A demagnetization method based on weak magnetic environment

Abstract

The present invention discloses a demagnetization method based on a weak magnetic environment. A three-axis geomagnetic compensation coil is built outside a passive shielding device. Current is injected into the coil to generate a reverse magnetic field to offset the geomagnetism, thereby providing a weak magnetic environment for the shielding device. Based on the weak magnetic environment, a demagnetization power supply control system and a demagnetization coil are used to demagnetize the passive shielding layer of the magnetic shielding device, thereby further improving the demagnetization performance. This method can not only reduce the cost of using high-performance shielding materials when the magnetic shielding device adopts multi-layer shielding, but also effectively reduce the residual magnetism inside the shielding space, thereby constructing an extremely weak magnetic environment.

Description

Technical Field

[0001] The invention relates to the technical field of magnetic shielding, and in particular to a demagnetization method based on a weak magnetic environment (provided by a coil). Background Art

[0002] The magnetic field contains a lot of information about magnetic materials and living things. By measuring the magnetic field signal and extracting the effective signal in combination with the inversion algorithm and database, we can obtain important information about the internal state of the relevant magnetic materials, living things or other objects under test, overcome the influence of the conduction resistivity of electrical signal acquisition, and realize non-destructive detection and acquisition of signals, which is of great significance to the development of engineering disciplines and clinical research in medicine.

[0003] According to data, the existing active and passive shielding methods mostly consider the demagnetization of active compensation and passive shielding layers separately, ignoring the coupling relationship between the active compensation coil and the passive shielding layer. For example, in order to improve the shielding performance, the passive shielding layer is first demagnetized, and then the active compensation coil is turned on. At this time, the magnetic field generated by the compensation coil will further magnetize the passive shielding layer, resulting in a significant reduction in demagnetization performance. Therefore, the demagnetization relationship between the active compensation coil and the passive shielding layer needs to be further considered to clarify the optimal active and passive shielding experimental method.

[0004] Chinese patent document CN110970191A discloses a "demagnetization method for a multi-layer shielding device". The demagnetization method is based on a demagnetization coil system to achieve demagnetization. The demagnetization coil system includes a multi-turn demagnetization coil, a plurality of connecting wires and a power supply module. The multi-layer shielding device includes at least two layers of shielding bodies, each layer of shielding bodies is set layer by layer from the inside to the outside, and each layer of shielding bodies is wound with a multi-turn demagnetization coil at intervals, and half of each turn of the demagnetization coil is located inside the wound shielding body, and the other half is located outside the wound shielding body; each demagnetization coil is connected to the power supply module through a corresponding connecting wire; the power supply module includes a controller, and the controller is connected to each connecting wire; the demagnetization method includes: passing a corresponding demagnetization current into each demagnetization coil, so that each layer of the shielding body is first demagnetized layer by layer from the inside to the outside, and then demagnetized layer by layer from the outside to the inside, and the intensity of the demagnetization current is set according to the size of each layer of the shielding body. Compared with the existing demagnetization method, this method can effectively improve the demagnetization effect. The above scheme is aimed at multi-layer magnetic shielding devices, and adopts the method of alternating demagnetization of inner and outer layers, which is difficult to meet the demagnetization requirements of single-layer shielding devices. At the same time, the material cost of the magnetic shielding device is relatively high. Summary of the invention

[0005] The present invention mainly addresses the technical problem that the demagnetization performance of a single-layer magnetic shielding device is difficult to further improve, and provides a demagnetization method based on a weak magnetic environment. A three-axis geomagnetic compensation coil is built outside the shielding device, and current is injected into the coil to generate a reverse magnetic field to offset the geomagnetism, thereby providing a weak magnetic environment for the passive shielding device. Based on the weak magnetic environment, a demagnetization power supply control system and a demagnetization coil are used to demagnetize the passive shielding layer of the passive magnetic shielding device, which can further improve the demagnetization performance. This can not only reduce the cost of using high-performance shielding materials when the passive magnetic shielding device adopts multi-layer shielding, but also effectively reduce the residual magnetism inside the shielding space to construct an extremely weak magnetic environment.

[0006] The above technical problem of the present invention is mainly solved by the following technical solution: The present invention comprises the following steps: S1 constructs a passive magnetic shielding device and measures the direction and magnitude of the three-axis geomagnetic field at the center position; S2 calculates the spacing, current and power requirements of the three-axis geomagnetic compensation coil according to the magnetic field value and builds it; S3 is wound and connected with the three-axis geomagnetic compensation coil and the demagnetization coil, and the geomagnetic compensation coil current is set to offset the geomagnetism; S4 driving power supply generates a sinusoidal demagnetizing current with a gradually decreasing amplitude to the demagnetizing coil to complete the demagnetization; S5 places the magnetic sensor at a specified point in the inner space of the shielding device to measure the residual magnetism.

