A low-noise magnetic shielding device in liquid nitrogen environment

Abstract

A low-noise magnetic shielding device for liquid nitrogen environments provides a stable, weak magnetic field environment for ultra-high-sensitivity magnetic field measurement devices, inertial measurement devices, and basic physics experimental equipment. The device primarily consists of a cooling chamber, sealing studs, a cooling chamber cover, a ferrite barrel, a temperature sensor, and a gasket. The ferrite barrel is placed in a cooling chamber filled with liquid nitrogen. By utilizing the low temperature of liquid nitrogen, the device reduces the magnetic noise generated by the ferrite barrel. This device can significantly improve the sensitivity of measurement devices that are otherwise limited by the magnetic noise generated by the magnetic shielding device.

Description

Technical Field

[0001] The present invention relates to the field of magnetic shielding technology, in particular to a low-noise magnetic shielding device in a liquid nitrogen environment, which can provide a stable weak magnetic environment for ultra-high-sensitivity magnetic field measurement devices, inertial measurement devices and basic physics experimental devices. Background Art

[0002] Ultra-high-sensitivity magnetic field and inertial measurements based on the atomic spin effect require, on the one hand, reducing the ambient magnetic field, thereby narrowing the magnetic field measurement range and improving sensitivity to extremely weak magnetic fields; on the other hand, lowering the magnetic field background noise of the shielding environment to ensure it is below the magnetic field measurement sensitivity, thereby fully utilizing the ultra-high-sensitivity magnetic field measurement capabilities of atomic spin. Therefore, multi-layer magnetic shielding barrels are typically constructed from high-permeability permalloy and high-resistivity ferrite materials to effectively attenuate the Earth's magnetic field while reducing the shielding barrel's magnetic noise.

[0003] Manganese-zinc ferrite with high resistivity and low hysteresis loss is used in the innermost layer of the multi-layer magnetic shielding barrel, and has achieved 0.7fT / Hz. 1 / 2 The magnetic noise level at @30Hz is low, but further reduction of magnetic noise is difficult to achieve, and has become a bottleneck restricting further improvement of magnetic field measurement and inertial measurement sensitivity. A new ultra-low noise magnetic shielding system needs to be designed to solve this problem. Summary of the Invention

[0004] The technical problem solved by the present invention is: to overcome the difficulty in further reducing the magnetic noise of the existing magnetic shielding barrel to meet the requirements of ultra-high sensitivity measurement, and to provide a low-noise magnetic shielding device in a liquid nitrogen environment, which can reduce the magnetic noise by four times.

[0005] The technical solutions of the present invention are as follows:

[0006] A low-noise magnetic shielding device in a liquid nitrogen environment is characterized by including a cooling chamber, wherein the cooling chamber has an outer peripheral wall extending upward from a chassis and an inner peripheral wall forming a central cavity, an annular cavity is formed between the outer peripheral wall and the inner peripheral wall, a ferrite barrel with a temperature sensor attached to the surface is located in the annular cavity, the left side, right side, front side and rear side of the waist of the cooling chamber are provided with screw holes, sealing studs are provided in the screw holes, the liquid nitrogen in the annular cavity immerses the ferrite barrel to reduce magnetic noise caused by Johnson current, and a cooling chamber cover is provided on the top of the cooling chamber.

[0007] A gasket is provided on the bottom surface of the annular cavity.

[0008] The material of the cooling chamber is polytetrafluoroethylene.

[0009] The temperature sensor adopts a platinum thermal resistor PT100 or a platinum thermal resistor PT1000, which is used to monitor the temperature of the ferrite barrel wall. The lead of the temperature sensor is led out from the hole left on the cooling chamber cover.

[0010] The cooling chamber cover is fixed to the top of the cooling chamber by screws.

[0011] The sealing stud is sealed with vacuum silicone grease to prevent liquid nitrogen from leaking out of the cooling cavity.

[0012] The cooling chamber cover is provided with four through holes, one for the lead outlet of the temperature sensor, one for the demagnetization line outlet, one for the liquid nitrogen replenishment port, and the remaining one for the exhaust hole.

[0013] The material of the ferrite barrel is manganese-zinc ferrite material, and the demagnetization coil wound on the surface of the ferrite barrel is led out from the hole on the cooling chamber cover.

