Composite gradient degaussing structure, magnetic shielding cabin and composite gradient degaussing method

Abstract

The invention relates to the technical field of magnetic shielding, and discloses a composite gradient degaussing structure, a magnetic shielding cabin and a composite gradient degaussing method. According to the composite gradient degaussing structure provided by the invention, the distribution density of the circumferential degaussing coils is set to be gradually increased from the closed end to the open end, and the axial degaussing coils are combined, so that an asymmetric composite degaussing magnetic field of which the strength is enhanced from the closed end to the open end in a gradient manner is actively constructed; residual magnetism distribution which is non-linearly enhanced from the closed end to the open end due to discontinuous magnetic circuits is compensated, the contradiction that an existing uniform demagnetization magnetic field is not matched with non-uniform residual magnetism distribution is solved, and accurate and adaptive demagnetization from the closed end to the open end in the shielding cabin is achieved.

Description

Technical Field

[0001] This invention relates to the field of magnetic shielding technology, specifically to a composite gradient demagnetization structure, a magnetic shielding chamber, and a composite gradient demagnetization method. Background Technology

[0002] In high-precision biomagnetic measurements such as magnetoencephalography (MEG) and magnetocardiography (MCG), a cylindrical shielded chamber with a single-end opening is commonly used as the core magnetic shielding component to facilitate easy access for the subject. This structure offers significant advantages in meeting the basic functions of the equipment while maintaining ease of operation, and has become a typical design for such measurement systems.

[0003] In existing technical solutions, the opening at one end of the cabin disrupts the magnetic circuit, allowing external magnetic fields to couple into the interior primarily from that point. This causes the magnetic field within the shield to exhibit nonlinear attenuation along the axial direction from the closed end to the open end, resulting in magnetic field distribution distortion and remanent magnetization gradient problems. To address these issues, existing demagnetizing technologies often employ spatially uniform demagnetizing coils (such as uniformly wound solenoids or circumferential coils).

[0004] However, in actual use, it was found that if the required strong demagnetizing field at the opening end is taken as the standard, it may cause over-demagnetization of the internal area. On the other hand, if the demagnetizing field strength is set according to the internal area, the opening end is often under-demagnetized. As a result, there is obvious residual magnetism in the opening area and the overall residual magnetism distribution is uneven. Summary of the Invention

[0005] This invention provides a composite gradient demagnetization structure, a magnetic shielding chamber, and a composite gradient demagnetization method to solve the problems of excessive demagnetization in the internal region or insufficient demagnetization at the open end when using demagnetizing coils with uniform spatial distribution.

[0006] In a first aspect, the present invention provides a composite gradient demagnetizing structure installed in a magnetically shielded chamber. The magnetically shielded chamber has a closed end and an open end. The demagnetizing structure includes an axial demagnetizing coil and a circumferential demagnetizing coil. The axial demagnetizing coil is arranged along the axial direction of the magnetically shielded chamber to generate a circumferential gradient demagnetizing field. The circumferential demagnetizing coil is arranged along the circumference of the magnetically shielded chamber, and its distribution density is set to gradually increase from the closed end to the open end to generate an axial gradient demagnetizing field. The axial demagnetizing coil and the circumferential demagnetizing coil are coupled to form a composite demagnetizing coil structure. When an alternating current with attenuated amplitude is applied to the composite demagnetizing coil structure, an asymmetric gradient-distributed composite demagnetizing magnetic field is generated to demagnetize the magnetically shielded chamber.

[0007] Beneficial effects: By setting the distribution density of the circumferential demagnetizing coils to gradually increase from the closed end to the open end, and combining them with the axial demagnetizing coils, an asymmetric composite demagnetizing magnetic field with gradient enhancement from the closed end to the open end is actively constructed. This compensates for the nonlinear enhancement of the residual magnetism distribution from the closed end to the open end caused by the discontinuity of the magnetic circuit, and solves the contradiction between the existing uniform demagnetizing magnetic field and the non-uniform residual magnetism distribution. This enables precise and adaptive demagnetization of the interior of the shielded cabin from the closed end to the open end.

[0008] In one optional embodiment, the axial demagnetizing coil includes an inner coil and an outer coil. The inner coil is attached to the inside of the magnetic shielding chamber, and the outer coil is attached to the outside of the magnetic shielding chamber. The current in the outer coil flows from the closed end to the open end, and the current direction of the inner coil is opposite to that of the outer coil.

[0009] In one optional embodiment, the axial demagnetizing coils are evenly distributed along the circumference. Group, , The axial demagnetizing coils of the group are connected in series.

[0010] In one optional implementation, the distribution density of the circumferential demagnetizing coil satisfies the following relationship:

[0011]

[0012] In the formula: Here are the axial position coordinates. Corresponding to the closed end, Corresponding to the open end, Let z be the circumferential coil density at position z. As the baseline density, These are the gradient coefficients. This is the normalized axial distribution function.

[0013] In one optional embodiment, the magnetic shielding chamber is divided axially into an open end, a middle section, and a closed end, with the distribution density gradient coefficient of the circumferential demagnetizing coils at the open end being... Distribution density gradient coefficient in the intermediate region Distribution density gradient coefficient at the closed end ,satisfy .

