A design method of a high-uniform radial magnetic field coil in a magnetic shielding barrel

Abstract

The application discloses a design method of a high-uniform radial magnetic field coil in a magnetic shielding barrel. Firstly, the effect of the magnetic shielding barrel on the coil is equivalent to a certain type of special current distribution on the surface of the magnetic shielding barrel, and the magnetic field expression generated by the continuous current density of the radial magnetic field coil in the magnetic shielding barrel is determined according to the boundary condition of the magnetic shielding barrel and in combination with the mirror method. Then, the magnetic field size generated by the radial magnetic field coil at each discrete point in the target area is calculated by discretizing the target area. Finally, the optimal coil structure parameters are found by combining the target field information and through a particle swarm optimization algorithm. The radial magnetic field coil in the magnetic shielding barrel is designed by considering the coupling effect between the magnetic shielding barrel and the coil, the problem of the coil uniformity reduction caused by the coupling is solved, and the uniformity of the radial magnetic field coil is greatly improved.

Description

Technical Field

[0001] This invention belongs to the field of magnetic shielding technology, specifically relating to a design method for a highly uniform radial magnetic field coil inside a magnetic shielding barrel. Background Technology

[0002] SERF atomic magnetometers have important applications in magnetoencephalography (MEG) and magnetocardiography (MCG), enabling groundbreaking non-invasive brain and heart detection. However, ultrasensitive SERF atomic magnetometers require extremely low ambient magnetic fields to achieve the non-relaxed state of atomic spin exchange. The most common method to reduce external magnetic field interference is to use passive magnetic shielding methods such as magnetic shielding barrels to reduce the Earth's magnetic field to a small order of magnitude. However, due to the limitations of passive magnetic shielding, environmental interference will always generate residual magnetic fields in the magnetically shielded environment, necessitating the use of active magnetic compensation technology to compensate for the residual magnetic field.

[0003] Especially in magnetocardiography (MCG) measurements, the radial magnetic field is perpendicular to the direction of the heart, and a highly uniform radial magnetic field coil is advantageous for the cardiac magnetic signal. However, when the radial magnetic field coil is installed inside a magnetic shielding layer, the magnetic field distribution generated by the coil will be altered by the surrounding high-permeability material, leading to a decrease in the uniformity of the radial magnetic field coil. Therefore, optimizing the magnetic field uniformity of the radial magnetic field coil by incorporating the coupling effect between the high-permeability material and the coil is crucial. Summary of the Invention

[0004] The purpose of this invention is to provide a design method for a highly uniform radial magnetic field coil inside a magnetically shielded barrel. This method solves the problem of decreased uniformity of the magnetic field generated by the radial magnetic field coil within a high permeability shielding layer, improves the uniformity of the radial magnetic field coil, and meets the requirement for a highly uniform radial magnetic field in SERF-based magnetocardiography measurements.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A design method for a highly uniform radial magnetic field coil inside a magnetically shielded barrel includes the following steps:

[0007] (1) The effect of the magnetic shielding barrel on the coil is equivalent to the current distribution on the surface of the magnetic shielding barrel. Based on the boundary conditions of the magnetic shielding barrel, the magnetic field expression generated by the continuous current density of the radial magnetic field coil inside the magnetic shielding barrel is determined by combining the image method.

[0008] (2) Parameter initialization: Set the height of the magnetic shielding barrel to 2H, the inner radius of the magnetic shielding barrel to b, and the outer radius to c; the length of the radial magnetic field coil is 2. The radius is a; the side length of the target region is 0.5a; the relative permeability is... Vacuum permeability ;

[0009] (3) Discretize the target region and calculate the magnitude of the magnetic field generated by the radial magnetic field coil at each discrete point in the target region;

[0010] (4) Combine the target field information and use the particle swarm optimization algorithm to find the optimal coil structure parameters.

[0011] Furthermore, in step (1), the expression for the magnetic field generated by the continuous current density of the radial magnetic field coil inside the magnetic shielding barrel is:

[0012]

[0013] in:

[0014]

[0015] in, This represents the continuous surface current density of the radial magnetic field coil at the target field point. The expression for the magnetic field generated at that location; ρ, , z represent the radial distance, azimuth angle and altitude of the target field point in the cylindrical coordinate system, respectively; ρ is the permeability of free space; a is the radius of the radial magnetic field coil; p is the number of mirror reflections. denoted as relative permeability; k, m, and j are all derived from the Green's function, where m takes values ​​from negative infinity to positive infinity, k is an integral variable, and j is an imaginary number. and Let represent the m-th order modified Bessel functions of the first and second kind, respectively. and , which are the corresponding first derivatives; b and c are the inner and outer radii of the magnetic shielding barrel, respectively; It is the Fourier transform of the continuous surface current density of the radial magnetic field coil in the azimuth component.

