Cylindrical coil compensation structure design method and system for inhibiting asymmetric magnetic interference

Abstract

The invention belongs to the field of high-performance magnetic shielding device design, and discloses a cylindrical coil compensation structure design method and system for inhibiting asymmetric magnetic interference, a compensation coil is composed of a plurality of closed coils with specific angles, all the coils are integrally in a cylindrical configuration, and a target field normal flow function used for calculating target magnetic field compensation is corrected, so that the target magnetic field compensation is realized. A current density coefficient is solved by using a target field method, then a flow function is discretized, so that a specific coil configuration is designed, clockwise or anticlockwise current is introduced into each coil, and the target of inhibiting asymmetric magnetic interference is achieved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of high-performance magnetic shielding device design, and relates to an active magnetic compensation method, in particular to a cylindrical coil compensation structure design method and system for suppressing asymmetric magnetic interference. BACKGROUND

[0002] With the rise of zero-magnetic medicine and other fields, medical applications based on ultra-high sensitivity extremely weak magnetic field measurement technology continue to expand. By detecting the magnetic field generated by human organs, the lesions of human heart and brain related diseases can be effectively located. However, the magnetic field generated by human organs is extremely weak, and the heart magnetic signal is only about one ten-millionth of the earth's magnetic field, while the environmental geomagnetic field, urban alternating magnetic noise and the like are much stronger. Therefore, when detecting the weak magnetic signal of the human body, effective magnetic shielding of strong environmental magnetic noise must be taken to obtain accurate and effective human magnetic information for medical applications such as disease diagnosis.

[0003] A medical device for detecting a magnetocardiogram relies on active and passive magnetic compensation technology to provide a necessary extremely weak magnetic field environment. Due to the principle limitation, passive shielding is difficult to achieve a zero-magnetic state, and the magnetic shielding cylinder commonly designed with an open end for easy use in the heart magnetic detection makes the residual magnetic level further increase. Therefore, it is necessary to design an active magnetic compensation coil to further improve the environmental magnetic field interference in the magnetic shielding cylinder.

[0004] The design of the active magnetic compensation coil belongs to the inverse problem of the magnetic field design, which needs to determine a certain coil structure that generates a specific magnetic field distribution. In the inverse design, the target field method is usually used to calculate the current distribution required for the target magnetic field, so as to obtain the coil configuration. The existing active magnetic compensation coil in the magnetic shielding cylinder suppresses the residual magnetic interference in the magnetic shielding cylinder by designing a uniform magnetic field and a gradient magnetic field.

[0005] In actual application, the coupling effect of the active coil and the high magnetic permeability metal inevitably leads to distortion of the compensation magnetic field, and due to the open structure of the magnetic shielding cylinder, the internal magnetic field distribution has asymmetry and belongs to a high-order gradient. Only a uniform magnetic field and a gradient magnetic field are not enough to meet the demand of near-zero magnetic field for high-resolution magnetocardiogram (MCG). SUMMARY

[0006] To solve the problems existing in the prior art, the present application provides a cylindrical coil compensation structure design method and system for suppressing asymmetric magnetic interference, which designs a cylindrical coil compensation structure for suppressing asymmetric magnetic interference, and enriches the magnetic field regulation mode of the cylindrical magnetic shielding bin. The asymmetric cylindrical coil structure can reduce the residual magnetic field and weaken the magnetic noise during the use of the MCG system, so as to meet the high resolution requirement of the MCG system.

[0007] To achieve the above object, the application provides the following scheme:

[0008] A design method of cylindrical coil compensation structure for suppressing asymmetric magnetic interference, the method comprises:

[0009] Step 1: determining the size of the required cylindrical magnetic shielding bin according to the requirements of a high-resolution cardiac magnetogram system, so as to determine the size of the required cylindrical magnetic compensation coil on the surface of the CMS and the range of the target magnetic field region in the CMS; wherein the high-resolution cardiac magnetogram system is an MCG system, and the required cylindrical magnetic shielding bin is a CMS;

