A multi-layer cylindrical magnetic shielding barrel structure with gradually varying air gap and wall thickness based on bosses.

Abstract

This invention discloses a multi-layer cylindrical magnetic shielding barrel structure with gradually varying air gaps and wall thicknesses based on bosses, relating to the field of nuclear magnetic resonance inertial sensor technology. The magnetic shielding barrel includes four nested magnetic shielding barrel bodies and magnetic shielding barrel lids, as well as barrel pads between the magnetic shielding barrel bodies and magnetic shielding barrel lids. By adding bosses to the outer side of the axial light-transmitting holes of each layer of magnetic shielding barrel lids, the axial remanent magnetization uniformity area inside the magnetic shielding barrel is widened, reducing the remanent magnetization inside the magnetic shielding barrel. Simultaneously, the gaps and wall thicknesses between the multi-layer magnetic shielding barrels are optimized, resulting in different axial air gaps between adjacent layers, different radial air gaps between adjacent layers, and different wall thicknesses for each layer, further reducing the remanent magnetization inside the barrel. Furthermore, the barrel pads between the magnetic shielding barrels not only ensure the independent magnetic circuit of each layer but also provide accurate positioning. This invention can meet the application scenarios of high-performance magnetic shielding barrels.

Description

Technical Field

[0001] This invention relates to the field of nuclear magnetic resonance inertial sensor technology, and in particular to a multi-layer cylindrical magnetic shielding barrel structure based on a boss with a gradually varying air gap and wall thickness. Background Technology

[0002] A nuclear magnetic resonance gyroscope is a sensor that senses angular velocity by detecting the change in the resonant frequency of Larmor precession generated by atomic spin in a static magnetic field and in an alternating magnetic field. Its main structure includes: an alkali metal gas chamber for sensing the rotation of the carrier, a gas chamber heating and temperature measurement system, a pump beam and a detection beam, a triaxial coil that generates a uniform working magnetic field and a compensation magnetic field, several gradient magnetic field compensation coils, and a multi-layer magnetic shielding barrel.

[0003] When the magnetic shielding performance is poor, fluctuations in the external magnetic field can penetrate the shielding and enter its interior, affecting the system's operation. Firstly, the fluctuating remanent magnetization leads to inaccurate measurements of the Larmor precession frequency of atoms, and this measurement error cannot be distinguished from the carrier's rotational frequency, ultimately resulting in errors in the carrier's angular rate measurement. Secondly, the remanent magnetization gradient within the shielding also increases nucleon spin exchange relaxation, leading to a decrease in relaxation time, a drop in the signal-to-noise ratio of the detected angular rate signal, and a reduction in the sensitivity of the NMR gyroscope.

[0004] To achieve the small, uniform, and stable remanent magnetic field environment required for nuclear magnetic resonance gyroscopes, a common approach is to combine an active magnetic compensation coil capable of generating a highly uniform magnetic field with a magnetic shield made of a high-permeability material. The passive magnetic shield can significantly attenuate interference from external environmental magnetic fields such as the Earth's magnetic field, shielding most of the environmental remanent magnetization. Then, an active compensation coil is used for partial remanent magnetization compensation. However, the active magnetic compensation process may introduce new uncertain magnetic field errors. Therefore, maximizing the shielding performance of the magnetic shield is a more effective method.

[0005] As the most important aspect of passive magnetic shielding, the structural design of the magnetic shielding barrel largely determines the magnetic shielding performance of the entire magnetic shielding device through the optimization of its structural form and parameters. Therefore, under the premise of unchanged material properties, optimizing the structural design of the magnetic shielding barrel is one of the effective ways to improve shielding performance.

