Calibration device and calibration method for magnetic field voltage conversion coefficient

Abstract

This invention provides a calibration device and a calibration method. The calibration device includes: a cryogenic device for containing cryogenic liquid to provide a cryogenic environment; a sensor disposed within the cryogenic device, including at least one three-dimensional gradiometer for measuring magnetic fields and obtaining voltage amplitude; a coil array disposed below the cryogenic device, including a first coil and several second coils, each second coil being disposed within the first coil, for sequentially generating magnetic fields under the action of an excitation signal; an excitation module electrically connected to the coil array, for sequentially applying excitation signals to each coil in the coil array, and detecting the magnitude of the excitation signal applied to each coil and obtaining a detection value; and a processing module electrically connected to the sensor and the excitation module, for calibrating the coefficients of the three-dimensional gradiometer based on the voltage amplitude and the detection value. This invention solves the problems of inconvenient operation and inability to be performed in a shielded room in existing calibration methods using large Helmholtz coils.

Description

Technical Field

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

[0002] A superconducting quantum interference device (SQUID) is an extremely sensitive instrument capable of measuring weak magnetic signals. Functionally, it is a magnetic flux sensor widely used in the detection of weak magnetic signals. To improve the sensitivity of SQUIDs and suppress environmental noise, gradiometer technology is widely applied in SQUIDs.

[0003] In recent years, studies have shown that three-dimensional gradiometers can be used to extend the magnetic field information within the detection area. Therefore, it is necessary to calibrate the sensor constructed from the three-dimensional gradiometer, and accurate sensor calibration results help to obtain more accurate magnetic source estimation information. Currently, for three-dimensional gradiometers, it is often necessary to use a large Helmholtz coil to generate a gradient magnetic field in a specified direction for sensor calibration. This calibration method is complex, inconvenient to operate, and cannot be performed in a shielded room.

[0004] It should be noted that the above description of the technical background is only for the purpose of providing a clear and complete explanation of the technical solutions of the present invention and facilitating understanding by those skilled in the art. It should not be assumed that the above technical solutions are known to those skilled in the art simply because they have been described in the background section of this invention. Summary of the Invention

[0005] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a calibration device and calibration method for the magnetic field voltage conversion coefficient, which solves the problems of inconvenient operation and inability to be carried out in a shielded room in the existing calibration method using large Helmholtz coils.

[0006] To achieve the above and other related objectives, the present invention provides a calibration device for a magnetic field-voltage conversion coefficient, the calibration device comprising:

[0007] Cryogenic devices are used to contain cryogenic liquids to provide a cryogenic environment.

[0008] A sensor, disposed within the cryogenic device, includes at least one three-dimensional gradiometer for measuring magnetic field and obtaining voltage amplitude.

[0009] A coil array, disposed below the cryogenic device, includes a first coil and several second coils, each of the second coils being disposed within the first coil, for sequentially generating a magnetic field under the action of an excitation signal;

[0010] An excitation module, electrically connected to the coil array, is used to sequentially apply excitation signals to each coil in the coil array, and to detect the magnitude of the excitation signal applied to each coil and obtain a detection value;

[0011] The processing module, electrically connected to the sensor and the excitation module, is used to calibrate the coefficients of the three-dimensional gradient meter based on the voltage amplitude and the detected 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. 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 the same as the radius of the three-dimensional gradient meter.

[0014] Optionally, 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 around the first second coil with equal center-to-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 sequentially apply the excitation signal to each coil; the excitation detector includes several current-sensing resistors, which are electrically connected to each output terminal of the signal generator and each coil, respectively, and are used to detect the magnitude of the excitation signal applied to each coil and obtain the detection value.

[0016] Optionally, 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 direction gradiometer according to the voltage amplitude and the detection value corresponding to each direction 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 described in any one of the above claims, the calibration method comprising:

[0018] Using any coil in the coil array as a reference coil, the relative position of the orientation gradient meter to be calibrated and the reference coil in the three-dimensional gradient meter is estimated and the estimated value is obtained.

