Active-passive combined zero magnetic device and design method

Abstract

The invention discloses an active and passive combined zero magnetic device and a design method, and belongs to the field of magnetic shielding. The active and passive combined zero magnetic device comprises a passive shielding cabin composed of multiple layers of permalloy, and an equal-interval structure is arranged between every two adjacent layers; provided is a demagnetization system. The permalloy has high magnetic permeability, when a magnetic field encounters the permalloy with high magnetic permeability, magnetic field lines tend to spread along a path with higher magnetic permeability, namely walk along a permalloy layer instead of penetrating through a material, so that the environmental magnetic field is further reduced, a near-zero magnetic field environment is realized by designing a multi-layer permalloy cabin structure, and the performance of the magnetic field is improved. The demagnetizing coil is wound on the inner side wall and the outer side wall of the permalloy cabin body, and the demagnetizing coil is communicated with the external demagnetizing equipment through the demagnetizing interface at the end part of the demagnetizing coil, so that the amplitude of the demagnetizing current is gradually attenuated to the demagnetizing coil, and the permalloy cabin body is demagnetized; and the magnetization intensity of the material caused by the influence of the external environment and irresistible stress in the processing process can be weakened through the demagnetizing coil.

Description

Technical Field

[0001] This invention relates to the field of magnetic shielding, specifically to a zero-magnetic device and design method that combines active and passive shielding. Background Technology

[0002] Near-zero magnetic field environments are generally achieved by using magnetic shielding devices composed of multilayer permalloy structures to shield most of the Earth's magnetic field and the ambient magnetic field. Aerospace, defense, space science, bioelectromagnetism research, and fundamental physics research all have applications requiring zero-magnetic environments. Multilayer permalloys possess high magnetic permeability, making them easily magnetized while shielding external magnetic fields. Furthermore, stress is introduced during processing, resulting in residual magnetic fields within the material, severely limiting the magnetic shielding performance of the magnetic shielding chamber. To reduce the magnetization intensity of the material, demagnetization treatment is necessary. In addition, magnetic shielding devices composed of multilayer permalloys are costly and heavy; therefore, measures need to be taken to compensate for the external magnetic field to partially replace the passive shielding effect of the permalloy, thereby reducing cost and weight. Therefore, those skilled in the art provide a combined active and passive zero-magnetic device and its design method to solve the problems mentioned in the background. Summary of the Invention

[0003] The purpose of this invention is to provide a zero-magnetic device and design method that combines active and passive operation to solve the problems mentioned in the background art.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] A zero-magnetic device combining active and passive operation, comprising:

[0006] The passive shielding chamber is made of multi-layer permalloy alloy with equal spacing between adjacent layers.

[0007] The demagnetizing system includes demagnetizing coils orthogonally arranged inside and outside each layer of shielding, and the coils achieve three-way synchronous demagnetization through segmented current;

[0008] An active compensation system includes a triaxial magnetic compensation coil for avoiding the hatch, wherein the triaxial magnetic compensation coil optimizes spatial parameters using a particle swarm optimization algorithm.

[0009] The dynamic control module detects the magnetic field inside the passively shielded cabin in real time and provides feedback to adjust the compensation current.

[0010] As a further aspect of the present invention: the passive shielding chamber has 3 layers, each layer has the same thickness and the interlayer spacing is 100-300mm, and the magnetic permeability is 80,000.

[0011] As a further aspect of the present invention: the demagnetizing coils are arranged in a combination of orthogonal uniform distribution and edge I-type structure, wherein:

[0012] The innermost layer adopts an orthogonal uniform distribution, with 6 groups of 4-turn coils arranged in the XOZ plane, 8 groups of 4-turn coils arranged in the XOY plane, and 6 groups of 3-turn coils arranged in the YOZ plane.

[0013] The middle and outermost layers adopt a combination structure of orthogonal uniform distribution and edge I type, and two sets of ×9-10 turn coils are arranged at the edge of the YOZ plane.

[0014] As a further aspect of the present invention: the demagnetizing current adopts an amplitude decay sequence to perform a bidirectional process of demagnetizing layer by layer from the inside out → demagnetizing layer by layer from the outside in, with a single-layer demagnetization saturation ratio of ≥95%.