[0014] The magnetic noise of the ferrite barrel is composed of hysteresis noise and Johnson current noise, among which hysteresis noise is the main magnetic noise. The magnetic noise calculation formula of the ferrite barrel with radius r, length L and thickness t is as follows:

[0015]

[0016] where δB L hyst (T) is the magnetic noise, μ0 is the vacuum magnetic permeability, k is the Boltzmann constant, T is the Kelvin temperature, G(α) is a factor related to the aspect ratio of the ferrite barrel, the aspect ratio α = L / 2r, μ′(T) is the real part of the ferrite complex permeability, μ″(T) is the imaginary part of the ferrite complex permeability, μ′(T) and μ″(T) are both temperature-dependent, and f is the frequency. The formula is used to calculate the magnetic noise of the ferrite barrel at different temperatures and sizes. At liquid nitrogen temperature, the magnetic noise is reduced by 3 to 5 times compared to room temperature.

[0017] The technical effects of the present invention are as follows: The present invention provides a low-noise magnetic shielding device in a liquid nitrogen environment, which can overcome the problem that the existing magnetic shielding barrel has high magnetic noise and is difficult to meet the requirements of ultra-high sensitivity physical quantity measurement. The present invention first places a gasket at the bottom of the cooling chamber, then places a ferrite barrel with a temperature sensor attached to the surface into the cooling chamber, rotates the sealing stud into a hole coaxial with the cooling chamber and the ferrite barrel, and pours liquid nitrogen into the cooling chamber until the ferrite barrel is submerged. Cover the cooling chamber with a cover and fix the cooling chamber and the cooling chamber cover with screws. The low-noise manganese-zinc ferrite is placed in a liquid nitrogen environment to reduce the temperature of the manganese-zinc ferrite, thereby reducing the magnetic noise. The cooling chamber, the cooling chamber cover and the sealing stud are made of polytetrafluoroethylene. The use of plastic materials with extremely high impedance instead of titanium steel, silver-plated glass, nickel-layered glass and other materials as liquid nitrogen containers reduces the magnetic noise caused by Johnson current.

[0018] Compared with the existing technology, the present invention: the conventional manganese-zinc ferrite magnetic shielding barrel at room temperature has large magnetic noise and cannot meet the magnetic field measurement of ultra-high sensitivity physical quantities. The present invention makes a cooling cavity and immerses the ferrite in liquid nitrogen to make a low-temperature magnetic shielding device, thereby reducing the magnetic noise of the device and meeting the application requirements of low magnetic field noise. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The figure is a schematic structural diagram of a low-noise magnetic shielding device in a liquid nitrogen environment according to the present invention.

[0020] Figure 2 for Figure 1 Schematic diagram of the cooling chamber structure.

[0021] Figure 3 for Figure 1 Schematic diagram of the cooling chamber cover structure.

[0022] Figure 4 for Figure 3 Schematic diagram of the cross-section structure.

[0023] The reference numerals are listed as follows: 1 - ferrite barrel; 2 - temperature sensor; 3 - gasket; 4 - cooling chamber cover; 5 - cooling chamber; 6 - sealing stud. DETAILED DESCRIPTION

[0024] Below is the attached figure ( Figures 1-4 ) and Examples illustrate the present invention.

[0025] Figure 1 The figure is a schematic structural diagram of a low-noise magnetic shielding device in a liquid nitrogen environment according to the present invention. Figure 2 for Figure 1 Schematic diagram of the cooling chamber structure. Figure 3 for Figure 1 Schematic diagram of the cooling chamber cover structure. Figure 4 for Figure 3 Schematic diagram of the cross-section structure. Figures 1 to 4 As shown, a low-noise magnetic shielding device in a liquid nitrogen environment includes a cooling chamber 5, wherein the cooling chamber 5 has an outer peripheral wall extending upward from a chassis and an inner peripheral wall forming a central cavity, wherein an annular cavity is formed between the outer peripheral wall and the inner peripheral wall, and a ferrite barrel 1 with a temperature sensor 2 attached to its surface is located in the annular cavity, and screw holes are provided on the left, right, front and rear sides of the waist of the cooling chamber, wherein sealing studs 6 are provided in the screw holes, and the liquid nitrogen in the annular cavity immerses the ferrite barrel 1 to reduce the magnetic noise caused by the Johnson current, and a cooling chamber cover 4 is provided on the top of the cooling chamber 5.