[0007] By energizing the three-axis geomagnetic compensation coil to generate a magnetic field in the opposite direction of the geomagnetic field, thereby offsetting the geomagnetic field, a certain weak magnetic environment can be provided for the large shielding device in the coil; according to the characteristics of the hysteresis-free magnetization curve of the soft magnetic material, the smaller the magnetic field environment, the higher the magnetic permeability of the shielding material. Therefore, in the weak magnetic environment provided by the above three-axis geomagnetic compensation coil, demagnetizing the shielding device can significantly improve the shielding performance of the device. Compared with the prior art, the above scheme not only has the characteristics of simplified construction and low cost of the passive magnetic shielding device; compared with the prior art that ignores the coupling between the active compensation coil and the passive shielding layer, the above scheme adopts the method of first powering on the active compensation coil and then demagnetizing the passive shielding layer, realizing the decoupling between the magnetic field generated by the active compensation coil and the passive shielding layer after demagnetization. This scheme does not have the problem of magnetization of the passive shielding layer caused by the current adjustment of the active compensation coil, and can also demagnetize the shielding device based on the weak magnetic environment provided by the compensation coil, significantly improving the shielding performance of the device.

[0008] Preferably, the passive magnetic shielding device includes a three-axis geomagnetic compensation coil and a compensation current source system connected thereto, and a residual magnetism testing system is arranged at the center of the three-axis geomagnetic compensation coil. The three-axis geomagnetic compensation coil includes an east-west direction coil combination, a north-south direction coil combination, and a sky-ground direction coil combination. The east-west direction compensation coil is six groups of circular coils, the north-south direction compensation coil is six groups of circular coils, and the sky-ground direction compensation coil is six groups of circular coils; optionally, the number of coil groups is adjustable, and square or elliptical coil shapes can also be applicable. The compensation current source system is used to inject a large current that meets the requirements into the three-axis geomagnetic compensation coil to generate a reverse magnetic field. The residual magnetism testing system includes a non-magnetic tooling and a high-precision magnetic field measurement device. The non-magnetic tooling is used to fix the magnetic field measurement device, and the high-precision magnetic field measurement device is used to measure the residual magnetism inside the shielded space.

[0009] Preferably, the passive magnetic shielding device also includes a passive magnetic shielding device arranged inside the three-axis geomagnetic compensation coil, and a uniformly distributed demagnetization coil is arranged on the surface of the passive magnetic shielding device, and the uniformly distributed demagnetization coil is connected to a demagnetization power supply control system. The passive magnetic shielding device is a closed space formed by splicing an aluminum alloy support frame and a multi-layer Permalloy composite panel, and the multi-layer Permalloy panel is used to shield external interference magnetic fields. The uniformly distributed demagnetization coil is a multi-strand single-turn copper wire evenly wound on the surface of the multi-layer Permalloy panel, which is mainly used to inject demagnetization current to generate an alternating attenuation magnetic field to change the direction of the magnetic domain inside the shielding material.

[0010] Preferably, the demagnetization power supply control system includes a drive control program, a digital-to-analog conversion circuit and a three-channel power amplifier, the drive control program controls the generation of a sinusoidal demagnetization current with a gradually decaying amplitude, the digital-to-analog conversion circuit converts the sinusoidal digital signal into an analog voltage signal, the three-channel power amplifier realizes the input of three-way voltage control signals, and converts the voltage signal into a high-power current signal and injects it into the demagnetization coil. The demagnetization power supply control system includes a drive control program, a digital-to-analog conversion circuit and a three-channel power amplifier, the drive control program is mainly used to control the generation of a sinusoidal signal with a gradually decaying amplitude, the digital-to-analog conversion circuit is used to convert the sinusoidal digital signal into an analog voltage signal, the three-channel power amplifier can realize the input of three-way voltage control signals, and convert the voltage signal into a high-power current signal and inject it into the demagnetization coil, generating a periodic decay current, and realizing the demagnetization function of the shielding layer.

[0011] Preferably, the step S2 measures the three-axis geomagnetic direction and magnitude B at the center of the coil. x , B y and B z , calculate the coil parameters according to the measured magnetic field value, the x-axis geomagnetic direction is: Where μ0 is the magnetic permeability, I x1 , I x2 , I x3 are the injected currents in the three pairs of coils in the x-axis, R1, R2, and R3 are the radii of the three pairs of coils, d1, d2, and d3 are the distances between the center points of each pair of coils, and B in the y-axis direction y And z-axis direction B z The calculation form is the same as above, and nine sets of current parameters are obtained through optimization calculation. Based on the power requirements of each pair of coils, a nine-channel high-power bidirectional programmable DC power supply that meets the requirements is built. Preferably, the power requirement for each pair of coils in step S2, and the calculation formula for the power of a single pair of coils are in the following form: Among them, ρ is the resistivity of the copper wire, l is the sum of the circumferences of a pair of coils, s is the cross-sectional area of ​​the copper wire, and I is the injected current in a pair of coils. A total of nine pairs of coil currents need to be calculated; based on the calculated power of each channel, a nine-channel bidirectional programmable DC power supply that meets the requirements is built.

