Preparation method of shielding sheet, shielding sheet and antenna

Abstract

The invention discloses a preparation method of a shielding sheet. The method comprises the steps that a soft magnet is provided, the soft magnet is subjected to crushing, ball grinding and sieving treatment, flaky nano powder is obtained, the thickness of the flaky nano powder ranges from 3 micrometers to 6 micrometers, and the flake diameter ranges from 75 micrometers to 150 micrometers. The preparation method comprises the following steps: performing surface activation treatment on flaky nano-powder to obtain activated nano-powder, and mixing the activated nano-powder with a resin solution to obtain slurry liquid; a magnetic field is provided, the slurry liquid is placed in the magnetic field to be coated and then dried, a shielding composite material is obtained, the shielding composite material is subjected to die cutting, and the shielding sheet is obtained. The flaky nano powder is directionally arranged in a magnetic field, so that the magnetic conduction energy in the long axis direction can be enhanced, the magnetic loss and the shielding effectiveness of the shielding material are maximized, and the generation of eddy current is reduced. The sheet-shaped nano powder is fully wrapped by the rubber solution, so that the rubber forms a compact insulating layer on the outer surface of the sheet-shaped nano powder, the contact between the sheet-shaped nano powder is reduced, and the eddy current loss under the high-frequency working condition is reduced.

Description

Technical Field

[0001] This application relates to the field of communication technology, and in particular to a method for preparing a shielding sheet, the shielding sheet, and an antenna. Background Technology

[0002] Near Field Communication (NFC) is a contactless communication method between devices similar to smartphones or tablets. An NFC antenna consists of a communication coil and shielding material. The communication coil primarily uses electromagnetic induction to transmit information, while the shielding material mainly functions to concentrate energy, improve transmission efficiency, and reduce electromagnetic field leakage that could affect other electronic components.

[0003] Nanocrystalline and amorphous soft magnetic materials possess relatively high permeability under high-frequency operating conditions (13.56MHz) in NFC communication and are commonly used as shielding materials. Nanocrystalline and amorphous materials require processes such as heat treatment, magnetization, lamination, and die-cutting to produce electromagnetic shielding sheets applicable to NFC antennas. While magnetization can break down soft magnetic materials, it cannot completely prevent contact between fragments, easily leading to increased eddy current losses and consequently increased power consumption of the NFC antenna. Summary of the Invention

[0004] This application aims to provide a method for preparing a shielding sheet, the shielding sheet itself, and an antenna, with the goal of reducing eddy current losses in soft magnetic materials.

[0005] In a first aspect, this application proposes a method for preparing a shielding sheet, comprising providing a soft magnetic material, crushing, grinding, and sieving the soft magnetic material to obtain sheet-like nanoparticles; the sheet-like nanoparticles have a thickness of 3 μm to 6 μm and a diameter of 75 μm to 150 μm. The sheet-like nanoparticles are then subjected to surface activation treatment to obtain activated nanoparticles. The activated nanoparticles are mixed with a resin solution to obtain a slurry. A magnetic field is provided, and the slurry is coated and dried in the magnetic field to obtain a shielding composite material. The shielding composite material is then die-cut to obtain a shielding sheet.

[0006] In some embodiments, the process of crushing, grinding, and sieving the soft magnet to obtain sheet-like nanoparticles includes: crushing the soft magnet and then grinding it into balls, adding an anti-oxidation medium during the grinding process; the anti-oxidation medium includes at least one selected from anhydrous ethanol, acetone, isoacetone, hexane, stearic acid, zinc stearate, and paraffin oil. The soft magnet after the grinding process is then subjected to several sieving processes to obtain the sheet-like nanoparticles.

[0007] In some embodiments, surface activation treatment of the sheet-like nanoparticles to obtain activated nanoparticles includes: adding the sheet-like nanoparticles to pure water to obtain a sheet-like nanoparticle solution; adding sodium citrate to the sheet-like nanoparticle solution, stirring and mixing, and then heating under reflux to obtain a mixture; filtering the mixture to obtain a solid powder; washing the solid powder with anhydrous ethanol and then drying it to obtain the activated nanoparticles.

[0008] In some embodiments, the soft magnet includes at least one of nanocrystals, amorphous materials, ferrites, and sheet-like iron-silicon-aluminum.