[0019] Excitation signals are sequentially applied to each coil in the coil array, and the voltage amplitude of the sensor under the action of each coil is read.

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

[0021] The voltage and magnetic field error function is calculated based on the voltage amplitude and magnetic field value of the sensor under the action of each second coil, and the voltage and magnetic field error function is minimized by an optimization algorithm to obtain the determined value of the relative position of the orientation gradient meter to be calibrated and the reference coil.

[0022] Based on the determined value and the detected 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 orientation gradient meter 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 step of sequentially applying excitation signals to each coil in the coil array and reading the voltage amplitude of the sensor under the action of each coil is repeated at least once, and the voltage amplitude of the sensor under the action of each coil is obtained by taking the average value.

[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 V represents the magnetic field value received by the sensor under the action of the i-th coil. i This represents the voltage amplitude of the sensor under the action of the i-th coil.

[0025] Optionally, the determined value is obtained by minimizing the voltage-magnetic field error function using a pattern search algorithm.

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

[0027] As described above, the calibration device and calibration method for the magnetic field voltage conversion coefficient of the present invention propose a small and convenient calibration device, which is characterized by miniaturization, simple operation, and the ability to work in a shielded room; and the calibration method based on the calibration device has the characteristics of high calibration accuracy, with a first-order gradient timing error of 0.8% in the calibration axis and a first-order gradient timing error of 0.2% in the calibration plane, and the calibration error is less than the typical value of gradient meter unbalance. Attached Figure Description

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

[0029] Figure 2 The diagram shown is a schematic representation of one structure of the coil array of the present invention.

[0030] Figure 3 The flowchart shown is a process for the calibration method of this invention.

[0031] Figure 4 The diagram shows the arrangement of each coil in the coil array according to an embodiment of the present invention.

[0032] Component designation explanation

[0033] 100 Calibration Device

[0034] 110 Cryogenic Devices

[0035] 120 sensor

[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 modules

[0043] 151 Readout Unit

[0044] 152 processing units

[0045] 200 shielded room Detailed Implementation

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

[0047] Please see Figures 1 to 4It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the illustrations only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the shape, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0048] like Figure 1 As shown, this embodiment provides a calibration device 100 for 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 flask, wherein the cryogenic liquid contained therein includes liquid helium; the Dewar flask has a high vacuum degree and thermal insulation performance, and also has a certain electromagnetic shielding function, which is beneficial to the high performance and stable operation of the sensor 120; in addition, the ambient temperature can be adjusted by adjusting the temperature of the liquid helium. In practical applications, the temperature of liquid helium is usually 4.2K, but other temperatures are also feasible, depending on the specific application requirements, and there is no limitation thereto.

[0050] Sensor 120 is disposed within cryogenic device 110, for example, in the central region of the bottom of cryogenic device 110, for measuring magnetic field and obtaining voltage amplitude. Sensor 120 includes at least one three-dimensional gradiometer (not shown in the figure). In practical applications, the number of three-dimensional gradiometers should be determined by specific application requirements and is not limited thereto. Specifically, 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. The first, second, and third directional gradiometers 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 chosen is also determined by specific application requirements and is not limited thereto.

[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 wherein the number of second coils 132 is greater than or equal to three, and each second coil 132 is disposed within the first coil 131, for sequentially generating 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 is usually the same as the radius of the three-dimensional gradiometer. The radius of the first coil 131 is designed according to the arrangement of the second coils 132 to ensure that all the second coils 132 are included. It should be noted that the size of the coil array 130 is the same as the size of the first coil 131, and the size of the first coil 131 is relatively small, usually a few centimeters. Therefore, the calibration device 100 proposed in this embodiment can be placed inside the shielded room 200.