[0010] Step 2: introducing a flow function to represent the current density on the inside of the CMS and decomposing it into three components of axial, radial and angle, wherein the radial component is zero, and then expanding the flow function by using a double Fourier series, and performing half-angle expansion on the double Fourier series to modify the flow function to be asymmetric, so as to realize the asymmetric distribution of the current density and the corresponding magnetic field;

[0011] Step 3: determining the relationship between the target magnetic field in the specified region and the current density on the inside of the cylindrical magnetic shielding bin according to the Biot-Savart law, then dividing the target region into Num field points, and using the target field method to solve the current density coefficient according to the expected magnetic field value of the target field point;

[0012] Step 4: obtaining the contour line after discretizing the flow function, so as to determine the magnetic compensation coil configuration, and winding the coil on the inside of the magnetic shielding cylinder, so as to realize the compensation of the asymmetric magnetic field after the coil is energized.

[0013] Preferably, the radius of the specified cylindrical magnetic compensation coil is R c , the length is H, and the cylindrical magnetic compensation coil is fixed in the inner cylinder of the magnetic shielding bin; the distance between the cylindrical magnetic compensation coil and the closed end of the cylindrical magnetic shielding bin with a radius of R M and a thickness of d M is h, and the square region where the target magnetic field is located is located at the center of the coil and has a length of d.

[0014] Preferably, the implementation process of step 2 comprises:

[0015] Step 2.1: in the cylindrical coordinate system, the continuously distributed surface current density on the inner cylinder surface of the magnetic shielding bin is J(r), which is composed of the axial component J θ (θ,z), the angle component J z (θ,z), and the radial current density component, wherein the radial current density component is zero, wherein the coordinate point on the surface of the magnetic shielding cylinder is r(R c,θ,z) represents, the target magnetic field position is represented by r'(p, θ', z'); the coordinate position vector of the inner surface of the magnetic shielding cylinder is represented by r(R c ,θ,z) represents, the target magnetic field position vector is represented by r'(p, θ', z'), wherein θ is the azimuth angle from the x-axis, z represents the height of different coordinate points in the magnetic shielding cylinder, S represents the stream function, p is the vertical distance of the target point to the central axis of the magnetic shielding cylinder, θ' is the azimuth angle of the target magnetic field position point, and z' represents the height of the target magnetic field in the magnetic shielding cylinder;

[0016] Step 2.2: The stream function is expanded by a double Fourier series, and then half-angle expansion is performed, and the stream function is further modified to be asymmetric, so as to realize the asymmetric distribution of the current density and the corresponding magnetic field; according to the symmetry and boundary continuity, all the current densities are determined by the to-be-solved parameters P mn , and the x-direction coil of the cylindrical magnetic compensation coil is simplified because the x-direction coil is converted into a y-direction coil by 90° rotation, the By and Bz coils and the dBy / dy coil are symmetrical in the x and y directions and are asymmetric in the z direction, and therefore the current density and the stream function in the By direction are represented as:

[0017]

[0018] The current density and the stream function in the By direction gradient are represented as:

[0019]

[0020]

[0021] The current density and the stream function in the Bz direction gradient are represented as:

[0022]

[0023] J Z (θ,z) = 0.

[0024]

[0025] wherein m and n are the orders of the Fourier series, and M and N are the orders selected according to engineering experience.

[0026] Preferably, the implementation process of step 3 comprises:

[0027] Step 3.1: According to the Biot-Savart law B(r) represents the magnetic field vector, and the target area magnetic field is calculated by the current density on the surface of the magnetic shielding cylinder:

[0028]

[0029] wherein μ0 is the vacuum permeability, A is the lateral surface area of the cylindrical magnetic compensation coil, U is the voltage applied to the coil, and B is the magnetic field. mn (r, θ', z) and V mn (r, θ', z) is the function part of the target magnetic field after substituting into the Fourier series;

[0030] Step 3.2: uniformly discretize the target magnetic field in the cubic region, and discretize a total of Num coordinate points in the x, y, and z directions.

[0031] Preferably, the step 3.2, which uniformly discretizes the magnetic field in the target region and discretizes a total of Num coordinate points in the x, y, and z directions, includes:

[0032] Step 3.2.1: construct an error function for the magnetic field distribution of the Num coordinate points and the preset target magnetic field distribution, convert the integral equation into a form of a finite number of algebraic equation groups for matrix solution, i.e.:

[0033] wherein B target is the target magnetic field, E is the error function, and B(ρ, θ', z') is the value of the magnetic field vector at the space point (ρ, θ', z').