[0026] A gasket 3 is provided on the bottom surface of the annular cavity. The material of the cooling cavity 5 is polytetrafluoroethylene. The temperature sensor 2 adopts a platinum thermal resistor PT100 or a platinum thermal resistor PT1000, which is used to monitor the temperature of the barrel wall of the ferrite barrel 1. The lead of the temperature sensor 2 is led out from the hole left on the cooling cavity cover 4. The cooling cavity cover 4 is fixed to the top of the cooling cavity 5 by screws. The sealing stud 6 is sealed with vacuum silicone grease to prevent liquid nitrogen from leaking out of the cooling cavity. There are four through holes on the cooling cavity cover 4, one for the lead outlet of the temperature sensor 2, one for the demagnetization line outlet, one for the liquid nitrogen replenishment port, and the remaining one is an exhaust hole. The material of the ferrite barrel 1 is manganese-zinc ferrite material, and the demagnetization coil wound on the surface of the ferrite barrel 1 is led out from the hole on the cooling cavity cover 4.

[0027] The magnetic noise of the ferrite barrel is composed of hysteresis noise and Johnson current noise, among which hysteresis noise is the main magnetic noise. The magnetic noise calculation formula of the ferrite barrel with radius r, length L and thickness t is as follows:

[0028]

[0029] where δB L hyst (T) is the magnetic noise, μ0 is the vacuum magnetic permeability, k is the Boltzmann constant, T is the Kelvin temperature, G(α) is a factor related to the aspect ratio of the ferrite barrel, the aspect ratio α = L / 2r, μ′(T) is the real part of the ferrite complex permeability, μ″(T) is the imaginary part of the ferrite complex permeability, μ′(T) and μ″(T) are both temperature-dependent, and f is the frequency. The formula is used to calculate the magnetic noise of the ferrite barrel at different temperatures and sizes. At liquid nitrogen temperature, the magnetic noise is reduced by 3 to 5 times compared to room temperature.

[0030] A low-noise magnetic shielding device for liquid nitrogen environments provides a stable, weak magnetic field environment for ultra-high-sensitivity magnetic field measurement devices, inertial measurement devices, and basic physics experimental equipment. The device primarily consists of a cooling chamber, sealing studs, a cooling chamber cover, a ferrite barrel, a temperature sensor, and a gasket. The ferrite barrel is placed in a cooling chamber filled with liquid nitrogen. By utilizing the low temperature of liquid nitrogen, the device reduces the magnetic noise generated by the ferrite barrel. This device can significantly improve the sensitivity of measurement devices that are otherwise limited by the magnetic noise generated by the magnetic shielding device.

[0031] A low-noise magnetic shielding device in a liquid nitrogen environment, consisting of Figure 1It can be seen that the device of the present invention includes a ferrite barrel 1, a temperature sensor 2, a gasket 3, a cooling chamber cover 4, a cooling chamber 5, and a sealing stud 6. First, the gasket (3) is placed at the bottom of the cooling chamber (5), and then the ferrite barrel (1) with the temperature sensor (2) attached to the surface is placed into the cooling chamber (5). The sealing stud (6) is rotated into the coaxial hole of the cooling chamber (5) and the ferrite barrel (1). Liquid nitrogen is poured into the cooling chamber (5) until it covers the ferrite barrel (1). The cooling chamber cover (4) is covered and the cooling chamber (5) and the cooling chamber cover (4) are fixed with screws.

[0032] The material of the cooling chamber (5) is polytetrafluoroethylene. This material does not become brittle at liquid nitrogen temperature and has good temperature characteristics. Using plastic materials with high impedance instead of titanium steel, silver-plated glass, nickel-coated glass and other materials as liquid nitrogen containers reduces magnetic noise caused by Johnson current.

[0033] The temperature sensor (2) is a PT100 or PT1000 sensor, and is used to monitor the temperature of the ferrite barrel wall. The lead of the temperature sensor (2) is led out from the hole left on the cooling chamber cover (4).