[0012] Preferably, the step S3 obtains the demagnetization power by finite element simulation according to the material properties of the passive magnetic shielding device and the layout of the demagnetization coil, winds and connects the three-axis geomagnetic compensation coil and the demagnetization coil, measures the resistance and inductance of each coil, and ensures that each coil loop is normal. According to the material properties of the passive magnetic shielding device and the layout of the demagnetization coil, the demagnetization power is obtained by finite element simulation, and a high-power demagnetization power supply control system is integrated, including a three-channel synchronous drive control program, a digital-to-analog conversion circuit, and a power amplifier.

[0013] Preferably, the step S3 connects the three-axis geomagnetic compensation coil to the magnetic compensation current source system, sets the three-axis geomagnetic compensation coil current, and ensures that the direction of the magnetic field generated by the coil is opposite to the geomagnetism to offset the geomagnetism.

[0014] Preferably, the step S4 specifically includes maintaining continuous injection of active compensation coil current, then connecting the demagnetization coil to a demagnetization power supply control system, and using a control program to drive the power supply to generate a sinusoidal demagnetization current with a gradually decaying amplitude to complete the demagnetization.

[0015] Preferably, after the demagnetization in step S5, the magnetic sensor is placed at a designated point in the internal space of the passive magnetic shielding device to measure the residual magnetism while maintaining the current injection in the active compensation coil. The residual magnetism test in the three-axis direction is measured twice in both positive and negative directions, and the sensor error is deducted to complete the residual magnetism measurement inside the large shielding device.

[0016] The beneficial effects of the present invention are as follows: by injecting current into the coil to generate a reverse magnetic field to offset the earth's magnetism, a weak magnetic environment is provided for a large shielding device; based on the weak magnetic environment, a demagnetization power supply control system and a demagnetization coil are used to demagnetize the passive shielding layer of the passive magnetic shielding device, which can further improve the demagnetization performance. This can not only reduce the cost of using high-performance shielding materials when the passive magnetic shielding device adopts multi-layer shielding, but also effectively reduce the residual magnetism inside the shielding space and construct an extremely weak magnetic environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a flow chart of the present invention.

[0018] Figure 2 It is a schematic diagram of a passive magnetic shielding device and a demagnetization line layout of the present invention.

[0019] Figure 3 It is a schematic diagram of magnetization curve characteristics of a soft magnetic material of the present invention.

[0020] Figure 4 It is a schematic diagram of a passive magnetic shielding device and a demagnetization line layout of the present invention.

[0021] Figure 5 It is a schematic diagram of a three-axis geomagnetic active compensation coil of the present invention.

[0022] In the figure, 1 is a compensation current source system, 2 is a three-axis geomagnetic compensation coil, 3 is a passive magnetic shielding device, 4 is a degaussing power supply control system, 5 is a uniformly distributed degaussing coil, and 6 is a residual magnetism testing system. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the technical solution of the present invention is further described in detail below through embodiments and in combination with the accompanying drawings. It should be understood that the specific implementation method described here is only an optimal embodiment of the present invention, which is only used to explain the present invention and does not limit the scope of protection of the present invention. All other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0024] Passive magnetic shielding devices are mainly used to shield the earth's magnetic field and the interference magnetic field caused by human activities, and can provide an extremely stable near-zero magnetic environment for the fields of cardio-cerebral magnetic measurement, cutting-edge physics research, etc. Traditional passive magnetic shielding devices are constructed in a purely passive shielding manner, such as using multiple layers of high magnetic permeability materials with different spacing.

[0025] As the number of shielding layers increases, the cost of high-performance magnetic permeability materials increases significantly. In order to reduce construction costs while achieving the same shielding effect, passive magnetic shielding devices are currently constructed using a combination of active and passive shielding. By setting a large three-axis geomagnetic compensation coil on the outside of the passive magnetic shielding device to offset the external interference magnetic field, the same shielding effect as the passive shielding material is achieved, while also reducing the difficulty of designing and manufacturing the splicing of multiple passive shielding layers.

[0026] However, most of the existing active and passive shielding methods consider the demagnetization of the active compensation and passive shielding layers separately, ignoring the coupling relationship between the active compensation coil and the passive shielding layer. For example, in order to improve the shielding performance, the passive shielding layer is first demagnetized, and then the active compensation coil is turned on. At this time, the magnetic field generated by the compensation coil will further magnetize the passive shielding layer, resulting in a significant reduction in the demagnetization performance. Therefore, the demagnetization relationship between the active compensation coil and the passive shielding layer needs to be further considered to clarify the optimal active and passive shielding experimental method.

