Double-plane active shielded PCB coil, design method thereof and magnetic shielding device

Abstract

The application provides a kind of double-plane active shielding type PCB coil and its design method, magnetic shielding device, wherein the design method comprises: S1, the magnetic field uniformity and uniform region volume are used as optimization index, the coil parameter is determined by reverse calculation based on target amplitude deviation rate, to establish the magnetic field analytical model of PCB coil corresponding to the magnetic field to be shielded;S2, the magnetic field analytical model is verified by FEM three-dimensional magnetic field method;If the magnetic field analytical model meets the requirements, execute S3, if the magnetic field analytical model does not meet the requirements, execute S1 and adjust the coil parameter;S3, the coil winding corresponding to the magnetic field analytical model is used for the wiring design of PCB coil;Wherein, the magnetic field to be shielded is the residual magnetic field in passive shielding cabin, and the magnetic field analytical model is the magnetic flux density distribution diagram of PCB coil.The application solves the problem of poor shielding effect caused by machining error of traditional active shielding coil.

Description

Technical Field

[0001] This invention relates to the field of active magnetic field compensation technology, and in particular to a dual-plane active shielded PCB coil and its design method, as well as a magnetic shielding device. Background Technology

[0002] Near-zero uniform magnetic field environments serve as fundamental experimental environments for cutting-edge experiments in aerospace, life sciences, and particle physics, among other disciplines, and have significant application requirements. Research on analytical models of the magnetic field of coils under ferromagnetic boundaries, and the mapping of key design indicators and parameters for coil design within zero-magnetic devices and their uniform magnetic field coil systems, provides a theoretical foundation for the design of geomagnetic field compensation coils and weak magnetic field reproduction coils in zero-magnetic devices, and even the design of large-volume uniform magnetic field generators. In geomagnetic environments, magnetic field disturbances and gradient changes severely affect the accuracy of magnetic field calibration experiments, particularly in verifying parameters such as zero bias, temperature correction, and orthogonality of magnetic field sensors. To obtain a near-zero uniform magnetic field, the geomagnetic field needs to be shielded or canceled.

[0003] There are two main methods for shielding or canceling the Earth's magnetic field: one is to use highly permeable materials to shun the magnetic circuit to shield the static magnetic field, which is called ferromagnetic shielding or passive shielding; the other is to use a coil with a controllable current to generate an artificial magnetic field that is opposite in direction and equal in magnitude to the ambient magnetic field to cancel the external magnetic field, which is called active shielding.

[0004] In passive shielding, high-permeability materials commonly used for shielding static and low-frequency magnetic fields include permalloy (iron-nickel alloy), mu-metal, and electrical pure iron. The principle of passive shielding determines its advantages such as strong anti-disturbance capability, minimal impact of external interference on the uniform magnetic field formed, and high reliability. However, its disadvantages include high cost, difficult manufacturing, and poor process operability in constructing large passive shielding layers. In addition, the shielding layer will be slowly magnetized under the influence of the Earth's magnetic field, causing the amplitude of the magnetic field created inside the system to gradually increase. In order to maintain its shielding effect, periodic demagnetization is required.

[0005] Active shielding primarily uses the ambient magnetic field data collected by the fluxgate sensor as a compensation basis. It utilizes a coil system to generate a large-volume uniform magnetic field with equal amplitude and opposite direction to cancel out the ambient magnetic field, thereby achieving magnetic field shielding and ultimately creating a relatively clean magnetic field environment inside the coil system. Among these methods, coils have low manufacturing costs and are easy to process. They also have high magnetic field stability and good linearity. Furthermore, by combining coils, a spatial magnetic field with a specific distribution can be generated, making them an important means of magnetic field shielding.

[0006] The combination of active and passive shielding is a growing trend in next-generation shielding technology. Passive shielding offers excellent protection against high-frequency and radio-frequency magnetic disturbances, but its ability to shield against low-frequency magnetic fields is limited. Improving shielding against low-frequency magnetic fields requires increasing the number of shielding layers and the distance between them, leading to exponentially higher costs. Active shielding, on the other hand, excels in compensating for low-frequency and static magnetic fields. Therefore, in large-scale shielding systems, initial magnetic field shielding is typically achieved through active shielding systems, reducing the need for multiple passive shielding layers and simultaneously achieving shielding against both high and low-frequency magnetic fields while lowering costs.

[0007] Currently, devices serving high-precision magnetometer calibration and cutting-edge physics experiments all employ a combination of active and passive shielding schemes. However, in the implementation of active shielding coils, errors in CNC (computer numerical control) machining of the coil, errors in manual winding, and errors in the relative position of the coil plane and the sensor can all cause discrepancies between theoretical and measured values, thus affecting the shielding effect.

[0008] It should be noted that the above description of the technical background is only for the purpose of providing a clear and complete explanation of the technical solutions of the present invention and facilitating understanding by those skilled in the art. It should not be assumed that the above technical solutions are known to those skilled in the art simply because they have been described in the background section of this invention. Summary of the Invention

[0009] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a dual-plane active shielded PCB coil and its design method, as well as a magnetic shielding device, which solves the problem of poor shielding effect caused by processing errors in traditional active shielded coils.

[0010] To achieve the above and other related objectives, this invention provides a design method for a dual-plane actively shielded PCB coil, the design method comprising:

[0011] S1, using magnetic field uniformity and uniform region volume as optimization indicators, and determining coil parameters through reverse calculation based on the target amplitude deviation rate, in order to establish a magnetic field analytical model of the PCB coil corresponding to the magnetic field to be shielded;

[0012] S2, verify the magnetic field analytical model using the FEM three-dimensional magnetic field method; if the magnetic field analytical model meets the requirements, proceed to S3; if the magnetic field analytical model does not meet the requirements, proceed to S1 and adjust the coil parameters.

[0013] S3, Design the PCB coil wiring based on the coil winding corresponding to the magnetic field analytical model;

[0014] Wherein, the magnetic field to be shielded is the residual magnetic field inside the passive shielding chamber, and the magnetic field analytical model is the magnetic flux density distribution diagram of the PCB coil.

[0015] Optionally, the magnetic field uniformity is the degree of deviation of the magnetic flux density between any point in the working area and the center point, which is measured by the amplitude deviation rate and satisfies the formula. ,in, Indicates the amplitude deviation rate. This represents the magnetic flux density at any point within the working area. The magnetic flux density at the center point of the working area is represented by the uniform region volume, which is the volume of the largest cube centered at the center point of the working area and satisfies an amplitude deviation rate of less than or equal to 1.5%. The working area is the region corresponding to the sensor inside the passive shielding chamber.

[0016] Optionally, the method for establishing the analytical model of the magnetic field includes:

[0017] S11, Define the magnetic field calculation area, and obtain several sampling points by sampling the magnetic field calculation area through a gridding function, wherein the magnetic field calculation area is determined by the compensation direction and spatial parameters;

[0018] S12, Set coil parameters, wherein the coil parameters include coil current, effective coil volume, Fourier expansion order of the stream function, and regularization coefficient;

[0019] S13, Based on the sampling points and the coil parameters, establish and solve the flow function equation to obtain the corresponding amplitude deviation rate;

[0020] S14, after iteratively adjusting the coil parameters, execute S13 until the iteration ends;

[0021] S15, based on the target amplitude deviation rate, select multiple sets of coil parameters that meet the amplitude deviation rate requirements, and select the set of coil parameters with the largest uniform region volume from them;

[0022] S16, superimpose the magnetic field of the selected coil parameters with the geomagnetic field to obtain a set of magnetic flux density data;

[0023] S17. Repeat S11~S16 at least once, and use a gradually increasing density method to adjust the number of sampling points to obtain multiple sets of magnetic flux density data, and use this to obtain a magnetic flux density distribution map.

