Calibration device and calibration method for magnetic field voltage conversion coefficient

Abstract

The invention provides a calibration device and a calibration method, and the calibration device comprises a low-temperature device which is used for containing low-temperature liquid to provide a low-temperature environment; the sensor is arranged in the low-temperature device, comprises at least one three-dimensional gradiometer and is used for measuring a magnetic field and obtaining a voltage amplitude; the coil array is arranged below the low-temperature device and comprises a first coil and a plurality of second coils, and the second coils are arranged in the first coil and used for sequentially generating magnetic fields under the action of the excitation signals; the excitation module is electrically connected with the coil array and used for sequentially applying excitation signals to the coils in the coil array and detecting the magnitude of the excitation signals applied to the coils to obtain detection values; and the processing module is electrically connected with the sensor and the excitation module and is used for realizing coefficient calibration of the three-dimensional gradiometer according to the voltage amplitude and the detection value. The problems that an existing calibration mode using a large Helmholtz coil is inconvenient to operate and cannot be carried out in a shielded room are solved.

Description

Technical Field

[0001] The invention belongs to the technical field of magnetic detection, and in particular relates to a calibration device and a calibration method for a magnetic field voltage conversion coefficient. Background Art

[0002] Superconducting quantum interference device (SQUID) is an extremely sensitive instrument that can measure weak magnetic signals. In terms of its function, it is a magnetic flux sensor and is widely used in the field of detecting weak magnetic signals. In order to improve the sensitivity of SQUID and suppress environmental noise, gradiometer technology is widely used in SQUID.

[0003] In recent years, studies have pointed out that three-dimensional gradiometers can be used to expand the magnetic field information in the detection area. Therefore, it is necessary to calibrate the sensors composed of three-dimensional gradiometers, and accurate sensor calibration results help to obtain more accurate magnetic source estimation information. At present, for three-dimensional gradiometers, large Helmholtz coils are often needed to generate gradient magnetic fields in a specified direction to calibrate the sensors. This calibration method is complex and inconvenient to operate, and cannot be performed in a shielded room.

[0004] It should be noted that the above introduction to the technical background is only for the convenience of providing a clear and complete description of the technical solutions of the present invention and for the convenience of understanding by those skilled in the art. It cannot be considered that the above technical solutions are well known to those skilled in the art simply because these solutions are described in the background technology section of the present invention. Summary of the invention

[0005] In view of the above-mentioned shortcomings of the prior art, the purpose of the present invention is to provide a calibration device and a calibration method for a magnetic field voltage conversion coefficient, so as to solve the problems that the existing calibration method using large Helmholtz coils is inconvenient to operate and cannot be performed in a shielded room.

[0006] In order to achieve the above-mentioned object and other related objects, the present invention provides a calibration device for a magnetic field voltage conversion coefficient, the calibration device comprising:

[0007] Cryogenic devices, used to contain cryogenic liquids to provide a low-temperature environment;

[0008] A sensor, disposed in the cryogenic device, comprising at least one three-dimensional gradiometer, for measuring the magnetic field and obtaining a voltage amplitude;

[0009] A coil array, disposed below the cryogenic device, comprising a first coil and a plurality of second coils, each of the second coils being disposed within the first coil, and configured to sequentially generate a magnetic field under the action of an excitation signal;

[0010] an excitation module, electrically connected to the coil array, for sequentially applying an excitation signal to each coil in the coil array, and detecting the magnitude of the excitation signal applied to each coil and obtaining a detection value;

[0011] A processing module is electrically connected to the sensor and the excitation module, and is used to calibrate the coefficients of the three-dimensional gradiometer according to the voltage amplitude and the detection value.

[0012] Optionally, the three-dimensional gradiometer includes a first directional gradiometer, a second directional gradiometer and a third directional gradiometer, the first directional gradiometer is located in the XY direction, the second directional gradiometer is located in the XZ direction, and the third directional gradiometer is located in the YZ direction, wherein the order of each directional gradiometer is equal and greater than or equal to zero.

[0013] Optionally, the number of the second coils is greater than or equal to three, and the radius of the second coil is consistent with the radius of the three-dimensional gradiometer.

[0014] Optionally, in each of the second coils, the center of a first second coil coincides with the center of the first coil, and the other second coils are arranged on the periphery of the first second coil with equal center spacing.

