Non-uniformity compensation method for magnetic field of torque-free solenoid coil

Abstract

The invention discloses a non-uniformity compensation method for a magnetic field of a torque-free solenoid coil. The method comprises the following steps: arranging a compensation coil group on the tube wall of the torque-free solenoid coil; num measuring points are selected on the non-moment solenoid coil, num is an even number, the geometric center point of the non-moment solenoid coil is also used as a measuring point, and the total number of the measuring points is num + 1; measuring a coil constant KBi of the torque-free solenoid coil at each measurement point; determining a coil constant K 'Bi of the compensation coil group at each measurement point; connecting a compensation coil group with the torque-free solenoid coil in series, and determining a combined coil constant KKBi after compensation of the compensation coil group; determining the magnetic field uniformity in the uniform region; and determining a parameter value of a parameter of the compensation coil group based on a combined coil constant compensated by the compensation coil group, and if the magnetic field uniformity does not reach a preset threshold value, continuing to adjust the parameter value of the parameter of the compensation coil group. According to the method, the non-uniformity of the internal magnetic field of the torque-free solenoid coil can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of magnetic metrology, and particularly relates to a method for compensating the magnetic field non-uniformity of a toroidal solenoid coil. Background Art

[0002] A toroidal solenoid coil is a combined magnetic field coil, and its main feature is that it is formed by reversely connecting two solenoid coils with approximately equal turn areas in series. Therefore, the overall coil shows a magnetic moment that is basically zero externally. Therefore, when a certain magnitude of excitation current is applied to the coil of this structure, a magnetic field with a certain degree of uniformity can be generated inside the coil, while the external magnetic field decays rapidly, which can effectively reduce the interaction with the external environment of the coil. It is mainly used inside magnetic shielding devices made of high-permeability materials such as magnetic shielding cylinders and magnetic shielding rooms.

[0003] During the assembly and debugging process of the toroidal solenoid coil, due to factors such as processing accuracy and assembly errors, there will be a certain deviation in the geometric centers of the two solenoid coils, that is, the magnetic axes of the two coils will not completely coincide, which will cause a deviation between the actual reproduced magnetic field non-uniformity inside the coil and the theoretical value, generally showing a certain gradient, and the magnitude of the magnetic field gradient is positively correlated with the degree of offset between the two centers.

[0004] According to the test data, when the offset distance is in the order of 0.5 mm to 2 mm, the magnetic field non-uniformity caused in the 20% effective working area is about 0.05% to 0.5%. In actual work, sometimes the offset distance is more than 2 mm. Therefore, after most toroidal coils are assembled, the magnetic field inside them will present a uniform magnetic field with a certain gradient, and certain technical means are required to eliminate this magnetic field gradient and improve the magnetic field non-uniformity. Summary of the Invention

[0005] In view of this, the present invention provides a method for compensating the magnetic field non-uniformity of a toroidal solenoid coil, which can solve the influence caused by the non-coincidence of the geometric centers of the two solenoid coils of the toroidal solenoid coil.

[0006] In order to solve the above technical problems, the present invention is implemented as follows.

[0007] A method for compensating the magnetic field non-uniformity of a toroidal solenoid coil, the method comprising:

[0008] Step S1: Set a compensation coil group symmetric about the center point of the toroidal solenoid coil on the tube wall of the toroidal solenoid coil. The compensation coil group includes a pair of compensation coils with equal number of turns, and the compensation coils are coaxial with the tube wall and have the same diameter;

[0009] Step S2: Select num measurement points symmetrically on both sides with the geometric center of the toroidal solenoid coil as the center, covering the uniform region of the toroidal solenoid coil and on the central axis of the toroidal solenoid coil. num is an even number, and the geometric center point of the toroidal solenoid coil is also used as a measurement point, for a total of num + 1 measurement points, where num ≥ 4 and num + 1 ≥ i ≥ 1;

[0010] Step S3: Measure the coil constant K of the toroidal solenoid coil at each measurement point Bi ;

[0011] Step S4: Determine the coil constant K' of the compensation coil group at each measurement point Bi ;

[0012] Step S5: Connect the compensation coil group in series with the toroidal solenoid coil;

[0013] Step S6: Determine the combined coil constant KK after compensation by the compensation coil group Bi ;

[0014] Step S7: Determine the magnetic field uniformity in the uniform region based on the combined coil constant after compensation by the compensation coil group;

[0015] Step S8: Determine the parameter values of the compensation coil group based on the combined coil constant after compensation by the compensation coil group. If the magnetic field uniformity does not reach the preset threshold, continue to adjust the parameter values of the compensation coil group.

