Magnetic sensor and its sensitivity measurement method, and magnetic field source detection device

Abstract

To maintain measurement sensitivity and reduce the amount of computation in a sensitivity measurement method of a magnetic sensor.SOLUTION: Provided is a sensitivity measurement method of a magnetic sensor comprising a sensor chip 20 having a magnetism-sensitive element, magnetism collecting bodies 30, 40 for collecting a magnetic field in the sensor chip 20, and a casing for housing the sensor chip 20 and the magnetism collecting bodies 30, 40. The method comprises the steps of: applying a magnetic field to a magnetic sensor 1; and calculating the sensitivity of the magnetic sensor on the basis of a simple average of theoretical magnetic field strength in multiple virtual sensitivity points P uniformly and dispersedly disposed inside the casing and an output value outputted from the sensor chip.SELECTED DRAWING: Figure 10

Description

[Technical Field]

[0001] The present disclosure relates to a magnetic sensor, a method for measuring the sensitivity thereof, and a magnetic field source detection device. [Background technology]

[0002] Non-Patent Document 1 discloses a method for measuring the sensitivity of a magnetic sensor including an MR element. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Adachi, Y. et al., Evaluation of Directional Dependence of Sensitivity for Room-Temperature Magnetic Flux Sensors with Wide Sensitivity Region, IEEE Transactions on Magnetics, 57(2), 4000105, 2021. Summary of the Invention [Problem to be solved by the invention]

[0004] However, the method for measuring the sensitivity of a magnetic sensor described in Non-Patent Document 1 involves assigning a weighting parameter called relative sensitivity to each of multiple sensitivity points, which makes the calculations complicated and in some cases prevents the calculations from converging.

[0005] This disclosure describes a technique for reducing the amount of calculation while maintaining measurement sensitivity in a method for measuring sensitivity of a magnetic sensor. [Means for solving the problem]

[0006] A method for measuring the sensitivity of a magnetic sensor according to one aspect of the present disclosure is a method for measuring the sensitivity of a magnetic sensor that includes a sensor chip having a magnetic sensing element, a magnetic collector that collects a magnetic field at the sensor chip, and a housing that houses the sensor chip and the magnetic collector, in which a magnetic field is applied to the magnetic sensor and the sensitivity of the magnetic sensor is calculated based on the simple average value of theoretical magnetic field strength at multiple virtual sensitivity points that are evenly distributed inside the housing and the output value output from the sensor chip. [Effects of the Invention]

[0007] According to the present disclosure, a technique for reducing the amount of calculation while maintaining measurement sensitivity is provided in a method for measuring sensitivity of a magnetic sensor. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic perspective view showing the appearance of a magnetic sensor 1 according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a schematic exploded perspective view showing the magnetic sensor 1 with the lower case 2 and upper case 3, which are housings, removed. [Figure 3] FIG. 3 is a schematic diagram showing a first example of an arrangement of the sensitivity points P. As shown in FIG. [Figure 4] FIG. 4 is a schematic diagram showing a second example of the arrangement of the sensitivity points P. In FIG. [Figure 5] FIG. 5 is a schematic diagram showing a third example of the arrangement of the sensitivity points P. In FIG. [Figure 6] FIG. 6 is a schematic diagram showing a fourth example of the arrangement of the sensitivity points P. In FIG. [Figure 7] FIG. 7 is a schematic perspective view of a jig 100 used to measure the sensitivity of the magnetic sensor 1. As shown in FIG. [Figure 8] FIG. 8 is a schematic diagram for explaining the positional relationship between the jig 100 and the magnetic sensor 1. As shown in FIG. [Figure 9] FIG. 9 is a graph showing the relationship between the position of the magnetic sensor 1 in the Z direction and the sensitivity g. [Figure 10] FIG. 10 is a graph showing the relationship between the number of sensitivity points P and the calculated sensitivity g. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the technology according to the present disclosure will be described in detail with reference to the accompanying drawings.

[0010] Fig. 1 is a schematic perspective view showing the appearance of a magnetic sensor 1 according to an embodiment of the present disclosure, and Fig. 2 is a schematic exploded perspective view showing the magnetic sensor 1 with a lower case 2 and an upper case 3, which are housings, removed.

[0011] 1 and 2, the magnetic sensor 1 according to this embodiment includes a magnetic sensor module 4, which is the main body, and a lower case 2 and an upper case 3 that house the magnetic sensor module 4. The lower case 2 and the upper case 3 are made of a non-magnetic insulating material such as resin, and the magnetic sensor module 4 is housed in an internal space formed by fitting them together in the Y direction. The magnetic sensor 1 is a rod-shaped body with the Z direction as its longitudinal direction, and the end on the -Z direction side forms the sensor head. Wiring (not shown) connected to the magnetic sensor module 4 is drawn out from the end on the +Z direction side.

