Large-size double-layer splicing type ferrite magnetic shielding structure

Abstract

The invention relates to a large-size double-layer splicing type ferrite magnetic shielding structure, in particular to a low-noise magnetic shielding barrel structure which is particularly suitable for an ultra-high sensitive magnetic field and inertial measurement device and miniaturization integration application of the ultra-high sensitive magnetic field and inertial measurement device. The magnetic shielding barrel is manufactured by splicing single large-size ferrite blocks into a double-layer cylinder. And the seam at the splicing part of the inner layer is blocked by the ferrite on the outer layer, so that the splicing does not generate large magnetic flux leakage. The double-layer configuration improves the shielding coefficient and reduces the magnetic noise at the same time. The novel large-size double-layer splicing type ferrite magnetic shielding structure shielding barrel is simple in processing technology, the shielding effect is not affected while the material cost is saved, the magnetic noise is reduced through the double-layer barrel structure, and the defect that the magnetic noise caused by a traditional single-layer ferrite magnetic shielding barrel cannot be further reduced is overcome.

Description

Technical Field

[0001] The invention relates to the technical field of magnetic shielding, in particular to a large-size double-layer spliced ​​ferrite magnetic shielding structure, in which a double-layer ferrite magnetic shielding barrel is realized by splicing a single large-size ferrite. Background Art

[0002] One of the necessary conditions for the magnetic field measurement method based on the SERF effect (SERF, Spin-Exchange Relaxation-Free, no spin exchange relaxation) is to attenuate the approximately 30000-50000 nT magnetic field that is prevalent on the earth's surface to the nT or even pT level through magnetic shielding technology to provide extremely weak magnetic field environment measurement conditions. In order to reduce the residual magnetism, the magnetic shielding with a high shielding coefficient currently usually uses a multi-layer magnetic shielding configuration made of a high magnetic permeability metal material Permalloy to shield the external magnetic field, but at the same time, its high conductivity will inevitably produce a large eddy current magnetic noise, thereby restricting the sensitivity of the magnetic field and inertial measurement device, hindering the further application of ultra-sensitive magnetic field and inertial measurement. Since the conductivity of high magnetic permeability ferrite is much lower than that of Permalloy, the ferrite magnetic shielding made of it can effectively reduce magnetic noise. Traditional ferrite is restricted by the manufacturing process, and a single ferrite ring cannot be further enlarged. The magnetic noise level has reached the theoretical limit and cannot meet the higher sensitivity requirements of ultra-high sensitivity magnetic field measurement. It is necessary to design a large-size double-layer spliced ​​ferrite magnetic shielding structure to solve the above problems. Summary of the invention

[0003] In view of the defects or shortcomings in the prior art, the present invention provides a large-sized double-layer spliced ​​ferrite magnetic shielding structure, which is made into a magnetic shielding barrel by splicing a single large-sized ferrite into a double-layer cylindrical barrel shape to meet the application needs of low magnetic field noise.

[0004] The technical solution of the present invention is as follows: A large-sized double-layer spliced ​​ferrite magnetic shielding structure, characterized in that it includes an outer barrel and an inner barrel arranged in the outer barrel, the inner barrel includes an inner ferrite body with a cylindrical structure, the upper and lower openings of the inner ferrite body are covered with respective inner ferrite covers, the outer barrel includes an outer ferrite body with a cylindrical structure, the upper and lower openings of the outer ferrite body are covered with respective outer ferrite covers, the outer ferrite cover and the inner ferrite cover both adopt a fan-shaped splicing structure, the annular surfaces of the inner ferrite body and the outer ferrite body both adopt a circumferentially segmented splicing structure, and the barrels of the inner ferrite body and the outer ferrite body both adopt an axially segmented splicing structure.

[0005] The inner layer axial segmented splicing seams and the outer layer axial segmented splicing seams are staggered, and the outer layer circumferential segmented splicing seams and the inner layer circumferential segmented splicing seams are staggered.

[0006] The outer barrel is located in a sleeve with a sleeve cover.

[0007] The waists of the outer barrel and the inner barrel are provided with penetrating radial light-through holes.

[0008] The inner surfaces of the inner ferrite body and the inner ferrite cover are provided with an inner ferrite support, the outer surface of the inner ferrite body is wrapped with an inner ferrite thermal demagnetization film, the outer ferrite body is located in the outer ferrite ring, the outer surface of the outer ferrite body is wrapped with an outer ferrite thermal demagnetization film, an inner ferrite cover fixing piece is provided between the inner ferrite cover and the outer ferrite cover, and the outer surface of the outer ferrite cover is provided with an outer ferrite cover fixing piece.