[0009] In some embodiments, the magnetic field strength is 0.5T to 1.8T, and the processing time of the magnetic field is 20min to 40min.

[0010] In some embodiments, the mass ratio of the resin to the activated nanoparticles is 1:0.5 to 1:1.

[0011] In some embodiments, the resin includes at least one selected from acrylic resin, epoxy resin, thermoplastic polyurethane, and phenolic resin.

[0012] In some embodiments, the thickness of the soft magnet is 12 μm to 18 μm.

[0013] Secondly, embodiments of this application also provide a shielding sheet, which is prepared by the shielding sheet preparation method described in any one of the first aspects.

[0014] Thirdly, embodiments of this application also provide an antenna, the antenna including the shielding sheet described in the second aspect.

[0015] Unlike existing technologies, this application provides a method for preparing a shielding sheet. The method includes providing a soft magnetic material, crushing, grinding, and sieving the soft magnetic material to obtain sheet-like nanoparticles. The thickness of the sheet-like nanoparticles is 3 μm to 6 μm, and the sheet diameter is 75 μm to 150 μm. The sheet-like nanoparticles are then surface-activated to obtain activated nanoparticles. The activated nanoparticles are mixed with a resin solution to obtain a slurry. A magnetic field is provided, and the slurry is coated and dried in the magnetic field to obtain a shielding composite material. The shielding composite material is then die-cut to obtain a shielding sheet. The sheet-like nanoparticles can be well oriented along their long axis in a magnetic field. This oriented arrangement enhances the magnetic conductivity along the long axis, guides the magnetic field distribution, maximizes the magnetic loss and shielding effectiveness of the shielding material, and reduces the generation of eddy currents. The sheet-like nanoparticles are mixed with a rubber solution, which fully encapsulates the sheet-like nanoparticles. After subsequent drying and curing, the rubber forms a dense insulating layer on the outer surface of the sheet-like nanoparticles. This facilitates isolation between the sheet-like nanoparticles, reduces contact between them, and thus reduces eddy current losses of soft magnetic materials under high-frequency operating conditions.

[0016] Additional aspects and advantages of the embodiments of this application will be described, shown, or illustrated in part by way of implementation of the embodiments of this application in the following description. Attached Figure Description

[0017] One or more embodiments are illustrated by way of example with reference to the accompanying drawings, which are not intended to limit the embodiments, and elements having the same reference numerals in the drawings are designated as similar elements.

[0018] Figure 1 Flowcharts illustrating some methods for preparing shielding sheets provided in the embodiments of this application; Figure 2 Schematic diagrams of the structure of some shielding sheets provided in the embodiments of this application; Figure 3 The diagram shows the structure of some antennas provided in the embodiments of this application. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of this application, but not all embodiments.

[0020] In this application, the reference to "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment that is mutually exclusive with other embodiments.

[0021] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0022] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0023] The technical features involved in the different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0024] Firstly, this application proposes a method for preparing a shielding sheet, please refer to... Figure 1 The preparation method of this shielding sheet includes the following steps: Step S1: Provide a soft magnet, crush, grind, and sieve the soft magnet to obtain flake-shaped nanoparticles; the thickness of the flake-shaped nanoparticles is 3μm to 6μm, and the diameter of the flakes is 75μm to 150μm.

[0025] Step S2: Perform surface activation treatment on the sheet-like nanoparticles to obtain activated nanoparticles.

[0026] Step S3: Mix the activated nanoparticles with the resin solution to obtain a slurry.

[0027] Step S4: Provide a magnetic field, place the slurry in the magnetic field for coating and then dry to obtain a shielding composite material, and then die-cut the shielding composite material to obtain a shielding sheet.

[0028] Soft magnets are a class of magnetic materials that are easily magnetized but also easily lose their magnetism. Soft magnets have high permeability and are widely used in fields such as power, electronics, and communications, often serving as core materials for electromagnetic shielding.

[0029] The soft magnetic material in this application is a sheet-like soft magnetic material, such as nanocrystalline, amorphous, ferrite, or sheet-like iron-silicon-aluminum. The thickness of the soft magnetic material is 12 μm to 18 μm. Sheet-like soft magnetic materials can increase the contact area with electromagnetic waves, facilitate directional alignment in a magnetic field, and improve magnetic loss efficiency.