[0034] Step 3.2.2: use Tikhonov regularization to introduce a penalty function in the formula wherein Γ is the Tikhonov matrix determined by the penalty function, and λ is the weight coefficient.

[0035] Step 3.2.3: select the curvature as the penalty function, solve the optimal value of P mn by minimizing the error E, and set the error E to zero in the algorithm.

[0036] Preferably, the implementation process of the step 4 includes:

[0037] Step 4.1: substitute the optimal value of the coefficient P mn into the flow function;

[0038] Step 4.2: set the maximum value of the current distribution flow function as S max , and the minimum value as S min , and divide the flow function into K contour lines, so that the expression of the contour lines of the discretized flow function is:

[0039]

[0040] Step 4.3: the current flow direction of the cylindrical magnetic compensation coil does not depend on the positive and negative of the contour lines, but is determined by the discretization order of each coordinate point of the contour lines, so the Stokes formula is selected: ​

[0041]

[0042] Wherein P, Q, R are respectively the components of the current vector field along the x, y, z axis direction, x, y, z are the space rectangular coordinates, used to describe the position, the direction of the current in the closed coil is judged, so as to determine the current flow direction;

[0043] Step 4.4: according to the actual demand, the performance of the cylindrical magnetic compensation coil and the processing capacity are balanced, the number of contour lines is determined;

[0044] Step 4.5: according to the discrete contour line data, combined with the size of the cylindrical surface where the cylindrical magnetic compensation coil is located, the calculated cylindrical magnetic compensation coil is subjected to coordinate transformation, the new track is calculated, and the cylindrical magnetic compensation coil is wound on the inner wall of the magnetic shielding inner cylinder, the magnetic shielding inner cylinder is a non-magnetic hollow clamp for fixing the cylindrical magnetic compensation coil, made of polyethylene material, the coil winding is wound along the groove on the magnetic shielding inner cylinder, and the magnetic shielding inner cylinder is subjected to numerical control cutting processing according to the design shape of the cylindrical magnetic compensation coil.

[0045] The application also provides a cylindrical coil compensation structure design system for inhibiting asymmetric magnetic interference, which is used to realize the method and comprises a parameter determination module, a correction module, a solving module and a discretization module.

[0046] The parameter determination module is used to determine the size of the required cylindrical magnetic shielding chamber according to the requirements of a high-resolution cardiac magnetogram system, so as to determine the size of the cylindrical magnetic compensation coil required by the CMS surface and the range of the target magnetic field region in the CMS, wherein the high-resolution cardiac magnetogram system is an MCG system, and the required cylindrical magnetic shielding chamber is a CMS.

[0047] The correction module is used to introduce a flow function to represent the current density on the inner side of the CMS and decompose into three components of axial, radial and angle, wherein the radial component is zero, then the flow function is expanded by a double Fourier series, and then the flow function is asymmetrically corrected by half-angle expansion, so as to realize the asymmetric distribution of the current density and the corresponding magnetic field.

[0048] The solving module is used to determine the relationship between the target magnetic field in the specified region and the current density on the inner side of the cylindrical magnetic shielding chamber according to the Biot-Savart law, then divide the target region into Num field points, and use the target field method to solve the current density coefficient according to the expected magnetic field value of the target field point.

[0049] The discretization module is used to obtain contour lines after discretization of the flow function, so as to determine the magnetic compensation coil configuration, and the magnetic compensation coil configuration is used to surround the coil on the inner side of the magnetic shielding cylinder, so that the compensation of the asymmetric magnetic field is realized after the coil is energized.