[0024] Optionally, the x-axis direction of the passive shielding chamber is set as the compensation direction, and the PCB coil includes a first YOZ single-plane coil and a second YOZ single-plane coil; the spatial parameters include a first spatial parameter and a second spatial parameter, wherein the first spatial parameter is the relative distance between the plane where the first YOZ single-plane coil is located and the plane where the second YOZ single-plane coil is located, and the second spatial parameter is the relative distance between the plane where the first YOZ single-plane coil or the second YOZ single-plane coil is located and the inner wall of the passive shielding chamber.

[0025] Optionally, in S13, the method for obtaining the corresponding amplitude deviation rate includes:

[0026] The current density distribution of the coil is determined based on the coil current and the effective volume of the coil, and a flow function S(x,y) is introduced such that... , , where J x This represents the component of the current density in the x-direction. J represents the partial derivative of the stream function with respect to y. y This represents the component of the current density in the y-direction. This represents the partial derivative of the stream function with respect to x;

[0027] The stream function is expanded using a two-dimensional Fourier series and a finite number of modes are retained according to the order of the Fourier expansion of the stream function. Then, based on the Biot-Savart law, a linear system of equations AP=b is established between the magnetic field values ​​of the sampling points and the coefficients of the stream function, where A represents the coefficient matrix, P represents the coefficient vector to be determined, and b represents the target magnetic field value vector.

[0028] Introducing a Tikhonov regularization term into the linear equation system transforms the problem into minimizing the functional T = ||AP-b||² + λ||ΓP||², where λ is the regularization coefficient and Γ is the regularization matrix.

[0029] By solving (P)=(A) T A+λΓ T Γ) -1 A T b. Obtain the stream function coefficients, substitute the stream function coefficients into the stream function, and draw the stream function contour lines to obtain the corresponding amplitude deviation rate.

[0030] Optionally, in S15, the method for selecting the set of coil parameters that maximizes the volume of the uniform region from multiple sets of coil parameters includes:

[0031] Two-dimensional coil models are established based on the flow function contour lines corresponding to each coil parameter, and then three-dimensional coil models are established based on each coil parameter.

[0032] Using the center point of the magnetic field calculation region as the center, calculate the maximum cube volume for each three-dimensional coil model with an amplitude deviation rate ≤1.5%;

[0033] The ratio of the calculated maximum cube volume to the preset volume is used as the quantitative index of the uniform region volume, and each quantitative index that is greater than or equal to the preset index is selected.

[0034] The selected quantitative indicators are sorted, and the coil parameters corresponding to the quantitative indicator with the largest value are taken as the group of coil parameters with the largest uniform region volume.

[0035] Optionally, the method for verifying the analytical magnetic field model using the FEM three-dimensional magnetic field method includes:

[0036] S21. The three-dimensional static magnetic field hybrid finite element method is selected, with one of the magnetic field strength and magnetic flux density as unknowns, and the FEM model is constructed with the help of spatial discretization technology.

[0037] S22, Solve the stream function equation corresponding to the magnetic field analytical model to obtain the coil current contour distribution and map it onto the FEM model as an excitation source to determine the control equation of the three-dimensional static magnetic field;

[0038] S23, The coil is constructed in the FEM model using an overall modeling method of stranded conductors;

[0039] S24, Set boundary conditions including Niemann boundary conditions and symmetric boundary conditions, and solve the governing equations to obtain intermediate quantities;

[0040] S25, perform post-processing on the intermediate quantity to obtain a set of magnetic flux density data;

[0041] S26. Repeat S21~S25 at least once, and use a gradually increasing density method to adjust the number of spatial discrete points to obtain multiple sets of magnetic flux density data, and use this to obtain a magnetic flux density distribution map.

[0042] S27. Based on the magnetic flux density distribution map obtained in S26, the magnetic flux density distribution map in S1 is compared and verified.

[0043] Optionally, in S25, after obtaining a set of magnetic flux density data, it also includes jumping to S21 and treating the other of the magnetic field strength and magnetic flux density as an unknown quantity to obtain two sets of magnetic flux density data and perform averaging.

[0044] Optionally, in S21, higher-order edge elements are used to spatially discretize the magnetic field calculation region, and the FEM model is constructed based on two vector equations: Ampere's circuital law and the zero magnetic flux density vector divergence.

[0045] Optionally, in step S21, before spatial discretization, a step of determining the number of discrete points is included: adjusting the number of discrete points by gradually increasing the density, and calculating L of the magnetic flux density at the center point of the corresponding region after each increase in the number of discrete points. 2 Error, and L 2 The number of discrete points corresponding to an error less than a preset threshold is used as the determined number of discrete points.

[0046] Optionally, when constructing the FEM model in S21, for the case where the shielding layer material in the passive shielding chamber is permalloy, due to the nonlinear characteristics of its magnetic permeability, the BH curve is used for material definition, and the Newton-Raphson iteration method is used to handle the nonlinear problem until convergence. The convergence criterion is that the relative residual is less than 10. -6 .

[0047] Optionally, in S22, the governing equations are described based on vector magnetic potential and magnetic field strength, including:

[0048] Formula 1: ;

[0049] Formula 2: ;

[0050] in, Represents the vector differential operator. Represents the magnetoresistance, and A represents the vector magnetic potential. Represents relative permeability, p represents the Lagrange multiplier. H represents the source current density, and H represents the magnetic field strength.

[0051] Optionally, after each encryption, the relative change in magnetic flux density at the center point of the magnetic field calculation region under two adjacent sampling densities is calculated, and the repetition ends when the relative change in magnetic flux density is less than a preset amount.

[0052] Alternatively, methods for designing PCB coil routing include:

[0053] S31, based on the passive shielding chamber and its support, design the size of the PCB board, and splice the four PCB boards together on the same plane with common edges through the central mounting hole, wherein the PCB board has a four-layer structure;

[0054] S32, The coil windings corresponding to the magnetic field analytical model are simulated and designed on four PCB boards respectively, following the principle of symmetry;

[0055] S33, establish a three-dimensional model of the PCB coil and perform performance evaluation. If it is not qualified, execute S32 and adjust the coil parameters corresponding to the magnetic field analysis model. If it is qualified, execute S34.

[0056] S34, Design the PCB coil wiring based on the coil parameters.

[0057] Optionally, in S32, before performing simulation design, the method of mirroring is used to pre-compensate the ferromagnetic boundary coupling effect of the passive shielding chamber: the six inner wall surfaces of the passive shielding chamber are regarded as mirror surfaces with high magnetic permeability, and mirror coils of the original coil are set outside the shielding layer, wherein the position of the mirror coil is determined by the thickness of the shielding layer and the distance between the original coil and the inner wall surface; the magnetic fields of the original coil and each of the mirror coils are superimposed to obtain a corrected magnetic field distribution, and the simulation design is performed based on the corrected magnetic field distribution.

[0058] Optionally, when performing performance evaluation, at least one of amplitude deviation rate, magnetic field uniformity, and uniform region volume may be used as an evaluation item.

[0059] The present invention also provides a dual-plane active shielded PCB coil, the PCB coil comprising a first YOZ single-plane coil and a second YOZ single-plane coil, which is designed using any of the design methods described above.

[0060] The present invention also provides a magnetic shielding device, the magnetic shielding device comprising:

[0061] Passive shielding chamber, covered with a shielding layer;

[0062] Non-magnetic supports are installed on the two side walls of the passive shielding chamber;

[0063] The dual-plane active shielded PCB coil described above is mounted on the non-magnetic bracket;

[0064] The sensor is located at the center point of the passive shielding chamber.

