is formed between the _{sensor array signal Φ Uncalib} indicated by the reference numeral 1410 and the M-dimensional vector ^ Φ _{Uncalib of the minimum squared solution indicated by the reference numeral 1450.} And the error angle γ indicated by reference numeral 1470 occurs. Here, the error vector ε and the error angle γ are expressed by the following equations.

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

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

FIG. 15 shows a flow in which the magnetic field measuring device 10 according to the present embodiment acquires a sensor array signal Φ (n) for calibration. In step 1510, the magnetic field measuring device 10 arranges the calibration magnetic field generating unit 144 on the side facing the object to be measured as viewed from the magnetic sensor array 210, preferably at a position indicated by a dot in FIG.

In step 1520, the magnetic field measuring device 10 substitutes 1 for n. Here, n is a number for identifying the calibration coil included in the calibration magnetic field generating unit 144, and indicates an integer from 1 to the number N of the calibration coils included in the calibration magnetic field generating unit 144.

In step 1530, the magnetic field measuring device 10 drives the calibration coil (n) and acquires the sensor array signal Φ (n). As an example, the calibration magnetic field generator 144 receives an alternating current corresponding to the frequency of the calibration clock signal supplied from the calibration clock generator 1170, and the calibration coil (n) receives the frequency of the clock signal. An alternating current corresponding to the frequency of the clock signal is applied to generate an alternating current according to the frequency of the clock signal from the calibration coil (n). At this time, the calibration magnetic field generated by the calibration coil (n) is close to the magnetic field generated from the magnetic dipole. The calibration magnetic field generated by the calibration coil (n) corresponds to the component of the first term in (Equation 6). At this time, by generating an AC magnetic field having a relatively strong strength from the calibration coil (n), the influence of the second term component in (Equation 6), that is, the disturbance magnetic field can be ignored at the time of calibration.

Then, the magnetic field measuring device 10 acquires the sensor array signal Φ (n) when the calibration magnetic field is generated from the calibration coil (n). More specifically, when a calibration magnetic field is generated from the calibration coil (n), the measurement data acquisition unit 1120 measures by a plurality of sensor units 300 [1] to 300 [M] included in the magnetic sensor array 210. The measured measurement data V [1] to V [M] are acquired respectively. Then, the synchronous detection unit 1130 receives the calibration clock signal supplied from the calibration clock generation unit 1170, and synchronously detects the calibration magnetic field according to the clock signal. Then, the synchronous detection unit 1130 extracts a frequency component synchronized with the calibration magnetic field, which is an AC magnetic field, from the measurement data V [1] to V [M], and measures data V [1] related to the extracted frequency component. ] To V [M] are supplied to the data output unit 1140, respectively. Then, when the data output unit 1140 generates a calibration magnetic field from the calibration coil (n) for the measurement data V [1] to V [M] supplied from the synchronous detection unit 1130, a plurality of sensor units. The sensor array signal Φ (n) for calibration, which has each sensor signal component Φ (n) [1] to Φ (n) [M] from 300 [1] to 300 [M], is the signal space separator 1160. Supply to. As a result, the signal space separation unit 1160 acquires the sensor array signal Φ (n) for calibration when the calibration magnetic field is generated from the calibration coil (n).

In step 1540, the magnetic field measuring device 10 determines whether n is equal to N. That is, the magnetic field measuring device 10 determines whether or not all the calibration coils included in the calibration magnetic field generating unit 144 have been driven. When it is determined that n is equal to N, that is, when it is determined that all the calibration coils have been driven, the magnetic field measuring device 10 ends the flow of acquiring the sensor array signal Φ (n) for calibration. do.

On the other hand, if it is determined in step 1540 that n is not equal to N, that is, if it is determined that all the calibration coils are not being driven, the magnetic field measuring device 10 increments n in step 1550. Then n = n + 1, the process is returned to step 1530, and the flow is continued.

As a result, the magnetic field measuring device 10 generates a calibration sensor array signal Φ (n) when N calibration coils are driven to generate a calibration magnetic field from n = 1 to n = N. Get each.

FIG. 16 shows a flow in which the magnetic field measuring device 10 according to the present embodiment calibrates. In step 1610, the magnetic field measuring device 10 substitutes 1 for i. Here, i means the number of times the calibration is executed, and indicates an integer from 1 to MAX_COUNT, which is the upper limit of the number of times the calibration is executed.

In step 1620, the magnetic field measuring device 10 calculates the separation error. More specifically, the signal space separation unit 1160 performs signal space separation for the sensor array signal Φ (n) for calibration for 1 ≦ n ≦ N, respectively. At this time, in step 1620 following step 1610, the signal space separation unit 1160 determines the solution of the equation shown in (Equation 16) from the equation shown in (Equation 15). At this time, the signal space separation unit 1160 sets the position where the calibration magnetic field generation unit 144 is arranged as the origin of the coordinates in the calculation when the spatial distribution of the calibration magnetic field is signal-separated. That is, the signal space separation unit 1160 sets the position where the calibration coil (1) is arranged as the origin of the coordinates in the calculation when the sensor array signal Φ (1) is separated. Similarly, the signal space separation unit 1160 sets the position where the calibration coil (n) is arranged as the origin of the coordinates in the calculation when the sensor array signal Φ (n) is signal-separated. In this way, when the calibration magnetic field generation unit 144 has N calibration coils and the calibration magnetic field is generated from each of the N calibration coils, the signal space separation unit 1160 is a calibration coil ( In performing signal space separation calculation and calculation of error ε for the sensor array signal Φ (n) when the calibration magnetic field is generated from n), the signal space is located at the position where the calibration coil (n) is arranged. The calculation is performed while sequentially matching the coordinate origins in the separation operation. As a result, the magnetic field measuring device 10 can greatly simplify the calibration of each magnetic sensor 520 in the M sensor units 300 included in the magnetic sensor array 210, and accelerate the convergence of the calibration parameters. Then, the error calculation unit 1180 calculates at least one of the error vector ε (n) and the error angle γ (n) as the separation error for 1 ≦ n ≦ N based on (Equation 18). do.