[0014] Secondly, the magnetic shielding chamber provided by the present invention includes the composite gradient demagnetization structure provided in the first aspect.

[0015] Beneficial effects: Since the magnetic shielding chamber includes a composite gradient demagnetization structure, it has the same effect as the composite gradient demagnetization structure, which will not be elaborated here.

[0016] In one optional embodiment, the magnetic shielding chamber further includes a demagnetizing power supply and a control terminal; the axial demagnetizing coil and the circumferential demagnetizing coil are electrically connected in series and then connected to the demagnetizing power supply to form a series control mode; or, the axial demagnetizing coil and the circumferential demagnetizing coil are independently connected to different demagnetizing power supplies to form a split control mode; the control terminal switches between the series control mode and the split control mode.

[0017] Thirdly, the present invention also provides a composite gradient demagnetization method, which is applied to the composite gradient demagnetization structure provided in the first aspect or the magnetic shielding chamber provided in the second aspect. The demagnetization method includes: determining the number of axial demagnetization coils based on the geometric parameters of the magnetic shielding chamber and the target residual magnetism distribution. gradient parameters of the circumferential demagnetizing coil ; Winding an axial demagnetizing coil; Based on gradient parameters A circumferential demagnetizing coil is wound so that its distribution density gradually increases from the closed end to the open end along the axial direction. The wound axial demagnetizing coil and the circumferential demagnetizing coil are installed in the magnetic shielding chamber to form a composite demagnetizing coil structure. An alternating current with attenuated amplitude is applied to the composite demagnetizing coil structure to generate a composite demagnetizing magnetic field with an asymmetric gradient distribution, thereby demagnetizing the magnetic shielding chamber.

[0018] Beneficial effects: Since the composite gradient demagnetization method is applied to the composite gradient demagnetization structure provided in the first aspect or the magnetic shielding chamber provided in the second aspect, it has the same effect as the composite gradient demagnetization structure or the magnetic shielding chamber, which will not be elaborated here.

[0019] In one optional embodiment, when the axial demagnetizing coil and the circumferential demagnetizing coil are connected in series, the current output port of the axial demagnetizing coil is... Current inlet of the circumferential demagnetizing coil The current inlet of the axial demagnetizing coil is connected in series. Current output of the circumferential demagnetizing coil Connect them to the output terminals of the demagnetizing power supply respectively.

[0020] In one optional implementation, after applying alternating current for demagnetization, an optimization process is further included: measuring the residual magnetism spatial distribution inside the magnetic shielding chamber after demagnetization; and adjusting gradient parameters based on the difference between the residual magnetism spatial distribution and a threshold. Based on the adjusted gradient parameters Repeat the coil winding and demagnetizing steps until the residual magnetism spatial distribution meets the requirements. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the specific embodiments of the present invention, the drawings used in the description of the specific embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 A perspective view of the composite gradient demagnetization structure provided in an embodiment of the present invention; Figure 2 This is a front view of the composite gradient demagnetization structure provided in an embodiment of the present invention; Figure 3 This is a partially enlarged perspective view of part A in the composite gradient demagnetization structure provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of the inlet and outlet of the circumferential demagnetizing coil and the inlet and outlet of the axial demagnetizing coil of the composite gradient demagnetizing structure provided in the embodiments of the present invention. Figure 5 A schematic flowchart of the composite gradient demagnetization method provided in an embodiment of the present invention; Figure 6 A partial flowchart illustrating the composite gradient demagnetization method provided in an embodiment of the present invention; Figure 7 This is a schematic diagram of the demagnetization process in series mode in the composite gradient demagnetization method provided in the embodiments of the present invention; Figure 8 This is a flowchart illustrating the split-control demagnetization mode in the composite gradient demagnetization method provided in this embodiment of the invention. Figure 9 This is a schematic diagram comparing the demagnetization effect of the composite gradient demagnetization method provided in this embodiment of the invention with the demagnetization effect of existing technical solutions. Figure 10 This is a schematic diagram comparing the demagnetization effect in the X direction using the composite gradient demagnetization method provided in this embodiment of the invention with the demagnetization effect in the X direction using existing technical solutions. Figure 11 This is a schematic diagram comparing the demagnetization effect in the Y direction using the composite gradient demagnetization method provided in this embodiment of the invention with the demagnetization effect in the Y direction using existing technical solutions. Figure 12 This is a schematic diagram comparing the demagnetization effect in the Z direction using the composite gradient demagnetization method provided in this embodiment of the invention with the demagnetization effect in the Z direction using existing technical solutions. Figure 13 A schematic diagram illustrating the demagnetization effect of the composite gradient demagnetization method provided in this embodiment of the invention. Figure 14 This is a schematic diagram comparing the remanence intensity in the X direction using the composite gradient demagnetization method provided in this embodiment of the invention with that using existing technical solutions. Figure 15 This is a schematic diagram comparing the remanence intensity in the X direction using the composite gradient demagnetization method provided in this embodiment of the invention with that using existing technical solutions. Figure 16 This is a schematic diagram comparing the synthesized remanent magnetization intensity when using the composite gradient demagnetization method provided in this embodiment of the invention with the synthesized remanent magnetization intensity when using the prior art solution. Figure 17 This is a schematic diagram comparing the synthesized remanent magnetization intensity when using the composite gradient demagnetization method provided in this embodiment of the invention with that when using existing technical solutions.