[0034] The material of the ferrite barrel (1) is manganese-zinc ferrite material. The demagnetization coil wound on the surface of the ferrite barrel (1) is led out from the hole on the cooling chamber cover (4). The magnetic noise of this material is composed of hysteresis noise and Johnson current noise, among which hysteresis noise is the main magnetic noise. The magnetic noise calculation formula of the ferrite barrel (1) with a radius of r, a length of L, and a thickness of t is:

[0035]

[0036] Where μ0 is the vacuum permeability, k is the Boltzmann constant, T is the Kelvin temperature, G(α) is a factor related to the ferrite's aspect ratio (α = L / 2r), μ′(T) is the real part of the ferrite's complex permeability, μ″(T) is the imaginary part of the ferrite's complex permeability, and both μ′(T) and μ″(T) are temperature-dependent. f is the frequency. This formula can be used to calculate the magnetic noise of ferrite barrel 1 at different temperatures and sizes. At liquid nitrogen temperature, magnetic noise can be reduced by approximately four times compared to room temperature.

[0037] After the sealing stud (6) is rotated into the cooling chamber (5), the two surfaces in contact with the air need to be sealed with vacuum silicone grease to prevent the liquid nitrogen from leaking out of the cooling chamber (5).

[0038] The cooling chamber cover (4) is made of polytetrafluoroethylene and has four through holes, one for the lead outlet of the temperature sensor (2), one for the demagnetization line outlet, one for the liquid nitrogen replenishment port, and the remaining one for the exhaust hole.

[0039] Any content not described in detail in this specification is prior art known to those skilled in the art. It should be noted that the above description is intended to help those skilled in the art understand the present invention, but does not limit the scope of protection of the present invention. Any equivalent substitution, modification, improvement, and / or simplification of the above description that does not depart from the essence of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A low-noise magnetic shielding device in a liquid nitrogen environment, characterized in that: The cooling chamber comprises a cooling chamber having an outer peripheral wall extending upward from the chassis and an inner peripheral wall forming a central cavity. An annular cavity is formed between the outer peripheral wall and the inner peripheral wall. A ferrite barrel with a temperature sensor attached to its surface is located within the annular cavity. Screw holes are provided on the left, right, front, and rear sides of the waist of the cooling chamber. Sealing studs are provided in the screw holes. Liquid nitrogen in the annular cavity submerges the ferrite barrel to reduce magnetic noise caused by Johnson current. A cooling chamber cover is provided on the top of the cooling chamber. The material of the cooling chamber is polytetrafluoroethylene; The material of the ferrite barrel is manganese-zinc ferrite material, and the degaussing coil wound on the surface of the ferrite barrel is led out from the hole on the cooling chamber cover; The magnetic noise of the ferrite barrel is composed of hysteresis noise and Johnson current noise, among which hysteresis noise is the main magnetic noise. The magnetic noise calculation formula of the ferrite barrel with radius r, length L and thickness t is as follows: where δB L hyst (T) is the magnetic noise, μ0 is the vacuum magnetic permeability, k is the Boltzmann constant, T is the Kelvin temperature, G(α) is a factor related to the aspect ratio of the ferrite barrel, the aspect ratio α = L / 2r, μ′(T) is the real part of the ferrite complex permeability, μ″(T) is the imaginary part of the ferrite complex permeability, μ′(T) and μ″(T) are both temperature-dependent, and f is the frequency. The formula is used to calculate the magnetic noise of the ferrite barrel at different temperatures and sizes. At liquid nitrogen temperature, the magnetic noise is reduced by 3 to 5 times compared to room temperature.

2. The low-noise magnetic shielding device in a liquid nitrogen environment according to claim 1, characterized in that: A gasket is provided on the bottom surface of the annular cavity.

3. The low-noise magnetic shielding device in a liquid nitrogen environment according to claim 1, characterized in that: The temperature sensor adopts a platinum thermal resistor PT100 or a platinum thermal resistor PT1000, which is used to monitor the temperature of the ferrite barrel wall. The lead of the temperature sensor is led out from the hole left on the cooling chamber cover.

4. The low-noise magnetic shielding device in a liquid nitrogen environment according to claim 1, characterized in that: The cooling chamber cover is fixed to the top of the cooling chamber by screws.

5. The low-noise magnetic shielding device in a liquid nitrogen environment according to claim 1, characterized in that: The sealing stud is sealed with vacuum silicone grease to prevent liquid nitrogen from leaking out of the cooling cavity.

6. The low-noise magnetic shielding device in a liquid nitrogen environment according to claim 1, characterized in that: The cooling chamber cover is provided with four through holes, one for the lead outlet of the temperature sensor, one for the demagnetization line outlet, one for the liquid nitrogen replenishment port, and the remaining one for the exhaust hole.

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