JP2019179038A - Measurement device and measurement method - Google Patents

Abstract

To configure devices accurately detecting fine magnetic fields at low costs and with simplicity.SOLUTION: A measurement device is provided that comprises: a plurality of measurement-purpose sensor units that is provided at a measurement position where a measurement object is measured, and detects input magnetic fields in a mutually different detection axis direction; a first conversion unit that converts outputs of the plurality of measurement-purpose sensor units to a plurality of measurement-purpose magnetic field signals indicative of a magnetic field direction in each coordinate axis direction; a plurality of reference-purpose sensor units that is provided at a reference position separated from the measurement position, and detects the input magnetic field in the mutually different detection axis direction; a second conversion unit that converts the output of the plurality of reference-purpose sensor units to a plurality of reference-purpose magnetic field signals indicative of the magnetic field direction in each coordinate axis direction; and a differential unit that calculates a plurality of differential signals indicative of a differential in each coordinate axis direction of the plurality of measurement-purpose magnetic field signals and the plurality of reference-purpose magnetic field signals.SELECTED DRAWING: Figure 7

Description

  The present invention relates to a measuring apparatus and a measuring method.

Conventionally, a sensor for detecting a weak magnetic field of about 10 pT has been known and used for a magnetocardiograph or the like for measuring a magnetocardiogram signal caused by electrical polarization of an organ such as the heart (for example, Patent Document 1). To 4). It has also been known that in a current sensor using a magnetoresistive effect element, the influence of an environmental magnetic field is canceled using a feedback coil (see, for example, Patent Document 5).
Patent Literature 1 JP 2000-217798 A Patent Literature 2 JP 2012-152515 A Patent Literature 3 US Pat. No. 5,642,045 Patent Literature 4 JP 2000-284032 A Patent Literature 5 US Patent Application Publication No. 2015 / No. 053412

  For example, a SQUID sensor using the Josephson effect can detect a weak magnetic field, but requires expensive liquid helium, a large-scale magnetic shield room, and the like. It was not easy. In addition, the current sensor using the magnetoresistive effect element is small and has high magnetic sensitivity, but the linearity of the input / output characteristics is poor, and it has other axis sensitivity, so it is difficult to accurately detect a weak magnetic field. Met.

  In the first aspect of the present invention, a plurality of measurement sensor units that are provided at measurement positions for measuring a measurement object and detect input magnetic fields in different detection axis directions, and outputs from the plurality of measurement sensor units, A first conversion unit that converts a plurality of measurement magnetic field signals indicating magnetic field components in each coordinate axis direction, and a plurality of reference sensors that are provided at a reference position separated from the measurement position and detect input magnetic fields in different detection axis directions A second conversion unit that converts outputs of the plurality of reference sensor units into a plurality of reference magnetic field signals indicating magnetic field components in the coordinate axis directions, a plurality of measurement magnetic field signals, and a plurality of reference magnetic field signals. A difference calculation unit that calculates a plurality of difference signals indicating differences in the respective coordinate axis directions, and each of the plurality of measurement sensor units and each of the plurality of reference sensor units includes a magnetic sensor and an input detected by the magnetic sensor. A first magnetic field generation unit that applies a feedback magnetic field to the magnetic sensor to reduce the magnetic field; and an output unit that outputs an output signal corresponding to a current that the first magnetic field generation unit passes to generate the feedback magnetic field; Provide a measuring method.

  It should be noted that the above summary of the invention does not enumerate all the necessary features of the present invention. In addition, a sub-combination of these feature groups can also be an invention.

An example of the input / output characteristics of the magnetic sensor having the magnetoresistive effect element according to the present embodiment is shown. The structural example of the sensor part 10 which concerns on this embodiment is shown. An example of the input-output characteristic of the sensor part 10 which concerns on this embodiment is shown. The schematic waveform of the magnetocardiogram signal which is an example of the signal under measurement concerning this embodiment is shown. An example of the frequency characteristic of the magnetocardiogram signal which is an example of the signal under measurement concerning this embodiment is shown. The structural example of the sensor part 100 for a measurement which concerns on this embodiment, and the sensor part 200 for a reference is shown. The structural example of the measuring apparatus 1000 which concerns on this embodiment is shown. An example in which a predetermined magnetic field is applied to the measurement sensor unit 100 and the reference sensor unit 200 according to the present embodiment will be described. The modification of the measuring apparatus 1000 which concerns on this embodiment is shown. The modification of the sensor part 10 which concerns on this embodiment is shown. The specific example of the magnetic sensor 20 which concerns on this embodiment is shown. The magnetic flux distribution when a magnetic feedback field is generated in the magnetic sensor 20 according to this example is shown. An example of the configuration of the magnetic sensor 20 according to this example is shown. In the magnetic sensor 20 according to this example, the simulation result of the magnetic amplification factor when the magnetic converging plate interval G_FC is changed is shown. In the magnetic sensor 20 according to this example, the simulation result of the magnetic amplification factor when the magnetic convergence plate length L_FC is changed is shown. In the magnetic sensor 20 according to this example, the simulation result of the magnetic amplification factor when the magnetic convergence plate thickness T_FC is changed is shown. In the magnetic sensor 20 according to the present specific example, a simulation result of the magnetic amplification factor when the magnetic converging plate interval G_FC is constant and the magnetic converging plate length L_FC / magnetic converging plate interval G_FC is changed is shown. In the magnetic sensor 20 according to the present specific example, a simulation result of the magnetic amplification factor when the magnetic convergence plate length L_FC is constant and the magnetic convergence plate length L_FC / magnetic convergence plate interval G_FC is changed is shown. The example which applied the magnetic sensor 20 which concerns on this example to the sensor part 100 for a measurement and the sensor part 200 for a reference is shown. The example which has arrange | positioned the sensor part 100 for a measurement to which the magnetic sensor 20 which concerns on this example is applied, and three reference sensor parts 200a-c is shown. A sensor array 2100 in which a plurality of sensor units to which the magnetic sensor 20 according to this example is applied is arranged in each of the X-axis direction, the Y-axis direction, and the Z-axis direction is shown. 9 illustrates an example computer 2200 in which aspects of the present invention may be embodied in whole or in part.

  Hereinafter, the present invention will be described through embodiments of the invention, but the following embodiments do not limit the invention according to the claims. In addition, not all the combinations of features described in the embodiments are essential for the solving means of the invention.

  FIG. 1 shows an example of input / output characteristics of a magnetic sensor having a magnetoresistive effect element according to this embodiment. In FIG. 1, the horizontal axis indicates the magnitude B of the input magnetic field input to the magnetic sensor, and the vertical axis indicates the magnitude V_xMR0 of the detection signal of the magnetic sensor. The magnetic sensor has, for example, a giant magneto-resistance (GMR) element, a tunnel magneto-resistance (TMR) element, and the like, and detects the magnitude of a predetermined uniaxial magnetic field. .

  Such a magnetic sensor has a high magnetic sensitivity which is the inclination 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 where the linearity of the input / output characteristics is good is narrow. Therefore, when a closed loop for generating a feedback magnetic field is added to such a magnetic sensor, the linearity of the magnetic sensor can be improved. Next, such a magnetic sensor will be described.

  FIG. 2 shows a configuration example of the sensor unit 10 according to the present embodiment. The sensor unit 10 includes a magnetic sensor 20, a first magnetic field generation unit 30, and an output unit 40.

  The magnetic sensor 20 has magnetoresistive elements such as a GMR element and a TMR element, like the magnetic sensor described in FIG. The magnetic sensor 20 is formed such that when the positive direction of the magnetosensitive axis is the + X direction, the resistance value increases when a magnetic field in the + X direction is input, and the resistance value decreases when a magnetic field in the -X direction is input. It's okay. That is, by observing a change in the resistance value of the magnetic sensor 20, the magnitude of the magnetic field B input to the magnetic sensor 20 can be detected. For example, if the magnetic sensitivity of the magnetic sensor 20 is S, the detection result for the input magnetic field B of the magnetic sensor 20 can be calculated as S × B. As an example, the magnetic sensor 20 is connected to a power source or the like, and outputs a voltage drop corresponding to a change in resistance value as a detection result of the input magnetic field.

  The first magnetic field generation unit 30 provides the magnetic sensor 20 with a feedback magnetic field that reduces the input magnetic field detected by the magnetic sensor 20. For example, the first magnetic field generation unit 30 operates to generate a feedback magnetic field B_FB that is opposite to the magnetic field B input to the magnetic sensor 20 and whose absolute value is substantially the same as the input magnetic field, and cancels the input magnetic field. The first magnetic field generation unit 30 includes an amplification circuit 32 and a coil 34.

  The amplification circuit 32 outputs a current corresponding to the detection result of the input magnetic field of the magnetic sensor 20 as a feedback current I_FB. The amplifier circuit 32 includes, for example, a transconductance amplifier, and outputs a feedback current I_FB corresponding to the output voltage of the magnetic sensor 20. For example, when the voltage / current conversion coefficient of the amplifier circuit 32 is G, the feedback current I_FB can be calculated as G × S × B.

The coil 34 generates a feedback magnetic field B_FB corresponding to the feedback current I_FB. The coil 34 preferably generates a uniform feedback magnetic field B_FB throughout the magnetic sensor 20. For example, if the coil coefficient of the coil 34 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 to cancel the input magnetic field B, the magnetic field input to the magnetic sensor 20 is reduced to BB_FB. Therefore, the feedback current I_FB is expressed as the following equation.

Equation (1) is solved for the feedback current I_FB, and the following equation is calculated assuming that the magnetic sensitivity S of the magnetic sensor 20 and the voltage / current conversion coefficient G of the amplifier circuit 32 are sufficiently large.

The output unit 40 outputs an output signal V_xMR corresponding to the feedback current I_FB that the first magnetic field generation unit 30 flows to generate the feedback magnetic field B_FB. The output unit 40 includes, for example, a resistive element having a resistance value R, and outputs a voltage drop caused by the feedback current I_FB flowing through the resistive element as an output signal V_xMR. In this case, the output signal V_xMR is calculated from the equation (2) as follows:

  As described above, since the sensor unit 10 generates the feedback magnetic field that reduces the magnetic field input from the outside, the magnetic field substantially input to the magnetic sensor 20 is reduced. Thereby, for example, the sensor unit 10 can use the magnetoresistive effect element having the characteristics shown in FIG. 1 as the magnetic sensor 20, and can prevent the detection signal V_xMR from being saturated even if the absolute value of the input magnetic field B exceeds 1 μT. . Next, the input / output characteristics of the sensor unit 10 will be described.