[0023] Explanation of reference numerals in the attached figures: 1. Axial demagnetizing coil; 11. Inner layer coil; 12. Outer layer coil; 2. Circumferential demagnetizing coil. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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, 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.

[0025] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0026] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0027] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0028] Magnetic shielding technology is fundamental to ensuring the accuracy of extremely weak magnetic signal measurements and is indispensable in fields such as biomagnetic measurements (e.g., magnetoencephalography (MEG) and magnetocardiography (MCG)), quantum sensing, and fundamental physics research. Demagnetization treatment aims to eliminate residual magnetism introduced into the shielding material during processing, assembly, or exposure to external magnetic fields, and is a key process for obtaining a highly stable, extremely weak internal magnetic field environment.

[0029] Especially in biomagnetic measurement fields such as magnetoencephalography (MEG) and magnetocardiography (MCG), where the uniformity of the magnetic field is extremely important, a cylindrical shielded chamber with a single opening is commonly used as the core magnetic shielding component to facilitate the entry and exit of the object being measured. While this structural choice meets functional requirements, the design of its open end disrupts the continuity of the magnetic circuit inside the shielded chamber, making magnetic field distribution distortion and remanent magnetic gradient problems particularly prominent, severely restricting further improvements in equipment performance.

[0030] Specifically, in the region near the opening, the material is in a relatively high ambient magnetic field (geomagnetic field), and its magnetization is close to saturation. A stronger reverse demagnetizing field is needed to effectively flip the magnetic domains and achieve demagnetization. However, deep inside the magnetic shielding chamber, the magnetic field is significantly shielded to an extremely weak level (e.g., The material is in the initial permeability region and is extremely sensitive to the demagnetizing field. An excessively strong demagnetizing field may cause unnecessary magnetization disturbances.

[0031] Existing demagnetizing technologies mostly employ spatially uniform demagnetizing coils (such as uniformly tightly wound solenoids or circumferential coils) to form a spatially uniform demagnetizing field. During use, if a stronger demagnetizing field is required at the open end, it may cause over-demagnetization of the internal area. Conversely, if the demagnetizing field strength is set based on the internal area, the open end is often under-demagnetized, resulting in an uneven distribution of residual magnetism overall.

[0032] To address this, the present invention provides a composite gradient demagnetization structure, a magnetic shielding chamber, and a composite gradient demagnetization method, which results in an asymmetrical gradient layout of the generated demagnetizing magnetic field. This layout actively matches the residual magnetism distribution characteristics inside the single-ended open magnetic shielding chamber, achieving directional and enhanced demagnetization of the high residual magnetism region. This significantly reduces the residual magnetism intensity in the open region, effectively expands the uniformity range of the magnetic field inside the magnetic shielding chamber, and enables the spatial distribution of the demagnetizing magnetic field to actively match the distribution characteristics of the residual magnetism.

[0033] The following is combined Figures 1 to 17 The following describes embodiments of the present invention.

[0034] According to an embodiment of the present invention, in one aspect, a composite gradient demagnetization structure is provided and installed in a magnetic shielding chamber, the magnetic shielding chamber having a closed end and an open end.

[0035] like Figure 1 As shown, the demagnetizing structure includes an axial demagnetizing coil 1 and a circumferential demagnetizing coil 2.

[0036] Specifically, the axial demagnetizing coil 1 is arranged along the axial direction of the magnetic shielding chamber to generate a circumferential demagnetizing field to eliminate axial residual magnetism. The circumferential demagnetizing coil 2 is arranged along the circumference of the magnetic shielding chamber, and its distribution density is set to gradually increase from the closed end to the open end to generate an axial gradient demagnetizing field to eliminate radial residual magnetism.

[0037] Among them, the axial demagnetizing coil 1 and the circumferential demagnetizing coil 2 are coupled to form a composite demagnetizing coil structure. When an alternating current with a decaying amplitude is applied to the composite demagnetizing coil structure, an asymmetric gradient distribution composite demagnetizing magnetic field is generated to demagnetize the magnetic shielding chamber.

[0038] This configuration, by setting the distribution density of the circumferential demagnetizing coils 2 to gradually increase from the closed end to the open end, and combining it with the axial demagnetizing coils 1, actively constructs an asymmetric composite demagnetizing magnetic field with gradient enhancement from the closed end to the open end. This compensates for the nonlinear enhancement of the residual magnetism distribution from the closed end to the open end caused by the discontinuity of the magnetic circuit, and resolves the contradiction between the existing uniform demagnetizing magnetic field and the non-uniform residual magnetism distribution, thereby achieving precise and adaptive demagnetization of the interior of the shielded cabin from the closed end to the open end.