[0015] As a further embodiment of the present invention: the innermost demagnetizing current is 120A in the X / Y direction and 90A in the Z direction; the middle layer is 280A in the X / Y direction and 315A in the Z direction; and the outermost layer is 300A in the X / Y direction and 350A in the Z direction.

[0016] As a further embodiment of the present invention: the triaxial magnetic compensation coil comprises:

[0017] East-west coil group: 4 groups of coils, with spacing of ±0.32m / ±0.98m / ±1.7m / ±2.07m;

[0018] North-South Coil Group: Two coil groups, wound along the edge of the hatch, with a spacing of ±0.35m / ±1.05m;

[0019] Earth-to-Earth Coil Group: 2 sets of coils, wound along the edge of the hatch, with a spacing of ±0.33m / ±0.99m.

[0020] As a further embodiment of the present invention: the magnetic field uniformity of the compensation coil is ≤4%, and the coil constants in the east-west direction, north-south direction, and celestial direction are 1.9107 A / m, 1.7639 A / m, and 1.7838 A / m, respectively.

[0021] As a further aspect of the present invention: the particle swarm optimization process includes:

[0022] Step S101: Generate a random swarm of particles through initialization, and then continuously update and iterate to find the global optimal solution from the local optimum.

[0023] Step S102: In each generation, each particle updates itself by comparing it with two data values: the first value is the best solution that the individual particle can currently find, called the individual extreme value; the other value is the best solution that the entire particle swarm can currently find, which is the global optimal solution. Assume there exists an M-dimensional optimization parameter space, and each swarm consists of N particles. The i-th particle can be represented by an M-dimensional vector Xi:

[0024] X i =(x i1 ,x i2 ,…,x iM ), i = 1, 2, ..., N

[0025] The velocity of the i-th particle itself can also be represented by an M-dimensional vector Vi:

[0026] V i =(v i1 ,v i2 ,…,v iM ), i = 1, 2, ..., N

[0027] The current best solution that the i-th particle can find is called the individual best solution, denoted as:

[0028] P best =(p i1 ,p i2 ,…,p iM ), i = 1, 2, ..., N

[0029] The best solution that the entire particle swarm can currently find is called the swarm optimal solution, denoted as:

[0030] g best =(p g1 ,p g2 ,…,p gM )

[0031] After obtaining the optimal solutions for individuals and the group, all particles update their velocities and positions according to the above formula, expressed as:

[0032] v im =wv im +c1r1(pim-x im )+c2r2(p gm -x im )

[0033] Where: w is the inertia weight of an individual, c1 is the individual learning factor, c2 is the group learning factor, r1 and r2 are random numbers in the range [0,1], the inertia weight w = 0.6, and the learning factors c1 = c2 = 1.8.

[0034] A design method for a zero-magnetic device combining active and passive operation includes the following steps:

[0035] Step S201, Initial Demagnetization: Perform bidirectional demagnetization according to the current sequence of claim 5;

[0036] Step S202: Real-time detection of the magnetic field strength in the central area of ​​the cabin. If the deviation is >1nT, compensation is initiated. The current parameters of the compensation coil are dynamically optimized to 30-35A using the particle swarm optimization algorithm to stabilize the magnetic field within ±0.5nT.

[0037] As a further aspect of the present invention: the particle swarm optimization algorithm has a maximum number of iterations of 500, a population size of 100, and a convergence threshold of 0.1nT.

[0038] Compared with the prior art, the beneficial effects of the present invention are:

[0039] In this invention, permalloy has high magnetic permeability. When a magnetic field encounters permalloy with high magnetic permeability, the magnetic field lines tend to propagate along the path with higher magnetic permeability, that is, along the permalloy layer, rather than penetrating the material, further reducing the ambient magnetic field. By designing a multi-layer permalloy cabin structure, a near-zero magnetic field environment is achieved. By winding demagnetizing coils on the inner and outer walls of the permalloy cabin and connecting the demagnetizing coils to external demagnetizing equipment through the demagnetizing interface at the end of the demagnetizing coils, it is convenient to demagnetize the permalloy cabin by a demagnetizing current with gradually decreasing amplitude. The demagnetizing coils can weaken the magnetization intensity of the material caused by the influence of the external environment and the uncontrollable stress during processing. Furthermore, a triaxial magnetic compensation coil is designed to compensate for the stable background magnetic field of the Earth's magnetic field and can effectively compensate for low-frequency alternating magnetic field interference. In summary, this active-passive combined zero-magnetic device meets the requirements for extremely weak magnetic fields in fields such as SERF measurement, aerospace defense, space science, bioelectromagnetism research, and basic physics research. It ensures that the magnetic field inside the magnetic shielding device can remain stable near zero for a long time, while also allowing for flexible adjustment of the magnetic field inside the magnetic shielding device. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the magnetic shielding device structure of the present invention;

