Magnetic sensor module and interface apparatus

Abstract

To provide a magnetic sensor that is compact, has higher sensitivity, and has a wider measurement range.SOLUTION: A magnetic sensor module includes: a magnetic body; a first coil wound around a first region of the magnetic body; a second coil wound around a second region of the magnetic body; a pulse supply circuit for supplying a pulse current to the magnetic body; a first signal detection circuit for detecting a first signal based on a voltage excited in the first coil; a second signal detection circuit for detecting a second signal based on a voltage excited in the second coil; a feedback circuit for supplying a feedback signal to the first coil and the second coil; and a detection signal output circuit for outputting a detection signal on the basis of the first signal and the second signal.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a magnetic sensor module and an interface device. [Background technology]

[0002] When a pulse current is passed through a wire made of a magnetic material, spin waves are generated on the surface of the wire, which induces a voltage in a detection coil wound around the wire. A GMI (Giant Magneto-Impedance) sensor is known that measures the magnetic field around the wire based on the voltage induced in the detection coil (see, for example, Patent Document 1 and Non-Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-3866 [Non-patent literature]

[0004] [Non-Patent Document 1] Aktham Asfour, Jean-Paul Yonnet, Manel Zidi, "A High Dynamic Range GMI Current Sensor", Journal of Sensor Technology, 2012, 2, 165-171 Summary of the Invention [Problem to be solved by the invention]

[0005] Since such GMI sensors can be manufactured compactly and inexpensively, they are expected to be used in a variety of applications. Therefore, there is a need for GMI sensors that have higher sensitivity and a wider measurement range while maintaining their compact size.

[0006] The present invention has been made in view of these points, and has as its object to provide a magnetic sensor that is small, has higher sensitivity, and has a wider measurement range. [Means for solving the problem]

[0007] In a first aspect of the present invention, there is provided a magnetic sensor module for measuring the magnetic field of a measurement area, the magnetic sensor module comprising: a magnetic body that forms a plurality of magnetic domains whose polarities differ in the longitudinal direction and whose magnetization direction is oriented in the lateral direction; a first coil wound around a first longitudinal region of the magnetic body; a second coil wound around a second longitudinal region of the magnetic body that is different from the first longitudinal region and is electrically connected to the first coil; a pulse supply circuit that supplies a pulse current to the magnetic body; a first signal detection circuit that detects a first signal based on a voltage excited in the first coil in response to the pulse current being supplied to the magnetic body; and a first signal detection circuit that is provided between the first coil and the first signal detection circuit and that propagates to the first signal detection circuit. a second signal detection circuit that detects a second signal based on a voltage excited in the second coil in response to the pulse current being supplied to the magnetic body; a second filter that is provided between the second coil and the second signal detection circuit and reduces the DC component of the signal propagating to the second signal detection circuit; a feedback circuit that supplies a signal based on the second signal as a feedback signal to the first coil and the second coil; and a detection signal output circuit that outputs a signal obtained by subtracting a signal twice the signal amplitude of the second signal detected by the second signal detection circuit from the first signal detected by the first signal detection circuit.

[0008] the first region of the magnetic body and the first coil are disposed within the region of the measurement area, The second region of the magnetic body and the second coil may be disposed outside the region to be measured.

[0009] At least one of the first signal detection circuit and the second signal detection circuit may detect a peak voltage value of a pulse voltage excited in response to the supply of the pulse current to the magnetic body.

[0010] At least one of the first signal detection circuit and the second signal detection circuit may detect a difference between a peak voltage value on the positive voltage side and a peak voltage value on the negative voltage side of a pulse voltage excited in response to supplying the pulse current to the magnetic body.

[0011] The feedback circuit may include an amplifier circuit that amplifies the second signal by a predetermined factor. The first filter and the feedback circuit may be configured by a bias tee. The magnetic material may be an amorphous magnetic material.

[0012] In a second aspect of the present invention, an interface device is provided, comprising a frame to be worn on the head of a human body, and a magnetic sensor module of the first aspect that is detachably attached to the frame, wherein the magnetic sensor module is attached to the frame so that the first region around which the first coil of the magnetic material is wound is closer to the head than the second region around which the second coil of the magnetic material is wound.

[0013] A plurality of the magnetic sensor modules may be attached to the frame, and the interface device may further include an analysis circuit provided on the frame, electrically connected to the detection signal output circuits of the plurality of the magnetic sensor modules, and configured to analyze the detection signals of the plurality of magnetic sensor modules and generate a status signal indicating the status of the head. [Effects of the Invention]

[0014] The present invention has the effect of providing a magnetic sensor that is small, has higher sensitivity, and has a wider measurement range. [Brief explanation of the drawings]

[0015] [Figure 1] Shows a configuration example of the GMI sensor S. [Figure 2] Shows an example of the pulsed current supplied to the magnetic body M of the GMI sensor S and the coil voltage generated in the coil C according to the pulsed current. [Figure 3] Shows an example of a magnetic detection circuit 10 using the GMI sensor S. [Figure 4] Shows a configuration example for reducing magnetic noise around the GMI sensor S. [Figure 5] Shows an example of a magnetic detection circuit 10 that applies a feedback magnetic field to the GMI sensor S. [Figure 6] Shows a configuration example of the magnetic sensor module 20 according to the present embodiment. [Figure 7] Shows a configuration example of the detection signal output circuit 30 according to the present embodiment. [Figure 8] Shows a configuration example of the feedback circuit 29 according to the present embodiment. [Figure 9] Shows a configuration example of the interface device 60 according to the present embodiment.