[0030] Soft magnets can be crushed to obtain micron- or millimeter-sized coarse powder. This coarse powder is then processed by grinding balls. The shearing and impact forces of the grinding balls break the coarse powder along the spherical surface of the grinding media, ensuring that the soft magnet retains its lamellar structure after grinding. The ball-processed soft magnet is then sieved, for example, using a graded sieve, to remove large and excessively small lamellar nanoparticles, retaining lamellar nanoparticles with a thickness of 3μm to 6μm and a diameter of 75μm to 150μm. Understandably, lamellar nanoparticles larger than 150μm will affect the uniformity of subsequent coating, while lamellar nanoparticles smaller than 75μm are prone to agglomeration, leading to unstable shielding performance and fluctuations. The uniform size distribution of lamellar nanoparticles with a diameter of 75μm to 150μm improves the uniformity of subsequent magnetic field orientation.

[0031] In some embodiments, a soft magnet is crushed, milled, and sieved to obtain sheet-like nanoparticles. This includes crushing the soft magnet and then milling it, adding an anti-oxidation medium during the milling process. The anti-oxidation medium includes at least one of anhydrous ethanol, acetone, isoacetone, hexane, stearic acid, zinc stearate, and paraffin oil. The milled soft magnet is then sieved several times to obtain the sheet-like nanoparticles.

[0032] During the grinding process, zirconia balls or agate balls can be used as grinding media, with the ball-to-material ratio controlled at 5:1 to 10:1 and the rotation speed at 200 rpm to 500 rpm.

[0033] The surface of sheet-like nanoparticles may be coated with an extremely thin insulating layer. If this layer is not treated before mixing with resin, it will lead to poor interfacial bonding. Especially in high-frequency environments, the conductivity of the powder will cause eddy current losses, affecting performance. Surface activation treatment of sheet-like nanoparticles can improve their dispersibility in resin and reduce agglomeration during mixing. The activated sheet-like nanoparticles form an extremely thin insulating layer on their surface, reducing eddy current losses in subsequent applications. Furthermore, the activated surface of the sheet-like nanoparticles provides more binding sites. When mixed with the resin solution, the functional groups on the resin molecular chains can form stronger physical adsorption or chemical bonds with the hydroxyl groups on the surface of the sheet-like nanoparticles, reducing the risk of the sheet-like nanoparticles falling off during subsequent die-cutting or bending, and improving the flexibility and reliability of the shielding material.

[0034] In some embodiments, the sheet-like nanoparticles are surface activated to obtain activated nanoparticles. This includes adding the sheet-like nanoparticles to pure water to obtain a sheet-like nanoparticle solution. Sodium citrate is added to the sheet-like nanoparticle solution, and after stirring and mixing, the mixture is heated under reflux to obtain a mixture. The mixture is then filtered to obtain a solid powder. The solid powder is washed with anhydrous ethanol and dried to obtain the activated nanoparticles.

[0035] Sodium citrate is a mild organic acid complexing and reducing agent that can partially reduce high-valence metal oxides on the surface of sheet-like nanoparticles, forming a dense and stable passivation layer. The passivation layer contains many polar groups such as hydroxyl groups, resulting in better compatibility when subsequently dissolved and mixed with resin. The activated sheet-like nanoparticles can reduce agglomeration in the resin solution, thus improving the shielding performance of the shielding material.

[0036] In some embodiments, the amount of sodium citrate added is 0.5% to 3% of the mass of the flake nanoparticles.

[0037] Resin generally refers to an organic polymer that softens or melts when heated, tends to flow under external force when softened, and is solid, semi-solid, or sometimes liquid at room temperature. Examples include acrylic resin, epoxy resin, thermoplastic polyurethane, and phenolic resin. It should be noted that acrylic resin and thermoplastic polyurethane are preferred for the subsequent preparation of flexible shielding sheets; while epoxy resin and phenolic resin are preferred for the subsequent preparation of rigid shielding sheets. A resin solution is obtained by dissolving the resin in an organic solvent; different resins require different organic solvents. For example, acrylic resin is dissolved using divalent esters, and thermoplastic polyurethane is dissolved using N,N-dimethylformamide.