[0052] In one embodiment, 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 around the first second coil 132 with equal center-to-center spacing. For example, there are five second coils 132; the center of the first second coil 132 coincides with the center of the first coil 131; the centers of the second second coil 132 (shown on the left side of the figure), the third second coil 132 (shown on the right side of the figure), and the first second coil 132 are located on a first straight line L1; the centers of the fourth second coil 132 (shown on the upper side of the figure), the fifth second coil 132 (shown on the lower side of the figure), and the first second coil 132 are located on a second straight line L2; and the first straight line L1 and the second straight line L2 are perpendicular to each other. In practical applications, 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 distance between the center of each of the other second coils 132 and the center of the first second coil 132 is equal. Taking five second coils 132 as an example, the center of the second second coil 132 has a first distance from the center of the first second coil 132, the center of the third second coil 132 has a second distance from the center of the first second coil 132, the center of the fourth second coil 132 has a third distance from the center of the first second coil 132, and the center of the fifth second coil 132 has a fourth distance from the center of the first second coil 132. Among these, the first, second, third, and fourth distances are equal.

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

[0055] In one embodiment, the excitation module 140 includes a signal generator 141 and an excitation detector 142. The signal generator 141 is electrically connected to each coil in the coil array 130 and is used to sequentially apply excitation signals to each coil in the coil array 130. The excitation detector 142 includes several current-sensing resistors (not shown in the figure), which are electrically connected to each output terminal of the signal generator 141 and each coil, respectively, and are used to detect the magnitude of the excitation signal applied to each coil and obtain the detection value. The signal generator 141 has 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, accurate real-time measurement of the excitation signal applied to each coil can be achieved, so as to subsequently estimate 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 gradient meter based on the voltage amplitude and the detected value.

[0057] In one embodiment, the processing module 150 includes a readout unit 151 and a processing unit 152. The readout unit 151 is electrically connected to the sensor 120 and is used to read the voltage amplitude. The processing unit 152 is electrically connected to the readout unit 151 and the excitation module 140, and is used to calculate the magnetic field-voltage conversion coefficient of each direction gradiometer based on the voltage amplitude and detected 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 control the sensor 130 for power-on, reset, heating, and adjustment. By controlling the heating of the sensor 130, the operating state of the three-dimensional gradiometer in the sensor 130 can be switched between a superconducting state and a non-superconducting state. By adjusting the bias of 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 the magnetic field voltage conversion coefficient based on the calibration device 100 described above, which includes the following steps.

[0059] Step S1: Using any coil in the coil array 130 as a reference coil, estimate the relative position of the orientation gradient meter to be calibrated and the reference coil in the three-dimensional gradient meter and obtain the 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 gradient meter to be calibrated in the coordinate system. In practical applications, the first coil 131 can be used as the reference coil, or any second coil 132 can be used as the reference coil; in one alternative, any second coil 132 can be used as the reference coil, for example, the second coil 132 whose center coincides with that of the first coil 131 can be used as the reference coil.

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

[0062] Furthermore, step S2 is repeated at least once, and the voltage amplitude of sensor 120 under the action of each coil is obtained by averaging, thereby improving the calibration accuracy. When step S2 is repeated at least once, there are multiple voltage amplitudes of sensor 120 under the action of each coil. For any coil, the voltage amplitude of sensor 120 under the action of that coil can be obtained by averaging the multiple voltage amplitudes. The voltage amplitude includes the voltage amplitude of sensor 120 under the action of the first coil 131 and the voltage amplitude of sensor 120 under the action of each second coil 132.

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

[0064] Specifically, the excitation detector 142 in the excitation module 140 detects the magnitude of the excitation signal applied to each coil and obtains the detection value. In practical applications, when step S2 is executed multiple times, detection can be performed only for one execution, and the detection result is the detection value. Alternatively, detection can be performed for at least two executions (e.g., for each execution), in which case the average of the detection results is taken 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 of the second coils 132.

