A device and method for measuring the residual magnetic field strength of a magnetic shielded cavity

Abstract

The application relates to the technical field of magnetic field detection, in particular to a magnetic shielding cavity residual magnetic field strength measuring device and method, which comprises a probe tube, a detection system, a stabilizing system and a data processing terminal, the probe tube can be telescoped and rotated, the detection system is fixedly installed on the probe tube, the stabilizing system is arranged outside the probe tube and is used for offsetting the gravity moment of the probe tube and feeding back the tilting state of the probe tube in real time, and the data processing terminal realizes data interpolation and residual magnetic field cloud map generation in the magnetic shielding device. In the method, the carbon fiber probe tube is inserted through a magnetic shielding cavity cover plate, a support frame is adjusted and locked, then the probe tube is telescopically adjusted stage by stage, the probe tube is rotated after each telescopic adjustment, magnetic field data of each point is recorded, spatial coordinates of each measuring point are calculated by combining a probe tube scale and a rotation angle, a three-dimensional residual magnetic field cloud map is generated by using a radial basis function interpolation method, the cloud map distribution is analyzed, a shielding weak area is located, and structure optimization is guided.

Description

Technical Field

[0001] This invention relates to the field of magnetic detection technology, and in particular to a device and method for measuring the residual magnetic field strength of a magnetically shielded cavity. Background Technology

[0002] Magnetic shielding cavities are widely used in quantum computing, biomagnetic measurement, and high-precision inertial navigation, and the accurate measurement of their internal residual magnetic field strength has a significant impact on equipment performance. Traditional measurement methods mainly include direct measurement with the cover open, pre-embedded fixed sensor arrays, indirect evaluation methods using external excitation, robotic arm-based mobile measurement devices, and pneumatically levitated scanning platforms. However, these methods all have significant limitations:

[0003] (1) The direct measurement method requires repeated disassembly of the cover plate, which damages the shielding integrity, introduces external magnetic field interference, and is cumbersome and has poor repeatability.

[0004] (2) Pre-embedded fixed sensor arrays have poor flexibility, high cost, and are difficult to maintain. Furthermore, the demagnetization process may affect the accuracy of the sensors.

[0005] (3) The external stimulus indirect evaluation method cannot measure the internal intrinsic remanence, relies on additional equipment, and has limited applicability.

[0006] (4) Although the robotic arm moving measurement device can realize automated scanning, the robotic arm itself is prone to magnetic contamination, and the control is complicated and the aperture requirement is large;

[0007] (5) The positioning accuracy of the pneumatic suspension scanning platform is low, making it difficult to achieve three-dimensional scanning, and the airflow disturbance affects the stability of the environment.

[0008] None of the methods described above can achieve high-precision, high-stability, and full-coverage measurement of the internal residual magnetic field while maintaining the integrity of the magnetically shielded cavity. Therefore, a novel measurement device and method are urgently needed to overcome the shortcomings of existing technologies. Summary of the Invention

[0009] The main objective of this invention is to overcome the shortcomings of existing technologies and provide a device and method for measuring the residual magnetic field strength of a magnetically shielded cavity. The technical solution adopted by this invention to achieve its technical objective is: a device for measuring the residual magnetic field strength of a magnetically shielded cavity, the device comprising:

[0010] A probe that is telescopic and rotatable;

[0011] A detection system is fixedly installed on a probe and includes a mounting bracket and a fluxgate sensor, wherein the fluxgate sensor is fixed on the probe by the mounting bracket.

[0012] A stabilization system is installed outside the probe to counteract the gravitational torque of the probe and to provide real-time feedback on the probe's tilt status.

[0013] The data processing terminal is based on MATLAB or Python algorithms to realize data interpolation and generate residual magnetic field cloud maps within the magnetic shielding device.

[0014] Preferably, the probe is a carbon fiber probe or other non-magnetic material, with an outer diameter of 28 mm, a wall thickness of 2 mm, and a magnetic susceptibility χ≈-1.6×10⁻⁶. -6 .

[0015] Preferably, the mounting bracket is configured as an L-shaped aluminum alloy bracket, and a set of three-axis orthogonal fluxgate sensors are set at each of its three ends, for a total of nine single-axis sensors with a range of ±100μT, a resolution of 0.1nT, and covering three-dimensional magnetic field components.