[0038] In some embodiments, the mass ratio of resin to activated nanoparticles is 1:0.5 to 1:1. The resin, as a matrix, plays a role in bonding and fixing the activated nanoparticles during mixing, exhibiting film-forming properties and providing flexibility and mechanical strength. If the proportion of activated nanoparticles is too low, the activated nanoparticles are sparsely dispersed in the resin solution, failing to achieve a good shielding function. If the proportion of activated nanoparticles is too high, the viscosity of the slurry increases, the coating process is easily hindered, film-forming properties are poor, and the activated nanoparticles are prone to agglomeration, affecting the uniformity of the shielding material. When the mass ratio of resin to activated nanoparticles is 1:0.5 to 1:1, the activated nanoparticles are uniformly dispersed in the resin solution, the viscosity of the slurry is suitable for film formation, and the activating groups of the activated nanoparticles can fully combine with the functional groups of the resin, reducing agglomeration.

[0039] In some embodiments, the slurry is distilled to remove some of the solvent, thereby reducing the viscosity of the slurry to a coatable state.

[0040] A magnetic field can generate magnetism, which can guide the oriented alignment of sheet-like nanoparticles, making them aligned in the long axis direction. The oriented sheet-like nanoparticles can enhance the magnetic conductivity energy in the long axis direction, guide the magnetic field distribution, maximize the magnetic loss and shielding effectiveness of the shielding material, and reduce the generation of eddy currents.

[0041] In some embodiments, the magnetic field strength is 0.5T to 1.8T, and the magnetic field treatment time is 20min to 40min. Insufficient magnetic field strength will result in irregular orientation of the sheet-like nanoparticles, while excessive magnetic field strength will result in localized sedimentation of the sheet-like nanoparticles in the slurry.

[0042] In some embodiments, blade coating is preferred, and the coating thickness is adjusted according to the shielding requirements. A thicker coating provides better shielding, but reduces flexibility. Specifically, the material thickness can be controlled by adjusting the slit width and coating speed. For example, the coating thickness can be controlled between 10 μm and 100 μm.

[0043] In some embodiments, a gradient temperature drying method is used during the drying process. For example, the film is first dried at a temperature of 50°C to 70°C for 20 to 30 minutes to remove most of the solvent, and then dried at a temperature of 90°C to 120°C for 1 to 2 hours. The gradient temperature method can reduce the phenomenon of blistering and cracking of the film layer caused by excessively rapid temperature rise, and reduce the damage to the oriented structure of the sheet-like nanoparticles.

[0044] In some embodiments, when the shielding composite material is die-cut, laser die-cutting or flat die-cutting can be used to cut the shielding composite material into a specific shape.

[0045] This application provides a method for preparing a shielding sheet. The method includes providing a soft magnetic material, crushing, grinding, and sieving the soft magnetic material to obtain sheet-like nanoparticles. The thickness of the sheet-like nanoparticles is 3 μm to 6 μm, and the sheet diameter is 75 μm to 150 μm. The sheet-like nanoparticles are then surface-activated to obtain activated nanoparticles. The activated nanoparticles are mixed with a resin solution to obtain a slurry. A magnetic field is provided, and the slurry is coated and dried in the magnetic field to obtain a shielding composite material. The shielding composite material is then die-cut to obtain a shielding sheet. The sheet-like nanoparticles can be well oriented along their long axis in a magnetic field. This oriented arrangement enhances the magnetic conductivity along the long axis, guides the magnetic field distribution, maximizes the magnetic loss and shielding effectiveness of the shielding material, and reduces the generation of eddy currents. The sheet-like nanoparticles are mixed with a rubber solution, which fully encapsulates the sheet-like nanoparticles. After subsequent drying and curing, the rubber forms a dense insulating layer on the outer surface of the sheet-like nanoparticles, which helps to isolate the sheet-like nanoparticles and reduce their contact, thereby reducing the eddy current loss of the soft magnetic material under high-frequency conditions.

[0046] Secondly, embodiments of this application provide a shielding sheet 10, which is prepared by the shielding sheet preparation method as described in any embodiment of the first aspect. Figure 2 The plurality of sheet-like nanoparticles 11 are arranged along the long axis direction and are connected by rubber 12. The rubber 12 is wrapped around the outer surface of the sheet-like nanoparticles 11, thereby isolating the sheet-like nanoparticles 11 from each other.