[0039] Specifically, by distributing the axial demagnetizing coil 1 with an increasing number of turns density along the axial direction of the cabin, the axial gradient demagnetizing field generated by it forms a strengthened demagnetizing region at the opening end, effectively blocking the non-uniform coupling path of the external magnetic field through the opening end and eliminating the nonlinear characteristics of axial magnetic field attenuation; and by designing the density gradient of the circumferential demagnetizing coil 2 (increasing from the closed end to the open end) in conjunction with the axial coil, a three-dimensional composite demagnetizing field is constructed, which dynamically compensates for the radial residual magnetism gradient caused by structural asymmetry in the magnetic shielding cabin, so that the residual magnetism level inside the entire magnetic shielding cabin (especially the critical opening region) can be reduced evenly.

[0040] At the same time, by relatively weakening the demagnetizing magnetic field strength at the closed end (internal region), the risk of over-demagnetization of the internal region is avoided when using a high-intensity uniform magnetic field to accommodate the open end.

[0041] That is, the axial gradient magnetic field mainly optimizes demagnetization for the axial remanent magnetic component, while the circumferential gradient magnetic field can effectively reduce the circumferential remanent magnetic component and the complex magnetization caused by the end effect, avoiding the problems of over-demagnetization or under-demagnetization caused by uniform demagnetization parameters in the existing technical solutions.

[0042] It can be noted that the composite demagnetizing magnetic field matches the residual magnetic field inside the magnetic shielding chamber.

[0043] In one embodiment, such as Figures 1 to 3 As shown, the axial demagnetizing coil 1 includes an inner coil 11 and an outer coil 12. The inner coil 11 is attached to the inside of the magnetic shielding chamber, and the outer coil 12 is attached to the outside of the magnetic shielding chamber. The current in the outer coil 12 flows from the closed end to the open end, and the current direction of the inner coil 11 is opposite to the current direction of the outer coil 12.

[0044] With this configuration, by setting the axial demagnetizing coil 1 as an inner coil 11 attached to the inside and an outer coil 12 attached to the outside, and making the current direction of the outer coil 12 flow from the closed end to the open end, the direction of the induced magnetic field generated is opposite to the direction of the external intruding magnetic field at the opening of the cabin wall. This can directly weaken or cancel a part of the magnetic field that is about to enter the magnetic shielding cabin near the outer wall of the cabin, thus forming protection.

[0045] Furthermore, by making the current direction of the inner coil 11 opposite to that of the outer coil 12, the current direction of the inner coil 11 is from the open end to the closed end, so that the direction of the generated magnetic field is opposite to the direction of the magnetic field of the residual magnetism on the inner surface of the cabin, thus actively canceling the magnetic field generated by the residual magnetism and preventing the residual magnetism from affecting the sensitive areas inside the cabin.

[0046] Meanwhile, the magnetic fields of the inner and outer coils are in the same direction inside the cabin, so they will be superimposed on the surface inside the cabin, thereby improving the cancellation effect of interference and residual magnetism.

[0047] It can be explained that the axial demagnetizing coil 1 has evenly distributed circumferences. Group, , Axial demagnetizing coil 1 is connected in series.

[0048] This configuration, by setting the axial demagnetizing coil 1 to be evenly distributed along the circumference... Group( They are connected in series to ensure that the current amplitude of each group of coils is consistent, thereby ensuring that the generated axial gradient demagnetizing field is evenly distributed and superimposed in the circumferential direction, avoiding hot spots or blind spots in the demagnetizing field that may be caused by the concentrated or asymmetrical arrangement of coils, thus improving the overall demagnetizing effect in three-dimensional space.

[0049] Preferably, such as Figures 1 to 3 As shown, there are six sets of axial demagnetizing coils 1, and the central angle between two adjacent sets of axial demagnetizing coils 1 is 60°.

[0050] It should be noted that the distribution density of the circumferential demagnetizing coil 2 satisfies the following relationship:

[0051] In the formula: Here are the axial position coordinates. Corresponding to the closed end, Corresponding to the open end, Let z be the circumferential coil density at position z. As the baseline density, These are the gradient coefficients. This is the normalized axial distribution function.

[0052] It should be noted that, The relation is:

[0053] In the formula, This is the decay characteristic coefficient, and its value affects the growth characteristics of the function. Specifically, The larger the value, Near the opening end ( near The faster the growth during the opening phase, the more concentrated the coil density distribution becomes in the open-end region; conversely, The smaller the value, the more uniform the coil density distribution. Axial position The range of values ​​is ;in denoted as axial net length of the magnetically shielded cabin, in cm. This function satisfies the boundary conditions. , .

[0054] It can be explained that, dividing the magnetic shielding chamber along the axial direction into an open end, a middle section, and a closed end, the distribution density gradient coefficient of the circumferential demagnetizing coil 2 at the open end is: Distribution density gradient coefficient in the intermediate region Distribution density gradient coefficient at the closed end ,satisfy .