[0016] Preferably, in step S4: determining the coil constant of the compensation coil group at each measurement point includes:

[0017] Step S41: Determine the distance z between each measurement point and the geometric center point i ;

[0018] Step S42: Determine the coil constant K' of the compensation coil group at each measurement point Bi ,

[0019]

[0020] where μ0 is the magnetic permeability of vacuum, also known as the magnetic constant, which is 4π × 10 -7 H / m; n is the number of turns of a single compensation coil in the compensation winding, r1 is the radius of the compensation winding; d is the half-spacing of the compensation winding; z i is the distance of the i-th measurement point from the center point of the toroidal solenoid coil;

[0021] In step S5, the series connection method is forward series connection or reverse series connection, with the magnetic field gradient in the compensation coil group being opposite to the magnetic field gradient reproduced by the toroidal solenoid coil as the criterion.

[0022] Preferably, in step S6, determine the combined coil constant after compensation by the compensation coil group, where the combined coil constant after compensation is denoted as KK Bi , KK Bi = K′ Bi + K Bi .

[0023] Preferably, in step S8, if the magnetic field uniformity does not reach the preset threshold, adjust the parameter values of the compensation coil group, including:

[0024] If the non-uniformity of the magnetic field in the compensated uniform region decreases, but the gradient is consistent with that before compensation, only the trend becomes slower, then shorten the distance between the two compensation coils in the compensation coil group, or increase the number of turns of the two compensation coils in the compensation winding;

[0025] If the distribution trend of the magnetic field gradient in the compensated uniform region is opposite to that before compensation, then increase the distance between the two compensation coils in the compensation coil group, or decrease the number of turns of the two compensation coils in the compensation winding.

[0026] Preferably, the parameters of the compensation coil group include the number of turns n of the compensation winding, the radius r1 of the compensation winding, and the half-spacing d of the compensation winding.

[0027] Preferably, the tube wall of the toroidal solenoid coil refers to the outer tube or the inner tube of the toroidal solenoid coil.

[0028] The beneficial technical effects brought by the present invention:

[0029] (1) The method for compensating the magnetic field non-uniformity of the toroidal solenoid coil of the present invention can improve the non-uniformity of the magnetic field inside the toroidal solenoid. The present invention designs a pair of circular coil on the surface of the toroidal solenoid coil, and uses the spacing, number of turns, etc. that are easy to implement in engineering to reduce the magnetic field gradient inside the coil, and obtain a toroidal solenoid coil that meets the requirements of magnetic field uniformity.

[0030] (2) Starting from the actual engineering requirements, the present invention selects the outer diameter of the inner tube or the outer tube of the toroidal solenoid coil as the diameter of the compensation coil, that is, the compensation winding can be fixed (glued) on the tube wall, or the original wire groove can be borrowed, without the need to additionally increase the winding skeleton;

[0031] (3) The present invention can adjust parameters such as the radius, spacing, number of turns, etc. of a pair of circular coils according to the magnitude of the magnetic field gradient inside the coil and the compensation effect, without complex calculations, and is easy to implement in engineering practice and convenient for engineers to operate;

[0032] (4) A pair of compensation windings of the present invention are connected in series with each other and the current flowing through them is the same, without the need for designs such as current shunting and non-integer number of turns;

[0033] (5) According to practical experience, the present invention can improve the magnetic field uniformity inside the non-toroidal solenoid coil by more than one order of magnitude. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a schematic flow chart of the method for compensating the magnetic field non-uniformity of the non-toroidal solenoid coil of the present invention;

[0035] Figure 2 is a schematic diagram of the principle of the method for compensating the magnetic field non-uniformity of the non-toroidal solenoid coil of the present invention;

[0036] Figure 3 is a schematic diagram of the technical effect of the method for compensating the magnetic field non-uniformity of the non-toroidal solenoid coil of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0037] The present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0038] As Figure 1 shown, the present invention provides a method for compensating the magnetic field non-uniformity of a non-toroidal solenoid coil, the method comprising:

[0039] Step S1: A compensation coil group symmetric about the center point of the non-toroidal solenoid coil is arranged on the tube wall of the non-toroidal solenoid coil. The compensation coil group includes a pair of compensation coils with equal number of turns, and the compensation coils are coaxial with the tube wall and have the same diameter;

[0040] Step S2: On the central axis of the non-toroidal solenoid coil, covering the uniform region of the non-toroidal solenoid coil, and symmetrically selecting num measurement points on both sides with the geometric center of the non-toroidal solenoid coil as the center. num is an even number. The geometric center point of the non-toroidal solenoid coil is also used as a measurement point, a total of num + 1 measurement points, num ≥ 4, num + 1 ≥ i ≥ 1;