[0041] Figure 2 This is a schematic diagram of the overall demagnetizing coil of the magnetic shielding device of the present invention;

[0042] Figure 3 This is a schematic diagram of the east-west oriented inner coil structure of the present invention;

[0043] Figure 4 This is a schematic diagram of the north-south oriented inner coil structure of the present invention;

[0044] Figure 5 This is a schematic diagram of the inward-facing coil structure of the present invention;

[0045] Figure 6 This is a particle swarm logic parameter diagram for the present invention. In the diagram: x represents the starting position of the particle, u represents the particle search speed, and p represents the optimal position that the current particle swarm can search for.

[0046] Figure 7 This is a schematic diagram of the sampling points in the uniform region of the present invention. Detailed Implementation

[0047] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0048] Please see Figures 1-7 In this embodiment of the invention, a zero-magnetic device combining active and passive operation includes:

[0049] The passive shielding chamber is made of multi-layer permalloy alloy with equal spacing between adjacent layers.

[0050] The demagnetizing system includes demagnetizing coils orthogonally arranged inside and outside each layer of shielding, and the coils achieve three-way synchronous demagnetization through segmented current;

[0051] An active compensation system includes a triaxial magnetic compensation coil for avoiding the hatch, wherein the triaxial magnetic compensation coil optimizes spatial parameters using a particle swarm optimization algorithm.

[0052] The dynamic control module detects the magnetic field inside the passively shielded cabin in real time and provides feedback to adjust the compensation current.

[0053] In this embodiment, permalloy has high magnetic permeability. When a magnetic field encounters permalloy with high magnetic permeability, the magnetic field lines tend to propagate along the path with higher magnetic permeability, that is, along the permalloy layer, rather than penetrating the material, further reducing the ambient magnetic field. By designing a multi-layer permalloy cabin structure, a near-zero magnetic field environment is achieved. By winding demagnetizing coils on the inner and outer walls of the permalloy cabin and connecting the demagnetizing coils to external demagnetizing equipment through the demagnetizing interface at the end of the demagnetizing coils, it is convenient to demagnetize the permalloy cabin by a demagnetizing current with gradually decreasing amplitude. The demagnetizing coils can weaken the magnetization intensity of the material caused by the influence of the external environment and uncontrollable stress during processing.

[0054] The innermost demagnetizing coils of the passive shielding chamber are arranged in an orthogonal, uniform distribution, meaning that n sets of coils are arranged parallel to each other on two planes in the same direction, and the coils on adjacent planes are arranged perpendicular to each other. For example... Figure 3As shown, six sets of coils are evenly arranged on the two planes corresponding to the XOZ plane of the innermost compartment, each with four turns, a current of 30A per turn, and a current carrying capacity of 120A per coil. Eight sets of coils are evenly arranged on the two planes corresponding to the XOY plane of the innermost compartment, each with four turns, a current of 30A per turn, and a current carrying capacity of 120A per coil. Six sets of coils are evenly arranged on the two planes corresponding to the YOZ plane of the innermost compartment, each with three turns, a current of 30A per turn, and a current carrying capacity of 90A per coil. The coils are evenly arranged more densely on the plane where the hatch is located to avoid affecting the opening and closing of the hatch.

[0055] The passive shielding chamber has three layers, each with the same thickness and a layer spacing of 250 mm, and a magnetic permeability of 80,000.

[0056] The demagnetizing coils are arranged in a combination of orthogonal uniform distribution and edge-I type structure, wherein:

[0057] The innermost layer adopts an orthogonal uniform distribution, with 6 groups of 4-turn coils arranged in the XOZ plane, 8 groups of 4-turn coils arranged in the XOY plane, and 6 groups of 3-turn coils arranged in the YOZ plane.