[0055] This configuration, by dividing the magnetic shielding chamber axially into an open end, a middle section, and a closed end, and setting... The gradient coefficient relationship, let the opening end To maximize the generation of the strongest circumferential demagnetizing field for concentrated correction, targeting the region with the strongest external magnetic field coupling and the most difficult-to-eliminate residual magnetism, the closed end... To minimize resource waste and potential over-demagnetization, a gentle gradient is adopted, enabling zoned differentiated design so that the spatial distribution of the circumferential demagnetizing field conforms to the actual decay law of the remanent magnetization.

[0056] According to an embodiment of the present invention, in a second aspect, a magnetic shielding chamber is also provided, comprising the composite gradient demagnetizing structure provided in the first aspect.

[0057] This configuration is based on the fact that the magnetic shielding chamber includes a composite gradient demagnetization structure, which has the same effect as the composite gradient demagnetization structure, and will not be elaborated further here.

[0058] It can be noted that the magnetic shielding chamber uses permalloy as the shielding material, which has high magnetic permeability.

[0059] Specifically, the walls of the magnetically shielded cabin are composed of multiple layers of permalloy or a single layer of permalloy, with a through-hole at the bottom of the sealed end for... The ends of the axial demagnetizing coil 1 are uniformly led out.

[0060] In one embodiment, the magnetic shielding chamber further includes a demagnetizing power supply and a control terminal; the axial demagnetizing coil 1 and the circumferential demagnetizing coil are electrically connected in series and then connected to the demagnetizing power supply to form a series control mode; or, the axial demagnetizing coil 1 and the circumferential demagnetizing coil are independently connected to different demagnetizing power supplies to form a split control mode; the control terminal switches from one of the series control mode and the split control mode to the other.

[0061] This configuration allows the axial and circumferential coils to operate as a single load in a series control mode, suitable for uniform demagnetization and routine demagnetization operations. In a separate control mode, the two coils can be driven by independent power supplies, allowing independent control of the axial and circumferential demagnetizing magnetic fields in terms of intensity and timing. This is suitable for complex scenarios requiring extremely high demagnetization accuracy or fine-grained demagnetization based on specific residual magnetism distributions. By switching between series and separate control modes using a control terminal, the magnetic shielding cabin can adapt to different application scenarios.

[0062] It can be noted that the control terminal is used to switch the demagnetization mode.

[0063] According to an embodiment of the present invention, a third aspect also provides a composite gradient demagnetization method, which is applied to the composite gradient demagnetization structure provided in the first aspect or the magnetic shielding chamber provided in the second aspect.

[0064] like Figure 5 As shown, the composite gradient demagnetization method includes: determining the number of axial demagnetization coils 1 based on the geometric parameters of the magnetic shielding chamber and the target residual magnetism distribution. gradient parameters of circumferential demagnetizing coil 2 ; Winding an axial demagnetizing coil 1; Based on gradient parameters A circumferential demagnetizing coil 2 is wound so that its distribution density gradually increases from the closed end to the open end along the axial direction. The wound axial demagnetizing coil 1 and circumferential demagnetizing coil 2 are installed in the magnetic shielding chamber to form a composite demagnetizing coil structure. An alternating current with attenuated amplitude is applied to the composite demagnetizing coil structure to generate a composite demagnetizing magnetic field with an asymmetric gradient distribution, thereby demagnetizing the magnetic shielding chamber.

[0065] This configuration is because the composite gradient demagnetization method, when applied to the composite gradient demagnetization structure provided in the first aspect or the magnetic shielding chamber provided in the second aspect, has the same effect as the composite gradient demagnetization structure or the magnetic shielding chamber, and will not be elaborated further here.

[0066] It can be explained that the process of winding the axial demagnetizing coil 1 includes: calculating the required wire specifications based on the size of the magnetic shielding chamber, the demagnetization requirements, and the principles of electromagnetics; selecting wires with suitable resistivity, mechanical strength, and insulation properties, such as BVR multi-core soft copper wire; and strictly determining parameters such as wire diameter and number of turns according to design requirements to ensure that the axial demagnetizing coil 1 can generate a magnetic field strength and distribution that meets the demagnetization requirements.

[0067] in, The axial demagnetizing coil 1 is wound in a circumferentially evenly distributed manner.

[0068] Specifically, the magnetic shielding chamber radiates outwards from the through-hole at the bottom of the chamber and then returns to the starting point, exhibiting a uniform and symmetrical distribution.

[0069] The following is a schematic illustration of the winding process of a set of axial demagnetizing coils 1.

[0070] Specifically, the axial demagnetizing coil 1 starts from the through hole, extends centrifugally in the radial direction along the outer wall of the bottom end of the magnetic shielding chamber, then extends in the axial direction towards the opening end along the outer wall of the side of the magnetic shielding chamber, until it reaches the opening end, then bends 180° and extends in the axial direction towards the closed end along the inner wall of the side of the magnetic shielding chamber, then extends in the radial direction towards the center along the inner wall of the bottom end of the magnetic shielding chamber, until it extends to the through hole and is led out.

[0071] In particular, it is necessary to ensure that the axial demagnetizing coil 1 is in close contact with the surface of the permalloy layer of the magnetic shielding chamber in order to improve the magnetic field coupling efficiency.

[0072] It should be noted that the number of turns of any set of axial demagnetizing coils 1 is designed according to the actual application. If a multi-turn coil is required, the winding process described above can be repeated as many times as needed.

