Composite magnetic shielding structure

Abstract

The application relates to a composite magnetic shielding structure, comprising: a metamaterial with near-zero magnetic permeability, the metamaterial comprising a substrate and a source coil assembly arranged on the substrate; a ferrite layer fixed to the surface of the metamaterial; and a metal layer fixed to the surface of the ferrite layer; wherein the ferrite layer and the metal layer form a Halbach-like magnetic circuit under the current excitation of the source coil assembly. The composite magnetic shielding structure solves the problem of transmission of the normal incidence wave, and has smaller eddy current heat effect, smaller mass and volume of the shielding body under the premise of ensuring higher shielding effectiveness.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of magnetic shielding, in particular to a composite magnetic shielding structure. BACKGROUND

[0002] The composite magnetic shielding structure is a structure capable of effectively shielding magnetic field interference, which is composed of magnetic materials and non-magnetic materials. Through reasonable preparation process, it has good magnetic shielding performance. It can be widely used in ultrasonic gas meters, ultrasonic probes, wireless energy transmission and other occasions susceptible to electromagnetic environment. Precise instruments and equipment such as ultrasonic gas meters usually need to be highly protected to avoid interference and damage from external magnetic fields. In the case of wireless energy transmission, external magnetic field interference may affect the efficiency of energy transmission, and strong magnetic field radiation on both sides of the coil may cause serious harm to the surrounding environment and human body. The application of the composite magnetic shielding structure can effectively solve these problems and improve the performance and reliability of instruments and equipment, and improve the stability of wireless energy transmission.

[0003] In practical applications, metal materials and ferrite materials can all play a magnetic shielding role, but their application in high frequency range is limited. The shielding cover made of metal material can shield high frequency alternating magnetic field. The high frequency alternating magnetic field can cause a large eddy current on the shielding cover. Due to the demagnetization effect of the eddy current, the magnetic field at the shielding cover is greatly weakened. The high frequency alternating magnetic field in the cover cannot penetrate out of the cover, and the magnetic field outside the cover cannot penetrate into the cover, thereby achieving the purpose of magnetic shielding. The disadvantage is that in high-power equipment, the eddy current will cause heating, which will affect the normal work of the equipment and has great safety hidden trouble. The main feature of the ferrite magnetic material is that the resistivity is much larger than that of the metal magnetic material, which causes a smaller eddy current, so that it can be applied to high-power scenes. However, the high-frequency power loss of the ferrite magnetic material is large, and the shielding effect is poor. Moreover, the shielding effectiveness of the ferrite magnetic material is related to its thickness. Therefore, in order to achieve high shielding effectiveness, a ferrite magnetic material with large mass and volume is usually required, which is not suitable for miniaturization and lightweight demand. In addition, David Smith of Duke University proposed a method of using longitudinal mu-near-zero (MNZ) metamaterial for magnetic field shielding. According to the effective medium theory, the near-zero permeability region near the local magnetic resonance generated by the metamaterial can be used to reflect the near-field magnetic field. According to Snell's law, the MNZ metamaterial can only shield the oblique incident wave, and cannot shield the normally incident magnetic field, which will cause part of the normally incident wave to be transmitted, resulting in magnetic leakage. Moreover, the shielding effectiveness (Shielding Effectiveness) SE (dB) is seriously dependent on the quality factor Q of the metamaterial, which means that each metamaterial unit needs to have more turns of wire to provide a larger inductance to achieve a higher Q. More turns of wire will increase the intrinsic loss of the unit, which is not conducive to improving the Q value of the unit. Moreover, this method still cannot effectively solve the problem of transmission of normally incident waves. SUMMARY

[0004] To solve the above problems, the present application provides a composite magnetic shielding structure, which uses a metamaterial with near-zero permeability combined with a composite magnetic shielding material with a Halbach structure, solves the problem of transmission of normally incident waves, achieves shielding effect within a certain bandwidth, and has smaller eddy current heat effect and smaller mass and volume of the shielding body while ensuring high shielding effectiveness.

[0005] The present application is implemented by the following scheme: a composite magnetic shielding structure, comprising:

[0006] A metamaterial with near-zero permeability, the metamaterial comprising a substrate and a source coil assembly provided on the substrate;

[0007] A ferrite layer fixed to the surface of the metamaterial;

[0008] a metal layer fixed on the surface of the ferrite layer;

[0009] The ferrite layer and the metal layer form a Halbach-like magnetic circuit under the current excitation of the source coil assembly.