Mode for Carrying Out the Invention

[0016] <Configuration Example of GMI Sensor S> FIG. 1 shows a configuration example of the GMI sensor S. The GMI sensor S has a magnetic body M and a coil C. FIG. 1(a) shows an example of the magnetic body M. The magnetic body M has the shape of a wire extending in the longitudinal direction. The length of the magnetic body M is, for example, about 10 mm or so. The magnetic body M is an amorphous magnetic body. The magnetic body M has different polarities in the longitudinal direction and forms a plurality of magnetic domains with the magnetization direction facing the short side direction. In FIG. 1(a), the magnetic domains are indicated by dotted lines and the magnetization direction is indicated by arrows.

[0017] FIG. 1(b) shows an example of the coil C. The coil C is wound around the magnetic body M. FIG. 1(c) shows an example of the GMI sensor S. When a pulsed current is applied to the magnetic body M of such a GMI sensor S, a voltage corresponding to the magnitude of the magnetic field at the position where the GMI sensor S is arranged is excited in the coil C. Therefore, by detecting the peak value of the voltage excited in the coil C according to the pulsed current, the magnetic field at the position where the GMI sensor S is arranged can be measured.

[0018] For example, by arranging the GMI sensor S in the measurement region where the magnetic field is to be measured, the magnetic field in the measurement region can be measured. Such a GMI sensor S is a known technique, so the detailed description of its operation is omitted. Next, a first technique for enhancing the sensitivity of the GMI sensor S will be described.

[0019] <Sensitivity Enhancement of GMI Sensor S 1> FIG. 2 shows an example of the pulsed current supplied to the magnetic body M of the GMI sensor S and the coil voltage generated in the coil C according to the pulsed current. The horizontal axis in FIG. 2 represents time, and the vertical axis represents the pulsed current and the coil voltage. In FIG. 2, corresponding to the rise of the pulsed current flowing through the magnetic body M, a pulsed voltage with a peak voltage value Vp1 on the positive voltage side is excited in the coil C. In other words, based on the peak voltage value Vp1, the magnitude of the magnetic field in the measurement region where the GMI sensor S is arranged can be detected. Here, let the time when the pulsed voltage excited in the coil C reaches the peak voltage value Vp1 be t1.

[0020] Also, corresponding to the fall of the pulsed current flowing through the magnetic body M, a pulsed voltage with a peak voltage value -Vp2 on the negative voltage side is excited in the coil C. Here, let the time when the pulsed voltage excited in the coil C reaches the peak voltage value -Vp2 be t2. For example, the absolute value of the differential voltage value Eout (=Vp1 + Vp2) between the peak voltage value Vp1 on the positive voltage side and the peak voltage value Vp2 on the negative voltage side is larger than the absolute value of the peak voltage on the positive voltage side Vp1 or the absolute value of the peak voltage on the negative voltage side Vp2.

[0021] If the magnitude of the magnetic field in the measurement area is the same but the direction of the magnetic field is opposite, the pulse voltage of coil C excited in response to the rising edge of the pulse current flowing through magnetic body M will be a negative voltage pulse with a peak voltage value of -Vp1. And the pulse voltage of coil C excited in response to the falling edge of the pulse current flowing through magnetic body M will be a positive voltage pulse with a peak voltage value of +Vp2.

[0022] Even in this case, the absolute value (Vp1 + Vp2) of the differential voltage value Eout (= -Vp1 - Vp2) is greater than the absolute value Vp1 of the negative-side peak voltage or the absolute value Vp2 of the positive-side peak voltage. Therefore, by determining the magnitude of the magnetic field in the measurement area where the GMI sensor S is located based on the larger differential voltage value Eout, the magnetic field detection sensitivity is improved. In this embodiment, detecting the differential voltage value between the positive-side peak voltage and the negative-side peak voltage is called Pk-Pk detection.

[0023] Fig. 3 shows an example of a magnetic detection circuit 10 using a GMI sensor S. Fig. 3 shows an example of a circuit that detects magnetic fields with high sensitivity using a GMI sensor S. The magnetic detection circuit 10 includes a GMI sensor S, a pulse supply circuit 11, a buffer circuit 12, a first sample-and-hold circuit 13, a second sample-and-hold circuit 14, and an amplifier circuit 15.

[0024] The pulse supply circuit 11 generates a pulse current and supplies it to the magnetic material M of the GMI sensor S. The pulse supply circuit 11 also generates a first timing signal and a second timing signal with two different timings, and supplies the first timing signal to the first sample-and-hold circuit 13 and the second timing signal to the second sample-and-hold circuit 14. The buffer circuit 12 supplies the output voltage of the GMI sensor S to the first sample-and-hold circuit 13 and the second sample-and-hold circuit 14 in the subsequent stage.

[0025] The first sample hold circuit 13 samples the output voltage of the GMI sensor S at the timing indicated by the first timing signal received from the pulse supply circuit 11. For example, the timing indicated by the first timing signal corresponds to the rising edge of the pulse current flowing through the magnetic body M, and is the timing when the pulse voltage excited in the coil C reaches the peak voltage value. As an example, the timing indicated by the first timing signal is the time t1 in FIG. 2.

[0026] The second sample hold circuit 14 samples the output voltage of the GMI sensor S at the timing indicated by the second timing signal received from the pulse supply circuit 11. For example, the timing indicated by the second timing signal corresponds to the falling edge of the pulse current flowing through the magnetic body M, and is the timing when the pulse voltage excited in the coil C reaches the peak voltage value. As an example, the timing indicated by the second timing signal is the time t2 in FIG. 2.