[0050] Compared with the prior art, the application has the following beneficial effects:

[0051] (1) The application proposes a new asymmetric magnetic interference suppression method, which corrects the target field method flow function for calculating the target magnetic field compensation, effectively suppresses the single-side-internal asymmetric magnetic field in the similar cylindrical magnetic shielding bin, and enriches the magnetic field regulation mode of the cylindrical magnetic shielding bin.(2) The asymmetric compensation magnetic field compensation method is applied to the high-resolution MCG for the first time, which can not only weaken the residual magnetic field, but also weaken the magnetic noise, which is helpful for the early screening of patients with heart disease risk by high-resolution MCG. BRIEF DESCRIPTION OF DRAWINGS

[0052] In order to more clearly illustrate the technical solutions of the present application, the following briefly introduces the drawings needed in the embodiments. Obviously, the drawings described in the following embodiments are only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor.

[0053] Figure 1 The figure is a schematic diagram of the cylindrical high-performance magnetic shielding device of the embodiment of the present application.

[0054] Figure 2 The figure is a specific implementation step flowchart of the embodiment of the present application.

[0055] In the figure, 1 is a cylindrical magnetic shielding bin; 2 is a cylindrical magnetic compensation coil; 3 is a magnetic shielding bin inner cylinder; 4 is a target magnetic field; 5 is a closed end; 6 is an open end. DETAILED DESCRIPTION

[0056] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0057] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the present application will be further described in detail below with reference to the drawings and specific embodiments.

[0058] Embodiment one

[0059] As can be known from the background art:

[0060] In the field of biological medicine, asymmetric gradient field coils are widely adapted to various magnetic resonance imaging (MRI) devices, providing strong support for precise medical imaging. However, in high-resolution magnetocardiogram (MCG) systems, the application of such coils is rarely studied.

[0061] The current MCG system commonly uses a single-side opening cylindrical cylinder shielding structure, so that the MCG system only relies on the uniform magnetic field and the conventional gradient magnetic field coil for active magnetic compensation during operation, and cannot effectively suppress the single-side-internal asymmetric magnetic field of the shielding cylinder. Therefore, the MCG system is difficult to realize high-resolution detection of the weak magnetic field of the human heart, thereby restricting the further improvement of the detection accuracy of the human heart disease of the MCG system, and hindering the exploration process of the biological medical technology to a higher precision and a more microscopic level.

[0062] Therefore, the present application designs a cylindrical coil compensation structure for suppressing asymmetric magnetic interference, which enriches the magnetic field regulation mode of the cylindrical magnetic shielding bin. The asymmetric cylindrical coil structure can reduce the residual magnetic field and weaken the magnetic noise during the use of the MCG system, thereby meeting the high-resolution requirement of the MCG system.

[0063] The present application will be described in detail below with the aid of the accompanying drawings and examples: Figure 1 The present application will be described in detail below with the aid of the accompanying drawings and examples:

[0064] The present application provides a cylindrical coil compensation design method for suppressing asymmetric magnetic interference. The compensation coil is composed of a plurality of pairs of specific angle closed coils, and all the coils are in a cylindrical configuration. The target field method flow function used for calculating the target magnetic field compensation is corrected, and then the target field method is used to solve the current density coefficient. The flow function is discretized to design a specific coil configuration. The clockwise or counterclockwise current in each coil is used to achieve the goal of suppressing asymmetric magnetic interference, which enriches the magnetic field regulation mode of the cylindrical magnetic shielding bin. The specific implementation steps are described below in conjunction with the accompanying drawings: Figure 2

[0065] (1) The size of the cylindrical magnetic shielding bin (CMS) 1 required according to the requirements of the similar MCG system is determined, one side is a closed end 5 and the other side is an opening end 6, so as to determine the size of the cylindrical magnetic compensation coil 2 required inside the cylindrical magnetic shielding bin 1, and the area range of the target magnetic field 4 in the CMS.

[0066] (2) The flow function is introduced to represent the current density inside the CMS, and is decomposed into three components of axial, radial and angle, wherein the radial component is zero. Then the flow function is expanded by double Fourier series, and the half-angle component is innovatively introduced to correct the flow function, so as to realize the asymmetric distribution of the current density and the corresponding magnetic field.

