SQUID magnetic gradient tensor probe structure based on planar cross layout and measurement system

Abstract

The invention relates to the technical field of superconducting weak magnetic detection, and particularly provides an SQUID magnetic gradient tensor probe structure based on a planar cross layout and a measurement system, the SQUID magnetic gradient tensor probe structure comprises a first differential SQUID sensor group and a second differential SQUID sensor group which are arranged in a cross shape, each sensor group comprises a plurality of three-axis SQUID sensors which are symmetrically arranged along an X axis and a Y axis, according to the invention, all independent components of the magnetic gradient tensor can be measured only by using four three-axis SQUID sensors, and compared with a traditional multi-sensor (such as a six-prismatic table structure or an eight-sensor structure) probe, the number of the SQUID sensors and the use amount of liquid helium are obviously reduced, the manufacturing and operation cost of the system is effectively reduced, and the system is suitable for large-scale popularization and application. And meanwhile, the number of each group of sensors can be further adjusted according to a measurement scene, so that the robustness and the sensitivity of gradient tensor precision are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of superconducting weak magnetic field detection, and in particular to a SQUID magnetic gradient tensor probe structure and a measurement system based on a planar cross layout. Background Art

[0002] Magnetic field detection can be categorized into magnetic field scalar measurement (measuring only magnetic field magnitude), three-component magnetic field vector measurement (measuring both magnetic field magnitude and direction), and magnetic gradient tensor measurement. Magnetic gradient tensor measurement is widely used in geophysical exploration, magnetic anomaly detection, and measurement of weak magnetic signals such as cardiac and cerebral magnetometry. The magnetic gradient tensor is a second-order tensor that describes the rate of change of the magnetic field in space. It reflects the speed of magnetic field variation in all directions and is the derivative matrix of the magnetic field vector with respect to spatial coordinates. Magnetic gradient tensor measurements are typically performed using a distributed array of probes fixed in a probe assembly, with the center gradient value approximated using a differential method. Therefore, proper probe structural design is crucial for magnetic gradient tensor measurement accuracy. Currently, common sensors used to construct magnetic gradient tensor detection include fluxgate sensors, magnetoresistive sensors, optical pump sensors, and superconducting quantum interference magnetic sensors. Among them, the fluxgate sensor uses the change between the saturation and unsaturation states of the magnetic core to detect changes in the external magnetic field and has good stability; the magnetoresistive sensor uses the anisotropic magnetoresistive effect AMR, the giant magnetoresistive effect GMR, and the tunnel magnetoresistive effect TMR to detect the resistance change caused by the magnetic field. It has the characteristics of miniaturization and is convenient for array arrangement. However, the above two magnetic sensors are less sensitive than the superconducting quantum interference device (SQUID). The optically pumped magnetometer can also perform spatial differential measurement through an array design, but the optically pumped sensor measures the magnetic field scalar. The subsequent calculation of the measurement array constructed for the magnetic gradient tensor vector measurement is complex and prone to introduce calculation errors. The SQUID sensor is a weak magnetic detection device constructed based on the Josephson effect and the magnetic flux quantization effect. Its sensitivity is as high as 10 -15 The SQUID magnetic gradient tensor detection system has a small size and is easy to arrange in space to achieve tensor gradient vector measurement. Therefore, many scholars have conducted extensive research on the probe structure of the SQUID magnetic gradient tensor detection system.

[0003] Schmidt et al. designed a rotating magnetic gradient tensor measurement probe, such as Figure 1 As shown in the figure, the probe structure utilizes two magnetometers designed as a differential magnetic gradiometer with a baseline length of 10 cm. This system measures all components of the magnetic gradient tensor using a rotating system whose axis is angled 45° with the horizontal plane. While this rotational approach reduces the number of sensors, it relies heavily on the mechanical precision and attitude control of the spatial rotation mechanism, limiting its application in real-time measurements and on dynamic platforms.