In step 1630, the magnetic field measuring device 10 determines whether or not the separation error exceeds a predetermined threshold value. For example, the magnetic field measuring device 10 determines whether or not the sum of squares of N separation errors exceeds a predetermined threshold value. That is, in the magnetic field measuring device 10, at least one of the sum of squares of the error vector ε (n) for 1 ≦ n ≦ N and the sum of squares of the error angle γ (n) is predetermined. Determine if it exceeds the threshold. If it is determined that the separation error does not exceed the threshold value, the magnetic field measuring device 10 terminates the process assuming that the calibration is completed.

On the other hand, if it is determined in step 1630 that the separation error exceeds a predetermined threshold value, the magnetic field measuring device 10 calibrates the sensor error in step 1640. For example, the calibration unit 1190 has a separation error as an objective function, that is, for 1 ≦ m ≦ M so that at least one of the error vector ε (n) and the error angle γ (n) is set to zero. The magnetic sensitivity vector S _Calib [m] is optimized. At this time, the calibration unit 1190 may use, for example, a computer science method such as stochastic annealing. Here, the basis vector after calibration is expressed by the following equation. In this way, the calibration unit 1190 changes the basis vector so as to minimize the separation error by optimizing _{the magnetic sensitivity vector S Calib [m].}

In step 1650, the magnetic field measuring device 10 determines whether i is equal to MAX_COUNT. That is, the magnetic field measuring device 10 determines whether or not the number of times the calibration is executed is the upper limit number of times.

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

On the other hand, when i is not equal to MAC_COUNT, the magnetic field measuring device 10 increments i to make i = i + 1 in step 1670, returns the process to step 1620, and continues the flow. In step 1620 following step 1670, the signal space separation unit 1160 may determine the solution of the equation by the following equation instead of (Equation 16).

Further, the signal space separation unit 1160 may determine _{the hat ^ Φ Calib} of the sensor array signal of the magnetic sensor array 210 having a sensor error as the M-dimensional vector of the minimum squared solution by the following equation.

Then, the signal space separation unit 1160 may calculate the separation error between the _{sensor array signal Φ Calib} and the M-dimensional vector ^ Φ _{Calib of the least squares solution by the same method as in (Equation 18).}

FIG. 17 geometrically shows a signal space separation operation using _{the calibrated basis vector [AB} ] Calib when the magnetic sensor array 210 is made with sensor error. In FIG. 17, members having the same functions and configurations as those in FIG. 14 are designated by the same reference numerals, and the description thereof will be omitted except for the following differences. According to the flow of FIG. 16, the magnetic field measuring device 10 updates the basis vector. Here, reference numeral 1720 indicates a linear subspace Span {A _Calib } _{stretched by the calibrated basis vector A Calib. Reference} numeral 1730 indicates a linear subspace Span {B _Calib } stretched by the calibrated basis vector B Calib. _Reference numeral 1740 indicates a linear subspace stretched by a _{basis vector [AB] Calib which} is a linear sum of the linear subspace Span {A Calib} and the linear subspace Span {B _Calib}. Reference numeral 1750 indicates an M-dimensional vector of a minimum squared solution. As shown in this figure, the sensor array signal Φ _Uncalib of the magnetic sensor array 210 with sensor error exists in a linear subspace stretched by the calibrated basis vector [ _{AB] Calib.} That is, the signal space separation unit 1160 separates the signal space into the target magnetic field component and the disturbance magnetic field component with respect to the magnetic field detected by the magnetic sensor array 210 by optimizing the basis vector so as to minimize the separation error. Can be done accurately.

In the above description, an example is obtained in which the magnetic field measuring device 10 changes the basis vector so as to minimize the separation error by optimizing _{the magnetic sensitivity vector S Calib [m] as a calibration parameter.} Shown as. However, as described above, as the sensor error, in addition to the magnetic sensitivity error of each sensor, a position error due to a deviation of the arrangement position of each sensor at the time of assembling the magnetic sensor array 210 may occur. Therefore, the magnetic field measuring device 10 _{replaces or in addition to the magnetic sensitivity vector S Calib} [m] as a calibration parameter, and position information in the magnetic sensor 520 of the M sensor units 300, in this case, signal space separation. The base vector may be changed so as to minimize the separation error by optimizing the position information in the calculated coordinate system of, that is, the radius r, the zenith angle θ, and the azimuth angle φ, respectively. That is, the basis vector may be changed with r, θ, and φ in (Equation 19) as calibration parameters. The magnetic field measuring device 10 can also realize such calibration of the position error by the same method as the calibration of the magnetic sensitivity error. Further, the magnetic field measuring device 10 may perform an operation so as to optimize the calibration of the magnetic sensitivity error and the calibration of the position error at the same time.

Further, in the above description, the case where the magnetic field measuring device 10 measures the magnetic field to be measured after performing the calibration is shown as an example. However, if it is placed at a position that does not interfere with the measurement of the magnetic field to be measured, and the frequency of the AC magnetic field as the calibration magnetic field is higher than the frequency band of the magnetic field to be measured, the magnetic field is measured. The device 10 may simultaneously perform the calibration and the measurement of the magnetic field to be measured. In this case, the magnetic field measuring device 10 may frequency-separate the calibration magnetic field signal and the measurement target magnetic field signal by using LPF, HPF, or the like.

FIG. 18 shows another example of a preferable arrangement position of the calibration magnetic field generating unit 144 at the time of calibration. In FIG. 18, members having the same functions and configurations as those in FIG. 10 are designated by the same reference numerals, and the description thereof will be omitted except for the following differences. As shown in this figure, in the magnetic sensor array 210, when a plurality of magnetic sensor cells 220 are arranged three-dimensionally so as to be arranged at lattice points included in a curved surface shape, the plurality of magnetic sensor cells 220 are viewed in cross section. It may be arranged in a U shape.

More specifically, some magnetic sensor cells 220 [1, j, 3] to 220 [8, j, 3] and 220 [1, j, 4] to 220 [8, j, 4] are inscribed circles. It may be linearly arranged outside the 910 and inside the circumscribed circle 920. The remaining magnetic sensor cells 220 [1, j, 1] to [1, j, 2] and 220 [8, j, 1] to 220 [8, j, 2] are located at one end of the linear shape. The magnetic sensor cells 220 [1, j, 3] and 220 [8, j, 3] may be arranged so as to extend in the minus direction of the Z axis. Even in such a configuration, the centers of the inscribed circle and the circumscribed circle are common and coincide with the coordinate origin in the signal separation calculation. Then, the calibration magnetic field generating unit 144 may be arranged inside the region surrounded by the arc 915 and the string 917 connecting both end points of the arc 915. That is, the calibration magnetic field generating unit 144 may be arranged in the region indicated by the dots in this figure.