[0027] The amplifier circuit 15 amplifies the difference between the voltage value sampled by the first sample hold circuit 13 and the voltage value sampled by the second sample hold circuit 14. In other words, the amplifier circuit 15 amplifies and outputs the difference between the peak voltage value on the positive voltage side and the peak voltage value on the negative voltage side of the pulse voltage excited in response to supplying the pulse current to the magnetic body M. The amplifier circuit 15 includes, for example, a differential amplifier circuit and an auto gain control circuit.

[0028] The above magnetic detection circuit 10 can output the differential voltage value Eout described in FIG. 2 or a voltage value obtained by multiplying the differential voltage value Eout by a predetermined amplification factor. Therefore, the magnetic detection circuit 10 using Pk - Pk detection can improve the detection sensitivity of the magnetic field by the GMI sensor S. Next, a second technique for increasing the sensitivity of the GMI sensor S will be described.

[0029] <Sensitivity improvement of GMI sensor S 2> FIG. 4 shows an example of a configuration for reducing magnetic noise around the GMI sensor S. A spatially uniform magnetic field, such as the geomagnetic field, is often applied to the measurement area where the GMI sensor S is placed. Such a spatially uniform magnetic field is superimposed on the detection signal of the GMI sensor S as magnetic noise. For example, when detecting a weak magnetic field that is the same level as or weaker than the magnetic noise, it can be difficult to separate the magnetic noise from the signal, resulting in a decrease in detection sensitivity.

[0030] Therefore, as shown in Figure 4, two sensors are used: GMI sensor S1 for acquiring a sensing signal and GMI sensor S2 for acquiring a reference signal. For example, GMI sensor S1 is placed in an area close to a target source, which is a source of a weak magnetic field, and detects a magnetic field in which the weak magnetic field generated by the target source is superimposed on the geomagnetic field. As an example, GMI sensor S1 is placed 10 mm away from the target source.

[0031] In the GMI sensor S1, for example, when a pulse current flows through the magnetic body M, a pulse voltage having a positive peak voltage value +Vs1 and a negative peak voltage value -Vs2 is excited in the coil C. The peak voltage values ​​+Vs1 and -Vs2 correspond to a magnetic field in which a weak magnetic field and the geomagnetic field are superimposed. In other words, the sensing signal acquired by the GMI sensor S1 corresponds to a magnetic field in which a weak magnetic field and the geomagnetic field are superimposed.

[0032] The GMI sensor S2 is placed in an area far enough away from the target source that it can barely detect the weak magnetic field generated by the target source. In this case, the GMI sensor S2 detects the earth's magnetic field. For example, the GMI sensor S2 is placed 30 mm away from the GMI sensor S1, or 40 mm away from the target source.

[0033] In the GMI sensor S2, for example, when a pulsed current flows through the magnetic body M, a pulsed voltage having a peak voltage value +Vr1 on the positive voltage side and a peak voltage value -Vr2 on the negative voltage side is excited in the coil C. The peak voltage values +Vr1 and -Vr2 are values corresponding to the geomagnetism. In other words, the reference signal that can be obtained by the GMI sensor S2 is a signal corresponding to the geomagnetism.

[0034] From the above, it can be seen that the signal corresponding to the weak magnetic field can be obtained by subtracting the reference signal from the sensing signal. For example, by subtracting the peak voltage value +Vr1 by the GMI sensor S2 from the peak voltage value +Vs1 by the GMI sensor S1, the detection result (Vs1 - Vr1) of the weak magnetic field with the influence of the geomagnetism reduced can be obtained. Thus, by using two sensors, a voltage value corresponding to the magnitude of the weak magnetic field can be extracted, so the configuration shown in FIG. 4 can improve the detection sensitivity of the magnetic field.

[0035] Note that the configuration shown in FIG. 4 and the configuration using the Pk - Pk detection described in FIGS. 2 and 3 may be combined. For example, let the detection result of the magnetic field by the GMI sensor S1 be the differential voltage value Eout1 = Vs1 + Vs2 of the peak voltage value +Vs1 on the positive voltage side and the peak voltage value -Vs2 on the negative voltage side. Similarly, let the detection result of the magnetic field by the GMI sensor S2 be the differential voltage value Eout2 = Vr1 + Vr2 of the peak voltage value +Vr1 on the positive voltage side and the peak voltage value -Vr2 on the negative voltage side.

[0036] And let the voltage value corresponding to the magnitude of the weak magnetic field be Eout1 - Eout2 = (Vs1 + Vs2) - (Vr1 + Vr2). Thereby, after improving the detection sensitivity of the magnetic fields of the GMI sensor S1 and the GMI sensor S2, the voltage value corresponding to the magnitude of the weak magnetic field is extracted, so the detection sensitivity of the magnetic field can be further improved. Next, a technique for widening the measurement range of the GMI sensor S will be described.

[0037] <Wide Range of the GMI Sensor S> 5 shows an example of a magnetic detection circuit 10 that applies a feedback magnetic field to a GMI sensor S. As described above, the GMI sensor S may measure a magnetic field at a position where a spatially uniform magnetic field, such as the geomagnetic field, is applied. In other words, the output signal of the GMI sensor S is a signal voltage on which a voltage corresponding to the spatially uniform magnetic field (e.g., the geomagnetic field) applied to the GMI sensor S is superimposed, resulting in a narrow measurement range (dynamic range).

[0038] Therefore, the magnetic detection circuit 10 shown in Figure 5 is configured to apply a feedback magnetic field to the GMI sensor S to reduce this offset voltage. The magnetic detection circuit 10 includes the GMI sensor S, a pulse supply circuit 11, a detection circuit 16, a feedback circuit 17, and a feedback coil 18. The pulse supply circuit 11 operates in the same manner as the pulse supply circuit 11 described in Figure 3, so its description will be omitted here.