[0015] Optionally, the excitation module includes a signal generator and an excitation detector; the signal generator is electrically connected to each coil in the coil array, and is used to apply the excitation signal to each coil in turn; the excitation detector includes a plurality of current-sensing resistors, which are electrically connected between each output end of the signal generator and each coil, respectively, and are used to detect the size of the excitation signal applied to each coil and obtain a detection value.

[0016] Optionally, the processing module includes a readout unit and a processing unit; the readout unit is electrically connected to the sensor for reading the voltage amplitude; the processing unit is electrically connected to the readout unit and the excitation module for calculating the magnetic field voltage conversion coefficient of each directional gradiometer according to the voltage amplitude and the detection value corresponding to each directional gradiometer in the three-dimensional gradiometer, thereby completing the coefficient calibration of the three-dimensional gradiometer.

[0017] The present invention also provides a calibration method for a magnetic field voltage conversion coefficient based on the calibration device as described in any one of the above items, the calibration method comprising:

[0018] Taking any coil in the coil array as a reference coil, estimating the relative position of the directional gradiometer to be calibrated in the three-dimensional gradiometer and the reference coil and obtaining an estimated value;

[0019] Applying an excitation signal to each coil in the coil array in turn, and reading the voltage amplitude of the sensor under the action of each coil;

[0020] Detecting the magnitude of the excitation signal applied to each coil to obtain a detection value, and obtaining a magnetic field value received by the sensor under the action of each second coil based on the estimated value and the detection value corresponding to each second coil;

[0021] Calculating a voltage-magnetic field error function based on the voltage amplitude and magnetic field value of the sensor under the action of each of the second coils, and minimizing the voltage-magnetic field error function through an optimization algorithm to obtain a determined value of the relative position of the directional gradiometer to be calibrated and the reference coil;

[0022] Based on the determined value and the detection value corresponding to the first coil, the magnetic field value received by the sensor under the action of the first coil is obtained, and the magnetic field voltage conversion coefficient of the directional gradiometer to be calibrated is calculated based on the voltage amplitude and magnetic field value of the sensor under the action of the first coil.

[0023] Optionally, the steps of applying an excitation signal to each coil in the coil array in turn and reading the voltage amplitude of the sensor under the action of each coil are repeated at least once, and the voltage amplitude of the sensor under the action of each coil is obtained by taking the average.

[0024] Optionally, the voltage magnetic field error function satisfies the formula Where E represents the voltage magnetic field error function, N represents the number of coils in the coil array, and B i Represents the magnetic field value received by the sensor under the action of the i-th coil, V i Represents the voltage amplitude of the sensor under the action of the i-th coil.

[0025] Optionally, the voltage-magnetic-field error function is minimized by a pattern search algorithm to obtain the determined value.

[0026] Optionally, the calibration method further comprises: repeating each calibration step twice to obtain the magnetic field voltage conversion coefficient of each direction gradiometer in the three-dimensional gradiometer, thereby completing the coefficient calibration of the three-dimensional gradiometer.

[0027] As described above, the calibration device and calibration method of the magnetic field voltage conversion coefficient of the present invention propose a small and portable calibration device, which has the characteristics of miniaturization, easy operation, and can work in a shielded room; and the calibration method implemented based on the calibration device has the characteristics of high calibration accuracy. The first-order gradient timing error in the calibration axis is 0.8%, and the first-order gradient timing error in the calibration plane is 20%. The calibration errors are both less than the typical value of the gradiometer imbalance. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Shown is a schematic structural diagram of the calibration device of the present invention.

[0029] Figure 2 Shown is a schematic structural diagram of the coil array of the present invention.

[0030] Figure 3 Shown is a flow chart of the calibration method of the present invention.

[0031] Figure 4 It is a schematic diagram showing the arrangement of coils in a coil array according to an embodiment of the present invention.