[0016] Preferably, the stabilization system includes a crank handle, a support sleeve, a slider, a pointer, a scale, a guide rail, a base plate support, a bushing and pad, a level, and a locking wrench;

[0017] The probe is fitted with a support sleeve and a bushing at both ends. The bushing is fixedly installed on the base plate support frame by a pad. The bushing is fitted on the outer wall of the probe, and its bottom is fixed on the base plate support frame by a pad.

[0018] The support sleeve is slidably connected to the base plate support frame via a slider and a guide rail. The support sleeve is rotatably connected to the probe, and its bottom is fixed to the slider. The slider is slidably connected to the guide rail. The guide rail is fixedly installed on the base plate support frame, and one end of it rests against one side of the pad block.

[0019] By setting a crank handle to be fixed to the side wall at the end of the probe, pushing the crank handle causes the support sleeve and one end of the probe to slide on the slider. Then, by turning the crank handle, the probe is rotated. Through the movement and rotation of the probe, it is easy to adjust the displacement and angle of the mounting bracket and the fluxgate sensor, and the detection accuracy can be controlled.

[0020] Preferably, the outer wall of the probe is marked with a rotation angle scale;

[0021] A pointer is fixedly installed on one side wall of the slider, and a scale corresponding to the pointer position is set on the base plate support, with the pointer pointing to the scale on the scale.

[0022] When the support sleeve and one end of the probe slide on the slider, the pointer points to the scale on the ruler in real time, which can know the distance the probe has moved in real time, and thus know the displacement of the mounting bracket and the fluxgate sensor in real time. By cooperating with the rotation angle scale marked on the outer wall of the probe, the rotation angle of the mounting bracket and the fluxgate sensor can be known in real time, so as to more precisely control the detection accuracy.

[0023] Preferably, a locking wrench is fixedly installed on the other side wall of the slider, which can lock the slider onto the guide rail.

[0024] Preferably, a level is also fixedly installed on the base plate support, with an accuracy of ±0.1°, to provide real-time feedback on the tilt status of the probe.

[0025] The present invention also provides a method for measuring the residual magnetic field strength of a magnetically shielded cavity, which employs the measuring device described above and includes the following steps:

[0026] Step 1: Insert probe 1 through the 30mm hole in the cover plate of the magnetic shielding cavity. The mounting bracket is located inside the magnetic shielding cavity. Adjust the base plate support to make the level reading less than 0.3° to maintain its balanced posture. Then keep the probe moving along the central axis of the magnetic shielding cavity.

[0027] Step 2: Extend and retract the probe in stages, and rotate the probe after each stage of extension to complete the circumferential test; a measurement point is moved every 30°, and the magnetic field data at each point is recorded. A groove is set at each rotation step point to ensure the accuracy of the test position.

[0028] Step 3: Based on the displacement and rotation angle of the probe, a cylindrical coordinate system is constructed for scanning. The spatial coordinates of each measuring point are calculated, and the coordinates of all measuring points and the magnetic field vector are generated. For the unmeasured area, the radial basis function interpolation method is used to generate a three-dimensional remanent magnetization cloud map.

[0029] Step 4: Analyze the cloud map distribution, locate the weak areas of shielding, and guide structural optimization by adding permalloy strips to the weak areas.

[0030] Preferably, the probe displacement ΔL in step 3, together with the rotation angle θ, forms a cylindrical coordinate system scan, satisfying:

[0031] ;

[0032] Where r is the length of the support arm, enabling scanning of a cylindrical surface with radius r.