[0012] The magnetic sensor module 4 includes a substrate 10, a sensor chip 20 and magnetic collectors 30, 40 mounted on a surface 11 constituting the XZ plane of the substrate 10, a compensation coil C wound around the magnetic collector 30, and molded members 50, 60 fixed to the magnetic collector 30. A magnetically sensitive element (not shown) is integrated on the sensor chip 20. The magnetically sensitive element is not particularly limited as long as it is an element whose electrical resistance changes depending on the direction and strength of magnetic flux, and for example, an MR element or the like can be used.

[0013] The magnetic collectors 30 and 40 are rod-shaped bodies with their longitudinal direction in the Z direction for collecting magnetic flux to the sensor chip 20, and are both made of a highly permeable material such as ferrite. The sensor chip 20 is disposed between the magnetic collectors 30 and 40, which selectively collects the magnetic field in the Z direction, and the collected magnetic field is applied to the sensor chip 20.

[0014] The compensation coil C is made of a wire (coated conductor) wound around the magnetic collector 30 so that the Z direction is the axial direction. The molded members 50 and 60 are made of a non-magnetic insulating material such as resin, and both are fixed to the magnetic collector 30 using an adhesive or the like. Of these, the molded member 50 is provided so as to cover the vicinity of the end of the magnetic collector 30 in the +Z direction, and the molded member 60 is provided so as to cover the vicinity of the end of the magnetic collector 30 in the -Z direction.

[0015] The forming member 50 holds U-shaped pins P1 and P2. One end of the compensation coil C is fixed to one end P1a of the pin P1, and the other end of the compensation coil C is fixed to one end P2a of the pin P2. In this way, one end and both ends of the compensation coil C are located on the forming member 50 side. For this reason, the compensation coil C needs to be wound so as to be folded back near the end of the magnetic collector 30 in the -Z direction, and the forming member 60 is used to assist this folding back.

[0016] The other end P1b of the pin P1 and the other end P2b of the pin P2 are connected to a connector 70 via wires W1 and W2, respectively. Wiring (not shown) is connected to the connector 70. A detection signal corresponding to the direction and strength of the magnetic field applied to the magnetic sensor 1 is output to the wiring connected to the connector 70.

[0017] The magnetic sensor 1 having such a configuration is designed to have a predetermined detection sensitivity to magnetic fields, but due to individual differences in elements, manufacturing variations, etc., the detection sensitivity may not always be as designed. In this embodiment, in order to perform more accurate magnetic detection using the magnetic sensor 1, the sensitivity of the magnetic sensor 1 is measured before actual measurement. A method for measuring the sensitivity of the magnetic sensor 1 will be described below.

[0018] In measuring the sensitivity of the magnetic sensor 1, a known magnetic field is actually applied to the magnetic sensor 1, and an output value output from the sensor chip 20 is measured. The output value V of the sensor chip 20 can be expressed by the following equation (1).

[0019]

number

[0020] In equation (1), g is the sensitivity of the magnetic sensor 1, n is the sensitivity direction of the magnetic sensor 1, and B is the magnetic field vector applied to the magnetic sensor 1. If the strength of the magnetic field to be generated, the distance between the magnetic field source and the magnetic sensor 1, and the sensitivity direction of the magnetic sensor 1 relative to the magnetic field source are known, it is possible to calculate the sensitivity direction n and the theoretical magnetic field strength B applied to the magnetic sensing element, and therefore the actual sensitivity g can be calculated by referring to the output value V of the sensor chip 20.

[0021] However, since the actual magnetic sensor 1 is not a virtual point but a physical device having a predetermined volume, if the magnetic field distribution within the magnetic sensor 1 is not uniform, the magnetic field strength B will vary slightly depending on the position within the magnetic sensor 1. For this reason, the original sensitivity g of the magnetic sensor 1 cannot be accurately calculated from a single sensitivity point defined within the magnetic sensor 1. In this embodiment, such errors are reduced by defining multiple virtual sensitivity points within the magnetic sensor 1.