[0009] The outer diameter of the inner ferrite body is φ270mm, the outer diameter of the outer ferrite body is φ350mm, the wall thickness of the inner ferrite body and the outer ferrite body are both δ25mm~30mm, the diameter φ of the inner ferrite cover is 270mm, the diameter of the outer ferrite cover is φ350mm, and the thickness of the inner ferrite cover and the outer ferrite cover are both δ25mm~30mm.

[0010] Include the following expressions: , in P eddy is the eddy current power loss, V is the voltage, σ is the conductivity, E is the electric field strength, P hyst is the hysteresis loss, ω is the angular frequency, μ '' is the imaginary part of the complex magnetic permeability, H is the magnetic field intensity, δB is magnetic noise, δB hyst is the hysteresis loss noise, k is the Boltzmann constant, T is the Kelvin temperature, A is the coil area, I is the power consumption, and f is the oscillation frequency.

[0011] The technical effects of the present invention are as follows: The present invention is a large-sized double-layer spliced ​​ferrite magnetic shielding structure, which is a low-noise magnetic shielding barrel structure particularly suitable for ultra-high sensitivity magnetic field and inertial measurement devices and their miniaturized integrated applications. A magnetic shielding barrel is made by splicing a single large-sized ferrite block into a double-layer cylinder. The seams at the inner layer splicing are blocked by the outer layer of ferrite, so the splicing will not produce large leakage magnetic flux. The double-layer configuration reduces magnetic noise while improving the shielding coefficient. The shielding barrel of the new large-sized double-layer spliced ​​ferrite magnetic shielding structure has a simple processing process, saves material costs, and does not affect the shielding effect. The configuration of the double-layer barrel reduces magnetic noise, solving the problem that the magnetic noise brought by the traditional single-layer ferrite magnetic shielding barrel cannot be further reduced.

[0012] Compared with the prior art, the present invention can further reduce the magnetic field noise of the conventional single-layer ferrite magnetic shielding barrel. The present invention can make a double-layer cylindrical barrel by splicing a single large-sized ferrite. The double-layer configuration can further increase the magnetic shielding coefficient. At the same time, the large-sized ferrite barrel has lower magnetic noise, and is made into a magnetic shielding barrel to meet the application requirements of low magnetic field noise. The structure of the present invention is also more conducive to processing and material saving. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a structural schematic diagram of a large-size double-layer spliced ​​ferrite magnetic shielding structure of the present invention.

[0014] Figure 2 yes Figure 1 Schematic diagram of the main structure of the middle and inner layer ferrite.

[0015] Figure 3 yes Figure 1 Schematic diagram of the main structure of the middle and outer layer ferrite.

[0016] The reference numerals in the accompanying drawings are explained as follows: 1-inner ferrite support; 2-inner ferrite body (cylindrical structure); 3-inner ferrite cover (circular plate structure, including inner upper cover and inner bottom cover); 4-inner ferrite thermal demagnetization film (wound on the outer wall of the inner ferrite body); 5-inner ferrite cover fixing member; 6-outer ferrite body (cylindrical structure); 7-outer ferrite cover (circular plate structure, including outer upper cover and outer bottom cover); 8-outer ferrite thermal demagnetization film (wound on the outer wall of the outer ferrite body); 9-outer ferrite cover fixing member (respectively arranged between the outer bottom cover and the inner bottom cover, and between the outer upper cover and the inner upper cover); 10-outer ferrite collar; 11-sleeve (with a sleeve bottom); 12-sleeve cover; 13-radial light-through hole (including transverse hole and longitudinal hole). DETAILED DESCRIPTION

[0017] Below is the attached figure ( Figure 1-Figure 3 ) and examples illustrate the present invention.

