Electromagnetic-thermal combined degaussing device and method

Abstract

The electromagnetic-thermal combined degaussing device and method solve the problem of excessive residual magnetism and residual magnetism gradient of the permalloy-ferrite combined magnetic shielding integrated electromagnetic degaussing. The permalloy material has low coercivity and high Curie temperature, and the multilayer magnetic shielding barrel made of the permalloy material can easily obtain extremely low residual magnetism and residual magnetism gradient by using electromagnetic degaussing. The ferrite material with high magnetic permeability has high coercivity and low Curie temperature, and perfect degaussing effect can be obtained by heating the ferrite magnetic shielding to above the Curie temperature of the material. The present application uses electromagnetic degaussing on the outer multilayer permalloy, and then heats the inner ferrite magnetic shielding to above the Curie temperature of the material and then water-cools to room temperature, and uses the electromagnetic-thermal combined degaussing method to realize that the residual magnetism and residual magnetism gradient in the permalloy-ferrite magnetic shielding are close to zero, thereby meeting the harsh requirements of ultra-high sensitivity magnetic field and inertial measurement on the magnetic field based on the atomic spin effect.

Description

Technical Field

[0001] This invention relates to the field of magnetic shielding demagnetization technology, and in particular to an electromagnetic-thermal combined demagnetization device and method for low remanence demagnetization of permalloy-ferrite magnetic shielding. Background Technology

[0002] Passive magnetic shielding provides a stable magnetic field environment for achieving ultra-high sensitivity magnetic field and inertial measurements based on atomic spin effects. The residual magnetic field and residual magnetic field noise inside the magnetic shield are related to the materials and structure used. Permalloy magnetic shielding has high permeability; using this material and employing a multilayer structure, permeability as high as 10⁻⁶ can be achieved. 7 The shielding coefficient of the permalloy is high, and the remanence within the magnetic shield can be suppressed from 50,000 nT in the Earth's magnetic field to approximately 0.1 nT. However, according to the fluctuation dissipation theorem, the high conductivity of permalloy leads to significant magnetic noise. Typically, a ferrite magnetic shield is added inside the permalloy magnetic shield to reduce magnetic noise by utilizing the high permeability and resistivity of ferrite. Passive magnetic shields exposed to the Earth's magnetic field for extended periods will become magnetized, increasing internal remanence, necessitating demagnetization before use. Currently, demagnetization methods are mainly divided into two types: thermal demagnetization and electromagnetic demagnetization. Previously, integrated electromagnetic demagnetization was commonly used for passive permalloy-ferrite magnetic shielding systems. However, due to the higher coercivity of ferrite materials compared to permalloy, ferrite magnetic shields are difficult to demagnetize, resulting in larger remanence and remanence gradient within the combined magnetic shielding system compared to a single permalloy magnetic shield. Larger remanence and remanence gradients negatively impact the performance of ultra-sensitive magnetic fields and inertial measurements based on atomic spin effects. For permalloy shielding-ferrite combined magnetic shielding, traditional integrated electromagnetic demagnetization methods cannot meet the magnetic field requirements of ultra-high sensitivity magnetic fields based on atomic spin effects and inertial measurements. New demagnetization devices and methods need to be studied to solve the above problems. Summary of the Invention

[0003] This invention addresses the deficiencies or shortcomings of existing technologies by providing an electromagnetic-thermal combined demagnetizing device and method for demagnetizing low remanence of permalloy-ferrite magnetic shields. By electromagnetically demagnetizing the permalloy magnetic shield and then thermally demagnetizing the ferrite shield, the advantage is that the remanence and remanence gradient of the permalloy-ferrite combined magnetic shield are close to zero.