[0065] As described above, the present invention provides a dual-plane active shielded PCB coil and its design method, as well as a magnetic shielding device. By establishing an analytical model of the magnetic field of the PCB coil through reverse calculation and verifying it through the FEM three-dimensional magnetic field method, the winding structure of the PCB coil is obtained and the wiring design is carried out. This avoids the mechanical implementation error of complex coil wiring, reduces the spatial position error between the coil plane and the sensor, and thus reduces the measurement error in amplitude and uniformity of the central uniform field area. Attached Figure Description

[0066] Figure 1 This is a flowchart of the PCB coil design method in this invention.

[0067] Figure 2 This is a flowchart of the method for establishing an analytical magnetic field model in this invention.

[0068] Figure 3This is a flowchart of the method for verifying the analytical model of the magnetic field in this invention.

[0069] Figures 4-6 This is a vector diagram of the numerical solution of magnetic flux density in this invention, wherein, Figure 4 Corresponding to the central YOZ plane, Figure 5 Corresponding to the central XOY plane, Figure 6 Corresponding to the central XOZ plane.

[0070] Figure 7 This is a schematic diagram showing the scalar values ​​of magnetic flux density at different spatial discrete points corresponding to different unknown quantities in this invention.

[0071] Figure 8 This is a schematic diagram illustrating the comparative verification of magnetic flux density distribution maps on two cross-sections perpendicular to the x-axis in this invention.

[0072] Figure 9 This is a flowchart of the PCB coil routing design method in this invention.

[0073] Figure 10 This is a schematic diagram of the PCB board splicing and symmetrical coil winding design in this invention.

[0074] Figure 11 This is a schematic diagram of the magnetic shielding device in this invention.

[0075] Component labeling: 100-Passive shielding chamber, 101-Mechanical support, 200-Non-magnetic bracket, 201-First bracket, 202-Second bracket, 300-PCB coil, 301-First YOZ single-plane coil, 302-Second YOZ single-plane coil, 400-Sensor, 500-Coil control module, 600-Reference module, 601-Fluorescence gate. Detailed Implementation

[0076] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0077] Please see Figures 1 to 11 It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the illustrations only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the shape, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0078] like Figure 1 As shown, this embodiment provides a design method for a dual-plane active shielded PCB coil, including the following steps, such as S1~S3; further, it also includes S4 (not shown in the figure).

[0079] S1 uses magnetic field uniformity and uniform region volume as optimization indicators. Based on the target amplitude deviation rate, the coil parameters are determined through reverse calculation to establish an analytical magnetic field model for the PCB coil corresponding to the magnetic field to be shielded. Here, the magnetic field to be shielded is the residual magnetic field within the passive shielding chamber, and the analytical magnetic field model is the magnetic flux density distribution map of the PCB coil. It is important to note that reverse calculation refers to the process of solving for the coil parameters based on the target amplitude deviation rate.

[0080] Specifically, magnetic field uniformity is the degree of deviation of magnetic flux density between any point in the working area and the center point, measured by the amplitude deviation rate; it satisfies the formula... ,in, Indicates the amplitude deviation rate. This represents the magnetic flux density at any point within the working area (i.e., the point defined by x, y, and z). This represents the magnetic flux density at the center point of the working area. Additionally, the volume of the uniform region is the volume of the largest cube centered at the center point of the working area, satisfying an amplitude deviation rate of less than or equal to 1.5%.

[0081] The working area refers to the region corresponding to the sensor within the passively shielded chamber. It is typically larger than the actual area of ​​the sensor but smaller than the internal area of ​​the passively shielded chamber. For example, if the internal area of ​​the passively shielded chamber is 1000mm*1000mm*1200mm, the actual area of ​​the sensor is 15mm*20mm*20mm, and the working area is 200mm*200mm*200mm. It should be noted that the dimensions of each of these areas can be designed according to actual application requirements, and there are no excessive restrictions on them.

[0082] In one implementation, such as Figure 2 As shown, the method for establishing an analytical model of the magnetic field includes the following steps, such as S11~S17.

[0083] S11, define the magnetic field calculation area, and obtain several sampling points by sampling the magnetic field calculation area through the gridding function. The magnetic field calculation area is determined by the compensation direction and spatial parameters.

[0084] Specifically, if the x-axis direction of the passive shielding chamber is set as the compensation direction, then the PCB coils include a first YOZ single-plane coil and a second YOZ single-plane coil, and the normal direction of the plane containing these two single-plane coils is the x-axis direction. Spatial parameters include a first spatial parameter and a second spatial parameter: the first spatial parameter is the relative distance between the plane containing the first YOZ single-plane coil and the plane containing the second YOZ single-plane coil, defined as the first distance; the second spatial parameter is the relative distance between the plane containing the first YOZ single-plane coil and the inner wall of the passive shielding chamber, defined as the second distance; or, the second spatial parameter is the distance between the plane containing the second YOZ single-plane coil and the inner wall of the passive shielding chamber, defined as the third distance. The first distance is denoted as 2xa, and the second distance is equal to the third distance and denoted as xb. The sum of the first distance and twice the second distance is the length of the internal region of the passive shielding chamber, such as 2xa + 2xb = 1000mm. In practical applications, the magnetic field calculation area is usually larger than the internal region of the passive shielding chamber, such as 10% to 30% larger.

[0085] The meshing function is the `meshgrid` function, but other types of functions can also be used as long as they achieve the relevant functionality; there are no strict restrictions. The `meshgrid` function samples the magnetic field calculation region, generating several discrete grid points as sampling points within that region. In practical applications, the number of sampling points is usually determined based on the Nyquist space sampling theorem. Taking a cubic region with a side length of 250mm as an example, the process for determining the number of sampling points is as follows: For a biplane PCB coil with a stream function Fourier expansion order M=N=4, the highest space wavenumber k of the magnetic field it generates in the corresponding region... max =πM / L≈0.025mm -1 Where L is the half-width of the coil and the corresponding minimum spatial wavelength λ min =2π / k max ≈250mm; According to the Nyquist space sampling theorem, the sampling interval Δ must satisfy Δ≤λ min / 2≈125mm, the number of sampling points K on one side needs to satisfy K≥250 / 125+1=3; in order to further accurately evaluate the amplitude deviation rate ≤1.5%, K=11 (sampling interval 25mm), and the total number of sampling points is 11×11×11=1331.

[0086] S12, set the coil parameters, which include coil current, effective coil volume, Fourier expansion order of the stream function M and N, and regularization coefficient λ; of course, it can also include line width, line spacing, plate thickness, etc.

[0087] The Fourier expansion orders M and N of the stream function determine the complexity of the current distribution and the accuracy of the magnetic field fitting, and their values ​​are positive integers, with M=N=4 being preferred. The regularization coefficient λ is used to balance the accuracy of the magnetic field with the feasibility of coil engineering, and its value ranges from 10. -6 ~10 -2 The optimal value is determined by the L-curve method or the generalized cross-validation method; the values ​​of other parameters are usually theoretical or empirical values ​​designed in combination with the actual application requirements.

[0088] S13. Based on the sampling points and coil parameters, establish and solve the flow function equation to obtain the corresponding amplitude deviation rate.

[0089] Specifically, methods for obtaining the corresponding amplitude deviation rate include: determining the current density distribution of the coil based on the coil current and the effective volume of the coil, and introducing a stream function S(x,y) such that... , It automatically satisfies the current continuity equation ▽·J=0, where J x This represents the component of the current density in the x-direction. J represents the partial derivative of the stream function with respect to y. y This represents the component of the current density in the y-direction. Let represent the partial derivative of the stream function with respect to x, ▽ represent the vector differential operator, and J represent the current density. The stream function is expanded using a two-dimensional Fourier series, and a finite number of modes are retained according to the order of the stream function Fourier expansion. Then, based on the Biot-Savart law, a linear equation system AP=b is established between the magnetic field values ​​at the sampling points and the coefficients of the stream function, where A represents the coefficient matrix, P represents the vector of coefficients to be solved, and b represents the target magnetic field value vector. This linear equation system is ill-conditioned and overdetermined. Introducing the Tikhonov regularization term, the problem is transformed into minimizing the functional T=||AP-b||²+λ||ΓP||², where λ is the regularization coefficient and Γ is the regularization matrix. By solving (P)=(A... T A+λΓ T Γ) -1 A T b. Obtain stable and physically realizable stream function coefficients P mn ; the stream function coefficient P mn Substitute the stream function and draw the stream function contour lines to obtain the corresponding amplitude deviation rate. The stream function contour lines are the physical winding profile of the coil.