[0018] Figure 1 It is a structural schematic diagram of a large-size double-layer spliced ​​ferrite magnetic shielding structure of the present invention. Figure 2 yes Figure 1 Schematic diagram of the main structure of the middle and inner layer ferrite. Figure 3 yes Figure 1 Schematic diagram of the main structure of the middle and outer layers of ferrite. Figures 1 to 3 As shown, a large-sized double-layer spliced ​​ferrite magnetic shielding structure includes an outer barrel and an inner barrel arranged in the outer barrel, the inner barrel includes an inner ferrite body 2 with a cylindrical structure, the upper and lower openings of the inner ferrite body 2 are covered with respective inner ferrite covers 3, the outer barrel includes an outer ferrite body 6 with a cylindrical structure, the upper and lower openings of the outer ferrite body 6 are covered with respective outer ferrite covers 7, the outer ferrite covers 7 and the inner ferrite cover 3 both adopt a fan-shaped splicing structure (for example, 3 fan-shaped splicing, each fan-shaped angle is 120 degrees), the annular surfaces of the inner ferrite body 2 and the outer ferrite body 6 both adopt a circumferential segmented splicing structure (for example, uniform 3-segment splicing, each segment angle is 120 degrees), and the barrels of the inner ferrite body 2 and the outer ferrite body 6 both adopt an axial segmented splicing structure (for example, the inner layer is axially uniformly spliced ​​with 5 segments, and the outer layer is axially uniformly spliced ​​with 7 segments).

[0019] The inner axial segmented joint seams are staggered with the outer axial segmented joint seams, and the outer circumferential segmented joint seams are staggered with the inner circumferential segmented joint seams. The outer barrel is located in a sleeve 11 with a sleeve cover 12. The waist of the outer barrel and the inner barrel is provided with a radial light-through hole 13. The inner surface of the inner ferrite body 2 and the inner ferrite cover 3 is provided with an inner ferrite support 1, and the outer surface of the inner ferrite body 2 is wrapped with an inner ferrite thermal demagnetization film 4. The outer ferrite body 6 is located in an outer ferrite collar 10, and the outer surface of the outer ferrite body 6 is wrapped with an outer ferrite thermal demagnetization film 8. An inner ferrite cover fixing part 5 is provided between the inner ferrite cover 3 and the outer ferrite cover 7, and an outer ferrite cover fixing part 9 is provided on the outer surface of the outer ferrite cover 7.

[0020] The outer diameter of the inner ferrite body 2 is φ270mm, the outer diameter of the outer ferrite body 6 is φ350mm, the wall thickness of the inner ferrite body 2 and the outer ferrite body 6 are both δ25mm~30mm, the diameter φ of the inner ferrite cover 3 is 270mm, the diameter of the outer ferrite cover 7 is φ350mm, and the thickness of the inner ferrite cover 3 and the outer ferrite cover 7 are both δ25mm~30mm.

[0021] Include the following expressions: , in P eddy is the eddy current power loss, V is the voltage, σ is the conductivity, E is the electric field strength, P hyst is the hysteresis loss, ω is the angular frequency, μ '' is the imaginary part of the complex magnetic permeability, H is the magnetic field intensity, δB is magnetic noise, δB hyst is the hysteresis loss noise, k is the Boltzmann constant, T is the Kelvin temperature, A is the coil area, I is the power consumption, and f is the oscillation frequency.

[0022] Depend on Figure 1 It can be seen that the device of the present invention includes an inner ferrite support 1, an inner ferrite body 2, an inner ferrite cover 3, an inner ferrite thermal demagnetization film 4, an inner ferrite cover fixing part 5, an outer ferrite body 6, an outer ferrite cover 7, an outer ferrite thermal demagnetization film 8, an outer ferrite cover fixing part 9, an outer ferrite ring 10, a sleeve 11, a sleeve cover 12, and a radial light hole 13. Figure 2 It shows the new large-size double-layer spliced ​​inner ferrite body 2 structure, which consists of Figure 2 It can be seen that the main single-layer structure is composed of three large-sized ferrite ring blocks. Figure 3 It shows that the new large-size double-layer spliced ​​outer ferrite body 6 structure consists of Figure 2 It can be seen that the main single-layer structure is spliced ​​together by three large-sized ferrite ring blocks, and its size is larger than that of the inner layer ferrite main body 2.

[0023] The shielding body includes an inner ferrite body 2, an inner ferrite cover 3, an outer ferrite body 6, and an outer ferrite cover 7. A radial light hole 13 has been reserved. When the laser needs to irradiate the inside of the shielding barrel in the axial direction, an axial light hole can be opened on the inner ferrite support 1, the inner ferrite cover 3, the inner ferrite thermal demagnetization film 4, the inner ferrite cover fixing part 5, the outer ferrite cover 7, the outer ferrite thermal demagnetization film 8, the outer ferrite cover fixing part 9, the sleeve 11, and the sleeve cover 12. The size of the light hole is larger than the spot diameter of the laser. The inner ferrite body 2 is supported by the inner ferrite support 1. The outer ferrite thermal demagnetization film 8 and the inner ferrite thermal demagnetization film 4 are intended to be fixed by adhesive bonding. The outer ferrite collar 10 is locked with a three-layer collar plus a non-magnetic Peek screw. Finally, the sleeve 11 and the sleeve cover 12 are added to fix the whole structure.