[0004] The technical solution of the present invention is as follows:

[0005] An electromagnetic-thermal combined demagnetizing device is used for demagnetizing permalloy-ferrite magnetic shields with low remanence. It is characterized by comprising demagnetizing cables wound around the inner and outer layers of the permalloy magnetic shield. The ferrite magnetic shield located within the permalloy magnetic shield is composed of a ferrite magnetic shield cover and ferrite magnetic shield sidewalls. The top surface of the ferrite magnetic shield cover is sequentially affixed with a ferrite magnetic shield cover heat-conducting layer and a ferrite magnetic shield cover heating film. The outer peripheral surface of the ferrite magnetic shield sidewalls is sequentially affixed with a ferrite magnetic shield sidewall heat-conducting layer and a ferrite magnetic shield sidewall heating film. Water-cooling pipes are wrapped around the heating film on the side wall of the ferrite magnetic shield. A triaxial magnetometer probe is set in the center of the ferrite magnetic shield. An electromagnetic demagnetizer, a temperature controller, a circulating water chiller, a triaxial magnetometer counting and display system, and a host computer are set on the outside of the permalloy magnetic shield. The host computer is connected to the triaxial magnetometer probe through the triaxial magnetometer counting and display system. The circulating water chiller is connected to the water-cooling pipes. The temperature controller is connected to both the heating film on the side wall of the ferrite magnetic shield and the heating film on the ferrite magnetic shield cover. The electromagnetic demagnetizer is connected to the demagnetizing cable.

[0006] The ferrite magnetic shield is located on the ferrite magnetic shield support, and the ferrite magnetic shield support is fixed to the inner bottom surface of the permalloy magnetic shield.

[0007] The permalloy magnetic shield is a multi-layer permalloy magnetic shield.

[0008] The ferrite magnetic shielding cover is connected to an LCR meter, which is used to measure the permeability of the ferrite magnetic shielding cover.

[0009] After the electromagnetic demagnetizer performs electromagnetic demagnetization on the permalloy magnetic shield, the temperature controller heats the ferrite magnetic shield to above the Curie temperature and then cools it to room temperature. The electromagnetic-thermal combined demagnetization achieves a near-zero remanence and remanence gradient inside the permalloy-ferrite magnetic shield.

[0010] An electromagnetic-thermal combined demagnetization method, characterized in that it includes the use of the above-mentioned electromagnetic-thermal combined demagnetization device.

[0011] Includes the following steps:

[0012] Step 1: Demagnetizing cable is uniformly wound on the multilayer permalloy magnetic shield. The demagnetizing cable is connected to the electromagnetic demagnetizer. The electromagnetic demagnetizer generates a 50Hz sinusoidal current signal that decays over time. The magnetic field corresponding to the maximum current signal generated by the electromagnetic demagnetizer is greater than the saturation magnetization of the permalloy. The current signal decays to zero in 60s.

[0013] Step 2: Place the triaxial magnetometer probe at the center of the multilayer permalloy magnetic shield and record the residual magnetism in the x, y, and z directions. When the residual magnetism is greater than 1 nT, increase the current of the electromagnetic demagnetizer until the residual magnetism is less than 1 nT.

[0014] Step 3: Apply the thermal conductive layer and heating film of the ferrite magnetic shielding cover to the ferrite magnetic shielding cover in sequence using high-temperature double-sided adhesive. Heat the ferrite magnetic shielding cover using a temperature controller. Measure the permeability of the ferrite magnetic shielding cover at different temperatures using an LCR meter. When the permeability is close to zero, record the temperature T1 of the temperature controller at this time.

[0015] Step 4: The ferrite magnetic shielding sidewall is sequentially attached with the ferrite magnetic shielding sidewall heat conduction layer and the ferrite magnetic shielding sidewall heating film. The outermost layer is wrapped with a water cooling pipe, which is connected to the circulating water chiller. After the attachment is completed, the ferrite magnetic shielding sidewall and the two ferrite magnetic shielding covers are combined to form a complete ferrite magnetic shield and placed on the ferrite magnetic shielding support base. It is then placed in the multilayer permalloy magnetic shield.

[0016] Step 5: Use a temperature controller to heat the ferrite magnetic shield to temperature T1 and maintain it for more than two hours. Then turn off the temperature controller and allow it to cool down.

[0017] Step 6: When the temperature drops to room temperature, place the triaxial magnetometer probe at the center of the ferrite magnetic shield and record the remanence and remanence gradient in the x, y, and z directions. The entire demagnetization process is now complete.

[0018] The shielding coefficient of the multilayer permalloy magnetic shield is greater than 104.