  FIG. 3 shows an example of input / output characteristics of the sensor unit 10 according to the present embodiment. In FIG. 3, the horizontal axis indicates the magnitude B of the input magnetic field input to the sensor unit 10, and the vertical axis indicates the magnitude V_xMR of the detection signal of the sensor unit 10. The sensor unit 10 has high magnetic sensitivity and can detect a minute magnetic field of about 10 pT. In addition, the sensor unit 10 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 10 according to this embodiment, for example, the detection result for the input magnetic field B has linearity in a predetermined range of the input magnetic field B such that the absolute value of the input magnetic field B is several hundred μT or less. Configured as follows. By using such a sensor unit 10, for example, a weak magnetic signal such as a magnetocardiogram signal can be easily detected. First, the magnetocardiogram signal will be described next.

  FIG. 4 shows a schematic waveform of a magnetocardiogram signal which is an example of a signal under measurement according to the present embodiment. In FIG. 4, the horizontal axis indicates time, and the vertical axis indicates an example of the strength of the magnetic field detected by the sensor unit 10 or the like. FIG. 4 shows the magnetocardiogram signal as B_sig. The magnetocardiogram signal B_sig is a magnetic signal generated in the heart due to electrical polarization that can be regarded as the generation of current.

  An electrocardiogram that electrically measures the activity of the heart is known. An electrocardiogram obtains a potential signal from an electrode attached in the vicinity of the heart to be measured, and is easily affected by non-uniformity in electrical conductivity of body tissue. On the other hand, since the magnetocardiogram signal directly detects a magnetic signal, it is known that more detailed diagnostic information can be obtained as compared with the electrocardiogram. Such a magnetocardiogram signal has a waveform having a peak signal level of about 10 pT called “R wave” and can be detected by using the sensor unit 10 described with reference to FIGS.

  However, even if the sensor unit 10 simply detects a magnetic field at a position close to the heart, a signal in which the environmental magnetic field signal B_Env is superimposed on the magnetocardiogram signal B_sig is detected. The environmental magnetic field signal B_Env includes a geomagnetic component B_Env_LF having a relatively low frequency and a random component B_Env_HF having a relatively high frequency.

  FIG. 5 shows an example of frequency characteristics of a magnetocardiogram signal, which is an example of a signal under measurement according to the present embodiment. In FIG. 5, the horizontal axis indicates the frequency, and the vertical axis indicates an example of the strength of the magnetic field detected by the sensor unit 10 or the like. FIG. 5 shows the magnetocardiogram signal as B_sig and the ambient magnetic field signal as B_Env. The environmental magnetic field signal B_Env includes a geomagnetic component B_Env_LF having a frequency lower than that of the magnetocardiogram signal B_sig and a random component B_Env_HF having a relatively higher frequency than the geomagnetic component B_Env_LF. Therefore, when the sensor unit 10 simply detects a magnetic field in the vicinity of the heart, a signal in which the geomagnetic component B_Env_LF and the random component B_Env_HF are superimposed on the magnetocardiogram signal B_sig is detected.

  Since the environmental magnetic field signal B_Env is a signal level higher than the peak signal level of the magnetocardiogram signal B_sig, it is difficult to acquire the magnetocardiogram signal B_sig from the detection result of the sensor unit 10. Therefore, the measurement apparatus according to the present embodiment includes a plurality of sensor units 10, and obtains the magnetocardiogram signal B_sig by canceling the environmental magnetic field signal B_Env. The sensor part of such a measuring apparatus will be described.

  FIG. 6 shows a configuration example of the measurement sensor unit 100 and the reference sensor unit 200 according to the present embodiment. In the present embodiment, an example in which the measurement target 50 is an animal heart is shown. A plurality of measurement sensor units 100 and reference sensor units 200 may be provided corresponding to the number of axes to be measured. FIG. 6 shows an example in which three measurement sensor units 100 and three reference sensor units 200 are provided for the purpose of detecting three-axis magnetic fields of the XYZ axes.

  The plurality of measurement sensor units 100 are provided at measurement positions where the measurement object 50 is measured, and detect the input magnetic field B in different detection axis directions. The measurement sensor unit 100 may have substantially the same configuration as the sensor unit 10 described in FIGS. FIG. 6 shows a sensor unit S0X that measures the input magnetic field Bx in the X-axis direction, a sensor unit S0X that measures the input magnetic field By in the Y-axis direction, and a sensor unit S0Y that detects the input magnetic field By in the Y-axis direction. An example is shown in which the sensor unit for measurement 100 for detecting Bz is a sensor unit S0Z, and three sensor units are arranged at coordinates (0, 0, 0). The coordinate (0, 0, 0) is a measurement position P0 that is close to the measurement object 50 so that the peak signal level of the magnetocardiogram signal B_sig in each detection axis direction can be detected at about 10 pT.

  The plurality of reference sensor units 200 are provided at a reference position separated from the measurement position, and detect the input magnetic field B in different detection axis directions. The reference sensor unit 200 may have substantially the same configuration as the sensor unit 10 described with reference to FIGS. FIG. 6 shows the sensor unit S1X for the reference sensor unit 200 for detecting the input magnetic field Bx in the X-axis direction, the sensor unit S1Y for the reference sensor unit 200 for detecting the input magnetic field By in the Y-axis direction, and the input magnetic field in the Z-axis direction. An example in which the reference sensor unit 200 for detecting Bz is a sensor unit S1Z and three sensor units are arranged at coordinates (L, L, L) is shown.

  The coordinates (L, L, L) are, for example, such that the peak signal level of the magnetocardiogram signal B_sig in each detection axis direction is sufficiently small (for example, 1/10 or less or 1/100 or less). The reference position P1 is spaced from the measurement position. Here, the distance L is approximately 5 cm as an example. As described above, the plurality of reference sensor units 200 detect the magnetic field at the reference position where the magnetocardiogram signal B_sig becomes sufficiently small, and thus detect the environmental magnetic field signal B_Env in each detection axis direction. Next, a measuring apparatus using the measurement sensor unit 100 and the reference sensor unit 200 will be described.

  FIG. 7 shows a configuration example of the measuring apparatus 1000 according to the present embodiment. The measurement apparatus 1000 uses the measurement sensor unit 100 and the reference sensor unit 200 to measure the magnetocardiogram signal B_sig of the animal heart that is the measurement target 50. The measuring apparatus 1000 measures the magnetocardiogram signal B_sig while correcting the other-axis sensitivity of each of the measurement sensor unit 100 and the reference sensor unit 200. The measuring apparatus 1000 includes a plurality of measurement sensor units 100, a plurality of reference sensor units 200, a first AD conversion unit 102, a second AD conversion unit 104, a clock generator 106, a first conversion unit 110, a second conversion unit 120, A storage unit 130, a difference calculation unit 140, an interface unit 150, and a signal processing unit 160 are provided.

  Each of the plurality of measurement sensor units 100 and each of the plurality of reference sensor units 200 has linear detection results for the input magnetic field in a predetermined input magnetic field range, as already described with reference to FIGS. Have sex. FIG. 7 shows an example in which the measurement apparatus 1000 includes three measurement sensor units 100 and operates as a three-axis magnetic sensor. Similarly, FIG. 7 shows an example in which the measurement apparatus 1000 includes three reference sensor units 200 and operates as a three-axis magnetic sensor.

  The first AD conversion unit 102 converts the outputs of the plurality of measurement sensor units 100 into digital signals, respectively. The first AD converter 102 may include a number of AD converters corresponding to the number of measurement sensor units 100. When the first AD conversion unit 102 includes a plurality of AD converters, it is desirable that the plurality of AD converters operate synchronously. For example, the first AD conversion unit 102 AD converts the detection results of the sensor unit S0X, the sensor unit S0Y, and the sensor unit S0Z, and outputs digital signals V0x, V0y, and V0z. The first AD converter 102 supplies the converted digital signal to the first converter 110.

  The second AD converter 104 converts the outputs of the plurality of reference sensor units 200 into digital signals, respectively. The second AD conversion unit 104 may include as many AD converters as the number of reference sensor units 200. When the second AD conversion unit 104 includes a plurality of AD converters, it is desirable that the plurality of AD converters operate synchronously. It is more desirable that all AD converters included in the first AD converter 102 and the second AD converter 104 operate synchronously. For example, the second AD conversion unit 104 AD converts the detection results of the sensor unit S1X, the sensor unit S1Y, and the sensor unit S1Z, and outputs digital signals V1x, V1y, and V1z. The second AD conversion unit 104 supplies the converted digital signal to the second conversion unit 120.

  The clock generator 106 generates a sampling clock and supplies the common sampling clock to all AD conversion units included in the first AD conversion unit 102 and the second AD conversion unit 104. The first AD conversion unit 102 and the second AD conversion unit 104 perform AD conversion according to the common sampling clock supplied from the clock generator 106. Therefore, the first AD converter that AD converts the output of the triaxial magnetic sensor provided at the measurement position P0, and the second AD converter that AD converts the output of the triaxial magnetic sensor provided at the measurement position P1, respectively. All operate synchronously. Thereby, the 1st AD conversion part 102 and the 2nd AD conversion part 104 can sample simultaneously the detection result of the triaxial magnetic sensor provided in the different space.

  The first conversion unit 110 converts the outputs of the plurality of measurement sensor units 100 into a plurality of measurement magnetic field signals indicating magnetic field components in the coordinate axis directions. The first conversion unit 110 converts the detection signal of the corresponding sensor unit into a measurement magnetic field signal using a predetermined coefficient.

Here, for example, the input magnetic field at the measurement position P0 is B0 (B0x, B0y, B0z), and the detection results of the three-axis magnetic sensor by the sensor unit S0X, the sensor unit S0Y, and the sensor unit S0Z are V0 (V0x, V0y, V0z). ). In this case, when the magnetic sensor characteristic of the three-axis magnetic sensor is a matrix S0, the following equation can be obtained.