[0090] S14 involves iteratively adjusting the coil parameters, followed by S13, until the iteration ends, to obtain the amplitude deviation rate corresponding to each group of coil parameters. In practical applications, the coil parameters are iteratively adjusted based on iterative conditions, which include the adjustment step size and the final adjustment value. These conditions should be designed according to the actual application requirements, without imposing too many restrictions.

[0091] S15. Based on the target amplitude deviation rate, select multiple sets of coil parameters that meet the amplitude deviation rate requirements, and select the set of coil parameters with the largest uniform region volume from them.

[0092] Specifically, the amplitude deviation rate corresponding to each group of coil parameters is compared with the target amplitude deviation rate. When the amplitude deviation rate corresponding to the coil parameter is less than the target amplitude deviation rate, it indicates that the amplitude deviation rate corresponding to that group of coil parameters meets the requirements; otherwise, it does not meet the requirements. In practical applications, before the comparison, a step of setting the target amplitude deviation rate is also included. The target amplitude deviation rate should be designed according to the actual application requirements, and there are no excessive restrictions on it.

[0093] The method for selecting the set of coil parameters with the largest uniform region volume from multiple sets of coil parameters includes: establishing two-dimensional coil models based on the flow function contour lines corresponding to each coil parameter, and then establishing three-dimensional coil models based on each coil parameter; calculating the maximum cube volume with an amplitude deviation rate ≤1.5% for each three-dimensional coil model, using the center point of the magnetic field calculation region as the center; using the ratio of each calculated maximum cube volume to a preset volume as a quantitative index of the uniform region volume, and selecting quantitative indices greater than or equal to the preset index; sorting the selected quantitative indices, and selecting the coil parameters corresponding to the quantitative index with the largest value as the set of coil parameters with the largest uniform region volume. Optionally, the preset index is 3.5; in addition, the preset volume is usually designed based on actual application requirements, and there are no excessive restrictions on it.

[0094] S16, the magnetic field of the selected coil corresponding to the coil parameters is superimposed with the geomagnetic field to obtain a set of magnetic flux density data.

[0095] Specifically, the magnetic field corresponding to the selected coil parameters can be obtained based on the three-dimensional coil model in S15. Of course, other methods to obtain the magnetic field corresponding to the coil parameters are also feasible and are not limited to this. In practical applications, the step of obtaining the geomagnetic field is also included before magnetic field superposition, which is a well-known technique in this field and will not be described in detail here.

[0096] S17. Repeat S11~S16 at least once, and use a gradually increasing density method to adjust the number of sampling points to obtain multiple sets of magnetic flux density data, and use this to obtain a magnetic flux density distribution map.

[0097] Furthermore, after obtaining magnetic flux density data by increasing the number of sampling points each time, the relative change in magnetic flux density at the center point of the magnetic field calculation region under two adjacent sampling densities is calculated and compared with a preset value. If the relative change in magnetic flux density is greater than the preset value, it indicates that the sampling density does not meet the accuracy requirements, and the number of sampling points needs to be increased, so the process repeats. If the relative change in magnetic flux density is less than the preset value, it indicates that the sampling density meets the accuracy requirements, and the number of sampling points does not need to be increased, so the process ends. In this step, the relative change in magnetic flux density satisfies the formula δ=|B Ki -B Ki-1 | / |B Ki |×100%, where δ represents the relative change in magnetic flux density, B Ki B represents the magnetic flux density vector calculated from the number of sampling points in the i-th encryption iteration. Ki-1 This represents the magnetic flux density vector calculated from the number of encrypted sampling points in the (i-1)th iteration, where i is a natural number greater than 1; alternatively, the preset value is 0.5%.

[0098] Methods for obtaining a magnetic flux density distribution map include: averaging multiple sets of magnetic flux density data to obtain the magnetic flux density distribution map. Optionally, the averaging is performed as a point-by-point arithmetic mean, and the standard deviation is calculated as an uncertainty index.

[0099] S2 verifies the magnetic field analytical model using the FEM three-dimensional magnetic field method; if the magnetic field analytical model meets the requirements, proceed to S3; if the magnetic field analytical model does not meet the requirements, proceed to S1 and adjust the coil parameters; in this way, the magnetic field uniformity and the volume of the uniform region can meet the practical application requirements.

[0100] In this step, since the axial direction of the PCB coil coincides with the x-axis direction of the passive shielding chamber, the three components of the magnetic flux density at the center point of the PCB coil can be calculated based on the Biot-Savart theorem, and this can be used to analyze and verify the rationality of the analytical magnetic field model. It should be noted that due to the symmetry of the coil structure, the magnetic flux density it generates is distributed in the y and z directions. Therefore, the magnetic flux density distribution perpendicular to the y-axis tangent is the same as the magnetic flux density distribution perpendicular to the z-axis tangent. During analysis and verification, the magnetic flux density distribution perpendicular to the y-axis tangent represents the magnetic flux density distribution perpendicular to both the y and z-axis tangents.

[0101] In one implementation, such as Figure 3 As shown, the method for verifying the analytical model of the magnetic field using the FEM three-dimensional magnetic field method includes the following steps, such as S21~S27.

[0102] S21. The three-dimensional static magnetic field hybrid finite element method is selected, with one of the magnetic field strength and magnetic flux density as unknowns, and the FEM model is constructed with the help of spatial discretization technology.

[0103] In this step, a hybrid method is used to calculate the three-dimensional magnetostatic problem. Electromagnetic field quantities (i.e., magnetic field strength or magnetic flux density) are directly used as unknowns, avoiding calculation errors caused by curl or gradient calculations and achieving higher computational accuracy. Furthermore, the magnetostatic field is the magnetic field generated by a permanent magnet or a constant current in a spatial region, where nonlinear ferromagnetic materials are commonly found.

[0104] Specifically, the method for constructing the FEM model includes: using higher-order edge elements to spatially discretize the magnetic field calculation region to ensure the continuity of the tangential component; and then constructing the FEM model based on Ampere's circuital law and two vector equations with zero magnetic flux density vector divergence, such as projecting Ampere's circuital law onto the discrete space and satisfying the condition that the magnetic flux density vector divergence is zero to construct the FEM model.

[0105] When constructing the FEM model, for the case where the shielding layer material in the passive shielding chamber is permalloy, due to the nonlinear characteristics of its magnetic permeability, the BH curve is used for material definition. The magnetic properties of permalloy include initial permeability ≥ 8000 Gs / Oe, maximum permeability ≥ 100000 Gs / Oe, saturation magnetic induction between 0.8 and 1.0 T, and coercivity ≤ 2 A / m. In the finite element solution process, the Newton-Raphson iterative method is used to handle the nonlinear problem: in each iteration step, the magnetic flux density B in each element (i.e., the smallest geometric subdomain corresponding to the spatial discretization) is calculated based on the current solution. The corresponding magnetic field strength H is obtained by referring to the BH curve, and then the reluctance ν(B) = H / B is updated. The stiffness matrix and residual vector are then reassembled until convergence. The convergence criterion is that the relative residual is less than 10. -6 It is important to note that the relative residual is obtained based on the residual vector.