[0010] The composite magnetic shielding structure is further improved in that:

[0011] The source coil assembly comprises a plurality of coil structures and a plurality of resonant capacitors connected one-to-one with the plurality of coil structures, and two ends of the coil structure are respectively connected to two ends of the corresponding resonant capacitor.

[0012] The ferrite layer comprises a plurality of ferrite assemblies fixed on the substrate and arranged one-to-one with the plurality of coil structures, and each ferrite assembly comprises a plurality of ferrite rings of similar shape, different size and concentric arrangement.

[0013] The metal layer comprises a plurality of metal assemblies fixed one-to-one on the plurality of ferrite assemblies, and each metal assembly comprises a plurality of metal rings of similar shape, different size and concentric arrangement, and the plurality of metal rings in each metal assembly are fixed one-to-one with the plurality of ferrite rings of the corresponding ferrite assembly.

[0014] The composite magnetic shielding structure is further improved in that the outer dimensions of the coil structure, the ferrite assembly and the metal assembly are consistent.

[0015] The composite magnetic shielding structure is further improved in that the innermost ferrite ring of the ferrite assembly extends inward to form a solid ferrite plate, and the innermost metal ring of the metal assembly extends inward to form a solid metal plate.

[0016] The composite magnetic shielding structure is further improved in that the coil structure comprises a first coil and a second coil arranged on the two side surfaces of the substrate respectively, the head end of the first coil is connected to the tail end of the second coil, and the tail end of the first coil and the head end of the second coil are respectively connected to two ends of the resonant capacitor, and the resonant capacitor is fixed on either side surface of the substrate.

[0017] The composite magnetic shielding structure is further improved in that the substrate is provided with a through hole for the first coil or the second coil to pass through.

[0018] The composite magnetic shielding structure is further improved in that the ferrite layer is fixed on the side surface of the substrate opposite to the resonant capacitor.

[0019] Further improvement of the composite magnetic shielding structure of the present application is that the substrate is a flexible PCB.

[0020] Further improvement of the composite magnetic shielding structure of the present application is that the source coil assembly is printed on the substrate.

[0021] Further improvement of the composite magnetic shielding structure of the present application is that the thickness of the substrate is equal to the sum of the thicknesses of the ferrite layer and the metal layer.

[0022] The composite magnetic shielding material of the present application adopts metamaterials with near-zero permeability combined with a Halbach-like structure, solves the problem of transmission of normally incident waves, and realizes shielding effect within a certain bandwidth. The Halbach-like structure is formed by combining a ferrite layer and a metal layer. On the one hand, the high permeability of the ferrite layer compresses the magnetic field to be shielded, weakening the magnetic field passing through the metal layer and reducing the eddy current heat effect of the metal layer. On the other hand, the high shielding performance of the metal layer avoids the need to increase the mass and volume of the ferrite layer to improve the shielding effectiveness. The flexible PCB is used as the substrate to fix the source coil assembly, the metal layer and the ferrite layer, so that the entire composite magnetic shielding structure can be freely bent and folded, and is light, thin and flat, which can improve the flexibility of the overall structure. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 A front view of the metamaterial structure in the composite magnetic shielding structure of the present application is shown.

[0024] Figure 2 A side view of the layered state of the composite magnetic shielding structure of the present application is shown.

[0025] Figure 3 A corresponding state schematic diagram of the coil, ferrite assembly and metal assembly of the present application is shown.

[0026] Figure 4 A schematic diagram of shielding effectiveness representation in a non-resonant system without magnetic isolation is shown.

[0027] Figure 5 A schematic diagram of shielding effectiveness representation of a traditional ferrite material in a non-resonant system is shown.

[0028] Figure 6 A schematic diagram of shielding effectiveness representation of the composite magnetic shielding structure of the present application in a non-resonant system is shown.