  Here, S0, xx, S0, yy, S0, zz represent the sensitivity in the principal axis direction of the sensor units S0X, S0Y, S0Z, and S0, xy, S0, xz, S0, yz, S0, yz, S0, S0, respectively. zx, S0, and zy represent the sensitivity in the other axis direction.

  Since each of the measurement sensor units 100 has a linear detection result with respect to the input magnetic field within the range of the input magnetic field to be detected, each element of the matrix S0 is substantially constant regardless of the magnitude of the input magnetic field B0. It becomes a coefficient. Further, even if the measurement sensor unit 100 has other-axis sensitivity, if the detection result of the measurement sensor unit 100 has linearity, each element of the matrix S0 has the magnitude of the input magnetic field B0. Is an unrelated, substantially constant coefficient.

Therefore, the first conversion unit 110 converts the detection signal V0 (V0x, V0y, V0z) into the magnetic field signal B0 (B0x, B0y, B0z) by using an inverse matrix of the matrix S0 as in the following equation. Can do. The first conversion unit 110 supplies the calculated magnetic field signal B0 to the difference calculation unit 140 as a measurement magnetic field signal. Here, a matrix R0 equal to the inverse matrix of the matrix S0 is set as a correction matrix of the measurement sensor unit 100.

  Similarly, the second conversion unit 120 converts the outputs of the plurality of reference sensor units 200 into a plurality of reference magnetic field signals indicating magnetic field components in the respective coordinate axis directions. The second conversion unit 120 converts the detection signal of the corresponding sensor unit into a reference magnetic field signal using a predetermined coefficient.

Here, for example, the input magnetic field at the reference position P1 is B1 (B1x, B1y, B1z), and the detection results of the three-axis magnetic sensor by the sensor unit S1X, the sensor unit S1Y, and the sensor unit S1Z are V1 (V1x, V1y, V1z). ). In this case, when the magnetic sensor characteristic of the three-axis magnetic sensor is a matrix S1, it can be expressed as follows.

  Since each of the reference sensor units 200 has a linear detection result for the input magnetic field in the range of the input magnetic field to be detected, each element of the matrix S1 is substantially constant regardless of the magnitude of the input magnetic field B1. It becomes a coefficient. Further, even if the reference sensor unit 200 has other axis sensitivity, if the detection result of the reference sensor unit 200 has linearity, each element of the matrix S1 has the magnitude of the input magnetic field B1. Is an unrelated, substantially constant coefficient.

Therefore, the second conversion unit 120 converts the detection signal V1 (V1x, V1y, V1z) into the magnetic field signal B1 (B1x, B1y, B1z) by using the inverse matrix of the matrix S1 as in the following equation. Can do. The second conversion unit 120 supplies the calculated magnetic field signal B1 to the difference calculation unit 140 as a reference magnetic field signal. Here, a matrix R1 equal to the inverse matrix of the matrix S1 is set as a correction matrix of the reference sensor unit 200.

  As described above, since each of the measurement sensor unit 100 and the reference sensor unit 200 has linearity, each of the first conversion unit 110 and the second conversion unit 120 converts into a magnetic field signal using a substantially constant coefficient. can do. That is, a substantially constant coefficient used by the first conversion unit 110 and the second conversion unit 120 can be determined in advance. The predetermined coefficient can also include a coefficient for correcting the other-axis sensitivity of each corresponding magnetic sensor.

  Storage unit 130 stores a predetermined coefficient used by first conversion unit 110 and second conversion unit 120. Thereby, the 1st conversion part 110 and the 2nd conversion part 120 can read the coefficient which should be used from the memory | storage part 130, and can each convert the magnetic field signal according to an input magnetic field.

The difference calculation unit 140 calculates a plurality of difference signals indicating differences in the coordinate axis directions between the plurality of measurement magnetic field signals and the plurality of reference magnetic field signals. The difference calculation unit 140 calculates, for example, the difference in each coordinate axis direction of the plurality of measurement magnetic field signals B0 (B0x, B0y, B0z) and the plurality of reference magnetic field signals B1 (B1x, B1y, B1z) as follows: To do.

  The difference calculation unit 140 outputs the calculation result as a difference signal Bgrad (Bgradx, Bgrady, Bgradz). Here, the reference magnetic field signal B1 (B1x, B1y, B1z) corresponds to the environmental magnetic field signal B_Env as described with reference to FIGS. The measurement magnetic field signal B0 (B0x, B0y, B0z) corresponds to a signal obtained by superimposing the environmental magnetic field signal B_Env on the magnetocardiogram signal B_sig. Therefore, each element of the differential signal Bgrad becomes a signal component corresponding to the magnetocardiogram signal B_sig in each axial direction.

  The interface unit 150 supplies the difference signal Bgrad to the signal processing unit 160. The measuring apparatus 1000 described above may sequentially execute the measurement of the input magnetic field in time series. In this case, the measurement apparatus 1000 may perform measurement at substantially constant time intervals. The interface unit 150 may sequentially supply the differential signal Bgrad measured in time series to the signal processing unit 160.

  The signal processing unit 160 calculates a magnetocardiogram signal of the animal's heart based on the difference signal Bgrad calculated by the difference calculation unit 140. The signal processing unit 160 may calculate a time waveform of the magnetocardiogram signal based on the difference signal Bgrad measured in time series. For example, the signal processing unit 160 sets the magnitude of the difference signal Bgrad (the square root of the sum of squares of each element) as the magnitude of the magnetocardiogram signal.

  The signal processing unit 160 may calculate the magnetocardiogram signal after performing numerical processing. The signal processing unit 160 performs a filtering process such as a low-pass filter, a high-pass filter, a band-pass filter, a band elimination filter, and a combination of each filter, and calculates a magnetocardiogram signal after reducing noise components. It's okay. Further, the signal processing unit 160 may calculate the magnetocardiogram signal after performing frequency conversion to acquire a signal in a predetermined band.

  As described above, since the measuring apparatus 1000 according to the present embodiment detects a weak magnetic field using a magnetoresistive element, the measurement apparatus 1000 can be measured with a simple configuration without a large-scale apparatus such as a SQUID sensor. A device can be realized. In addition, since the measuring apparatus 1000 maintains a linear characteristic in the range of the input magnetic field by adding a closed loop configuration to the magnetic sensor, the magnetic field conversion and the other axis sensitivity correction are simply performed using predetermined coefficients. be able to.

  In addition, although a magnetoresistive effect element etc. may use the magnetic converging plate etc. which bend a magnetic force line locally, there exists a tendency for other-axis sensitivity to increase by such a magnetic converging plate. However, if the arrangement of the magnetoresistive effect element and the magnetic converging plate is fixed, the input / output characteristics remain linear, so even if a magnetic converging plate is used, magnetic field conversion and other axis sensitivity correction are performed. Can be simply executed using a predetermined coefficient. Therefore, the measuring apparatus 1000 can accurately detect a weak magnetic field with a simple configuration at low cost.

  Further, at least a part of the measuring apparatus 1000 can be integrated in one element. In this case, the interface unit 150 may function as an interface of the element. The signal processing unit 160 may be provided outside the element, and may have other processing functions. Alternatively, if the signal processing unit 160 is also integrated in one element, the interface unit 150 may not be provided.

  Since such a measuring apparatus 1000 can set a predetermined coefficient used for magnetic field conversion and other axis sensitivity correction to a substantially constant value regardless of the magnitude of the magnetic field, the coefficient is determined and calibrated. Can be easily implemented. For example, the measuring apparatus 1000 determines a predetermined coefficient by applying a magnetic field having a predetermined direction and magnitude.

  FIG. 8 shows an example in which a predetermined magnetic field is applied to the measurement sensor unit 100 and the reference sensor unit 200 according to the present embodiment. 8 shows an example in which the measurement sensor unit 100 and the reference sensor unit 200 shown in FIG. 8 are arranged substantially the same as the arrangement of the measurement sensor unit 100 and the reference sensor unit 200 described in FIG.

  As shown in FIG. 8, the measurement sensor unit 100 and the reference sensor unit 200 include a test input magnetic field Btx (1, 0, 0) in the X-axis direction and a test input magnetic field Bty (0, 1, 0 in the Y-axis direction). ) And a test input magnetic field Btz (0, 0, 1) in the Z-axis direction, respectively. Then, the measuring apparatus 1000 determines a predetermined coefficient according to the detection signal of each test input magnetic field.

For example, when the detection signal from the measurement sensor unit 100 becomes V0 (V0x, V0y, V0z) in response to the input of the test input magnetic field Btx (1, 0, 0), the detection signal V0 is used for measurement. Using the magnetic sensor characteristic S0 of the sensor unit 100, the following equation can be obtained.

  That is, the detection signal V0 substantially coincides with each element of the first column of the magnetic sensor characteristic S0. Here, the values of V0y and V0z, which are detection results in the Y-axis direction and the Z-axis direction, indicate values corresponding to the other-axis sensitivity of the magnetic sensor.

  Similarly, the detection signal V0 (V0x, V0y, V0z) detected in response to the input of the test input magnetic field Bty (0, 1, 0) substantially matches each element of the second column of the magnetic sensor characteristic S0. Further, the detection signal V0 (V0x, V0y, V0z) detected in response to the input of the test input magnetic field Btz (0, 0, 1) substantially coincides with each element of the third column of the magnetic sensor characteristic S0. As described above, the measuring apparatus 1000 can acquire the magnetic sensor characteristic S0 and the magnetic sensor characteristic S1 of the measurement sensor unit 100 and the reference sensor unit 200 according to input magnetic fields in three different directions. Accordingly, by calculating an inverse matrix of the acquired magnetic sensor characteristic S0 and magnetic sensor characteristic S1, predetermined coefficients, that is, correction matrices R0 and R1 can be determined.

  As described above, a predetermined coefficient can be determined by inputting magnetic fields in a plurality of predetermined directions to the measurement sensor unit 100 and the reference sensor unit 200. In this case, as a magnetic field in a plurality of predetermined directions, a rotating magnetic field that rotates substantially parallel to the XY plane, a rotating magnetic field that rotates approximately parallel to the XZ plane, a rotating magnetic field that rotates approximately parallel to the YZ plane, and the like are used. May be. Further, the measuring apparatus 1000 may automatically determine and update a predetermined coefficient in accordance with the input of such a test input magnetic field. Such a measuring apparatus 1000 will be described next.