[0039] The detection circuit 16 receives the output of the GMI sensor S and outputs the peak voltage value on the positive voltage side or the peak voltage value on the negative voltage side of the pulse voltage excited in response to the supply of the pulse current to the magnetic material M of the GMI sensor S. The detection circuit 16 may also output the differential voltage value between the peak voltage value on the positive voltage side and the peak voltage value on the negative voltage side of the excited pulse voltage. The detection circuit 16 includes, for example, the buffer circuit 12, first sample-and-hold circuit 13, second sample-and-hold circuit 14, and amplifier circuit 15 described in FIG. 3.

[0040] The feedback circuit 17 generates a feedback signal corresponding to the DC component of the voltage signal output by the detection circuit 16, and supplies the generated feedback signal to the feedback coil 18. In other words, the feedback circuit 17 generates a feedback signal based on the voltage corresponding to the geomagnetic component detected by the GMI sensor S, and supplies the feedback signal to the feedback coil 18. The feedback circuit 17 includes, for example, a high-pass filter, an amplifier circuit, etc. The feedback signal has a DC component.

[0041] The feedback coil 18 is disposed so as to surround the GMI sensor S. A current corresponding to the feedback signal flows through the feedback coil 18, applying a uniform magnetic field to the GMI sensor S. The winding direction of the feedback coil 18 is determined so that the direction of the magnetic field applied to the GMI sensor S is opposite to the direction of the geomagnetic field. It is also desirable to determine in advance the signal strength of the feedback signal, the number of turns of the feedback coil 18, the size of the feedback coil 18, etc. so that the absolute value of the magnitude of the magnetic field applied to the GMI sensor S by the feedback coil 18 is approximately equal to the absolute value of the magnitude of the geomagnetic field applied to the GMI sensor S.

[0042] In the magnetic detection circuit 10 described above, the feedback coil 18 applies a magnetic field to the GMI sensor S so as to reduce the magnitude of the geomagnetic field at the location where the GMI sensor S is located. This allows the magnetic detection circuit 10 to reduce the component corresponding to the geomagnetic field from the voltage output by the GMI sensor S, thereby widening the measurement range. Note that it is desirable for the absolute value of the magnitude of the magnetic field applied to the GMI sensor S by the feedback coil 18 to match the absolute value of the magnitude of the geomagnetic field at the GMI sensor S, but it goes without saying that the measurement range can be widened even if the two do not match.

[0043] However, when improving multiple characteristics of a GMI sensor S, simply combining various technologies may not be enough to achieve the goal. For example, the configuration shown in Figure 4 requires two independent detection circuits corresponding to the two GMI sensors S, resulting in a large circuit size. Furthermore, if the configuration shown in Figure 5 is applied to the two GMI sensors S shown in Figure 4, a feedback circuit 17 and feedback coil 18 are required for each of the two GMI sensors S, further increasing the circuit size.

[0044] Therefore, it has been difficult to construct a magnetic sensor that is small, has high sensitivity, and has a wide measurement range. Therefore, a magnetic sensor according to this embodiment that is small and has improved characteristics will be described below.

[0045] 6 shows an example of the configuration of a magnetic sensor module 20 according to this embodiment. The magnetic sensor module 20 measures the magnetic field in a measurement area. As will be described later, a portion of the magnetic sensor module 20 is placed in the measurement area, and measures the magnetic field at the location in the measurement area where the portion of the magnetic sensor module 20 is located. The magnetic sensor module 20 includes a pulse supply circuit 21, a magnetic body 22, a first coil 23, a second coil 24, a first filter 25, a first signal detection circuit 26, a second filter 27, a second signal detection circuit 28, a feedback circuit 29, and a detection signal output circuit 30.

[0046] The pulse supply circuit 21 generates a pulse current and supplies the generated pulse current to the magnetic body 22. Similarly to the pulse supply circuit 11 described in FIG. 3, the pulse supply circuit 21 generates a first timing signal and a second timing signal having two different timings and supplies them to the first signal detection circuit 26. The pulse supply circuit 21 further generates a third timing signal and a fourth timing signal having two different timings and supplies them to the second signal detection circuit 28. The third timing signal and the fourth timing signal will be described later.

[0047] The magnetic body 22 has the shape of a wire extending in the longitudinal direction. The length of the magnetic body 22 is, for example, about 40 mm. The magnetic body 22 is an amorphous magnetic body, similar to the magnetic body M described in FIG. 1. The magnetic body 22 forms a plurality of magnetic domains whose polarity differs in the longitudinal direction and whose magnetization direction is oriented in the lateral direction. One end of the magnetic body 22 is connected to the pulse supply circuit 21, and the other end opposite to the one end of the magnetic body 22 is connected to a reference potential such as ground.

[0048] The first coil 23 is wound around a first region in the longitudinal direction of the magnetic body 22. The first region is a region on one end side of the magnetic body 22. The first region is, for example, a region extending from one end of the magnetic body 22 to approximately 10 mm in the longitudinal direction. The first region of the magnetic body 22 and the first coil 23 function as, for example, the GMI sensor S described with reference to FIG. 1. In other words, when a pulse current is supplied to the magnetic body 22, a voltage corresponding to the magnetic field of the first region is excited in the first coil 23.