[0029] Figure 7 A shielding effectiveness comparison schematic diagram of the magnetic isolation system, the traditional ferrite material shielding system and the composite magnetic shielding structure shielding system under the same conditions of the present application is shown. DETAILED DESCRIPTION

[0030] In order to solve the problem that the traditional shielding material cannot have high shielding effectiveness, low eddy current heat effect and small size of the shielding body, and the problem that the shielding by the metamaterial cannot solve the transmission of the normal incidence wave, the application provides a composite magnetic shielding structure, which can solve the transmission of the normal incidence wave, and can have small eddy current heat effect and small mass and volume of the shielding body while ensuring high shielding effectiveness.

[0031] Referring to Figures 1 to 3 The composite magnetic shielding structure comprises a metamaterial 1 with near-zero magnetic permeability, the metamaterial 1 comprising a substrate 11 and a source coil assembly arranged on the substrate 11; a ferrite layer 2 fixed to the surface of the metamaterial 1; and a metal layer 3 fixed to the surface of the ferrite layer 2; wherein the ferrite layer 2 and the metal layer 3 form a Halbach-like magnetic circuit under the current excitation of the source coil assembly.

[0032] In the embodiment, the source coil assembly comprises a plurality of coil structures 12 and a plurality of resonant capacitors 13 connected one by one with the plurality of coil structures 12, and two ends of the coil structure 12 are respectively connected to two ends of the corresponding resonant capacitor 13. Specifically, the coil structure 12 is a double-layer structure comprising a first coil and a second coil arranged on two side surfaces of the substrate 11, a head end of the first coil is connected to a tail end of the second coil, and a tail end of the first coil and a head end of the second coil are respectively connected to two ends of the resonant capacitor 13. Wherein, the first coil and the second coil are both square planar coils with a size of 30mm*30mm, a number of turns of 40 turns, a wire diameter of 0.15mm, and a wire-to-wire spacing of 0.15mm. The plurality of coil structures 12 are distributed in a matrix on the substrate 11, and the boundary spacing between adjacent coil structures 12 is 0.35mm. The center position and the outside of a top corner corresponding to each coil structure 12 on the substrate 11 are respectively provided with through holes, the head end of the first coil passes through the through hole at the center position and is connected to the tail end of the second coil, the tail end of the first coil passes through the through hole at the top corner and is connected to the resonant capacitor 13, and the hole diameter of the through hole is 0.2mm. The coil structure 12 is not limited to the above double-layer structure, and it can be single-layer or more layers. Of course, the more the number of layers, the greater the inductance and the better the quality factor can be provided. Whether it is single-layer, double-layer or more layers, it is connected with the resonant capacitor 13, and the resonant capacitor 13 can be made of NPO or X7R material, and the low-loss capacitor quality factor of NPO material is slightly higher than the high-loss quality factor of X7R material.

[0033] The ferrite layer 2 comprises a plurality of ferrite assemblies 21 fixed on the substrate 11 and corresponding to the plurality of coil structures 12, each ferrite assembly 21 comprising a plurality of ferrite rings 211 of similar shape, different sizes and concentrically arranged; the metal layer 3 comprises a plurality of metal assemblies 31 fixed on the plurality of ferrite assemblies 21 one by one, each metal assembly 31 comprising a plurality of metal rings 311 of similar shape, different sizes and concentrically arranged, and the plurality of metal rings 311 in each metal assembly 31 are fixed one by one corresponding to the plurality of ferrite rings 211 in the ferrite assembly 21. The coil structure 12, the ferrite assembly 21 and the metal assembly 31 have the same size, that is, the outermost ferrite ring 211 in the ferrite assembly 21 and the outermost metal ring 311 in the metal assembly 31 are both square rings with a size of 30mm*30mm, the distance between each adjacent ferrite ring 211 is the same, the distance between each adjacent metal ring 311 is also the same, and the innermost ferrite ring 211 extends inward to form a solid ferrite plate, and the innermost metal ring 311 extends inward to form a solid metal plate. The solid ferrite plate is opposite to the middle space of the coil structure 12 wound by the coil. Each ferrite assembly 21 is fixed on the substrate 11 to form the ferrite layer 2, and each metal assembly 31 is fixed on the ferrite assembly 21 to form the metal layer 3, and the thickness of the ferrite layer 2 and the thickness of the metal layer 3 are both d=0.1mm, and the thickness of the substrate is 2d=0.2mm.

