Radial self-shielded magnetic field coil of micro nuclear magnetic resonance gyroscope and design method thereof

Abstract

The application discloses a radial self-shielded magnetic field coil of a micro nuclear magnetic resonance gyroscope and a design method thereof. The coil comprises an inner cylindrical coil framework, an outer cylindrical coil framework, an inner radial main coil and an outer radial shield coil. The inner radial main coil and the outer radial shield coil are composed of multiple pairs of saddle-shaped coils. The inner cylindrical coil framework and the outer cylindrical coil framework are externally provided with grooves for pasting and fixing the inner radial main coil and the outer radial shield coil. The coil structure parameters are optimized by the derivative of the coil center origin and the relative error and the decay rate of the magnetic field of the target area point. The radial self-shielded magnetic field coil designed by the application generates a high-uniform magnetic field in the gas chamber area, the magnetic field outside the shield coil rapidly decays, the coupling between the coil and the magnetic shield cylinder is inhibited, the magnetic shield system is prevented from being magnetized for a long time in the strong magnetic field, and the magnetic field fluctuation caused by the change of the magnetic shield factor is reduced.

Description

Technical Field

[0001] This invention relates to the field of self-shielding magnetic field coil technology, and in particular to a radial self-shielding magnetic field coil for a miniature nuclear magnetic resonance gyroscope and its design method. Background Technology

[0002] Miniature nuclear magnetic resonance gyroscopes (NMR gyroscopes) possess characteristics such as small size, low power consumption, high performance, and large dynamic range, making them a key research focus and hot topic in novel inertial devices. The performance of an NMR gyroscope is influenced by the macroscopic magnetic moment of the atomic nuclei's spin, and is directly related to the density of polarized alkali metal atoms. To ensure a high signal-to-noise ratio for the gyroscope's rotation signal, the working chamber of the NMR gyroscope requires a stable and uniform magnetic field environment. Therefore, it is necessary to study highly uniform and stable magnetic field coils.

[0003] Traditionally, single-layer saddle-shaped coils are used to generate radially uniform magnetic fields. However, when used in small, high-precision atomic sensors such as miniature nuclear magnetic resonance gyroscopes, problems arise such as large size and insufficient uniformity of the magnetic field in the uniform region. Coil design optimization methods based on the target region's magnetic field and the origin derivative offer advantages such as high adaptability.

[0004] In conventional inertial measurement, a magnetic field coil is used to generate a high-precision and highly uniform magnetic field. However, this method results in magnetic field coupling between the magnetic shielding cylinder and the coil, amplifying the coil constant and introducing magnetic field noise related to the coupling coefficient, which reduces the accuracy of the nuclear magnetic resonance gyroscope. Summary of the Invention

[0005] This invention addresses the problems of coil coupling with magnetic shielding in the radial magnetic field control of existing nuclear magnetic resonance gyroscopes, and the insufficient uniformity of the magnetic field generated by existing radial coils. It provides a radial self-shielded magnetic field coil for miniature nuclear magnetic resonance gyroscopes, which has higher uniformity of radial magnetic field at the center of the gas chamber and rapid attenuation of the magnetic field outside the shielding coil, as well as its design method.

[0006] To achieve the above objectives, the technical solution provided by the present invention is as follows:

[0007] On the one hand, this invention first proposes a design method for a radial self-shielding magnetic field coil of a miniature nuclear magnetic resonance gyroscope, including the following steps:

[0008] S1. Determine the basic structure of the coil: The radial self-shielded magnetic field coil includes an inner radial main coil and an outer radial shielding coil. The radius R of the two coil layers is determined according to the actual requirements of the application scenario. m With R s The number of saddle-shaped coils that make up the two layers of coils is k pairs and n pairs;

[0009] S2. Calculate the magnetic field generated by the coil at the target point:

[0010] S3. Find the second derivative at the origin of the coil center;

[0011] S4. Combining the derivative information of the origin of the coil center and the magnetic field information of the target area, the coil parameter design is completed through an optimization algorithm: taking the magnetic field uniformity of the air chamber region and the magnetic field decay rate outside the shielding coil as common optimization objectives, the parameters of the radial self-shielding magnetic field coil are optimized through a genetic algorithm to minimize the value of the objective function.