[0067] (3) According to the Biot-Savart law, the relationship between the target magnetic field 4 in the specified area and the current density inside the cylindrical magnetic shielding bin 1 is determined. Then the target area is divided into Num field points, and the current density coefficient is solved by using the target field method according to the expected magnetic field value of the target field point. ​

[0068] (4) Discretize the stream function to get the contour lines, thus determine the configuration of the magnetic compensation coil, and wind the coil around the inside of the magnetic shielding cylinder in this shape. After the coil is energized, the compensation of the asymmetric magnetic field is realized.

[0069] The step (1) is implemented as follows:

[0070] Step (1.1) The radius of the cylindrical magnetic compensation coil 2 is R c , and the length is H. The cylindrical magnetic compensation coil 2 is fixed on the inner cylinder 3 of the magnetic shielding chamber. The distance between the cylindrical magnetic compensation coil 2 and the closed end 5 of the cylindrical magnetic shielding chamber 1 with a radius of R M is h. The cube region where the target magnetic field 4 is located is located at the center of the coil, and the length is d.

[0071] The step (2) is implemented as follows:

[0072] Step (2.1) In the cylindrical coordinate system, the continuously distributed surface current density on the surface of the inner cylinder 3 of the magnetic shielding chamber is J(r), which is composed of the axial component J θ (θ,z), the angular component J z (θ,z), and the radial current density component, where the radial current density component is zero. Wherein The coordinate position vector of the surface of the inner cylinder of the magnetic shielding chamber is represented by r(R c ,θ,z), and the position vector of the target magnetic field is represented by r'(ρ,θ',z'), wherein θ is the azimuth angle from the x-axis, z represents the height of different coordinate points in the inner cylinder of the magnetic shielding, S represents the stream function, ρ is the vertical distance from the target point to the central axis of the inner cylinder of the magnetic shielding chamber, θ' is the azimuth angle of the target magnetic field position point, and z' represents the height of the target magnetic field in the inner cylinder of the magnetic shielding.

[0073] Step (2.2) The current density is expanded by using the trigonometric function base to adopt the double Fourier series, and according to the symmetry and boundary continuity, all the current densities are determined by the to-be-solved parameters P mn . Moreover, the x-direction coil of the cylindrical magnetic compensation coil 2 is simplified because it can be converted into the y-direction coil by 90° rotation. The current density in the By direction and the stream function are represented as:

[0074]

[0075] Wherein m and n are the order of the Fourier series, and M and N are the order selected according to engineering experience.

[0076] The current density gradient in the By direction and the stream function are represented as:

[0077]

[0078] The current density and flow function of the Bz direction gradient are expressed as:

[0079]

[0080] J Z (θ,z)=0;

[0081]

[0082] The step (3) is specifically implemented as follows:

[0083] Step (3.1) is according to the Biot-Savart law B(r) represents the magnetic field vector, and the target area magnetic field is calculated by the surface current density of the magnetic shielding warehouse inner cylinder 3:

[0084]

[0085] Wherein, μ0 is the vacuum permeability, A is the surface area of the side of the cylindrical magnetic compensation coil 2, U mn (r,θ′,z) and V mn (r,θ′,z) is the function part after the target magnetic field is substituted into the Fourier series.

[0086] Step (3.2) uniformly disperses the target magnetic field 4 located in the cubic region, and disperses a total of Num coordinate points in the x, y, and z directions.

[0087] Step (3.2.1) constructs an error function for the magnetic field distribution of the Num coordinate points and the preset target magnetic field distribution, converts the integral equation into a form of a finite number of algebraic equation groups, and solves the matrix. That is:

[0088] Wherein B(ρ,θ′,z′) is the value of the magnetic field vector at the space point (ρ,θ′,z′), B target is the target magnetic field, and E is the error function.

[0089] Step (3.2.2) since Num is usually greater than m×n, the calculation of formula becomes a high-order ill-posed problem, and the solution is not unique. In order to overcome this problem, a penalty function is introduced by using Tikhonov regularization in formula , which can be expressed as: Wherein Γ is the Tikhonov matrix determined by the penalty function, and λ is the weight coefficient.

[0090] Step (3.2.3) curvature is selected as the penalty function in the present application. P mnThe optimal value of P can be solved by minimizing the error E, which can be set to zero by an algorithm.