[0032] Component number description

[0033] 100 Calibration device

[0034] 110 Low temperature devices

[0035] 120 Sensors

[0036] 130 Coil Array

[0037] 131 First Coil

[0038] 132 Second coil

[0039] 140 Incentive Module

[0040] 141 Signal Generator

[0041] 142 Excitation Detector

[0042] 150 Processing Module

[0043] 151 Readout unit

[0044] 152 Processing Units

[0045] 200 Shielded Room DETAILED DESCRIPTION

[0046] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0047] See also Figures 1 to 4It should be noted that the illustrations provided in this embodiment are only used to illustrate the basic concept of the present invention in a schematic manner, and the illustrations only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the form, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0048] like Figure 1 As shown, this embodiment provides a calibration device 100 for a magnetic field voltage conversion coefficient, including a cryogenic device 110 , a sensor 120 , a coil array 130 , an excitation module 140 and a processing module 150 .

[0049] The cryogenic device 110 is used to contain cryogenic liquid to provide a cryogenic environment. In one embodiment, the cryogenic device 110 includes a dewar, wherein the cryogenic liquid contained therein includes liquid helium; the dewar has a high vacuum degree and heat insulation performance, and has a certain electromagnetic shielding function, which is conducive to the high performance and stable operation of the sensor 120; in addition, by adjusting the temperature of the liquid helium, the ambient temperature can be adjusted. In practical applications, the temperature of the liquid helium is usually 4.2K. Of course, other temperatures are also feasible, which is determined by the specific application requirements and is not limited to this.

[0050] The sensor 120 is arranged in the cryogenic device 110, for example, in the central area at the bottom of the cryogenic device 110, for measuring the magnetic field and obtaining the voltage amplitude; wherein the sensor 120 includes at least one three-dimensional gradiometer (not shown in the figure), and in actual applications, the number of three-dimensional gradiometers should be determined by the specific application requirements, and there is no restriction on this. Specifically, the three-dimensional gradiometer includes a first direction gradiometer, a second direction gradiometer and a third direction gradiometer, the first direction gradiometer is located in the XY direction, the second direction gradiometer is located in the XZ direction, and the third direction gradiometer is located in the YZ direction; wherein the first direction gradiometer, the second direction gradiometer and the third direction gradiometer have the same order, and the order is greater than or equal to zero. It should be noted that a directional gradiometer with an order of zero is usually called a magnetometer, that is, the directional gradiometer is a magnetometer, a first-order gradiometer, a second-order gradiometer, etc. The specific order selected is also determined by the specific application requirements, and there is no restriction on this.

[0051] The coil array 130 is disposed below the cryogenic device 110, for example, directly below the cryogenic device 110; wherein the coil array 130 includes a first coil 131 and a plurality of second coils 132, further, the number of the second coils 132 is greater than or equal to three, and each second coil 132 is disposed in the first coil 131, and is used to sequentially generate a magnetic field under the action of an excitation signal, such as Figure 2As shown. In practical applications, the first coil 131 is a large coil, and the second coil 132 is a small coil, that is, the radius of the first coil 131 is larger than the radius of the second coil 132; the radius of the second coil 132 is determined by the radius of the three-dimensional gradiometer, and usually the radius of the second coil 132 is consistent with the radius of the three-dimensional gradiometer; the radius of the first coil 131 is designed according to the arrangement of each second coil 132 to ensure that all second coils 132 are included. It should be noted that the size of the coil array 130 is the size of the first coil 131, and the size of the first coil 131 is relatively small, usually a few centimeters, so the calibration device 100 proposed in this embodiment can be placed in the shielding room 200.

[0052] In one embodiment, in each second coil 132, the center of the first second coil 132 coincides with the center of the first coil 131, and the other second coils 132 are arranged at the periphery of the first second coil 132 with equal center spacing. As an example, the number of second coils 132 is five; wherein the center of the first second coil 132 coincides with the center of the first coil 131, the center of the second second coil 132 (as shown on the left side in the figure), the center of the third second coil 132 (as shown on the right side in the figure) and the center of the first second coil 132 are located on the first straight line L1, the center of the fourth second coil 132 (as shown on the upper side in the figure), the center of the fifth second coil 132 (as shown on the lower side in the figure) and the center of the first second coil 132 are located on the second straight line L2, and the first straight line L1 and the second straight line L2 are perpendicular to each other; in actual application, the direction of the first straight line L1 is the X-axis direction, and the direction of the second straight line L2 is the Y-axis direction.