  FIG. 9 shows a modification of the measuring apparatus 1000 according to this embodiment. In the measurement apparatus 1000 of the present modification, the same reference numerals are given to the same operations as those of the measurement apparatus 1000 according to the present embodiment shown in FIG. 7, and the description thereof is omitted. The measuring apparatus 1000 according to the present modification further includes an adjusting unit 170 and an updating unit 180.

  The adjusting unit 170 and the updating unit 180 operate when the plurality of measurement sensor units 100 and the plurality of reference sensor units 200 are arranged in a predetermined uniform magnetic field apart from the measurement target 50. It's okay. Here, the predetermined uniform magnetic field may be an environmental magnetic field, or may be a magnetic field having a constant intensity larger than the environmental magnetic field. For example, the test input magnetic field as described in FIG. 8 may be used.

  The adjustment unit 170 may adjust the predetermined coefficient so that the difference signal calculated by the difference calculation unit 140 falls within a predetermined signal range. Here, since a uniform magnetic field is input to the measurement sensor unit 100 and the reference sensor unit 200, the difference signal calculated by the difference calculation unit 140 is preferably substantially zero. However, since the measurement sensor unit 100 and the reference sensor unit 200 include a ferromagnetic material or the like, when a strong magnetic field is applied from the outside after product shipment, the magnetic characteristics may change. In other words, even if the difference signal is calibrated to approximately 0 at the shipping stage of the measuring apparatus 1000, there may be a deviation in the value of the difference signal after shipment.

Therefore, the adjustment unit 170 is a coefficient that is set in advance so that the difference signal calculated by the difference calculation unit 140 is approximately zero when a uniform magnetic field is input to the measurement sensor unit 100 and the reference sensor unit 200. Adjust. That is, the adjustment unit 170 may adjust the coefficient so that the vector represented by Equation (8) becomes a zero vector. The adjustment unit 170 executes, for example, an LMS (Least Mean Square) algorithm that minimizes a square error ε ² expressed by the following equation. Here, R1, xx, R1, xy, R1, xz, R1, yx, R1, yy, R1, yz, R1, zx, R1, zy, and R1, zz are correction matrices R1 of the reference sensor unit 200. Is a matrix element.

In this case, as an example, the adjustment unit 170 minimizes each of εx ² , εy ² , and εz ² . Since each of εx ² , εy ² , and εz ² is a linear algebra of the digital signals V1x, V1y, and V1z, the matrix elements of the correction matrix R1 can be updated using a recurrence formula. As an example, for the purpose of the .epsilon.x ² minimizes shows the first column of the coefficient R1, xx correction matrix R1, R1, xy, and a recurrence formula for updating the R1, xz then.

  The recurrence formulas for updating the coefficients in the second column and the third column of the correction matrix R1 can be similarly derived, and the adjustment unit 170 may use such an algorithm. Note that the algorithm shown by the equation (11) is an algorithm known as the steepest descent method. Here, μ is a parameter that determines the time constant of the algorithm.

  The adjustment unit 170 outputs the detection signal V0 (V0x, V0y, V0z) and the detection signal V1 (V1x, V1y, V1z) from the measurement sensor unit 100 and the reference sensor unit 200 to which a uniform magnetic field is applied. Each time, the coefficient of the correction matrix R1 may be updated. The adjustment unit 170 may update the coefficients of the correction matrix R1 until the difference signal calculated by the difference calculation unit 140 becomes less than a predetermined threshold value.

  When the adjustment by the adjustment unit 170 is completed, the update unit 180 updates the predetermined coefficient stored in the storage unit 130 with the adjustment result of the adjustment unit 170. By using the coefficient updated by the updating unit 180 after reading it from the storage unit 130, the measuring apparatus 1000 can prevent deterioration in measurement accuracy even when using a sensor unit whose magnetic characteristics have changed after product shipment.

  The measurement sensor unit 100 and the reference sensor unit 200 according to the present embodiment described above have explained that the first magnetic field generation unit 30 having a closed loop configuration generates a feedback magnetic field. In addition, each of the measurement sensor unit 100 and the reference sensor unit 200 may further generate a substantially constant offset magnetic field. Next, the sensor unit 10 will be described.

  FIG. 10 shows a modification of the sensor unit 10 according to the present embodiment. In the sensor unit 10 of the present modification, the same reference numerals are given to the substantially same operations as those of the sensor unit 10 according to the present embodiment shown in FIG. The sensor unit 10 according to this modification further includes a second magnetic field generation unit 60.

  The second magnetic field generation unit 60 gives the magnetic sensor 20 an offset magnetic field for attenuating the environmental magnetic field B_Env. As described with reference to FIGS. 4 and 5, the environmental magnetic field B_Env has an intensity that is one digit or more larger than the magnetocardiogram signal B_sig to be measured by the measuring apparatus 1000. That is, the sensor unit 10 occupies most of the linear operation range by the environmental magnetic field B_Env having a substantially constant intensity, and measures the magnetocardiogram signal B_sig in the remaining part of the range. Therefore, the sensor unit 10 uses most of the dynamic range for detection of a constant magnetic field, and, for example, measures the magnetocardiogram signal B_sig in an area of 1/10 or less of the dynamic range, thereby degrading the resolution and the like. There is.

  Therefore, the sensor unit 10 of the present modification appropriately adjusts the balance between the magnitude of the magnetocardiogram signal B_sig and the dynamic range by causing the second magnetic field generation unit 60 to generate an offset magnetic field so as to reduce the environmental magnetic field B_Env. can do. Thereby, the sensor unit 10 can accurately measure the magnetocardiogram signal B_sig without degrading the resolution or the like.

  The second magnetic field generation unit 60 may include a coil, and generates a magnetic field in a direction opposite to the environmental magnetic field B_Env when a current I_Comp flows through the coil. The coil preferably generates a uniform feedback magnetic field throughout the magnetic sensor 20. The cancel current I_Comp that flows through the coil of the second magnetic field generation unit 60 may be supplied from a power source or the like that flows a predetermined current value. The cancel current I_Comp may be supplied by a circuit that generates a current corresponding to the environmental magnetic field B_Env detected by the reference sensor unit 200. The measuring apparatus 1000 can measure the magnetocardiogram signal B_sig with higher accuracy by employing such a sensor unit 10 as the measurement sensor unit 100 and the reference sensor unit 200.

  FIG. 11 shows a specific example of the magnetic sensor 20 according to the present embodiment. In this specific example, the magnetic sensor 20 includes a magnetoresistive effect element 1110 and magnetic converging plates 1120 and 1130 disposed at both ends of the magnetoresistive effect element 1110. The magnetic converging plates 1120 and 1130 are arranged at both ends of the magnetoresistive effect element 1110 so as to sandwich the magnetoresistive effect element 1110 therebetween. In this figure, the magnetic focusing plate 1120 is provided on the negative side of the magnetoresistive effect element 1110 along the magnetosensitive axis, and the magnetic focusing plate 1130 is provided on the positive side of the magnetoresistive effect element 1110 along the magnetosensitive axis. It has been. Here, the magnetosensitive axis may be along the direction of magnetization fixed by the magnetization fixed layer forming the magnetoresistive effect element 1110. Further, when a magnetic field is input from the negative side of the magnetosensitive axis toward the positive side, the resistance of the magnetoresistive element 1110 may increase or decrease. The magnetic flux concentrating plates 1120 and 1130 are made of a material having high magnetic permeability such as permalloy, for example. When the magnetic sensor 20 is configured as shown in this specific example, the coil 34 has a cross section of the magnetoresistive effect element 1110 and the magnetic convergence plates 1120 and 1130 disposed at both ends of the magnetoresistive effect element 1110. It is wound around. Moreover, when the magnetic sensor 20 has a plurality of magnetoresistive effect elements 1110 in one magnetic sensor 20, it may have a plurality of sets including the magnetoresistive effect elements and the magnetic converging plates disposed at both ends thereof. In that case, the coil 34 may be wound so as to surround the group including the magnetoresistive effect element and the magnetic flux concentrating plates disposed at both ends thereof with one coil.

  In such a magnetic sensor 20, when a magnetic field is input from the negative side to the positive side of the magnetosensitive axis, the magnetic converging plates 1120 and 1130 formed of a material having a high magnetic permeability are magnetized. Magnetic flux distribution as shown by the broken line occurs. Then, the magnetic flux generated by magnetizing the magnetic converging plates 1120 and 1130 passes through the position of the magnetoresistive effect element 1110 sandwiched between the two magnetic converging plates 1120 and 1130. For this reason, the magnetic flux density at the position of the magnetoresistive effect element 1110 can be significantly increased by arranging the magnetic converging plates 1120 and 1130. Further, as in this specific example, by sampling the spatial distribution of the magnetic field using the magnetoresistive effect element 1110 disposed in a narrow position between the magnetic focusing plates 1120 and 1130, the sampling points in the space are clearly defined. can do.

  FIG. 12 shows a magnetic flux distribution when a feedback magnetic field is generated in the magnetic sensor 20 according to this example. In FIG. 12, members having the same functions and configurations as those in FIG. In the magnetic sensor 20 according to this example, when a feedback current is supplied to the coil 34, the coil 34 generates a feedback magnetic field, thereby generating a magnetic flux distribution as indicated by a one-dot chain line in the drawing. The magnetic flux generated by the feedback magnetic field is spatially distributed so as to cancel the spatial distribution of the magnetic field input to the magnetoresistive effect element 1110 and magnetically amplified by the magnetic focusing plates 1120 and 1130. Therefore, the magnetic sensor 20 feeds back the magnetic field distribution at the position of the magnetoresistive effect element 1110 when the magnetic converging plates 1120 and 1130 are arranged at both ends of the magnetoresistive effect element 1110 as shown in this specific example. Since the magnetic field can be accurately canceled, a sensor with high linearity between the input magnetic field and the output voltage can be realized.

  FIG. 13 shows an example of the configuration of the magnetic sensor 20 according to this example. In FIG. 13, members having the same functions and configurations as in FIG. In this figure, the magnetoresistive effect element 1110 has a magnetization free layer 1310 and a magnetization fixed layer 1320. In general, the magnetoresistive element 1110 has a structure in which an insulating thin film layer is sandwiched between two ferromagnetic layers. The magnetization free layer 1310 is a layer whose magnetization direction changes according to an external magnetic field among the two ferromagnetic layers. Also, the magnetization fixed layer 1320 is a layer whose magnetization direction does not change with respect to an external magnetic field, out of the two ferromagnetic layers.