[0058] The middle and outermost layers adopt a combination structure of orthogonal uniform distribution and edge I type, and two sets of ×9-10 turn coils are arranged at the edge of the YOZ plane.

[0059] The demagnetizing coils in the middle layer of the passive shielding chamber are arranged using a combination of orthogonal uniform distribution and edge-type I arrangement. The edge-type I arrangement refers to four edges in the same direction forming a group, creating a closed magnetic circuit on the chamber's annular surface. A demagnetizing current is then applied to demagnetize the four annular surfaces. The specific structure is as follows: Figure 3 As shown. Four sets of coils are evenly arranged on the two planes corresponding to the XOZ plane of the intermediate layer, each coil having 8 turns, a current of 35A per turn, and a current carrying capacity of 280A per coil. Four sets of coils are also evenly arranged on the two planes corresponding to the XOY plane of the intermediate layer, each coil having 8 turns, a current of 35A per turn, and a current carrying capacity of 280A per coil. Two sets of coils are arranged at the edges on the two planes corresponding to the YOZ plane of the intermediate layer, each coil having 9 turns, a current of 35A per turn, and a current carrying capacity of 315A per coil.

[0060] The outermost demagnetizing coils of the passive shielding chamber are arranged in a combination of orthogonal uniform distribution and edge I-type arrangement. In the edge I-type arrangement, four sets of coils are evenly distributed on the two planes corresponding to the XOZ plane of the outermost chamber, with each set of coils having 10 turns, a current of 30A per turn, and a current carrying capacity of 300A per set. Four sets of coils are evenly distributed on the two planes corresponding to the XOY plane of the outermost chamber, with each set of coils having 10 turns, a current of 30A per turn, and a current carrying capacity of 300A per set. Two sets of coils are arranged at the edges on the two planes corresponding to the YOZ plane of the outermost chamber, with each set of coils having 10 turns, a current of 35A per turn, and a current carrying capacity of 350A per set. The demagnetizing scheme can be determined by optimizing the arrangement of the demagnetizing coils, the number of coil groups, and the coil current carrying capacity. The simulation results for the innermost, middle, and outermost magnetic shielding layers show the following: In the innermost layer, the current carrying capacity in the X, Y, and Z directions is 120A, 120A, and 90A respectively, with a saturation rate of 96.45%; in the middle layer, the current carrying capacity in the X, Y, and Z directions is 280A, 280A, and 315A respectively, with a saturation rate of 95.68%; and in the outermost layer, the current carrying capacity in the X, Y, and Z directions is 300A, 300A, and 350A respectively, with a saturation rate of 95.51%. The saturation rate after demagnetization of all three layers is higher than 95%. By passing a gradually decreasing demagnetizing current through the demagnetizing coils, the magnetic shielding material is demagnetized.

[0061] By adopting the above technical solution, the problem of incomplete demagnetization in traditional single-mode systems can be solved through orthogonal uniform distribution and edge I-type layered topology.

[0062] The demagnetizing current employs an amplitude attenuation sequence to perform a bidirectional process of demagnetizing layer by layer from the inside out and then from the outside in. The demagnetization saturation ratio of a single layer is ≥95%. Through the current attenuation sequence from the inside to the outside to the inside, the demagnetization saturation ratio is increased from the conventional 90% to ≥95%.

[0063] The innermost demagnetizing current is 120A in the X / Y direction and 90A in the Z direction; the middle layer is 280A in the X / Y direction and 315A in the Z direction; and the outermost layer is 300A in the X / Y direction and 350A in the Z direction.

[0064] The triaxial magnetic compensation coil includes:

[0065] East-west coil group: 4 groups of coils, with spacing of ±0.32m / ±0.98m / ±1.7m / ±2.07m;

[0066] North-South Coil Group: Two coil groups, wound along the edge of the hatch, with a spacing of ±0.35m / ±1.05m;

[0067] Earth-to-Earth Coil Group: 2 sets of coils, wound along the edge of the hatch, with a spacing of ±0.33m / ±0.99m.

[0068] like Figure 3 As shown, there are four groups of inward coils running east-west, with distances di from the center point of ±0.32m, ±0.98m, ±1.7m and ±2.07m respectively, and each coil has 1 turn.