[0004] Stolz et al. designed a hexagonal probe structure, such as Figure 2 As shown, this probe structure consists of six SQUID magnetic gradiometers arranged on the inclined surfaces of a hexagonal pyramid. It can simultaneously record all magnetic gradient tensors, but is affected by gradiometer imbalance. Chwala et al. built on this by placing a triaxial SQUID magnetometer at the center of the hexagonal pyramidal probe structure as compensation to record the full magnetic field tensor. J. Voigt et al. developed a magnetic gradient tensor probe structure consisting of 13 cryogenic SQUIDs. This structure acquires magnetic gradient tensor data through multi-channel probes symmetrically distributed on each facet of a hollow solid and a compensating magnetometer at the center. However, the larger probe volume implies high liquid helium costs and greater structural errors. TJ Gamey reported on a magnetic gradient tensor detection system designed with eight SQUID magnetometers. To reduce the number of sensors, this probe structure reuses sensors at a single location multiple times and distributes them along the three axes of the probe assembly, forming a differential sensor measurement pair using a face-to-face arrangement.

[0005] In practical applications, the above-mentioned multi-sensor probe configurations (such as eight-sensor arrays and hexagonal pyramid sensor arrays) often introduce differential center offsets due to baseline and structural space layout problems, resulting in large errors in tensor component calculations, thereby reducing measurement accuracy. In particular, they are more susceptible to the amplification of system noise and structural errors in weak magnetic environments. Summary of the Invention

[0006] In view of this, the present invention proposes a SQUID magnetic gradient tensor probe structure and measurement system based on a planar cross layout. Specifically, a planar cross SQUID magnetic gradient tensor probe structure with a simple structure, high differential accuracy, good symmetry, and easy implementation and manufacturing is provided. On the basis of ensuring the complete measurement of tensor components, this structure simplifies the differential calculation path through geometric symmetry, effectively suppresses the error accumulation caused by the differential center offset, and improves the tensor measurement consistency and robustness of the system, so as to solve the problems existing in the existing magnetic gradient measurement system, such as large differential center offset error, complex probe layout, and difficulty in error modeling.

[0007] On the one hand, to achieve the above-mentioned object, the present invention proposes a SQUID magnetic gradient tensor probe structure based on a planar cross layout, characterized in that it includes a first differential SQUID sensor group and a second differential SQUID sensor group, wherein the first differential SQUID sensor group and the second differential SQUID sensor group are arranged in the same plane;

[0008] The first differential SQUID sensor group includes a plurality of first three-axis SQUID sensors symmetrically arranged on a central support along the X axis;

[0009] The second differential SQUID sensor group includes a plurality of second three-axis SQUID sensors symmetrically arranged along the Y axis on the central support;

[0010] A plurality of the first three-axis SQUID sensors and the second three-axis SQUID sensors are distributed in a cross shape.

[0011] Furthermore, a plurality of the first three-axis SQUID sensors and the second three-axis SQUID sensors are fixed to the central support by non-magnetic materials.

[0012] Furthermore, the spacing between the plurality of first three-axis SQUID sensors and the second three-axis SQUID sensors is adjusted according to baseline optimization requirements of the measurement scenario.

[0013] Furthermore, the probe structure is arranged in a Dewar system, and a superinsulating material and a magnetic shielding gasket are provided on the top of the Dewar.

[0014] Furthermore, in the SQUID magnetic gradient tensor probe structure based on a planar cross layout, the magnetic gradient tensor component value of the center of the probe structure is obtained by combining and differentially calculating the magnetic field measurement value of each sensor itself and the magnetic field measurement value of the symmetrical sensor.

[0015] Furthermore, the magnetic gradient tensor matrix of the SQUID magnetic gradient tensor probe structure based on the planar cross layout is as follows:

[0016] ,

[0017] in, is a symmetric matrix, represents the magnetic gradient tensor, represents the magnetic field vector, represents the magnetic field coordinates.

[0018] On the other hand, to achieve the above-mentioned purpose, the present invention proposes a magnetic gradient tensor measurement system of the above-mentioned probe structure, characterized in that it includes an upper cover plate, the upper cover plate is connected to a planar cross-shaped sensor mounting plate via a connecting shaft, and the planar cross-shaped sensor mounting plate is provided with the probe structure described in any one of claims 1-4.

[0019] Furthermore, a liquid helium infusion port, a liquid level gauge monitoring port, an air pressure balance port and a central through hole are provided in the upper cover plate.