[0027] The present invention discloses a demagnetization method based on a weak magnetic environment. The constructed weak magnetic environment includes: a three-axis geomagnetic compensation coil, a compensation current source system, a passive magnetic shielding device, a uniformly distributed demagnetization coil, a demagnetization power supply control system, and a residual magnetism testing system. The key point is to build a three-axis geomagnetic compensation coil outside the shielding device, and inject current into the coil to generate a reverse magnetic field to offset the geomagnetism, thereby providing a weak magnetic environment for a large shielding device. Based on this environment, a demagnetization power supply control system and a demagnetization coil are used to demagnetize the passive shielding layer of the passive magnetic shielding device, which can further improve the demagnetization performance. The use of the method of the present invention can not only reduce the use cost of high-performance shielding materials when the passive magnetic shielding device adopts multi-layer shielding, but also effectively reduce the residual magnetism inside the shielding space to construct an extremely weak magnetic environment.

[0028] Before discussing the exemplary embodiments in more detail, it should be mentioned that some exemplary embodiments are described as processes or methods depicted as flow charts. Although the flow charts describe the operations (or steps) as sequential processes, many of the operations (or steps) therein can be implemented in parallel, concurrently, or simultaneously. In addition, the order of the operations can be rearranged. The process can be terminated when its operation is completed, but can also have additional steps not included in the drawings; the process can correspond to a method, function, procedure, subroutine, subprogram, etc.

[0029] The technical solution of the present invention is further specifically described below through embodiments and in conjunction with the accompanying drawings.

[0030] Embodiment: A demagnetization method based on a weak magnetic environment in this embodiment, such as Figure 1 As shown, the following steps are included: S1 constructs a passive magnetic shielding device and measures the three-axis geomagnetic direction and magnitude at the center position.

[0031] like Figure 2 As shown, the passive magnetic shielding device includes a three-axis geomagnetic compensation coil (2) and a compensation current source system (1) connected thereto, wherein a residual magnetism test system (6) is arranged at the center of the three-axis geomagnetic compensation coil (2). The three-axis geomagnetic compensation coil includes an east-west direction coil combination, a north-south direction coil combination, and a sky-ground direction coil combination, wherein the east-west direction compensation coil is three pairs of circular coils, the north-south direction compensation coil is three pairs of circular coils, and the sky-ground direction compensation coil is three pairs of circular coils; optionally, the number of coil groups is adjustable, and square or elliptical coil shapes may also be applicable. The compensation current source system is used to inject a large current that meets the requirements into the three-axis geomagnetic compensation coil to generate a reverse magnetic field. The residual magnetism test system includes a non-magnetic tooling and a high-precision magnetic field measurement device, wherein the non-magnetic tooling is used to fix the magnetic field measurement device, and the high-precision magnetic field measurement device is used to measure the residual magnetism inside the shielded space.

[0032] like Figure 4 , Figure 5 As shown, the passive magnetic shielding device also includes a passive magnetic shielding device (3) arranged inside the three-axis geomagnetic compensation coil (2), and the surface of the passive magnetic shielding device (3) is provided with a uniformly distributed demagnetization coil (5), and the uniformly distributed demagnetization coil (5) is connected to a demagnetization power supply control system (4). The passive magnetic shielding device is a closed space formed by splicing an aluminum alloy support frame and a multi-layer Permalloy composite panel, and the multi-layer Permalloy panel is used to shield the external interference magnetic field. The uniformly distributed demagnetization coil is a multi-strand single-turn copper wire uniformly wound on the surface of the multi-layer Permalloy panel, which is mainly used to inject a demagnetization current to generate an alternating attenuation magnetic field to change the direction of the magnetic domain inside the shielding material.

[0033] The demagnetization power supply control system includes a drive control program, a digital-to-analog conversion circuit and a three-channel power amplifier. The drive control program controls the generation of an attenuated oscillating sinusoidal signal. The digital-to-analog conversion circuit converts the sinusoidal digital signal into an analog voltage signal. The three-channel power amplifier can realize the input of three-way voltage control signals, and convert the voltage signal into a high-power current signal and inject it into the demagnetization coil. The demagnetization power supply control system includes a drive control program, a digital-to-analog conversion circuit and a three-channel power amplifier. The drive control program is mainly used to control the generation of an attenuated oscillating sinusoidal signal. The digital-to-analog conversion circuit is used to convert the sinusoidal digital signal into an analog voltage signal. The three-channel power amplifier can realize the input of three-way voltage control signals, and convert the voltage signal into a high-power current signal and inject it into the demagnetization coil to generate a periodic attenuation current, thereby realizing the demagnetization function of the shielding layer.

[0034] S2 calculates the spacing, current, and power requirements of the three-axis geomagnetic compensation coil based on the magnetic field value and builds it.