  In this specific example, the magnetoresistive effect element 1110 has a magnetization free layer 1310 disposed below, and a magnetization fixed layer 1320 disposed above the magnetization free layer 1310 via an insulating thin film layer (not shown). This is a so-called bottom-free magnetoresistive element. Since the magnetoresistive effect element having the bottom free structure can form the magnetization free layer 1310 with a relatively wide area, high magnetic sensitivity can be obtained.

  In this specific example, the magnetic sensor 20 includes a magnetic converging plate 1120 and 1130 on the magnetoresistive effect element 1110 via an insulating layer (not shown) so that the magnetoresistive effect element 1110 is sandwiched in the center. It is arranged at both ends. Thereby, the magnetoresistive effect element 1110 is arrange | positioned in the narrow space pinched | interposed into the magnetic converging plates 1120 and 1130.

  Here, in this figure, the length along the magnetosensitive axis direction in the magnetization free layer 1310 is defined as the magnetization free layer length L_Free. Further, the length along the axis perpendicular to the magnetosensitive axis direction in the top view in the magnetization free layer 1310 is defined as the magnetization free layer width W_Free. In addition, the length along the magnetosensitive axis direction in the magnetization fixed layer 1320 is defined as a magnetization fixed layer length L_Pin. Further, the length along the axis perpendicular to the magnetosensitive axis direction in the top view of the magnetization fixed layer 1320 is defined as a magnetization fixed layer width W_Pin. Further, the length along the magnetosensitive axis direction from the outer end of the magnetic flux concentrating plate to the outer end of the magnetization free layer (in this figure, the length along the magnetosensitive axis direction from the left end to the right end of the magnetic converging plate 1120 The length and the length along the magnetosensitive axis direction from the right end to the left end of the magnetic converging plate 1130) are defined as the magnetic converging plate length L_FC. Further, the length along the axis perpendicular to the direction of the magnetosensitive axis in the top view of the magnetic converging plate is defined as the magnetic converging plate width W_FC. Further, the length along the axis perpendicular to the direction of the magnetosensitive axis in a side view of the magnetic converging plate is defined as the magnetic converging plate thickness T_FC. Further, an interval along the magnetic sensitive axis direction of the two magnetic flux concentrating plates 1120 and 1130 (in this figure, a length along the magnetic sensitive axis direction from the right end of the magnetic converging plate 1120 to the left end of the magnetic converging plate 1130). It is defined as the magnetic convergence plate interval G_FC. Further, the distance along the axis perpendicular to the magnetosensitive axis direction in a side view from the center in the thickness direction of the magnetization free layer 1310 to the bottom surface of the magnetic focusing plate is defined as a magnetic focusing plate height H_FC.

  FIG. 14 shows a simulation result of the magnetic amplification factor when the magnetic converging plate interval G_FC is changed in the magnetic sensor 20 according to this example. In this figure, the horizontal axis indicates the magnetic focusing plate interval G_FC in μm, and the vertical axis indicates the magnetic amplification factor. In this simulation, the magnetization free layer length L_Free is 100 μm, the magnetization free layer width W_Free is 140 μm, the magnetization fixed layer length L_Pin is 40 μm, the magnetization fixed layer width W_Pin is 20 μm, the magnetic converging plate width W_FC is 300 μm, and the magnetic The convergent plate height H_FC was 0.6 μm. These parameters are all common values in the following simulation. In this simulation, the magnetic convergence plate length L_FC was 10 mm, and the magnetic convergence plate thickness T_FC was 10 μm, 30 μm, 50 μm, and 100 μm.

  As shown in this figure, the magnetic sensor 20 has a higher magnetic amplification factor as the magnetic converging plate interval G_FC is narrowed. Here, since the magnetization free layer length L_Free is 100 μm, when the magnetic focusing plate interval G_FC is 100 μm, the side surface of the magnetic focusing plate and the side surface of the magnetization free layer 1310 are aligned in a side view (that is, in FIG. 13). The right end of the magnetic focusing plate 1120 and the left end of the magnetization free layer 1310, and the left end of the magnetic focusing plate 1130 and the right end of the magnetization free layer 1310 are aligned in a side view). According to this simulation result, the magnetic sensor 20 has a higher magnetic amplification factor when the magnetic converging plate interval G_FC is smaller than 100 μm. Therefore, in the magnetic sensor 20, the distance between the magnetic focusing plates 1120 and 1130 arranged at both ends of the magnetoresistive effect element 1110 in the magnetosensitive axis direction (magnetic focusing plate spacing G_FC) is the magnetization free layer 1310 of the magnetoresistive effect element 1110. Is smaller than the length in the magnetic sensitive axis direction (magnetization free layer length L_Free), since a higher magnetic amplification factor can be obtained. In the magnetic sensor 20, the magnetic converging plate interval G_FC may be smaller than the magnetization fixed layer length L_Pin (40 μm). That is, in the magnetic sensor 20, the magnetic converging plate may be disposed so that the magnetic converging plate overlaps a part of the magnetization fixed layer in a top view.

  FIG. 15 shows a simulation result of the magnetic amplification factor when the magnetic convergence plate length L_FC is changed in the magnetic sensor 20 according to this example. In this figure, the horizontal axis indicates the magnetic convergence plate length L_FC in mm, and the vertical axis indicates the magnetic amplification factor. In this simulation, the simulation was performed with the magnetic convergence plate thickness T_FC being 10 μm and the magnetic convergence plate interval G_FC being 20 μm.

  As shown in the figure, the magnetic sensor 20 has a higher magnetic amplification factor as the magnetic convergence plate length L_FC is increased. This can be said that the longer the magnetic converging plate made of a material with high magnetic permeability, the more magnetic flux that is generated. Therefore, when the magnetic sensor 20 is provided with magnetic converging plates at both ends of the magnetoresistive effect element 1110, if the length of the magnetic converging plate in the magnetosensitive axis direction (magnetic converging plate length L_FC) is increased as much as possible, It is preferable because a higher magnetic amplification factor can be obtained. Specifically, it is preferable that the length of the magnetic focusing plate in the direction of the magnetic sensitive axis (magnetic focusing plate length L_FC) is 1 mm or more because a high magnetic amplification effect can be obtained. In particular, as shown in the figure, the magnetic sensor 20 has a high effect of increasing the magnetic gain in the range where the magnetic convergence plate length L_FC is smaller than 10 mm. Further, when the magnetic convergence plate length L_FC is 10 mm or more, a magnetic amplification factor of 100 times or more can be obtained. Therefore, in biomagnetic field measurement such as a magnetocardiograph, the length of the magnetic focusing plate in the direction of the magnetic axis (magnetic focusing plate length L_FC) is 10 mm or more in order to more accurately detect a weak magnetic field. More preferred.

  FIG. 16 shows a simulation result of the magnetic amplification factor when the magnetic convergence plate thickness T_FC is changed in the magnetic sensor 20 according to this example. In this figure, the horizontal axis indicates the magnetic convergence plate thickness T_FC in μm, and the vertical axis indicates the magnetic amplification factor. In this simulation, the simulation was performed with the magnetic convergence plate length L_FC being 10 mm, the magnetic convergence plate thickness T_FC being 10 μm, and the magnetic convergence plate interval G_FC being 20 μm.

  As shown in this figure, in the magnetic sensor 20, as the magnetic convergence plate thickness T_FC is increased, the magnetic amplification factor increases to a certain point, and then the magnetic amplification factor tends to decrease. is there. To a certain point, the thicker the magnetic converging plate made of a material having a high magnetic permeability, the more magnetic flux is generated, so the magnetic amplification factor increases. After a certain point, the magnetic amplification effect is higher than the magnetic amplification effect. It can be said that the center in the thickness direction of the converging plate is moved away from the magnetoresistive effect element 1110 and the magnetic flux converged by the magnetic converging plate is less likely to pass through the magnetoresistive effect element 1110. Therefore, it is preferable that the thickness of the magnetic focusing plate (magnetic focusing plate thickness T_FC) is approximately 100 μm or less because a higher magnetic amplification effect can be obtained.

  FIG. 17 shows the simulation result of the magnetic amplification factor in the magnetic sensor 20 according to this example when the magnetic converging plate interval G_FC is constant and the magnetic converging plate length L_FC / magnetic converging plate interval G_FC is changed. In this figure, the horizontal axis indicates the value obtained by dividing the magnetic convergence plate length L_FC by the magnetic convergence plate interval G_FC, and the vertical axis indicates the magnetic amplification factor. In this simulation, the simulation was performed with the magnetic convergence plate thickness T_FC being 10 μm and the magnetic convergence plate interval G_FC being 20 μm.

  As shown in FIG. 17, in the magnetic sensor 20, the magnetic amplification factor increases as the magnetic converging plate length L_FC / magnetic converging plate interval G_FC increases. This can be said to reflect that the magnetic gain increases as the magnetic convergence interval G_FC in FIG. 14 decreases, and that the magnetic gain increases as the magnetic convergence plate length L_FC in FIG. 15 increases. As shown in this figure, the magnetic sensor 20 includes a magnetic converging plate 1120 in which the length of the magnetic converging plate in the magnetosensitive axis direction (magnetic converging plate length L_FC) is arranged at both ends of the magnetoresistive effect element 1110, and It is preferable to be larger than 10 times the interval in the magnetosensitive axis direction 1130 (magnetic converging plate interval G_FC) because a high magnetic amplification effect can be obtained. In particular, in the magnetic sensor 20, the spacing in the magnetosensitive axis direction (magnetic focusing plate spacing G_FC) between the magnetic focusing plates 1120 and 1130 disposed at both ends of the magnetoresistive effect element 1110 is the magnetization free layer 1310 of the magnetoresistive effect element 1110. Is smaller than the length in the direction of the magnetic sensitive axis (magnetization free layer length L_Free), and the length in the direction of the magnetic sensitive axis of the magnetic converging plate (magnetic converging plate length L_FC) is the magnetization free layer of the magnetoresistive effect element 1110 It is more preferable that it is larger than 10 times the length of 1310 in the direction of the magnetic sensitive axis because a higher magnetic amplification effect can be obtained. Furthermore, in the magnetic sensor 20, when the magnetization free layer length is 100 μm from the simulation result of FIG. 14, the magnetic converging plate interval G_FC is more preferably smaller than 100 μm, and from the simulation result of FIG. Based on these facts, it is shown that the length of the magnetic focusing plate in the direction of the magnetosensitive axis (magnetic focusing plate length L_FC) is a magnetic focusing plate 1120 disposed at both ends of the magnetoresistive effect element 1110. And 1130 or more of the interval in the magnetosensitive axis direction (magnetic convergence plate interval G_FC) is more preferable because a higher magnetic amplification factor can be obtained. As described above, the magnetic sensor 20 can achieve a high magnetic amplification factor by appropriately designing the magnetic convergence plate length L_FC and the magnetic convergence plate interval G_FC.