[0020] Furthermore, a plurality of super-insulating materials are connected to the connecting shaft, and a magnetic shielding gasket structure is provided between the plurality of super-insulating materials.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The proposed planar cross-shaped probe structure features a strictly symmetrical layout, with the sensors of each differential sensor group arranged symmetrically along their corresponding axes, effectively eliminating differential center offset errors. Simulation results demonstrate that this probe structure improves measurement accuracy by approximately one order of magnitude compared to a traditional eight-sensor structure under low-noise conditions. The average relative error of the tensor invariant C is reduced by 17.79% when the sensor resolution ranges from 1 fT to 0.1 nT.

[0023] The present invention uses only four three-axis SQUID sensors to achieve the measurement of all independent components of the magnetic gradient tensor. Compared with traditional multi-sensor probes (such as hexagonal pyramid structures or eight-sensor structures), the number of SQUID sensors and the amount of liquid helium used are significantly reduced, effectively reducing the manufacturing and operating costs of the system.

[0024] All sensors in the probe structure of the present invention are located in the same horizontal plane, ensuring temperature uniformity between sensors, thereby avoiding measurement errors caused by temperature differences and improving the robustness and long-term stability of the system in actual engineering environments.

[0025] The probe structure of the present invention is designed as a planar cross-shaped layout, and the installation hole position of each sensor can be accurately processed and determined according to actual measurement requirements. The structure is simple and easy to manufacture, which is convenient for practical engineering application and promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Various other advantages and benefits will become apparent to those skilled in the art by reading the detailed description of the preferred embodiment below. The accompanying drawings are only for the purpose of illustrating the preferred embodiment and are not to be considered as limiting the present invention. In the accompanying drawings:

[0027] Figure 1 This is an existing rotating magnetic gradient tensor measurement probe in the background technology of the present invention, wherein (a) is a probe structure diagram, and (b) is a schematic diagram of the measurement principle;

[0028] Figure 2 Schematic diagram of the structure of an existing hexagonal pyramid probe in the background technology and embodiments of the present invention;

[0029] Figure 3 Schematic diagram of the existing 8-sensor probe structure in an embodiment of the present invention, where (a) is the probe structure and (b) is the sensor position design principle;

[0030] FIG4 is a schematic diagram of the planar cross-shaped probe structure proposed in the present invention, wherein (a) is the front structure and (b) is the back structure;

[0031] Figure 5 The sensor position design principle of the planar cross-shaped probe structure of the present invention;

[0032] Figure 6 This is a schematic diagram of the structure of the magnetic gradient tensor measurement system based on a planar cross-shaped probe structure proposed in the present invention;

[0033] Figure numerals: 1. upper cover plate; 2. superinsulation material; 3. magnetic shielding gasket structure; 4. liquid helium infusion tube; 5. connecting shaft; 6. flat cross-shaped sensor mounting plate. DETAILED DESCRIPTION

[0034] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art. It should be noted that, unless there is a conflict, the embodiments of the present disclosure and the features described in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0035] According to the description of existing probe structures in the background technology, all current probes have the problem of detection point offset. The following two probe structures with the widest application are used as examples:

[0036] 1. Hexagonal pyramid structure: The hexagonal pyramid structure uses 6 SQUID magnetic gradiometers arranged on each inclined plane of the hexagonal pyramid structure to achieve non-coplanar measurement, and then uses the linear solution process to calculate the magnetic gradient tensor matrix, and finally achieve tensor measurement. Among them, the SQUID magnetic gradiometer also uses the Josephson effect and the magnetic flux quantization effect to form a magnetic sensitive unit. At the same time, when designing the device, the pickup coil is reversely wound to form a special configuration of a double-loop device. The magnetic flux difference of the two pickup coils is coupled with the Josephson junction in the SQUID to directly achieve gradient measurement. When the sensor is working, the SQUID magnetic gradiometer responds to the gradient value at the center position of the two pickup coils. Figure 2 As shown in the figure, according to its structural characteristics, the gradiometer actually measures the gradient values ​​at the center of the six slopes, and finally approximates the gradient value at the center of the probe structure by solving a linear equation. This structural layout will cause the final measurement to have a measurement point position offset problem. This measurement point position offset causes serious errors in achieving high-precision positioning and weak magnetic target inversion.