[0012] Furthermore, in step S1, the radial self-shielding magnetic field coil, the inner radial main coil and the outer radial shielding coil are each composed of k pairs and n pairs of saddle-shaped coils, respectively, where k and n are both 5, and the ratio of the height of the two coil layers to the radius of the cylindrical surface is less than 3.

[0013] Furthermore, in step S2, taking the x-axis radial self-shielding magnetic field coil as an example, the x-axis component of the magnetic field generated at the target point is:

[0014]

[0015] Among them, B x This refers to the total magnetic field in the x-direction generated at this point by the radially self-shielded magnetic field coil. Let x be the magnetic field in the x-direction generated at this point by the i-th pair of saddle-shaped coils in the inner radial main coil. Let θ be the magnetic field in the x-direction generated at this point by the j-th pair of saddle-shaped coils in the outer radial shielding coil. i m Let θ be the central angle of the arc segment of the i-th inner radial master coil. j s h is the central angle of the j-th outer radial shielding coil arc segment. i m h is the height of the long side of the i-th inner layer radial main coil. j s Let be the height of the long side of the j-th outer radial shielding coil.

[0016] The y-axis radial self-shielding magnetic field coil is obtained by rotating the x-axis radial self-shielding magnetic field coil 90° around the z-axis, and the y-axis component B of the magnetic field generated at the target point is... y With B x They are the same size.

[0017] Furthermore, in step S3, the second derivative at the origin (0,0,0) of the coil center contains... Three non-zero derivatives:

[0018]

[0019]

[0020]

[0021] in, Let be the second derivatives in the x, y, and z directions produced by the radial self-shielding magnetic field coil at the origin (0,0,0) at the coil's center. Let be the second derivatives in the x, y, and z directions of the i-th pair of saddle-shaped coils in the inner radial main coil at the origin (0,0,0) at the coil center. Let be the second derivatives in the x, y, and z directions of the j-th pair of saddle-shaped coils in the outer radial shielding coil at the origin (0,0,0) of the coil center.

[0022] Furthermore, the objective function for step S4 is as follows:

[0023]

[0024] Among them, (x p ,y p ,z p (x) represents the coordinates of the p-th target point in the sensitive area of ​​the air chamber. q ,y q ,z q B represents the coordinates of the q-th target point outside the shielding coil and inside the shielding cylinder. x (x p ,y p ,z p B is the magnetic field at the p-th target point within the sensitive region of the air chamber. x (x q ,y q ,z q ( ) represents the magnetic field at the q-th target point outside the shielding coil and inside the shielding cylinder. This represents the relative error between the magnetic field at the target point within the sensitive area of ​​the gas chamber and the magnetic field at the origin. θ1 represents the attenuation rate of the magnetic field at the target point outside the shielding coil and inside the shielding cylinder, u is the number of target points in the sensitive area of ​​the central air chamber of the coil, v is the number of target points outside the shielding coil and inside the shielding cylinder, w1, w2, w3, w4, and w5 are weighting parameters, (θ1 m ,…θ k m θ1 s ,…,θ n s h1 s , ..., h k s h1 s , ..., h n s ) represents the parameter to be determined.

[0025] On the other hand, the present invention also proposes a radial self-shielding magnetic field coil for a micro-nuclear magnetic resonance gyroscope obtained by the design method of the radial self-shielding magnetic field coil of the micro-nuclear magnetic resonance gyroscope described above. The radial self-shielding magnetic field coil is composed of an inner cylindrical main coil skeleton, an inner radial main coil, an outer cylindrical shielding coil skeleton, an outer radial shielding coil, and a magnetic shielding cylinder, from the inside out. The air chamber center is placed inside the inner cylindrical main coil skeleton. The inner cylindrical main coil skeleton and the outer cylindrical shielding coil skeleton are provided with grooves on the outside for pasting and fixing the inner radial main coil and the outer radial shielding coil. The outer radial shielding coil and the inner radial main coil together generate magnetic fields in the x and y directions.