[0035] Measure the three-axis geomagnetic direction and magnitude B at the center of the coil x , B y and B z , calculate the coil parameters according to the measured magnetic field value, the x-axis geomagnetic direction is: Where μ0 is the magnetic permeability, I x1 , I x2 , I x3 are the injected currents in the three pairs of coils in the x-axis, R1, R2, and R3 are the radii of the three pairs of coils, d1, d2, and d3 are the distances between the center points of each pair of coils, and B in the y-axis direction y And z-axis direction B z The calculation form is the same as above, and nine sets of current parameters are obtained by optimizing the calculation. According to the power requirements of each pair of coils, a nine-channel high-power bidirectional programmable DC power supply that meets the requirements is built; the calculation formula for the power of a single pair of coils has the following form: Among them, ρ is the resistivity of the copper wire, l is the sum of the circumferences of a pair of coils, s is the cross-sectional area of ​​the copper wire, and I is the injected current in a pair of coils. A total of nine pairs of coil currents need to be calculated; based on the calculated power of each channel, a nine-channel bidirectional programmable DC power supply that meets the requirements is built.

[0036] S3 is wound and connected with the three-axis geomagnetic compensation coil and the demagnetization coil, and the geomagnetic compensation coil current is set to offset the geomagnetism. According to the material properties of the passive magnetic shielding device and the layout of the demagnetization coil, the demagnetization power is obtained by finite element simulation, and the three-axis geomagnetic compensation coil and the demagnetization coil are wound and connected. The resistance and inductance of each coil are measured to ensure that the loop of each coil is normal. According to the material properties of the passive magnetic shielding device and the layout of the demagnetization coil, the demagnetization power is obtained by finite element simulation, and a high-power demagnetization power supply control system is integrated, including a three-channel synchronous drive control program, a digital-to-analog conversion circuit, and a power amplifier. Connect the three-axis geomagnetic compensation coil to the magnetic compensation current source system, set the geomagnetic compensation coil current, and ensure that the direction of the magnetic field generated by the coil is opposite to the geomagnetism to offset the geomagnetism.

[0037] S4 keeps the active compensation coil current continuously injected, then connects the demagnetization coil to the demagnetization power supply control system (4), and uses the control program to drive the power supply to generate a sinusoidal demagnetization current with a gradually decaying amplitude to complete the demagnetization.

[0038] After S5 demagnetization, while keeping the current injection in the active compensation coil, the magnetic sensor is fixed on the non-magnetic tooling, and the non-magnetic tooling is placed at a designated point inside the shielding device to measure the residual magnetism (supplementary detailed data, details supplement, etc.). The residual magnetism test in the three-axis direction is measured twice in both positive and negative directions to deduct the sensor error. Finally, the residual magnetism measurement inside the large shielding device is completed.

[0039] By energizing the three-axis geomagnetic compensation coil to generate a magnetic field in the opposite direction of the geomagnetic field, thereby offsetting the geomagnetic field, a certain weak magnetic environment can be provided for the large shielding device in the coil; according to the characteristics of the hysteresis-free magnetization curve of the soft magnetic material, the smaller the magnetic field environment, the higher the magnetic permeability of the shielding material. Therefore, in the weak magnetic environment provided by the above three-axis geomagnetic compensation coil, demagnetizing the shielding device can significantly improve the shielding performance of the device. Compared with the prior art, the above scheme not only has the characteristics of simplified construction and low cost of the passive magnetic shielding device; compared with the prior art that ignores the coupling between the active compensation coil and the passive shielding layer, the above scheme adopts the method of first powering on the active compensation coil and then demagnetizing the passive shielding layer, realizing the decoupling between the magnetic field generated by the active compensation coil and the passive shielding layer after demagnetization. This scheme does not have the problem of magnetization of the passive shielding layer caused by the current adjustment of the active compensation coil, and can also demagnetize the shielding device based on the weak magnetic environment provided by the compensation coil, significantly improving the shielding performance of the device.

[0040] Example 1 In view of the problems of great difficulty and high cost in constructing passive magnetic shielding devices and coupling between active and passive shielding, the present invention proposes a demagnetization method for passive magnetic shielding devices based on a weak magnetic environment. The core of the demagnetization method is to first power on a three-axis geomagnetic compensation coil to provide a weak magnetic environment for the passive magnetic shielding device. On this basis, the demagnetization power supply control system is used to demagnetize the shielding layer, thereby achieving high-performance demagnetization of the passive magnetic shielding device.

[0041] The basic principle of the present invention is shown in Figure 2 , because the magnetization curve of soft magnetic materials includes the initial magnetization curve and the hysteresis-free magnetization curve, where the hysteresis-free magnetization curve is the curve obtained after demagnetization under different magnetic field environments. The initial permeability μ1 of the hysteresis-free magnetization curve and the initial permeability μ2 of the initial magnetization curve are Figure 2 It can be seen from the hysteresis-free magnetization curve that as the magnetic field intensity decreases, the magnetic permeability of the material increases significantly after demagnetization. Based on the above principle, the present invention proposes to construct a passive magnetic shielding device by establishing a three-axis geomagnetic active compensation coil externally, using the coil to provide a weak magnetic environment, and demagnetizing the shielding device on this basis, which can significantly improve the shielding performance of the device.

[0042] The present invention provides a demagnetization method based on a weak magnetic environment. Figure 2 As shown, the constructed weak magnetic environment includes: a compensation current source system, a three-axis geomagnetic compensation coil, a passive magnetic shielding device, a degaussing power supply control system, a uniformly distributed degaussing coil, and a residual magnetism testing system.