[0006] Existing structural design methods for magnetic shielding barrels, such as the high-performance, low-noise magnetic shielding barrel design method disclosed in CN114169246A, are highly complex and contain numerous redundant parameters. Furthermore, the magnetic shielding barrel designed using this method only improves the axial shielding factor by one order of magnitude compared to the unoptimized version, which is far from sufficient to meet the application requirements of high-performance magnetic shielding barrels. Summary of the Invention

[0007] The purpose of this invention is to propose a multi-layer cylindrical magnetic shielding barrel structure based on a boss with a gradually varying air gap and wall thickness, which can effectively shield the disturbance of the external environment's magnetic field and ensure the magnetic field environment with small remanence and remanence gradient required for the normal operation of the nuclear magnetic resonance gyroscope.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] This invention provides a multi-layer cylindrical magnetic shielding barrel structure based on a boss with a gradually varying air gap and wall thickness, consisting of four nested cylindrical magnetic shielding barrels, each of which consists of a magnetic shielding barrel body and a magnetic shielding barrel cover.

[0010] Each layer of magnetic shielding barrel and magnetic shielding barrel cover has an axial light-transmitting hole at its axial center. A boss is added to the outside of the axial light-transmitting hole of each layer of magnetic shielding barrel cover. Demagnetization lines and signal lines are opened in the axial direction of each layer of magnetic shielding barrel and magnetic shielding barrel cover. The demagnetization lines and signal lines are evenly distributed around the circumference of the axial light-transmitting hole. Each layer of magnetic shielding barrel has radial light-transmitting holes that are coaxial with each other in the radial direction.

[0011] The magnetic shielding barrel body and the magnetic shielding barrel cover fit together tightly in a nested manner, and are accurately positioned by the positioning groove on the edge of the magnetic shielding barrel body and the positioning boss on the inner side of the magnetic shielding barrel cover, so that the axial light transmission hole, demagnetization line and signal line hole of each layer of magnetic shielding barrel cover are coaxially aligned.

[0012] The axial air gap between two adjacent magnetic shielding barrels is different, the radial air gap between two adjacent magnetic shielding barrels is different, and both the axial and radial air gaps between two magnetic shielding barrels increase from the inside to the outside; the wall thickness of each magnetic shielding barrel is different and increases from the inside to the outside.

[0013] Furthermore, the ratio of the axial or radial air gap between two adjacent magnetic shielding barrels is equal to the ratio of the average lengths of the inner and outer magnetic shielding barrels of three adjacent magnetic shielding barrels, where the average length is the average of the sum of the outer and inner wall lengths of a single magnetic shielding barrel.

[0014] Furthermore, the ratio of two adjacent axial or radial air gaps is 0.60-0.75.

[0015] Furthermore, the ratio of the thickness of two adjacent magnetic shielding barrels is equal to the ratio of the average radius of the inner and outer magnetic shielding barrels of three adjacent magnetic shielding barrels, where the average radius is the average of the sum of the outer and inner diameters of a single magnetic shielding barrel.

[0016] Furthermore, the ratio of the thickness of two adjacent magnetic shielding barrels is 0.60-0.75.

[0017] Furthermore, a tubular boss structure is provided on the outside of the axial light-transmitting hole of the magnetic shielding barrel, and the height of the tubular boss structure is the radius of the axial light-transmitting hole.

[0018] Furthermore, an upper barrel pad and a lower barrel pad are provided between two adjacent magnetic shielding barrels. The inner and outer surfaces of the upper barrel pad are tightly fitted to the adjacent magnetic shielding barrel body, and the inner and outer surfaces of the lower barrel pad are tightly fitted to the adjacent magnetic shielding barrel cover.

[0019] Furthermore, the lower barrel pad has a positioning groove and a positioning boss, which are closely fitted with the positioning boss and positioning groove of the adjacent magnetic shielding barrel cover to achieve accurate positioning, so that the axial light-transmitting hole, radial light-transmitting hole, demagnetizing line and signal line hole are coaxially aligned.

[0020] Furthermore, both the upper and lower tub mats are made of PEEK material.

[0021] Furthermore, all four layers of magnetic shielding barrels are made of 1J85 permalloy.

[0022] Furthermore, the wall thickness of the i-th layer of magnetic shielding barrel is 1-2 mm.

