Radial shimming coil of hollow cylindrical working area

Abstract

The invention relates to a radial shimming coil of a hollow cylindrical working area, which is characterized in that decoupling is carried out through a coupling effect of a magnetic shielding barrel and a coil magnetic field, a radial magnetic field component analytic function of the coil at any point in space is obtained through derivation based on a magnetic field superposition principle, and iterative solution is carried out by adopting a particle swarm optimization algorithm; the optimal coil design parameters meeting the target magnetic field distribution are obtained; a magnetic field with magnetic lines in a radial diverging shape and uniform size is formed in a hollow cylindrical working area and is used for magnetic compensation and probe calibration of magnetometers distributed in an annular array in the muscle magnetism and leg magnetism testing process, and the matching degree of the shimming effect and the sensitive direction of a sensor is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of biomagnetic test equipment, in particular to a radial field uniformity coil of a hollow cylindrical working area. BACKGROUND

[0002] In recent years, with the rapid development of biomagnetic measurement technology, the detection method based on muscle magnetic signal has gradually attracted attention in the application of neural rehabilitation, neuromuscular function evaluation and electromyographic substitution. Muscle magnetic signal, i.e. the extremely weak magnetic field signal generated by human muscle in the contraction process, is only in the order of pT, and the signal intensity is extremely low, and it is highly sensitive to external magnetic field interference. Therefore, in order to obtain effective signal with high signal-to-noise ratio, accurate measurement needs to be realized in a low-noise environment.

[0003] In the existing muscle magnetic measurement system, the sensor structure is usually distributed in a ring array inside a single-end opening magnetic shielding structure, and its magnetic sensitive axis (i.e. the direction with the strongest response to the magnetic field) is mostly in the radial direction, i.e. perpendicular to the longitudinal axis of the human body or the limb stretching direction. This makes the sensor more sensitive to the fluctuation of external interference magnetic field in the radial direction, especially the non-uniformity and gradient change of the static magnetic field, which is easy to introduce errors.

[0004] In order to improve the measurement accuracy of the system, a local magnetic field uniformity compensation system needs to be established in the working area. Especially for the radial sensitivity characteristics of the sensor, a radial field uniformity coil is designed in the hollow cylindrical area to compensate for the non-ideal distribution of the external background magnetic field, improve the measurement stability, realize the static calibration of the sensor response characteristics, establish the magnetic response baseline, and improve the reliability of subsequent signal processing and interpretation.

[0005] However, the traditional uniformity coil mainly focuses on the uniformity characteristics in the three-dimensional rectangular coordinate system, and it is difficult to directly adapt to the biomagnetic test application with radial field uniformity requirement; at the same time, limited by the coupling effect of the magnetic shielding structure and the human body layout, the coil needs to realize high radial uniformity magnetic field in limited space, which is difficult to design. SUMMARY

[0006] The technical problem to be solved by the present application is how to design a radial field uniformity coil suitable for a circular cylindrical working area, realize high uniformity control of the radial magnetic field, and improve the matching degree of the uniformity effect and the sensitive direction of the sensor.

[0007] This invention provides a radial shimming coil for a hollow cylindrical working area. The radial shimming coil is located inside a cylindrical magnetic shielding barrel with a single open end, and is used to generate a uniform radial magnetic field within the hollow cylindrical working area coaxial with the magnetic shielding barrel. The radial shimming coil is mounted on a hollow cylindrical fixture inside the magnetic shielding barrel and outside the magnetic resonance imaging (MRI) testing area. The radial shimming coil includes several pairs of inner loop coils and several outer loop coils arranged coaxially. The inner loop coils are wound around the inner circumferential surface of the fixture, and the outer loop coils are wound around the outer circumferential surface of the fixture. Each pair of inner loop coils and each pair of outer loop coils are symmetrically arranged with respect to the radial plane at the center point of the working area. The current directions between the same pair of inner loop coils are opposite, and the current directions between the same pair of outer loop coils are opposite.

[0008] Compared with the prior art, this application has the following advantages: it adopts several pairs of inner ring coils coaxially arranged on the inner circumferential surface of the fixed fixture and several pairs of outer ring coils coaxially arranged on the outer circumferential surface of the fixed fixture. Based on the radial sensitivity characteristics of the magnetometer with ring array distribution, it realizes the shimming coil that generates a radial uniform field in the hollow cylindrical working area, thereby improving the measurement stability.