[0033] Preferably, the interpolation method in step 3 includes:

[0034] S1. Normalize the coordinates of the measuring points:

[0035] Calculate the spatial coordinates of the measuring point in the rectangular coordinate system from the displacement and rotation angle of the probe. and magnetic field vector The coordinates of the measurement points are normalized so that all coordinate values ​​fall within the [0,1] interval to improve interpolation stability. The normalization process is as follows:

[0036] ;

[0037] S2. Construct a system of linear equations based on radial basis functions to solve for the weight coefficients:

[0038] Choose basis functions that adapt to the magnetic field decay characteristics. Where r is the distance matrix, the Euclidean distance between the measuring points is calculated:

[0039] ;

[0040] The parameters controlling the decay rate of the control function can be selected. Reconstructing the magnetic field at unmeasured points based on radial basis functions:

[0041] ;

[0042] Wherein, weight w i Obtained by fitting from measured points;

[0043] Solve the system of linear equations , where Φ is an N×N matrix with elements of . , The weight to be determined This is the measured magnetic field value;

[0044] S3. Calculate the magnetic field values ​​at unmeasured points using weighting coefficients and basis functions, and generate a contour map:

[0045] In the radial basis function interpolation method, once the weight coefficients are determined, they will remain unchanged. When calculating the magnetic field value at any new point, it is only necessary to recalculate the basis function values ​​between that point and the known points, without having to resolve the weights. This allows us to obtain the magnetic field strength at any point and thus the residual magnetic field cloud map.

[0046] The working principle of the device and method for measuring the residual magnetic field strength of a magnetically shielded cavity is as follows: A multi-channel magnetic field detection system is inserted deep into the sealed magnetically shielded cavity for scanning and measurement through a mechanically stable system that can precisely control displacement and angle. Without compromising the integrity of the cavity's shielding, an algorithm is used to reconstruct the distribution cloud map of the three-dimensional residual magnetic field inside. Specifically, a non-magnetic carbon fiber probe is inserted into the cavity through an opening in the cover plate of the magnetically shielded cavity. Three sets of triaxial fluxgate sensors are fixed at the end by an L-shaped mounting bracket, forming a nine-channel magnetic field detection system. A crank pushes the support sleeve to move the probe along the slider and guide rail, and a pointer and scale indicate the displacement. Turning the crank rotates the probe, and the scale on its outer wall indicates the angle, achieving precise three-dimensional positioning. A level monitors the tilt state in real time, and a locking wrench fixes the position. The data processing terminal collects sensor data and generates a three-dimensional cloud map of the residual magnetic field based on a radial basis function interpolation algorithm. The entire process does not require opening the cover, maintaining the integrity of the shielding.

[0047] Compared with the prior art, the beneficial effects of the present invention are:

[0048] The device and method for measuring the residual magnetic field strength of the magnetically shielded cavity can achieve closed-state measurement, maintain the integrity of the shield, and achieve internal measurement by inserting a non-magnetic probe through a limited aperture on the cover of the magnetically shielded cavity without opening the cover, effectively avoiding external magnetic field interference and maintaining the integrity and stability of the shielding structure.

[0049] The device and method for measuring the residual magnetic field strength of the magnetically shielded cavity can achieve high-precision three-dimensional scanning. Through a combined telescopic and rotary motion mechanism, combined with scale positioning and step control, it can achieve sub-centimeter-level three-dimensional spatial scanning and cover the measurement of residual magnetic field across the entire area.

[0050] The device and method for measuring the residual magnetic field strength of the magnetically shielded cavity have high stability and anti-interference capabilities. It adopts a carbon fiber probe and counterweight system design, and the probe tilt angle is controlled within ±0.3°, which effectively counteracts the gravitational torque and avoids mechanical vibration and magnetic contamination.

[0051] The device and method for measuring the residual magnetic field strength of the magnetically shielded cavity can realize intelligent data processing and visualization. Based on the radial basis function interpolation algorithm, it can efficiently generate a three-dimensional residual magnetic field cloud map, intuitively display the weak areas of shielding performance, and provide accurate data support for structural optimization.

[0052] The device and method for measuring the residual magnetic field strength of the magnetically shielded cavity adopts an L-shaped triaxial sensor array, which can cover nine magnetic field components in a single measurement, greatly improving the measurement efficiency. It does not require external excitation equipment, reducing system complexity and cost, and has the characteristics of high efficiency and low cost. Attached Figure Description

[0053] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0054] Figure 1 This is a three-dimensional structural diagram of a device for measuring the residual magnetic field strength of a magnetically shielded cavity.

[0055] Figure 2 for Figure 1 A three-dimensional structural diagram of the measuring device from another perspective.

[0056] Figure 3 The flowchart shows the operational steps for measuring the residual magnetic field strength of a magnetically shielded cavity.