[0026] Furthermore, the outer radial shielding coil consists of 5 pairs of saddle-shaped coils symmetrically bonded around the outer cylindrical main coil frame, with the central angle θ of the arc segment of the outer radial shielding coil being... s The range is 15° to 150°.

[0027] Furthermore, the inner radial main coil consists of 5 pairs of saddle-shaped coils symmetrically bonded around the inner cylindrical main coil skeleton, with the central angle θ of the arc segment of the inner radial main coil being... m The range is 15° to 150°.

[0028] Furthermore, the current flows of the outer radial shielding coil and the inner radial main coil are opposite, and their magnitudes are in a fixed ratio.

[0029] Compared with the prior art, the technical effects of the present invention are as follows:

[0030] The radial self-shielding magnetic field coil of the miniature nuclear magnetic resonance gyroscope of the present invention includes an inner cylindrical coil frame, an outer cylindrical coil frame, an inner radial main coil, and an outer radial shielding coil. The inner cylindrical coil frame houses an air chamber, an oven, and related optical components. Grooves on the exterior of both the inner and outer coil frames are used to attach and fix the inner radial main coil and the outer radial shielding coil. The inner radial main coil and the outer radial shielding coil are composed of multiple pairs of saddle-shaped coils. The coil structure parameters are optimized by using the derivative at the origin of the coil center and the relative error and attenuation rate of the magnetic field at the target area. A fixed-ratio, opposite-direction current flows between the main coil and the shielding coil. The radial self-shielded magnetic field coil structure designed in this invention generates a magnetic field of a specified magnitude in the sensitive region of the atomic gas cell at the center of the coil to compensate for the magnetic field. The generated magnetic field has high uniformity in the gas cell region, and at the same time, it rapidly attenuates the magnetic field between the outer and outer sides of the radial self-shielded magnetic field coil to zero. This helps to reduce the magnetic field coupling between the shielding cylinder and the coil, and can prevent the outer magnetic shielding system from being magnetized in a strong magnetic field for a long time. This reduces the magnetic field fluctuation caused by changes in the magnetic shielding factor and improves the accuracy of inertial measurement.

[0031] The advantages of this invention compared to the prior art are:

[0032] (1) The self-shielded radial magnetic field coil of the present invention generates a highly uniform magnetic field near the atomic gas cell of the nuclear magnetic resonance gyroscope;

[0033] (2) The self-shielded radial magnetic field coil of the present invention has a shielding effect, and the magnetic field it generates itself decays rapidly outside the magnetic shielding coil.

[0034] (3) The self-shielded radial magnetic field coil designed in this invention can be designed with constraints on its size. The ratio of the long side to the radius of the saddle-shaped coil is less than 3, which meets the requirements of miniaturized atomic devices. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0036] Figure 1 A flowchart illustrating a radial self-shielding coil design method for a miniature nuclear magnetic resonance gyroscope, provided in an embodiment of the present invention;

[0037] Figure 2 A schematic diagram of the radial self-shielding magnetic field coil structure of a miniature nuclear magnetic resonance gyroscope provided in an embodiment of the present invention;

[0038] Figure 3 A schematic diagram of a saddle-shaped coil structure constituting a radial self-shielding magnetic field coil provided in an embodiment of the present invention;

[0039] Figure 4 This is a schematic diagram of the wiring structure of the outer radial self-shielding coil and the inner radial main coil provided in an embodiment of the present invention;

[0040] Figure 5 This is a schematic diagram illustrating the magnetic field decoupling effect generated by the radial self-shielding magnetic field coil provided in an embodiment of the present invention.