[0043] The three-axis geomagnetic compensation coil includes two pairs of east-west coil combinations, three pairs of north-south coil combinations, and three pairs of sky-ground coil combinations. It is mainly used to offset the geomagnetic field, reduce the residual magnetism in the target area, and improve the uniformity of the magnetic field.

[0044] The magnetic compensation current source system is a nine-channel high-power bidirectional programmable DC power supply, which is mainly used to inject a large current that meets the requirements into the three-axis geomagnetic compensation coil to generate a reverse magnetic field.

[0045] The passive magnetic shielding device is a closed space formed by splicing an aluminum alloy support frame and multi-layer Permalloy composite panels. The aluminum alloy support frame is used to install and splice multi-layer Permalloy panels, and the multi-layer Permalloy panels are used to shield external interference magnetic fields.

[0046] The uniformly distributed degaussing coil is a multi-strand single-turn copper wire evenly wound on the surface of a multi-layer Permalloy panel. It is mainly used to inject demagnetization current to generate an alternating attenuation magnetic field to change the direction of the magnetic domain inside the shielding material.

[0047] The demagnetization power supply control system includes a drive control program, a digital-to-analog conversion circuit and a three-channel power amplifier. The drive control program is mainly used to control the generation of a sinusoidal demagnetization current with a gradually decaying amplitude. The digital-to-analog conversion circuit is used to convert the sinusoidal digital signal into an analog voltage signal. The three-channel power amplifier can realize the input of three voltage control signals, convert the voltage signal into a high-power current signal and inject it into the demagnetization coil, thereby generating a periodic decay current and realizing the demagnetization function of the shielding layer.

[0048] The residual magnetism testing system includes a non-magnetic tooling and a high-precision magnetic field measuring device. The non-magnetic tooling is used to fix the magnetic field measuring device, and the high-precision magnetic field measuring device is used to measure the residual magnetism inside the shielding space.

[0049] The demagnetization method of the passive magnetic shielding device based on a weak magnetic environment includes the following steps: Step 1: Measure the three-axis geomagnetic direction and magnitude (B x , B y , B z ), calculate the spacing, current and power requirements of the three-axis geomagnetic compensation coils according to the magnetic field value, and build a nine-channel high-power bidirectional programmable DC power supply that meets the requirements based on the power requirements of each pair of coils; the formula for calculating the coil spacing and other parameters according to the measured magnetic field value has the following form: Where μ0 is the magnetic permeability, I x1 , I x2 , I x3are the injected currents in the three pairs of coils in the x-axis, R1, R2, and R3 are the radii of the three pairs of coils, and d1, d2, and d3 are the distances between the center points of each pair of coils. y With z-axis direction B z The calculation form is similar, and nine sets of current parameters are obtained through optimization calculation. According to the power requirements of each pair of coils, a nine-channel high-power bidirectional programmable DC power supply that meets the requirements is built; the calculation formula for the power of a single pair of coils has the following form: Among them, ρ is the resistivity of the copper wire, l is the sum of the circumferences of a pair of coils, s is the cross-sectional area of ​​the copper wire, and I is the injected current in a pair of coils. A total of nine pairs of coil currents need to be calculated; based on the calculated power of each channel, a nine-channel bidirectional programmable DC power supply that meets the requirements is built.

[0050] Step 2, according to the material properties of the passive magnetic shielding device and the layout of the degaussing coil, the degaussing power is obtained by finite element simulation, and a high-power degaussing power supply control system is integrated, including a three-channel synchronous drive control program, a digital-to-analog conversion circuit, and a power amplifier; Step 3, winding and connecting the three-axis geomagnetic compensation coil and the degaussing coil, measuring the resistance value of each coil, and ensuring that each coil circuit is normal; Step 4: Connect the three-axis geomagnetic compensation coil to the magnetic compensation current source system and set the geomagnetic compensation coil current (I x1 , I x2 , I x3 , I y1 , I y2 , I y3 , I z1 , I z2 , I z3 ), ensure that the direction of the magnetic field generated by the coil is opposite to the geomagnetic field, which has the effect of offsetting the geomagnetic field.

[0051] Step 5, based on step 4, keep the active compensation coil current continuously injected, then connect the demagnetization coil to the magnetic power supply control system, use the control program to drive the power supply to generate a sinusoidal demagnetization current with a gradually decaying amplitude to complete the demagnetization.

[0052] Step 6: After demagnetization, while keeping the current injection in the active compensation coil, fix the magnetic sensor on the non-magnetic tooling, and place the non-magnetic tooling at a specified point inside the shielding device to measure the residual magnetism. The residual magnetism test in the three-axis direction is measured twice in both positive and negative directions, and the sensor error has been deducted. Finally, the residual magnetism measurement inside the large shielding device is completed.