In the above description, the calibration magnetic field generator 144 is arranged inside the region surrounded by the arc 915 of the circle 910 inscribed in the magnetic sensor array 210 and the chord 917 connecting both end points of the arc 915. The case is shown as an example. However, it is not limited to this. By arranging the source of the calibration magnetic field in the vicinity of the magnetic sensor array 210, the calibration magnetic field applied to each magnetic sensor 520 can be made relatively strong with respect to the environmental magnetic field. On the other hand, when each magnetic sensor 520 includes the magnetic focusing plates 720 and 730, if the source of the calibration magnetic field is arranged in the vicinity of the magnetic sensor array 210, distortion of the magnetic field due to the magnetic focusing plates 720 and 730 may occur. That is, the gradient of the magnetic field depending on the distance from the source of the calibration magnetic field cannot be ignored, and the strength of the magnetic flux distribution occurs at one end and the multiple ends of the magnetic focusing plates 720 and 730. Further, the influence of such a magnetic field gradient on each axial direction of the magnetic sensor 520 depends on the direction of the source of the calibration magnetic field as seen from each magnetic sensor 520. For this reason, the sensitivity of each magnetic sensor 520 may vary depending on the position of the source of the calibration magnetic field. Therefore, in such a case, the source of the calibration magnetic field may be separated from the magnetic sensor array 210 to some extent. This will be described in detail with reference to the drawings.

FIG. 19 shows another arrangement example of the calibration magnetic field generating unit 144 at the time of calibration. As described above, the magnetic field measuring device 10 has a plurality of magnetic sensor cells 220 each having a magnetic sensor 520 including a magnetoresistive element 710 and a magnetic focusing plate 720 and 730, at least a part of a measurement object (for example, a heart). A magnetic sensor array 210 is provided which is arranged so as to form a surface covering the above. Each of the plurality of magnetic sensor cells 220 responds to a magnetic field generation unit 530 that generates a feedback magnetic field that reduces the input magnetic field detected by the magnetic sensor 520 and a feedback current that the magnetic field generation unit 530 flows to generate the feedback magnetic field. It also has an output unit 540 that outputs the output signal. Then, the magnetic field measuring device 10 is based on the measurement data acquisition unit 1120 that acquires the measurement data measured by the magnetic sensor array 210 and the position and magnetic sensitivity of each magnetic sensor 520, and in particular, the normal orthogonal function and each. The signal space separation unit 1160 that separates the spatial distribution of the magnetic field indicated by the measurement data based on the position of the magnetic sensor 520 and the base vector calculated from the magnetic sensitivity, and the calibration magnetic field generation unit 144 that generates the calibration magnetic field. And the calibration unit 1190 that calibrates the sensor error in the magnetic sensor 520 based on the separation error when the spatial distribution of the calibration magnetic field is signal-separated. The orthonormal function may be a spherical harmonic function.

In such a magnetic field measuring device 10, in order to suppress the distortion of the magnetic field due to the magnetic focusing plates 720 and 730, the calibration magnetic field generating unit 144 may be arranged at a position as shown in this figure. That is, the calibration magnetic field generating unit 144 is composed of the smallest convex polygon 1910 including all the plurality of magnetic sensor cells 220 in the cross-sectional view, and the plurality of magnetic sensor cells 220 in the closed space (enclosed by the thick line in this figure). Is not arranged (hatched in this figure), outside the measurement space 1920, at a position on a straight line that can be drawn from the measurement space 1920 without passing through a plurality of magnetic sensor cells 220, the calibration magnetic field. May be generated. As shown in this figure, in the magnetic field measuring device 10, for example, the calibration magnetic field generating unit 144 may be arranged on the negative side of the Z axis with respect to the magnetic sensor array 210. In this way, the magnetic field measuring device 10 applies the calibration magnetic field at a position where the source of the calibration magnetic field is located at a certain distance from each magnetic sensor 520 and at a position where the directions viewed from the magnetic sensors 520 are aligned at a certain degree. generate. As a result, according to the magnetic field measuring device 10, it is possible to apply a uniform calibration magnetic field to each magnetic sensor 520 so that the influence of the gradient of the magnetic field can be ignored, so that the distortion of the magnetic field due to the magnetic focusing plates 720 and 730 is suppressed. can do.

However, if the source of the calibration magnetic field is separated from the magnetic sensor array 210, the distortion of the magnetic field due to the magnetic focusing plates 720 and 730 can be suppressed, while the calibration magnetic field applied to the magnetic sensor 520 is relatively weak with respect to the environmental magnetic field. There is a trade-off that it becomes. In addition, the accuracy of expressing the spatial distribution of the magnetic field with the basis vector deteriorates. Therefore, it is preferable to limit the relative positional relationship between the magnetic sensor array 210 and the calibration magnetic field generating unit 144 to some extent.

FIG. 20 shows the relative positional relationship between the magnetic sensor array 210 and the calibration magnetic field generator 144. As shown in this figure, the magnetic sensor array 210 may be configured by arranging a plurality of magnetic sensor cells three-dimensionally in a cross-sectional view arc shape. Here, the straight line 2060 connecting the center 2040 of the plane formed by the strings 2030 connecting the two end points 2020 of the arc 2010 and the center 2050 of the calibration magnetic field generating unit 114, and the arc on the same cross section as the center 2040 of the plane. The angle formed by the straight line 2070 connecting the contact point 2020 of 2010 and the string 2030 with the center of the calibration magnetic field generating unit 114 is defined as the angle W. Here, the string 2030 is defined by the lower limit position in the Z-axis direction in the magnetic sensor 520 of the magnetic sensor cells 220 [1, j, 1] and [8, j, 1], and the position is set as the origin of the Z-axis coordinates. I will do it. Further, the distance from the magnetic sensor array 210 to the calibration magnetic field generation unit 144 is defined as the distance from the center 2040 of the plane formed by the strings 2030 to the center 2050 of the calibration magnetic field generation unit 144.