[0037] 2. 8-sensor structure: The 8-sensor probe structure uses SQUID magnetometers to be differentially arranged in space to achieve gradient tensor measurement. Each sensor forms a differential measurement sensor pair with another sensor in the baseline direction. SQUID magnetometers are sensitive to magnetic field strength perpendicular to the sensor plane. Therefore, this characteristic is utilized to achieve magnetic gradient tensor measurement through a reasonable layout in three-axis space. The magnetic gradient tensor reflects the change in magnetic field. The tensor matrix has 9 components and is defined as follows:

[0038] Magnetic field vector The gradient in space is the magnetic gradient tensor, symbolized by G.

[0039]

[0040] In the formula, G represents the magnetic gradient tensor matrix, etc. represent the components in the tensor matrix. For example, Bxx represents the gradient value of the Bx component in the X-axis direction. According to Maxwell's equations, in a passive static magnetic field, the curl and divergence of the magnetic field vector are both 0, which means that the matrix G is symmetric and traceless. Therefore, only five components in the matrix are independent. In actual measurement, it is only necessary to obtain These five independent components can obtain all 9 tensor components in space.

[0041] 8Sensor probe structure according to Figure 3 The position shown is installed on the magnetic gradient tensor probe. The Cartesian coordinate system is defined with the origin located at the center of the probe structure. The first-order planar SQUID magnetometer can measure the magnetic field strength in the direction of the normal vector of the SQUID magnetometer pickup coil. The normal vector is defined as the sensitive axis of the sensor. , the sensitive axes of magnetometers S1-S3 are parallel to the x-axis, the sensitive axes of magnetometers S4-S6 are parallel to the y-axis, and the sensitive axes of magnetometers S7 and S8 are parallel to the z-axis. The tensor matrix of this structure is expressed as:

[0042]

[0043] In the formula It represents the magnetic field strength measurement value of sensor i at the corresponding position (i=1~8). It represents the baseline length in the corresponding direction. From the above formula, we can know that Bzz is the gradient component at the center position of the probe, but Bxx represents the gradient value of the center point in the direction of the line connecting sensors 5 and 6. Such a spatial layout causes the measurement point offset of the Bxx component, which ultimately causes the overall gradient tensor measurement error, thereby affecting the subsequent target positioning accuracy of magnetic detection.

[0044] Example 1

[0045] From the above analysis, it can be seen that most existing differential magnetic gradient tensor probes use SQUID sensors at measurement points located near the probe support structure to approximate the magnetic gradient tensor value at the center of the entire probe structure (there is a differential center offset), making it difficult to achieve accurate single-point gradient tensor measurement. Based on this, this embodiment proposes a SQUID magnetic gradient tensor probe structure based on a planar cross layout, as shown in Figure 4, including:

[0046] Center bracket, used to install the sensor and provide mechanical support for the entire probe;

[0047] Multiple sensor mounting holes on the center bracket allow for flexible baseline selection in different detection scenarios;

[0048] A first differential SQUID sensor group includes two SQUID magnetic sensors, which are symmetrically arranged on both sides of the central support along the X-axis and are equidistant from the center of the support;

[0049] The second differential SQUID sensor group includes two SQUID magnetic sensors, which are symmetrically arranged on both sides of the central support along the Y-axis and are equidistant from the center of the support;

[0050] Each of the above-mentioned SQUID sensors is a three-axis SQUID magnetometer that uses the principle of superconducting quantum interference to achieve high-precision measurement of magnetic flux. The spacing between the two sensors in each differential sensor group along the corresponding axis (i.e., the differential baseline) is strictly identical, thus forming a precise central differential structure, avoiding measurement errors caused by offset of the differential center position.

[0051] like Figure 5 As shown, the first differential SQUID sensor group and the second differential SQUID sensor group are perpendicular to each other in the same horizontal plane, forming a cross-shaped layout. This structure ensures that the probe has a clear and symmetrical differential structure in the three spatial directions of XYZ, effectively reducing the differential calculation error caused by structural deviation.

[0052] In particular, the first differential SQUID sensor group and the second differential SQUID sensor need to work in liquid helium. All sensor groups are located on the same horizontal plane to ensure that the temperature of the liquid helium they are in is consistent, avoiding the temperature inconsistency caused by the volatilization of liquid helium in the upper layer of the Dewar, which affects the measurement of the three-axis SQUID magnetometer.