[0016] Furthermore, in step (1), the continuous current density of the radial magnetic field coil inside the magnetic shielding barrel is:

[0017] ;

[0018] Where n is the number of turns in the radial magnetic field coil, and I is the magnitude of the current in the radial magnetic field coil. H is the angle of the radial magnetic field coil, and H is half the height of the magnetic shielding barrel. It is half the length of the cylindrical surface where the radial magnetic field coil is located. This indicates that m can be an odd number.

[0019] Furthermore, step (3) is divided into the following two steps:

[0020] Step (31): Determine the target region as a cube with a side length of 0.5a at the center of the radial magnetic field coil, discretize the cube target region, and divide it into... One grid point;

[0021] Step (32): Determine the coordinates of each grid point Substituting this into the expression for the magnetic field generated by the continuous current density of the radial magnetic field coil inside the magnetic shielding barrel, we obtain the induced magnetic field generated at each discrete point in the target area.

[0022] Furthermore, step (4) is divided into the following two steps:

[0023] Step (41): From the perspective of optimization, the minimum value of the maximum non-uniformity of the magnetic field in the target area is used as the objective function, the structural parameters of the radial magnetic field coil are used as optimization variables, and the constraint conditions of the radial magnetic field coil are determined.

[0024] Among them, the non-uniformity of the magnetic field is the ratio of the difference between the magnetic fields generated by each discrete point in the target area and the magnetic field generated by the center point of the target area to the magnetic field generated by the center point of the target area, which is used to reflect the uniformity of the magnetic field.

[0025] Step (42): Implement the particle swarm optimization algorithm. The particle swarm is initialized as a group of random particles. The optimal solution is found through iteration. In each iteration, the particles update their velocity and position by tracking the individual extreme value of the particles and the global optimal solution of the particle swarm. If the termination requirement is met, the optimal coil parameters are output. If the requirement is not met, the velocity and position of each particle are updated until the maximum number of iterations is reached and the optimal coil structure parameters are output.

[0026] In D-dimensional space, there are M particles searching for the best position. The position of the i-th particle is denoted as... Its optimal position is denoted as Let g be the number of the particle with the best position among all particles, and let denot the velocity of the i-th particle be denoted as . Then the next position of the i-th particle is:

[0027] ;

[0028] ;

[0029] in, For inertial weights, for Generate a random number. The individual learning factor for each particle. The social learning factor for each particle, .

[0030] The advantages of this invention compared to the prior art are:

[0031] (1) In designing the radial magnetic field coil, this invention takes into account the length, thickness and permeability of the magnetic shielding barrel and accurately analyzes the coupling effect between the magnetic shielding barrel and the coil.

[0032] (2) When designing the magnetic compensation coil, the present invention takes into account the interaction between the active current-carrying coil and the high permeability passive shielding material, thus solving the problem of the decrease in magnetic field uniformity caused by the coupling effect of the coil;

[0033] (3) The present invention uses particle swarm optimization algorithm combined with target field information to improve the uniformity of the magnetic field generated by the radial magnetic field coil inside the magnetic shielding barrel. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the magnetic shielding barrel and radial magnetic field coil in this invention;

[0035] Figure 2 This is a flowchart illustrating the design method of the highly uniform radial magnetic field coil inside the magnetic shielding barrel in this invention.

[0036] Figure 3 This is a schematic diagram of the magnetic field deviation distribution of the radial magnetic field coil inside the magnetic shielding barrel of the present invention on the xz plane of the target area. The horizontal axis is the x direction and the vertical axis is the z direction. The radial magnetic field coil is composed of six nested saddle-shaped coils. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0038] The design method for a highly uniform radial magnetic field coil inside a magnetically shielded barrel according to the present invention is as follows: First, the effect of the magnetic shielding barrel on the coil is equivalent to a specific current distribution on the surface of the magnetic shielding barrel. Based on the boundary conditions of the magnetic shielding barrel, the magnetic field expression generated by the continuous current density of the radial magnetic field coil inside the magnetic shielding barrel is determined using the image method. Then, by discretizing the target region, the magnitude of the magnetic field generated by the radial magnetic field coil at each discrete point in the target region is calculated. Finally, combined with the target field information, the optimal coil structure parameters are found using a particle swarm optimization algorithm.

[0039] Figure 1 This is a schematic diagram of the magnetic shielding barrel and radial magnetic field coil in this invention. The radial magnetic field coil is surrounded by a high-permeability magnetic shielding barrel with an inner diameter of 2b and an outer diameter of 2c, and a relative permeability of [missing information]. The radial magnetic field coils consist of N pairs of coils with radius a and angle φ. q 2l in length q The number of ampere-turns is n q It is composed of nested saddle-shaped coils, q=1,2,...,N.