[0047] Thirdly, embodiments of this application also provide an antenna 100, which includes a shielding sheet 10 and a coil 20 as described in the second aspect above. Figure 3 As shown, coil 20 can be disposed on the surface of shield 10 to form antenna 100.

[0048] The preparation method of the shielding sheet is described below with reference to specific embodiments: Example 1 (1) Provide nanocrystals with a thickness of 15μm, crush the nanocrystals and then grind them into balls. Add anhydrous ethanol as an anti-oxidation medium during the grinding process. Then, sieve the nanocrystals after grinding multiple times to screen out sheet-like nanocrystal powders with a thickness of 3μm to 6μm and a sheet diameter of 75μm to 150μm.

[0049] (2) Add pure water to the sheet-like nanocrystalline powder and stir to obtain a sheet-like nanocrystalline powder solution. Add sodium citrate to the sheet-like nanocrystalline powder solution, stir and mix, heat and reflux, filter and obtain solid powder. Wash the solid powder with anhydrous ethanol and dry to obtain activated nanocrystalline powder.

[0050] (3) Mix and stir the activated nanocrystalline powder with the acrylic resin solution to obtain a slurry. The mass ratio of acrylic resin to activated nanocrystalline powder is 1:0.5.

[0051] (4) Provide a magnetic field with a magnetic field strength of 1T and a magnetic field treatment time of 30min. Place the slurry in the magnetic field for coating and then dry it to obtain a shielding composite material. Die-cut the shielding composite material to obtain a shielding sheet with a thickness of 100μm.

[0052] Comparative Example 1 (1) Provide ferrite with a thickness of 15μm, crush the ferrite and then grind it. Add acetone as an anti-oxidation medium during the grinding process. The ferrite after grinding is sieved multiple times to screen out sheet-like ferrite powder with a thickness of 3μm to 6μm and a sheet diameter of 75μm to 150μm.

[0053] (2) Add pure water to the flake ferrite powder and stir to obtain a flake ferrite powder solution. Add sodium citrate to the flake ferrite powder solution, stir and mix, heat and reflux, filter and obtain solid powder. Wash the solid powder with anhydrous ethanol and dry to obtain activated ferrite powder.

[0054] (3) Mix the activated ferrite powder with pure water and stir to obtain a slurry; (4) Provide a magnetic field with a magnetic field strength of 1T and a magnetic field treatment time of 30min. Place the slurry in the magnetic field for coating and sintering to obtain a shielding composite material. Die-cut the shielding composite material to obtain a shielding sheet with a thickness of 100μm.

[0055] Comparative Example 2 Nanocrystals with a thickness of 15 μm are provided and distributed on an acrylic pressure-sensitive tape. The nanocrystals with acrylic pressure-sensitive tape are subjected to multiple crushing processes to obtain sheet-like nanocrystal powder. (2) Multiple sheet-like nanocrystal powders with acrylic pressure-sensitive tape are stacked to form a shielding composite material with a thickness of 100 μm. The shielding composite material is die-cut to obtain a shielding sheet.

[0056] The shielding sheets from Example 1, Comparative Example 1, and Comparative Example 2 were installed in the same NFC module, and basic performance tests were performed at 13.56MHz. The test structure is shown in Table 1.

[0057] Table 1:

[0058] Note: Ls: Inductance, Rs: Series Resistance, Q: Quality Factor As shown in Table 1, Comparative Example 1 has the lowest Rs at 738 mΩ, resulting in low energy loss, but also the lowest permeability at 110, the lowest Ls at 0.78 μH, and a moderate overall Q value of 90.05. Comparative Example 2 has the highest permeability at 250, a relatively high Ls of 0.94 μH, and the highest Rs at 937 mΩ, resulting in high energy loss and a slightly lower-than-average overall Q value of 90.05. In Example 1, the highest permeability is 250, the highest Ls is 0.95 μH, but Rs is only 752 mΩ, and the best overall Q value is 107.63.