[0041] Step S3: Measure the coil constant K of the non-toroidal solenoid coil at each measurement point Bi ;

[0042] Step S4: Determine the coil constant K' of the compensation coil group at each measurement point Bi ;

[0043] Step S5: Connect the compensation coil group in series with the non-toroidal solenoid coil;

[0044] Step S6: Determine the combined coil constant KK of the compensation coil group after compensation Bi ;

[0045] Step S7: Determine the magnetic field uniformity in the uniform region based on the combined coil constant of the compensation coil group after compensation;

[0046] Step S8: Determine the parameter values of the compensation coil group based on the combined coil constant after compensation by the compensation coil group. If the magnetic field uniformity does not reach the preset threshold, continue to adjust the parameter values of the compensation coil group.

[0047] Further, the tube wall of the toroidal solenoid coil refers to the outer tube or the inner tube of the toroidal solenoid coil.

[0048] Further, the parameters of the compensation coil group include the winding radius, the number of turns, and the distance between the two compensation coils.

[0049] Step S2 includes: determining the tube wall radius r1, the half length l1, and the uniform region length L of the toroidal solenoid coil; setting the initial distance 2d between the two compensation coils, the winding radius r2, and the initial number of turns n, and letting n = 1; symmetrically selecting num measurement points on the central axis of the toroidal solenoid coil, covering the uniform region of the toroidal solenoid coil, and centered on the geometric center of the toroidal solenoid coil. num is an even number. The geometric center point of the toroidal solenoid coil is also used as a measurement point, for a total of num + 1 measurement points, where num ≥ 4.

[0050] In the present invention, a pair of compensation coils is designed on the surface of the toroidal solenoid coil, and parameters such as the winding radius, the distance, and the number of turns of the compensation coils are adjusted according to the magnetic field gradient inside the coil. By designing a pair of circular coil on the surface of the toroidal solenoid coil, using parameters such as the distance and the number of turns that are easy to implement in engineering, the magnetic field gradient inside the coil is reduced, and a toroidal solenoid coil that meets the requirements of magnetic field uniformity is obtained.

[0051] Further, the radius r1 and the half length l1 of the toroidal solenoid are determined by actual measurement or determined according to the parameters of the inner tube or the outer tube of the toroidal solenoid in the drawing. Initially, let r2 = r1. num is greater than or equal to 4.

[0052] In the present invention, let r2 = r1, that is, the radius of the compensation winding is the same as the radius of the inner tube or the outer tube of the toroidal solenoid. During engineering implementation, the compensation winding can be wound on the outer wall of the inner tube / outer tube, which is convenient for implementation.

[0053] Step S4: Determine the coil constants of the compensation coil group at each measurement point, including:

[0054] Step S41: Determine the distance z between each measurement point and the geometric center point i ;

[0055] Step S42: Determine the coil constant K' of the compensation coil group at each measurement point Bi ,

[0056]

[0057] Among them, μ0 is the magnetic permeability of vacuum, also known as the magnetic constant, which is 4π×10 -7 H / m; n is the number of turns of a single compensation coil in the compensation winding, r1 is the radius of the compensation winding; d is the half-spacing of the compensation winding; z i is the distance of the i-th measurement point from the center point of the toroidal solenoid coil;

[0058] In step S5, the series connection method is forward series connection or reverse series connection, with the criterion that the magnetic field gradient in the compensation coil group is opposite to the magnetic field gradient reproduced by the toroidal solenoid coil.

[0059] In the present invention, after the diameter and half-spacing parameters of the compensation winding are determined, assuming the number of turns of the compensation coil is n, according to the Biot-Savart law, the reproduced magnetic field coil constants of the two circular coil rings at the selected measurement points are calculated. The calculation formula is as follows:

[0060]

[0061]

[0062] ……

[0063] It is possible to set n = 1 to obtain a set of coil constants of the compensation winding, and add (or subtract) this set of constants to the constants of the toroidal solenoid coil to obtain the compensated coil constants. If the non-uniformity in the uniform region meets the target requirements at this time, the compensation ends.

[0064] Further, in step S6, determine the combined coil constant KK Bi , KK Bi = K′ Bi + K Bi .

[0065] Step S8: Determine the parameter values of the compensation coil group based on the combined coil constant of the compensation coil group after compensation. Among them, the parameters of the compensation coil group include the number of turns n of the compensation winding, the radius r1 of the compensation winding, and the half-spacing d of the compensation winding.