[0040] like Figure 2 As shown, the design method for a highly uniform radial magnetic field coil inside a magnetically shielded barrel according to the present invention specifically includes the following steps:

[0041] Step (1) equates the effect of the magnetic shielding barrel on the coil to a specific type of current distribution on the surface of the magnetic shielding barrel. Based on the boundary conditions of the magnetic shielding barrel and combined with the method of images, the expression for the magnetic field generated by the continuous current density of the radial magnetic field coil inside the magnetic shielding barrel is determined as follows:

[0042] ;

[0043] in:

[0044] ;

[0045] in, This represents the continuous surface current density of the radial magnetic field coil at the target field point. The expression for the magnetic field generated at that location; ρ, , z represent the radial distance, azimuth angle and altitude of the target field point in the cylindrical coordinate system, respectively; ρ is the permeability of free space; a is the radius of the radial magnetic field coil; p is the number of mirror reflections. denoted as relative permeability; k, m, and j are all derived from the Green's function, where m takes values ​​from negative infinity to positive infinity, k is an integral variable, and j is an imaginary number. and Let represent the m-th order modified Bessel functions of the first and second kind, respectively. and , which are the corresponding first derivatives; b and c are the inner and outer radii of the magnetic shielding barrel, respectively; It is the Fourier transform of the continuous surface current density of the radial magnetic field coil in the azimuth component.

[0046] The continuous current density of the radial magnetic field coil inside the magnetic shielding barrel is:

[0047] ;

[0048] Where n is the number of turns in the radial magnetic field coil, and I is the magnitude of the current in the radial magnetic field coil. H is the angle of the radial magnetic field coil, and H is half the height of the magnetic shielding barrel. It is half the length of the cylindrical surface where the radial magnetic field coil is located. This indicates that m can be an odd number.

[0049] Step (2) Parameter initialization: Set the height of the magnetic shielding barrel to 2H, the inner radius of the magnetic shielding barrel to b, and the outer radius to c; the length of the radial magnetic field coil is 2. The radius is a; the side length of the target region is 0.5a; the relative permeability is... Vacuum permeability ;

[0050] Step (3) involves discretizing the target region and calculating the magnitude of the magnetic field generated by the radial magnetic field coil at each discrete point in the target region. This process consists of the following two steps:

[0051] Step (31): Determine the target region as a cube with a side length of 0.5a at the center of the radial magnetic field coil, discretize the cube target region, and divide it into... One grid point;

[0052] Step (32): Determine the coordinates of each grid point Bring it into step (1) The induced magnetic field generated at each discrete point in the target area is obtained.

[0053] Step (4) involves combining the target field information with the particle swarm optimization algorithm to find the optimal coil structure parameters. This process consists of the following two steps:

[0054] Step (41): From the perspective of optimization, the minimum value of the maximum non-uniformity of the magnetic field in the target area is used as the objective function, the structural parameters of the radial magnetic field coil are used as optimization variables, and the constraint conditions of the radial magnetic field coil are determined.

[0055] The non-uniformity of the magnetic field is the ratio of the difference between the magnetic fields generated by each discrete point in the target area and the magnetic field generated by the center point of the target area to the magnetic field generated by the center point of the target area, which is used to reflect the uniformity of the magnetic field.

[0056] Step (42): Implement the particle swarm optimization algorithm. The particle swarm is initialized as a group of random particles. The optimal solution is found through iteration. In each iteration, the particles update their velocity and position by tracking two extreme values ​​(the individual extreme value of the particle and the global optimal solution of the particle swarm). If the termination requirement is met, the optimal coil parameters are output. If the requirement is not met, the velocity and position of each particle are updated until the maximum number of iterations is reached, and the optimal coil structure parameters are output.

[0057] In D-dimensional space, there are M particles searching for the best position. The position of the i-th particle is denoted as... Its optimal position is denoted as Let g be the number of the particle with the best position among all particles, and let denot the velocity of the i-th particle be denoted as . Then the next position of the i-th particle is:

[0058] ;

[0059] ;

[0060] in, For inertial weights, for Generate a random number. The individual learning factor for each particle. The social learning factor for each particle, .

[0061] Figure 3 This is a schematic diagram showing the magnetic field deviation distribution of the radial magnetic field coil inside the magnetic shielding barrel of the present invention on the xz plane of the target region. Figure 3 It can be seen that the radial magnetic field coil inside the magnetic shielding barrel of the present invention can achieve a magnetic field uniformity of 4×10⁻⁶ within a cube centered on the target area. -5 It has a high degree of uniformity.

