Magnetic field stabilization system and method for stabilizing magnetic field

Abstract

The present invention provides a magnetic field stabilization system and a method for stabilizing a magnetic field, comprising: a three-axis magnetometer for detecting the earth's magnetic field in the horizontal direction; a readout module for reading two signals detected by the three-axis magnetometer; a total field detection module for detecting the total field of the earth's magnetic field; a comparison module for comparing the frequency signal output by the total field detection module with a reference signal; a feedback module for feeding back the signals detected by the three-axis magnetometer and the total field detection module to the corresponding three-axis compensation coil; and the three-axis compensation coil for compensating the magnetic field in the horizontal direction of the earth's magnetic field based on the three-axis magnetometer and compensating the magnetic field in the vertical direction of the earth's magnetic field based on the total field detection module to form a total field stabilization. The present invention uses the total field detection module and the three-axis magnetometer for total field-vector joint stabilization, and can obtain a more superior magnetic field stabilization effect.

Description

Technical Field

[0001] The present invention relates to the field of magnetic field detection, and in particular to a magnetic field stabilization system and a method for stabilizing a magnetic field. Background Art

[0002] In the field of magnetic reference metrology, in order to accurately calibrate the performance of highly sensitive magnetic sensors, it is necessary to provide a stable magnetic field in the earth's magnetic field environment.

[0003] The fluxgate meter is a highly sensitive vector detector with a magnetic field noise of up to pT / Hz. 1 / 2 It is widely used in the field of magnetic field measurement. Superconducting quantum interference device (SQUID) is the most sensitive magnetic sensor known so far. The sensitivity of low-temperature superconducting SQUID can reach 1fT (1fT = 10 -15 The sensitivity of high-temperature superconducting SQUID can reach 10fT, and it is an important high-end application magnetic sensor, widely used in biomedicine, geophysical exploration, and basic research.

[0004] The existing total field stabilization system can achieve a stabilization effect of 3-5pT. However, the existing system can only achieve total field stabilization. According to the total field formula of the magnetic field:

[0005]

[0006] It can be seen that in the process of total field stabilization, only the total field B can be ensured. T If the X-direction vector Bx or the Y-direction vector By fluctuates to a certain extent, the Z-direction vector Bz will change accordingly, and the vector fields will affect each other, which is what we do not want to see. Therefore, the total field stabilization system can only ensure that the total field fluctuation in the small space near the probe is small, but cannot ensure that the magnetic field fluctuation in each vector field direction is small, and the sensitivity of the system needs to be improved.

[0007] Therefore, how to simultaneously achieve the stabilization of the total field and the vector field and improve the magnetic field sensitivity has become one of the problems that technical personnel in this field need to solve urgently. Summary of the invention

[0008] In view of the above-mentioned shortcomings of the prior art, an object of the present invention is to provide a magnetic field stabilization system and a method for stabilizing the magnetic field, so as to solve the problems in the prior art that the vector of the total field stabilization is easy to fluctuate and the magnetic field sensitivity is low.

[0009] To achieve the above objectives and other related objectives, the present invention provides a magnetic field stabilization system, which at least includes:

[0010] Three-axis magnetometer, readout module, total field detection module, comparison module, feedback module and three-axis compensation coil;

[0011] The three-axis magnetometer is immersed in the cooling liquid and is arranged in the three-axis compensation coil, and the three-axis magnetometer is used to detect the earth's magnetic field in the horizontal direction;

[0012] The input end of the readout module is connected to the output end of the three-axis magnetometer, and is used to read out two signals detected by the three-axis magnetometer;

[0013] The total field detection module is arranged at the center of the three-axis compensation coil and is used to detect the total field of the earth's magnetic field;

[0014] The comparison module is connected to the output end of the total field detection module, compares the frequency signal output by the total field detection module with a reference signal, and outputs a comparison result;

[0015] The input end of the feedback module is connected to the output end of the comparison module and the readout module, and is connected to the three-axis compensation coil, so as to feed back the signals detected by the total field detection module and the three-axis magnetometer to the corresponding three-axis compensation coil;

[0016] The three-axis compensation coil compensates for the horizontal magnetic field of the earth's magnetic field based on the three-axis magnetometer, and compensates for the vertical magnetic field of the earth's magnetic field based on the total field detection module to form a total field stabilization.