[0057] The components include: 1. Probe; 2. Mounting bracket; 3. Fluxgate sensor; 4. Handle; 5. Support sleeve; 6. Slider; 7. Pointer; 8. Ruler; 9. Guide rail; 10. Base plate support; 11. Bushing; 12. Pad; 13. Level; 14. Locking wrench. Detailed Implementation

[0058] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. However, it should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0059] In the description of this invention, it should be noted that when an element is referred to as being "fixed to" or "set on" another element, it can be directly on or indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to or indirectly connected to the other element.

[0060] In the description of this invention, it should be noted that the terms "center," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified. "Several" means one or more, unless otherwise explicitly specified.

[0061] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0062] Example 1:

[0063] Please see Figures 1-2 A measuring device for the residual magnetic field strength of a magnetically shielded cavity, the measuring device comprising a probe 1, a detection system, a stabilization system and a data processing terminal.

[0064] The probe 1 is telescopic and rotatable. Probe 1 is made of carbon fiber or other non-magnetic materials, with an outer diameter of 28 mm, a wall thickness of 2 mm, and a magnetic susceptibility χ≈-1.6×10⁻⁶. -6 .

[0065] The detection system is fixedly mounted on the probe 1, and includes a mounting bracket 2 and fluxgate sensors 3. The fluxgate sensors 3 are fixed to the probe 1 via the mounting bracket 2. The mounting bracket is an L-shaped aluminum alloy bracket, and a set of three-axis orthogonal fluxgate sensors 3 is set at each of its three ends, for a total of nine single-axis sensors with a range of ±100μT, a resolution of 0.1nT, and covering three-dimensional magnetic field components.

[0066] The stabilization system is installed outside the probe tube 1 to counteract the gravitational torque of the probe tube 1 and to provide real-time feedback on the tilt status of the probe tube.

[0067] The data processing terminal uses MATLAB or Python algorithms to perform data interpolation and generate residual magnetic field cloud maps within the magnetic shielding device.

[0068] Furthermore, in this embodiment, the stabilization system includes a crank handle 4, a support sleeve 5, a slider 6, a pointer 7, a scale 8, a guide rail 9, a base plate support 10, a bushing 11, a pad block 12, a level 13, and a locking wrench 14.

[0069] Support sleeves 5 and bushings 11 are respectively fitted at both ends of the probe 1. Bushings 11 are fixedly installed on the base plate support 10 by pads 12. Bushings 11 are fitted on the outer wall of the probe 1, and their bottom is fixed to the base plate support 10 by pads 12. Support sleeves 5 are slidably connected to the base plate support 10 by sliders 6 and guide rails 9. Support sleeves 5 and probe 1 are rotatably connected, and their bottom is fixed to sliders 6. Sliders 6 and guide rails 9 are slidably connected. Guide rails 9 are fixedly installed on the base plate support 10, and one end of them rests against one side of pads 12. A crank handle 4 is fixed to the end side wall of the probe 1. Pushing the crank handle 4 causes the support sleeves 5 and one end of the probe 1 to slide on sliders 6. Then, by turning the crank handle 4, the probe 1 is rotated. The movement and rotation of the probe 1 facilitate the adjustment of the displacement and angle of the mounting frame 2 and the fluxgate sensor 3, and the detection accuracy can be controlled.

[0070] The outer wall of the probe 1 is marked with a rotation angle scale; a pointer 7 is fixedly installed on one side wall of the slider 6, and a scale 8 corresponding to the position of the pointer 7 is set on the base plate support 10, with the pointer 7 pointing to the scale on the scale 8; when the support sleeve 5 and one end of the probe 1 slide on the slider 6, the pointer 7 points to the scale on the scale 8 in real time, so that the distance moved by the probe 1 can be known in real time, and thus the displacement of the mounting frame 2 and the fluxgate sensor 3 can be known in real time. By cooperating with the rotation angle scale marked on the outer wall of the probe 1, the rotation angle of the mounting frame 2 and the fluxgate sensor 3 can be known in real time, so that the detection accuracy can be controlled more precisely.