[0059] In Comparative Example 1, ferrite, as a traditional magnetic material, has a high resistivity and low eddy current loss at a high frequency of 13.56MHz, resulting in less energy waste. However, the permeability of ferrite is only 110, which results in Ls of only 0.78μH for the same thickness. If used in an NFC antenna, the signal transmission distance may be shortened and the sensitivity may decrease due to insufficient magnetic field storage capacity.

[0060] In Comparative Example 2, the permeability of nanocrystals is as high as 250, and Ls reaches 0.94μH, indicating strong magnetic field storage capacity. However, the resistivity of nanocrystal materials is low, resulting in significant eddy current loss at a high frequency of 13.56MHz, leading to Rs as high as 937mΩ. Even with a high Ls, a large amount of energy is consumed by the resistance, ultimately resulting in a Q value lower than that of ferrite, making it the worst in terms of overall performance.

[0061] The powder in Example 1 still has a nanocrystalline structure and maintains a magnetic permeability of 250, thus achieving an Ls of 0.95 μH. This provides sufficient magnetic field energy storage for the NFC antenna, ensuring signal transmission distance and sensitivity. After combining the nanocrystalline powder with resin, the nanocrystalline powder is separated by an insulating phase, significantly suppressing eddy current losses and reducing the formation of large loops within the material, thereby lowering Rs to 752 mΩ. Example 1 exhibits the best Q value at 107.63, which is 19.5% higher than ferrite and 26% higher than nanocrystalline powder. This indicates that at a frequency of 13.56 MHz, the NFC antenna prepared in Example 1 can efficiently store magnetic field energy while minimizing energy loss, achieving the requirements of high sensitivity and low loss.

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them; under the concept of this application, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of this application as described above, which are not provided in detail for the sake of brevity; although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for preparing a shielding sheet, characterized in that, include: A soft magnetic material is provided, and the soft magnetic material is crushed, ground into balls, and sieved to obtain flake-shaped nanoparticles; the thickness of the flake-shaped nanoparticles is 3μm to 6μm, and the flake diameter is 75μm to 150μm. The flaky nanoparticles are subjected to surface activation treatment to obtain activated nanoparticles; The activated nanoparticles are mixed with a resin solution to obtain a slurry. A magnetic field is provided, and the slurry is coated and dried in the magnetic field to obtain a shielding composite material. The shielding composite material is then die-cut to obtain a shielding sheet.

2. The preparation method according to claim 1, characterized in that, The process of crushing, grinding, and sieving the soft magnet to obtain flake-like nanoparticles includes: The soft magnet is crushed and then subjected to grinding ball treatment, during which an anti-oxidation medium is added; the anti-oxidation medium includes at least one of anhydrous ethanol, acetone, isoacetone, hexane, stearic acid, zinc stearate, and paraffin oil; The soft magnet, after being treated with the grinding ball, is subjected to several sieve treatments to obtain the sheet-like nanopowder.

3. The preparation method according to claim 1, characterized in that, The surface activation treatment of the sheet-like nanoparticles to obtain activated nanoparticles includes: The sheet-like nanoparticles were added to pure water to obtain a sheet-like nanoparticle solution. Sodium citrate was added to the sheet-like nanopowder solution, and after stirring and mixing, the mixture was heated and refluxed to obtain a mixture. The mixture was then filtered to obtain a solid powder. The solid powder was washed with anhydrous ethanol and then dried to obtain the activated nanopowder.

4. The preparation method according to claim 1, characterized in that, The soft magnet includes at least one of nanocrystalline, amorphous, ferrite, and sheet-like iron-silicon-aluminum.

5. The preparation method according to claim 1, characterized in that, The magnetic field strength is 0.5T to 1.8T, and the processing time of the magnetic field is 20min to 40min.

6. The preparation method according to claim 1, characterized in that, The mass ratio of the resin to the activated nanoparticles is 1:0.5 to 1:

1.

7. The preparation method according to any one of claims 1 to 6, characterized in that, The resin includes at least one of acrylic resin, epoxy resin, thermoplastic polyurethane, and phenolic resin.

8. The preparation method according to any one of claims 1 to 6, characterized in that, The thickness of the soft magnet is 12 μm to 18 μm.

9. A shielding sheet, characterized in that, It is prepared by the method of preparing the shielding sheet as described in any one of claims 1 to 8.

10. An antenna, characterized in that, The antenna includes the shielding sheet as described in claim 9.

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