  FIG. 18 shows a simulation result of the magnetic amplification factor when the magnetic convergence plate length L_FC is constant and the magnetic convergence plate length L_FC / magnetic convergence plate interval G_FC is changed in the magnetic sensor 20 according to this example. . In this figure, the horizontal axis indicates the value obtained by dividing the magnetic convergence plate length L_FC by the magnetic convergence plate interval G_FC, and the vertical axis indicates the magnetic amplification factor. In this simulation, the magnetic convergence plate length L_FC was 10 mm, and the magnetic convergence plate thickness T_FC was 10 μm, 30 μm, 50 μm, and 100 μm.

  FIG. 19 shows an example in which the magnetic sensor 20 according to this example is applied to the measurement sensor unit 100 and the reference sensor unit 200. In FIG. 19, members having the same functions and configurations as those in FIG. In this figure, the measurement sensor unit 100 uses the magnetic sensor 20 according to the specific example shown in FIG. 11 as the magnetic sensor 20 in the three sensor units S0X, S0Y, and S0Z. The reference sensor unit 200 uses the magnetic sensor 20 according to the specific example shown in FIG. 11 as the magnetic sensor 20 in the three sensor units S1X, S1Y, and S1Z. The measurement sensor unit 100 and the reference sensor unit 200 use the magnetic sensor 20 in which the magnetic converging plates 1120 and 1130 are arranged at both ends of the magnetoresistive effect element 1110 in the respective sensor units, so that the magnetic amplification as described above is performed. While obtaining an effect, the sampling point in space can be clarified.

  In addition, the measuring apparatus 1000 includes a magnetic sensor 20 in which the magnetic convergence plate length L_FC and the magnetic convergence plate interval G_FC are optimized as the magnetic sensor 20 in each of the measurement sensor unit 100 and the reference sensor unit 200. For example, a magnetic amplification factor exceeding 100 times can be realized, and a weak magnetic field can be detected more accurately in a biomagnetic field measurement such as a magnetocardiograph.

  Furthermore, as shown in this figure, the sensor units S0X, S0Y, and S0Z, which are three-axis magnetic sensors in the measurement sensor unit 100, are viewed from the three-dimensional directions of the X-axis, Y-axis, and Z-axis, One end is provided in the gap provided between the three-axis magnetic sensors without overlapping each other, and the other end is arranged extending in each axial direction of the three-axis direction so as to be separated from the gap. As an example, in this drawing, a gap (gap) is provided in the lower left corner of the measurement sensor unit 100 when viewed from the front, and the sensor units S0X, S0Y, and S0Z are provided so that one end is in contact with the gap. An example in which the ends are extended and arranged in each of the X-axis, Y-axis, and Z-axis directions so as to leave the gap is shown. Further, it is preferable that the coils or magnetic bodies included in the sensor units S0X, S0Y, and S0Z are arranged so as not to overlap each other. As a result, the sampling point can be further clarified, and each component of the magnetic field can be grasped more easily. Further, the other-axis sensitivities of the sensor units S0X, S0Y, and S0Z can be regarded as equivalent to each other, and the linear algebra calibration calculation is facilitated. The other-axis sensitivity is generated by mutual interference caused by coils or magnetic materials of the sensor units S0X, S0Y, and S0Z. The reference sensor unit 200 has the same calibration as the measurement sensor unit 100. By making each of the measurement sensor unit 100 and the reference sensor unit 200 calibrate as described above, the measurement apparatus 1000 can more accurately detect a weak magnetic field in biomagnetic field measurement such as a magnetocardiograph. It becomes possible to do.

  FIG. 20 shows an example in which a measurement sensor unit 100 to which the magnetic sensor 20 according to this example is applied and three reference sensor units 200a to 200c are arranged. In the figure, a measurement sensor unit 100 and three reference sensor units 200a to 200c are arranged. The measurement sensor unit 100 is at coordinates (0, 0, 0), the reference sensor unit 200a is at coordinates (L, 0, 0), and the reference sensor unit 200b is at coordinates (0, L, 0). The sensor units 200c are arranged at coordinates (0, 0, L), respectively. The measurement sensor unit 100 and the three reference sensor units 200a to 200c are arranged so as to be closest to each other. For example, in a magnetocardiograph, since the electrical activity in the heart is detected by measuring the spatial distribution of the cardiac magnetic field, it is desirable that adjacent sensor units are arranged close to each other, for example, for ischemic heart failure. When used for diagnosis or the like, in order to obtain the required spatial resolution, it is desirable that the distance between the sensor parts adjacent in the magnetosensitive axis direction (L in this figure) be 3 cm or less.

  In order to obtain high magnetic sensitivity even in such a limited interval, the measurement sensor unit 100 and the three reference sensor units 200a to 200c make the length L_FC of the magnetic focusing plate in the magnetosensitive axis direction as large as possible. It is desirable. More specifically, the sum of the length of the two magnetic flux concentrating plates in the direction of the magnetic sensitive axis and the distance between the two magnetic converging plates in the direction of the magnetic sensitive axis is greater than half of the interval between the adjacent sensor portions in the direction of the magnetic sensitive axis. When the magnetic sensor 20 in each sensor unit is designed so as to satisfy (that is, 2 × magnetic converging plate length L_FC + magnetic converging plate interval G_FC> 0.5 × L), high magnetism is achieved even within a limited interval. It is preferable because sensitivity can be obtained.

  In general, when the sensor units are arranged close to each other as described above, mutual magnetic interference between the three-axis sensors cannot be ignored. However, according to the measurement apparatus 1000 according to the present embodiment, as described above ( According to the mathematical formulas of (Equation 6) and (Equation 7), not only the magnetic sensitivity error (main axis sensitivity mismatch and multi-axis sensitivity in X, Y, and Z axes) of each triaxial sensor itself but also adjacent sensor units It is possible to correct without magnetic interference.

  Further, by arranging the measurement sensor unit 100 and the three reference sensor units 200a to 200c as shown in the figure, the measurement apparatus 1000 can change the gradient of each magnetic field in the X-axis, Y-axis, and Z-axis directions. Can be acquired.

That is, the measuring apparatus 1000 obtains a magnetic field gradient in the X-axis direction by the following equation using the respective magnetic fields measured by the measurement sensor unit 100 and the reference sensor unit 200a. Here, Bax indicates the magnetic field in the X-axis direction measured by the reference sensor unit 200a, Bay indicates the magnetic field in the Y-axis direction measured by the reference sensor unit 200a, and Baz is measured by the reference sensor unit 200a. The magnetic field in the Z-axis direction is shown. Then, the measurement apparatus 1000 subtracts the magnetic field Bay from the magnetic field B0x in the X-axis direction measured by the measurement sensor unit 100, thereby obtaining Bgrad01x as a magnetic field gradient in the X-axis direction with respect to the magnetic field in the X-axis direction. The measuring apparatus 1000 subtracts the magnetic field Bay from the magnetic field B0y in the Y-axis direction measured by the measurement sensor unit 100, thereby obtaining Bgrad01y as a magnetic field gradient in the X-axis direction with respect to the magnetic field in the Y-axis direction. The measuring apparatus 1000 subtracts the magnetic field Baz from the magnetic field B0z measured in the measurement sensor unit 100 to obtain Bgrad01z as a magnetic field gradient in the X-axis direction with respect to the magnetic field in the Z-axis direction.

In addition, the measuring apparatus 1000 obtains a magnetic field gradient in the Y-axis direction by the following equation using the magnetic fields measured by the measuring sensor unit 100 and the reference sensor unit 200b. Here, Bbx represents the magnetic field in the X-axis direction measured by the reference sensor unit 200b, Bby represents the magnetic field in the Y-axis direction measured by the reference sensor unit 200b, and Bbz is measured by the reference sensor unit 200b. The magnetic field in the Z-axis direction is shown. Then, the measuring apparatus 1000 obtains a magnetic field gradient in the Y-axis direction with respect to each of the magnetic field in the X-axis direction, the magnetic field in the Y-axis direction, and the magnetic field in the Z-axis direction by the same method as the magnetic field gradient in the X-axis direction.

Furthermore, the measuring apparatus 1000 uses the respective magnetic fields measured by the measurement sensor unit 100 and the reference sensor unit 200c to obtain a gradient magnetic field in the Z-axis direction according to the following equation. Here, Bcx indicates a magnetic field in the X-axis direction measured by the reference sensor unit 200c, Bcy indicates a magnetic field in the Y-axis direction measured by the reference sensor unit 200c, and Bcz is measured by the reference sensor unit 200c. The magnetic field in the Z-axis direction is shown. Then, the measuring apparatus 1000 obtains a magnetic field gradient in the Z-axis direction with respect to each of the magnetic field in the X-axis direction, the magnetic field in the Y-axis direction, and the magnetic field in the Z-axis direction by the same method as the magnetic field gradient in the X-axis direction.

  As described above, the measurement apparatus 1000 can obtain the magnetic field gradient in the triaxial direction with respect to each of the magnetic fields in the triaxial direction by disposing the measurement sensor unit 100 and the reference sensor unit 200, so that a more detailed magnetic field can be obtained. Can be obtained.