[0091] The step (4) is implemented as follows:

[0092] Step (4.1) substitutes the optimal value of P into the flow function. mn

[0093] Step (4.2) defines the maximum value of the current distribution flow function as S max , and the minimum value as S min , and divides the flow function into K contours, so that the expression of the discrete flow function is:

[0094]

[0095] Step (4.3) Since the current flow direction in the cylindrical magnetic compensation coil 2 directly affects the distribution of the magnetic field generated by the cylindrical magnetic compensation coil 2, it is necessary to determine the current flow direction in the discrete cylindrical magnetic compensation coil 2. According to the analysis, the current flow direction in the cylindrical magnetic compensation coil 2 does not depend on the positive and negative of the contours, but is determined by the discrete order of each coordinate point of the contours. Therefore, the current flow direction is determined by using the Stokes formula to judge the current direction in the closed coil, and the formula is as follows: Where P, Q, and R are the components of the current vector field along the x, y, and z axes, respectively, and x, y, and z are the spatial rectangular coordinates used to describe the position.

[0096] Step (4.4) determines the number of contours. The number of contours directly affects the performance of the cylindrical magnetic compensation coil 2. If the number of contours is too small, the cylindrical magnetic compensation coil 2 is too dispersed, and the performance of the generated magnetic field will be reduced to some extent; if the number of contours is too large, the cylindrical magnetic compensation coil 2 is densely distributed, which is difficult to process. Therefore, in order to ensure the performance of the cylindrical magnetic compensation coil 2, the number of contours needs to be increased as much as possible under the premise of being able to be processed.

[0097] Step (4.5) compares the radius of the cylindrical magnetic compensation coil 2 with the radius R c ​The matching is performed according to the distribution function of the plurality of discrete isopleths, the linear trajectory of the cylindrical magnetic compensation coil 2 is calculated, the coordinates are converted into rectangular coordinates, the new trajectory is calculated to facilitate modeling, and finally the cylindrical magnetic compensation coil 2 is wound on the inner wall of the magnetic shielding inner cylinder 3. The magnetic shielding inner cylinder 3 is a non-magnetic hollow clamp for fixing the coil, which can be made of polyethylene material. The groove shape on the magnetic shielding inner cylinder 3 is determined by the modeling of the cylindrical magnetic compensation coil 2, and the groove width and depth are determined according to the outer diameter of the current-carrying wire used by the cylindrical magnetic compensation coil 2. The magnetic shielding inner cylinder 3 with the determined shape can be subjected to numerical control cutting processing to realize the clamp for customizing the cylindrical magnetic compensation coil 2 for different cylindrical shielding devices.

[0098] Embodiment two

[0099] The application also provides a cylindrical coil compensation structure design system for inhibiting asymmetric magnetic interference, which is used to realize the method described above, and comprises a parameter determination module, a correction module, a solving module and a discretization module.

[0100] The parameter determination module is used to determine the size of the required cylindrical magnetic shielding chamber according to the requirements of a high-resolution cardiac magnetogram system, so as to determine the size of the cylindrical magnetic compensation coil required by the surface of the CMS and the range of the target magnetic field region in the CMS; wherein the high-resolution cardiac magnetogram system is an MCG system, and the required cylindrical magnetic shielding chamber is a CMS.

[0101] The correction module is used to introduce a flow function to represent the current density on the inner side of the CMS and decompose it into three components of axial, radial and angle, wherein the radial component is zero, then expand the flow function by using a double Fourier series, and further correct the flow function to realize the asymmetric distribution of the current density and the corresponding magnetic field.

[0102] The solving module is used to determine the relationship between the target magnetic field in the specified region and the current density on the inner side of the cylindrical magnetic shielding chamber according to the Biot-Savart law, divide the target region into Num field points, and use the target field method to solve the current density coefficient according to the expected magnetic field value of the target field point.

[0103] The discretization module is used to obtain isopleths after discretizing the flow function, so as to determine the configuration of the magnetic compensation coil, and to wrap the coil on the inner side of the magnetic shielding cylinder. After the coil is energized, the asymmetric magnetic field is compensated.