[0023] Furthermore, the radius of the axial light-transmitting hole is 4-4.5 mm, and the radius of the demagnetizing wire and signal wire hole is 1-2 mm.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] This invention proposes a multi-layer cylindrical magnetic shielding barrel structure based on a boss, a gradually varying air gap, and a wall thickness. It comprises four nested magnetic shielding barrel bodies and lids, as well as a gasket between the barrel bodies and lids. This gasket ensures that the magnetic circuits of each layer are independent and that the components are coaxially aligned, achieving accurate positioning. Simultaneously, the bosses and the gradually varying air gap and wall thickness widen the axial remanent magnetization uniformity region within the magnetic shielding barrel, reducing the remanent magnetization and further minimizing the overall remanent magnetization. Simulation experiments demonstrate that this multi-layer cylindrical magnetic shielding barrel structure effectively reduces the magnetic field at the center of the shielding barrel from an external 5×10⁻⁶... -5 T decreased to 1.19 × 10 -11 T, the lateral shielding factor is 4.2×10 6 This represents a six-order-of-magnetic-shield improvement, meeting the application scenarios of high-performance magnetic shielding barrels. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0027] Figure 1 A simplified axial cross-sectional view of a four-layer multi-cylindrical magnetic shielding barrel provided in an embodiment of the present invention.

[0028] Figure 2 An axial cross-sectional view of a four-layer multi-cylindrical magnetic shielding barrel provided in an embodiment of the present invention.

[0029] Figure 3 A schematic diagram of the magnetic shielding barrel cover structure provided in an embodiment of the present invention. Figure 1 (Outer side)

[0030] Figure 4 A schematic diagram of the magnetic shielding barrel cover structure provided in an embodiment of the present invention. Figure 2 (Inner side).

[0031] Figure 5 This is a schematic diagram of the magnetic shielding barrel structure provided in an embodiment of the present invention.

[0032] Figure 6 This is a schematic diagram of the magnetic shielding barrel pad structure provided in an embodiment of the present invention.

[0033] Figure 7 This is a cross-sectional view of the upper barrel pad of the magnetic shielding barrel provided in an embodiment of the present invention.

[0034] Figure 8 A schematic diagram of the magnetic shielding barrel lower barrel pad structure provided in this embodiment of the invention. Detailed Implementation

[0035] To better understand this technical solution, the method of the present invention will be described in detail below with reference to the accompanying drawings.

[0036] Please see Figure 1-8 This invention proposes a multi-layer cylindrical magnetic shielding barrel structure with gradually varying air gap and wall thickness based on a boss. The axial magnetic shielding factor and radial shielding factor of the finite-length closed cylindrical magnetic shielding barrel are calculated according to the magnetic scalar potential method.

[0037] When the wall thickness of the i-th layer of magnetic shielding barrel is t i Much smaller than its average radius In this embodiment, the wall thickness is 1-2 mm, the average radius is 32-52 mm, and the relative permeability μ of the magnetic shielding material is... ri When the value is much greater than 1, in this embodiment, the magnetic shielding barrel material is 1J85 permalloy, with a typical initial relative permeability as high as 5×10⁻⁶.5 The radial shielding factor of a single-layer cylindrical shell is simplified as follows:

[0038] Due to the axial end cap effect of the cylindrical structure, the demagnetization factor K is introduced as follows:

[0039]

[0040] In the formula, a = L / R, and α and β need to be determined by measuring the standard magnetic flux distribution on the end face and side wall of the cylinder, respectively.

[0041] The axial shielding factor of a single-layer cylindrical shell is:

[0042]

[0043] The total radial shielding factor of the i-layer cylindrical shell is:

[0044]

[0045] The total axial shielding factor of the i-layer cylindrical shell is:

[0046]

[0047] in, The average length of the i-th layer of magnetic shielding barrel is 52.5-73 mm in this embodiment.

[0048] like Figure 2 As shown, this embodiment of the invention provides a four-layer cylindrical magnetic shielding barrel, including a magnetic shielding barrel body 1, a magnetic shielding barrel lid 2, an upper barrel pad 3, and a lower barrel pad 4, which are assembled into a complete magnetic shielding barrel device using a nested arrangement. This embodiment distributes the magnetic field at the center of the magnetic shielding barrel from an external 5×10... -5 T decreased to 1.19 × 10 -11 T, the lateral shielding factor is 4.2×10 6 .