[0009] In one possible implementation, the design parameters of the radial shim coil are calculated through the following steps: Step 1: Construct constraints for coil design parameters based on the structural parameters of the magnetic shielding barrel and the working area; Step 2, discretize the working area radially and axially. A set of discrete points, with a preset target value for the radial magnetic field at each discrete point; Step 3: Decouple the coupling effect between the magnetic shielding barrel and the magnetic field of the coil. Based on the principle of magnetic field superposition, construct the analytical function of the radial magnetic field component of the radial uniform field coil at any discrete point in space. Step 4: The particle swarm optimization algorithm is used to iteratively solve the analytical function of the radial magnetic field component to obtain the coil design parameters that make the magnetic field component at each discrete point satisfy the target value of the radial magnetic field.

[0010] Compared with existing technologies, the method of this application has the following advantages: by decoupling the coupling effect between the magnetic shielding barrel and the magnetic field of the coil, based on the principle of magnetic field superposition, the analytical function of the radial magnetic field component at any point in space of the radial shimming coil is derived, and the particle swarm optimization algorithm is used for iterative solution, thereby obtaining the optimal coil design parameters that satisfy the target magnetic field distribution; a magnetic field with radially divergent magnetic field lines and uniform size is formed in the hollow cylindrical working area, which is used for magnetic compensation and probe calibration of the magnetometer distributed in the ring array during muscle magnetometry and leg magnetometry testing, and improves the matching degree between the shimming effect and the sensor's sensitive direction.

[0011] In a possible implementation, the structure parameters of the magnetic shielding barrel and the working area in step 1 specifically include that the radial shim coils are located in the magnetic shielding barrel with an inner diameter of and an outer diameter of , the working area is in the shape of a hollow cylinder, the inner diameter of the working area is , the outer diameter is , the height is , and the distance between the center point of the working area and the closed end of the magnetic shielding barrel is ; the coil design parameters include the radius of each pair of radial shim coils , the distance between each pair of radial shim coils and the center point of the working area , and the turn ratio of each pair of radial shim coils ; is a non-zero integer, ; The constraint condition for constructing the coil design parameters is: .

[0012] In a possible implementation, step 2 specifically includes: step 201, dividing the working area into and discrete layers with equal intervals in the radial direction and the axial direction respectively, forming discrete points, which constitute a target point set , ; Step 202, according to the magnetic field distribution characteristics of the radial shim coils, presetting the radial magnetic field target value of each discrete point .

[0013] In a possible implementation, step 3 specifically includes: Step 301, decoupling the coupling effect of the magnetic shielding barrel and the magnetic field of the coils includes: decoupling the coupling effect of the end face of the magnetic shielding barrel and the magnetic field of the coils by the mirror method; decoupling the coupling effect of the cylindrical surface of the magnetic shielding barrel on the magnetic field of the coils by the equivalent current density; The expression of the analytical function of the radial magnetic field component of the radial shim coils at any discrete point in space is: In the formula, represents the radial magnetic field component generated by any pair of radial shim coils passing through a unit current at the coordinate point in the magnetic shielding barrel, represents the vacuum permeability represents the radius of the pair of radial shim coils, and respectively the inner diameter and the outer diameter of the magnetic shield barrel, denotes the derivative of the zeroth order modified Bessel function of the first kind, denotes the derivative of the zeroth order modified Bessel function of the second kind, denotes the z-direction wave number, is the imaginary unit, denotes the mirror order; denotes the Fourier series expansion of the coil current density with respect to the angular variable, is the Fourier series expansion of the equivalent current density on the inner surface of the magnetic shield barrel with respect to the angular variable, is the Fourier series expansion of the equivalent current density on the outer surface of the magnetic shield barrel with respect to the angular variable, and the specific expression is: ; ; ; ; ; ; ; ; ; wherein, denotes the relative permeability of the magnetic shield barrel, denotes the derivative of the zeroth order modified Bessel function of the first kind, denotes the derivative of the zeroth order modified Bessel function of the second kind; Step 302, based on the analytical function of the radial magnetic field component, constructing the influence matrix between the radial magnetic field component of each discrete point and the coil design parameters ; each matrix element in the influence matrix denotes the radial magnetic field component of the th radial shim coil when a unit current is passed through it at the th discrete point ; Step 303, according to the superposition theorem of the magnetic field, constructing a linear equation group to obtain the magnetic field of all radial shim coils at each discrete point, and the expression is: , wherein, = denotes the magnetic field component of all radial shim coils at each discrete point, , is the number of turns of the qth radial shim coil, and is a positive integer.