[0065] Substituting the estimated value obtained in step S1 and the detection value corresponding to each second coil 132 into the following formula, the magnetic field value received by sensor 120 under the action of each second coil 132 is obtained. Here, the estimated value obtained in step S1 is denoted as (x, y, z), and the detection values ​​obtained in step S3 are denoted as VD1 to VD2. N Convert it into current values ​​and denot them as ID1 to ID2. N N is the number of coils in coil array 130; when calculating the magnetic field value received by sensor 120 under the action of the i-th second coil 132, the following condition is met:

[0066]

[0067]

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

[0069] Step S4: Calculate the voltage and 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 minimize the voltage and magnetic field error function through an optimization algorithm to obtain the determined value of the relative position of the direction gradient meter to be calibrated and the reference coil.

[0070] Specifically, based on the voltage amplitude of sensor 120 under the action of each second coil 132 obtained in step S2, and the magnetic field value of sensor 120 under the action of each second coil 132 obtained in step S3, a 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 coil array 130, and B i V represents the magnetic field value received by sensor 120 under the action of the i-th coil. i This represents the voltage amplitude of sensor 120 under the action of the i-th coil.

[0071] The voltage-magnetic field error function E is minimized using a pattern search algorithm to determine the relative position of the orientation gradient meter 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 using the pattern search algorithm, and the relative position of the orientation gradient meter to be calibrated and the reference coil is determined based on the obtained voltage amplitude and magnetic field values ​​(by substituting the obtained voltage amplitude and magnetic field values ​​into the formula involved in step S3 to obtain the relative position of the orientation gradient meter to be calibrated and the reference coil).

[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 the magnetic field voltage conversion coefficient of the orientation gradient meter to be calibrated is calculated based on the voltage amplitude and magnetic field value of the sensor 120 under the action of the first coil 131.

[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 and the magnetic field value received by the sensor 120 under the action of the first coil 131 obtained in step S2, the magnetic field voltage conversion coefficient of the orientation gradient meter to be calibrated is calculated, wherein the magnetic field 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 just an example and is not intended to limit the execution order of each step. Making appropriate adjustments to the execution order of the above steps will not have a substantial impact on the implementation of the scheme. 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 steps S1 to S5 once, the magnetic field voltage conversion coefficient of one directional gradiometer is calibrated. Since the three-dimensional gradiometer includes three directional gradiometers, in order to calibrate the magnetic field voltage conversion coefficients of the other two directional gradiometers, steps S1 to S5 need to be repeated twice more. Specifically, after the first repetition of steps S1 to S5, the magnetic field voltage conversion coefficient of another directional gradiometer is calibrated. After the second repetition of steps S1 to S5, the magnetic field voltage conversion coefficient of yet another directional gradiometer is calibrated. In this way, the coefficient calibration of the three-dimensional gradiometer is completed.

[0076] The advantages of the calibration device 100 and calibration method of this application will be explained below with reference to specific embodiments and comparative examples; wherein, in both the embodiments and comparative examples, a Dewar is used as a cryogenic device, and the sensor includes a three-dimensional gradiometer, which is composed of three first-order gradiometers.

[0077] In this embodiment: the coil array 130 is placed directly below the Dewar and the calibration device 100 is placed in a shielded room. The coil array 130 is used to calibrate the magnetic field-voltage conversion coefficient of the first-order gradiometer in the XZ direction. The coil array 130 includes one first coil 131 and five second coils 132. The radius of the first coil 131 is 7.4 cm, and the radius of the second coils 132 is 0.9 cm. The arrangement of the coils is as follows... Figure 4 As shown, the six coils are labeled with numbers 1 to 6 respectively. The center of coil 1 coincides with that of coil 6. The distance between the center of coil 1 and the centers of coil 2, coil 3, coil 4 and coil 5 is 4cm. Coils 2, coil 3, coil 4 and coil 5 are arranged in a diamond shape around the periphery of coil 1.