[0071] Furthermore, in this embodiment, a locking wrench 14 is fixedly installed on the other side wall of the slider 6, which can lock the slider 6 onto the guide rail 9.

[0072] Furthermore, in this embodiment, a level 13 is also fixedly installed on the base plate support 10. The level 13 has an accuracy of ±0.1° and provides real-time feedback on the tilt status of the probe.

[0073] Specifically, in use, the measuring device extends into the sealed internal space through a pre-drilled hole in the cover plate of the magnetically shielded cavity via a non-magnetic carbon fiber probe 1. Three sets of triaxially orthogonal fluxgate sensors 3 are fixed to the end of the probe via an L-shaped aluminum alloy mounting bracket 2, forming a magnetic field detection array with nine independent measurement channels. During operation, the crank 4 pushes the support sleeve 5, causing the probe 1 to move precisely along the slider 6 and guide rail 9. The pointer 7, in conjunction with a high-precision scale 8, indicates the displacement in real time. Simultaneously, turning the crank 4 rotates the probe 1 around its axis, using the outer wall of the probe as a reference. The rotating angle scale of the probe enables precise circumferential positioning, thereby achieving point-by-point scanning measurement of the three-dimensional space inside the cavity; the level 13 monitors the tilt state of the probe in real time with an accuracy of ±0.1°, and the locking wrench 14 can lock the relative position of the slider 6 and the guide rail 9 at any position to ensure stable measurement posture; the measurement data is collected through the data processing terminal, and the three-dimensional distribution cloud map of the residual magnetic field in the cavity is reconstructed based on the radial basis function interpolation algorithm. The entire measurement process is completed in a sealed state in the magnetically shielded cavity, effectively avoiding external magnetic field interference and maintaining shielding integrity.

[0074] Example 2:

[0075] Please see Figures 1-3 Based on the above embodiments, this invention also provides a method for measuring the residual magnetic field strength of a magnetically shielded cavity, which uses the measuring device described in Embodiment 1 and includes the following steps:

[0076] Step 1: Insert probe 1 through the 30mm hole in the cover plate of the magnetic shielding cavity. The mounting bracket 2 is located inside the magnetic shielding cavity. Adjust the base plate support 10 to make the level reading less than 0.3° to maintain its balanced posture. Then keep probe 1 moving along the central axis of the magnetic shielding cavity.

[0077] Step 2: Extend and retract probe 1 in stages, and rotate probe 1 after each extension and retraction to complete the circumferential test; wherein, a measurement point is moved every 30°, and the magnetic field data at each point is recorded. A groove is set at each rotation step point to ensure the accuracy of the test position.

[0078] Step 3: Based on the displacement and rotation angle of probe 1, a cylindrical coordinate system is formed for scanning. The spatial coordinates of each measuring point are calculated, and the coordinates of all measuring points and the magnetic field vector are generated. For the unmeasured area, the radial basis function interpolation method is used to generate a three-dimensional remanent magnetization cloud map.

[0079] Wherein: the displacement ΔL of probe 1 in step 3, together with the rotation angle θ, forms a cylindrical coordinate system scan, satisfying:

[0080] ;

[0081] In the formula, r is the length of the support arm, which enables scanning of a cylindrical surface with radius r.

[0082] The interpolation methods in step 3 include:

[0083] S1. Normalize the coordinates of the measuring points:

[0084] Calculate the spatial coordinates of the measuring point in the rectangular coordinate system based on the displacement and rotation angle of probe 1. and magnetic field vector The coordinates of the measurement points are normalized so that all coordinate values ​​fall within the [0,1] interval to improve interpolation stability. The normalization process is as follows:

[0085] .

[0086] S2. Construct a system of linear equations based on radial basis functions to solve for the weight coefficients:

[0087] Choose basis functions that adapt to the magnetic field decay characteristics. Where r is the distance matrix, the Euclidean distance between the measuring points is calculated:

[0088] ;

[0089] The parameters controlling the decay rate of the control function can be selected. Reconstructing the magnetic field at unmeasured points based on radial basis functions:

[0090] ;

[0091] Wherein, weight w i Obtained by fitting from measured points;

[0092] Solve the system of linear equations , where Φ is an N×N matrix with elements of . , The weight to be determined This is the measured magnetic field value.