  FIG. 21 shows a sensor array 2100 in which a plurality of sensor units to which the magnetic sensor 20 according to this example is applied are arranged in the X-axis direction, the Y-axis direction, and the Z-axis direction, respectively. In this figure, as an example, four sensor units are arranged in an array in the X-axis direction, four in the Y-axis direction, and two in the Z-axis direction. The measuring apparatus 1000 uses the sensor array 2100 as one sensor unit arranged at each coordinate as the measurement sensor unit 100, and three sensor units adjacent to the sensor unit in the respective axial directions are used as reference sensors. By using the units 200a to 200c, it is possible to acquire the magnetic field gradient in the triaxial direction with respect to the magnetic field in the triaxial direction at each coordinate.

  It has been described that the measuring apparatus 1000 according to the present embodiment measures the magnetocardiogram signal B_sig by calculating the difference signal between the measurement magnetic field signal and the reference magnetic field signal. In addition, the measurement apparatus 1000 may calculate a difference signal between the measurement magnetic field signal and the reference magnetic field signal after executing a process of removing a noise component or the like in advance. For example, the measuring apparatus 1000 may further include a filter that allows high-frequency components of the detection signal of the magnetic sensor 20 to pass. The filter may be configured with hardware and / or software. The filter may be a high pass filter.

  The filter may be provided between the measurement sensor unit 100 and the first AD conversion unit 102 and between the reference sensor unit 200 and the second AD conversion unit 104. Instead of or in addition to this, the filter may be provided in the subsequent stage of the first AD conversion unit 102 and the subsequent stage of the second AD conversion unit 104. The high-pass filter is an example of a filter that removes a noise component, and the measurement apparatus 1000 may use a low-pass filter, a band-pass filter, a band elimination filter, a combination of each filter, and the like.

  As shown in FIG. 6, the measurement apparatus 1000 according to the present embodiment described above uses an example using a three-axis sensor by the measurement sensor unit 100 and a three-axis sensor by the reference sensor unit 200 that are separated by a predetermined distance. Although described, it is not limited to this. The measurement apparatus 1000 may include more measurement sensor units 100 and reference sensor units 200.

  For example, the plurality of measurement sensor units 100 may be provided at each of the plurality of measurement positions of the measurement object 50. In this case, a plurality of measurement sensor units 100 may be provided at a plurality of different measurement positions where a magnetocardiogram signal can be detected so as to operate as a multi-axis sensor. It is desirable that a plurality of measurement sensor units 100 be provided for each measurement position so as to be configured as a triaxial sensor. As an example, the plurality of measurement sensor units 100 are arranged three by three in a lattice shape or concentric shape on the body surface near the heart.

  In this case, the first AD conversion unit 102 and the first conversion unit 110 may convert the outputs of the plurality of measurement sensor units 100 into a plurality of measurement magnetic field signals for each measurement position of the measurement target 50. A plurality of first conversion units 110 may be provided.

  Similarly, the plurality of reference sensor units 200 may be provided at each of a plurality of reference positions spaced apart from the plurality of measurement positions corresponding to the plurality of measurement positions. In this case, a plurality of reference sensor units 200 may be provided so that each of the plurality of reference sensor units 200 operates as a multi-axis sensor at a plurality of different reference positions where the magnetocardiogram signal is sufficiently reduced and only the environmental magnetic field can be detected. It is desirable that a plurality of reference sensor units 200 be provided for each reference position so as to be configured as a three-axis sensor. As an example, the plurality of reference sensor units 200 are arranged three by three in a lattice shape or concentric shape on a surface separated from the body surface in the vicinity of the heart.

  In this case, the second AD conversion unit 104 and the second conversion unit 120 may convert the outputs of the plurality of reference sensor units 200 into a plurality of reference magnetic field signals for each reference position. A plurality of second conversion units 120 may be provided.

  And the difference calculation part 140 may calculate the some difference signal which shows the difference of each coordinate-axis direction of the corresponding some magnetic field signal for a measurement and several magnetic field signals for a reference for every measurement position of the measuring object 50. FIG. A plurality of difference calculation units 140 may be provided. According to the measuring apparatus 1000 described above, the magnetocardiogram signals at a plurality of measurement positions can be measured, respectively, and more detailed information can be acquired.

  In addition, although the measuring apparatus 1000 demonstrated the example provided with the several triaxial sensor by the some sensor part 100 for a measurement, and the several triaxial sensor by the some sensor part 200 for a reference, it is limited to this. There is no. For example, the number of triaxial sensors by the reference sensor unit 200 may be smaller than the number of triaxial sensors by the measurement sensor unit 100. In this case, the difference calculation unit 140 subtracts the reference magnetic field signal of one three-axis sensor by the reference sensor unit 200 from the measurement magnetic field signals of the plurality of three-axis sensors by the measurement sensor unit 100 to obtain the difference signal. May be calculated.

  For example, the plurality of reference sensor units 200 are provided at one reference position separated from the plurality of measurement positions. The plurality of reference sensor units 200 may operate as one triaxial sensor. The second AD conversion unit 104 and the second conversion unit 120 may convert the outputs of the plurality of reference sensor units 200 at one reference position into a plurality of reference magnetic field signals. Thereby, the difference calculation unit 140 calculates a plurality of difference signals indicating differences in the respective coordinate axis directions between the plurality of measurement magnetic field signals corresponding to the plurality of measurement positions and the plurality of reference magnetic field signals at one reference position. To do. Therefore, the measuring apparatus 1000 can acquire detailed information with a smaller number of reference sensor units 200.

  The measurement apparatus 1000 according to the present embodiment has been described with respect to an example in which a magnetocardiogram signal is measured using the measurement target 50 as an animal heart. However, the measurement apparatus 1000 is not limited thereto. The measuring object 50 may be anything that outputs a magnetic signal, and may be another organ of an animal. For example, the measurement object 50 may be a brain, and in this case, the measurement apparatus 1000 measures an electroencephalogram. Moreover, the measurement object 50 may be a steel frame or the like inside the concrete. In this case, the measurement apparatus 1000 measures the occurrence of scratches or corrosion near the surface of the ferromagnetic material such as the steel frame. The measurement target 50 may be a biological sample, an environmental sample, or the like, and the measurement apparatus 1000 may be a measurement apparatus such as a magnetic bead distribution or a counter.

  Various embodiments of the invention may be described with reference to flowcharts and block diagrams, where a block is either (1) a stage in a process in which the operation is performed or (2) an apparatus responsible for performing the operation. May represent a section of Certain stages and sections are implemented by dedicated circuitry, programmable circuitry supplied with computer readable instructions stored on a computer readable medium, and / or processor supplied with computer readable instructions stored on a computer readable medium. It's okay. Dedicated circuitry may include digital and / or analog hardware circuitry and may include integrated circuits (ICs) and / or discrete circuits. Programmable circuits include 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. Reconfigurable hardware circuitry, including and the like.

  Computer readable media may include any tangible device capable of storing instructions to be executed by a suitable device, such that a computer readable medium having instructions stored thereon is specified in a flowchart or block diagram. A product including instructions that can be executed to create a 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 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 can be assembler instructions, instruction set architecture (ISA) instructions, machine instructions, machine dependent instructions, microcode, firmware instructions, state setting data, or object oriented programming such as Smalltalk, JAVA, C ++, etc. Including any source code or object code written in any combination of one or more programming languages, including languages and conventional procedural programming languages such as "C" programming language or similar programming languages Good.

  Computer readable instructions may be directed to a general purpose computer, special purpose computer, or other programmable data processing device processor or programmable circuit locally or in a wide area network (WAN) such as a local area network (LAN), the Internet, etc. The computer-readable instructions may be executed to create a means for performing the operations provided via and 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. 22 illustrates an example of a computer 2200 in which aspects of the present invention may be embodied in whole or in part. The program installed in the computer 2200 can cause the computer 2200 to function as an operation associated with the apparatus according to the embodiment of the present invention or one or more sections of the apparatus, or to perform the operation or the one or more sections. The section can be executed and / or the computer 2200 can execute a process according to an embodiment of the present invention or a stage of the process. Such a program may be executed by CPU 2212 to cause computer 2200 to perform certain operations associated with some or all of the blocks in the flowcharts and block diagrams described herein.

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

  The CPU 2212 operates according to programs stored in the ROM 2230 and the RAM 2214, thereby controlling each unit. The graphic controller 2216 obtains the image data generated by the CPU 2212 in a frame buffer or the like provided in the RAM 2214 or itself so that the image data is displayed on the display device 2218.

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

  The ROM 2230 stores therein a boot program executed by the computer 2200 at the time of activation and / or a program depending on the hardware of the computer 2200. The input / output chip 2240 may also connect various input / output units to the input / output controller 2220 via parallel ports, serial ports, keyboard ports, mouse ports, and the like.

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

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

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

  Various types of information, such as various types of programs, data, tables, and databases, may be stored on a recording medium and subjected to information processing. The CPU 2212 describes various types of operations, information processing, conditional judgment, conditional branching, unconditional branching, information retrieval, which are described in various places in the present disclosure and specified by the instruction sequence of the program with respect to the data read from the RAM 2214. Various types of processing may be performed, including / replacement etc., and the result is written back to the RAM 2214. Further, the CPU 2212 may search for information in files, databases, etc. 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 2212 specifies the attribute value of the first attribute. The entry that matches the condition is searched from the plurality of entries, the attribute value of the second attribute stored in the entry is read, and thereby the first attribute that satisfies the predetermined condition is associated. The attribute value of the obtained second attribute may be acquired.

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

  As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment. It will be apparent to those skilled in the art that various modifications or improvements can be added to the above-described embodiment. It is apparent from the scope of the claims that the embodiments added with such changes or improvements can be included in the technical scope of the present invention.

  The order of execution of each process such as operations, procedures, steps, and stages in the apparatus, system, program, and method shown in the claims, the description, and the drawings is particularly “before” or “prior to”. It should be noted that the output can be realized in any order unless the output of the previous process is used in the subsequent process. Regarding the operation flow in the claims, the description, and the drawings, even if it is described using “first”, “next”, etc. for convenience, it means that it is essential to carry out in this order. It is not a thing.