[0078] When calibrating the coefficients of the first-order gradient meter using the calibration device 100 described above, the specific steps are as follows: 1) Establish a coordinate system with coil 1 as the reference coil and the center of coil 1 as the origin. Based on the position of the first-order gradient meter in the coordinate system, estimate the relative position of the first-order gradient meter and coil 1, and obtain the estimated value as (X, Y, Z) = (0cm, 0cm, 3cm); 2) Excite coils 1 to 6 sequentially with a 10Hz sinusoidal signal, and record the voltage amplitude output by sensor 120; 3) Repeat step 2) multiple times and take the average value to obtain the voltage amplitude V1 = 0.324V under the action of coil 1, the voltage amplitude V2 = 1.18V under the action of coil 2, and the voltage amplitude V3 under the action of coil 3. Value V3 = 1.36V, voltage amplitude V4 = 1.28V under the action of coil 4, voltage amplitude V5 = 1.39V under the action of coil 5, and voltage amplitude V6 = 0.44V under the action of coil 6; 4) Based on the estimated relative position of the first-order gradient meter and coil 1, and the detected values ​​of the excitation signals applied to coils 1 to 5, the magnetic field values ​​received by sensor 120 under the action of coils 1 to 5 are calculated, wherein the magnetic field value under the action of coil 1 is denoted as B1, the magnetic field value under the action of coil 2 is denoted as B2, the magnetic field value under the action of coil 3 is denoted as B3, the magnetic field value under the action of coil 4 is denoted as B4, and the magnetic field value under the action of coil 5 is denoted as B5; 5) Based on the formula 6) Minimize the voltage-magnetic field error function using an optimization algorithm to obtain the relative position of the first-order gradiometer and coil 1, where the determined value is (X, Y, Z) = (0.12cm, -0.06cm, 2.4cm); 7) Based on the determined relative position of the first-order gradiometer and coil 1 and the detected value of the excitation signal applied to coil 6, calculate the magnetic field value received by sensor 120 under the action of coil 6, where the magnetic field value under the action of coil 6 is denoted as B6, B6 = 2.024nT; 8) Calculate the magnetic field-to-voltage conversion coefficient K of the first-order gradiometer based on the magnetic field value and voltage amplitude under the action of coil 6. 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 a first-order gradient meter 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 a shielded room.

[0080] When calibrating the coefficients of this first-order gradient meter using a 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 10Hz sinusoidal signal to generate a gradient magnetic field in the XZ direction, and calculate the magnitude of the gradient magnetic field in the XZ direction under this sinusoidal signal as G. XZ = 10.15 nT / cm; the baseline of this first-order gradiometer is 5 cm, therefore the magnitude of the gradient magnetic field received by this first-order gradiometer is calculated to be B. S =50.76nT; 3) Rotate the Dewar to maximize the sensor output voltage and record the voltage amplitude of the sensor output, 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] Based on the above embodiments and comparative examples, it can be seen that: the comparative examples use large Helmholtz coils to calibrate the first-order gradiometer, which has the problem that the coil size is too large to be performed in a shielded room, and the need to rotate the Dewar, etc., which makes the operation inconvenient; while the embodiments use the calibration device 100 of this application to calibrate the first-order gradiometer, which can be performed in a shielded room because the size of the coil array 130 is small, and there is no need to rotate the Dewar, making the operation convenient.

[0082] In summary, the present invention provides a calibration device and method for the magnetic field voltage conversion coefficient. It proposes a small and convenient calibration device, characterized by its miniaturization, ease of operation, and ability to operate within a shielded room. The calibration method based on this device offers high calibration accuracy, with a timing error of 0.8% for the first-order gradient in the calibration axis and 0.2% for the first-order gradient in the calibration plane. Both calibration errors are less than the typical value of the gradient meter's unbalance (since the gradient meter's frame is made of epoxy resin, the typical value of the gradient meter's unbalance is approximately 0.15% to 0.25%). Therefore, the present invention effectively overcomes the various shortcomings of the prior art and possesses high industrial applicability.