[0104] The above-described embodiments are only descriptions of the preferred modes of the application, and do not limit the scope of the application. Without departing from the design spirit of the application, various modifications and improvements to the technical solutions of the application made by those skilled in the art shall fall within the protection scope determined by the claims of the application.

Claims

1. A method for designing a cylindrical coil compensation structure for suppressing asymmetric magnetic interference, characterized in that: The method comprises: Step 1: Determine the size of the cylindrical magnetic shielding chamber required based on the requirements of the high-resolution magnetocardiography system, thereby determining the size of the cylindrical magnetic compensation coil required on the CMS surface and the target magnetic field area within the CMS. The high-resolution magnetocardiography system is the MCG system, and the required cylindrical magnetic shielding chamber is the CMS. Step 2: Introduce the stream function to represent the current density inside the CMS and decompose it into three components: axial, radial, and angular. The radial component is zero. Then, the stream function is expanded using a double Fourier series. To adapt to the asymmetric current density and magnetic field design requirements, the double Fourier series is expanded at a half angle. Then, the stream function is asymmetrically corrected to achieve an asymmetric distribution of current density and corresponding magnetic field. Step 3: According to the Biot-Savart law, determine the relationship between the target magnetic field in the specified area and the current density inside the cylindrical magnetic shielding chamber. Then divide the target area into Num field points. Based on the expected magnetic field values ​​at the target field points, use the target field method to solve the current density coefficient. Step 4: Discretize the stream function to obtain contour lines, thereby determining the configuration of the magnetic compensation coil. The magnetic compensation coil configuration is then placed around the coil inside the magnetic shielding tube. When the coil is energized, compensation for the asymmetric magnetic field is achieved.

2. The method according to claim 1, characterized in that The radius of the cylindrical magnetic compensation coil is specified as R c , length H, fixed to the inner tube of the magnetic shielding chamber, cylindrical magnetic compensation coil with radius R M , thickness d M The distance between the closed ends of the cylindrical magnetic shielding chamber is set to h, and the cube area where the target magnetic field is located is located at the center of the coil and has a length of d.

3. The method according to claim 2, characterized in that The implementation process of step 2 includes: Step 2.1: In the cylindrical coordinate system, let the surface current density of the magnetic shielding chamber be J(r), and the axial component J θ (θ,z), the angular component is J z (θ, z), and the radial current density component, where the radial current density component is zero, The coordinate points on the surface of the magnetic shield tube are represented by r(R c ,θ,z), the target magnetic field position is represented by r′(ρ,θ′,z′); the coordinate position vector of the inner cylinder surface of the magnetic shielding chamber is represented by r(R c ,θ,z), the target magnetic field position vector is represented by r′(ρ,θ′,z′), where θ is the azimuth angle from the x-axis, z represents the height of different coordinate points in the magnetic shielding inner cylinder, S represents the stream function, ρ is the vertical distance from the target point to the central axis of the magnetic shielding inner cylinder, θ′ is the azimuth angle of the target magnetic field position point, and z′ represents the height of the target magnetic field in the magnetic shielding inner cylinder; Step 2.2: The convection function is expanded by double Fourier series and then half-angle expanded, and then the convection function is asymmetric modified to achieve asymmetric distribution of current density and corresponding magnetic field; according to symmetry and boundary continuity, all current densities are determined by the parameter P to be determined. mn The cylindrical magnetic compensation coil in the x-direction is simplified because the coil in the x-direction is converted into the coil in the y-direction by a 90° rotation. The By, Bz, and dBy / dy coils are symmetrical in the x- and y-directions but asymmetrical in the z-direction. Therefore, the current density and stream function in the By-direction are expressed as: The current density and stream function of the By direction gradient are expressed as: The current density and stream function of the Bz direction gradient are expressed as: J Z (θ,z)=0; Where m and n are the orders of the Fourier series, and M and N are the orders selected based on engineering experience.

4. The method according to claim 3, characterized in that The implementation process of step 3 includes: Step 3.1: According to the Biot-Saffar law B(r) represents the magnetic field vector. The magnetic field in the target area is calculated by the current density on the surface of the magnetic shielding chamber: Where μ0 is the vacuum magnetic permeability, A is the side surface area of ​​the cylindrical magnetic compensation coil, and U is mn (r,θ′,z) and V mn (r,θ′,z) is the function part after the target magnetic field is substituted into the Fourier series; Step 3.2: Uniformly discretize the target magnetic field in the cube area into Num coordinate points in the x, y, and z directions.