[0069] like Figure 4 As shown, there are two sets of inner coils running north-south, with distances di from the center point of ±0.35m and ±1.05m respectively, and each coil has 1 turn. To avoid affecting the opening and closing of the door, the coil closest to the door is wound along the edge of the door.

[0070] like Figure 5 As shown, there are two sets of coils facing inwards from the top and bottom, with distances di from the center point of ±0.33m and ±0.99m respectively, and each coil has 1 turn. To avoid affecting the opening and closing of the door, the coil set closer to the door is wound along the edge of the door. Simulation analysis of the above coils shows that, by optimizing parameters such as coil spacing and current magnitude, the uniformity of the three-axis magnetic field control range is less than 4%. Specifically, the magnetic field uniformity of the east-west facing coil in the working area is 3.78%, and the coil constant is 1.9107 A / m; the magnetic field uniformity of the north-south facing coil in the working area is 3.43%, and the coil constant is 1.7639 A / m; the magnetic field uniformity of the top-bottom facing coil in the working area is 2.38%, and the coil constant is 1.7838 A / m.

[0071] By using a structure that bypasses the edge of the door, the limitations of open-door magnetic shielding rooms in terms of compact wiring are overcome. A triaxial magnetic compensation coil compensates for the stable background magnetic field of the Earth's magnetic field and can also effectively compensate for low-frequency alternating magnetic field interference. Combining the above design features, this active-passive combined zero-magnetic device meets the requirements for extremely weak magnetic fields in fields such as SERF measurement, aerospace defense, space science, bioelectromagnetism research, and basic physics research. It ensures that the magnetic field inside the magnetic shielding device can remain stable near zero for a long time, while also allowing for flexible adjustment of the magnetic field inside the magnetic shielding device.

[0072] The magnetic field uniformity of the compensation coil is ≤4%, and the coil constants for the east-west, north-south, and celestial directions are 1.9107 A / m, 1.7639 A / m, and 1.7838 A / m, respectively.

[0073] The particle swarm optimization process includes:

[0074] Step S101: Generate a random swarm of particles through initialization, and then continuously update and iterate to find the global optimal solution from the local optimum.

[0075] Step S102: In each generation, each particle updates itself by comparing it with two data values: the first value is the best solution that the individual particle can currently find, called the individual extreme value; the other value is the best solution that the entire particle swarm can currently find, which is the global optimal solution. Assume there exists an M-dimensional optimization parameter space, and each swarm consists of N particles. The i-th particle can be represented by an M-dimensional vector Xi:

[0076] X i =(x i1 ,x i2 ,…,x iM ), i = 1, 2, ..., N

[0077] The velocity of the i-th particle itself can also be represented by an M-dimensional vector Vi:

[0078] V i =(v i1 ,v i2 ,…,v iM ), i = 1, 2, ..., N

[0079] The current best solution that the i-th particle can find is called the individual best solution, denoted as:

[0080] P best =(p i1 ,p i2 ,…,p iM ), i = 1, 2, ..., N

[0081] The best solution that the entire particle swarm can currently find is called the swarm optimal solution, denoted as:

[0082] g best =(p g1 ,p g2 ,…,p gM )

[0083] After obtaining the optimal solutions for individuals and the group, all particles update their velocities and positions according to the above formula, expressed as:

[0084] v im =wv im +c1r1(p im -x im )+c2r2(p gm -x im )

[0085] Where: w is the inertia weight of an individual, c1 is the individual learning factor, c2 is the group learning factor, r1 and r2 are random numbers in the range [0,1], the inertia weight w = 0.6, and the learning factors c1 = c2 = 1.8.

[0086] The magnetic compensation coil in the zero-magnetic device causes magnetic field distortion due to coupling effect. The conclusion that the maximum uniform region is generated when the spacing is equal to the coil radius, which was originally derived from the analytical formula of magnetic induction intensity in air, no longer holds. Therefore, it is necessary to consider the optimization of coil parameters. However, the calculation efficiency of interpolation by finite element method is low and it is difficult to find the optimal value. Therefore, the particle swarm optimization algorithm is combined with the analytical method to find the most suitable parameter value.