[0106] Furthermore, before spatial discretization, the process includes determining the number of discrete points: adjusting the number of discrete points gradually (e.g., from 128→500→2000→7000), and calculating L of the magnetic flux density at the center point of the corresponding region after each increase in the number of discrete points. 2 Error, and L 2 The number of discrete points corresponding to an error less than a preset threshold is used as the determined number of discrete points, so that higher-order edge elements can perform spatial discretization based on this determined number of discrete points. Optionally, the preset threshold is 10. -4 In practical applications, to avoid over-encrypting non-critical areas and reduce unnecessary computational costs, the corresponding area for determining the number of discrete points is usually the core working area, rather than the magnetic field calculation area.

[0107] S22, solve the stream function equation corresponding to the magnetic field analytical model to obtain the coil current contour distribution and map it to the FEM model as the excitation source, so as to determine the governing equation of the three-dimensional static magnetic field.

[0108] For the three-dimensional static magnetic field open-domain problem, a sufficiently large air domain is taken to surround the passive shielding chamber and the PCB coil, wherein the boundary size of the air domain is 5 to 10 times that of the passive shielding chamber. A parallel magnetic field boundary condition (i.e., the normal component of the magnetic flux density is zero) is applied to the outer boundary of the air domain. The governing equations are described using a dual description based on vector magnetic potential A and magnetic field strength H. In the conductor region (i.e., the routing region of the PCB coil), the formula ▽×(ν▽×A)=J is used. s In the current-free region (i.e., the air domain and inside the shielding layer), the formulas ▽×H=0 and ▽·B=0 are used, and the two regions satisfy the interface conditions of continuous tangential magnetic field component and continuous normal magnetic flux density component at the interface. Thus, the final governing equations are determined to include Formula 1 and Formula 2, where the governing equations define the curl and divergence of the magnetic field strength H, satisfying the condition that the current density vector in the coil is zero.

[0109] Formula 1: Formula 2: ; where ▽ represents the vector differential operator, Represents the magnetoresistance, and A represents the vector magnetic potential. Represents relative permeability, p represents the Lagrange multiplier. The source current density is the current density in the PCB coil winding, which is determined by the conductor current corresponding to the flow function contour lines. H represents the magnetic field strength.

[0110] S23, the coil is constructed using a stranded conductor integral modeling method in the FEM model. In magnetic field calculation, the current density distribution of the conductor serves as the "source" of the magnetic field; in this embodiment, the current is uniformly distributed between the conductors on the upper and lower planes, and each group of windings of the coil is mutually insulated, so the coil entity can be constructed using a stranded conductor integral modeling method.

[0111] S24. Set boundary conditions, including Niemann boundary conditions and symmetric boundary conditions, and solve the governing equations to obtain intermediate quantities, such as vector magnetic potential A and magnetic field strength H.

[0112] The Niemann boundary condition (also known as the natural boundary condition) is applied to the outer boundary of the air domain, indicating that the magnetic field direction is tangent to the surface and no magnetic flux passes through it. The symmetry boundary condition is an even-symmetry boundary condition (i.e., the magnetic field lines are parallel to the boundary). In this embodiment, for the three centrally symmetric planes (x=0, y=0, z=0 planes) of the passive shielding chamber, the magnetic field distribution satisfies the even-symmetry boundary condition. For the symmetrical design of the PCB coils (symmetric in all four quadrants), the even-symmetry boundary condition is still applied to reduce computational complexity. By setting the boundary conditions, and according to the Helmholtz vector field uniqueness theorem, the boundary value problem has a unique solution.

[0113] S25 involves post-processing the intermediate quantities to obtain a set of magnetic flux density data. Further, it includes jumping to S21 and using either the magnetic field strength or the magnetic flux density as an unknown quantity to obtain two sets of magnetic flux density data, which are then averaged to obtain the final magnetic flux density data. It is important to note that when obtaining two sets of magnetic flux density data based on different unknown quantities, the number of spatially discrete points corresponding to the two spatial discretizations is the same.

[0114] Specifically, at least one of the following methods—the normalized vector magnetic potential method, the gradient-corrected source field scalar magnetic potential method, and the hybrid method—is used to post-process the intermediate quantities to obtain magnetic flux density data. When two or more methods are used for post-processing of the intermediate quantities, averaging (such as point-by-point averaging) is required to obtain the magnetic flux density data. In practical applications, if the relative deviation of the magnetic flux density data exceeds 5% when using two or more methods for post-processing, it is usually necessary to check whether the number of discrete points and the boundary conditions are reasonable and to recalculate.

[0115] In this step, the numerical solution vector diagram corresponding to the magnetic flux density data is as follows: Figures 4-6 As shown, where, Figure 4 Corresponding to the central YOZ plane, Figure 5 Corresponding to the central XOY plane, Figure 6 Corresponding to the central XOZ plane; from Figures 4-6 As can be seen, the magnetic field in the working area is relatively uniform, the residual magnetism is well distributed in space, the area with the smallest residual magnetism is basically located in the central area of ​​the passive shielding chamber, and it shows a consistent distribution from front to back.

[0116] S26. Repeat S21~S25 at least once, and use a gradually increasing density method to adjust the number of spatial discrete points to obtain multiple sets of magnetic flux density data, and use these to obtain a magnetic flux density distribution map.

[0117] Furthermore, after obtaining magnetic flux density data for each encrypted discrete point, the relative change in magnetic flux density at the center point of the magnetic field calculation region under adjacent sampling densities is calculated and compared with a preset value. If the relative change in magnetic flux density is greater than the preset value, it indicates that the sampling density does not meet the accuracy requirements, and the number of sampling points needs to be further encrypted, so the process repeats. If the relative change in magnetic flux density is less than the preset value, it indicates that the sampling density meets the accuracy requirements, and the number of sampling points does not need to be further encrypted, so the process ends. For details regarding the relative change in magnetic flux density and the preset value, please refer to S17 above, which will not be elaborated further. Figure 7 As shown, as the number of spatial discrete points increases, the mean value of the magnetic flux density scalar obtained with magnetic field strength and magnetic flux density as unknowns continuously approaches the reference solution. FEM1 is a schematic diagram of the distribution of magnetic flux density scalar values ​​with magnetic field strength as an unknown, and FEM2 is a schematic diagram of the distribution of magnetic flux density scalar values ​​with magnetic flux density as an unknown.

[0118] A method for obtaining a magnetic flux density distribution map includes averaging multiple sets of magnetic flux density data to obtain the magnetic flux density distribution map. Optionally, the averaging process is a point-by-point arithmetic mean.

[0119] S27, based on the magnetic flux density distribution map obtained in S26, compares and verifies the magnetic flux density distribution map in S1 to verify whether the analytical magnetic field model meets the requirements; among them, the comparison and verification of the magnetic flux density distribution maps perpendicular to the x-axis is as follows. Figure 8 As shown, the two are highly consistent.

[0120] S3, based on the magnetic field analytical model, performs PCB coil routing design.

[0121] In one implementation, such as Figure 9 As shown, the method for designing PCB coil routing includes the following steps, such as S31~S34.

[0122] S31, based on the passive shielding chamber and its support, designs the PCB board dimensions and splices four PCB boards together on the same plane with common edges through a central mounting hole, such as... Figure 10 As shown, the PCB board has a four-layer structure.

[0123] In this step, the overall dimensions are determined based on the passive shielding chamber and its support. The overall dimensions refer to the dimensions of the four PCBs assembled together. Then, the dimensions of each individual PCB are determined, with the individual PCB dimensions (i.e., the board frame size) being 450mm x 400mm. By planarly assembling the four PCBs, conventional size limitations can be overcome, enabling large-scale designs. Furthermore, the four-layer PCB structure, from top to bottom, consists of the first routing layer, power layer, ground layer, and second routing layer. It should be noted that those skilled in the art should understand that the PCB in this step is not a real PCB, but rather a simulated PCB design.