[0083] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can 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 those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A calibration method for the magnetic field-voltage conversion coefficient based on a calibration device, characterized in that, The calibration device includes: a cryogenic device for containing cryogenic liquid to provide a cryogenic environment; a sensor disposed within the cryogenic device, including at least one three-dimensional gradiometer for measuring magnetic fields and obtaining voltage amplitude; a coil array disposed below the cryogenic device, including a first coil and several second coils, each second coil being disposed within the first coil, for sequentially generating magnetic fields under the action of an excitation signal; an excitation module electrically connected to the coil array, for sequentially applying excitation signals to each coil in the coil array, and detecting the magnitude of the excitation signal applied to each coil and obtaining a detection value; and a processing module electrically connected to the sensor and the excitation module, for calibrating the coefficients of the three-dimensional gradiometer based on the voltage amplitude and the detection value; the calibration method includes: Using any coil in the coil array as a reference coil, the relative position of the orientation gradient meter to be calibrated and the reference coil in the three-dimensional gradient meter is estimated and the estimated value is obtained. Excitation signals are sequentially applied to each coil in the coil array, and the voltage amplitude of the sensor under the action of each coil is read. The magnitude of the excitation signal applied to each coil is detected to obtain a detection value, and based on the estimated value and the detection value corresponding to each second coil, the magnetic field value received by the sensor under the action of each second coil is obtained; The voltage and magnetic field error function is calculated based on the voltage amplitude and magnetic field value of the sensor under the action of each second coil, and the voltage and magnetic field error function is minimized by an optimization algorithm to obtain the determined value of the relative position of the orientation gradient meter to be calibrated and the reference coil. Based on the determined value and the detected 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 orientation gradient meter to be calibrated is calculated based on the voltage amplitude and magnetic field value of the sensor under the action of the first coil.

2. The calibration method for the magnetic field-voltage conversion coefficient based on a calibration device according to claim 1, characterized in that, 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. The order of each gradiometer is equal and greater than or equal to zero.

3. The calibration method for the magnetic field-voltage conversion coefficient based on a calibration device 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 the same as the radius of the three-dimensional gradient meter.

4. The calibration method for the magnetic field-voltage conversion coefficient based on a calibration device 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 around the first second coil with equal center-to-center spacing.

5. The calibration method for the magnetic field-voltage conversion coefficient based on a calibration device 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 sequentially apply the excitation signal to each coil; the excitation detector includes several current-sensing resistors, which are electrically connected to each output terminal of the signal generator and each coil, respectively, and are used to detect the magnitude of the excitation signal applied to each coil and obtain the detection value.

6. The calibration method for the magnetic field-voltage conversion coefficient based on a calibration device 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 direction gradiometer according to the voltage amplitude and the detection value corresponding to each direction gradiometer in the three-dimensional gradiometer, thereby completing the coefficient calibration of the three-dimensional gradiometer.

7. The calibration method for the magnetic field-voltage conversion coefficient based on a calibration device according to claim 1, characterized in that, The steps of sequentially applying excitation signals to each coil in the coil array 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 value.

8. The calibration method for the magnetic field-voltage conversion coefficient based on a calibration device according to claim 1, 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 V represents the magnetic field value received by the sensor under the action of the i-th coil. i This represents the voltage amplitude of the sensor under the action of the i-th coil.

9. The calibration method for the magnetic field-voltage conversion coefficient based on a calibration device according to claim 1, characterized in that, The determined value is obtained by minimizing the voltage-magnetic field error function using a pattern search algorithm.

10. The calibration method for the magnetic field-voltage conversion coefficient based on a calibration device according to any one of claims 1 to 9, characterized in that, The calibration method further includes: repeating each calibration step twice to obtain the magnetic field voltage conversion coefficient of each direction gradient meter in the three-dimensional gradient meter, thereby completing the coefficient calibration of the three-dimensional gradient meter.

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