A uniform zone dual-plane coil design method based on multiple mirror method

Abstract

The application provides a large uniformity area double-plane coil design method based on a multiple mirror method, and relates to the technical field of magnetic shielding compensation.The method comprises the following steps: S1: regarding the shielding layer of a magnetic shielding box as an infinite plane by reflecting a magnetic source and a magnetic material with high magnetic permeability, generating mirror current, and repeatedly mirroring the mirror current by other shielding layers; S2: establishing the relationship between actual current and mirror current; S3: based on the double-plane current, the current enters the shielding layer from the air at the Q point and is refracted, the refraction angle is 45 degrees, the current is reflected at the W point in the shielding layer, enters the air from the shielding layer at the G point, the refraction angle is theta, and the R point is the position point of the current after reflection through the shielding layer.The method can improve the uniformity and the uniformity of the coil under the premise of ensuring the space utilization rate of the magnetic shielding room, so that the development cost and the weight of the magnetic shielding room are reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of magnetic shielding compensation, in particular to a uniform zone double-plane coil design method based on a multiple mirror image method. BACKGROUND

[0002] Currently, the common "extremely weak magnetic" or "zero magnetic" environment is mainly shielded by the external magnetic field through the high magnetic permeability permalloy material, and in order to achieve better magnetic shielding performance, a multi-layer permalloy nested structure design method is often used. Because the price of permalloy is relatively high and the density is relatively large, the cost of the traditional shielding room is relatively high, and the weight is relatively large, so it is difficult to be widely applied. In order to reduce the cost and the weight of the magnetic shielding room, the current stage often uses a combination of active and passive magnetic shielding design methods, and uses a coil to generate a reverse magnetic field to actively compensate for the external magnetic field to replace the passive shielding effect of part of the permalloy, so as to achieve the purpose of reducing the cost and the weight. In order to improve the space utilization rate of the magnetic shielding box, the current double-plane coil is installed next to the shielding layer. However, the magnetic field generated by the above design method and installation method is coupled with the high magnetic permeability material, so that the uniform zone of the generated magnetic field is small, the uniformity is poor, and the residual magnetism in the effective working area of the shielding room after shielding is difficult to meet the application requirements. SUMMARY

[0003] The problem solved by the present application is how to reduce the cost and the weight of the magnetic shielding room while ensuring the performance of the shielding room.

[0004] To solve the above problems, the present application provides a uniform zone double-plane coil design method based on a multiple mirror image method, comprising the following steps:

[0005] S1: The shielding layer of the magnetic shielding box is regarded as an infinite plane by reflecting the magnetic source and the magnetic material of the high magnetic permeability material, mirror current is generated, and the mirror current is repeatedly mirrored by other shielding layers;

[0006] S2: The relationship between the actual current and the mirror current is established;

[0007] S3: Based on the current of the double-plane coil, the current enters the shielding layer from the air at the Q point and is refracted, the refraction angle is 45°, the current is reflected at the W point in the shielding layer, and the current enters the air from the shielding layer at the G point, the refraction angle is , and R point is the position point of the current after reflection through the shielding layer;

[0008] S4: The uniform field BC in the mirror image shielding box is equivalent to an infinite coil array, the magnetic field generated by the uniform field BC under the coupling effect of the magnetic shielding material is obtained by calculating the superposition field of the coil array;

[0009] S5: Based on the target field method, the distribution of the current density of the double plane coil is calculated according to the distribution of the magnetic field required by the target area, and the specific structure of the coil winding is obtained after the current density is discretized.

[0010] In the above method, the mirror method refers to the infinite surface of the material with high magnetic permeability can reflect the magnetic source and the magnetic material. The shielding layer of the magnetic shielding box can be regarded as an infinite plane, thereby generating mirror currents, which are repeatedly mirrored by other shielding layers. Since the shielding layer is not of infinite thickness in actual application, but is limited, there is a non-negligible error between the magnetic flux density under the infinite shielding thickness and the actual shielding thickness. Therefore, the influence of the non-infinite shielding layer thickness is considered in this method.