[0049] The second coil 24 is wound around a second region of the magnetic body 22, which is different from the first region in the longitudinal direction. The second region is a region on the other end side opposite one end of the magnetic body 22. The second region is, for example, a region extending approximately 10 mm in the longitudinal direction from the other end of the magnetic body 22. One end of the second coil 24 is electrically connected to the first coil 23, and the other end opposite the one end of the second coil 24 is connected to a reference potential. The second region of the magnetic body 22 and the second coil 24 function as, for example, the GMI sensor S described with reference to FIG. 1. In other words, when a pulse current is supplied to the magnetic body 22, a voltage corresponding to the magnetic field in the second region is excited in the second coil 24.

[0050] In this way, the magnetic body 22, the first coil 23, and the second coil 24 function as two GMI sensors S. For example, when measuring the magnetic field of a measurement area using the magnetic detection circuit 10, the first area of ​​the magnetic body 22 and the first coil 23 are arranged within the measurement area, and the second area of ​​the magnetic body 22 and the second coil 24 are arranged outside the measurement area. For example, the first area of ​​the magnetic body 22 and the first coil 23 function as the GMI sensor S1 for acquiring a sensing signal, as described in FIG. 4, and the second area of ​​the magnetic body 22 and the second coil 24 function as the GMI sensor S2 for acquiring a reference signal.

[0051] The first filter 25 is provided between the first coil 23 and the first signal detection circuit 26, and reduces the DC component of the signal propagating from the first coil 23 to the first signal detection circuit 26. The first filter 25 is, for example, a high-pass filter. The first filter 25 may also be a capacitor.

[0052] The first signal detection circuit 26 detects a first signal based on a voltage excited in the first coil 23 in response to the supply of a pulse current to the magnetic body 22. The first signal detection circuit 26 detects, as the first signal, a pulse voltage obtained by reducing the DC component of the voltage output from the first coil 23 by the first filter 25. The first signal detection circuit 26 may perform the Pk-Pk detection described with reference to FIGS.

[0053] The first signal detection circuit 26 detects, for example, the difference between the peak voltage value on the positive voltage side and the peak voltage value on the negative voltage side of the pulse voltage excited in response to the supply of a pulse current to the magnetic body 22, as the first signal. The first signal detection circuit 26 has, for example, a buffer circuit 12, a first sample-and-hold circuit 13, a second sample-and-hold circuit 14, and an amplifier circuit 15, like the magnetic detection circuit 10 described in FIG. 3. The first signal detection circuit 26 samples two peak voltage values ​​output by the first coil 23 in response to the rising and falling edges of the pulse current flowing through the magnetic body 22. The first signal detection circuit 26 samples the two peak voltage values ​​in response to the first timing signal and the second timing signal supplied from the pulse supply circuit 21.

[0054] Since the first coil 23 is connected in series to the second coil 24, the first signal is a voltage signal in which the voltage excited in the first coil 23 and the voltage excited in the second coil 24 are superimposed. For example, when a pulse current flows through the magnetic body 22, the peak voltage value on the positive voltage side excited in the first coil 23 is +Vs1, the peak voltage value on the negative voltage side is -Vs2, and the peak voltage value on the positive voltage side excited in the second coil 24 is +Vr1, and the peak voltage value on the negative voltage side is -Vr2.

[0055] In this case, for example, the peak voltage value sampled by the first signal detection circuit 26 in response to the first timing signal is a voltage value Vs1+Vr1 obtained by superimposing the peak voltage value Vr1 excited in the second coil 24 on the peak voltage value Vs1 excited in the first coil 23. Similarly, the peak voltage value sampled by the first signal detection circuit 26 in response to the second timing signal is a voltage value −Vs2−Vr2.

[0056] Therefore, the difference between the peak voltage value on the positive voltage side and the peak voltage value on the negative voltage side detected by the first signal detection circuit 26 is Vs1+Vr1+Vs2+Vr2=Eout1+Eout2. Here, as described in FIG. 4, Eout1=Vs1+Vs2 and Eout2=Vr1+Vr2. The first signal detection circuit 26 supplies the detected first signal (differential voltage Eout1+Eout2) to the detection signal output circuit 30.

[0057] The second filter 27 is provided between the second coil 24 and the second signal detection circuit 28, and reduces the DC component of the signal propagating from the second coil 24 to the second signal detection circuit 28. The second filter 27 is, for example, a high-pass filter, similar to the first filter 25. The second filter 27 may be a capacitor.

[0058] The second signal detection circuit 28 detects a second signal based on a voltage excited in the second coil 24 in response to the supply of a pulse current to the magnetic body 22. The second signal detection circuit 28 detects, as the second signal, a pulse voltage obtained by reducing the DC component of the voltage output from the second coil 24 by the second filter 27. The second signal detection circuit 28 may perform the Pk-Pk detection described with reference to FIGS. 2 and 3.

[0059] The second signal detection circuit 28, similar to the first signal detection circuit 26, detects, as a second signal, the difference between the peak voltage value on the positive voltage side and the peak voltage value on the negative voltage side of the pulse voltage excited in response to the supply of the pulse current to the magnetic body 22. The second signal detection circuit 28 has, for example, a buffer circuit 12, a first sample-and-hold circuit 13, a second sample-and-hold circuit 14, and an amplifier circuit 15, like the magnetic detection circuit 10 described with reference to FIG. 3. The second signal detection circuit 28 samples two peak voltage values ​​output by the second coil 24 in response to the rising and falling edges of the pulse current flowing through the magnetic body 22.

[0060] The second signal detection circuit 28 samples two peak voltage values ​​in response to a third timing signal and a fourth timing signal supplied from the pulse supply circuit 21. The third timing signal may be the same as the first timing signal, and the fourth timing signal may be the same as the second timing signal. For example, if the peak voltage value on the positive voltage side excited in the second coil 24 is +Vr1 and the peak voltage value on the negative voltage side is −Vr2, the peak voltage value sampled by the second signal detection circuit 28 with the third timing signal is +Vr1, and the peak voltage value sampled with the fourth timing signal is −Vr2.