[0041] Explanation of reference numerals in the attached figures:

[0042] 1. Magnetic shielding cylinder; 2. Outer radial shielding coil; 3. Outer radial shielding coil frame; 4. Inner radial main coil; 5. Inner radial main coil frame; 6. Air chamber center. Detailed Implementation

[0043] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0044] This invention first proposes a design method for a radial self-shielding magnetic field coil of a miniature nuclear magnetic resonance gyroscope, such as... Figure 1 The steps shown are as follows:

[0045] S1. Determine the basic structure of the coil: The radial self-shielded magnetic field coil includes an inner radial main coil and an outer radial shielding coil. Determine the radii Rm and Rs of the two coil layers according to the actual needs of the application scenario, and the number of saddle-shaped coils k pairs and n pairs that make up the two coil layers;

[0046] S2. Calculate the magnetic field generated by the coil at the target point:

[0047] S3. Find the second derivative at the origin of the coil center;

[0048] S4. Combining the derivative information of the origin of the coil center and the magnetic field information of the target area, the coil parameter design is completed through an optimization algorithm: taking the magnetic field uniformity of the air chamber region and the magnetic field decay rate outside the shielding coil as common optimization objectives, the parameters of the radial self-shielding magnetic field coil are optimized through a genetic algorithm to minimize the value of the objective function.

[0049] Furthermore, in step S1, the radial self-shielding magnetic field coil, the inner radial main coil and the outer radial shielding coil are each composed of k pairs and n pairs of saddle-shaped coils, respectively, where k and n are equal to 5, and the ratio of the height of the two coil layers to the radius of the plane they are located is less than 3.

[0050] Furthermore, in step S2, taking the x-axis radial self-shielding magnetic field coil as an example, the x-axis component of the magnetic field generated at the target point is:

[0051]

[0052] Among them, B x This refers to the total magnetic field in the x-direction generated at this point by the radially self-shielded magnetic field coil. Let x be the magnetic field in the x-direction generated at this point by the i-th pair of saddle-shaped coils in the inner radial main coil. Let θ be the magnetic field in the x-direction generated at this point by the j-th pair of saddle-shaped coils in the outer radial shielding coil. i m Let θ be the central angle of the arc segment of the i-th inner radial master coil. j s h is the central angle of the j-th outer radial shielding coil arc segment. i m h is the height of the long side of the i-th inner layer radial main coil. j s Let be the height of the long side of the j-th outer radial shielding coil.

[0053] The y-axis radial self-shielding magnetic field coil is obtained by rotating the x-axis radial self-shielding magnetic field coil 90° around the z-axis, and the y-axis component B of the magnetic field generated at the target point is... y With B x They are the same size.

[0054] In step S3, the second derivative at the origin (0,0,0) of the coil center exists. Three non-zero derivatives:

[0055]

[0056]

[0057]

[0058] in, Let be the second derivatives in the x, y, and z directions produced by the radial self-shielding magnetic field coil at the origin (0,0,0) at the coil's center. Let be the second derivatives in the x, y, and z directions of the i-th pair of saddle-shaped coils in the inner radial main coil at the origin (0,0,0) at the coil center. Let be the second derivatives in the x, y, and z directions of the j-th pair of saddle-shaped coils in the outer radial shielding coil at the origin (0,0,0) of the coil center.

[0059] Furthermore, the objective function for step S4 is as follows:

[0060]

[0061] Among them, (x p ,y p ,z p (x) represents the coordinates of the p-th target point in the sensitive area of ​​the air chamber. q ,y q ,z q B represents the coordinates of the q-th target point outside the shielding coil and inside the shielding cylinder. x (x p ,y p ,z p B is the magnetic field at the p-th target point within the sensitive region of the air chamber. x (x q ,y q ,z q ( ) represents the magnetic field at the q-th target point outside the shielding coil and inside the shielding cylinder. This represents the relative error between the magnetic field at the target point within the sensitive area of ​​the gas chamber and the magnetic field at the origin. θ1 represents the attenuation rate of the magnetic field at the target point outside the shielding coil and inside the shielding cylinder, u is the number of target points in the sensitive area of ​​the central air chamber of the coil, v is the number of target points outside the shielding coil and inside the shielding cylinder, w1, w2, w3, w4, and w5 are weighting parameters, (θ1 m ,…θ k m θ1 s ,…,θ n s h1 s , ..., h k s h1 s , ..., h n s ) represents the parameter to be determined.

[0062] During the design process, the ratio of the height of the inner and outer coils of the radial self-shielded magnetic field coil to the radius of the plane on which it is located is greater than or less than 3, resulting in a small volume that meets the requirements for miniaturization of nuclear magnetic resonance gyroscopes.