DESCRIPTION OF SYMBOLS 10 Sensor part, 20 Magnetic sensor, 30 1st magnetic field generation part, 32 Amplifier circuit, 34 Coil, 40 Output part, 50 Measurement object, 60 2nd magnetic field generation part, 100 Measurement sensor part, 102 1st AD conversion part, 104 2nd AD conversion unit, 106 clock generator, 110 1st conversion unit, 120 2nd conversion unit, 130 storage unit, 140 difference calculation unit, 150 interface unit, 160 signal processing unit, 170 adjustment unit, 180 update unit, 200 Sensor unit, 1000 measuring device, 1110 magnetoresistive effect element, 1120 magnetic focusing plate, 1130 magnetic focusing plate, 1310 magnetization free layer, 1320 magnetization fixed layer, 2200 computer, 2201 DVD-ROM, 2210 host controller, 2212 CPU, 2214 RAM, 2216 graphics Controller, 2218 a display device, 2220 an input / output controller, 2222 a communication interface, 2224 hard drive, 2226 DVD-ROM drive, 2230 ROM, 2240 I / O chip, 2242 keyboard

In the first aspect of the present invention, a plurality of measurement sensor units that are provided at measurement positions for measuring a measurement object and detect input magnetic fields in different detection axis directions, and outputs from the plurality of measurement sensor units, A first conversion unit that converts a plurality of measurement magnetic field signals indicating magnetic field components in each coordinate axis direction, and a plurality of reference sensors that are provided at a reference position separated from the measurement position and detect input magnetic fields in different detection axis directions A second conversion unit that converts outputs of the plurality of reference sensor units into a plurality of reference magnetic field signals indicating magnetic field components in the coordinate axis directions, a plurality of measurement magnetic field signals, and a plurality of reference magnetic field signals. A difference calculation unit that calculates a plurality of difference signals indicating differences in the respective coordinate axis directions, and each of the plurality of measurement sensor units and each of the plurality of reference sensor units includes a magnetic sensor and an input detected by the magnetic sensor. Possess a first magnetic field generator to provide feedback magnetic field to reduce the magnetic field to the magnetic sensor, and an output portion in which the first magnetic field generating unit outputs an output signal corresponding to the current supplied to generate a feedback magnetic field, a plurality of Each of the measurement sensor units has a triaxial magnetic sensor arranged close to each other at one of the measurement positions, and each of the plurality of reference sensor units is close to each other at one of the reference positions. A measuring apparatus and a measuring method having a triaxial magnetic sensor arranged are provided.

Claims (21)

A plurality of measurement sensor units that are provided at measurement positions for measuring a measurement object and detect input magnetic fields in different detection axis directions;
A first conversion unit that converts the outputs of the plurality of measurement sensor units into a plurality of measurement magnetic field signals indicating magnetic field components in the coordinate axis directions;
A plurality of reference sensor units that are provided at a reference position separated from the measurement position and detect input magnetic fields in different detection axis directions;
A second conversion unit that converts the outputs of the plurality of reference sensor units into a plurality of reference magnetic field signals indicating magnetic field components in the coordinate axis directions;
A difference calculating unit that calculates a plurality of difference signals indicating differences in the coordinate axis directions of the plurality of measurement magnetic field signals and the plurality of reference magnetic field signals;
Each of the plurality of measurement sensor units and each of the plurality of reference sensor units is
A magnetic sensor;
A first magnetic field generation unit that provides the magnetic sensor with a feedback magnetic field that reduces the input magnetic field detected by the magnetic sensor;
An output unit that outputs an output signal corresponding to a current that the first magnetic field generation unit generates to generate the feedback magnetic field;
The first conversion unit corrects the other axis sensitivity of the magnetic sensor of the plurality of measurement sensor units, and the second conversion unit corrects the other axis sensitivity of the magnetic sensor of the plurality of reference sensor units. And
Each of the plurality of measurement sensor units has the three-axis magnetic sensor arranged close to each other at one of the measurement positions,
Each of the plurality of reference sensor units includes the three-axis magnetic sensor arranged close to each other at one of the reference positions.   In the correction of the other axis sensitivity of the magnetic sensor of the plurality of measurement sensor units and the magnetic sensor of the plurality of reference sensor units, the first conversion unit and the second conversion unit may use predetermined coefficients. The measuring apparatus according to claim 1 used.   Each of the plurality of measurement sensor units and each of the plurality of reference sensor units has a linearity in a detection result for the input magnetic field in a predetermined input magnetic field range. Measuring device.   The measuring apparatus according to claim 2, further comprising a storage unit that stores the predetermined coefficient. When the plurality of measurement sensor units and the plurality of reference sensor units are spaced apart from the measurement target and disposed in a predetermined uniform magnetic field,
An adjustment unit that adjusts the predetermined coefficient so that the difference signal calculated by the difference calculation unit falls within a predetermined signal range;
An update unit that updates the predetermined coefficient stored in the storage unit to an adjustment result of the adjustment unit;
The measurement apparatus according to claim 4, further comprising:   The measuring apparatus according to claim 5, wherein the predetermined uniform magnetic field is a magnetic field having a strength greater than an environmental magnetic field.   Each of the plurality of measurement sensor units and each of the plurality of reference sensor units includes a second magnetic field generation unit that applies an offset magnetic field for attenuating an environmental magnetic field to the magnetic sensor. The measuring apparatus as described in any one.   The measuring apparatus according to claim 1, wherein the magnetic sensor includes a magnetoresistive effect element.   The measuring apparatus according to claim 1, further comprising a filter that allows a high-frequency component of a detection signal of the magnetic sensor to pass therethrough. The plurality of measurement sensor units are provided at each of the plurality of measurement positions of the measurement target,
The first conversion unit converts the outputs of the plurality of measurement sensor units into a plurality of measurement magnetic field signals for each measurement position of the measurement target,
The plurality of reference sensor units correspond to the plurality of measurement positions, and are provided at each of a plurality of reference positions separated from the plurality of measurement positions.
The second conversion unit converts the outputs of the plurality of reference sensor units into a plurality of reference magnetic field signals for each reference position,
The difference calculation unit calculates, for each measurement position of the measurement target, a plurality of difference signals indicating differences in the coordinate axis directions of the corresponding plurality of measurement magnetic field signals and the plurality of reference magnetic field signals. The measuring apparatus according to any one of 1 to 9. The plurality of measurement sensor units are provided at each of the plurality of measurement positions of the measurement target,
The first conversion unit converts the outputs of the plurality of measurement sensor units into a plurality of measurement magnetic field signals for each measurement position of the measurement target,
The plurality of reference sensor units are provided at one reference position spaced apart from the plurality of measurement positions,
The second conversion unit converts outputs of the plurality of reference sensor units at the one reference position into a plurality of reference magnetic field signals,
The difference calculation unit is configured to output a plurality of difference signals indicating differences in each coordinate axis direction between the plurality of measurement magnetic field signals corresponding to the plurality of measurement positions and the plurality of reference magnetic field signals at the one reference position. The measuring apparatus according to claim 1, wherein the measuring apparatus calculates. The measurement object is an animal heart,
A signal processing unit that calculates a magnetocardiogram signal of the animal's heart based on the difference signal calculated by the difference calculation unit;
The measuring apparatus according to claim 1.   The measuring device according to claim 1, wherein each of the plurality of measurement sensor units and the plurality of reference sensor units further includes a magnetic convergence plate.   The plurality of measurement sensor units and the plurality of reference sensor units each further include a magnetoresistive effect element and two magnetic converging plates disposed at both ends of the magnetoresistive effect element, The measuring apparatus according to claim 13, wherein the resistance effect element is disposed at a position sandwiched between the two magnetic focusing plates.   The measurement apparatus according to claim 14, wherein an interval between the two magnetic converging plates is smaller than a length of the magnetization free layer of the magnetoresistive effect element in a magnetic sensitive axis direction.   The measuring device according to claim 14 or 15, wherein a length of the two magnetic converging plates in a magnetic sensitive axis direction is larger than 10 times an interval between the two magnetic converging plates.   The sum of the length of the two magnetic converging plates in the direction of the magnetic sensitive axis and the distance between the two magnetic converging plates is greater than half of the distance between the adjacent sensor portions in the direction of the magnetic sensitive axis. A measuring device according to claim 1.   The measuring apparatus according to claim 14, wherein a coil for generating the feedback magnetic field is wound so as to surround the magnetoresistive element and the two magnetic converging plates. The three-axis magnetic sensors do not overlap each other when viewed in three-dimensional directions, and one end is provided in a gap provided between the three-axis magnetic sensors, and the other end is separated from the gap. Arranged extending in each axial direction of the three axial directions,
The measuring device according to any one of claims 1 to 18. A first AD converter that converts the outputs of the plurality of measurement sensor units from analog to digital and supplies the converted signals to the first converter;
A second AD conversion unit that converts the output of the plurality of reference sensor units from analog to digital and supplies the second AD conversion unit to the second AD conversion unit;
The first AD converter and the second AD converter perform AD conversion according to a common sampling clock.
The measuring device according to any one of claims 1 to 19. Detecting input magnetic fields in mutually different detection axis directions using a plurality of measurement sensor units at a measurement position for measuring a measurement object;
Converting the outputs of the plurality of measurement sensor units into a plurality of measurement magnetic field signals indicating magnetic field components in respective coordinate axis directions;
Detecting an input magnetic field in different detection axis directions using a plurality of reference sensor units at a reference position separated from the measurement position;
Converting the outputs of the plurality of reference sensor units into a plurality of reference magnetic field signals indicating magnetic field components in the respective coordinate axis directions;
Calculating a plurality of difference signals indicating differences in the respective coordinate axis directions of the plurality of measurement magnetic field signals and the plurality of reference magnetic field signals,
Each of the plurality of measurement sensor units and each of the plurality of reference sensor units outputs an output signal corresponding to a current that flows to generate a feedback magnetic field that reduces the input magnetic field detected by the magnetic sensor,
Converting the outputs of the plurality of measurement sensor units into the plurality of measurement magnetic field signals includes correcting the other-axis sensitivity of the magnetic sensor included in the plurality of measurement sensor units;
Converting the outputs of the plurality of reference sensor units into the plurality of reference magnetic field signals includes correcting the other-axis sensitivity of the magnetic sensor included in the plurality of reference sensor units;
Each of the plurality of measurement sensor units has the three-axis magnetic sensor arranged close to each other at one of the measurement positions,
Each of the plurality of reference sensor units includes the three-axis magnetic sensor arranged close to each other at one of the reference positions.