[0014] In a possible implementation, the step 4 specifically comprises: a step 401 of optimizing an objective function with a minimum magnetic field distribution non-uniformity, the non-uniformity being expressed by a weighted sum of a maximum deviation of each discrete point magnetic field from a central point magnetic field and a mean square error, the expression being: A step 402 of iteratively solving the coil design parameters for the minimum magnetic field distribution non-uniformity according to the optimized objective function by using a particle swarm optimization algorithm.

[0015] In a possible implementation, the particle swarm optimization algorithm in the step 402 specifically comprises: initializing the particle swarm in a coil design parameter constraint space and setting an inertia weight and a learning factor; calculating the discrete point radial magnetic field distribution by substituting the particle position into an analytical function of the radial magnetic field component and obtaining a fitness value; updating the individual optimal position and the global optimal position of the particle swarm based on the fitness value; iteratively updating the particle swarm according to a speed and position updating formula; and outputting the global optimal particle position as the optimal design parameter of the radial field uniformity coil to achieve the preset magnetic field uniformity target when the convergence condition is met or the maximum iteration number is reached. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 FIG. 1 is a structural schematic diagram of the magnetic shielding barrel, the SERF magnetometer assembly and the radial field uniformity coil of the present application; Figure 2 FIG. 2 is a structural schematic diagram of the SERF magnetometer assembly and the radial field uniformity coil of the present application; Figure 3 FIG. 3 is a design schematic diagram of the radial field uniformity coil of the present application; Figure 4 FIG. 4 is a setting diagram of each pair of radial field uniformity coils of the present application.

[0017] REFERENCE SIGNS: 1, magnetic shielding barrel; 2, SERF magnetometer assembly; 2.1, fixed tooling; 2.2, SERF magnetometer probe; 3, radial field uniformity coil; 3.1, inner ring coil; 3.2, outer ring coil. DETAILED DESCRIPTION

[0018] First of all, those skilled in the art should understand that these implementations are only used to explain the technical principles of the embodiments of the present application and are not intended to limit the protection scope of the embodiments of the present application. Those skilled in the art can make adjustments as needed in order to adapt to specific application occasions.

[0019] In the description of the embodiments of the present application, it should be noted that unless specifically defined and limited, the terms "connected", "connected" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or it can be integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium. For those skilled in the art, the specific meaning of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0020] In the embodiments of the present application, unless specifically defined and limited, the first feature is "on" or "under" the second feature. The first and second features can be in direct contact, or the first and second features can be in indirect contact through an intermediate medium. Moreover, the first feature "above", "above" and "above" the second feature can be that the first feature is directly above or obliquely above the second feature, or it can only mean that the horizontal height of the first feature is higher than that of the second feature. The first feature "below", "below" and "below" the second feature can be that the first feature is directly below or obliquely below the second feature, or it can only mean that the horizontal height of the first feature is less than that of the second feature.

[0021] The present application will be further described in detail below in conjunction with the drawings and specific embodiments.

[0022] As shown in Figures 1-2 , the present application discloses a radial field uniformity coil of a hollow cylindrical working area, the radial field uniformity coil 3 is located in a single-end opening cylindrical magnetic shielding barrel 1, for generating a uniform radial magnetic field in a hollow cylindrical working area coaxial with the magnetic shielding barrel 1; the radial field uniformity coil 3 is arranged on a hollow cylindrical fixed tool 2.1 outside the magnetic shielding barrel 1 and the muscle magnetic test area, the radial field uniformity coil 3 comprises a plurality of pairs of inner ring coils 3.1 and a plurality of pairs of outer ring coils 3.2 arranged coaxially, the inner ring coils 3.1 are arranged around the inner circumferential surface of the fixed tool 2.1, and the outer ring coils 3.2 are arranged around the outer circumferential surface of the fixed tool 2.1; each pair of inner ring coils 3.1 and each pair of outer ring coils 3.2 are symmetrically arranged with the radial plane at the center point of the working area as the symmetry plane, as shown in Figure 4 ; the current direction between the same pair of inner ring coils 3.1 is opposite; the current direction between the same pair of outer ring coils 3.2 is opposite.