[0053] It should be noted that equal center spacing means that the distances between the centers of the other second coils 132 and the center of the first second coil 132 are equal; taking the case where there are five second coils 132 as an example, there is a first distance between the center of the second second coil 132 and the center of the first second coil 132, a second distance between the center of the third second coil 132 and the center of the first second coil 132, a third distance between the center of the fourth second coil 132 and the center of the first second coil 132, and a fourth distance between the center of the fifth second coil 132 and the center of the first second coil 132, wherein the first distance, the second distance, the third distance and the fourth distance are equal.

[0054] The excitation module 140 is electrically connected to the coil array 130 , and is used to sequentially apply an excitation signal to each coil in the coil array 130 , and detect the magnitude of the excitation signal applied to each coil and obtain a detection value.

[0055] In one embodiment, the excitation module 140 includes a signal generator 141 and an excitation detector 142; wherein the signal generator 141 is electrically connected to each coil in the coil array 130, and is used to sequentially apply an excitation signal to each coil in the coil array 130; the excitation detector 142 includes a plurality of current-sensing resistors (not shown in the figure), which are electrically connected between each output end of the signal generator 141 and each coil, and are used to detect the magnitude of the excitation signal applied to each coil and obtain a detection value. The signal generator 141 has an internal resistance, so the actual value of the excitation signal applied to each coil is not equal to the theoretical value. By adding the excitation detector 142, it is possible to achieve accurate real-time measurement of the excitation signal applied to each coil, so as to facilitate the subsequent estimation of the magnitude of the magnetic field generated by each coil.

[0056] The processing module 150 is electrically connected to the sensor 120 and the excitation module 140, and is used to calibrate the coefficients of the three-dimensional gradiometer according to the voltage amplitude and the detection value.

[0057] In one embodiment, the processing module 150 includes a readout unit 151 and a processing unit 152; wherein the readout unit 151 is electrically connected to the sensor 120 for reading the voltage amplitude; the processing unit 152 is electrically connected to the readout unit 151 and the excitation module 140 for respectively calculating the magnetic field voltage conversion coefficient of each direction gradiometer according to the voltage amplitude and detection value corresponding to each direction gradiometer in the three-dimensional gradiometer, thereby completing the coefficient calibration of the three-dimensional gradiometer. Furthermore, the readout unit 151 is also used to perform power-on, reset, heating, and adjustment control on the sensor 130; wherein, by performing heating control on the sensor 130, the working state of the three-dimensional gradiometer in the sensor 130 can be switched between the superconducting state and the non-superconducting state; by performing bias adjustment on the sensor 130, the stability of the sensor 130 can be optimized.

[0058] like Figure 3 As shown, this embodiment also provides a calibration method for a magnetic field voltage conversion coefficient based on the calibration device 100 as described above, comprising the following steps.

[0059] Step S1 : taking any coil in the coil array 130 as a reference coil, estimating the relative position of the directional gradiometer to be calibrated in the three-dimensional gradiometer and the reference coil and obtaining an estimated value.

[0060] Specifically, the method for obtaining the estimated value includes: establishing a coordinate system with the center of the reference coil as the origin, and obtaining the estimated value based on the position of the directional gradiometer to be calibrated in the coordinate system. In practical applications, the first coil 131 can be used as a reference coil, or any second coil 132 can be used as a reference coil; in an optional solution, any second coil 132 can be used as a reference coil, for example, the second coil 132 that coincides with the center of the first coil 131 can be used as a reference coil.

[0061] Step S2, applying an excitation signal to each coil in the coil array 130 in sequence to generate a magnetic field, and reading the voltage amplitude of the sensor 120 under the effect of the magnetic field generated by each coil. In practical applications, in order to facilitate the execution of subsequent algorithms, the excitation signals applied to each coil in sequence are usually designed to be consistent; in addition, there is no restriction on the order in which the excitation signals are applied to each coil in sequence, as long as the excitation signals are applied to all coils.

[0062] Further, step S2 is repeated at least once, and the voltage amplitude of the sensor 120 under the action of each coil is obtained by taking the average value, so as to improve the calibration accuracy; when step S2 is repeated at least once, the voltage amplitude of the sensor 120 under the action of each coil is multiple, and for any coil, the voltage amplitude of the sensor 120 under the action of the coil can be obtained by taking the average value of multiple voltage amplitudes. Among them, the voltage amplitude includes the voltage amplitude of the sensor 120 under the action of the first coil 131 and the voltage amplitude of the sensor 120 under the action of each second coil 132.