[0024] Compared with traditional ferrite, the structure of the present invention has more seams, but the seams of the inner ferrite barrel are blocked by the outer layer, the magnetic leakage is further reduced, and the shielding coefficient is further increased through simulation. At the same time, the double-layer configuration is equivalent to a single barrel with increased wall thickness, and its magnetic noise is further suppressed while breaking through the process limitations of the single-layer ferrite barrel. Generally, magnetic noise mainly comes from the irregular thermal motion of electrons in the shielding material and the thermal fluctuations of the magnetic domain. The irregular thermal motion of electrons in the conductor material, especially in the case of uneven temperature distribution, will produce a weak Johnson thermal current; and the thermal fluctuations of the magnetic domain will also cause induced currents, and the superposition of these current pulses will form thermal noise. According to the Nay equation, magnetic noise can be calculated by energy loss in the material, and magnetic noise and power loss are linked by energy spectrum density, and complex magnetic noise calculations are converted into loss solutions. For ferrite materials with higher resistivity, hysteresis loss dominates at frequencies below 100 Hz, and eddy current loss and excess loss are much lower than hysteresis loss. When calculating the magnetic noise of ferrite materials, only the thermal magnetization noise can be calculated and the Johnson current noise can be ignored.

[0025] Magnetic noise can be calculated based on the power loss in the source material. In a magnetic shield, the magnetic noise at any point is caused by the dissipated power of the material. Assume that there is an excitation coil in the shielding barrel, and an oscillating current flows in the coil, which causes power loss in the magnetic shielding barrel material. According to Faraday's law, when the magnetic field fluctuates, the pickup coil will generate a power spectral density of S B (f) Fluctuating voltage , Where A is the coil area, N is the number of turns, and ω is the angular frequency. At the same time, the fluctuation dissipation theorem shows that the fluctuation voltage of the pickup coil has the following relationship , Where T is the Kelvin temperature, k is the Boltzmann constant, and Reff is the effective resistance. Consider the time-averaged power consumption caused by the oscillating current ,

[0026] The magnetic noise formula is derived from the above formula:

[0027] For the high permeability ferrite used in the present invention, the main sources of power dissipation are eddy current power loss and hysteresis loss, which are expressed as follows: , in μ ''is the imaginary part of the complex permeability, σ is the conductivity, E is the electric field strength, and H is the magnetic field strength.

[0028] At low frequencies (<100 Hz), the main magnetic noise of ferrite magnetic shielding is hysteresis loss, and the magnetic noise can be expressed as:

[0029] A novel large-scale double-layer spliced ​​ferrite magnetic shielding structure, from inside to outside, is an inner ferrite support 1, an inner ferrite body 2, an inner ferrite cover 3 divided into an upper and lower cover, an outer ferrite body 6, and an outer ferrite sleeve 10 three layers are screwed and locked, and a sleeve 11 fixes the overall structure. The inner ferrite thermal demagnetization film 4 and the outer ferrite thermal demagnetization film 8 are evenly wound on the outer side of the inner ferrite body 2 and the outer ferrite body 6, and finally the inner ferrite cover 3 is fixed by the inner ferrite cover fixing part 5; the outer ferrite cover fixing part 9 fixes the outer ferrite cover 7 and the sleeve cover 12 respectively, and finally the large-scale double-layer spliced ​​ferrite magnetic shielding is closed.

[0030] A novel large-size double-layer spliced ​​ferrite magnetic shielding structure includes a Permalloy strip, an inner ferrite body 2, an inner ferrite cover 3, an outer ferrite body 6, and an outer ferrite cover 7, all of which are spliced ​​from a single large-size ferrite block.

[0031] The inner ferrite support 1, the inner ferrite cover fixing part 5, the outer ferrite cover fixing part 9, the outer ferrite ring 10, the sleeve 11, and the sleeve cover 12 are all made of non-magnetic epoxy resin material, which has excellent temperature, non-magnetic properties and excellent mechanical properties, and is used to support, position and carry the ferrite shielding barrel.