FIG. 21 shows a simulation result of the sensor error when the calibration magnetic field generating unit 144 is separated from the magnetic sensor array 210. Here, in carrying out this simulation, the sensor area size of the magnetic sensor array 210 was set to a width of about 40 cm, a depth of about 20 cm, and a height of about 30 cm. Further, the magnetic sensor array 210 and the calibration magnetic field generator 144 are provided so that the X-axis coordinates and the Y-axis coordinates of the center 2040 of the plane formed by the strings 2030 and the center 2050 of the calibration magnetic field generator 144 are the same. Was placed. In this figure, the horizontal axis indicates the Z coordinate of the center 2050 of the calibration magnetic field generating unit 144 when the position of the string 2030 is 0, in units of [m]. That is, the absolute value of the value on the horizontal axis in this figure indicates the distance from the magnetic sensor array 210 to the calibration magnetic field generating unit 144. Further, below this figure, the value of the angle W calculated from the distance is shown. Further, in this figure, the left side of the vertical axis shows the position error in [mm] units, and the right side of the vertical axis shows the magnetic sensitivity error in [%] units.

As shown in this figure, the position error and magnetic sensitivity of the magnetic sensor 520 from the point where the distance from the magnetic sensor array 210 to the calibration magnetic field generator 144 exceeds 1.916 m, that is, the angle W falls below 5.955 °. It can be seen that the error is starting to rise. This is because the calibration magnetic field generator 144, which is the calculation origin of the base vector calculated based on the position and magnetic sensitivity of each magnetic sensor 520 of the magnetic sensor array 210, is too far away from the magnetic sensor array 210. It is considered that it is limited to a part of the spatial distribution of the magnetic field expressed by the ground vector, and the accuracy of expressing the spatial distribution of the magnetic field deteriorates. Therefore, when the calibration magnetic field generating unit 144 is separated from the magnetic sensor array 210, a straight line connecting the center 2040 of the plane formed by the strings 2030 connecting both end points 2020 of the arc 2010 and the center 2050 of the calibration magnetic field generating unit 144. The angle W formed by the straight line 2070 connecting the contact point 2020 of the arc 2010 and the chord 2030 on the same cross section as the center 2040 of the plane and the center 2040 of the plane and the center 2050 of the calibration magnetic field generator 144 is made larger than 6 degrees. , The calibration magnetic field generator 144 may be arranged.

On the other hand, as shown in this figure, the position error of the magnetic sensor 520 and the position error of the magnetic sensor 520 from the point where the distance from the magnetic sensor array 210 to the calibration magnetic field generating unit 144 is less than 0.416 m, that is, the angle W exceeds 25.668 ° It can be seen that the magnetic sensitivity error has begun to increase. It is considered that this is due to the distortion of the magnetic field due to the magnetic focusing plates 720 and 730. Therefore, it is preferable to arrange the calibration magnetic field generating unit 144 so that the angle W is smaller than 26 degrees.

In the above description, a case where the calibration magnetic field generating unit 144 is arranged away from the magnetic sensor array 210 to suppress the distortion of the magnetic field due to the magnetic focusing plates 720 and 730 is shown as an example. However, it is not limited to this. The magnetic field measuring device 10 may suppress the distortion of the magnetic field due to the magnetic focusing plates 720 and 730 by dividing and calibrating the entire magnetic sensor array 210 instead of calibrating the entire magnetic sensor array 210 at once.

FIG. 22 shows an example of division calibration for the first magnetic sensor cell group 2210. In the division calibration, the measurement data acquisition unit 1120 may acquire the measurement data measured by the magnetic sensor cell group which is at least a part of the plurality of magnetic sensor cells 220 in the magnetic sensor array 210. Further, the signal space separation unit 1160 may signal-separate the spatial distribution of the magnetic field indicated by the measurement data based on the position and magnetic sensitivity of each magnetic sensor 520 in the magnetic sensor cell group. Then, the calibration magnetic field generation unit 144 may generate the calibration magnetic field at a plurality of different positions. As an example, as described above, the calibration magnetic field generator 144 generates a calibration magnetic field in the three-axis directions (for example, the X-axis direction, the Y-axis direction, and the Z-axis direction) that are orthogonal to each other. It may have a plurality of shock coils. Then, the magnetic field measuring device 10 generates a calibration magnetic field from one or a plurality of first calibration coils 2220 arranged at the first position, and among the plurality of magnetic sensor cells 220 constituting the magnetic sensor array 210. The magnetic sensor 520 of the first magnetic sensor cell group 2210 of the above is calibrated. In this figure, a calibration magnetic field is generated from a plurality of first calibration coils 2220a, 2220b, and 2220c (collectively referred to as "first calibration coil 2220") arranged at the first position. The case where the sensor error is calibrated only for the magnetic sensor 520 of the magnetic sensor cells 220 [5, j, 1] to 220 [8, j, 2] is shown as an example. In this case, the magnetic field measuring device 10 uses the position of the first calibration coil 2220 as the origin of the coordinates in the calculation, and is based on the position and magnetic sensitivity of the magnetic sensor 520 of the first magnetic sensor cell group 2210, and in particular, a normal orthogonal function. The calibration magnetic field generated at the first position is measured by the first magnetic sensor cell group 2210 based on the position of the magnetic sensor 520 and the base vector calculated from the magnetic sensitivity. Then, the calibration unit 1190 determines the magnetism of the first magnetic sensor cell group 2210 among the plurality of magnetic sensor cells 220 based on the separation error when the spatial distribution of the calibration magnetic field generated at the first position is signal-separated. Calibrate the sensor error in the sensor 520. The sensor error calibration in the division calibration is the same as the procedure for calibrating the entire magnetic sensor array 210 at once, except that the magnetic sensor 520 to be calibrated is limited. The description is omitted here.