[0017] Optionally, the total field detection module adopts an optical pump.

[0018] Optionally, the three-axis magnetometer is a fluxgate three-axis magnetometer or a giant magnetoresistance sensor three-axis magnetometer.

[0019] Optionally, the three-axis magnetometer adopts a SQUID three-axis magnetometer, and the SQUID three-axis magnetometer includes three SQUID magnetometers, which are respectively arranged on three mutually perpendicular planes and corresponding to the three axial directions of the three-axis compensation coil.

[0020] Optionally, the feedback module includes three proportional-integral-differential circuits, and the input end of each proportional-integral-differential circuit is respectively connected to an axial magnetometer detection signal, and the output end is respectively connected to a corresponding compensation coil.

[0021] More optionally, the proportional-integral-differential circuit includes a proportional amplifier, an integrator and a power amplifier connected in sequence.

[0022] Optionally, the three-axis compensation coil includes compensation coils respectively arranged in three mutually perpendicular axial directions.

[0023] More optionally, the compensation coil is a regular polygon or a circle.

[0024] More optionally, each plane includes two compensation coils, and the two compensation coils in any plane are respectively arranged on both sides of the total field detection module and the SQUID three-axis magnetometer.

[0025] Optionally, the refrigeration liquid is contained in a non-magnetic Dewar, and the refrigeration liquid includes liquid nitrogen or liquid helium.

[0026] To achieve the above-mentioned object and other related objects, the present invention further provides a method for stabilizing a magnetic field, the method for stabilizing a magnetic field at least comprising:

[0027] The total field detection module is arranged at the center of the three-axis compensation coil, and the current of the coil for adjusting the horizontal magnetic field in the three-axis compensation coil is adjusted to make the horizontal magnetic field zero field and retain the vertical magnetic field;

[0028] The total field detection module works normally, compares the frequency signal output by the total field detection module with a reference signal, and drives the compensation coil of the vertical magnetic field based on the comparison result to generate a compensation magnetic field;

[0029] Immersing the three-axis magnetometer in the cooling liquid at the center of the three-axis compensation coil, and adjusting the working point of the three-axis magnetometer to make the three-axis magnetometer work normally;

[0030] The horizontal magnetic field detected by the three-axis magnetometer is fed back to the coil for adjusting the horizontal magnetic field in the three-axis compensation coil through a feedback module, so as to achieve horizontal magnetic field stabilization and thus form a total field stabilization.

[0031] As described above, the magnetic field stabilization system and the method for stabilizing the magnetic field of the present invention have the following beneficial effects:

[0032] The magnetic field stabilization system and the method for stabilizing the magnetic field of the present invention introduce vector stabilization in two other directions on the basis of total field stabilization to form a vector-total field combined stabilization. The magnetic field stabilization system and the method for stabilizing the magnetic field of the present invention can be applied to magnetic reference measurement, and the stability of the total magnetic field and the component field can be obtained at the same time, and good application is obtained in the calibration process of magnetic sensors, especially vector magnetic sensors; the device can also be applied to other occasions where a stable magnetic field is required. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Shown is a schematic structural diagram of the magnetic field stabilization system of the present invention.

[0034] Figure 2 Shown is a schematic structural diagram of the SQUID three-axis magnetometer of the present invention.

[0035] Figure 3 Shown is a structural schematic diagram of the feedback module of the present invention.

[0036] Component number description

[0037] 1 Magnetic field stabilization system

[0038] 11 Three-axis magnetometer

[0039] 11a~11c The first to third SQUID magnetometers

[0040] 12 Readout module

[0041] 13 Total field detection module

[0042] 14 Feedback module

[0043] 141~143 The first to third proportional integral differential circuits

[0044] 1411 Proportional Amplifier

[0045] 1412 Integrator

[0046] 1413 Power Amplifier

[0047] 15 Three-axis compensation coil

[0048] 16 Non-magnetic Dewar DETAILED DESCRIPTION

[0049] 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.