[0073] In this group, the multi-turn axial demagnetizing coil 1 within each group is parallel to each other, and the multiple groups of axial demagnetizing coil 1 are parallel to each other.

[0074] Furthermore, multiple sets of axial demagnetizing coils 1 are connected in series via connecting wires.

[0075] It should be noted that after any set of axial demagnetizing coils 1 is wound, it will have an L-shaped structure.

[0076] It should be noted that the inlet and outlet ends of the axial demagnetizing coil 1 are led out to the outside of the magnetic shielding chamber through insulating sleeves to ensure the insulation performance between the conductors and between the conductors and the chamber.

[0077] Furthermore, each output terminal surface is marked with identification marks, such as color coding, to clearly distinguish the connection ports of the inner coil 11 and the outer coil 12, so as to facilitate correct connection with power supply and other equipment in the future.

[0078] It can be explained that the process of winding the circumferential demagnetizing coil 2 includes: determining the wire specifications and number of turns of the circumferential demagnetizing coil 2 based on the circumferential dimensions of the magnetic shielding chamber and the requirements of the demagnetizing magnetic field strength; using a winding mold or special equipment to wind the wire into a ring coil according to the design requirements, ensuring that the coil has a regular shape and an accurate number of turns.

[0079] The circumferential demagnetizing coil 2 is wound along the circumferential direction of the outer wall of the side of the magnetic shielding cabin to form a closed-loop demagnetizing coil. The axial and radial tangents of the magnetic shielding cabin are intersected by a dividing line. In the direction from the central dividing line to the closed end region of the magnetic shielding cabin, the circumferential demagnetizing coil 2 is sparsely distributed and its magnetic field saturation energy is small. In the direction from the central dividing line to the open end region of the magnetic shielding cabin, the circumferential demagnetizing coil 2 is densely distributed and its magnetic field saturation energy is large.

[0080] It should be noted that the number of turns of the circumferential demagnetizing coil 2 is designed according to the actual application. If a multi-turn coil is required, the coil wire should be stranded and the winding process should be repeated as many times as required.

[0081] Preferably, the circumferential demagnetizing coil 2 is provided in multiple sets, and the multiple sets of circumferential demagnetizing coil 2 are connected in series by connecting wires, and the current direction of each circumferential demagnetizing coil 2 is the same, so as to ensure the continuity and closure of the magnetic circuit.

[0082] It should be noted that, as Figure 4As shown, the inlet and outlet of the circumferential demagnetizing coil 2 are uniformly arranged and protected with the inlet and outlet of the axial demagnetizing coil 1.

[0083] Specifically, when the axial demagnetizing coil 1 and the circumferential demagnetizing coil 2 are connected in series, the current output port of the axial demagnetizing coil 1 is... Current inlet of circumferential demagnetizing coil 2 The current inlet of the axial demagnetizing coil 1 is connected in series. Current output port of circumferential demagnetizing coil 2 Connect them to the output terminals of the demagnetizing power supply respectively.

[0084] It should be noted that, as Figure 6 As shown, a demagnetizing current with a value decaying over time is generated, and its waveform exhibits an exponential decay. The demagnetizing current signal is converted into an analog demagnetizing drive signal in the form of a digital signal by a digital-to-analog converter (DAC). Then, it is amplified by a power amplifier and impedance matched and DC biased by a transformer. Finally, a low-voltage, high-current demagnetizing current is output to the coil terminals, thereby generating an alternating magnetic field with a gradually decaying amplitude in the coil, completing one complete demagnetizing cycle.

[0085] It should be noted that the series mode demagnetization process is as follows: Figure 7 As shown, specifically: when the axial demagnetizing coil 1 and the circumferential demagnetizing coil 2 are connected in series to the same demagnetizing power supply system, they form a single closed loop driven by the same demagnetizing power supply. The demagnetizing power supply outputs a decaying alternating current, which flows sequentially through the axial and circumferential demagnetizing coils. The axial coil generates an alternating magnetic field along the workpiece axis, and the radial coil generates an alternating magnetic field surrounding the workpiece. The two magnetic fields are superimposed to form a decaying magnetic field. A digital-to-analog converter (DAC) and a power amplifier module are then used to convert the digital control signal into an analog current signal and amplify it to the power required to drive the coil. The amplitude of the output current is gradually decayed and the frequency is adjustable through program control to achieve smooth decay of the magnetic field and avoid residual magnetism. The power supply output is connected to the coil circuit through a transformer coupling. After demagnetization is completed, the demagnetization effect is verified and tested.

[0086] It should be noted that for scenarios with abnormally complex remanent magnetization distribution, imbalance between axial and circumferential remanent magnetization components, or where extreme performance optimization is required, a split-type control mode should be adopted.

[0087] Specifically, such as Figure 8As shown, by setting up an outer coil 12 circuit and an inner coil 11 circuit, two digital command signals are generated synchronously. The waveform is an alternating current, and the amplitude gradually decays over time. The two digital signals are converted into analog signals by a digital-to-analog converter (DAC) and then amplified to drive the coils with the required power. The amplified signals are then synchronously output to the inner and outer coils 12 through a transformer. After demagnetization is completed, the spatial magnetic field is monitored to verify and test the demagnetization effect.