[0063] Step S3 , detecting the magnitude of the excitation signal applied to each coil to obtain a detection value, and obtaining the magnetic field value received by the sensor 120 under the action of each second coil 132 based on the estimated value and the detection value corresponding to each second coil 132 .

[0064] Specifically, the excitation detector 142 in the excitation module 140 detects the size of the excitation signal applied to each coil and obtains the detection value; in actual application, when step S2 is repeatedly executed multiple times, detection can be performed only for a certain execution, and at this time, the detection result is the detection value. Of course, detection can also be performed for at least two executions (for example, for each execution), and at this time, the detection results need to be averaged to obtain the detection value. The detection value includes the detection value corresponding to the first coil 131 and the detection value corresponding to each second coil 132.

[0065] Substitute the estimated value obtained in step S1 and the detection value corresponding to each second coil 132 into the following formula to obtain the magnetic field value received by the sensor 120 under the action of each second coil 132. The estimated value obtained in step S1 is recorded as (x, y, z), and the detection values ​​obtained in step S3 are recorded as VD1~VD N , convert it into current value and record it as ID1~ID N , N is the number of coils in the coil array 130; when calculating the magnetic field value received by the sensor 120 under the action of the i-th second coil 132, it satisfies:

[0066]

[0067]

[0068] B x is the X-direction magnetic field value received by the sensor under the action of the i-th second coil, B y is the Y-direction magnetic field value received by the sensor under the action of the i-th second coil, B z is the Z-direction magnetic field value received by the sensor under the action of the i-th second coil, B ρ is the radial magnetic field value in the cylindrical coordinate system, θ is the angle value in the cylindrical coordinate system, c0 is the magnetic permeability coefficient, ID i is the current value converted from the detection value corresponding to the i-th second coil, R i is the radius of the i-th second coil, ρ is the radial distance in the cylindrical coordinate system, E(k 2 ) is the first kind of complete elliptic integral, K(k 2 ) is the complete elliptic integral of the second kind, k 2 is the complete elliptic integral coefficient, x is the X-axis coordinate value in the estimated value, y is the Y-axis coordinate value in the estimated value, z is the Z-axis coordinate value in the estimated value, and x p is the X-axis coordinate value of the center of the i-th second coil, y p is the Y-axis coordinate value of the center of the i-th second coil, z p is the Z-axis coordinate value of the center of the i-th second coil.

[0069] Step S4, calculating the voltage-magnetic field error function based on the voltage amplitude and magnetic field value of the sensor 120 under the action of each second coil 132, and minimizing the voltage-magnetic field error function through an optimization algorithm to obtain a determined value of the relative position of the directional gradiometer to be calibrated and the reference coil.

[0070] Specifically, based on the voltage amplitude of the sensor 120 under the action of each second coil 132 obtained in step S2, and based on the magnetic field value of the sensor 120 under the action of each second coil 132 obtained in step S3, the voltage-magnetic field error function is calculated; wherein the voltage-magnetic field error function satisfies the formula E represents the voltage magnetic field error function, N represents the number of coils in the coil array 130, and B i represents the magnetic field value received by the sensor 120 under the action of the i-th coil, V i It represents the voltage amplitude of the sensor 120 under the action of the i-th coil.

[0071] The voltage-magnetic field error function E is minimized by a pattern search algorithm to obtain a determined value of the relative position of the directional gradiometer to be calibrated and the reference coil. Specifically, the voltage amplitude and magnetic field value of the sensor 120 under the action of the reference coil are obtained by minimizing the voltage-magnetic field error function E by a pattern search algorithm, and the determined value of the relative position of the directional gradiometer to be calibrated and the reference coil is obtained based on the obtained voltage amplitude and magnetic field value (the determined value of the relative position of the directional gradiometer to be calibrated and the reference coil is obtained by substituting the obtained voltage amplitude and magnetic field value into the formula involved in step S3).

[0072] Step S5, based on the determined value and the detection value corresponding to the first coil 131, the magnetic field value received by the sensor 120 under the action of the first coil 131 is obtained, and based on the voltage amplitude and magnetic field value of the sensor 120 under the action of the first coil 131, the magnetic field voltage conversion coefficient of the directional gradiometer to be calibrated is calculated.