[0050] See also Figure 1 to Figure 3 It 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 drawings 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 type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0051] Compared with the total field stabilization system, the SQUID vector magnetic field stabilization system can not only obtain a stable total field, but also ensure that the vector fields in three directions can be stabilized. However, the SQUID usually needs to work in a low-temperature environment (immersed in liquid helium), and the distance between it and the device under test at room temperature is subject to certain restrictions.

[0052] The present invention introduces vector stabilization in two other directions on the basis of total field stabilization to form a vector-total field combined stabilization device, and the specific scheme is as follows.

[0053] like Figure 1 As shown, the present invention provides a magnetic field stabilization system 1, and the magnetic field stabilization system 1 includes:

[0054] A three-axis magnetometer 11 , a readout module 12 , a total field detection module 13 , a comparison module (not shown in the figure), a feedback module 14 and a three-axis compensation coil 15 .

[0055] like Figure 1 As shown, the three-axis magnetometer 11 is immersed in the cooling liquid and is arranged in the three-axis compensation coil 15. The three-axis magnetometer 11 is used to detect the earth's magnetic field in the horizontal direction.

[0056] Specifically, the three-axis magnetometer 11 is implemented by, but not limited to, a fluxgate three-axis magnetometer, a giant magnetoresistance sensor three-axis magnetometer, or a SQUID three-axis magnetometer. In this embodiment, the three-axis magnetometer 11 is implemented by a SQUID three-axis magnetometer, such as Figure 2 As shown, the SQUID three-axis magnetometer includes three SQUID magnetometers, which are respectively arranged on three mutually perpendicular planes, corresponding to the three axial directions of the three-axis compensation coil. As an example, the first SQUID magnetometer 11a, the second SQUID magnetometer 11b and the third SQUID magnetometer 11c are respectively arranged on the front surface, the upper surface and the left surface (three mutually perpendicular surfaces) of a regular cube. Each SQUID magnetometer is a ring, and the SQUID magnetometer is made of superconducting material and is used to convert the detected magnetometer signal into a voltage signal.

[0057] Specifically, the SQUID three-axis magnetometer operates in a low-temperature environment that causes it to enter a superconducting state. The SQUID three-axis magnetometer is placed in a non-magnetic dewar 16, which contains a refrigerant liquid that provides a low-temperature environment. The SQUID three-axis magnetometer is immersed in the refrigerant liquid to ensure that the SQUID three-axis magnetometer operates in a superconducting state. If the SQUID three-axis magnetometer is made of a high-temperature superconducting material, the refrigerant liquid is liquid nitrogen (temperature is about 77K); if the SQUID three-axis magnetometer is made of a low-temperature superconducting material, the refrigerant liquid is liquid helium (temperature is about 4.2K). In actual use, the refrigerant liquid can be replaced as needed, and is not limited to this embodiment.

[0058] like Figure 1 As shown, the input end of the readout module 12 is connected to the output end of the three-axis magnetometer 11 , and is used to read out the signal detected by the three-axis magnetometer 11 .

[0059] Specifically, in this embodiment, the readout module 12 is a SQUID readout module. The SQUID readout module works in a room temperature environment, is connected to the SQUID three-axis magnetometer through a wire, and uses a multi-channel readout method to debug the working point of each SQUID magnetometer, so that each SQUID magnetometer works normally, and processes the signal detected by the SQUID magnetometer in the SQUID three-axis magnetometer and reads it out. In this embodiment, only two signals for detecting the horizontal magnetic field need to be read out. The SQUID readout module 12 can be implemented by any SQUID readout circuit in the prior art, and its structure will not be described one by one here.

[0060] like Figure 1 As shown, the total field detection module 13 is arranged at the center of the three-axis compensation coil 15, and is used to detect the total field of the earth's magnetic field.

[0061] Specifically, in this embodiment, the total field detection module 13 is implemented by an optical pump. In actual use, any device that can perform total field detection is applicable to the present invention.

[0062] like Figure 1 As shown, the comparison module is connected to the output end of the total field detection module 13, compares the frequency signal output by the total field detection module 13 with a reference signal, and outputs a comparison result.