[0019] The heat-conducting layer is made of a material resistant to high temperatures up to 200℃, and the temperature of the circulating water chiller is set to 20℃.

[0020] The process of recording the remanence in the x, y, and z directions in step 6 includes: connecting the triaxial magnetometer system to the host computer and continuously collecting data for 5 minutes; recording the remanence gradient includes: recording the magnetic field value every time it changes by 0.5 cm, plotting the magnetic field versus distance curve, and obtaining the magnetic field gradient through polynomial fitting.

[0021] The technical effects of this invention are as follows: This invention provides an electromagnetic-thermal combined demagnetizing device and method, which overcomes the problem of large remanence and remanence gradient after electromagnetic demagnetization of existing permalloy-ferrite magnetic shielding integrated shields. Electromagnetic demagnetization is performed on permalloy with low coercivity, creating a small magnetic field environment with low remanence and remanence gradient for the ferrite magnetic shield. For ferrite magnetic shields with high coercivity that are difficult to demagnetize electromagnetically, thermal demagnetization is used. The ferrite magnetic shield is heated to above the Curie temperature of the material and then cooled. This combined electromagnetic-thermal demagnetization method achieves excellent demagnetization effect on the remanence and remanence gradient of the permalloy-ferrite magnetic shield.

[0022] Compared with existing technologies, conventional permalloy-ferrite magnetic shielding methods using integrated electromagnetic demagnetization are limited by the high coercivity of ferrite magnetic shielding, making demagnetization difficult and resulting in significant remanence and magnetic gradient within the shield. This invention addresses the permalloy-ferrite combined magnetic shielding system by employing a combined electromagnetic-thermal demagnetization method to achieve near-zero remanence and magnetic gradient within the permalloy-ferrite magnetic shield, thus meeting the stringent requirements of ultra-high sensitivity magnetic fields based on atomic spin effects and inertial measurements. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the structure of an electromagnetic-thermal combined demagnetizing device for implementing the present invention. Figure 1 The electromagnetic-thermal combined demagnetizing device is used for demagnetizing low remanence permalloy-ferrite magnetic shielding. Figure 1 The system includes a demagnetizing cable 2 connected to the electromagnetic demagnetizer 12, with multiple layers of permalloy magnetic shielding 1 evenly wound around its inner and outer layers. Inside the multiple layers of permalloy magnetic shielding 1, a ferrite magnetic shielding support 10 and the ferrite magnetic shielding itself are placed. The ferrite magnetic shielding is composed of a ferrite magnetic shielding cover 5 and ferrite magnetic shielding sidewalls 9. A ferrite magnetic shielding cover heat-conducting layer 4 and a ferrite magnetic shielding cover heating film 3 are respectively attached to the ferrite magnetic shielding cover 5. A ferrite magnetic shielding sidewall heat-conducting layer 8 and a ferrite magnetic shielding sidewall heating film 7 are respectively attached to the outside of the ferrite magnetic shielding sidewalls 9. A water-cooling pipe 6 is wrapped around the outermost layer and connected to a circulating water chiller 17. A triaxial magnetometer probe 11 is placed in the center inside the ferrite magnetic shielding. The triaxial magnetometer probe 11 is connected to a triaxial magnetometer counting and display system 16, and the signal output serial port of the triaxial magnetometer counting and display system 16 is connected to a host computer 15. The ferrite magnetic shielding cover heating film 3 and the ferrite magnetic shielding sidewall heating film 7 are respectively connected to the temperature controller 13. The LCR meter 14 measures the magnetic permeability of the ferrite magnetic shielding cover 5.

[0024] The following are the annotations in the attached diagram: 1-Multi-layer permalloy magnetic shield; 2-Demagnetizing cable; 3-Ferrite magnetic shielding cover heating film; 4-Ferrite magnetic shielding cover heat-conducting layer; 5-Ferrite magnetic shielding cover; 6-Water cooling pipe; 7-Ferrite magnetic shielding sidewall heating film; 8-Ferrite magnetic shielding sidewall heat-conducting layer; 9-Ferrite magnetic shielding sidewall; 10-Ferrite magnetic shielding support base; 11-Triaxial magnetometer probe; 12-Electromagnetic demagnetizer; 13-Temperature controller; 14-LCR meter (electronic energy measuring instrument, L represents inductance, C represents capacitance, R represents resistance); 15-Host computer; 16-Triaxial magnetometer display system; 17-Circulating water chiller; xyz-Cartesian coordinate three axes (i.e., x-axis, y-axis, and z-axis). Detailed Implementation

[0025] The following is in conjunction with the attached diagram ( Figure 1 The invention will be described in the following sections and examples.