[0053] As a preferred embodiment, the SQUID sensors in each sensor group are fixed to the central bracket using copper or non-magnetic stainless steel bolts to reduce magnetic field interference introduced by the mounting material;

[0054] As a preferred embodiment, the above-mentioned central bracket is a cross-shaped rigid support structure, and the installation position of each differential SQUID sensor on the bracket is precisely processed and determined in advance to ensure that the differential center of each differential group is accurately located at the central reference sensor position, thereby significantly improving the accuracy of gradient tensor measurement.

[0055] As a preferred embodiment, the central bracket is connected to a rigid connecting shaft, and the upper and lower ends of the connecting shaft are provided with threads connected to the upper cover plate and the bottom mounting plate respectively;

[0056] As a preferred embodiment, the probe is externally cooled by a Dewar system with liquid helium, and the connecting shaft passes through the Dewar to ensure effective connection between the internal sensor mounting plate and the external readout circuit;

[0057] As a preferred embodiment, super-insulating material and magnetic shielding gaskets are provided on the top of the Dewar to prevent interference from the environmental magnetic field and temperature.

[0058] Cross-shaped probe structure design process: During probe design, to prevent SQUID measurement errors caused by inconsistent liquid helium temperature, all three-axis SQUID sensors were designed on a single plane, within the bottom slot of the probe structure. The placement of all sensors on the same plane ensures temperature consistency in the measurement environment. The sensors were installed in the bottom slot for easy wiring, facilitating low-temperature cable connection from the liquid helium low-temperature environment to the room temperature environment. The sensor output was connected to the LEMO aviation plug-in interface of the electronic readout unit at the top of the probe rod via a special low-temperature twisted-pair insulated copper wire. Precision machining was used to achieve precise sensor fitting at the bottom of the probe structure, ensuring orthogonality between the two sets of SQUID three-axis sensors and consistent slot depth, ensuring that the SQUID sensors were on the same horizontal plane in the liquid helium. The baseline distance was designed based on the magnetic moment of the target being measured, the detection distance, and the background magnetic field noise level. In particular, the described multiple sensor groups enable high-order differential measurements: When using SQUIDs to measure the magnetic gradient tensor, tensor measurements can be achieved using four SQUID sensors arranged equidistant from the central through-hole. To further improve the accuracy and anti-interference capability of gradient tensor measurements, the present invention also proposes an expanded design for high-order differential measurement based on multiple sensor groups. Building on the existing planar cross layout, multiple groups of three-axis SQUID magnetometers can be added in the X and Y axes, forming a multi-level symmetrically distributed differential measurement structure, enabling first-order, second-order, and even higher-order differential approximations.

[0059] In terms of structural design, the extended sensor groups are symmetrically arranged along the X and Y axes, ensuring that the geometric center of each differential pair is strictly aligned with the probe center reference point. The differential baseline distance between each sensor can be adaptively optimized based on the magnetic moment of the measured target, the observation distance, and the background noise level. For example, by adding three-axis sensors at ±2a, ±3a, and other positions to the original ±a position, second- and third-order differential formats can be constructed.

[0060] In terms of measurement principle, high-order differential measurement can approximate a more accurate gradient expression by weighted combination of magnetic field values ​​measured by multiple sensors. For example, in the x-direction, the three-point second-order central difference of the gradient can be expressed as:

[0061]

[0062] Where Bx represents the SQUID magnetic sensor measurement value at the current position, d represents the baseline distance (from the center position to the fixed hole position), It represents the partial derivative of the X-axis measurement value of the three-axis magnetometer in the x-direction. Specifically, it is represented as the Bxx tensor in the magnetic gradient tensor matrix. The other components in the matrix are not listed one by one, but are similar to this.

[0063] Specifically, the above probe structure solves the technical problem in the following ways:

[0064] (1) The two sensors of each differential SQUID sensor group are arranged strictly symmetrically along the corresponding direction. Their role is to ensure that the central differential position error is minimized during the differential calculation process, thereby reducing the gradient measurement error and improving the system sensitivity;

[0065] (3) Each three-axis SQUID sensor is connected and fixed to the central bracket by non-magnetic materials (non-magnetic stainless steel screws / copper screws). Its function is to avoid magnetic field disturbances introduced by metal materials and ensure the stability and accuracy of the measurement.

[0066] In practical applications, through the above-mentioned cross-shaped layout structure, all independent components of the magnetic gradient tensor (B_xx, B_yy, B_xy, B_xz, B_yz, etc.) can be directly obtained, and the spatial position and characteristics of the magnetic field source can be accurately inverted.