[0049] The inner and outer surfaces of the upper barrel pads (from outside to inside: upper barrel pad one 41, upper barrel pad two 42, upper barrel pad three 43) are tightly fitted to the adjacent magnetic shielding barrel bodies. The inner and outer surfaces of the lower barrel pads (from outside to inside: lower barrel pad one 31, lower barrel pad two 32, lower barrel pad three 33) are tightly fitted to the adjacent magnetic shielding barrel lids. Each pad has a positioning groove and a positioning boss, which are tightly fitted to the positioning boss and positioning groove of the adjacent magnetic shielding barrel lids for accurate positioning, ensuring that the axial light-transmitting holes, demagnetizing lines, and signal line holes are coaxially aligned. This effectively solves the problem of coaxial assembly of multi-layer cylindrical magnetic shielding barrels.

[0050] In this embodiment, both the upper and lower barrel pads are made of PEEK material, ensuring that the processed structure is not easily deformed and that assembly accuracy is maintained. The magnetic shielding barrel body 1 and the magnetic shielding barrel lid 2 are both made of high-permeability material 1J85 permalloy, with a typical initial relative permeability of up to 2×10⁻⁶. 4 This ensures the excellent magnetic shielding performance of the magnetic shielding barrel.

[0051] The magnetic shielding barrel comprises four nested magnetic shielding barrels (from outside to inside: first magnetic shielding barrel 11, second magnetic shielding barrel 12, third magnetic shielding barrel 13, and fourth magnetic shielding barrel 14) and magnetic shielding barrel covers (from outside to inside: first magnetic shielding barrel cover 21, second magnetic shielding barrel cover 22, third magnetic shielding barrel cover 23, and fourth magnetic shielding barrel cover 24). Each magnetic shielding barrel and cover has an axial light-transmitting hole at its axial center and four uniformly arranged demagnetizing lines and signal line holes. Because the cylindrical magnetic shielding barrel is radially perfectly symmetrical, the radial light-transmitting hole is only located at the center of symmetry of one axis. A tubular boss structure is located on the upper surface of the axial light-transmitting hole of the magnetic shielding barrel, with a height approximately equal to the radius of the axial light-transmitting hole. This design improves the uniformity and uniformity of the axial remanent magnetization within the magnetic shielding barrel. Due to the high permeability of the magnetic shielding material, it also concentrates magnetic field lines. Without the protrusion, magnetic field lines converge at the axial light-transmitting hole of the barrel, directly entering the interior of the magnetic shielding barrel through the light-transmitting hole, resulting in a residual magnetic field. When a protrusion is added outside the axial light-transmitting hole, the magnetic field lines will first converge on the wall of the protrusion, away from the barrel wall axis, thus changing the propagation path of the magnetic field lines before reaching the barrel wall. This reduces the number of magnetic field lines entering the barrel, and expands the uniform area of ​​residual magnetism inside the barrel. In addition, the magnetic shielding barrel body and the magnetic shielding barrel cover fit tightly together in a nested manner. The positioning groove on the edge of the magnetic shielding barrel body and the positioning protrusion on the inner side of the magnetic shielding barrel cover fit together to accurately position the magnetic field lines, ensuring that the axial light-transmitting hole, radial light-transmitting hole, demagnetizing line, and signal line hole are coaxially aligned.