[0093] S3. Calculate the magnetic field values ​​at unmeasured points using weighting coefficients and basis functions, and generate a contour map:

[0094] In the radial basis function interpolation method, once the weight coefficients are determined, they will remain unchanged. When calculating the magnetic field value at any new point, it is only necessary to recalculate the basis function values ​​between that point and the known points, without having to resolve the weights. This allows us to obtain the magnetic field strength at any point and thus the residual magnetic field cloud map.

[0095] Step 4: Analyze the cloud map distribution, locate the weak areas of shielding, and guide structural optimization by adding permalloy strips to the weak areas.

[0096] Specifically, in use, the probe 1 is first inserted through the 30mm hole in the cover plate of the magnetic shielding cavity, so that the mounting bracket 2 is located inside the cavity. The level reading is kept less than 0.3 degrees by adjusting the base plate support 10 to maintain balance, while ensuring that the probe 1 moves along the central axis of the magnetic shielding cavity. Then, the probe 1 is extended and retracted in stages, and the probe 1 is rotated after each extension and retraction to perform circumferential testing. A measurement point is moved every 30 degrees and the magnetic field data of each point is recorded. At the same time, the groove structure ensures the accuracy of the test position. Next, the cylindrical coordinate system is scanned based on the displacement ΔL of the probe 1 and the rotation angle θ to calculate the spatial coordinates of each measurement point and generate the coordinates of all measurement points and the magnetic field vector. Then, the radial basis function interpolation method is used to interpolate the unmeasured area to generate a three-dimensional remanent magnetization cloud map. Finally, the distribution of the cloud map is analyzed to locate the weak shielding area, and structural optimization is guided by adding permalloy strips, etc.

[0097] The solution in this embodiment can be selectively combined with solutions in other embodiments.

[0098] The specific operating procedure for the device and method for measuring the residual magnetic field strength of the magnetically shielded cavity is as follows:

[0099] (1) Installation and leveling of the device: First, insert the probe 1 into the sealed magnetic shielded cavity through the reserved hole (e.g., 30mm diameter) on the cavity cover plate, so that the mounting bracket 2 fixed at its end and the fluxgate sensor 3 are located inside the cavity. By adjusting the base plate support 10 of the entire device, observe the level 13 to ensure that its reading is less than 0.3°, so that the probe 1 is roughly balanced along the central axis of the cavity.

[0100] (2) Three-dimensional spatial scanning measurement: The operator pushes the crank handle 4, causing the support sleeve 5 to move one end of the probe tube 1 along the guide rail 9 and the slider 6. The moving distance is indicated in real time by the pointer 7 fixed on the slider 6 and the scale 8 installed on the base plate support 10. After moving to a predetermined depth, the crank handle 4 is turned to rotate the probe tube 1 and the sensor on it (the outer wall of the probe tube 1 is marked with the rotation angle scale), and a circumferential scan is performed in 30° increments. At each measurement point (accuracy can be ensured by positioning through mechanical grooves), three sets of triaxial fluxgate sensors 3 (a total of nine single axes) record the three-dimensional magnetic field vector data of that point. During the scanning process, the slider 6 can be locked on the guide rail 9 to fix its position by using the locking wrench 14.

[0101] (3) Data processing and cloud map generation: The data processing terminal (such as a computer) collects the magnetic field data of all measurement points. Then, based on the MATLAB or Python platform, the spatial coordinates of each measurement point in the rectangular coordinate system are calculated according to the displacement ΔL of probe 1 (read by scale 8) and the rotation angle θ (read by probe scale), forming a cylindrical coordinate system scan. For areas not directly measured, the radial basis function interpolation algorithm is used for data interpolation, and finally a three-dimensional residual magnetic field distribution cloud map of the entire cavity interior space is generated.

[0102] (4) Results analysis and application: By analyzing the generated three-dimensional remanent magnetization cloud map, the weak magnetic shielding area in the magnetic shielding cavity can be located intuitively, thus providing accurate data support for guiding subsequent structural optimization (such as adding permalloy strips at specific locations).