5. The method according to claim 4, characterized in that The process of uniformly discretizing the magnetic field in the target area into Num coordinate points in the x, y, and z directions in step 3.2 includes: Step 3.2.1: Construct an error function based on the magnetic field distribution of Num coordinate points and the preset target magnetic field distribution, and convert the integral equation into a finite set of algebraic equations for matrix solution, namely: Among them B target is the target magnetic field, E is the error function, and B(ρ,θ′,z′) is the value of the magnetic field vector at the spatial point (ρ,θ′,z′); Step 3.2.2: In the formula The penalty function introduced by Tikhonov regularization is expressed as: Where Γ is the Tikhonov matrix determined by the penalty function, and λ is the weight coefficient; Step 3.2.3: Select curvature as the penalty function and solve P by minimizing the error E mn The optimal value of , the error E is set to zero in the algorithm.

6. The method according to claim 5, characterized in that The implementation process of step 4 includes: Step 4.1: Set the coefficient P mn Substitute the optimal value of into the stream function; Step 4.2: Define the maximum value of the current distribution stream function as S max , the minimum is S min , and divide the stream function into K contour lines, and the contour line expression of the discretized stream function is: Step 4.3: The current flow direction of the cylindrical magnetic compensation coil does not depend on the positive or negative value of the contour line, but is determined by the discrete order of each coordinate point of the contour line. Therefore, the Stokes formula is used: Where P, Q, and R are the components of the current vector field along the x, y, and z axes, respectively. x, y, and z are spatial rectangular coordinates used to describe position and judge the direction of current in a closed coil, thereby determining the direction of current flow. Step 4.4: Balance the performance of the cylindrical magnetic compensation coil and the processing capacity according to actual needs and determine the number of contour lines; Step 4.5: Based on the discretized contour data and the size of the cylindrical surface where the cylindrical magnetic compensation coil is located, the calculated cylindrical magnetic compensation coil is transformed into a coordinate. After calculating the new trajectory, the cylindrical magnetic compensation coil is wound around the inner wall of the magnetic shielding chamber inner cylinder. The magnetic shielding chamber inner cylinder is a non-magnetic hollow fixture used to fix the cylindrical magnetic compensation coil. It is made of polyethylene material. The coil winding is wound along the groove on the magnetic shielding inner cylinder. The magnetic shielding chamber inner cylinder is CNC-machined according to the designed shape of the cylindrical magnetic compensation coil.

7. A cylindrical coil compensation structure design system for suppressing asymmetric magnetic interference, the system being used to implement the method according to any one of claims 1 to 6, characterized in that: The system includes: a parameter determination module, a correction module, a solution module, and a discrete module; The parameter determination module is used to determine the size of the required cylindrical magnetic shielding chamber according to the requirements of the high-resolution cardiac magnetograph system, thereby determining the size of the cylindrical magnetic compensation coil required on the CMS surface and the range of the target magnetic field area within the CMS; wherein the high-resolution cardiac magnetograph system is the MCG system, and the required cylindrical magnetic shielding chamber is the CMS; The correction module is used to introduce a stream function to represent the current density inside the CMS and decompose it into three components: axial, radial, and angular, where the radial component is zero. The stream function is then expanded using a double Fourier series and then expanded at a half angle to perform an asymmetric correction on the stream function, thereby achieving an asymmetric distribution of the current density and the corresponding magnetic field. The solution module is used to determine the relationship between the target magnetic field in the specified area and the current density inside the cylindrical magnetic shielding chamber according to the Biot-Savart law, then divide the target area into Num field points, and use the target field method to solve the current density coefficient based on the expected magnetic field value of the target field point; The discrete module is used to discretize the stream function to obtain isovalue lines, thereby determining the configuration of the magnetic compensation coil, and surrounding the coil with the magnetic compensation coil configuration inside the magnetic shielding tube. After the coil is energized, compensation of the asymmetric magnetic field is achieved.

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