[0052] The shielding factor is not only related to the magnetic permeability of the material, but also closely related to geometric dimensions such as radius, thickness, length, and number of layers. This invention considers the design of multi-layer magnetic shielding. When each layer is in a uniform static magnetic field, the magnetic shielding coefficient calculated according to existing theories is relatively accurate. However, in reality, due to the converging effect of high-permeability magnetic shielding materials on magnetic field lines, often only the outermost layer of magnetic shielding is in a relatively uniform magnetic field, while the inner layers are in a rapidly decaying and highly non-uniform magnetic field. Therefore, the shielding effect of each layer is different, which is related to the gap between layers. In order to efficiently design a high-performance magnetic shielding barrel, this invention optimizes the gap and wall thickness between multi-layer magnetic shielding barrels based on the principle of magnetic flux compression between layers, and proposes a multi-layer cylindrical magnetic shielding barrel structure with gradually varying air gaps and wall thicknesses based on bosses. Specifically, the axial air gaps between adjacent magnetic shielding barrels are different, and the radial air gaps between adjacent magnetic shielding barrels are different. Specifically, the axial and radial air gaps between the two magnetic shielding layers increase sequentially from the inside to the outside. The ratio of any two adjacent axial or radial air gaps is equal to the ratio of the average lengths of the inner and outer layers of the three adjacent magnetic shielding layers, approximately 0.60-0.75. The average length is the average of the sum of the outer and inner wall lengths of a single magnetic shielding layer. Each magnetic shielding layer has a different wall thickness, increasing sequentially from the inside to the outside. The ratio of the thicknesses of any two adjacent magnetic shielding layers is equal to the ratio of the average radii of the inner and outer layers of the three adjacent magnetic shielding layers, approximately 0.60-0.75. The beneficial result is that the shielding effect can be improved within limited structural dimensions.

[0053] like Figure 3 and Figure 4 As shown, the outermost magnetic shielding barrel cover 22 includes an axially oriented light-transmitting hole 223 at its axial center, and four uniformly arranged demagnetizing wire and signal wire holes 221. The outer diameter of the tubular boss 222 is equal to... Figure 8 The inner diameter of the demagnetizing wire and signal wire hole 312 of the lower barrel pad 31 fits perfectly during assembly, serving as a positioning element between the barrel lid 22 and the lower barrel pad 31, ensuring... Figure 5 The radial light-transmitting hole 123 of the middle magnetic shielding barrel 12 is aligned with the radial light-transmitting holes of other magnetic shielding barrels 11, 13, and 4. The outer diameter of the tubular boss 225 is equal to the inner diameter of the demagnetization wire and signal wire hole 312 of the lower barrel pad 32. The heights of the tubular boss 323, tubular boss 225, and tubular boss 122 are equal to the radii of the corresponding axial light-transmitting hole 223. The positioning groove 224 and Figure 5The positioning boss 124 in the middle serves to position the magnetic shielding barrel 1 and the magnetic shielding barrel cover 2, ensuring that the centers of all axial light-transmitting holes 223 and demagnetizing wire and signal wire holes 221 are aligned. In this embodiment, the height of the tubular boss is equal to the axial light-transmitting hole, which is 4.25mm, widening the uniform residual magnetism area at 35mm axially inside the magnetic shielding barrel by 9mm. In addition, the radius of the demagnetizing wire and signal wire holes is 1.5mm.

[0054] like Figure 5 As shown, the magnetic shielding barrel 12 has an axial light-transmitting hole and four uniformly arranged demagnetizing lines and signal line holes 122 at its axial center. In addition to serving as a positioning structure, the tubular boss 121 at the axial center of the magnetic shielding barrel 12 can improve the axial shielding factor of the magnetic shielding barrel and improve the uniformity of the axial magnetic field.

[0055] like Figure 6 and Figure 7 As shown, the upper barrel pad 41 fits against the inner bottom of the magnetic shielding barrel 1 during assembly. When the magnetic shielding barrel 1 is relatively deep and the fit is tight, it is not easy to remove the upper barrel pad 41. Therefore, the recessed step 411 is designed to facilitate the assembly of the magnetic shielding barrel.

[0056] like Figure 8 As shown, the lower barrel pad 4 includes an axial light-transmitting hole 311, the inner diameter of which is equal to the outer diameter of the central tubular boss 223 of the magnetic shielding barrel body 1. This hole serves to ensure that the lower barrel pad 4 and the magnetic shielding barrel cover 2 are coaxial with the axial light-transmitting hole 311. At the same time, the inner diameter of the demagnetizing wire and signal wire hole 312 is equal to the outer diameter of the tubular boss 222. This hole also serves to ensure that the lower barrel pad 4 and the magnetic shielding barrel cover 2 are coaxial with the demagnetizing wire and signal wire hole 312.