[0023] Referring to Figure 3 , the design parameters of the radial field uniformity coil 3 are calculated by the following steps: Step 1, constructing the constraint condition of the coil design parameter with the structural parameters of the magnetic shielding barrel 1 and the working area; the structural parameters of the magnetic shielding barrel 1 and the working area include that the radial field uniformity coil 3 is located in the magnetic shielding barrel 1 with an inner diameter of , an outer diameter of , and the working area is a hollow cylinder, the design parameters of the working area include an inner diameter , outer diameter , height , distance between the center point of the working area and the closed end of the magnetic shielding barrel 1 ; the design parameters of the radial shim coil 3 include the radius of each pair of radial shim coils , the distance between each pair of radial shim coils and the center point of the working area , and the number of turns ratio of each pair of radial shim coils , and is a non-zero integer; ; ; The constraint conditions for constructing the coil design parameters are: .

[0024] Step 2, discretize the working area into discrete points in the radial and axial directions, and preset the target magnetic field strength of each discrete point; specifically including: Step 201, divide the working area into and discrete layers with equal spacing in the radial and axial directions, respectively, forming discrete points, which constitute the target point set , ; Step 202, according to the magnetic field distribution characteristics of the radial shim coil, preset the radial magnetic field target value of each discrete point .

[0025] Step 3, decouple the coupling effect of the magnetic shielding barrel 1 and the coil magnetic field, based on the principle of superposition of magnetic fields, construct the radial magnetic field component analytical function of the radial shim coil 3 at any discrete point in space; specifically including: Step 301, expand the current density of the coil pair into a Fourier series form; use Green's function to solve the divergence of the magnetic vector potential, and separate variables through modified Bessel functions to obtain the radial magnetic field component of each discrete point in the unshielded state, the expression is: Then, decouple the coupling effect of the magnetic shielding barrel 1 and the coil magnetic field, decouple the coupling effect of the end face of the closed end of the magnetic shielding barrel and the coil magnetic field by mirror method, and replace the coupling effect of the cylindrical surface of the magnetic shielding barrel 1 to the coil magnetic field by the equivalent current density , restricted to the inner and outer surfaces of the magnetic shielding barrel 1, based on the target magnetic field strength of each discrete point in the working area and the coil design parameters, construct the radial magnetic field component analytical function, and specifically construct the radial magnetic field component analytical function expression of the radial shim coil 3 with any pair of any parameters passing through a unit current at any discrete point in the magnetic shielding barrel 1: wherein, represents the radial component of the magnetic field generated by any pair of radial shim coils 3 with unit current at any point in space, the coordinates of which are , represents the vacuum permeability, represents the radius of the pair of radial shim coils, and are the inner diameter and the outer diameter of the magnetic shield bucket, respectively, represents the derivative of the zeroth-order modified Bessel function of the first kind, represents the derivative of the zeroth-order modified Bessel function of the second kind, k represents the z-direction wave number, i is the imaginary unit, and p is the mirror order. is the Fourier series expansion form of the coil current density according to the angle variable, is the Fourier series expansion form of the equivalent current density on the inner surface of the magnetic shield bucket 1 according to the angle variable, is the Fourier series form of the equivalent current density on the outer surface of the magnetic shield bucket 1 according to the angle variable, which can be specifically expressed as: ; ; ; ; ; ; ; ; ; wherein, represents the relative permeability of the magnetic shield bucket, represents the zeroth-order modified Bessel function of the first kind, represents the zeroth-order modified Bessel function of the second kind; Step 302, based on the analytical function of the radial magnetic field component, an influence matrix between the radial magnetic field components of each discrete point and the coil design parameters is constructed ; each matrix element in the influence matrix represents the radial magnetic field component at the th discrete point when the th pair of radial shim coils passes unit current; Step 303, according to the superposition theorem of the magnetic field, a linear equation group is constructed to obtain the magnetic field of all radial shim coils at each discrete point, and the expression is: , wherein, denotes the magnetic field components of all the pairs of radial shim coils at each discrete point, is the number of turns of the qth pair of radial shim coils, and is a positive non-zero integer.