[0124] S32, the coil windings corresponding to the analytical magnetic field model are simulated and designed on four PCB boards according to the principle of symmetry to reduce magnetic field distortion and increase the volume of the uniform region, such as... Figure 10 As shown.

[0125] In this step, the stream function contour lines are plotted by solving the stream function equation corresponding to the analytical magnetic field model to obtain the corresponding coil windings. When performing simulation design based on the coil parameters corresponding to the analytical magnetic field model, the coil windings are divided into nine groups of wires according to the current flow direction, and routing is designed on the first and second routing layers. Electrical interconnection is then achieved through interconnecting vias (e.g., blind vias, through-holes). In practical applications, electrical factors such as board thickness, interlayer symmetry, interlayer coupling, and interlayer interconnection are also considered during routing design. Furthermore, to ensure that each coil winding is completely symmetrical in shape and size, the wire drawing file can be corrected. It should be noted that this is for complete illustration and better understanding. Figure 10 The nine groups of conductors distributed in the first and second wiring layers are shown in the same layer.

[0126] Furthermore, before performing simulation design, a pre-compensation step is included using the Image Method (IM) to compensate for the ferromagnetic boundary coupling effect of the passive shielding chamber. Specifically, this involves treating the six inner walls of the passive shielding chamber as having high permeability (μ). r A mirror image of the original coil (>50000) is constructed, and a mirror coil of the original coil is placed outside its shielding layer. The position of the mirror coil is determined by the shielding layer thickness and the distance between the original coil and the inner wall. The magnetic fields of the original coil and each mirror coil are superimposed to obtain a corrected magnetic field distribution that considers the ferromagnetic boundary coupling effect, so as to perform simulation design based on this corrected magnetic field distribution. In practical applications, the mirror method only considers the first-order mirror (mirror order CA=1), because for μ... r For permalloy materials with a reflectance greater than 50,000, the reflectance coefficient R = (μ r -1) / (μ r +1)≈1, transmission coefficient T=4μ r / (μr +1)² ≈ 4×10 -5 The intensity of the second-order mirror image is proportional to T² < 10. -9 The effect on the magnetic field of the target area is negligible. Furthermore, the first-order mirror image of the original coil, which is at a distance d from the inner wall, is located at a distance d+2t on the other side of the inner wall, where t is the thickness of the shielding layer (e.g., t=1.5mm).

[0127] S33, establish a three-dimensional model of the PCB coil and perform performance evaluation. If it fails, execute S32 and adjust the coil parameters. If it passes, execute S34. When performing performance evaluation, at least one of amplitude deviation rate, magnetic field uniformity and uniform region volume is used as evaluation item.

[0128] For amplitude deviation rate, the passing standard for performance evaluation is: the maximum amplitude deviation rate within the working area ≤ 1.5%; for magnetic field uniformity, the passing standard for performance evaluation is: the maximum non-uniformity error ≤ 1.5% (simulation value); for uniform region volume, the passing standard for performance evaluation is: the ratio of uniform region volume to working area volume ≥ 3.0.

[0129] In practical applications, when there are two or more evaluation items, if any one of them fails to meet the pass / fail standard, the application is deemed unqualified. Furthermore, when adjusting coil parameters, the following priority order is typically followed: first, adjust the regularization coefficient λ (e.g., a step size of 0.5 to 2 times the current value); second, adjust the Fourier expansion order M and N of the stream function; and finally, adjust the coil current and the effective coil volume. It is important to note that if the adjustment still fails to meet the requirements, return to S1 to re-establish the analytical magnetic field model.

[0130] S34, Design the PCB coil routing based on coil parameters; for example, draw the coil winding at a 1:1 scale according to the actual size using drawing software, and then design the routing using routing software.

[0131] Furthermore, after completing the PCB coil routing design, the coil constant of the PCB coil is calculated. The coil constant is defined as the ratio of the magnetic flux density generated at the center point of the working area to the excitation current. For uniform field coils, the unit of the coil constant is nT / A, and for gradient coils, the unit is nT / m / A. The magnitude of the coil constant determines the magnetic field strength generated under a given current, and also determines the level of magnetic noise introduced by current source noise. In this embodiment, through a dual-plane coil design, the coil constant in the Bx direction is optimized to 69.43 nT / A, the coil constant in the Bz direction to 101.67 nT / A, the coil constant in the dBx / dz direction to 351.22 nT / m / A, and the coil constant in the dBz / dz direction to 572.03 nT / m / A; compared to the traditional single coil, the optimization rate can reach 45%~70%. In practical applications, the coil constant is usually recorded as a design output parameter.

[0132] The method for PCB coil routing design, following S33 but before S34, also includes S334, which constructs a coupling loss model between the shielding layer and the PCB coil in the passive shielding chamber to evaluate the relationship between the uniform region volume and the coil bias position (not shown in the figure). The coupling loss includes eddy current loss, hysteresis loss, and resistive loss. Eddy current loss P eddy =π²f²B²d² / (6ρ)·(μ r ² / (1+μ r ²), where f is the frequency of the alternating magnetic field (for geomagnetic field compensation, f≈0Hz, eddy current loss can be ignored; for power frequency interference compensation, f=50Hz), B is the magnetic flux density, d is the shielding layer thickness (e.g., d=1.5 mm), ρ is the resistivity of the shielding layer material (e.g., the resistivity of permalloy is ρ≈0.55μΩ·m), μ r Relative permeability. Hysteresis loss. Where η represents the hysteresis loss coefficient, μ0 represents the free permeability, and V represents the shielding layer volume. Resistance loss P res =I²R coil Where I is the coil current, R coil Let P be the DC resistance of the PCB coil. Based on the above coupling loss model, evaluate the influence of the distance (e.g., xb) between the PCB coil and the inner wall of the passive shielding chamber on the volume of the uniform region. eddy +P hyst +P res When the system power consumption budget is exceeded (e.g., 5 W), the coil bias position or coil parameters need to be adjusted.

[0133] S4, targeting the application goal of near-zero uniform magnetic field environment in passive shielding chamber, uses PCB coils and sensors to build an experimental platform in passive shielding chamber to facilitate experimental verification of PCB coils in actual environment; among which, experimental verification includes static performance verification and dynamic performance verification.

[0134] Static performance verification was completed by comparing the theoretical design value and experimental measurement value of the center magnetic flux density deviation rate, where the center magnetic flux density deviation rate includes the relative deviation ΔB. rel and root mean square deviation ΔB RMS Relative deviation ΔB rel Satisfy the formula Root mean square deviation ΔB RMS Satisfy the formula Among them, B max B represents the maximum value of the magnetic field strength. min B represents the minimum value of the magnetic field strength. avg The value represents the average magnetic field strength, N represents the number of sampling points, and B represents the average magnetic field strength. i This represents the magnetic field strength at the i-th sampling point.

[0135] Dynamic performance verification was achieved by introducing a PID-based closed-loop control system to realize automatic field zeroing (AFN). This PID-based closed-loop control system uses the residual magnetic field monitored in real-time by sensors as feedback, and the target magnetic field value of 0 pT as the setpoint. It generates a compensation control quantity through proportional-integral-derivative operations to drive the PCB coil to generate a compensation magnetic field opposite to the direction of the residual magnetic field. The quantitative targets for dynamic performance are: in the time domain, to suppress the maximum background field fluctuation from the nT level to ≤2.1 pT; and in the frequency domain, to achieve a noise suppression ratio of ≥30 dB in the 0.01 Hz low-frequency range.