[0057] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. However, these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A multi-layer cylindrical magnetic shielding barrel structure with gradually varying air gap and wall thickness based on bosses, characterized in that, It consists of four nested cylindrical magnetic shielding barrels, each of which consists of a magnetic shielding barrel body and a magnetic shielding barrel lid; Each layer of magnetic shielding barrel and magnetic shielding barrel cover has an axial light-transmitting hole at its axial center. A boss is added to the outside of the axial light-transmitting hole of each layer of magnetic shielding barrel cover. Demagnetization lines and signal lines are opened in the axial direction of each layer of magnetic shielding barrel and magnetic shielding barrel cover. The demagnetization lines and signal lines are evenly distributed around the circumference of the axial light-transmitting hole. Each layer of magnetic shielding barrel has radial light-transmitting holes that are coaxial with each other in the radial direction. The magnetic shielding barrel body and the magnetic shielding barrel cover fit together tightly in a nested manner, and are accurately positioned by the positioning groove on the edge of the magnetic shielding barrel body and the positioning boss on the inner side of the magnetic shielding barrel cover, so that the axial light transmission hole, demagnetization line and signal line hole of each layer of magnetic shielding barrel cover are coaxially aligned. The axial air gap between two adjacent magnetic shielding barrels is different, the radial air gap between two adjacent magnetic shielding barrels is different, and both the axial and radial air gaps between two magnetic shielding barrels increase from the inside to the outside; the wall thickness of each magnetic shielding barrel is different and increases from the inside to the outside.

2. The multi-layer cylindrical magnetic shielding barrel structure with gradually varying air gap and wall thickness based on a boss as described in claim 1, characterized in that, The ratio of the axial or radial air gap between two adjacent magnetic shielding barrels is equal to the ratio of the average lengths of the inner and outer magnetic shielding barrels of three adjacent magnetic shielding barrels. The average length is the average of the sum of the outer and inner wall lengths of a single magnetic shielding barrel.

3. The multi-layer cylindrical magnetic shielding barrel structure with gradually varying air gap and wall thickness based on a boss as described in claim 2, characterized in that, The ratio of two adjacent axial or radial air gaps is 0.60-0.

75.

4. The multi-layer cylindrical magnetic shielding barrel structure with gradually varying air gap and wall thickness based on a boss as described in claim 1, characterized in that, The ratio of the thickness of two adjacent magnetic shielding barrels is equal to the ratio of the average radius of the inner and outer magnetic shielding barrels of three adjacent magnetic shielding barrels. The average radius is the average of the sum of the outer and inner diameters of a single magnetic shielding barrel.

5. The multi-layer cylindrical magnetic shielding barrel structure with gradually varying air gap and wall thickness based on a boss as described in claim 4, characterized in that, The ratio of the thickness of two adjacent magnetic shielding barrels is 0.60-0.

75.

6. The multi-layer cylindrical magnetic shielding barrel structure with gradually varying air gap and wall thickness based on a boss as described in claim 1, characterized in that, The magnetic shielding barrel has a tubular boss structure on the outside of the axial light-transmitting hole, and the height of the tubular boss structure is the radius of the axial light-transmitting hole.

7. The multi-layer cylindrical magnetic shielding barrel structure with gradually varying air gap and wall thickness based on a boss as described in claim 1, characterized in that, Between two adjacent magnetic shielding barrels, there is an upper barrel pad and a lower barrel pad. The inner and outer surfaces of the upper barrel pad are tightly fitted to the adjacent magnetic shielding barrel body, and the inner and outer surfaces of the lower barrel pad are tightly fitted to the adjacent magnetic shielding barrel lid.

8. The multi-layer cylindrical magnetic shielding barrel structure with gradually varying air gap and wall thickness based on a boss as described in claim 7, characterized in that, The lower barrel pad has a positioning groove and a positioning boss, which are closely fitted with the positioning boss and positioning groove of the adjacent magnetic shielding barrel cover to achieve accurate positioning, so that the axial light transmission hole, radial light transmission hole, demagnetizing line and signal line hole are coaxially aligned.

9. The multi-layer cylindrical magnetic shielding barrel structure with gradually varying air gap and wall thickness based on a boss as described in claim 1, characterized in that, The radius of the axial light-transmitting hole is 4-4.5 mm, and the radius of the demagnetizing wire and signal wire hole is 1-2 mm.

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