[0053] Compared with the prior art, the above scheme adopts a combination of active and passive shielding to construct a passive magnetic shielding device. Under the premise of achieving the same shielding performance, it reduces the difficulty of splicing and manufacturing the multi-layer passive shielding layer of the passive magnetic shielding device and the construction cost; compared with the prior art that ignores the coupling between the active compensation coil and the passive shielding layer, the above scheme adopts the method of first powering on the active compensation coil and then demagnetizing the passive shielding layer, thereby realizing the decoupling between the magnetic field generated by the active compensation coil and the passive shielding layer after demagnetization. This scheme does not have the problem of magnetization of the passive shielding layer caused by the current regulation of the active compensation coil, and can also demagnetize the shielding device based on the weak magnetic environment provided by the compensation coil, significantly improving the shielding performance of the device.

[0054] Example 2 In this implementation case, the three-axis geomagnetic compensation coil system is supported by an aluminum alloy frame and wound with coils to form a spherical space. Each pair of coils can be powered by a magnetic compensation current source system. The passive magnetic shielding device is a spherical cabin built of Permalloy, with a weak magnetic field space formed inside. The demagnetization wire is evenly wound on the surface of the device, and the demagnetization current can be provided to the demagnetization wire by a demagnetization power supply. The entire passive magnetic shielding device can be placed inside the spherical space formed by the three-axis geomagnetic compensation coil. By constructing a three-axis geomagnetic compensation coil system in the earth's magnetic field environment to provide a magnetic field environment with a residual magnetism of less than 3000nT in a space of 4m*4m*2m, a weak magnetic environment is provided for the demagnetization of the passive magnetic shielding device. Under this working condition, the residual magnetism in the internal space of the passive magnetic shielding device can be reduced by the demagnetization wire 1m 3 30nT reduced to 1m 3 Remanence level within 3nT.

[0055] In this implementation case, the steady-state components of the measured environmental geomagnetic field are 33859nT in the north-south direction, 25880nT in the sky-sky direction, and 5300nT in the east-west direction. The spacing range of each pair of three pairs of coils in the east-west direction is preferably 1.8m, 4.1m, and 5.5m; the number of coil turns is preferably 16 turns, the current range is preferably 7.25A, 1.45A, and 1.08A, and the coil diameter is preferably 3.9m, 6.7m, and 10m, respectively. The same is true for the north-south and sky-sky coils. The three-axis geomagnetic compensation coil is wound on a circular aluminum alloy frame with a multi-core pure copper busbar. According to the current value calculated in step 1 and the coil resistance, the power is less than 1kW, and an integrated magnetic compensation current source system capable of simultaneously outputting nine currents is built based on the power demand. The power supply system has an output port for easy connection to the geomagnetic compensation coil for power supply.

[0056] According to step 2, through the material properties of the passive magnetic shielding device and the layout of the demagnetization coil, the finite element simulation shows that the demagnetization current is not less than 80A and the demagnetization power is not less than 50kW. An integrated high-power demagnetization power supply control system is built based on power requirements. A driver program for digital-to-analog conversion is written based on FPGA to convert discrete digital waveforms into analog signals, thereby generating a drive voltage to control the output current of the demagnetization power supply.

[0057] According to step 3, the degaussing line is connected to the degaussing control system, the three-axis geomagnetic compensation coil is connected to the magnetic compensation current source system, and the resistance value of each coil is tested. The resistance of the active compensation coil is about 1 to 8 ohms. The resistance of the degaussing coil is not greater than 6 ohms, and all coils are connected to the power supply system normally.

[0058] According to step 4, the designed current value is input into the digital panel of the active magnetic compensation current source system, and the power is turned on (according to , the designed value is obtained).

[0059] According to step 5, while maintaining the continuous output of the active magnetic compensation current source system in step 4, the demagnetization current control program is started to demagnetize the passive magnetic shielding device.

[0060] According to step 6, after demagnetization is completed, the magnetic sensor is fixed on the non-magnetic tooling while maintaining the current injection in the active compensation coil. The non-magnetic tooling is placed at a specified point in the internal space of the shielding device to measure the residual magnetism. The residual magnetism test in the three-axis direction of each point is measured twice in both directions, and the difference between the two results is taken to deduct the sensor measurement error, and finally the residual magnetism test of the entire internal space is completed.

[0061] The implementation case provided by the present invention can be applied to the performance improvement of high-end medical equipment. By providing a weak magnetic environment through active compensation coils, the demagnetization performance of the magnetic shielding cabin is improved, thereby providing an extremely weak stable magnetic field environment for cardio-cerebral magnetic measurements in the shielding cabin. At the same time, this case can also be applied to some cutting-edge physics research fields that require extremely weak magnetic fields, such as high-precision measurement of electric dipole moment to verify CP conservation, research on singular spin interactions, etc.