[0063] In a nuclear magnetic resonance gyroscope, a radial magnetic field coil is required to generate a highly uniform static magnetic field in the x and y directions to compensate for the residual magnetic field, and an excitation magnetic field of a certain frequency is applied to resonate with the nuclei of the inert gas, thereby achieving accurate measurement of angular velocity.

[0064] This invention utilizes the aforementioned design method for the radial self-shielding magnetic field coil of a miniature nuclear magnetic resonance gyroscope to obtain a radial self-shielding magnetic field coil for a miniature nuclear magnetic resonance gyroscope. The radial self-shielding magnetic field coil can generate a highly uniform radial magnetic field within the sensitive range of the atomic gas cell. Simultaneously, the generated total magnetic field rapidly attenuates outside the outer shielding coil, reducing the coupling effect between the coil and the magnetic shield.

[0065] like Figure 2 As shown, the radial self-shielded magnetic field coil of the present invention is composed of an inner cylindrical main coil frame 5, an inner radial main coil 4, an outer cylindrical shielding coil frame 2, an outer radial shielding coil 3, and a magnetic shielding cylinder 1, from the inside out. The inner cylindrical main coil frame 5 houses the air chamber center 6, the oven, and related optical components. The outer surfaces of both the inner cylindrical main coil frame 5 and the outer cylindrical shielding coil frame 2 are provided with grooves for attaching and fixing the inner radial main coil 4 and the outer radial shielding coil 3.

[0066] The non-uniformity of the magnetic field generated by the coil in the central region of the air chamber is represented by the derivative at the origin of the central region of the coil, and the relative error between the magnetic field at each point in the air chamber and the magnetic field at the origin.

[0067] like Figure 3-4As shown, after parameter design and optimization using the above design method, the outer radial shielding coil 3 consists of 5 pairs of saddle-shaped coils symmetrically pasted around the outer cylindrical main coil skeleton 2, and the inner radial main coil 4 consists of 5 pairs of saddle-shaped coils symmetrically pasted around the inner cylindrical main coil skeleton 5. The central angle θ of the arc segment of the saddle-shaped coil ranges from 15° to 150°.

[0068] like Figure 4 As shown. The current flows in opposite directions to the current in the outer radial shielding coil 3 and the inner radial main coil 4, and their magnitudes are in a fixed ratio.

[0069] like Figure 5 As shown, taking the generation of the x-axis magnetic field as an example, the radius R of the innermost layer of the magnetic shielding cylinder 1 is designed. b The radius R of the outer radial shielding coil 3 is 50mm. s The radius R of the inner radial main coil 4 is 25mm. m The diameter is 20mm, and the center radius of the air chamber is 2mm. It can be seen that within the center range of the air chamber, the magnetic field uniformity is better than one-thousandth, while the magnetic field rapidly attenuates by 100 times at 50mm inside the magnetic shielding tube, effectively reducing the coupling between the coil and the magnetic shielding tube.