[0011] Further, the relationship between the actual current and the mirror current in step S2 is:

[0012] ;

[0013] wherein, and respectively represent the mirror current and the actual current, and respectively represent the magnetic permeability of the shielding material and air.

[0014] Further, the refractive index of the shielding layer into the air in step S3 is:

[0015] ;

[0016] wherein, represents the magnetic permeability of the air.

[0017] In the above method, the high magnetic permeability material uses 1J85, and the magnetic permeability is =80000, T≈2.

[0018] Further, according to the triangular relationship, the x coordinate, y coordinate and z coordinate of the current at point R are respectively:

[0019] ;

[0020] ;

[0021] ;

[0022] wherein, represents the 1 / 2 side length of the double plane coil, , , respectively represent the distance of the double plane coil in x, y, z directions from the shielding layer, denotes the thickness of the shielding layer, denotes the coordinate point in front of the mirror image of the double planar coil.

[0023] Further, the magnetic field generated by the mirror method in the step S4 is:

[0024] ;

[0025] wherein, ;

[0026] ;

[0027] ;

[0028] ;

[0029] ;

[0030] ;

[0031] wherein, denotes the number of mirror images of the coil.

[0032] The present application adopts the above technical solutions and has the following beneficial effects:

[0033] The present application considers the influence of the non-infinite shielding layer thickness, can effectively avoid the coupling effect between the double planar coil and the shielding layer, effectively improves the uniform area and uniformity of the active magnetic compensation coil of the shielding room, and finally realizes the high performance, low cost and light weight of the shielding room, and realizes the wide application of the magnetic shielding room. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 A uniform area double planar coil design method flowchart based on a multiple mirror image method is provided for the embodiments of the present application.

[0035] Figure 2 The mirror image structure of the shielding layer, the double planar coil and the target area in the uniform area double planar coil design method based on the multiple mirror image method is provided for the embodiments of the present application. Figure One ;

[0036] Figure 3 The mirror image structure of the shielding layer, the double planar coil and the target area in the uniform area double planar coil design method based on the multiple mirror image method is provided for the embodiments of the present application. Figure Two ;

[0037] Figure 4 The mirror image structure of the shielding layer, the double planar coil and the target area in the uniform area double planar coil design method based on the multiple mirror image method is provided for the embodiments of the present application.Figure Three ;

[0038] Figure 5 A structure diagram of a double-plane coil installed in a shielding box in a uniform region double-plane coil design method based on a multiple mirror image method provided by an embodiment of the present application;

[0039] Figure 6 A coil optimization flowchart in a uniform region double-plane coil design method based on a multiple mirror image method provided by an embodiment of the present application;

[0040] Explanation of reference signs:

[0041] 1 - shielding layer, 2 - double-plane coil, 3 - target region. DETAILED DESCRIPTION

[0042] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the specific embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0043] The following are specific embodiments of the present application and further describe the technical solutions of the present application in combination with the accompanying drawings, but the present application is not limited to these embodiments.

[0044] Embodiment 1

[0045] This embodiment provides a uniform region double-plane coil design method based on a multiple mirror image method, as shown in the following figure, the method includes the following steps: Figures 1 to 4

[0046] S1: By reflecting the magnetic source and the magnetic material of the infinite surface of the high magnetic permeability material, the shielding layer of the magnetic shielding box is regarded as an infinite plane, mirror current is generated, and the mirror current is repeatedly mirrored by other shielding layers;

[0047] S2: Establish the relationship between the actual current and the mirror current;

[0048] S3: Based on the current of the double-plane coil, the current enters the shielding layer from the air at the Q point and is refracted, the refraction angle is 45°, the current is reflected at the W point in the shielding layer, and the current enters the air from the shielding layer at the G point, the refraction angle is , and R point is the position point of the current after reflection through the shielding layer;

[0049] S4: The uniform field BC in the shielding box is equivalent to an infinite coil array by the mirror method, and the magnetic field generated by the uniform field BC under the coupling action of the magnetic shielding material is obtained by calculating the superposition field of the coil array;

[0050] ​S5: Based on the target field method, the current density distribution of the double-plane coil is calculated according to the distribution of the magnetic field required to be generated by the target area, and the specific structure of the coil winding is obtained after the current density is discretized.