[0022] The multiple virtual sensitivity points defined within the magnetic sensor 1 are evenly distributed within the housing. For example, as shown in FIG. 3, multiple sensitivity points P are arranged along the magnetic collector 40, the sensor chip 20, and the magnetic collector 30. In the example shown in FIG. 3, one sensitivity point P is arranged on the sensor chip 20, and seven sensitivity points P are arranged on each of the magnetic collectors 30 and 40. These 15 sensitivity points P are arranged in a row in the Z direction, which is the sensitivity axis direction of the magnetic sensor 1, and the arrangement pitch is constant. The position of the sensitivity point P in the X direction is located at the center of the width of the magnetic collector 40, the sensor chip 20, and the magnetic collector 30 in the X direction. The position of the sensitivity point P in the Y direction may be on the surfaces of the magnetic collector 40, the sensor chip 20, and the magnetic collector 30, or may be inside the magnetic collector 40, the sensor chip 20, and the magnetic collector 30.

[0023] Next, the sensitivity of the magnetic sensor 1 is calculated based on the simple average value of the theoretical magnetic field strength B at these multiple sensitivity points P and the output value V of the sensor chip 20. When multiple sensitivity points P are defined, the output value V of the sensor chip 20 can be expressed by the following equation (2).

[0024]

number

[0025] In equation (2), N is the number of sensitivity points P, B(r n ) is the theoretical magnetic field strength at each sensitivity point P. If the strength of the magnetic field to be generated, the distance between the magnetic field source and each sensitivity point P, and the direction of each sensitivity point P relative to the magnetic field source are known, the actual sensitivity g can be calculated by simply averaging the theoretical magnetic field strength B at each sensitivity point P.

[0026] As described above, in this embodiment, the simple average value of the theoretical magnetic field strengths B at a plurality of virtual sensitivity points P that are uniformly distributed inside the housing of the magnetic sensor 1 is calculated, and therefore it is possible to easily calculate the sensitivity g of the magnetic sensor 1 based on the output value V that is actually output from the sensor chip 20. In other words, the simple average value of the magnetic field strengths B at a plurality of sensitivity points P is calculated without assigning a weighting parameter to each sensitivity point P, and therefore the sensitivity g of the magnetic sensor 1 can be calculated by a relatively simple calculation. In other words, if a weighting parameter is assigned to each of a small number of sensitivity points P, not only will it take a long calculation time but there will also be cases where a stable solution cannot be obtained, whereas by setting a large number of sensitivity points P as in this embodiment and calculating the simple average value of the theoretical magnetic field strengths at these points, the amount of calculation is reduced and calculation accuracy is maintained.

[0027] The number of sensitivity points P can be determined based on the size of the sensitivity region, the magnetic field gradient in the region, and the required accuracy, i.e., the allowable error. However, while the greater the number of sensitivity points P, the more accurately the sensitivity g can be calculated, if the number of sensitivity points P is too large, the more complicated the calculation becomes. Considering this point, it is preferable that the number of sensitivity points P is 10 or more and 100 or less in practical use. If the number of sensitivity points P is 10 or more, it becomes possible to reduce the required amount of calculation while maintaining the same or higher calculation accuracy compared to the case where a weighting parameter is assigned to each of several (e.g., five) sensitivity points P and calculation is performed.

[0028] Furthermore, the position of the sensitivity point P does not necessarily have to be a position where the magnetic collector is present, as long as it is inside the housing of the magnetic sensor 1 or in the vicinity thereof.

[0029] 3, the sensitivity points P are arranged in a line in the Z direction, which is the sensitivity axis direction of the magnetic sensor 1; however, the arrangement of the sensitivity points P is not limited to this. For example, as shown in FIG. 4, if the magnetic collectors 30, 40 have a T-shape, the sensitivity points P may be arranged in the X direction on the magnetic collectors 30, 40, and may also be arranged in the Z direction in the portions sandwiching the sensor chip 20. Furthermore, as shown in FIG. 5, if the magnetic collectors 30, 40 have a tapered shape in which the width in the X direction narrows toward the sensor chip 20, the number of sensitivity points P arranged in the X direction may be reduced as they approach the sensor chip 20. Furthermore, as shown in FIG. 6, the sensitivity points P may be three-dimensionally dispersed inside the magnetic collectors 30, 40.

[0030] As described above, in this embodiment, it is possible to accurately calculate the sensitivity g of the magnetic sensor 1 through a relatively simple calculation. As a result, by using the magnetic sensor 1 whose sensitivity has been calculated by the sensitivity measurement method according to this embodiment, it is possible to perform more accurate magnetic measurements. Furthermore, by configuring a magnetic field source detection device by arranging a plurality of such magnetic sensors 1 in an array, it becomes possible to accurately identify the spatial position of the magnetic field source.