[0026] Figure 1 This is a schematic diagram of an electromagnetic-thermal combined demagnetizing device for implementing the present invention. (Reference) Figure 1 As shown, an electromagnetic-thermal combined demagnetizing device is used for demagnetizing low remanence permalloy-ferrite magnetic shields. It includes demagnetizing cables 2 wound around the inner and outer layers of the permalloy magnetic shield. The ferrite magnetic shield located within the permalloy magnetic shield is composed of a ferrite magnetic shield cover 5 and ferrite magnetic shield sidewalls 9. A ferrite magnetic shield cover heat-conducting layer 4 and a ferrite magnetic shield cover heating film 3 are sequentially attached to the top surface of the ferrite magnetic shield cover 5. A ferrite magnetic shield sidewall heat-conducting layer 8 and a ferrite magnetic shield sidewall heating film 7 are sequentially attached to the outer peripheral surface of the ferrite magnetic shield sidewalls 9. The ferrite magnetic shield sidewalls are heated... A water-cooling pipe 6 is wound around the membrane 7. A triaxial magnetometer probe 11 is positioned at the center of the ferrite magnetic shield. An electromagnetic demagnetizer 12, a temperature controller 13, a circulating water chiller 17, a triaxial magnetometer counting and display system 16, and a host computer 15 are arranged outside the permalloy magnetic shield. The host computer 15 is connected to the triaxial magnetometer probe 11 through the triaxial magnetometer counting and display system 16. The circulating water chiller 17 is connected to the water-cooling pipe 6. The temperature controller 13 is connected to both the heating membrane 7 on the side wall of the ferrite magnetic shield and the heating membrane 3 on the cover of the ferrite magnetic shield. The electromagnetic demagnetizer 12 is connected to the demagnetizing cable 2. The ferrite magnetic shield is located on a ferrite magnetic shield support 10, which is fixed to the inner bottom surface of the permalloy magnetic shield. The permalloy magnetic shield is a multi-layer permalloy magnetic shield 1.

[0027] The ferrite magnetic shielding cover 5 is connected to an LCR meter 14, which is used to measure the permeability of the ferrite magnetic shielding cover 5. After the electromagnetic demagnetizer 12 performs electromagnetic demagnetization on the permalloy magnetic shield, the temperature controller 13 heats the ferrite magnetic shield to above the Curie temperature and then cools it to room temperature. This electromagnetic-thermal combined demagnetization achieves a remanence and remanence gradient inside the permalloy-ferrite magnetic shield that are close to zero.

[0028] An electromagnetic-thermal combined demagnetization method includes using the above-mentioned electromagnetic-thermal combined demagnetization device.

[0029] The process includes the following steps: Step 1: A demagnetizing cable is uniformly wound around the multilayer permalloy magnetic shield. The demagnetizing cable is connected to an electromagnetic demagnetizer. The electromagnetic demagnetizer generates a 50Hz sinusoidal current signal that decays over time. The magnetic field corresponding to the maximum current signal generated by the electromagnetic demagnetizer is greater than the saturation magnetization of the permalloy. The current signal decays to zero in 60 seconds. Step 2: A triaxial magnetometer probe is placed at the center of the multilayer permalloy magnetic shield. The residual magnetism in the x, y, and z directions is recorded. When the residual magnetism is greater than 1nT, the current of the electromagnetic demagnetizer is increased until the residual magnetism is less than 1nT. Step 3: The ferrite magnetic shield cover is covered with a heat-conducting layer and a heating film using high-temperature double-sided adhesive tape. The ferrite magnetic shield cover is heated using a temperature controller, and the ferrite magnetism at different temperatures is measured using an LCR meter. The permeability of the magnetic shielding cover is recorded. When the permeability is close to zero, the temperature T1 of the temperature controller is recorded. Step 4: The ferrite magnetic shielding sidewall thermal conductive layer and the ferrite magnetic shielding sidewall heating film are attached to the ferrite magnetic shielding sidewall in sequence. The outermost layer is wrapped with a water-cooling pipe, which is connected to a circulating water chiller. After attachment, the ferrite magnetic shielding sidewall and the two ferrite magnetic shielding covers are combined to form a complete ferrite magnetic shield and placed on the ferrite magnetic shielding support base, and then placed in the multilayer permalloy magnetic shield. Step 5: The ferrite magnetic shield is heated to T1 temperature using a temperature controller and maintained for more than two hours. Then the temperature controller is turned off to allow cooling. Step 6: When the temperature drops to room temperature, the triaxial magnetometer probe is placed at the center of the ferrite magnetic shield and the remanence and remanence gradient in the x, y, and z directions are recorded. The entire demagnetization process is complete.