FIG. 23 shows an example of division calibration for the second magnetic sensor cell group 2310. The magnetic field measuring device 10 generates a calibration magnetic field from one or a plurality of second calibration coils 2320 arranged at a second position, and generates a calibration magnetic field to form a magnetic sensor array 210, which is the first of a plurality of magnetic sensor cells 220. The magnetic sensor 520 of the magnetic sensor cell group 2310 of 2 is calibrated. In this figure, a calibration magnetic field is generated from a plurality of second calibration coils 2320a, 2320b, and 2320c (collectively referred to as "second calibration coil 2320") arranged at the second position. As an example, a case where the sensor error is calibrated for only the magnetic sensors 520 of the magnetic sensor cells 220 [1, j, 1] to 220 [4, j, 2] is shown. In this case, the magnetic field measuring device 10 uses the position of the second calibration coil 2320 as the origin of the coordinates in the calculation, and is based on the position and magnetic sensitivity of the magnetic sensor 520 of the second magnetic sensor cell group 2310, and in particular, a normal orthogonal function. The calibration magnetic field generated at the second position is measured by the second magnetic sensor cell group 2310 based on the position of the magnetic sensor 520 and the base vector calculated from the magnetic sensitivity. Then, the calibration unit 1190 determines the magnetism of the second magnetic sensor cell group 2310 among the plurality of magnetic sensor cells 220 based on the separation error when the spatial distribution of the calibration magnetic field generated at the second position is signal-separated. Calibrate the sensor error in the sensor 520.

In this way, the magnetic field measuring device 10 may calibrate the entire magnetic sensor array 210 by sequentially repeating the division calibration. As a result, according to the magnetic field measuring device 10, by limiting the magnetic sensors 520 to be calibrated at the same time, the calibrated magnetic field can be made a certain uniform magnetic field from the viewpoint of each magnetic sensor 520 to be calibrated. , The distortion of the magnetic field due to the magnetic focusing plates 720 and 730 can be suppressed. Further, according to the magnetic field measuring device 10, since the calculation related to the calibration can be divided and executed, the calculation can be executed at high speed.

In the above description, the case where the magnetic field measuring device 10 divides the plurality of magnetic sensor cells 220 in the magnetic sensor array 210 into two groups is shown as an example, but the present invention is not limited to this. The magnetic field measuring device 10 may divide, for example, a plurality of magnetic sensor cells 220 in the magnetic sensor array 210 into three or more groups. For example, the magnetic field measuring device 10 places the plurality of magnetic sensor cells 220 in the magnetic sensor array 210 on the first magnetic sensor cell group located on the left side when viewed from the measured object and the second magnetism located on the right side when viewed from the measured object. It may be divided into a sensor cell group and a third magnetic sensor cell group located between the first magnetic sensor cell group and the second magnetic sensor cell group. Then, the calibration unit 1190 calibrates the sensor error in the magnetic sensor 520 of the first magnetic sensor cell group based on the separation error when the spatial distribution of the calibration magnetic field generated at the first position is signal-separated. Calibration generated at position 2 The sensor error in the magnetic sensor 520 of the second magnetic sensor cell group is calibrated based on the separation error when the spatial distribution of the magnetic field is signal-separated, and the calibration generated at position 3 is performed. The sensor error in the magnetic sensor 520 of the third magnetic sensor cell group may be calibrated based on the separation error when the spatial distribution of the ion magnetic field is signal-separated.

Instead, the calibration unit 1190 uses the magnetism of the first magnetic sensor cell group and the third magnetic sensor cell group based on the separation error when the spatial distribution of the calibration magnetic field generated at the first position is signal-separated. The magnetic sensors of the second magnetic sensor cell group and the third magnetic sensor cell group based on the separation error when the sensor error in the sensor 520 is calibrated and the spatial distribution of the calibration magnetic field generated at the second position is signal-separated. The sensor error at 520 may be calibrated. That is, the magnetic field measuring device 10 has a case where the magnetic sensor 520 of the third magnetic sensor cell group generates a calibration magnetic field at the first position and a case where the calibration magnetic field is generated at the second position. Both may be subject to overlapping calibration targets.

Further, in the above description, the case where the magnetic field measuring device 10 separately includes the calibration magnetic field generating unit 144 in order to generate the calibration magnetic field is shown as an example. However, it is not limited to this. The magnetic field measuring device 10 may substitute the function of the calibration magnetic field generating unit 144 with a part of the magnetic sensor array 210. That is, the magnetic field measuring device 10 may generate a calibration magnetic field from the magnetic field generation unit 530 of at least one of the plurality of magnetic sensor cells 220 in the magnetic sensor array 210. In this case, at least one magnetic sensor cell 220 may further have a switching unit for switching whether the magnetic field generation unit 530 generates a feedback magnetic field or a calibration magnetic field.

In other words, the magnetic field measuring device 10 is configured by arranging a plurality of magnetic sensor cells 220 each having a magnetic sensor 520 and a magnetic field generating unit 530, and the plurality of magnetic sensor cells 220 are magnetic to output a signal corresponding to the magnetic field. A sensor array 210 may be provided. Further, the magnetic field measuring device 10 is a calculation unit (for example, signal space separation) capable of calculating the magnetic field distribution in space based on the signals output by the plurality of magnetic sensor cells 220 and the magnetic sensor information indicating the information of the magnetic sensor 520. A unit 1160) may be provided. Further, the magnetic field measuring device 10 may include a calibration unit 1190 for calibrating magnetic sensor information. Then, the magnetic field generation unit 530 generates a feedback magnetic field that reduces the magnetic field detected by the magnetic sensor 520 when detecting the magnetic field generated by the object to be measured, and generates a calibration magnetic field when calibrating the magnetic sensor cell 220. It may be configured as follows. Further, the calibration unit 1190 is different from the first magnetic sensor cell 220 in accordance with the calibration magnetic field generated by the magnetic field generation unit 530 of the first magnetic sensor cell 220 among the plurality of magnetic sensor cells 220. The magnetic sensor information of the magnetic sensor cell 220 may be calibrated. As a result, the magnetic field measuring device 10 does not need to separately provide the calibration magnetic field generating unit 144 for generating the calibration magnetic field, and the device can be miniaturized.

Further, in the above description, it has been explained that the calibration magnetic field generated by the calibration magnetic field generator 144 is preferably an AC magnetic field having a frequency higher than 50 Hz (frequency f0> 50 Hz), but each magnetic sensor 520 is magnetic. When the converging plates 720 and 730 are included, the frequency of the AC magnetic field may be further limited.