[0136] In practical applications, when performance verification fails, it is necessary to check the processing accuracy of the PCB coil, assembly position error, and sensor calibration error, and correct the coil parameters accordingly.

[0137] like Figure 11 As shown, this embodiment also provides a dual-plane actively shielded PCB coil 300, including a first YOZ single-plane coil 301 and a second YOZ single-plane coil 302. The PCB coil 300 is designed using the design method described above. In this embodiment, each single-plane coil includes four mutually symmetrical PCB structures, as shown... Figure 10 As shown.

[0138] like Figure 11 As shown, this embodiment also provides a magnetic shielding device, including a passive shielding chamber 100, a non-magnetic support 200, a PCB coil 300 and a sensor 400, and further includes a coil control module 500.

[0139] The passive shielding chamber 100 is covered with a shielding layer (not shown in the figure) to provide a low magnetic reluctance bypass based on a high magnetic permeability material, and to shunt the magnetic field component to form a shielding effect against external magnetic fields such as the Earth's magnetic field and the power frequency noise of the device.

[0140] Specifically, the passive shielding chamber 100 includes a mechanical support 101 and a shielding layer (not shown in the figure). The mechanical support 101 supports the shielding layer to form an internal hollow structure, and the shielding layer forms the chamber body. In this embodiment, the internal dimensions of the passive shielding chamber 100 are 1000mm*1000mm*1200mm, and the chamber body has a three-layer structure, consisting of two 1.5mm layers of high-permeability ferromagnetic material and one 5mm layer of aluminum material.

[0141] A non-magnetic bracket 200 is disposed on the two side walls of the passive shielding chamber 100 for mounting and positioning PCB coils. As an optional feature, the non-magnetic bracket 200 is made of epoxy resin. In practical applications, the non-magnetic bracket 200 includes a first bracket 201 and a second bracket 202. For example, the first bracket 201 is disposed on the left side wall of the passive shielding chamber 100, and the second bracket 202 is disposed on the right side wall of the passive shielding chamber 100.

[0142] The dual-plane active shielded PCB coil 300 described above is mounted on a non-magnetic support 200 and is used to compensate for the residual magnetic field within the passively shielded chamber. In practical applications, the PCB coil 300 includes a first YOZ single-plane coil 301 and a second YOZ single-plane coil 302. For example, the first YOZ single-plane coil 301 is mounted on the first support 201, and the second YOZ single-plane coil 302 is mounted on the second support 202. Each single-plane coil includes four mutually symmetrical PCB structures.

[0143] Sensor 400 is located at the center of passive shielding chamber 100 to monitor the residual magnetic field inside passive shielding chamber 100, so that the residual magnetic field can be compensated by PCB coil 300 to form a near-zero magnetic field.

[0144] The coil control module 500 is located outside the passive shielding chamber 100. It is used to provide current excitation and perform PID control to zero the magnetic field. For example, the target magnetic field value is set to 0pT. The residual magnetic field inside the passive shielding chamber 100 is monitored in real time by a sensor and the measured magnetic field value is obtained. By performing proportional, integral and derivative operations on the deviation between the target magnetic field value and the measured magnetic field value, a corresponding compensation control quantity is generated to feed back control of the PCB coil and generate a compensation magnetic field opposite to the direction of the residual magnetic field.

[0145] In practical applications, the magnetic shielding device of this embodiment also includes a reference module 600, used to obtain more comprehensive residual magnetic field information, and to assist the coil control module 500 in achieving residual magnetic field compensation more stably and accurately. In practical applications, the reference module 600 includes a fluxgate 601 and a magnetic field spectrum analyzer (not shown in the figure), wherein the fluxgate 601 is disposed inside the passive shielding chamber 100, and the magnetic field spectrum analyzer (not shown in the figure) is disposed outside the passive shielding chamber 100.

[0146] In summary, the dual-plane active shielded PCB coil and its design method, along with the magnetic shielding device of this invention, establish an analytical model of the PCB coil's magnetic field through reverse calculation and verify it using the FEM three-dimensional magnetic field method. This yields the winding structure of the PCB coil and allows for wiring design, avoiding mechanical implementation errors associated with complex coil routing and reducing spatial position errors between the coil plane and the sensor. Consequently, it reduces measurement errors in amplitude and uniformity of the central uniform field region. Furthermore, the PCB coil of this invention provides a uniform low magnetic field environment by compensating for residual magnetic fields within a passively shielded chamber. This improves the design efficiency and structural accuracy of the active residual magnetic field compensation PCB coil in small zero-magnetic devices, providing a basic magnetic field environment for small-scale weak magnetic field measurement experiments. It also provides a design theory for the efficient and accurate physical realization and parameter control of compensation coils in larger cubic and non-centrosymmetric shielding environments. Therefore, this invention effectively overcomes the various shortcomings of existing technologies and possesses high industrial applicability.

[0147] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A design method for a dual-plane actively shielded PCB coil, characterized in that, The design method includes: S1, using magnetic field uniformity and uniform region volume as optimization indicators, and determining coil parameters through reverse calculation based on the target amplitude deviation rate, in order to establish a magnetic field analytical model of the PCB coil corresponding to the magnetic field to be shielded; S2, verify the magnetic field analytical model using the FEM three-dimensional magnetic field method; if the magnetic field analytical model meets the requirements, proceed to S3; if the magnetic field analytical model does not meet the requirements, proceed to S1 and adjust the coil parameters. S3, Design the PCB coil wiring based on the coil winding corresponding to the magnetic field analytical model; Wherein, the magnetic field to be shielded is the residual magnetic field inside the passive shielding chamber, and the magnetic field analytical model is the magnetic flux density distribution diagram of the PCB coil.

2. The design method of the dual-plane active shielded PCB coil according to claim 1, characterized in that, The magnetic field uniformity refers to the degree of deviation of the magnetic flux density between any point in the working area and the center point, which is measured by the amplitude deviation rate and satisfies the formula. ,in, Indicates the amplitude deviation rate. This represents the magnetic flux density at any point within the working area. The magnetic flux density at the center point of the working area is represented by the uniform region volume, which is the volume of the largest cube centered at the center point of the working area and satisfies an amplitude deviation rate of less than or equal to 1.5%. The working area is the region corresponding to the sensor inside the passive shielding chamber.

3. The design method for a dual-plane actively shielded PCB coil according to claim 1, characterized in that, The method for establishing the analytical model of the magnetic field includes: S11, Define the magnetic field calculation area, and obtain several sampling points by sampling the magnetic field calculation area through a gridding function, wherein the magnetic field calculation area is determined by the compensation direction and spatial parameters; S12, Set coil parameters, wherein the coil parameters include coil current, effective coil volume, Fourier expansion order of the stream function, and regularization coefficient; S13, Based on the sampling points and the coil parameters, establish and solve the flow function equation to obtain the corresponding amplitude deviation rate; S14, after iteratively adjusting the coil parameters, execute S13 until the iteration ends; S15, based on the target amplitude deviation rate, select multiple sets of coil parameters that meet the amplitude deviation rate requirements, and select the set of coil parameters with the largest uniform region volume from them; S16, superimpose the magnetic field of the selected coil parameters with the geomagnetic field to obtain a set of magnetic flux density data; S17. Repeat S11~S16 at least once, and use a gradually increasing density method to adjust the number of sampling points to obtain multiple sets of magnetic flux density data, and use this to obtain a magnetic flux density distribution map.

4. The design method for a dual-plane actively shielded PCB coil according to claim 3, characterized in that, The x-axis direction of the passive shielding chamber is set as the compensation direction. The PCB coil includes a first YOZ single-plane coil and a second YOZ single-plane coil. The spatial parameters include a first spatial parameter and a second spatial parameter, wherein the first spatial parameter is the relative distance between the plane where the first YOZ single-plane coil is located and the plane where the second YOZ single-plane coil is located, and the second spatial parameter is the relative distance between the plane where the first YOZ single-plane coil or the second YOZ single-plane coil is located and the inner wall of the passive shielding chamber.