[0062] The specific embodiments described herein are merely examples of the spirit of the present invention. The above embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that technicians in the technical field to which the present invention belongs can make various modifications or supplements to the described specific embodiments or replace them in a similar manner, but will not deviate from the spirit of the present invention or exceed the scope defined in the attached claims. For ordinary technicians in this field, multiple deformations and improvements can also be made without departing from the concept of the present invention. Therefore, the scope of protection of the patent of the present invention shall be based on the attached claims.

Claims

1. A demagnetization method based on a weak magnetic environment, characterized in that: The following steps are involved: S1 builds a passive magnetic shielding device and measures the direction and magnitude of the three-axis geomagnetic field at the center; S2 calculates the spacing, current and power requirements of the three-axis geomagnetic compensation coil according to the magnetic field value and builds it; S3 winds and connects the three-axis geomagnetic compensation coil and the demagnetization coil, and sets the geomagnetic compensation coil current to offset the geomagnetism; S4 drives the power supply to generate a sinusoidal demagnetization current with a gradually decaying amplitude to the demagnetization coil to complete the demagnetization; S5 places the magnetic sensor at a specified point in the inner space of the shielding device to measure the residual magnetism.

2. A demagnetization method based on a weak magnetic environment according to claim 1, characterized in that: The passive magnetic shielding device comprises a three-axis geomagnetic compensation coil (2) and a compensation current source system (1) connected thereto, wherein a residual magnetism testing system (6) is arranged at the center of the three-axis geomagnetic compensation coil (2).

3. A demagnetization method based on a weak magnetic environment according to claim 2, characterized in that: The passive magnetic shielding device also includes a passive magnetic shielding device (3) arranged inside the three-axis geomagnetic compensation coil (2), a surface of the passive magnetic shielding device (3) is provided with a uniformly distributed demagnetization coil (5), and the uniformly distributed demagnetization coil (5) is connected to a demagnetization power supply control system (4).

4. A demagnetization method based on a weak magnetic environment according to claim 3, characterized in that: The demagnetization power supply control system includes a drive control program, a digital-to-analog conversion circuit and a three-channel power amplifier. The drive control program controls the generation of a sinusoidal signal with a gradually decaying amplitude. The digital-to-analog conversion circuit converts the sinusoidal digital signal into an analog voltage signal. The three-channel power amplifier realizes the input of three-way voltage control signals and converts the voltage signal into a high-power current signal to be injected into the demagnetization coil.

5. The demagnetization method based on a weak magnetic environment according to claim 1, characterized in that: The step S2 measures the three-axis geomagnetic direction and magnitude B at the center of the coil x , B y and B z , calculate the coil parameters according to the measured magnetic field value, the x-axis geomagnetic direction is: Where μ0 is the magnetic permeability, I x1 , I x2 , I x3 are the injected currents in the three pairs of coils in the x-axis, R1, R2, and R3 are the radii of the three pairs of coils, d1, d2, and d3 are the distances between the center points of each pair of coils, and B in the y-axis direction y And z-axis direction B z The calculation form is the same as above, and nine sets of current parameters are obtained through optimization calculation.

6. The demagnetization method based on a weak magnetic environment according to claim 1, characterized in that: The power requirement for each pair of coils in step S2, the calculation formula for the power of a single pair of coils has the following form: Among them, ρ is the resistivity of the copper wire, l is the sum of the circumferences of a pair of coils, s is the cross-sectional area of ​​the copper wire, and I is the injected current in a pair of coils. A total of nine pairs of coil currents need to be calculated; based on the calculated power of each channel, a nine-channel bidirectional programmable DC power supply that meets the requirements is built.

7. A demagnetization method based on a weak magnetic environment according to claim 1, 5 or 6, characterized in that: In step S3, the degaussing power is obtained by finite element simulation according to the material properties of the passive magnetic shielding device and the layout of the degaussing coil, the three-axis geomagnetic compensation coil and the degaussing coil are wound and connected, and the resistance and inductance of each coil are measured to ensure that each coil loop is normal.

8. A demagnetization method based on a weak magnetic environment according to claim 1, 5 or 6, characterized in that: The step S3 connects the three-axis geomagnetic compensation coil to the magnetic compensation current source system, sets the three-axis geomagnetic compensation coil current, and ensures that the direction of the magnetic field generated by the coil is opposite to the geomagnetism to offset the geomagnetism.

9. The demagnetization method based on a weak magnetic environment according to claim 3, characterized in that: The step S4 specifically includes maintaining the continuous injection of the active compensation coil current, then connecting the demagnetization coil to the demagnetization power supply control system (4), and using the control program to drive the power supply to generate a demagnetization current with attenuated oscillation to complete the demagnetization.

10. A demagnetization method based on a weak magnetic environment according to claim 9, characterized in that: After demagnetization in step S5, the magnetic sensor is placed at a designated point in the interior of the passive magnetic shielding device to measure the residual magnetism while maintaining the current injection in the active compensation coil. The residual magnetism test in the three-axis direction is measured twice in both the forward and reverse directions, and the sensor error is deducted to complete the residual magnetism measurement inside the passive shielding device.

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