[0026] Step 4, using a particle swarm optimization algorithm to iteratively solve the general expression of the radial magnetic field components to obtain the optimal design parameters that make the magnetic field distribution of each discrete point meet the predefined target value; specifically including: Step 401, taking the minimum magnetic field distribution non-uniformity as the optimization objective function, and the non-uniformity is expressed by the weighted sum of the maximum deviation of the magnetic field of each discrete point relative to the magnetic field of the center point and the mean square error, and the expression is: wherein, and are weight factors; The root mean square error of the magnetic field intensity in the target point set reflects the overall deviation between the optimization result and the ideal magnetic field distribution; the maximum deviation term is used to limit the destruction of local magnetic field abnormal points to the overall shim effect, as a supplement to the root mean square error.

[0027] Step 402, using a particle swarm optimization algorithm to iteratively solve the coil design parameters that minimize the magnetic field distribution non-uniformity as the optimization objective; specifically including: Initialize the particle swarm in the coil design parameter constraint space and set the inertia weight and learning factor; substitute the particle position into the analytical function of the radial magnetic field components to calculate the radial magnetic field distribution of the discrete points and obtain the fitness value; update the individual optimal position and global optimal position of the particle based on the fitness value; iteratively update the particle swarm according to the speed and position update formula; output the global optimal particle position as the optimal design parameters of the radial shim coils when the convergence condition is met or the maximum iteration number is reached, to achieve the preset magnetic field uniformity target.

[0028] In the description of the embodiments of the present application, it should be explained that in the description of the present application, the terms indicating the direction or position relationship such as "inner", "outer" and the like are based on the direction or position relationship shown in the drawings, which is only for the convenience of description, and does not indicate or imply that the device or member must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application.

[0029] ​​In the description of the application, the description of the terms "one embodiment", "some embodiments", "in this embodiment", "specific example", or "some examples" and the like means that the specific features, mechanisms, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the application. In the description, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, mechanisms, materials or characteristics described can be combined in any suitable manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine the different embodiments or examples described in the specification and the features of the different embodiments or examples without contradiction.

[0030] The above description is merely a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art can easily think of changes or replacements within the technical scope disclosed in the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A radial shim coil for a hollow cylindrical working region, characterized in that The radial field uniformity coil (3) is located in a single-end opening cylindrical magnetic shielding barrel (1) for generating a uniform radial magnetic field in a hollow cylindrical working area coaxial with the magnetic shielding barrel (1); the radial field uniformity coil (3) is arranged on a hollow cylindrical fixed tooling (2.1) outside the muscle magnetic testing area in the magnetic shielding barrel (1), the radial field uniformity coil (3) comprises a plurality of pairs of inner ring coils (3.1) and a plurality of pairs of outer ring coils (3.2) arranged coaxially, the inner ring coils (3.1) are arranged around the inner circumferential surface of the fixed tooling (2.1), and the outer ring coils (3.2) are arranged around the outer circumferential surface of the fixed tooling (2.1); each pair of inner ring coils (3.1) and each pair of outer ring coils (3.2) are symmetrically arranged with the radial plane at the center point of the working area as the symmetry plane; the current directions of the same pair of inner ring coils (3.1) are opposite, and the current directions of the same pair of outer ring coils (3.2) are opposite.

2. A radial shim coil for a hollow cylindrical working region, characterized in that The design parameters of the radial field uniformity coil (3) are calculated by the following steps: Step 1, constructing the constraint conditions of the coil design parameters based on the structural parameters of the magnetic shielding barrel (1) and the working area; Step 2, discretizing the working area into a plurality of discrete points along the radial and axial directions, presetting a target value of the radial magnetic field of each discrete point; Step 2, discretizing the working area into a plurality of discrete points along the radial and axial directions, presetting a target value of the radial magnetic field of each discrete point; Step 3, decoupling the coupling effect of the magnetic shielding barrel (1) and the coil magnetic field, constructing the analytical function of the radial magnetic field component of the radial field uniformity coil (3) at any discrete point in space based on the magnetic field superposition principle; Step 4, using the particle swarm optimization algorithm to iteratively solve the analytical function of the radial magnetic field component to obtain the coil design parameters that make the magnetic field components of each discrete point meet the target value of the radial magnetic field.