5. The design method for a dual-plane actively shielded PCB coil according to claim 3, characterized in that, In S13, the methods for obtaining the corresponding amplitude deviation rate include: The current density distribution of the coil is determined based on the coil current and the effective volume of the coil, and a flow function S(x,y) is introduced to make... , , where J x This represents the component of the current density in the x-direction. J represents the partial derivative of the stream function with respect to y. y This represents the component of the current density in the y-direction. This represents the partial derivative of the stream function with respect to x; The stream function is expanded using a two-dimensional Fourier series and a finite number of modes are retained according to the order of the Fourier expansion of the stream function. Then, based on the Biot-Savart law, a linear system of equations AP=b is established between the magnetic field values ​​of the sampling points and the coefficients of the stream function, where A represents the coefficient matrix, P represents the coefficient vector to be determined, and b represents the target magnetic field value vector. Introducing a Tikhonov regularization term into the linear equation system transforms the problem into minimizing the functional T = ||AP-b||² + λ||ΓP||², where λ is the regularization coefficient and Γ is the regularization matrix. By solving (P)=(A) T A+λΓ T Γ) -1 A T b. Obtain the stream function coefficients, substitute the stream function coefficients into the stream function, and draw the stream function contour lines to obtain the corresponding amplitude deviation rate.

6. The design method of the dual-plane active shielded PCB coil according to claim 5, characterized in that, In S15, the method for selecting the set of coil parameters that maximizes the volume of the uniform region from multiple sets of coil parameters includes: Two-dimensional coil models are established based on the flow function contour lines corresponding to each coil parameter, and then three-dimensional coil models are established based on the coil parameters. Using the center point of the magnetic field calculation region as the center, calculate the maximum cube volume for each three-dimensional coil model with an amplitude deviation rate ≤1.5%; The ratio of the calculated maximum cube volume to the preset volume is used as the quantitative index of the uniform region volume, and each quantitative index that is greater than or equal to the preset index is selected. The selected quantitative indicators are sorted, and the coil parameters corresponding to the quantitative indicator with the largest value are taken as the group of coil parameters with the largest uniform region volume.

7. The design method of the dual-plane active shielded PCB coil according to claim 1, characterized in that, The methods for verifying the analytical magnetic field model using the FEM three-dimensional magnetic field method include: S21. The three-dimensional static magnetic field hybrid finite element method is selected, with one of the magnetic field strength and magnetic flux density as unknowns, and the FEM model is constructed with the help of spatial discretization technology. S22, Solve the stream function equation corresponding to the magnetic field analytical model to obtain the coil current contour distribution and map it onto the FEM model as an excitation source to determine the control equation of the three-dimensional static magnetic field; S23, The coil is constructed in the FEM model using an overall modeling method of stranded conductors; S24, Set boundary conditions including Niemann boundary conditions and symmetric boundary conditions, and solve the governing equations to obtain intermediate quantities; S25, perform post-processing on the intermediate quantity to obtain a set of magnetic flux density data; S26. Repeat S21~S25 at least once, and use a gradually increasing density method to adjust the number of spatial discrete points to obtain multiple sets of magnetic flux density data, and use this to obtain a magnetic flux density distribution map. S27. Based on the magnetic flux density distribution map obtained in S26, the magnetic flux density distribution map in S1 is compared and verified.

8. The design method of the dual-plane active shielded PCB coil according to claim 7, characterized in that, In S25, after obtaining a set of magnetic flux density data, it also includes jumping to S21 and taking the other of the magnetic field strength and magnetic flux density as an unknown quantity to obtain two sets of magnetic flux density data and perform averaging.

9. The design method for a dual-plane actively shielded PCB coil according to claim 7 or 8, characterized in that, In S21, higher-order edge elements are used to spatially discretize the magnetic field calculation region, and the FEM model is constructed based on two vector equations: Ampere's circuital theorem and the zero magnetic flux density vector divergence.

10. The design method of the dual-plane active shielded PCB coil according to claim 9, characterized in that, In S21, before spatial discretization, the step of determining the number of discrete points is included: adjusting the number of discrete points by gradually increasing the density, and calculating L of the magnetic flux density at the center point of the corresponding region after each increase in the number of discrete points. 2 Error, and L 2 The number of discrete points corresponding to an error less than a preset threshold is used as the determined number of discrete points.

11. The design method of the dual-plane active shielded PCB coil according to claim 9, characterized in that, When constructing the FEM model in S21, for the case where the shielding layer material in the passive shielding chamber is permalloy, due to the nonlinear characteristics of its magnetic permeability, the BH curve is used for material definition, and the Newton-Raphson iteration method is used to handle the nonlinear problem until convergence. The convergence criterion is that the relative residual is less than 10. -6 .

12. The design method of the dual-plane active shielded PCB coil according to claim 7 or 8, characterized in that, In S22, the governing equations are described based on vector magnetic potential and magnetic field strength, including: Formula 1: ; Formula 2: ; in, Represents the vector differential operator. Represents the magnetoresistance, and A represents the vector magnetic potential. Represents relative permeability, p represents the Lagrange multiplier. H represents the source current density, and H represents the magnetic field strength.

13. The design method for a dual-plane actively shielded PCB coil according to claim 3 or 7, characterized in that, After each encryption, the relative change in magnetic flux density at the center point of the magnetic field calculation region under two adjacent sampling densities is calculated, and the repetition ends when the relative change in magnetic flux density is less than a preset amount.

14. The design method of the dual-plane active shielded PCB coil according to claim 1, characterized in that, Methods for designing PCB coil routing include: S31, based on the passive shielding chamber and its support, design the size of the PCB board, and splice the four PCB boards together on the same plane with common edges through the central mounting hole, wherein the PCB board has a four-layer structure; S32, The coil windings corresponding to the magnetic field analytical model are simulated and designed on four PCB boards respectively, following the principle of symmetry; S33, establish a three-dimensional model of the PCB coil and perform performance evaluation. If it is not qualified, execute S32 and adjust the coil parameters corresponding to the magnetic field analysis model. If it is qualified, execute S34. S34, Design the PCB coil wiring based on the coil parameters.

15. The design method of the dual-plane active shielded PCB coil according to claim 14, characterized in that, In S32, before performing simulation design, the method of mirroring is used to pre-compensate the ferromagnetic boundary coupling effect of the passive shielding chamber: the six inner wall surfaces of the passive shielding chamber are regarded as mirror surfaces with high magnetic permeability, and mirror coils of the original coil are set outside the shielding layer. The position of the mirror coils is determined by the thickness of the shielding layer and the distance between the original coil and the inner wall surface. The magnetic fields of the original coil and each of the mirror coils are superimposed to obtain the corrected magnetic field distribution, and the simulation design is performed based on the corrected magnetic field distribution.

16. The design method of the dual-plane active shielded PCB coil according to claim 14, characterized in that, When conducting performance evaluation, at least one of amplitude deviation rate, magnetic field uniformity, and uniform region volume is used as an evaluation item.

17. A dual-plane actively shielded PCB coil, characterized in that, The PCB coil includes a first YOZ single-plane coil and a second YOZ single-plane coil, and is designed using the design method described in any one of claims 1 to 16.

18. A magnetic shielding device, characterized in that, The magnetic shielding device includes: Passive shielding chamber, covered with a shielding layer; Non-magnetic supports are installed on the two side walls of the passive shielding chamber; The dual-plane active shielded PCB coil as described in claim 17 is disposed on the non-magnetic bracket; The sensor is located at the center point of the passive shielding chamber.

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