[0030] The multilayer permalloy magnetic shield has a shielding coefficient greater than 10⁴. The heat-conducting layer uses a high-temperature resistant material of 200℃, and the temperature of the circulating water chiller is set to 20℃. Step 6, recording the remanence in the x, y, and z directions, includes: connecting the triaxial magnetometer system to the host computer and continuously collecting data for 5 minutes; recording the remanence gradient includes: recording the magnetic field value every 0.5 cm change, plotting the magnetic field versus distance curve, and obtaining the magnetic field gradient through polynomial fitting.

[0031] A low-remanence electromagnetic-thermal combined demagnetizing device and method for permalloy-ferrite magnetic shielding is disclosed. This method is particularly suitable for use in ultra-high sensitive magnetic fields and inertial measurements based on atomic spin effects, solving the problem of excessive remanence and remanence gradient after integrated electromagnetic demagnetization of permalloy-ferrite magnetic shielding. Permalloy material has low coercivity and high Curie temperature; multilayer magnetic shielding barrels made from it can easily achieve extremely low remanence and remanence gradient using electromagnetic demagnetization. Ferrite material with high permeability has high coercivity and low Curie temperature; by heating the ferrite magnetic shielding above the material's Curie temperature, perfect demagnetization can be achieved. This invention addresses the permalloy-ferrite combined magnetic shielding system. By electromagnetically demagnetizing the outer layer of multi-layered permalloy, and then heating the inner ferrite magnetic shielding to above the Curie temperature of the material followed by water cooling to room temperature, this electromagnetic-thermal combined demagnetization method achieves near-zero remanence and remanence gradient within the permalloy-ferrite magnetic shielding. This satisfies the stringent requirements of ultra-high sensitivity magnetic fields based on atomic spin effects and inertial measurements for magnetic fields.

[0032] A low-remanence electromagnetic-thermal combined demagnetizing device and method for permalloy-ferrite magnetic shielding includes a multi-layer permalloy magnetic shield (1); a demagnetizing cable (2); a ferrite magnetic shielding cover heating film (3); a ferrite magnetic shielding cover heat-conducting layer (4); a ferrite magnetic shielding cover (5); a water-cooled pipe (6); a ferrite magnetic shielding sidewall heating film (7); a ferrite magnetic shielding sidewall heat-conducting layer (8); a ferrite magnetic shielding sidewall (9); a ferrite magnetic shielding support base (10); a triaxial magnetometer probe (11); a demagnetizer (12); a temperature controller (13); an LCR meter (14); a host computer (15); a triaxial magnetometer counting and display system (16); and a circulating water chiller (17). The electromagnetic-thermal combined demagnetization method first applies electromagnetic demagnetization to the multilayer permalloy magnetic shield (1), then heats the ferrite magnetic shield to above the Curie temperature of the material, and then cools it to room temperature. By using the electromagnetic-thermal combined demagnetization method, the remanence and remanence gradient inside the permalloy-ferrite magnetic shield are brought close to zero.