[0088] Furthermore, regardless of whether demagnetization is performed in separate units or in series, after demagnetization is completed, it is necessary to recalculate indicators such as remanence at the open end, remanence at the closed end, and uniformity of axial remanence. If analysis reveals that the remanence at the open end is still significantly high, the axial demagnetization field gradient is insufficient. If high remanence appears in the middle region, it indicates that the gradient is unreasonable, and the gradient parameters need to be adjusted. The values ​​are then recalculated. The winding, demagnetization, and performance testing processes are then repeated to determine whether the indicators meet the requirements. If they do, the optimization is complete; otherwise, reasonable values ​​are recalculated, and the process is repeated.

[0089] In one embodiment, after applying alternating current for demagnetization, an optimization process is also included: measuring the residual magnetism spatial distribution inside the magnetic shielding chamber after demagnetization; and adjusting the gradient parameters based on the difference between the residual magnetism spatial distribution and a threshold. Based on the adjusted gradient parameters Repeat the coil winding and demagnetizing steps until the residual magnetism spatial distribution meets the requirements.

[0090] This setup, through optimization processes, enables dynamic correction and precise control of the demagnetization effect, ensuring that the final residual magnetism spatial distribution meets the requirements.

[0091] Specifically, the optimization process includes: obtaining the axial length L, diameter D, and material of the magnetic shielding chamber; and based on the measured original axial remanent magnetization distribution and aspect ratio... Preliminary selection The recommended value will Substitute into the formula and calculate. Demagnetization tests are conducted using finite element simulation or by building a prototype to measure the residual magnetism distribution, and fine-tuning is performed based on the measurement results. The value is adjusted until the optimal demagnetization effect is achieved.

[0092] Furthermore, during the optimization process, the number of sets of axial demagnetizing coil 1 can be adjusted as needed. .

[0093] The axial distances of the magnetic shielding cabin are defined below as the working area, transition area, and opening end area, respectively.

[0094] For example, the axial net length of the magnetic shielding chamber 150cm is defined as the distance from the sealed end of the magnetic shielding chamber. cm represents the working area, and the distance from the sealed end of the magnetic shielding cabin. cm is the transition zone, the distance from the sealed end of the magnetic shielding cabin. cm represents the open end region.

[0095] The remanent magnetization components are defined as follows: the X-direction is the axial remanent magnetization component pointing from the closed end to the open end of the magnetically shielded cabin; the Y and Z directions are two mutually perpendicular radial remanent magnetization components. The combined remanent magnetization is the root mean square value of the three-axis remanent magnetization components. .

[0096] like Figures 9 to 12 As shown, the residual magnetism suppression effects of existing demagnetization schemes and the composite asymmetric gradient demagnetization scheme proposed in this invention in three directions (axial X, radial Y, and Z) of the barrel are compared. Figure 9 , Figure 10 It can be seen that, within the entire axial distance range of 1cm–140cm, the present invention forms a large-area improved region (green shaded area), with its absolute remanence intensity generally lower than that of existing technologies. Only a few points, such as around 10cm, exhibit potentially deteriorating regions (red shaded areas), but the degree of deterioration is slight and has limited impact on the overall demagnetization effect. The curves further demonstrate that, throughout the entire axial range, especially in the open-end region where remanence is stronger (z>80cm), the present invention significantly suppresses remanence in the X direction, thereby effectively reducing the overall remanence level, with suppression effects superior to existing technologies. This verifies that the asymmetric gradient coil design can effectively match the axial remanence distribution, achieving enhanced demagnetization from the closed end to the open end.

[0097] like Figure 13 As shown, this paper demonstrates the improvement of the present invention's solution in key performance indicators compared to existing technologies. Specifically, by comparing the remanent magnetization attenuation rate in different regions, it is evident that the present invention has significant advantages in magnetic field gradient control and residual magnetic field uniformity, further verifying the practicality and advancement of the technology. With an improvement target of 20%, actual analysis shows that the overall average optimization reaches 38.7%, significantly exceeding expectations, demonstrating the comprehensive advantages of this solution in gradient control and demagnetization efficiency.

[0098] like Figures 14 to 17As shown, the linear relationship and differences between the remanence in the X-direction and the resultant remanence (root mean square value) are analyzed in detail. The figure uses a scatter plot to illustrate the correlation between the two, along with a difference curve, intuitively reflecting the advantages of the present invention in controlling the coordinated attenuation of remanence in the axial direction (X-direction). Specifically, the blue curve represents the prior art solution, the red curve represents the present invention solution, and the light gray area represents the range of difference between the two. The maximum difference in X-direction remanence is 575.5 nT, located at a distance of 140 cmc from the axial direction, while the maximum difference in resultant remanence is 139.5 nT, located at a distance of 132 cm from the axial direction. The difference curve further shows that after adopting this solution, the attenuation trend of the X-direction remanence is more consistent with the attenuation trend of the resultant remanence, indicating better demagnetization coordination of the system in three-dimensional space, which is beneficial for achieving balanced elimination of the overall magnetic moment. Especially in the open end region ( The remanent magnetic non-uniformity (cm) was significantly improved (the larger the difference area, the more obvious the improvement in remanent magnetic non-uniformity), further verifying the effectiveness of the asymmetric gradient coil design.