[0034] Suppose that the effective induced current of the coil structure 12, the ferrite ring 21 and the metal ring 31 are represented by I, I1 and I2 respectively, and the coil structure 12 has a current I from inside to outside, then the current I1 of the ferrite region is in the same direction as I, and since the metal has diamagnetism, the direction of the current I2 is opposite to that of I1 and I. By generating clockwise and counterclockwise alternating magnetic moment distribution between air and metal, the ferrite layer 2 and the metal layer 3 finally form a Halbach-like magnetic circuit in the magnetic field, and the Halbach-like magnetic moment structure constructed under the excitation of the magnetic dipole source is similar to the magnetic circuit of the Halbach permanent magnet array. The Halbach-like magnetic circuit structure can compress the magnetic field to be shielded by using the high magnetic permeability of the ferrite layer, thereby weakening the magnetic field passing through the metal layer and reducing the eddy current heat effect of the metal layer, and on the other hand, it avoids the way of increasing the mass and volume of the ferrite layer to improve the shielding effectiveness by using the high shielding performance of the metal layer. In addition, through the Halbach-like magnetic circuit structure on one side of the substrate 11, the magnetic circuit of the metamaterial 1 can be further precisely controlled, effectively reducing the magnetic leakage, thereby improving the shielding effectiveness.

[0035] In a preferred embodiment, the ferrite layer 2 is fixed to the surface of the substrate 11 facing away from the resonant capacitor. This ensures that the ferrite layer 2 can be smoothly attached to the substrate 11.

[0036] In a preferred embodiment, the substrate is a flexible PCB, the source coil assembly is printed on the substrate 11, and the resonant capacitor 13 is soldered onto the substrate 11. This embodiment, based on the antimagnetic properties of traditional metamaterials, replaces the non-magnetic substrate with a flexible PCB, prints the coil on the PCB, and attaches and fixes the aforementioned Halbach-like magnetic circuit structure to one side of the PCB. This effectively shields the magnetic field to one side, providing good shielding on one side. Furthermore, the flexible PCB material and the Halbach-like magnetic circuit structure can be freely bent and folded, are relatively thin and flat, improving the overall flexibility of the structure. Simultaneously, this structure has good shielding performance and can be applied to high-shield applications in small spaces.

[0037] This design exhibits superior and more significant shielding effectiveness within the operating frequency range of approximately 500kHz. It is a composite structure with high shielding effectiveness capable of narrowband shielding of incident waves at specific frequencies. The shielding effectiveness of a non-magnetic shielding system, a traditional ferrite material shielding system, and a composite magnetic shielding structure shielding system are compared experimentally below.

[0038] See Figures 4 to 7 As shown, Figure 4 The diagram illustrates the shielding effectiveness characterization of a non-resonant system without magnetic shielding. The system comprises a pair of identical non-resonant transmitting coils 2 and 3, spaced 2S apart, each with 10 turns. Both coils are wound with 400 strands of enameled wire (each with a cross-sectional diameter of 0.078 mm) and the wire diameter is 15 mm. Specifically, transmitting coil 2 is connected to port 1 of the network analyzer, and receiving coil 3 is connected to port 2 of the network analyzer. There is no magnetic shielding material or structure between the two coils.

[0039] Figure 5 The diagram shows a schematic representation of the shielding effectiveness of traditional ferrite materials in a non-resonant system. The specifications and dimensions of the transmitting coil 2 and receiving coil 3 in this system are shown in the diagram. Figure 4 The non-resonant system shown is identical to the one without magnetic shielding, except that ferrite material 1 is placed between the two coils as a magnetic shielding material. The distance between ferrite material 1 and the transmitting coil 2 is S, and the distance between ferrite material 1 and the receiving coil 3 is also S.

[0040] Figure 6 The diagram shows the shielding effectiveness characterization of the composite magnetic shielding structure of the present invention in a non-resonant system. The specifications and dimensions of the transmitting coil 2 and receiving coil 3 in this system are shown in the figure. Figure 4The non-resonant system in the shown no-gap state is consistent, and the difference is that the composite magnetic shielding structure 1 of the application is placed in the middle of the two coils as a magnetic shielding material. Figure 5 The placement position of the ferrite material shown is consistent, that is, the distance between the composite magnetic shielding structure 1 and the transmitting coil 2 is S, and the distance between the composite magnetic shielding structure 1 and the receiving coil 3 is also S.