[0067] Working principle of the planar cross SQUID magnetic gradient tensor probe structure:

[0068] The cross-shaped SQUID magnetic gradient tensor probe in the present invention uses two sets of orthogonally arranged differential three-axis SQUID sensor groups, which are symmetrically distributed along the X-axis and Y-axis on both sides of the central bracket. The four three-axis sensors are arranged in a planar cross shape. Each three-axis SQUID sensor can sense the B at its location.x , B y , B z Three magnetic field vector components. The magnetic gradient tensor G = ∇B represents the rate of change of the magnetic field in space and is a 3×3 matrix containing a total of 9 components. However, in a passive static magnetic field, the tensor is symmetric and traceless due to the constraints of Maxwell's equations, and ultimately only 5 independent components need to be measured (such as Bxx, Byy, Bxy, Bxz, and Byz). The present invention uses the following differential approximation method to obtain the first-order derivative of the magnetic field with respect to the spatial coordinates, that is, the individual components of the tensor: it can be calculated by the difference of the Bx measurement values ​​of two sensors arranged symmetrically on the x-axis:

[0069]

[0070] Where +d and −d are the symmetrical distances of the sensor relative to the center position. Similarly, the remaining components such as Byy, Bxy, Bxz, and Byz can be derived by combining and differentiating the Y-axis and the measured components on each axis. The final tensor matrix derivation process is:

[0071] Magnetic gradient tensor definition The magnetic gradient tensor is the magnetic field vector Space coordinates The derivative of:

[0072]

[0073] According to Maxwell's equations for passive static magnetic field:

[0074] (Traceless)

[0075] is a symmetric matrix: Therefore, only the following five independent components need to be measured to fully determine the magnetic gradient tensor:

[0076]

[0077] The difference expression of the tensor components of the cross-shaped planar structure is:

[0078] Assume that the sensors along the X axis are numbered S1 (-d), S2 (+d), and those along the Y axis are numbered S3 (-d), S4 (+d), and each sensor is a three-axis SQUID, where

[0079]

[0080]

[0081]

[0082]

[0083] The remaining components are completed according to symmetry and tracelessness: , , , .

[0084] In addition, the present invention also provides an alternative form of technical solution: according to the actual measurement accuracy requirements, the number of differential sensors can be appropriately increased, such as adding multiple groups of SQUID sensors on each axis to form a multi-baseline differential measurement structure, thereby further improving the robustness and sensitivity to the gradient tensor accuracy.

[0085] The above-mentioned SQUID magnetic gradient tensor probe structure, due to its clear symmetrical layout, strict differential baseline precision control, central reference point setting and other technical features, effectively overcomes the defects of structural complexity, insufficient differential accuracy and sensitivity to environmental noise in the existing technology, significantly improves the accuracy and reliability of measurement, and is particularly suitable for high-precision magnetic gradient detection fields such as aerial magnetic detection, geophysical exploration, biomagnetic field detection, and unexploded ordnance detection.

[0086] Example 2

[0087] This embodiment proposes a SQUID magnetic gradient tensor measurement system based on the above-mentioned planar cross layout SQUID magnetic gradient tensor probe structure. Figure 6 As shown, it includes an upper cover plate 1, superinsulation material 2, a magnetic shielding gasket structure 3, a liquid helium infusion tube 4, a connecting shaft 5, and a flat cross-shaped sensor mounting plate 6;

[0088] The upper cover 1 is used to support and fix the entire probe structure, including a liquid helium infusion port, a liquid level gauge monitoring port, an air pressure balance port, and a central through hole for the support rod 5 to pass through the cover and connect to the lower flat cross-shaped sensor mounting plate 6;

[0089] Superinsulation material 2 is used to achieve liquid helium insulation. Its characteristic is that it is consistent with the size of the Dewar aperture to prevent frost on the top structure due to temperature drop, which would affect the measurement results.

[0090] The magnetic shielding gasket structure 3 is used to shield external magnetic field interference;

[0091] The liquid helium infusion pipe 4 is used to transport liquid helium to the middle section of the Dewar to avoid liquid helium consumption caused by transporting liquid helium from the top;

[0092] The connecting shaft 5 is used to connect the external readout circuit to the bottom sensor and support the entire structure. It is characterized by: the top and bottom ends are mounting threads, connecting the lower end of the flat cross-shaped probe structure;

[0093] The flat cross-shaped sensor mounting plate 6 is installed at the position of the SQUID magnetometer. The plate has precise sensor mounting slots arranged in a cross shape to ensure that the sensor is strictly symmetrical and located in the center of the structure.