[0070] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. However, these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A design method for a radial self-shielding magnetic field coil of a miniature nuclear magnetic resonance gyroscope, characterized in that, Includes the following steps: S1. Determine the basic structure of the coil: The radial self-shielded magnetic field coil includes an inner radial main coil and an outer radial shielding coil. The radius R of the two coil layers is determined according to the actual size constraints of the application scenario. m With R s The number of saddle-shaped coils k pairs and n pairs that make up the two layers of coils; the radial self-shielding magnetic field coil in step S1, the inner radial main coil and the outer radial shielding coil are composed of k pairs and n pairs of saddle-shaped coils respectively, k and n are both 5, and the ratio of the height of the two layers of coils to the radius of the cylindrical surface is less than 3. S2. Calculate the magnetic field generated by the coil at the target point; the x-axis component of the magnetic field generated by the radial self-shielding magnetic field coil at the target point is: ， in, This refers to the total magnetic field in the x-direction generated at this point by the radially self-shielded magnetic field coil. Let x be the magnetic field in the x-direction generated at this point by the i-th pair of saddle-shaped coils in the inner radial main coil. Let θ be the magnetic field in the x-direction generated at this point by the j-th pair of saddle-shaped coils in the outer radial shielding coil. i m Let θ be the central angle of the arc segment of the i-th inner radial master coil. j s h is the central angle of the j-th outer radial shielding coil arc segment. i m h is the height of the long side of the i-th inner layer radial main coil. j s Let j be the height of the long side of the outermost radial shielding coil; The y-axis radial self-shielded magnetic field coil is obtained by rotating the x-axis radial self-shielded magnetic field coil 90° around the z-axis, and generates the y-axis component of the magnetic field at the target point. and They are the same size; S3. Find the second derivative at the origin of the coil center; in step S3, the second derivative at the origin of the coil center (0,0,0) contains... , , Three non-zero derivatives: ， ， ， in, , , Let be the second derivatives in the x, y, and z directions of the radially self-shielded magnetic field coil at the origin (0,0,0) at the coil's center. , , Let be the second derivatives in the x, y, and z directions of the i-th pair of saddle-shaped coils in the inner radial main coil at the origin (0,0,0) at the coil center. , , Let be the second derivatives in the x, y, and z directions of the j-th pair of saddle-shaped coils in the outer radial shielding coil at the origin (0,0,0) at the coil center. S4. Combining the derivative information of the coil's center origin and the magnetic field information of the target area, the coil parameters are designed using an optimization algorithm: the magnetic field uniformity of the air chamber region and the attenuation rate of the magnetic field outside the shielding coil are taken as common optimization objectives. The parameters of the radial self-shielding magnetic field coil are optimized using a genetic algorithm to minimize the value of the objective function; the objective function of step S4 is as follows: in, This represents the coordinates of the p-th target point within the sensitive area of ​​the air chamber. This represents the coordinates of the q-th target point outside the shielding coil and inside the shielding cylinder. It is the magnetic field in the x-direction at the p-th target point within the sensitive region of the air chamber. The magnetic field in the x-direction at the q-th target point outside the shielding coil and inside the shielding cylinder. This represents the relative error between the magnetic field in the x-direction at the target point within the sensitive area of ​​the air chamber and the magnetic field at the origin. denoted by , u represents the attenuation rate of the magnetic field in the x-direction at the target point outside the shielding coil and inside the shielding cylinder, u represents the number of target points within the sensitive area of ​​the central air chamber of the coil, and v represents the number of target points outside the shielding coil and inside the shielding cylinder. , , , , Let θ1 be the weighting parameter. m ,…θ k m θ1 s ,…,θ n s h1 m , ..., h k m h1 s , ..., h n s These are the parameters to be determined.

2. A radially self-shielding magnetic field coil for a miniature nuclear magnetic resonance gyroscope, characterized in that, According to the design method of the radial self-shielding magnetic field coil of the micro nuclear magnetic resonance gyroscope as described in claim 1, the inner cylindrical main coil skeleton (5), the inner radial main coil (4), the outer cylindrical shielding coil skeleton (2), the outer radial shielding coil (3) and the magnetic shielding cylinder (1) are arranged from the inside to the outside. The inner cylindrical main coil skeleton (5) has an air chamber (6) inside. The inner cylindrical main coil skeleton (5) and the outer cylindrical shielding coil skeleton (2) are provided with grooves on the outside for pasting and fixing the inner radial main coil (4) and the outer radial shielding coil (3). The outer radial shielding coil (3) and the inner radial main coil (4) jointly generate magnetic fields in the x and y directions.

3. The radial self-shielding magnetic field coil of the miniature nuclear magnetic resonance gyroscope according to claim 2, characterized in that, The outer radial shielding coil (3) consists of 5 pairs of saddle-shaped coils symmetrically pasted around the outer cylindrical shielding coil skeleton (2). The central angle θ of the arc segment of the outer radial shielding coil (3) s The range is 15° to 150°.

4. The radial self-shielding magnetic field coil of the miniature nuclear magnetic resonance gyroscope according to claim 2, characterized in that, The inner radial main coil (4) consists of 5 pairs of saddle-shaped coils symmetrically pasted around the inner cylindrical main coil skeleton (5). The central angle θ of the arc segment of the inner radial main coil (4) m The range is 15° to 150°.

Images