FIG. 24 shows how an eddy current 2410 is generated in the magnetic sensor 520 including the magnetic focusing plates 720 and 730. Generally, when a conductor is moved in a magnetic field or when the magnetic flux density is changed, an vortex-shaped induced current is generated in the conductor by electromagnetic induction. That is, when an alternating current input magnetic field is given as the calibration magnetic field, eddy currents 2410 are generated in the magnetic focusing plates 720 and 730 by electromagnetic induction due to the time change of the magnetic field. Then, the eddy current 2410 generates a magnetic field 2420 in the direction opposite to the input magnetic field. As a result, as the frequency of the input magnetic field increases, the gain is attenuated by the magnetic field 2420 due to the eddy current 2410. That is, the magnetic focusing plates 720 and 730 act as a low-pass filter with respect to the magnetic field.

FIG. 25 shows the gain characteristics of the magnetic field due to the eddy current 2410. In order to acquire this characteristic, the materials of the magnetic focusing plates 720 and 730 were nickel-iron alloy (Ni—Fe), and the size was 1 mm × 1 mm × 25 mm. As shown in this figure, the gain is flat up to around 1 kHz, but the gain is attenuated from around 1 kHz, and it can be seen that the cutoff frequency Fc exists 10 kHz before. Therefore, when the magnetic sensor 520 includes the magnetic convergence plates 720 and 730, the frequency of the AC magnetic field generated by the calibration magnetic field generator 144 as the calibration magnetic field is such that the magnetic field attenuation characteristics of the magnetic convergence plates 720 and 730 are cut. It is preferable that the frequency is below the off frequency, for example, 1 kHz or less, which is a region where the gain is flat.

In addition to the commercial power supply (50 Hz or 60 Hz), for example, ventilation fan noise exists as an environmental magnetic field. Such ventilation fan noise has a frequency of 20 Hz and can affect up to approximately the fourth harmonic as a disturbance. Therefore, the frequency of the AC magnetic field generated as the calibration magnetic field is preferably higher than 80 Hz and less than or equal to the cutoff frequency of the magnetic field attenuation characteristics by the magnetic focusing plates 720 and 730, more preferably further multiplied by 50 Hz or 60 Hz. , And a frequency that avoids multiplication by 20 Hz is preferable. As a result, according to the magnetic field measuring device 10, it is possible to use the region where the influence of the gain attenuation by the magnetic focusing plates 720 and 730 is small as the calibration magnetic field while suppressing the environmental magnetic field to the order of several tens of pT.

Various embodiments of the present invention may be described with reference to flowcharts and block diagrams, wherein the block is (1) a stage of the process in which the operation is performed or (2) a device responsible for performing the operation. May represent a section of. Specific stages and sections are implemented by dedicated circuits, programmable circuits supplied with computer-readable instructions stored on a computer-readable medium, and / or processors supplied with computer-readable instructions stored on a computer-readable medium. You can. Dedicated circuits may include digital and / or analog hardware circuits, and may include integrated circuits (ICs) and / or discrete circuits. Programmable circuits are memory elements such as logical AND, logical OR, logical XOR, logical NAND, logical NOR, and other logical operations, flip-flops, registers, field programmable gate arrays (FPGA), programmable logic arrays (PLA), etc. May include reconfigurable hardware circuits, including, etc.

The computer readable medium may include any tangible device capable of storing instructions executed by the appropriate device, so that the computer readable medium having the instructions stored therein is specified in a flowchart or block diagram. It will be equipped with a product that contains instructions that can be executed to create means for performing the operation. Examples of computer-readable media may include electronic storage media, magnetic storage media, optical storage media, electromagnetic storage media, semiconductor storage media, and the like. More specific examples of computer-readable media include floppy (registered trademark) disks, diskettes, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), Electrically erasable programmable read-only memory (EEPROM), static random access memory (SRAM), compact disc read-only memory (CD-ROM), digital versatile disc (DVD), Blu-ray (RTM) disc, memory stick, integrated A circuit card or the like may be included.

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

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

FIG. 26 shows an example of a computer 9900 in which a plurality of aspects of the present invention may be embodied in whole or in part. A program installed on the computer 9900 can cause the computer 9900 to function as an operation or one or more sections of the device according to an embodiment of the invention, or the operation or the one or more. Sections can be run and / or computer 9900 can be run a process according to an embodiment of the invention or a stage of such process. Such a program may be run by the CPU 9912 to cause the computer 9900 to perform certain operations associated with some or all of the blocks in the flowcharts and block diagrams described herein.

The computer 9900 according to this embodiment includes a CPU 9912, a RAM 9914, a graphics controller 9916, and a display device 9918, which are interconnected by a host controller 9910. Computer 9900 also includes input / output units such as communication interface 9922, hard disk drive 9924, DVD-ROM drive 9926, and IC card drive, which are connected to host controller 9910 via input / output controller 9920. There is. The computer also includes legacy input / output units such as the ROM 9930 and keyboard 9942, which are connected to the input / output controller 9920 via an input / output chip 9940.

The CPU 9912 operates according to the programs stored in the ROM 9930 and the RAM 9914, thereby controlling each unit. The graphic controller 9916 acquires the image data generated by the CPU 9912 in a frame buffer or the like provided in the RAM 9914 or itself so that the image data is displayed on the display device 9918.

Communication interface 9922 communicates with other electronic devices via a network. Hard disk drive 9924 stores programs and data used by CPU 9912 in computer 9900. The DVD-ROM drive 9926 reads the program or data from the DVD-ROM9901 and provides the program or data to the hard disk drive 9924 via the RAM 9914. The IC card drive reads programs and data from the IC card and / or writes programs and data to the IC card.

The ROM 9930 stores in it a boot program or the like that is executed by the computer 9900 at the time of activation, and / or a program that depends on the hardware of the computer 9900. The input / output chip 9940 may also connect various input / output units to the input / output controller 9920 via a parallel port, serial port, keyboard port, mouse port, and the like.

The program is provided by a computer-readable medium such as a DVD-ROM9901 or an IC card. The program is read from a computer-readable medium, installed on a hard disk drive 9924, RAM 9914, or ROM 9930, which is also an example of a computer-readable medium, and executed by the CPU 9912. The information processing described in these programs is read by the computer 9900 and provides a link between the program and the various types of hardware resources described above. The device or method may be configured to perform manipulation or processing of information in accordance with the use of computer 9900.