[0033] The aforementioned low-remanence electromagnetic-thermal combined demagnetizing device and method for permalloy-ferrite magnetic shielding is characterized by the following steps:

[0034] S1: A demagnetizing cable (2) is uniformly wound on a multilayer permalloy magnetic shield (1). The demagnetizing cable (2) is connected to an electromagnetic demagnetizer (12). The electromagnetic demagnetizer generates a sinusoidal current signal that decays with time at 50Hz. The magnetic field corresponding to the maximum current signal generated by the electromagnetic demagnetizer is greater than the saturation magnetization of the permalloy. The current signal decays to zero in 60s.

[0035] S2: Place the triaxial magnetometer probe (11) at the center of the multilayer permalloy magnetic shield (1), and record the residual magnetism in the x, y, and z directions. When the residual magnetism is greater than 1nT, increase the current of the electromagnetic demagnetizer until the residual magnetism is less than 1nT.

[0036] S3: Apply high-temperature double-sided adhesive to the ferrite magnetic shielding cover (5) and attach the ferrite magnetic shielding cover heat-conducting layer (4) and the ferrite magnetic shielding cover heating film (3) in sequence. Use a temperature controller (13) to heat the ferrite magnetic shielding cover (5). Use an LCR meter (14) to measure the permeability of the ferrite magnetic shielding cover (5) at different temperatures. When the permeability is close to zero, record the temperature T1 of the temperature controller at this time.

[0037] S4: Ferrite magnetic shielding sidewall (9) is sequentially covered with ferrite magnetic shielding cover heat-conducting layer (8) and ferrite magnetic shielding cover heating film (7), and the outermost layer is wrapped with water-cooling pipe (6), which is connected to circulating water chiller (17). After being covered, the ferrite magnetic shielding sidewall (9) and the two ferrite magnetic shielding covers (5) are combined to form a complete ferrite magnetic shield and placed on ferrite magnetic shielding support base (10), and then placed in multilayer permalloy magnetic shield (1).

[0038] S5: Use a temperature controller (13) to heat the ferrite magnetic shield to T1 temperature, maintain it for more than two hours, and then turn off the temperature controller to cool it down.

[0039] S6: When the temperature reaches room temperature, place the triaxial magnetometer probe (11) at the center of the ferrite magnetic shield, record the remanence and remanence gradient in the x, y, and z directions, and use it to complete the entire demagnetization process.

[0040] The aforementioned low remanent magnetization electromagnetic-thermal combination demagnetization device and method for permalloy-ferrite magnetic shielding includes a multilayer permalloy magnetic shield (1), characterized in that, in order to prevent the influence of the external environmental magnetic field on the remanent magnetization inside the magnetic shield, the shielding coefficient of the multilayer permalloy magnetic shield (1) is greater than 104.

[0041] The aforementioned low remanence electromagnetic-thermal combined demagnetizing device and method for permalloy-ferrite magnetic shielding includes a ferrite magnetic shielding cover heating film (3), a ferrite magnetic shielding cover heat-conducting layer (4), a water-cooling pipe (6), a ferrite magnetic shielding sidewall heating film (7), and a ferrite magnetic shielding sidewall heat-conducting layer (8), characterized in that it is a material resistant to high temperatures of 200℃.

[0042] The low remanence electromagnetic-thermal combination demagnetizing device and method for permalloy-ferrite magnetic shielding is characterized in that: the cooling method in S5 is to first cool naturally to below 100°C, and then turn on the circulating water chiller (17) connected to the water cooling pipe (6) to perform water cooling. The temperature of the circulating water chiller (17) is set to 20°C.

[0043] The low remanence electromagnetic-thermal combined demagnetizing device and method for permalloy-ferrite magnetic shielding is characterized by the following: The method for recording remanence in three directions in step S6 involves connecting a triaxial magnetometer display system (16) to a host computer (15) and continuously collecting data for 5 minutes. The method for measuring the remanence gradient involves recording the magnetic field value every 0.5 cm change, plotting the magnetic field versus distance curve, and obtaining the magnetic field gradient through polynomial fitting.