[0099] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and all such modifications and variations fall within the scope defined by the appended claims.

Claims

1. A composite gradient demagnetization structure, installed in a magnetic shielding chamber, the magnetic shielding chamber having a closed end and an open end, characterized in that, The demagnetizing structure includes: An axial demagnetizing coil (1) is arranged along the axial direction of the magnetic shielding chamber to generate a circumferential demagnetizing field. A circumferential demagnetizing coil (2) is arranged along the circumference of the magnetic shielding chamber, and its distribution density is set to gradually increase from the closed end to the open end, in order to generate an axial gradient demagnetizing field. The axial demagnetizing coil (1) and the circumferential demagnetizing coil (2) are coupled to form a composite demagnetizing coil structure. When an alternating current with attenuated amplitude is applied to the composite demagnetizing coil structure, an asymmetric gradient distribution composite demagnetizing magnetic field is generated to demagnetize the magnetic shielding chamber.

2. The composite gradient demagnetization structure according to claim 1, characterized in that, The axial demagnetizing coil (1) includes an inner coil (11) and an outer coil (12). The inner coil (11) is attached to the inside of the magnetic shielding chamber, and the outer coil (12) is attached to the outside of the magnetic shielding chamber. The current of the outer coil (12) flows from the closed end to the open end. The current direction of the inner coil (11) is opposite to the current direction of the outer coil (12).

3. The composite gradient demagnetization structure according to claim 1, characterized in that, The axial demagnetizing coil (1) is evenly distributed along the circumference. Group, , The axial demagnetizing coils (1) of the group are connected in series.

4. The composite gradient demagnetizing structure according to any one of claims 1-3, characterized in that, The distribution density of the circumferential demagnetizing coil (2) satisfies the following relationship: In the formula: For axial position coordinates, Corresponding to the closed end, Corresponding to the open end, For position Circumferential coil density at the location, As the baseline density, These are the gradient coefficients. This is the normalized axial distribution function.

5. The composite gradient demagnetizing structure according to claim 4, characterized in that, The magnetic shielding chamber is divided into an open end, a middle section, and a closed end along the axial direction. The distribution density gradient coefficient of the circumferential demagnetizing coil (2) at the open end is: Distribution density gradient coefficient in the intermediate region Distribution density gradient coefficient at the closed end ,satisfy .

6. A magnetically shielded cabin, characterized in that, The composite gradient demagnetizing structure includes any one of claims 1-5.

7. The magnetic shielding cabin according to claim 6, characterized in that, It also includes a demagnetizing power supply and a control terminal; The axial demagnetizing coil (1) and the circumferential demagnetizing coil (2) are electrically connected in series and then connected to the demagnetizing power supply, forming a series control mode; or, The axial demagnetizing coil (1) and the circumferential demagnetizing coil (2) are independently connected to different demagnetizing power supplies, forming a split control mode; The control terminal switches between one of the serial control mode and the split control mode.

8. A composite gradient demagnetization method, characterized in that, The demagnetization method applied to the composite gradient demagnetization structure of any one of claims 1-5 or the magnetic shielding chamber of claim 6 or 7 includes the following steps: Based on the geometric parameters of the magnetic shielding chamber and the target remanent magnetization distribution, the number of sets of axial demagnetizing coils (1) is determined. gradient parameters of the circumferential demagnetizing coil (2) ; Winding an axial demagnetizing coil (1); Based on gradient parameters Circumferential demagnetizing coil (2) is wound so that its distribution density gradually increases from the closed end to the open end along the axial direction; The wound axial demagnetizing coil (1) and circumferential demagnetizing coil (2) are installed in the magnetic shielding chamber to form a composite demagnetizing coil structure; An alternating current with decreasing amplitude is applied to the composite demagnetizing coil structure to generate a composite demagnetizing magnetic field with an asymmetric gradient distribution, thereby demagnetizing the magnetic shielding chamber.

9. The composite gradient demagnetization method according to claim 8, characterized in that, When the axial demagnetizing coil (1) and the circumferential demagnetizing coil (2) are connected in series, the current output port of the axial demagnetizing coil (1) is... Current inlet of circumferential demagnetizing coil (2) The current inlet of the axial demagnetizing coil (1) is connected in series. Current output port of circumferential demagnetizing coil (2) Connect them to the output terminals of the demagnetizing power supply respectively.

10. The composite gradient demagnetization method according to claim 8, characterized in that, After applying alternating current for demagnetization, an optimization process is also included: Measure the spatial distribution of residual magnetism inside the magnetically shielded chamber after demagnetization; The gradient parameters are adjusted based on the difference between the spatial distribution of remanence and the threshold. ; Based on the adjusted gradient parameters Repeat the coil winding and demagnetizing steps until the residual magnetism spatial distribution meets the requirements.

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