For example, when communication is executed between the computer 9900 and an external device, the CPU 9912 executes a communication program loaded in the RAM 9914, and performs communication processing on the communication interface 9922 based on the processing described in the communication program. You may order. Under the control of the CPU 9912, the communication interface 9922 reads and reads the transmission data stored in the transmission buffer processing area provided in the recording medium such as the RAM 9914, the hard disk drive 9924, the DVD-ROM9901, or the IC card. The data is transmitted to the network, or the received data received from the network is written to the reception buffer processing area or the like provided on the recording medium.

Further, the CPU 9912 makes the RAM 9914 read all or necessary parts of a file or a database stored in an external recording medium such as a hard disk drive 9924, a DVD-ROM drive 9926 (DVD-ROM9901), or an IC card. Various types of processing may be performed on the data on the RAM 9914. The CPU 9912 then writes back the processed data to an external recording medium.

Various types of information, such as various types of programs, data, tables, and databases, may be stored on the recording medium and processed. The CPU 9912 describes various types of operations, information processing, conditional judgment, conditional branching, unconditional branching, and information retrieval described in various parts of the present disclosure with respect to the data read from the RAM 9914. Various types of processing may be performed, including / replacement, etc., and the results are written back to RAM 9914. Further, the CPU 9912 may search for information in a file, a database, or the like in the recording medium. For example, when a plurality of entries each having an attribute value of the first attribute associated with the attribute value of the second attribute are stored in the recording medium, the CPU 9912 specifies the attribute value of the first attribute. Search for an entry that matches the condition from the plurality of entries, read the attribute value of the second attribute stored in the entry, and associate it with the first attribute that satisfies the predetermined condition. The attribute value of the second attribute obtained may be acquired.

The program or software module described above may be stored on or near a computer 9900 on a computer-readable medium. Also, a recording medium such as a hard disk or RAM provided in a dedicated communication network or a server system connected to the Internet can be used as a computer-readable medium, thereby providing the program to the computer 9900 over the network. do.

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

The order of execution of operations, procedures, steps, steps, etc. in the devices, systems, programs, and methods shown in the claims, specification, and drawings is particularly "before" and "prior to". It should be noted that it can be realized in any order unless the output of the previous process is used in the subsequent process. Even if the scope of claims, the specification, and the operation flow in the drawings are explained using "first", "next", etc. for convenience, it means that it is essential to carry out in this order. It's not a thing.

10 Magnetic field measuring device 100 Main body 110 Magnetic sensor unit 120 Head 125 Drive unit 130 Base unit 140 Pole unit 142 Support unit 144 Calibration Magnetic field generator 150 Information processing unit 210 Magnetic sensor array 220 Magnetic sensor cell 230 Sensor data collection unit 232 AD conversion Instrument 234 Clock generator 300 Sensor unit 520 Magnetic sensor 530 Magnetic field generator 532 Amplification circuit 534 Feedback coil 540 Output unit 710 Magnetic resistance element 720, 730 Magnetic convergence plate 1100 Sensor data processing unit 1120 Measurement data acquisition unit 1130 Synchronous detection unit 1140 data Output unit 1150 Base vector storage unit 1160 Signal space separation unit 1170 Calibration clock generation unit 1180 Error calculation unit 1190 Calibration unit 2210 First magnetic sensor cell group 2220 First calibration coil 2310 Second magnetic sensor cell group 2320 Second Calibration coil 9900 Computer 9901 DVD-ROM
9910 Host controller 9912 CPU
9914 RAM
9916 Graphic controller 9918 Display device 9920 I / O controller 9922 Communication interface 9924 Hard disk drive 9926 DVD-ROM drive 9930 ROM
9940 Input / Output Chip 9942 Keyboard

Claims (18)