[0061] Therefore, the difference between the peak voltage value on the positive voltage side and the peak voltage value on the negative voltage side detected by the second signal detection circuit 28 is Vr1+Vr2=Eout2. The second signal detection circuit 28 supplies the detected second signal (difference voltage Eout2) to the feedback circuit 29 and the detection signal output circuit 30.

[0062] The feedback circuit 29 supplies a signal based on the second signal as a feedback signal to the first coil 23 and the second coil 24. The feedback circuit 29 generates a feedback signal that causes the first coil 23 and the second coil 24 to generate a voltage that has approximately the same absolute value as, but a different sign from, the voltage excited in the first coil 23 and the second coil 24 by the geomagnetism. The feedback circuit 29 supplies the generated feedback signal between the first coil 23 and the first filter 25.

[0063] Since the second signal detected by the second signal detection circuit 28 is the detection result of the voltage excited by the geomagnetic field, the feedback circuit 29 can generate the feedback signal by, for example, having an amplifier circuit that amplifies the second signal by a predetermined factor. By supplying such a feedback signal to the first coil 23 and the second coil 24, the feedback circuit 29 can reduce the voltage excited in the first coil 23 and the second coil 24 by the geomagnetic field.

[0064] Therefore, the first coil 23 and the first region of the magnetic body 22, which function as a GMI sensor, can widen the measurement range, as described with reference to Fig. 5. In other words, the second coil 24, the second signal detection circuit 28, the feedback circuit 29, and the first coil 23 function similarly to the GMI sensor S described with reference to Fig. 5. For example, the second coil 24 and the second region of the magnetic body 22 have the function of the GMI sensor S shown in Fig. 5, the second signal detection circuit 28 has the function of the detection circuit 16 that detects components of the geomagnetic field, and the feedback circuit 29 has the function of the feedback circuit 17 that generates a feedback signal.

[0065] Furthermore, since the feedback circuit 29 supplies a feedback signal directly to the first coil 23, the first coil 23 functions as part of the GMI sensor and also functions as the feedback coil 18 shown in FIG. 5. In this way, the magnetic sensor module 20 according to this embodiment can widen the measurement range without the feedback coil 18. In other words, the magnetic sensor module 20 can widen the measurement range without increasing the size of the module by using the feedback coil 18.

[0066] The feedback signal supplied to the first coil 23 by the feedback circuit 29 is a DC signal, so it is reduced by the first filter 25 and has almost no effect on the detection result of the first signal detection circuit 26. Similarly, the feedback signal is reduced by the second filter 27 and has almost no effect on the detection result of the second signal detection circuit 28.

[0067] The detection signal output circuit 30 outputs a detection signal corresponding to the magnetic field of the measurement region based on the first signal detected by the first signal detection circuit 26 and the second signal detected by the second signal detection circuit 28. The detection signal output circuit 30 outputs, as the detection signal, a signal (Eout1-Eout2=Vs1+Vr1-Vs2-Vr2) obtained by subtracting a signal having twice the signal amplitude of the second signal (Eout2) detected by the second signal detection circuit 28 from the first signal (Eout1+Eout2) detected by the first signal detection circuit 26.

[0068] This allows the magnetic sensor module 20 to have the function of reducing magnetic noise around the GMI sensor S described in Fig. 4. In other words, the first coil 23 and the first region of the magnetic body 22 function as the GMI sensor S1 for acquiring the sensing signal in Fig. 4, and the second coil 24 and the second region of the magnetic body 22 function as the GMI sensor S2 for acquiring the reference signal in Fig. 4. Therefore, the magnetic sensor module 20 can improve the detection sensitivity of the magnetic field.

[0069] As described above, the magnetic sensor module 20 according to this embodiment detects the pulse voltages Pk-Pk input to the first signal detection circuit 26 and the second signal detection circuit 28, thereby improving the magnetic field detection sensitivity as described with reference to Figures 2 and 3. Furthermore, the magnetic sensor module 20 supplies a feedback signal to the first coil 23 and the second coil 24 based on the detection result of a uniform magnetic field using the second coil 24 and the magnetic body 22, thereby widening the magnetic field measurement range as described with reference to Figure 5. Furthermore, the magnetic sensor module 20 can reduce the influence of a uniform magnetic field applied from the outside, so it can detect a weak magnetic field without being placed in a magnetically shielded room or the like.

[0070] In the magnetic sensor module 20, the other end opposite to one end of the first coil 23 is connected to one end of the second coil 24, and the other end opposite to the one end of the second coil 24 is connected to a reference potential. In this way, in the magnetic sensor module 20, the first coil 23 and the second coil 24 are connected in series, and therefore, by one feedback circuit 29 supplying a feedback signal to one end of the first coil 23, a common feedback can be provided to the first coil 23 and the second coil 24. In other words, the magnetic sensor module 20 can reduce the circuit size by sharing the circuit and wiring that provide feedback to the first coil 23 and the second coil 24.

[0071] Furthermore, the magnetic sensor module 20 can improve the magnetic field detection sensitivity as described in FIG. 4 by subtracting the second signal detected using the second coil 24 and the second region of the magnetic material 22 from the first signal detected using the first coil 23 and the first region of the magnetic material 22. The magnetic sensor module 20 can achieve the above two techniques for improving the magnetic field detection sensitivity and for widening the magnetic field measurement range with a simple circuit configuration, without using a coil covering the GMI sensor, multiple feedback circuits, complex arithmetic circuits, etc. In other words, the magnetic sensor module 20 according to this embodiment can provide a magnetic sensor that is small, has higher sensitivity, and has a wider measurement range.