[0073] Specifically, the determined value obtained in step S4 and the detection value corresponding to the first coil 131 obtained in step S3 are substituted into the formula involved in step S3 to calculate the magnetic field value received by the sensor 120 under the action of the first coil 131; then based on the voltage amplitude of the sensor 120 under the action of the first coil 131 obtained in step S2 and the magnetic field value received by the sensor 120 under the action of the first coil 131, the magnetic field-to-voltage conversion coefficient of the directional gradiometer to be calibrated is calculated, wherein the magnetic field-to-voltage conversion coefficient is equal to the magnetic field value divided by the voltage amplitude.

[0074] It should be noted that the execution order of the steps shown above is only an example and does not limit the execution order of the steps. Appropriate adjustments to the execution order of the above steps will not have a substantial impact on the implementation of the solution. For example, step S1 can be executed before step S2, or after step S2 but before step S3, or even in step S3, etc.

[0075] In practical applications, after executing the above steps S1 to S5 once, the calibration of the magnetic field voltage conversion coefficient of one directional gradiometer is completed; since the three-dimensional gradiometer includes three directional gradiometers, in order to complete the calibration of the magnetic field voltage conversion coefficients of the other two directional gradiometers, the above steps S1 to S5 need to be repeated twice, wherein, after repeating the above steps S1 to S5 for the first time, the calibration of the magnetic field voltage conversion coefficient of another directional gradiometer is completed, and after repeating the above steps S1 to S5 for the second time, the calibration of the magnetic field voltage conversion coefficient of another directional gradiometer is completed, thus completing the coefficient calibration of the three-dimensional gradiometer.

[0076] Below, please combine specific embodiments and comparative examples to illustrate the advantages of the calibration device 100 and the calibration method of the present application; wherein, both the embodiments and the comparative examples use a Dewar as a low-temperature device, and the sensor includes a three-dimensional gradiometer, which is composed of three first-order gradiometers.

[0077] In the embodiment: the coil array 130 is placed directly below the dewar and the calibration device 100 is placed in the shielded room, and the first-order gradiometer in the XZ direction is calibrated for the magnetic field voltage conversion coefficient using the coil array 130; wherein the coil array 130 includes a first coil 131 and five second coils 132, the radius of the first coil 131 is 7.4 cm, the radius of the second coil 132 is 0.9 cm, and the arrangement of each coil is as follows Figure 4 As shown, numbers 1 to 6 are used to mark the six coils respectively, the centers of coil 1 and coil 6 coincide, the centers of coil 1, coil 2, coil 3, coil 4 and coil 5 are all 4 cm apart, and coil 2, coil 3, coil 4 and coil 5 are arranged in a diamond shape on the periphery of coil 1.

[0078] When the coefficients of the first-order gradiometer are calibrated based on the calibration device 100 as described above, the specific steps are as follows: 1) Coil 1 is used as a reference coil and a coordinate system is established with the center of coil 1 as the origin. Based on the position of the first-order gradiometer in the coordinate system, the relative position of the first-order gradiometer and coil 1 is estimated, and the estimated value is (X, Y, Z) = (0 cm, 0 cm, 3 cm); 2) Coils 1 to 6 are excited in sequence with a 10 Hz sinusoidal signal, and the voltage amplitude output by the sensor 120 is recorded; 3) Step 2) is repeated multiple times and the average is taken to obtain the voltage amplitude V1 = 0.324 V under the action of coil 1, the voltage amplitude V2 = 1.18 V under the action of coil 2, and the voltage amplitude V3 = 0.61 V under the action of coil 3. The value V3 is 1.36V, the voltage amplitude V4 under the action of coil 4 is 1.28V, the voltage amplitude V5 under the action of coil 5 is 1.39V, and the voltage amplitude V6 under the action of coil 6 is 0.44V; 4) Based on the estimated value of the relative position of the first-order gradiometer and coil 1 and the detected value of the excitation signal applied to coils 1 to 5, the magnetic field value received by the sensor 120 under the action of coils 1 to 5 is calculated, wherein the magnetic field value under the action of coil 1 is recorded as B1, the magnetic field value under the action of coil 2 is recorded as B2, the magnetic field value under the action of coil 3 is recorded as B3, the magnetic field value under the action of coil 4 is recorded as B4, and the magnetic field value under the action of coil 5 is recorded as B5; 5) Based on the formula Calculate the voltage-magnetic field error function; 6) Minimize the voltage-magnetic field error function through an optimization algorithm to obtain the determined value of the relative position of the first-order gradiometer and the coil 1, wherein the determined value is (X, Y, Z) = (0.12 cm, -0.06 cm, 2.4 cm); 7) Based on the determined value of the relative position of the first-order gradiometer and the coil 1 and the detected value of the excitation signal applied to the coil 6, calculate the magnetic field value received by the sensor 120 under the action of the coil 6, wherein the magnetic field value under the action of the coil 6 is recorded as B6, B6 = 2.024nT; 8) Based on the magnetic field value and voltage amplitude under the action of the coil 6, calculate the magnetic field voltage conversion coefficient K of the first-order gradiometer BV , where K BV =B6 / V6=2.024nT / 0.44V=4.6nT / V.