A magnetic sensor array configured by arranging a plurality of magnetic sensor cells each having a magnetic sensor including a magnetoresistive element and a magnetic focusing plate so as to form a surface covering at least a part of an object to be measured.
A measurement data acquisition unit that acquires measurement data measured by the magnetic sensor array,
A signal space separator that separates the spatial distribution of the magnetic field indicated by the measurement data based on the position and magnetic sensitivity of each magnetic sensor.
In a closed space composed of the smallest convex polygons including all of the plurality of magnetic sensor cells in a cross-sectional view, the plurality of magnetic sensor cells are squeezed from the measurement space outside the measurement space in which the plurality of magnetic sensor cells are not arranged. A calibration magnetic field generator that generates a calibration magnetic field at a position on a straight line that can be pulled without intervention.
A magnetic field measuring device including a calibration unit that calibrates a sensor error in the magnetic sensor based on a separation error when the spatial distribution of the calibration magnetic field is signal-separated. The magnetic sensor array is configured by arranging the plurality of magnetic sensor cells three-dimensionally in a cross-sectional view arc shape.
A straight line connecting the center of a plane formed by a chord connecting both end points of an arc and the center of the calibration magnetic field generating portion, a contact point between the arc and the chord on the same cross section as the center of the plane, and the above. The magnetic field measuring device according to claim 1, wherein the angle formed by a straight line connecting the center of the calibration magnetic field generating portion is larger than 6 degrees. Each of the plurality of magnetic sensor cells
A magnetic field generator that generates a feedback magnetic field that reduces the input magnetic field detected by the magnetic sensor,
The magnetic field measuring device according to claim 1 or 2, further comprising an output unit that outputs an output signal corresponding to a feedback current that the magnetic field generating unit flows to generate the feedback magnetic field. Each of the magnetic sensors includes the magnetoresistive element and two magnetoconverging plates arranged at both ends of the magnetoresistive element, and the magnetoresistive element is located at a position sandwiched between the two magnetic converging plates. The magnetic field measuring device according to claim 3, which is arranged. 4. The magnetic field generating unit includes a feedback coil wound along the axial direction of the magnetic field to be detected by the magnetic sensor so as to surround the magnetic resistance element and the two magnetic focusing plates. The magnetic field measuring device described. The magnetic field measuring device according to any one of claims 1 to 5, wherein the calibration magnetic field generating unit has at least three or more calibration coils that generate the calibration magnetic field in different axial directions. The magnetic field measuring device according to claim 6, wherein the different axial directions are axial directions orthogonal to each other. The signal space separation unit is any one of claims 1 to 7, wherein the position where the calibration magnetic field generation unit is arranged is the origin of the coordinates in the calculation when the spatial distribution of the calibration magnetic field is signal-separated. The magnetic field measuring device according to the section. The signal space separation unit signals the spatial distribution of the magnetic field based on the normal orthogonal function, the position of each magnetic sensor, and the basis vector calculated from the magnetic sensitivity, any one of claims 1 to 8. The magnetic field measuring device according to the section. The magnetic field measuring device according to claim 9, wherein the calibration unit calibrates the sensor error by changing the basis vector. The magnetic field measuring device according to claim 10, wherein the calibration unit optimizes the basis vector so as to minimize the separation error. The magnetic field measuring device according to any one of claims 1 to 11, further comprising a synchronous detection unit that detects the calibration magnetic field, which is an AC magnetic field, using a signal having a frequency of the AC magnetic field. The magnetic field measuring device according to claim 12, wherein the frequency of the AC magnetic field is higher than 80 Hz and equal to or lower than the cutoff frequency of the magnetic field attenuation characteristic by the magnetic focusing plate. It was measured by a magnetic sensor array composed of a plurality of magnetic sensor cells each having a magnetic sensor including a magnetoresistive element and a magnetic focusing plate arranged so as to form a surface covering at least a part of a measurement object. Acquiring measurement data and
Signal separation of the spatial distribution of the magnetic field indicated by the measurement data based on the position and magnetic sensitivity of each magnetic sensor.
In a closed space composed of the smallest convex polygons including all of the plurality of magnetic sensor cells in a cross-sectional view, the plurality of magnetic sensor cells are squeezed from the measurement space outside the measurement space in which the plurality of magnetic sensor cells are not arranged. To generate a calibration magnetic field at a position on a straight line that can be pulled without intervention,
A magnetic field measurement method comprising calibrating a sensor error in the magnetic sensor based on a separation error when the spatial distribution of the calibration magnetic field is signal-separated. Performed by a computer, said computer,
The measurement was performed by a magnetic sensor array composed of a plurality of magnetic sensor cells each having a magnetic sensor including a magnetoresistive element and a magnetic focusing plate arranged so as to form a surface covering at least a part of an object to be measured. The measurement data acquisition unit that acquires measurement data,
A signal space separator that separates the spatial distribution of the magnetic field indicated by the measurement data based on the position and magnetic sensitivity of each magnetic sensor.
In a closed space composed of the smallest convex polygons including all of the plurality of magnetic sensor cells in a cross-sectional view, the plurality of magnetic sensor cells are squeezed from the measurement space outside the measurement space in which the plurality of magnetic sensor cells are not arranged. A calibration magnetic field generator that generates a calibration magnetic field at a position on a straight line that can be pulled without intervention.
A magnetic field measurement program that functions as a calibration unit that calibrates the sensor error in the magnetic sensor based on the separation error when the spatial distribution of the calibration magnetic field is signal-separated. A magnetic sensor array configured by arranging a plurality of magnetic sensor cells each having a magnetic sensor including a magnetoresistive element and a magnetic focusing plate so as to form a surface covering at least a part of an object to be measured.
A measurement data acquisition unit that acquires measurement data measured by a group of magnetic sensor cells that is at least a part of the plurality of magnetic sensor cells in the magnetic sensor array.
A signal space separation unit that separates signals from the spatial distribution of the magnetic field indicated by the measurement data based on the position and magnetic sensitivity of each magnetic sensor in the magnetic sensor cell group.
A calibration magnetic field generator that generates a calibration magnetic field at multiple different positions,
Based on the separation error when the spatial distribution of the calibration magnetic field generated at the first position is signal-separated, the sensor error in the magnetic sensor of the first magnetic sensor cell group among the plurality of magnetic sensor cells is calibrated. Then, based on the separation error when the spatial distribution of the calibration magnetic field generated at the second position is signal-separated, the sensor error in the magnetic sensor of the second magnetic sensor cell group among the plurality of magnetic sensor cells. A magnetic field measuring device equipped with a calibration unit for calibrating. The plurality of magnetic sensor cells in a magnetic sensor array configured by arranging a plurality of magnetic sensor cells each having a magnetic sensor including a magnetoresistive element and a magnetic focusing plate so as to form a surface covering at least a part of an object to be measured. Acquiring measurement data measured by a group of magnetic sensor cells, which is at least a part of the magnetic sensor cells,
Signal separation of the spatial distribution of the magnetic field indicated by the measurement data based on the position and magnetic sensitivity of each magnetic sensor in the magnetic sensor cell group.
To generate a calibration magnetic field at multiple different positions,
Based on the separation error when the spatial distribution of the calibration magnetic field generated at the first position is signal-separated, the sensor error in the magnetic sensor of the first magnetic sensor cell group among the plurality of magnetic sensor cells is calibrated. Then, based on the separation error when the spatial distribution of the calibration magnetic field generated at the second position is signal-separated, the sensor error in the magnetic sensor of the second magnetic sensor cell group among the plurality of magnetic sensor cells. A magnetic field measurement method that includes calibrating. Performed by a computer, said computer,
The plurality of magnetic sensor cells in a magnetic sensor array configured by arranging a plurality of magnetic sensor cells each having a magnetic sensor including a magnetoresistive element and a magnetic focusing plate so as to form a surface covering at least a part of an object to be measured. A measurement data acquisition unit that acquires measurement data measured by a group of magnetic sensor cells, which is at least a part of the magnetic sensor cells,
A signal space separation unit that separates signals from the spatial distribution of the magnetic field indicated by the measurement data based on the position and magnetic sensitivity of each magnetic sensor in the magnetic sensor cell group.
A calibration magnetic field generator that generates a calibration magnetic field at multiple different positions,
Based on the separation error when the spatial distribution of the calibration magnetic field generated at the first position is signal-separated, the sensor error in the magnetic sensor of the first magnetic sensor cell group among the plurality of magnetic sensor cells is calibrated. Then, based on the separation error when the spatial distribution of the calibration magnetic field generated at the second position is signal-separated, the sensor error in the magnetic sensor of the second magnetic sensor cell group among the plurality of magnetic sensor cells. A magnetic field measurement program that functions as a calibration unit for calibrating.

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