[0031] The above describes embodiments of the technology according to the present disclosure, but the technology according to the present disclosure is not limited to the above embodiments, and various modifications are possible within the scope of the gist of the technology, and it goes without saying that these modifications are also included within the scope of the technology according to the present disclosure.

[0032] The technology according to the present disclosure includes, but is not limited to, the following configuration examples.

[0033] A method for measuring the sensitivity of a magnetic sensor according to one aspect of the present disclosure includes a sensor chip having a magnetic sensing element, a magnetic collector that collects a magnetic field on the sensor chip, and a housing that houses the sensor chip and the magnetic collector, and the method applies a magnetic field to the magnetic sensor and calculates the sensitivity of the magnetic sensor based on a simple average value of theoretical magnetic field strengths at multiple virtual sensitivity points that are evenly distributed within the housing and an output value output from the sensor chip. This method enables the sensitivity of the magnetic sensor to be calculated with a small amount of calculation.

[0034] In the magnetic sensor, a plurality of sensitivity points may be arranged on the magnetic collector and the sensor chip, which allows the sensitivity of the magnetic sensor to be calculated more accurately.

[0035] In the above magnetic sensor, the magnetic collector may include first and second magnetic collectors, the sensor chip may be disposed between the first and second magnetic collectors, at least one of the plurality of sensitivity points may be disposed on the sensor chip, and the remaining of the plurality of sensitivity points may be disposed on the first and second magnetic collectors, thereby enabling more accurate calculation of the sensitivity of the magnetic sensor.

[0036] In the magnetic sensor described above, ten or more sensitivity points may be defined, which allows the sensitivity of the magnetic sensor to be calculated more accurately.

[0037] A magnetic sensor according to one aspect of the present disclosure is a magnetic sensor whose sensitivity is calculated by the sensitivity measurement method described above. Also, a magnetic field source detection device according to one aspect of the present disclosure includes a plurality of the magnetic sensors described above. [Example]

[0038] The sensitivity of the magnetic sensor 1 was measured using a jig 100 shown in FIG. 7. The jig 100 includes a plate 110 having an XY plane and eight magnetic field generators 121 to 128 fixed to the surface of the plate 110. The magnetic field generators 121 to 128 include a spherical bobbin 130 and an X-axis coil Cx, a Y-axis coil Cy, and a Z-axis coil Cz wound around the bobbin 130. The X-axis coil Cx is wound so that its coil axis is in the X-axis direction, the Y-axis coil is wound so that its coil axis is in the Y-axis direction, and the Z-axis coil Cz is wound so that its coil axis is in the Z-axis direction. The X-axis coil Cx, the Y-axis coil Cy, and the Z-axis coil Cz are independent coils, and it is possible to generate any magnetic field in any of the three axis directions by passing a current through each coil.

[0039] FIG. 8(a) is a schematic diagram for explaining the positions of the magnetic field generators 121 to 128 on the XY plane. As shown in FIG. 8(a), the four magnetic field generators 121 to 124 are arranged near the four corners of the plate 110, and the four magnetic field generators 125 to 128 are arranged in positions surrounded by these magnetic field generators 121 to 124. In the initial state, the magnetic sensor 1 is arranged in the center of the area surrounded by the magnetic field generators 125 to 128 on the XY plane. As shown in FIG. 8(b), the position of the magnetic sensor 1 in the Z direction in the initial state is arranged at the same height position in the Z direction as the magnetic field generators 121 to 128, relative to the surface of the plate 110. The Z direction position in this initial state is defined as 0 mm.

[0040] In this state, a current is passed through each of the coils Cx, Cy, and Cz included in the magnetic field generating units 121 to 128, and the magnetic field generated thereby is measured by the magnetic sensor 1 to obtain an output value V. This operation is performed one by one for each of the coils Cx, Cy, and Cz included in each of the magnetic field generating units 121 to 128, and an inverse problem is solved using the least squares method or the like from the magnetic field data obtained thereby, thereby determining the output value V at that position. Furthermore, theoretical magnetic field strengths B at multiple sensitivity points P defined within the magnetic sensor 1 are calculated, and the sensitivity g of the magnetic sensor 1 is calculated by solving the above equation (2) based on these.

[0041] Next, while keeping the position of the magnetic sensor 1 fixed in the XY plane, the magnetic sensor 1 is moved in the +Z direction, and the above measurement is performed again at the moved position to obtain the output value V. Furthermore, the theoretical magnetic field strength B at multiple sensitivity points P defined within the magnetic sensor 1 is calculated, and the sensitivity g of the magnetic sensor 1 is calculated by solving the above equation (2) based on these. Here, since the position of the magnetic sensor 1 in the Z direction and the sensitivity g of the magnetic sensor 1 are unrelated, ideally the calculated value of sensitivity g will be constant regardless of the position of the magnetic sensor 1 in the Z direction.