[0032] The inner ferrite thermal demagnetization film 4 and the outer ferrite thermal demagnetization film 8 are tightly wound on the outer walls of the inner ferrite body 2 and the outer ferrite body 6, and are demagnetized and heated to above the Curie temperature for one hour. When the temperature is above the Curie point, the magnetic induction intensity generated by the thermal demagnetization film is much larger than the saturation magnetization intensity of the magnetic shielding barrel.

[0033] The outer diameter of the inner ferrite body is φ270mm, and the wall thickness of the inner ferrite body is δ25mm~30mm. The outer diameter of the outer ferrite body is φ350mm, and the wall thickness of the outer ferrite body is δ25mm~30mm. The inner ferrite cover (inner upper cover and inner bottom cover) are both φ270mm in diameter and δ25mm~30mm in thickness. The outer ferrite cover (outer upper cover and outer bottom cover) are both φ350mm in diameter and δ25mm~30mm in thickness.

[0034] The contents not described in detail in the specification of the present invention belong to the prior art known to the professional and technical personnel in the field. It is pointed out here that the above description helps those skilled in the art to understand the invention, but does not limit the protection scope of the invention. Any equivalent replacement, modification and / or simplification of the above description without departing from the essence of the invention falls within the protection scope of the invention.

Claims

1. A large-size double-layer spliced ​​ferrite magnetic shielding structure, characterized in that: It includes an outer barrel and an inner barrel arranged in the outer barrel, the inner barrel includes an inner ferrite body with a cylindrical structure, the upper and lower openings of the inner ferrite body are covered with respective inner ferrite covers, the outer barrel includes an outer ferrite body with a cylindrical structure, the upper and lower openings of the outer ferrite body are covered with respective outer ferrite covers, the outer ferrite cover and the inner ferrite cover both adopt a fan-shaped splicing structure, the annular surfaces of the inner ferrite body and the outer ferrite body both adopt a circumferentially segmented splicing structure, and the barrels of the inner ferrite body and the outer ferrite body both adopt an axially segmented splicing structure.

2. The large-size double-layer spliced ​​ferrite magnetic shielding structure according to claim 1 is characterized in that: The inner layer axial segmented splicing seams and the outer layer axial segmented splicing seams are staggered, and the outer layer circumferential segmented splicing seams and the inner layer circumferential segmented splicing seams are staggered.

3. The large-size double-layer spliced ​​ferrite magnetic shielding structure according to claim 1 is characterized in that: The outer barrel is located in a sleeve with a sleeve cover.

4. The large-size double-layer spliced ​​ferrite magnetic shielding structure according to claim 1 is characterized in that: The waists of the outer barrel and the inner barrel are provided with penetrating radial light-through holes.

5. The large-size double-layer spliced ​​ferrite magnetic shielding structure according to claim 1 is characterized in that: The inner surfaces of the inner ferrite body and the inner ferrite cover are provided with an inner ferrite support, the outer surface of the inner ferrite body is wrapped with an inner ferrite thermal demagnetization film, the outer ferrite body is located in the outer ferrite ring, the outer surface of the outer ferrite body is wrapped with an outer ferrite thermal demagnetization film, an inner ferrite cover fixing piece is provided between the inner ferrite cover and the outer ferrite cover, and the outer surface of the outer ferrite cover is provided with an outer ferrite cover fixing piece.

6. The large-size double-layer spliced ​​ferrite magnetic shielding structure according to claim 1 is characterized in that: The outer diameter of the inner ferrite body is φ270mm, the outer diameter of the outer ferrite body is φ350mm, the wall thickness of the inner ferrite body and the outer ferrite body are both δ25mm~30mm, the diameter φ of the inner ferrite cover is 270mm, the diameter of the outer ferrite cover is φ350mm, and the thickness of the inner ferrite cover and the outer ferrite cover are both δ25mm~30mm.

7. The large-size double-layer spliced ​​ferrite magnetic shielding structure according to claim 1 is characterized in that: Include the following expressions: ， in P eddy is the eddy current power loss, V is the voltage, σ is the conductivity, E is the electric field strength, P hyst is the hysteresis loss, ω is the angular frequency, μ '' is the imaginary part of the complex magnetic permeability, H is the magnetic field intensity, δB is magnetic noise, δB hyst is the hysteresis loss noise, k is the Boltzmann constant, T is the Kelvin temperature, A is the coil area, I is the power consumption, and f is the oscillation frequency.

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