[0051] Specifically, the target field method is a reverse method of coil design, which is different from the forward design of pre-determining the geometric shape of the coil. The reverse design can calculate the current density distribution of the coil according to the magnetic field distribution required to be generated by the target area, and the specific structure of the coil winding can be obtained after the current density is discretized. The overall design method is the reverse process of "electromagnetic".

[0052] Referring to Figure 5 , the double-plane coil is installed in the structure of the shielding box, wherein the shielding layer 1 is provided with the double-plane coil 2, and the double-plane coil 2 corresponds to a target area 3. First, the size of the target area 3 in the middle of the double-plane coil 2 is determined, and the target area is a cube with a side length of a according to Figure 5 .

[0053] Discretization of the target point in the target area 3. The target area 3 is discretized into n target points according to the x-axis, y-axis and z-axis at equal intervals. At the same time, the magnetic field intensity of the discretized point is set as a constant target magnetic field, , and b is a constant.

[0054] Suppose the coordinates of the current source on the double-plane coil 2 are . The double-plane coil 2 is regarded as a two-dimensional fluid, . Wherein, , the following can be obtained: .

[0055] Suppose the stream function of the plane fluid is S, and the differential equation of the stream function is .

[0056] The stream function is expressed by using two-dimensional Fourier series:

[0057] ;

[0058] The Bx coil requires anti-symmetry about x, symmetry about y, and anti-symmetry about z, and the stream function of Bx is obtained as:

[0059] ;

[0060] The By coil requires symmetry about x, anti-symmetry about y, and anti-symmetry about z, and the stream function of By is obtained as:

[0061] ;

[0062] The Bz coil requires symmetry about x, symmetry about y, symmetry about y, and the stream function of Bz is obtained:

[0063] ;

[0064] According to the current continuity equation , where .

[0065] The design process of the three coils is consistent, and here we take the Bx coil design as an example.

[0066] According to the above formula, the stream function of the xoy plane can be derived as:

[0067] ;

[0068] where, ;

[0069] The current density in the y direction is:

[0070] ;

[0071] According to the Biot-Savart law, the relationship between the current density and the magnetic field can be obtained as:

[0072] ;

[0073] where, is expressed as the vacuum permeability.

[0074] ;

[0075] ;

[0076] Let , then a overdetermined equation system can be obtained.

[0077] Using the least squares method, the above equation is transformed into the error function form:

[0078] ;

[0079] Using the Tikhonov regularization method to conditionally limit the above equation, we can get:

[0080] ;

[0081] where is the Tikhonov matrix, is its weight coefficient. The Tikhonov matrix can be solved by the penalty function, and the above equation can be limited by using the coil curvature as the penalty function to get:

[0082] ;

[0083] Rewrite the above error function into matrix form:

[0084] ;

[0085] Wherein:

[0086] ;

[0087] ;

[0088] ;

[0089] Referring to Figure 4 , specifically, assuming that the double plane current enters into the shielding layer from the air at the Q point and is refracted, the refraction angle is 45°, the current is reflected at the W point in the shielding layer, and enters into the air from the shielding layer at the G point, the refraction angle is , R point is the position of the current after reflection through the shielding layer.

[0090] Wherein, the relationship between the actual current and the mirror current in step S2 is:

[0091]

[0092] Wherein, and respectively represent the mirror current and the actual current, and respectively represent the permeability of the shielding material and the air.

[0093] Wherein, the refractive index of the shielding layer to the air in step S3 is:

[0094] ;

[0095] Wherein, represents the permeability of the air; the high permeability material adopts 1J85, the permeability is =80000, T≈2.

[0096] Referring to Figure 2 and Figure 3 , , is the mirror image of x axis, , is the mirror image of y axis, 2L is the side length of the double plane coil, and 2h is the distance between the double plane coils.

[0097] Wherein, according to the triangle relationship, the x coordinate, y coordinate and z coordinate of the current at point R are respectively:

[0098] ;

[0099] ;

[0100] ;

[0101] Wherein, Indicates the 1 / 2 side length of the double plane coil, , , Indicate the distance of the double plane coil to the shielding layer in x, y and z directions respectively, Indicate the thickness of the shielding layer, Indicate the coordinate point of the double plane coil in front of the mirror image.