[0062] The above description is only one specific implementation method of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the protection scope of the present invention.

[0063] The contents not described in detail in this specification are prior art known to those skilled in the art. Those skilled in the art will readily understand that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A design method for a highly uniform radial magnetic field coil inside a magnetically shielded barrel, characterized in that, The radial magnetic field coils consist of N pairs of coils with radius a and angle φ. q 2l in length q The number of ampere-turns is n q The design method comprises nested saddle-shaped coils, q=1,2,...,N; the design method includes the following steps: (1) The effect of the magnetic shielding barrel on the coil is equivalent to the current distribution on the surface of the magnetic shielding barrel. Based on the boundary conditions of the magnetic shielding barrel, the magnetic field expression generated by the continuous current density of the radial magnetic field coil inside the magnetic shielding barrel is determined by combining the image method. The expression for the magnetic field generated by the continuous current density of the radial magnetic field coil inside the magnetic shielding barrel is: ； in: ； in, This represents the continuous surface current density of the radial magnetic field coil at the target field point. The expression for the magnetic field generated at that location; ρ, , z represent the radial distance, azimuth angle and altitude of the target field point in the cylindrical coordinate system, respectively; ρ is the permeability of free space; a is the radius of the radial magnetic field coil; p is the number of mirror reflections. denoted as relative permeability; k, m, and j are all derived from the Green's function, where m takes values ​​from negative infinity to positive infinity, k is an integral variable, and j is an imaginary number. and Let represent the m-th order modified Bessel functions of the first and second kind, respectively. and , which are the corresponding first derivatives; b and c are the inner and outer radii of the magnetic shielding barrel, respectively; It is the Fourier transform of the continuous surface current density of the radial magnetic field coil in the azimuth component; The continuous current density of the radial magnetic field coil inside the magnetic shielding barrel is: ； Where n is the number of turns in the radial magnetic field coil, and I is the magnitude of the current in the radial magnetic field coil. H is the angle of the radial magnetic field coil, and H is half the height of the magnetic shielding barrel. It is half the length of the cylindrical surface where the radial magnetic field coil is located. This indicates that m can be an odd number; (2) Parameter initialization: Set the height of the magnetic shielding barrel to 2H, the inner radius of the magnetic shielding barrel to b, and the outer radius to c; the length of the radial magnetic field coil is 2. The radius is a; the side length of the target region is 0.5a; the relative permeability is... Vacuum permeability ; (3) Discretize the target region and calculate the magnitude of the magnetic field generated by the radial magnetic field coil at each discrete point in the target region; (4) Combine the target field information and use the particle swarm optimization algorithm to find the optimal coil structure parameters.

2. The design method of a highly uniform radial magnetic field coil inside a magnetically shielded barrel according to claim 1, characterized in that: Step (3) consists of the following two steps: Step (31): Determine the target region as a cube with a side length of 0.5a at the center of the radial magnetic field coil, discretize the cube target region, and divide it into... One grid point; Step (32): Determine the coordinates of each grid point Substituting this into the expression for the magnetic field generated by the continuous current density of the radial magnetic field coil inside the magnetic shielding barrel, we obtain the induced magnetic field generated at each discrete point in the target area.

3. The design method for a highly uniform radial magnetic field coil inside a magnetically shielded barrel according to claim 1, characterized in that: Step (4) consists of the following two steps: Step (41): From the perspective of optimization, the minimum value of the maximum non-uniformity of the magnetic field in the target area is used as the objective function, the structural parameters of the radial magnetic field coil are used as optimization variables, and the constraint conditions of the radial magnetic field coil are determined. Among them, the non-uniformity of the magnetic field is the ratio of the difference between the magnetic fields generated by each discrete point in the target area and the magnetic field generated by the center point of the target area to the magnetic field generated by the center point of the target area, which is used to reflect the uniformity of the magnetic field. Step (42): Implement the particle swarm optimization algorithm. The particle swarm is initialized as a group of random particles. The optimal solution is found through iteration. In each iteration, the particles update their velocity and position by tracking the individual extreme value of the particles and the global optimal solution of the particle swarm. If the termination requirement is met, the optimal coil parameters are output. If the requirement is not met, the velocity and position of each particle are updated until the maximum number of iterations is reached and the optimal coil structure parameters are output. In D-dimensional space, there are M particles searching for the best position. The position of the i-th particle is denoted as... Its optimal position is denoted as Let g be the number of the particle with the best position among all particles, and let denot the velocity of the i-th particle be denoted as . Then the next position of the i-th particle is: ； ； in, For inertial weights, for Generate a random number. The individual learning factor for each particle. The social learning factor for each particle, .

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