[0044] To prevent the influence of the external environmental magnetic field on the residual magnetism inside the magnetic shield, the shielding coefficient of the multilayer permalloy magnetic shield (1) is optimized to be greater than 10⁴. When the multilayer permalloy magnetic shield (1) is placed in a geomagnetic environment for a long time, it will be magnetized by the geomagnetic field. A demagnetizing cable (2) is uniformly wound on it, and the demagnetizing cable is connected to an electromagnetic demagnetizer (12). The electromagnetic demagnetizer generates a 50Hz sinusoidal current signal that decays over time. The magnetic field corresponding to the maximum current signal generated by the electromagnetic demagnetizer is greater than the saturation magnetization of the permalloy, and the current signal decays to zero in 60 seconds.

[0045] The purpose of the heat-conducting layer is to increase the uniformity of heating of the ferrite magnetic shield.

[0046] Turn off the temperature controller to cool down. First, let it cool naturally to below 100°C, then turn on the circulating water chiller (17) connected to the water cooling pipe (6) to cool down with water. The temperature of the circulating water chiller (17) is set to 20°C.

[0047] When the temperature reaches room temperature, place the triaxial magnetometer probe (11) at the center of the ferrite magnetic shield, connect the triaxial magnetometer display system (16) and the host computer (15), and continuously collect data for 5 minutes. The method for measuring the remanent magnetic gradient is as follows: record the magnetic field value every time the distance changes by 0.5 cm, plot the magnetic field versus distance curve, and obtain the magnetic field gradient through polynomial fitting. If the remanence is less than 0.5 nT and the remanent magnetic gradient is less than 0.5 nT / cm, the entire demagnetization process is completed. If the value is greater than the above, increase the heating temperature and the holding time, and repeat the above process.

[0048] Demagnetization experiments were conducted on permalloy-ferrite magnetic shielding using both a single integrated electromagnetic demagnetization method and the electromagnetic-thermal combined demagnetization method proposed in this invention. The following data were obtained through comparison (the permalloy shielding coefficient used in the test was 106, and the Curie temperature of the ferrite magnetic shielding was 80℃):

[0049] Remanence in the x-direction 2nT 0.2nT Remanence in the y direction 0.5nT 0.1nT Z-direction residual magnetism 1.5nT 0.2nT Remanent magnetization gradient in the x-direction 0.6nT / cm 0.3nT / cm Remanent gradient in the y direction 0.5nT / cm 0.3nT / cm Remanent magnetic gradient in the z-direction 0.8nT / cm 0.4nT / cm

[0050] The data above clearly demonstrates that the low remanence electromagnetic-thermal combined demagnetizing device and method for permalloy-ferrite magnetic shielding disclosed in this invention can achieve excellent demagnetizing effects on the remanence and remanence gradient of the permalloy-ferrite magnetic shielding.

[0051] Contents not described in detail in this specification are prior art known to those skilled in the art. It is hereby indicated that the above description is intended to help those skilled in the art understand this invention, but does not limit the scope of protection of this invention. Any equivalent substitutions, modifications, improvements, and / or simplifications of the above descriptions that do not depart from the essential content of this invention fall within the scope of protection of this invention.

Claims

1. An electromagnetic-thermal combined demagnetizing device for demagnetizing low remanence permalloy-ferrite magnetic shielding, characterized in that, The system includes demagnetizing cables wound around the inner and outer layers of the permalloy magnetic shield. The ferrite magnetic shield located within the permalloy magnetic shield is composed of a ferrite magnetic shield cover and ferrite magnetic shield sidewalls. The top surface of the ferrite magnetic shield cover is sequentially affixed with a ferrite magnetic shield cover heat-conducting layer and a ferrite magnetic shield cover heating film. The outer circumferential surface of the ferrite magnetic shield sidewalls is sequentially affixed with a ferrite magnetic shield sidewall heat-conducting layer and a ferrite magnetic shield sidewall heating film. Water-cooling pipes are wound around the ferrite magnetic shield sidewall heating film. A triaxial magnetometer probe is installed at the center of the ferrite magnetic shield. An electromagnetic demagnetizer, a temperature controller, a circulating water chiller, a triaxial magnetometer counting and display system, and a host computer are installed on the outside of the permalloy magnetic shield. The host computer is connected to the triaxial magnetometer probe through the triaxial magnetometer counting and display system. The circulating water chiller is connected to the water cooling pipe. The temperature controller is connected to the heating film on the side wall of the ferrite magnetic shield and the heating film on the cover of the ferrite magnetic shield. The electromagnetic demagnetizer is connected to the demagnetizing cable. After the electromagnetic demagnetizer performs electromagnetic demagnetization on the permalloy magnetic shield, the temperature controller heats the ferrite magnetic shield to above the Curie temperature and then cools it to room temperature. The electromagnetic-thermal combined demagnetization achieves a near-zero remanence and remanence gradient inside the permalloy-ferrite magnetic shield.