[0094] The bottom and top of the connecting shaft 5 are screwed to a planar cross-shaped sensor mounting plate 6 and the upper cover plate 1, respectively, ensuring overall structural stability and robustness. Multiple sensors are precisely fixed to the bottom planar cross-shaped sensor mounting plate 6 with copper non-magnetic bolts to achieve accurate magnetic gradient tensor measurement. At the lowest end of the structure, a planar cross-shaped sensor mounting plate 6 is provided with a precise cross-shaped slot for mounting the SQUID magnetic field sensor, ensuring the central symmetry of the detection system and effectively avoiding differential center offset errors. A connecting rod 5 runs through the entire structure, ensuring a tight connection between the bracket and the gasket, ensuring the overall structural strength and stability.

[0095] The above structural layout is clear and compact, the positions of the components are clear, and it has good stability and measurement accuracy, meeting the needs of high-precision magnetic gradient tensor measurement.

[0096] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the scope of protection of the claims of the present invention.

Claims

1. A SQUID magnetic gradient tensor probe structure based on a planar cross layout, characterized in that: The device comprises a first differential SQUID sensor group and a second differential SQUID sensor group, wherein the first differential SQUID sensor group and the second differential SQUID sensor group are arranged in the same plane; The first differential SQUID sensor group includes a plurality of first three-axis SQUID sensors symmetrically arranged on a central support along the X axis; The second differential SQUID sensor group includes a plurality of second three-axis SQUID sensors symmetrically arranged along the Y axis on the central support; A plurality of the first three-axis SQUID sensors and the second three-axis SQUID sensors are distributed in a cross shape.

2. The SQUID magnetic gradient tensor probe structure based on a planar cross layout according to claim 1 is characterized in that: A plurality of the first three-axis SQUID sensors and the second three-axis SQUID sensors are fixed to a central support through non-magnetic materials.

3. The SQUID magnetic gradient tensor probe structure based on a planar cross layout according to claim 1, characterized in that: The spacing between the plurality of first three-axis SQUID sensors and the plurality of second three-axis SQUID sensors is adjusted according to the baseline optimization requirements of the measurement scenario.

4. The SQUID magnetic gradient tensor probe structure based on a planar cross layout according to claim 1, characterized in that: The probe structure is arranged in a dewar system, and a superinsulating material and a magnetic shielding gasket are arranged on the top of the dewar.

5. The SQUID magnetic gradient tensor probe structure based on a planar cross layout according to claim 1, characterized in that: In the SQUID magnetic gradient tensor probe structure based on a planar cross layout, the tensor gradient component at the center of the probe structure is obtained by combining and differentially calculating the magnetic field measurement values ​​at the locations of each sensor and the magnetic field measurement values ​​of the symmetrical sensors.

6. The SQUID magnetic gradient tensor probe structure based on a planar cross layout according to claim 1, characterized in that: The magnetic gradient tensor matrix of the SQUID magnetic gradient tensor probe structure based on the planar cross layout is as follows: ， in, is a symmetric matrix, represents the magnetic gradient tensor, represents the magnetic field vector, represents the magnetic field coordinates.

7. A magnetic gradient tensor measurement system according to the probe structure according to any one of claims 1 to 6, characterized in that: The device comprises an upper cover plate (1), wherein the upper cover plate (1) is connected to a planar cross-shaped sensor mounting plate (6) via a connecting shaft (5), and the planar cross-shaped sensor mounting plate (6) is provided with a probe structure according to any one of claims 1 to 4.

8. The magnetic gradient tensor measurement system according to claim 7, characterized in that: The upper cover plate (1) is provided with a liquid helium infusion port, a liquid level gauge monitoring port, an air pressure balance port and a central through hole.

9. The magnetic gradient tensor measurement system according to claim 7, characterized in that: A plurality of super-insulating materials (2) are also connected to the connecting shaft (5), and a magnetic shielding gasket structure (3) is provided between the plurality of super-insulating materials (2).

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