[0063] Specifically, the differential input end of the comparison module is respectively connected to the output end of the total field detection module 13 and the output end of a frequency counter (not shown in the figure), compares the detected frequency signal with a reference signal, and outputs the amplified comparison result.

[0064] like Figure 1 As shown, the input end of the feedback module 14 is connected to the output end of the readout module 12 and the comparison module, and the output end is connected to the three-axis compensation coil 15, which is used to feed back the signals detected by the three-axis magnetometer 11 and the total field detection module 13 to the corresponding three-axis compensation coil.

[0065] Specifically, Figure 3As shown, in this embodiment, the feedback module 14 includes a first proportional integral differential circuit 141, a second proportional integral differential circuit 142 and a third proportional integral differential circuit 143, and the input end of each proportional integral differential circuit is respectively connected to the two output ends of the readout circuit 12 and the output end of the comparison module, and the output end is respectively connected to the corresponding compensation coil. The signal detected by the total field detection module 13 is input to the input end Ina of the first proportional integral differential circuit 141, and after being processed by the first proportional integral differential circuit 141, it is output to the compensation coil for adjusting the magnetic field in the vertical direction in the three-axis compensation coil 15 (in this embodiment, the compensation coils located in this direction include two, and the output end Outa of the first proportional integral differential circuit 141 is connected to the two compensation coils, Figure 1 For simplicity, only one compensation coil is connected). The first proportional integral differential circuit 141 includes a proportional amplifier 1411, an integrator 1412 connected to the output end of the proportional amplifier 1411, and a power amplifier 1413 connected to the output end of the integrator 1412. Similarly, the signal of the horizontal magnetic field detected by the three-axis magnetometer 11 is respectively input to the input end Inb of the second proportional integral differential circuit 142 and the input end Inc of the third proportional integral differential circuit 143, the output end Outb of the second proportional integral differential circuit 142 and the output end Outc of the third proportional integral differential circuit 143 are respectively connected to the corresponding compensation coil (the SQUID magnetometer is arranged in parallel with the corresponding compensation coil), and the specific circuit structures of the second proportional integral differential circuit 142 and the third proportional integral differential circuit 143 are similar to those of the first proportional integral differential circuit 141, which will not be described in detail here.

[0066] It should be noted that the structures of the proportional-integral-differential circuits include but are not limited to those listed in this embodiment, and any circuit structure that can realize proportional-integral-differential is applicable to the present invention.

[0067] like Figure 1 As shown, the three-axis compensation coil 15 compensates for the horizontal magnetic field of the earth's magnetic field based on the three-axis magnetometer 11, and compensates for the vertical magnetic field of the earth's magnetic field based on the total field detection module 12 to form a total field stabilization.

[0068] Specifically, the three-axis compensation coil 15 includes compensation coils respectively arranged in three mutually perpendicular axes, corresponding to the three axes of the SQUID three-axis magnetometer. In this embodiment, each compensation coil is square, and two compensation coils are arranged in the same axis, respectively located on both sides of the three-axis magnetometer 11 and the total field detection module 12 (to improve the uniformity of the magnetic field); the centers of the two compensation coils in the same axis coincide with each other on a plane perpendicular to the axis, and the outer contour of the three-axis compensation coil 15 is a cube, and the three-axis magnetometer 11 and the total field detection module 12 are located in the central area of ​​the cube structure.

[0069] It should be noted that the shape of the compensation coil includes but is not limited to other annular structures, and is preferably a regular polygon or a circle to improve the uniformity of the magnetic field. The number of compensation coils on the same axis is at least one, and the number of compensation coils can be set as needed, not limited to this embodiment.

[0070] The method for stabilizing the magnetic field by the magnetic field stabilization system is as follows:

[0071] 1) The total field detection module 13 is set at the center of the three-axis compensation coil 15, and the current of the coil for adjusting the horizontal magnetic field in the three-axis compensation coil 15 is adjusted to make the horizontal magnetic field zero field and retain the vertical magnetic field (that is, only the vertical component of the earth's magnetic field remains).