[0087] The target area is the working area inside the cabin, which is a cubic space, such as... Figure 7 As shown, the length, width, and height of the square space can be set according to requirements. To ensure the accuracy of the uniformity calculation, n points are uniformly selected within the square space. The number of n is determined according to the required precision; for example, 27 points are used. The uniformity of the space is obtained by subtracting the minimum value from the maximum value among the 27 points and then dividing by the magnetic induction intensity at the geometric center of the square space. By optimizing the particle swarm optimization algorithm for magnetic field compensation, the optimization efficiency is greatly improved compared to the traditional finite element method.

[0088] A design method for a zero-magnetic device combining active and passive operation includes the following steps:

[0089] Step S201, Initial Demagnetization: Perform bidirectional demagnetization according to the current sequence of claim 5;

[0090] Step S202: Real-time detection of the magnetic field strength in the central area of ​​the cabin. If the deviation is >1nT, compensation is initiated. The current parameters of the compensation coil are dynamically optimized to 35A using the particle swarm optimization algorithm to stabilize the magnetic field within ±0.5nT.

[0091] As a further aspect of the present invention: the particle swarm optimization algorithm has a maximum number of iterations of 500, a population size of 100, and a convergence threshold of 0.1nT.

[0092] In this embodiment, the demagnetization process

[0093] Current parameters:

[0094] hierarchy X-direction current Y-direction current Z-direction current saturation percentage Innermost layer 120A 120A 90A 96.45％ Intermediate layer 280A 280A 315A 95.68％ outermost layer 300A 300A 350A 95.51％

[0095] Operating procedures:

[0096] Step 1: Introduce attenuating current layer by layer from the inside out (amplitude attenuation rate 10% / second);

[0097] Step 2: Repeat demagnetization from the outside in to eliminate residual magnetic domains.

[0098] Dynamic compensation

[0099] After initialization, the magnetic field inside the chamber (center point P0) is detected;

[0100] If |B|>1nT, start the particle swarm optimization algorithm to optimize the current;

[0101] Uniformity of each axis after adjustment:

[0102] East-west direction: 3.78% (coil constant 1.9107 A / m)

[0103] North-South orientation: 3.43% (coil constant 1.7639 A / m)

[0104] Top and bottom directions: 2.38% (coil constant 1.7838 A / m).

[0105] Experimental verification:

[0106] index Traditional solution This embodiment Increase Demagnetization saturation percentage 90.2％ 96.45％ ↑6.25％ Magnetic field uniformity 8.7％ 2.38% (Z-direction) ↓72.6％ Compensation response time 2 seconds 0.1 seconds ↓95％

[0107] Analysis shows that: the edge-type I demagnetizing coil increases magnetic flux coverage by 12% (compared to traditional orthogonal layout); the door edge winding design reduces the footprint of the compensation coil by 40%; after adopting the particle swarm optimization algorithm, the optimization time is less than 25 minutes (ANSYS requires 8 hours), and the efficiency is improved by 20 times; dynamic compensation makes the magnetic field drift less than ±0.5nT (traditional PID control is ±5nT).

[0108] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A passive-active combined zero magnetic device, characterized in that: The application relates to a passive shielding cabin body composed of multiple layers of permalloy, wherein equal intervals are arranged between adjacent layers. A demagnetization system comprises demagnetization coils arranged orthogonally on the inner and outer sides of each layer of the shielding body, and the coils realize three-way synchronous demagnetization through segmented current. An active compensation system comprises three-axis magnetic compensation coils which avoid cabin doors, and the three-axis magnetic compensation coils are optimized in space parameters through a particle swarm algorithm. A dynamic regulation module detects the cabin magnetic field of the passive shielding cabin body in real time and feeds back and adjusts compensation current. The passive shielding cabin body has three layers, each layer has the same thickness, the interval between layers is 100-300 mm, and the magnetic permeability is 80,000.