[0079] In the comparative example: a large Helmholtz coil is used to generate a gradient magnetic field in a specified direction to calibrate the magnetic field voltage conversion coefficient of the first-order gradiometer in the XZ direction; since the large Helmholtz coil is too large to be placed in a shielded room, the calibration cannot be performed in the shielded room.

[0080] When the coefficient of the first-order gradiometer is calibrated based on the large Helmholtz coil, the specific steps are as follows: 1) Place the Dewar at the center of the large Helmholtz coil so that the sensor inside is in the gradient magnetic field with the highest uniformity; 2) Drive the large Helmholtz coil with a sinusoidal signal with a frequency of 10 Hz to generate a gradient magnetic field in the XZ direction, and calculate the size of the gradient magnetic field in the XZ direction under the sinusoidal signal as G XZ =10.15nT / cm; the baseline of the first-order gradiometer is 5cm, and the magnitude of the gradient magnetic field received by the first-order gradiometer is calculated as B S =50.76nT; 3) Rotate the Dewar so that the voltage output by the sensor is the highest, and record the voltage amplitude output by the sensor, where the voltage amplitude is V S =10.8V; 4) Calculate the magnetic field voltage conversion coefficient K BV =B S / V S =50.76nT / 10.8V=4.7nT / V.

[0081] In combination with the above-mentioned embodiments and comparative examples, it can be seen that: the comparative example uses a large Helmholtz coil to calibrate the first-order gradiometer, but there is a problem that the coil size is too large to be performed in a shielded room, and the need to rotate the dewar causes inconvenience in operation; while the embodiment uses the calibration device 100 of the present application to calibrate the first-order gradiometer, because the size of the coil array 130 is small, it can be performed in a shielded room, and there is no need to rotate the dewar, which is convenient to operate.

[0082] In summary, the calibration device and calibration method of the magnetic field voltage conversion coefficient of the present invention proposes a small and portable calibration device, which has the characteristics of miniaturization, easy operation, and can work in a shielded room; and the calibration method based on the calibration device has the characteristics of high calibration accuracy, the first-order gradient timing error in the calibration axis is 0.8%, and the first-order gradient timing error in the calibration plane is 20%. The calibration errors are all less than the typical value of the gradiometer imbalance (because the frame of the gradiometer is epoxy resin, the typical value of the gradiometer imbalance is about 15 to 25 thousandths). Therefore, the present invention effectively overcomes the various shortcomings of the prior art and has a high industrial utilization value.

[0083] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A device for calibrating a magnetic field voltage conversion coefficient, characterized in that: The calibration device comprises: Cryogenic devices, used to contain cryogenic liquids to provide a low-temperature environment; A sensor, disposed in the cryogenic device, comprising at least one three-dimensional gradiometer, for measuring the magnetic field and obtaining a voltage amplitude; A coil array, disposed below the cryogenic device, comprising a first coil and a plurality of second coils, each of the second coils being disposed within the first coil, and configured to sequentially generate a magnetic field under the action of an excitation signal; an excitation module, electrically connected to the coil array, for sequentially applying an excitation signal to each coil in the coil array, and detecting the magnitude of the excitation signal applied to each coil and obtaining a detection value; A processing module is electrically connected to the sensor and the excitation module, and is used to calibrate the coefficients of the three-dimensional gradiometer according to the voltage amplitude and the detection value.