[0072] It should be noted that the horizontal magnetic field described in the present invention is zero field, which means that the horizontal magnetic field is near 0°, and the difference from 0° is within a preset range, which is considered to be zero field, not an absolute zero field, and a static stable field is sufficient. The preset range can be specifically set according to needs, and will not be described one by one here.

[0073] 2) adjusting the total field detection module 13 so that the total field detection module 13 works normally, comparing the frequency signal output by the total field detection module 13 with a reference signal, and driving the compensation coil of the vertical magnetic field based on the comparison result to generate a compensation magnetic field.

[0074] 3) The three-axis magnetometer 11 is immersed in the non-magnetic Dewar 16 at the center of the three-axis compensation coil 15, wherein the non-magnetic Dewar 16 contains a cooling liquid, and the working point of the three-axis magnetometer 11 is debugged based on the readout circuit 12 to make the three-axis magnetometer 11 work normally.

[0075] 4) The detected horizontal magnetic field is fed back to the coil for adjusting the horizontal magnetic field in the three-axis compensation coil 15 through the feedback module 14, so as to achieve a stable magnetic field in the horizontal direction, thereby forming a stable total field.

[0076] Specifically, the outputs of the two SQUID magnetometers for detecting the horizontal magnetic field in the three-axis magnetometer 11 are connected to the input end of the feedback module 14, and the output end of the feedback module 14 is connected to the corresponding feedback coil; the three-axis magnetometer 11 is placed at the center of the three-axis compensation coil 15. In this embodiment, the three-axis directions of the SQUID three-axis magnetometer are respectively consistent with the directions of the three-axis compensation coil 15; in actual use, the directions of the two axes in the SQUID three-axis magnetometer are parallel to the two coils in the three-axis compensation coil 15 that generate the horizontal magnetic field. Then the whole system is placed in a quiet earth magnetic field environment.

[0077] Specifically, the feedback module 14 is turned on and its parameters are adjusted to achieve a stabilization of the magnetic field in the horizontal direction, thereby achieving simultaneous stabilization of the total field and the vector field.

[0078] It should be noted that the steps of the method for stabilizing the magnetic field of the present invention are not limited to those listed in this embodiment. Any logical adjustment of the steps that can achieve the method for stabilizing the magnetic field of the present invention is applicable to the present invention and will not be described in detail here.

[0079] The present invention adopts a total field detection module, a set of three-axis magnetometers, a feedback module (three-way feedback circuit) and a three-axis feedback coil to achieve magnetic field vector stabilization and total field stabilization in a quiet earth magnetic field environment, and provide an extremely stable magnetic field environment for weak magnetic reference devices and other applications. The present invention stabilizes the component magnetic fields while obtaining a highly stable total magnetic field; at the same time, the optical pump is a room temperature working device, which can shorten the distance between the stabilization detector and the detector to be tested compared to the pure SQUID three-axis stabilization method.

[0080] In summary, the present invention provides a magnetic field stabilization system and a method for stabilizing the magnetic field. Two sets of coils are used to compensate the horizontal direction of the earth's magnetic field to near zero field (static stabilization), so that only the vertical magnetic field is left. Then, an optical pump is used as a total field magnetic probe, and its output is compared with a frequency counter to drive the vertical feedback coil to generate a stabilizing magnetic field opposite to the external fluctuation, forming a total field stabilization system; on this basis, a three-axis magnetometer (only its horizontal direction probe is used) and a feedback module and a compensation coil are used to form two horizontal compensation devices. The present invention places a SQUID three-axis magnetometer working in a low temperature environment at the center of the compensation coil, detects the environmental magnetic field fluctuation and feeds it to the feedback module, and the feedback module then drives the compensation coil to generate a compensation magnetic field opposite to the environmental magnetic field fluctuation, so as to achieve the purpose of stabilizing the horizontal magnetic field fluctuation. On the basis of the traditional total field stabilization, the present invention upgrades the stabilization mode and uses the total field-vector field joint stabilization method to upgrade the system from the total field stabilization capability to the total field and vector field stabilization capability. The field stability performance of the magnetic reference device is greatly improved, and a new method is provided for the calibration of low-noise magnetic sensors, especially the calibration of vector sensors. Therefore, the present invention effectively overcomes various shortcomings in the prior art and has high industrial utilization value.