2. The electromagnetic-thermal combined demagnetizing device according to claim 1, characterized in that, The ferrite magnetic shield is located on the ferrite magnetic shield support, and the ferrite magnetic shield support is fixed to the inner bottom surface of the permalloy magnetic shield.

3. The electromagnetic-thermal combined demagnetizing device according to claim 1, characterized in that, The permalloy magnetic shield is a multi-layer permalloy magnetic shield.

4. The electromagnetic-thermal combined demagnetizing device according to claim 1, characterized in that, The ferrite magnetic shielding cover is connected to an LCR meter, which is used to measure the permeability of the ferrite magnetic shielding cover.

5. A combined electromagnetic-thermal demagnetization method, characterized in that, It includes the electromagnetic-thermal combined demagnetizing device described in any one of claims 1-4.

6. The electromagnetic-thermal combined demagnetization method according to claim 5, characterized in that, Includes the following steps: Step 1: Demagnetizing cable is uniformly wound on the multilayer permalloy magnetic shield. The demagnetizing cable is connected to the electromagnetic demagnetizer. The electromagnetic demagnetizer generates a 50Hz sinusoidal current signal that decays over time. The magnetic field corresponding to the maximum current signal generated by the electromagnetic demagnetizer is greater than the saturation magnetization of the permalloy. The current signal decays to zero in 60s. Step 2: Place the triaxial magnetometer probe at the center of the multilayer permalloy magnetic shield and record the residual magnetism in the x, y, and z directions. When the residual magnetism is greater than 1 nT, increase the current of the electromagnetic demagnetizer until the residual magnetism is less than 1 nT. Step 3: Apply the thermal conductive layer and heating film of the ferrite magnetic shielding cover to the ferrite magnetic shielding cover in sequence using high-temperature double-sided adhesive. Heat the ferrite magnetic shielding cover using a temperature controller. Measure the permeability of the ferrite magnetic shielding cover at different temperatures using an LCR meter. When the permeability is close to zero, record the temperature T1 of the temperature controller at this time. Step 4: The ferrite magnetic shielding sidewall is sequentially attached with the ferrite magnetic shielding sidewall heat conduction layer and the ferrite magnetic shielding sidewall heating film. The outermost layer is wrapped with a water cooling pipe, which is connected to the circulating water chiller. After the attachment is completed, the ferrite magnetic shielding sidewall and the two ferrite magnetic shielding covers are combined to form a complete ferrite magnetic shield and placed on the ferrite magnetic shielding support base. It is then placed in the multilayer permalloy magnetic shield. Step 5: Use a temperature controller to heat the ferrite magnetic shield to temperature T1 and maintain it for more than two hours. Then turn off the temperature controller and allow it to cool down. Step 6: When the temperature drops to room temperature, place the triaxial magnetometer probe at the center of the ferrite magnetic shield and record the remanence and remanence gradient in the x, y, and z directions. The entire demagnetization process is now complete.

7. The electromagnetic-thermal combined demagnetization method according to claim 6, characterized in that, The shielding coefficient of the multilayer permalloy magnetic shield is greater than 10. 4 .

8. The electromagnetic-thermal combined demagnetization method according to claim 6, characterized in that, The heat-conducting layer is made of a material resistant to high temperatures up to 200℃, and the temperature of the circulating water chiller is set to 20℃.

9. The electromagnetic-thermal combined demagnetization method according to claim 6, characterized in that, The process of recording the remanence in the x, y, and z directions in step 6 includes: connecting the triaxial magnetometer system to the host computer and continuously collecting data for 5 minutes; recording the remanence gradient includes: recording the magnetic field value every time it changes by 0.5 cm, plotting the magnetic field versus distance curve, and obtaining the magnetic field gradient through polynomial fitting.

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