[0072] <Configuration example of detection signal output circuit 30> 7 shows an example of the configuration of the detection signal output circuit 30 according to this embodiment. FIG. 7(a) shows an example of the configuration of the detection signal output circuit 30 using three operational amplifiers. The first operational amplifier 41 outputs a third signal (Eout1) obtained by subtracting the second signal (Eout2) from the first signal (Eout1+Eout2). The second operational amplifier 42 outputs a second signal (Eout2) obtained by subtracting a reference potential (0 V) from the second signal (Eout2). The third operational amplifier 43 outputs a signal (Eout1-Eout2) obtained by subtracting the second signal (Eout2) from the third signal (Eout1) as the detection signal.

[0073] FIG. 7(b) shows an example configuration of a detection signal output circuit 30 using digital signal processing. A first AD converter 44 converts a first signal (Eout1+Eout2) into a first digital signal. A second AD converter 45 converts a second signal (Eout2) into a second digital signal. A CPU 46 outputs a signal (Eout1-Eout2) obtained by subtracting twice the value of the second signal from the first signal as a detection signal. As described above, the detection signal output circuit 30 can be configured using a variety of simple circuits, etc.

[0074] <Configuration example of feedback circuit 29> 8A and 8B show an example of the configuration of a feedback circuit 29 according to this embodiment. Fig. 8A shows an example of the configuration of the feedback circuit 29 using a resistor and an operational amplifier. The feedback circuit 29 has a first resistor 51, a second resistor 52, an operational amplifier 53, a reference potential 54, and a power supply voltage 55.

[0075] The first resistor 51 is disposed between the reference potential 54 and the power supply voltage 55, and generates a predetermined comparison potential by a voltage drop. The operational amplifier 53 receives the comparison potential and the second signal supplied from the second signal detection circuit 28, and outputs a predetermined amplified voltage as a feedback signal when the second signal becomes greater than the comparison potential. The predetermined amplified voltage is, for example, a voltage value determined in advance by detecting a uniform magnetic field. As described above, by inserting an amplifier inside the feedback circuit 29, it is possible to reduce the backflow of the voltage excited in the first coil 23 to the upstream stage of the feedback circuit 29.

[0076] 8(b) shows an example of the configuration of the first filter 25 and the feedback circuit 29. Fig. 8(b) shows an example in which the first filter 25 and the feedback circuit 29 are configured using a bias tee 56. A first terminal T1 of the bias tee 56 is connected to the second signal detection circuit 28, a second terminal T2 is connected between the first coil 23 and the first filter 25, and a third terminal T3 is connected to the first signal detection circuit 26.

[0077] The bias tee 56 propagates the second signal, which is a DC signal output by the second signal detection circuit 28, as a feedback signal to one end of the first coil 23, while preventing the second signal from propagating to the first signal detection circuit 26. The bias tee 56 also propagates the pulse voltage excited in the first coil 23 to the first signal detection circuit 26. As described above, the feedback circuit 29 can be configured using various simple circuits, etc.

[0078] 2 and 3, the magnetic sensor module 20 according to this embodiment has been described above as an example in which the first signal detection circuit 26 and the second signal detection circuit 28 perform the Pk-Pk detection described above, but this is not limiting. One of the first signal detection circuit 26 and the second signal detection circuit 28 may perform the Pk-Pk detection, or alternatively, neither may perform the Pk-Pk detection. In this case, instead of Pk-Pk detection, the first signal detection circuit 26 and the second signal detection circuit 28 detect the peak voltage value on the positive voltage side or the negative voltage side of the pulse voltage excited in response to the supply of a pulse current to the magnetic body 22.

[0079] As described above, the magnetic sensor module 20 according to this embodiment operates as a small-sized magnetic sensor with higher sensitivity and a wider measurement range. Such a magnetic sensor module 20 can be used in electronic compasses, current sensors, biomagnetic measurements, etc. For example, it can be used in headgear devices that detect electroencephalogram signals.

[0080] 9 shows an example of the configuration of an interface device 60 according to this embodiment. The interface device 60 is worn on the head of a human body and detects a weak magnetic field corresponding to an electroencephalogram signal exchanged within the brain. The interface device 60 includes a plurality of magnetic sensor modules 20, a frame 61, and an analysis circuit 62.

[0081] The frame 61 is worn on the head of a human body. The plurality of magnetic sensor modules 20 are detachably attached to the frame 61. The attachment positions of the magnetic sensor modules 20 on the frame 61 are preferably configured to be finely adjustable. The frame 61 is preferably configured to allow attachment of the plurality of magnetic sensor modules 20 in a predetermined arrangement such as the 10-20 method.

[0082] The magnetic sensor module 20 is attached to the frame 61 so that the first region around which the first coil 23 of the magnetic body 22 is wound is closer to the head than the second region around which the second coil 24 of the magnetic body 22 is wound. In this way, the magnetic sensor module 20 is attached so that the first region of the magnetic body 22 and the first coil 23 for acquiring the sensing signal are closer to the head than the second region of the magnetic body 22 and the second coil 24 for acquiring the reference signal.