[0103] It should be noted that although the above embodiments have been described herein, this does not limit the scope of patent protection of this invention. Therefore, any changes and modifications made to the embodiments described herein based on the innovative concept of this invention, or equivalent structural, procedural, or functional transformations made using the description and drawings of this invention, directly or indirectly applying the above technical solutions to other related technical fields, are all included within the scope of protection of this invention.

Claims

1. A device for measuring the residual magnetic field strength of a magnetically shielded cavity, characterized in that, The measuring device includes: The probe (1) is capable of extension, retraction, and rotation; The detection system is fixedly installed on the probe (1) and includes a mounting bracket (2) and a fluxgate sensor (3), wherein the fluxgate sensor (3) is fixed on the probe (1) by the mounting bracket (2); A stabilization system is installed outside the probe (1) to counteract the gravitational torque of the probe (1) and to provide real-time feedback on the tilt status of the probe. A data processing terminal, which is based on MATLAB or Python algorithms, to realize data interpolation and generate residual magnetic field cloud maps inside the magnetic shielding device; The probe (1) is fitted with a support sleeve (5) and a bushing (11) at both ends, and the bushing (11) is fixedly installed on the base plate support (10) by a pad (12); The support sleeve (5) is slidably connected to the base plate support frame (10) via a slider (6) and a guide rail (9); By setting the handle (4) to be fixed on the side wall of the end of the probe (1), pushing the handle (4) causes the support sleeve (5) and one end of the probe (1) to slide on the slider (6), and then turning the handle (4) causes the probe (1) to rotate. The outer wall of the probe (1) is marked with a rotation angle scale; A pointer (7) is fixedly installed on one side wall of the slider (6), and a scale (8) corresponding to the position of the pointer (7) is set on the base plate support (10), with the pointer (7) pointing to the scale on the scale (8); A level (13) is also fixedly installed on the base plate support (10), and the level (13) has an accuracy of ±0.1°; It also includes the method of using the measuring device, the specific steps of which are as follows: Step 1: Insert the probe (1) through the 30mm hole on the cover plate of the magnetic shielding cavity. The mounting bracket (2) is located inside the magnetic shielding cavity. Adjust the base plate support (10) to make the level reading less than 0.3° and keep it in a balanced position. Then keep the probe (1) moving along the central axis of the magnetic shielding cavity. Step 2: Extend and retract the probe (1) in stages, and rotate the probe (1) after each stage of extension and retraction to complete the circumferential test; wherein, a measurement point is advanced every 30°, and the magnetic field data of each measurement point is recorded. A groove is set at each measurement point to ensure the accuracy of the test position; Step 3: Based on the displacement and rotation angle of the probe (1), a cylindrical coordinate system is formed for scanning. The spatial coordinates of each measurement point are calculated, and the coordinates of all measurement points and the magnetic field vector are generated. For the unmeasured area, the radial basis function interpolation method is used to generate a three-dimensional remanent cloud map. Step 4: Analyze the cloud map distribution, locate the weak shielding areas, and guide structural optimization by adding permalloy strips to the weak areas.

2. The measuring device for the residual magnetic field strength of a magnetically shielded cavity according to claim 1, characterized in that: The probe (1) is a carbon fiber probe with an outer diameter of 28 mm, a wall thickness of 2 mm, and a magnetic susceptibility χ≈-1.6×10⁻⁶. -6 .

3. The measuring device for the residual magnetic field strength of a magnetically shielded cavity according to claim 1, characterized in that: The mounting bracket is set as an L-shaped aluminum alloy bracket, and a set of three-axis orthogonal fluxgate sensors (3) are set at each of its three ends, for a total of nine single-axis sensors with a range of ±100μT and a resolution of 0.1nT, covering three-dimensional magnetic field components.

4. The measuring device for the residual magnetic field strength of a magnetically shielded cavity according to claim 1, characterized in that: A locking wrench (14) is fixedly installed on the other side wall of the slider (6), and the slider (6) can be locked and fixed on the guide rail (9) by the locking wrench (14).

5. The measuring device for the residual magnetic field strength of a magnetically shielded cavity according to claim 1, characterized in that: The displacement ΔL of the probe (1) in step 3, together with the rotation angle θ, forms a cylindrical coordinate system scan, satisfying: ； Where r is the length of the support arm, enabling scanning of a cylindrical surface with radius r.

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