[0042] FIG. 9 is a graph showing the relationship between the position in the Z direction of the magnetic sensor 1 and the sensitivity g. In the example shown in FIG. 9, the actual sensitivity g of the magnetic sensor 1 measured using a Holm-Hertz coil is 45 mV / nT. As shown in FIG. 9, when the number of sensitivity points P defined in the magnetic sensor 1 is one, it can be seen that the calculated sensitivity g changes significantly depending on the position in the Z direction. It was found that the change in the calculated sensitivity g depending on the position in the Z direction becomes smaller as the number of sensitivity points P defined in the magnetic sensor 1 increases.

[0043] Figure 10 is a graph showing the relationship between the number of sensitivity points P and the calculated sensitivity g for two different types of magnetic sensors 1A and 1B. The Z-direction positions of the magnetic sensors 1A and 1B were fixed at 150 mm. The actual sensitivity g of the magnetic sensors 1A and 1B measured using a Holm-Hertz coil was 44.3 mV / nT, as shown by the dashed line. As shown in Figure 10, the calculated sensitivity g became closer to the actual value as the number of sensitivity points P defined within the magnetic sensors 1A and 1B increased.

[0044] Specifically, when the number of sensitivity points P is less than 10, the calculated sensitivity g deviates from the actual sensitivity by 10% or more, whereas when the number of sensitivity points P is set to 11, the deviation is reduced to less than 10%. Furthermore, when the number of sensitivity points P is set to 21, the deviation is less than 5%, and when the number of sensitivity points P is set to 51, the calculated sensitivity g almost matches the actual sensitivity.

[0045] When the number of sensitivity points P is set to 11, one sensitivity point P is defined on the sensor chip 20, and of the remaining 10 sensitivity points P, five are defined on one magnetic collector 30, and another five are defined on the other magnetic collector 40. When the number of sensitivity points P is set to 21, one sensitivity point P is defined on the sensor chip 20, and of the remaining 20 sensitivity points P, ten are defined on one magnetic collector 30, and another ten are defined on the other magnetic collector 40. When the number of sensitivity points P is set to 51, one sensitivity point P is defined on the sensor chip 20, and of the remaining 50 sensitivity points P, 25 are defined on one magnetic collector 30, and another 25 are defined on the other magnetic collector 40. [Explanation of symbols]

[0046] 1,1A,1B magnetic sensor 2 Lower case 3 Upper case 4 Magnetic Sensor Module 10 Substrate 11 Surface 20 sensor chips 30,40 magnetic collector 50,60 Molded parts 70 Connector 100 Jig 110 Plate 121~128 Magnetic generator 130 Bobbin C Compensation coil Cx X-axis coil Cy Y-axis coil Cz Z-axis coil P sensitivity point P1, P2 pins P1a, P2a One end of the pin Other end of P1b, P2b pins W1, W2 wire

Claims

1. A method for measuring sensitivity of a magnetic sensor including a sensor chip having a magnetic sensing element, a magnetic collector that collects a magnetic field on the sensor chip, and a housing that accommodates the sensor chip and the magnetic collector, A method for measuring the sensitivity of a magnetic sensor, comprising applying a magnetic field to the magnetic sensor and calculating the sensitivity of the magnetic sensor based on the simple average value of theoretical magnetic field strength at multiple virtual sensitivity points evenly distributed within the housing and the output value output from the sensor chip.

2. the plurality of sensitive points are arranged on the magnetic collector and on the sensor chip; The method for measuring the sensitivity of a magnetic sensor according to claim 1 .

3. the magnetic collector includes a first magnetic collector and a second magnetic collector, the sensor chip is disposed between the first magnetic collector and the second magnetic collector; At least one of the plurality of sensitive points is disposed on the sensor chip, and the remaining of the plurality of sensitive points are disposed on the first and second magnetic collectors. The method for measuring the sensitivity of a magnetic sensor according to claim 2.

4. 10 or more sensitivity points are defined; The method for measuring the sensitivity of a magnetic sensor according to claim 3.

5. The sensitivity is calculated by the sensitivity measurement method according to any one of claims 1 to 4. Magnetic sensor.

6. a plurality of magnetic sensors according to claim 5; Magnetic field source detection device.

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