[0102] Wherein, the magnetic field generated by the uniform field BC obtained by the mirror method in step S4 is:

[0103] ;

[0104] Wherein, ;

[0105] ;

[0106] ;

[0107] ;

[0108] ;

[0109] ;

[0110] Wherein, Indicates the number of mirror images of the coil.

[0111] Referring to Figure 6 , specifically, the optimization process of the double plane coil includes: starting to set the flow function according to the type of the double plane coil, setting the parameters of the flow function and the parameters of the double plane coil respectively, and setting the target area and discretizing the target area; Then set the position of each surface of the double plane coil and the shielding layer, the current density of the mirror image of the coil, set the normalization parameter of the double plane coil, get the position parameter of the flow function , Import And Into the particle swarm optimization algorithm, set the parameters of the particle swarm optimization algorithm respectively, and set Upper limit and lower limit value, the particle swarm algorithm is optimized to get the best and calculate and determine whether it is less than 0.1, if yes, obtain the coil winding according to the contour of the flow function and end; if no, return to the particle swarm algorithm for optimization to obtain the best and calculate loop.

[0112] The method considers the influence of the non-infinite shielding layer thickness, can effectively avoid the coupling effect between the double-plane coil and the shielding layer, effectively improves the uniform region and the uniformity of the active magnetic compensation coil of the shielding room, and finally realizes the high performance, low cost and light weight of the shielding room, and realizes the wide range of popularization and application of the magnetic shielding room.

[0113] Although the present disclosure is disclosed as above, the protection scope of the present disclosure is not limited to this. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present disclosure, and these changes and modifications will fall within the protection scope of the present disclosure.

Claims

1. A method for designing a uniform zone biplane coil based on a multiple mirror method, characterized by, The method comprises the steps of: S1: generating mirror current by reflecting the magnetic source and the magnetic material through the infinite surface of the high magnetic permeability material, regarding the shielding layer of the magnetic shielding box as an infinite plane, and repeatedly mirroring the mirror current by other shielding layers; S2: establishing the relationship between the actual current and the mirror current; S3: the current based on the dual-plane coil enters from the air into the shielding layer at the Q point and is refracted at an angle of 45°, the current is reflected at the W point in the shielding layer, and enters from the shielding layer into the air at the G point at an angle of , and the R point is the position point of the current after reflection through the shielding layer; S4: equivalently regarding the uniform field BC in the mirror method shielding box as an infinite coil array, obtaining the magnetic field generated by the uniform field BC under the coupling effect of the magnetic shielding material by calculating the superposition field of the coil array; S5: based on the target field method, calculating the current density distribution of the double-plane coil position according to the distribution of the magnetic field required to be generated by the target region, and obtaining the specific structure of the coil winding after the current density is discretized.

2. The uniform zone biplane coil design method based on the multiple mirror method according to claim 1, characterized by, The relationship between the actual current and the mirror current in the step S2 is: ； wherein, and are denoted as the mirror current and the real current, respectively, and are denoted as the permeability of the shielding material and air, respectively.

3. The uniform zone biplane coil design method based on the multiple mirror method of claim 2, wherein, The refractive index of the shielding layer to the air in the step S3 is: ； wherein denotes the permeability of air.

4. The uniform zone biplane coil design method based on the multiple mirror method of claim 1, wherein, According to the triangular relationship, the x coordinate, the y coordinate and the z coordinate of the current at the point R are respectively: ； ； ； wherein, represents the 1 / 2 side length of the bi-plane coil, represents the distance of the bi-plane coil from the shield layer in the direction, represents the thickness of the shield layer, represents the coordinate point of the bi-plane coil in front of the mirror.

5. The uniform zone biplane coil design method based on the multiple mirror method of claim 4, wherein, The magnetic field generated by the uniform field BC obtained by the mirror method in the step S4 is: ； wherein ; ； ； ； ； ； wherein, represents the number of coil mirrorings.

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