3. The radial shim coil for a hollow cylindrical working region of claim 1, wherein, The structural parameters of the magnetic shielding barrel (1) and the working area in step 1 specifically include: the inner diameter of the magnetic shielding barrel (1) is... The outer diameter is The working area is a hollow cylinder, and the inner diameter of the working area is... , outer diameter ,high And the distance between the center point of the working area and the closed end of the magnetic shielding barrel (1). The coil design parameters include the radius of each pair of radial shim coils (3). The distance between each pair of radial shim coils (3) and the center point of the working area and the turns ratio of each pair of radial shim coils (3) ; It is a non-zero integer. ; The constraint conditions of the coil design parameters are constructed as follows: 。 4. The radial shim coil for a hollow cylindrical working region of claim 2, wherein, The step 2 specifically includes: Step 201, dividing the working area into and discrete layers along the radial and axial directions respectively, forming discrete points, constituting the target point set , ; Step 202, preset the radial magnetic field target value of each discrete point according to the magnetic field distribution characteristics of the radial shim coil .

5. A radial shim coil for a hollow cylindrical working region according to claim 4, wherein, The step 3 specifically includes: Step 301, the decoupling of the coupling effect of the magnetic shielding barrel (1) and the coil magnetic field includes: Decoupling the coupling effect of the end surface of the closed end of the magnetic shielding barrel (1) and the coil magnetic field by the mirror method; Decoupling the coupling effect of the cylindrical surface of the magnetic shielding barrel (1) on the coil magnetic field by the equivalent current density; The expression of the analytical function of the radial magnetic field component of the radial field uniformity coil (3) at any discrete point in space is: wherein, B (r) denotes the radial magnetic field component generated by a unit current in any one of the radial shim coils (3) at a coordinate point (r, 0, z) within the magnetic shield bucket (1), denotes the vacuum permeability denotes the radius of the rth radial shim coil, and are the inner and outer diameters of the magnetic shield bucket (1), respectively, denotes the derivative of the zeroth-order modified Bessel function of the first kind, denotes the derivative of the zeroth-order modified Bessel function of the second kind, denotes the z-direction wave number, is the imaginary unit, denotes the mirror number; represents the coil current density expanded as a Fourier series in the angular variable, represents the equivalent current density on the inner surface of the magnetic shield can (1) expanded as a Fourier series in the angular variable, represents the equivalent current density on the outer surface of the magnetic shield can (1) expanded as a Fourier series in the angular variable, ； ； ； ； ； ； ； ； ； wherein denotes the relative permeability of the magnetic shield barrel, denotes the zeroth-order modified Bessel function of the first kind, denotes the zeroth-order modified Bessel function of the second kind; Step 302, constructing an influence matrix between the radial magnetic field component of each discrete point and the coil design parameters based on the radial magnetic field component analytical function ; each matrix element in the influence matrix represents the radial magnetic field component of the first radial shim coil pair when passing a unit current, at the first discrete point ; Step 303, according to the superposition theorem of magnetic field, construct linear equations to get all the magnetic field of radial shim coils at each discrete point, expression is: , wherein, = represents the magnetic field component of all radial shim coils at each discrete point, , is the number of turns of the qth pair of radial shim coils, and is a non-zero positive integer.

6. A radial shim coil for a hollow cylindrical working region according to claim 4, wherein, The step 4 specifically includes: Step 401, taking the minimum magnetic field distribution non-uniformity as the optimization objective function, and expressing the non-uniformity as the weighted sum of the maximum deviation of the magnetic field of each discrete point relative to the center point and the mean square error, and the expression is: Step 402, using the particle swarm optimization algorithm to iteratively solve the coil design parameters that make the magnetic field distribution non-uniformity minimum according to the optimization objective function.

7. A radial shim coil for a hollow cylindrical working region according to claim 6, characterized in that The particle swarm optimization algorithm in the step 402 specifically includes: Initializing the particle swarm in the constraint space of the coil design parameters and setting the inertia weight and the learning factor; substituting the particle position into the analytical function of the radial magnetic field component to calculate the radial magnetic field distribution of the discrete points and obtain the fitness value; updating the individual optimal position and the global optimal position of the group based on the fitness value; iteratively updating the particle swarm according to the speed and position updating formula; outputting the global optimal particle position as the optimal design parameters of the radial field uniformity coil when the convergence condition is met or the maximum iteration number is reached, so as to achieve the preset magnetic field uniformity target.

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