2. The device for calibrating the magnetic field voltage conversion coefficient according to claim 1, characterized in that: The three-dimensional gradiometer includes a first directional gradiometer, a second directional gradiometer and a third directional gradiometer, wherein the first directional gradiometer is located in the XY direction, the second directional gradiometer is located in the XZ direction, and the third directional gradiometer is located in the YZ direction, wherein the order of each directional gradiometer is equal and greater than or equal to zero.

3. The device for calibrating the magnetic field voltage conversion coefficient according to claim 1, characterized in that: The number of the second coils is greater than or equal to three, and the radius of the second coil is consistent with the radius of the three-dimensional gradiometer.

4. The device for calibrating the magnetic field voltage conversion coefficient according to claim 3, characterized in that: In each of the second coils, the center of the first second coil coincides with the center of the first coil, and the other second coils are arranged on the periphery of the first second coil with equal center spacing.

5. The device for calibrating the magnetic field voltage conversion coefficient according to claim 1, characterized in that: The excitation module includes a signal generator and an excitation detector; the signal generator is electrically connected to each coil in the coil array, and is used to apply the excitation signal to each coil in turn; the excitation detector includes a plurality of current-sensing resistors, which are electrically connected between each output end of the signal generator and each coil, and are used to detect the size of the excitation signal applied to each coil and obtain a detection value.

6. The device for calibrating the magnetic field voltage conversion coefficient according to claim 1, characterized in that: The processing module includes a readout unit and a processing unit; the readout unit is electrically connected to the sensor and is used to read the voltage amplitude; the processing unit is electrically connected to the readout unit and the excitation module and is used to calculate the magnetic field voltage conversion coefficient of each directional gradiometer according to the voltage amplitude and the detection value corresponding to each directional gradiometer in the three-dimensional gradiometer, thereby completing the coefficient calibration of the three-dimensional gradiometer.

7. A method for calibrating a magnetic field voltage conversion coefficient based on the calibration device according to any one of claims 1 to 6, characterized in that: The calibration method comprises: Taking any coil in the coil array as a reference coil, estimating the relative position of the directional gradiometer to be calibrated in the three-dimensional gradiometer and the reference coil and obtaining an estimated value; Applying an excitation signal to each coil in the coil array in turn, and reading the voltage amplitude of the sensor under the action of each coil; Detecting the magnitude of the excitation signal applied to each coil to obtain a detection value, and obtaining a magnetic field value received by the sensor under the action of each second coil based on the estimated value and the detection value corresponding to each second coil; Calculating a voltage-magnetic field error function based on the voltage amplitude and magnetic field value of the sensor under the action of each of the second coils, and minimizing the voltage-magnetic field error function through an optimization algorithm to obtain a determined value of the relative position of the directional gradiometer to be calibrated and the reference coil; Based on the determined value and the detection value corresponding to the first coil, the magnetic field value received by the sensor under the action of the first coil is obtained, and the magnetic field voltage conversion coefficient of the directional gradiometer to be calibrated is calculated based on the voltage amplitude and magnetic field value of the sensor under the action of the first coil.

8. The method for calibrating the magnetic field voltage conversion coefficient according to claim 7, characterized in that: The steps of applying an excitation signal to each coil in the coil array in turn and reading the voltage amplitude of the sensor under the action of each coil are repeated at least once, and the voltage amplitude of the sensor under the action of each coil is obtained by taking the average.

9. The method for calibrating the magnetic field voltage conversion coefficient according to claim 7, characterized in that: The voltage magnetic field error function satisfies the formula Where E represents the voltage magnetic field error function, N represents the number of coils in the coil array, and B i Represents the magnetic field value received by the sensor under the action of the i-th coil, V i Represents the voltage amplitude of the sensor under the action of the i-th coil.

10. The method for calibrating the magnetic field voltage conversion coefficient according to claim 7, characterized in that: The voltage-magnetic-field error function is minimized by a pattern search algorithm to obtain the determined value.

11. The method for calibrating the magnetic field voltage conversion coefficient according to any one of claims 7 to 10, characterized in that: The calibration method further comprises: repeating each calibration step twice to obtain the magnetic field voltage conversion coefficient of each direction gradiometer in the three-dimensional gradiometer, thereby completing the coefficient calibration of the three-dimensional gradiometer.

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