2. The passive and active combined zero magnetic device according to claim 1, characterized in that: The demagnetization coils are arranged in a combination structure of orthogonal uniform distribution and edge I type, wherein:

3. The passive and active combined zero magnetic device according to claim 1, characterized in that: The innermost layer is arranged in the combination structure of orthogonal uniform distribution, 6 groups of 4-turn coils are arranged in the XOZ plane, 8 groups of 4-turn coils are arranged in the XOY plane, and 6 groups of 3-turn coils are arranged in the YOZ plane; The middle layer and the outermost layer are arranged in the combination structure of orthogonal uniform distribution and edge I type, and 2 groups of 9-10-turn coils are arranged in the YOZ plane at the edges. The demagnetization current adopts an amplitude attenuation sequence, and a bidirectional process of layer-by-layer demagnetization from inside to outside and layer-by-layer demagnetization from outside to inside is performed, and the single-layer demagnetization saturation proportion is greater than or equal to 95%.

4. The passive and active combined zero magnetic device according to claim 1, characterized in that: The demagnetization current of the innermost layer is 120 A in the X / Y direction and 90 A in the Z direction, the demagnetization current of the middle layer is 280 A in the X / Y direction and 315 A in the Z direction, and the demagnetization current of the outermost layer is 300 A in the X / Y direction and 350 A in the Z direction.

5. The passive and active combined zero magnetic device according to claim 1, characterized in that: The three-axis magnetic compensation coils comprise:

6. The passive and active combined zero magnetic device according to claim 1, characterized in that: East-west coil groups: 4 groups of coils, with intervals of +0.32 m, +0.98 m, +1.7 m and +2.07 m; North-south coil groups: 2 groups of coils, which are arranged along the edges of the cabin door, with intervals of +0.35 m and +1.05 m; Sky-ground coil groups: 2 groups of coils, which are arranged along the edges of the cabin door, with intervals of +0.33 m and +0.99 m. The magnetic field uniformity of the compensation coils is less than or equal to 4%, and the east-west / north-south / sky-ground coil constants are 1.9107 A / m, 1.7639 A / m and 1.7838 A / m respectively.

7. The passive and active combined zero magnetic device according to claim 1, characterized in that: The particle swarm algorithm optimization process comprises:

8. The passive and active combined zero magnetic device according to claim 1, characterized in that: Step S101: a group of random particle populations are generated through initialization, and then a global optimal solution is found from a local optimal solution through continuous updating and iteration; Step S102: each particle in each generation is updated by comparing with two data values: the first value is the optimal solution that can be found by the particle itself, and the solution is called individual extreme value; the other value is the optimal solution that can be found by the whole particle group, and the extreme value is a global optimal solution. Assuming that there is a group of M-dimensional optimization parameter spaces, each population is set to be composed of N particles, and the i-th particle can be represented by an M-dimensional vector Xi: The speed of the i-th particle itself can also be represented by an M-dimensional vector Vi: X i = (x i1 , x i2 , …, x iM ), i = 1, 2, …, N The current optimal solution searched by the i-th particle itself is called an individual optimal solution, and is represented as: V i = (v i1 ,v i2 ,…,v iM ), i = 1, 2, …, N The optimal solution searched by the whole particle group is called a group optimal solution, and is represented as: P best = (p i1 , p i2 , …, p iM ), i = 1, 2, …, N After the individual and group optimal solutions are obtained, the speed and position of all particles are updated according to the above formula, and are represented as: gbest = (p g1 ,p g2 ,…,p gM ) ​ v im = wv im + c1r1(pim - x im ) + c2r2(p gm - x im ) Wherein: w is the inertia weight of the individual, c1 is the individual learning factor, c2 is the group learning factor, r1 and r2 are random numbers in the range of [0, 1], the inertia weight w = 0.6, the learning factor c1 = c2 = 1.

8.

9. A design method of a passive-active combined zero magnetic device, applied to the passive-active combined zero magnetic device according to any one of claims 1-8, characterized in that: It comprises the following steps: Step S201, initializing demagnetization: performing bidirectional demagnetization according to the current sequence of claim 5; Step S202, detecting the magnetic field intensity of the central area in the cabin in real time, and starting compensation if the deviation is greater than 1nT; the current parameters of the compensation coil are dynamically optimized to 30-35A through the particle swarm algorithm, so that the magnetic field is stabilized within ±0.5nT.

10. The design method of a zero magnetic device combined with active and passive according to claim 9, characterized in that: The maximum iteration number of the particle swarm algorithm is 500, the population size is 100, and the convergence threshold is set to 0.1nT.

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