[0081] 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 magnetic field stabilization system, characterized in that: The magnetic field stabilization system at least comprises: Three-axis magnetometer, readout module, total field detection module, comparison module, feedback module and three-axis compensation coil; The three-axis magnetometer is immersed in the cooling liquid and is arranged in the three-axis compensation coil, and the three-axis magnetometer is used to detect the earth's magnetic field in the horizontal direction; The input end of the readout module is connected to the output end of the three-axis magnetometer, and is used to read out two signals detected by the three-axis magnetometer; The total field detection module is arranged at the center of the three-axis compensation coil and is used to detect the total field of the earth's magnetic field; The comparison module is connected to the output end of the total field detection module, compares the frequency signal output by the total field detection module with a reference signal, and outputs a comparison result; The input end of the feedback module is connected to the output end of the readout module and the comparison module, and is connected to the three-axis compensation coil, and is used to feed back the signals detected by the three-axis magnetometer and the total field detection module to the corresponding three-axis compensation coil; The three-axis compensation coil compensates for the horizontal magnetic field of the earth's magnetic field based on the three-axis magnetometer, and compensates for the vertical magnetic field of the earth's magnetic field based on the total field detection module to form a total field stabilization.

2. The magnetic field stabilization system according to claim 1, characterized in that: The total field detection module adopts an optical pump.

3. The magnetic field stabilization system according to claim 1, characterized in that: The three-axis magnetometer is a fluxgate three-axis magnetometer or a giant magnetoresistance sensor three-axis magnetometer.

4. The magnetic field stabilization system according to claim 1, characterized in that: The three-axis magnetometer adopts a SQUID three-axis magnetometer, and the SQUID three-axis magnetometer includes three SQUID magnetometers, which are respectively arranged on three mutually perpendicular planes and corresponding to the three axial directions of the three-axis compensation coil.

5. The magnetic field stabilization system according to claim 1, characterized in that: The feedback module includes three proportional-integral-differential circuits, wherein the input end of each proportional-integral-differential circuit is respectively connected to an axial magnetometer detection signal, and the output end is respectively connected to a corresponding compensation coil.

6. The magnetic field stabilization system according to claim 5, characterized in that: The proportional-integral-differential circuit comprises a proportional amplifier, an integrator and a power amplifier which are connected in sequence.

7. The magnetic field stabilization system according to claim 1, characterized in that: The three-axis compensation coil includes compensation coils respectively arranged in three mutually perpendicular axial directions.

8. The magnetic field stabilization system according to claim 7, characterized in that: The compensation coil is a regular polygon or a circle.

9. The magnetic field stabilization system according to claim 7, characterized in that: Each axial direction includes two compensation coils, and the two compensation coils on any axial direction are respectively arranged on both sides of the total field detection module and the three-axis magnetometer.

10. The magnetic field stabilization system according to claim 1, characterized in that: The refrigeration liquid is contained in a non-magnetic Dewar, and the refrigeration liquid includes liquid nitrogen or liquid helium.

11. A method for stabilizing a magnetic field, based on the magnetic field stabilization system according to any one of claims 1 to 10, characterized in that: The method for stabilizing the magnetic field at least comprises: The total field detection module is arranged at the center of the three-axis compensation coil, and the current of the coil for adjusting the horizontal magnetic field in the three-axis compensation coil is adjusted to make the horizontal magnetic field zero field and retain the vertical magnetic field; The total field detection module works normally, compares the frequency signal output by the total field detection module with a reference signal, and drives the compensation coil of the vertical magnetic field based on the comparison result to generate a compensation magnetic field; Immersing the three-axis magnetometer in the cooling liquid at the center of the three-axis compensation coil, and adjusting the working point of the three-axis magnetometer to make the three-axis magnetometer work normally; The horizontal magnetic field detected by the three-axis magnetometer is fed back to the coil for adjusting the horizontal magnetic field in the three-axis compensation coil through a feedback module, so as to achieve horizontal magnetic field stabilization and thus form a total field stabilization.

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