[0066] If the magnetic field uniformity does not reach the preset threshold, adjusting the parameter values of the compensation coil group includes:

[0067] If the non-uniformity of the magnetic field in the uniform region decreases after compensation, but the gradient is consistent with the trend before compensation, only the trend becomes slower, then shorten the distance between the two compensation coils in the compensation coil group, or increase the number of turns of the two compensation coils in the compensation winding;

[0068] If the distribution trend of the magnetic field gradient in the uniform region after compensation is opposite to that before compensation, increase the spacing between the two compensation coils in the compensation coil group, or reduce the number of turns of the two compensation coils in the compensation winding.

[0069] In the present invention, if the distribution trend of the magnetic field gradient in the uniform region after compensation is opposite to that before compensation, it means overcompensation, and it is necessary to reduce the coil constant of the compensation winding until the magnetic field non-uniformity inside the coil is significantly improved.

[0070] As Figure 3 shown, the present invention increases the magnetic field non-uniformity inside the toroidal solenoid coil from 0.48% to 0.05%, and the effect is remarkable.

[0071] The above specific embodiments only describe the design principle of the present invention. The shapes and names of the components in this description can be different and are not limited. Therefore, those skilled in the art of the present invention can modify or equivalently replace the technical solutions recorded in the foregoing embodiments; and these modifications and replacements do not depart from the spirit and technical solutions of the present invention, and shall all fall within the protection scope of the present invention.

Claims

1. A method for compensating the magnetic field non-uniformity of a toroidless solenoid coil, characterized in that, Including: Step S1: A compensation coil group symmetrical about the center point of the toroidal solenoid coil is arranged on the tube wall of the toroidal solenoid coil. The compensation coil group includes a pair of compensation coils with equal number of turns, and the compensation coils are coaxial with the tube wall and have the same diameter; Step S2: On the central axis of the toroidal solenoid coil, covering the uniform region of the toroidal solenoid coil, and symmetrically selecting num measurement points on both sides with the geometric center of the toroidal solenoid coil as the center. num is an even number. The geometric center point of the toroidal solenoid coil is also used as a measurement point, with a total of num + 1 measurement points. num ≥ 4, num + 1 ≥ i ≥ 1; Step S3: Measure the coil constant K of the torque-free solenoid coil at each measurement point Bi ; Step S4: Determine the coil constant K′ of the compensation coil group at each measurement point Bi ; Step S5: Connect the compensation coil group and the toroidal solenoid coil in series with each other; Step S6: Determine the combined coil constant KK after compensation by the compensation coil group Bi ; Step S7: Determine the magnetic field uniformity in the uniform region based on the combined coil constant after compensation by the compensation coil group; Step S8: Determine the parameter values of the parameters of the compensation coil group based on the combined coil constant after compensation by the compensation coil group. If the magnetic field uniformity does not reach the preset threshold, continue to adjust the parameter values of the parameters of the compensation coil group.

2. The method according to claim 1, wherein The step S4: Determining the coil constants of the compensation coil group at each measurement point includes: Step S41: Determine the distance z between each measurement point and the geometric center point i ; Step S42: Determine the coil constant K' of the compensation coil group at each measurement point Bi , Among them, μ0 is the magnetic permeability of vacuum, also known as the magnetic constant, which is 4π×10 -7 H / m; n is the number of turns of a single compensation coil in the compensation winding, r1 is the radius of the compensation winding; d is the half-spacing of the compensation winding; z i is the distance of the i-th measurement point from the center point of the torque-free solenoid coil; In the step S5, the series connection method is forward series connection or reverse series connection, with the magnetic field gradient in the compensation coil group being opposite to the magnetic field gradient reproduced by the toroidal solenoid coil as the criterion.

3. The method according to claim 2, characterized in that In step S6, determine the combined coil constant after compensation by the compensation coil group, where the combined coil constant after compensation is denoted as KK Bi , KK Bi = K' Bi + K Bi .

4. The method according to claim 3, characterized in that In the step S8, if the magnetic field uniformity does not reach the preset threshold and the parameter values of the parameters of the compensation coil group are adjusted, it includes: If the magnetic field non-uniformity in the uniform region decreases after compensation, but the gradient is consistent with the trend before compensation, only the trend becomes slower, then shorten the distance between the two compensation coils in the compensation coil group, or increase the number of turns of the two compensation coils in the compensation winding; If the distribution trend of the magnetic field gradient in the uniform region after compensation is opposite to that before compensation, then increase the distance between the two compensation coils in the compensation coil group, or decrease the number of turns of the two compensation coils in the compensation winding.

5. The method according to any one of claims 1-4, characterized in that, The parameters of the compensation coil group include the number of turns n of the compensation winding, the radius r1 of the compensation winding, and the half-spacing d of the compensation winding.

6. The method according to any one of claims 1-4, characterized in that, The tube wall of the toroidal solenoid coil refers to the outer tube or the inner tube of the toroidal solenoid coil.

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