[0041] After connecting port1 and port2, the transmission coefficient values of the network analyzer at the working frequency of 400kHz-600kHz are recorded, and the shielding effectiveness of the three systems in the working frequency range of 400kHz-600kHz is calculated. Figure 7 As shown, Figure 7 The shielding effectiveness comparison diagram of the no-gap system, the traditional ferrite material shielding system and the composite magnetic shielding structure shielding system under the same conditions of the application is shown. In the range of 400kHz-600kHz: the transmission coefficient range of the system without gap is about -22 to -28dB, and at 500kHz, the transmission coefficient of the system is -24.574dB; in the range of 400kHz-600kHz, when the traditional ferrite material is used as the magnetic shielding material, the transmission coefficient range of the system is about -33 to -39dB, and at 500kHz, the transmission coefficient of the system is -35.315dB; in the range of 400kHz-600kHz, when the composite magnetic shielding structure is used, the transmission coefficient range of the system is about -35 to -43dB, and at 500kHz, the transmission coefficient of the system is -43.202dB. In addition, when the composite magnetic shielding structure uses low-loss NPO capacitor, the shielding area is -46 to -48dB, and when the composite magnetic shielding structure uses high-loss X7R capacitor, the shielding area is -43 to -44dB.

[0042] As can be clearly seen from the above, the composite magnetic shielding structure provided by the application has the best shielding effect at 500kHz, and can be applied to shielding occasions with a working frequency of 500kHz, such as ultrasonic sensors, ultrasonic gas meters and the like.

[0043] The application has been described in detail in the above embodiments combined with the drawings, and those skilled in the art can make various changes to the application according to the above description. Therefore, some details in the embodiments should not constitute a limitation on the application, and the scope of protection of the application will be defined by the appended claims.

Claims

1. A composite magnetic shielding structure, characterized in that, include: A metamaterial with near-zero permeability, the metamaterial comprising a substrate and a source coil assembly disposed on the substrate; A ferrite layer fixed to the surface of the metamaterial; A metal layer fixed to the surface of the ferrite layer; wherein, The ferrite layer and the metal layer form a Halbach-like magnetic circuit under the current excitation of the source coil assembly. in, The source coil assembly includes several coil structures and several resonant capacitors connected one-to-one with the several coil structures, with the two ends of each coil structure connected to the two ends of the corresponding resonant capacitor. The ferrite layer includes a plurality of ferrite components, which are fixed on the substrate and are arranged in a one-to-one correspondence with the plurality of coil structures. Each ferrite component includes a plurality of ferrite rings of similar shape, different size and concentrically arranged. The metal layer includes a plurality of metal components, which are fixed one-to-one with the plurality of ferrite components. Each metal component includes a plurality of metal rings of similar shape, different size and concentrically arranged, and the plurality of metal rings in each metal component are attached and fixed one-to-one with the plurality of ferrite rings of the corresponding ferrite component.

2. The composite magnetic shielding structure as described in claim 1, characterized in that, The coil structure, the ferrite assembly, and the metal assembly have the same external dimensions.

3. The composite magnetic shielding structure as described in claim 1, characterized in that, The innermost ferrite ring of the ferrite assembly extends inward to form a solid ferrite plate, and the innermost metal ring of the metal assembly extends inward to form a solid metal plate.

4. The composite magnetic shielding structure as described in claim 1, characterized in that, The coil structure includes a first coil and a second coil respectively disposed on two sides of the substrate. The first end of the first coil is connected to the tail end of the second coil. The tail end of the first coil and the first end of the second coil are respectively connected to the two ends of the resonant capacitor. The resonant capacitor is fixed on either side of the substrate.

5. The composite magnetic shielding structure as described in claim 4, characterized in that, The substrate has through holes through which the first coil or the second coil passes.

6. The composite magnetic shielding structure as described in claim 4, characterized in that, The ferrite layer is fixed on the surface of the substrate facing away from the resonant capacitor.

7. The composite magnetic shielding structure as described in claim 1, characterized in that, The substrate is a flexible PCB.

8. The composite magnetic shielding structure as described in claim 7, characterized in that, The source coil assembly is printed on the substrate.

9. The composite magnetic shielding structure as described in claim 1, characterized in that, The thickness of the substrate is equal to the sum of the thicknesses of the ferrite layer and the metal layer.

Images