[0083] With this arrangement, the magnetic sensor module 20 can operate as a magnetic sensor with higher sensitivity and a wider measurement range, as described above. Furthermore, since the magnetic body 22 extends in the longitudinal direction and the first coil 23 and the second coil 24 are wound around the magnetic body 22, the magnetic sensor module 20 has a cylindrical shape extending in the longitudinal direction. The frame 61 is configured to be attached so that the longitudinal direction of the cylindrical magnetic sensor module 20 is approximately perpendicular to the surface of the head, and therefore the area in which the magnetic sensor module 20 is attached can be reduced.

[0084] In other words, the frame 61 can increase the space between adjacent magnetic sensor modules 20, making it possible to easily attach and detach the magnetic sensor modules 20 and also facilitating the arrangement of wiring between the magnetic sensor modules 20 and the outside. Furthermore, more magnetic sensor modules 20 can be attached to the frame 61 as needed.

[0085] The analysis circuit 62 is provided on the frame 61 and is electrically connected to the detection signal output circuits 30 of the multiple magnetic sensor modules 20. The analysis circuit 62 analyzes the detection signals of the multiple magnetic sensor modules 20 to generate a status signal indicating the state of the head. Because the magnetic sensor modules 20 can output detection signals independently, the analysis circuit 62 can omit a circuit for processing the detection signals from the multiple sensing signals. Therefore, the analysis circuit 62 only needs to include, for example, a simple digital signal processing circuit, and the circuit size can be reduced. In other words, the multiple magnetic sensor modules 20 and the analysis circuit 62 can be formed in a size that allows for easy implementation in the frame 61.

[0086] The present invention has been described above using embodiments, but the technical scope of the present invention is not limited to the scope described in the above embodiments, and various modifications and changes are possible within the scope of the gist of the present invention. For example, all or part of the device can be configured by functionally or physically distributing or integrating any unit. Furthermore, new embodiments resulting from any combination of multiple embodiments are also included in the embodiments of the present invention. The effects of the new embodiments resulting from the combination also have the effects of the original embodiments. [Explanation of symbols]

[0087] 10 Magnetic detection circuit 11 Pulse supply circuit 12 Buffer circuit 13 First sample and hold circuit 14 Second sample and hold circuit 15 Amplification circuit 20 Magnetic Sensor Module 21 Pulse supply circuit 22 Magnetic material 23 First coil 24 Second coil 25 First filter 26 First signal detection circuit 27 Second Filter 28 Second signal detection circuit 29 Feedback Circuit 30 Detection signal output circuit 41 First operational amplifier 42 Second operational amplifier 43 Third operational amplifier 44 1st AD converter 45 Second AD converter 46 CPU 51 1st resistance 52 2nd resistor 53 Operational Amplifier 54 Reference potential 55 Power supply voltage 56 Bias Tee 60 Interface Device 61 frames 62 Analysis circuit

Claims

1. A magnetic sensor module for measuring a magnetic field in a measurement area, a magnetic body that forms a plurality of magnetic domains whose polarity differs in the longitudinal direction and whose magnetization direction is oriented in the lateral direction; a first coil wound around a first region in the longitudinal direction of the magnetic body; a second coil wound around a second region of the magnetic body that is different from the first region in the longitudinal direction of the magnetic body and electrically connected to the first coil; a pulse supply circuit for supplying a pulse current to the magnetic body; a first signal detection circuit that detects a first signal based on a voltage excited in the first coil in response to the pulse current being supplied to the magnetic body; a first filter provided between the first coil and the first signal detection circuit, the first filter reducing a DC component of a signal propagating to the first signal detection circuit; a second signal detection circuit that detects a second signal based on a voltage excited in the second coil in response to the pulse current being supplied to the magnetic body; a second filter provided between the second coil and the second signal detection circuit, the second filter reducing a DC component of a signal propagating to the second signal detection circuit; a feedback circuit that supplies a signal based on the second signal as a feedback signal to the first coil and the second coil; a detection signal output circuit that outputs, as a detection signal, a signal obtained by subtracting a signal having twice the signal amplitude of the second signal detected by the second signal detection circuit from the first signal detected by the first signal detection circuit; A magnetic sensor module comprising:

2. the first region of the magnetic body and the first coil are disposed within the region of the measurement target region, the second region of the magnetic body and the second coil are disposed outside the region to be measured. The magnetic sensor module according to claim 1 .

3. 2. The magnetic sensor module according to claim 1, wherein at least one of the first signal detection circuit and the second signal detection circuit detects a peak voltage value of a pulse voltage excited in response to supplying the pulse current to the magnetic material.

4. 2. The magnetic sensor module of claim 1, wherein at least one of the first signal detection circuit and the second signal detection circuit detects the difference between the peak voltage value on the positive voltage side and the peak voltage value on the negative voltage side of the pulse voltage excited in response to the supply of the pulse current to the magnetic material.

5. The magnetic sensor module according to claim 1 , wherein the feedback circuit includes an amplifier circuit that amplifies the second signal by a predetermined factor.

6. The magnetic sensor module according to claim 1 , wherein the first filter and the feedback circuit are configured by a bias tee.

7. The magnetic sensor module according to claim 1 , wherein the magnetic material is an amorphous magnetic material.

8. a frame to be attached to the head of a human body; The magnetic sensor module according to claim 1 , which is detachably attached to the frame. Equipped with the magnetic sensor module is attached to the frame such that the first region of the magnetic body around which the first coil is wound is closer to the head than the second region of the magnetic body around which the second coil is wound. Interface device.

9. A plurality of the magnetic sensor modules are attached to the frame; an analysis circuit provided on the frame, electrically connected to the detection signal output circuits of the plurality of magnetic sensor modules, and configured to analyze the detection signals of the plurality of magnetic sensor modules and generate a status signal indicating a status of the head; 9. An interface device according to claim 8.

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