CN114957786A - Asymmetric electromagnetic shielding composite material, preparation method thereof and electromagnetic shielding device - Google Patents

Abstract

The invention relates to the technical field of functional materials, in particular to an electromagnetic shielding composite material with an asymmetric structure, a preparation method thereof, and an electromagnetic shielding device. In the present invention, a porous structure is first introduced into the matrix through gas foaming technology, and then a conductive metal electromagnetic shielding layer is coated on the surface of the matrix to form an asymmetric structure, the porous polymer matrix is used as the wave-absorbing foam layer, and the conductive metal shielding layer is combined. The reflection effect of the layer on the electromagnetic wave makes the electromagnetic wave go through the process of "low reflection-absorption-reflection-reabsorption" when the electromagnetic wave is incident from one side of the wave-absorbing foam; at the same time, the invention adopts the process of low temperature and high pressure impregnation and then processed by high temperature supercritical gas. The bubble process method forms a uniform cell structure inside the matrix material, so that the electromagnetic wave entering the material is repeatedly reflected and scattered to extend its attenuation path, so that the prepared composite material has both extremely low reflection characteristics and ultra-high electromagnetic waves. Shielding performance, can be used in electronic communication equipment, aerospace, medical care and other fields.

Description

Asymmetric structure electromagnetic shielding composite material and preparation method thereof, and electromagnetic shielding device

technical field

The invention relates to the technical field of functional materials, in particular to an electromagnetic shielding composite material with an asymmetric structure, a preparation method thereof, and an electromagnetic shielding device.

Background technique

With the rapid development of the electronic information industry and the widespread use of integrated and high-power electronic equipment, the problem of electromagnetic radiation pollution has become increasingly serious, which not only affects the normal operation of precision instruments and equipment, but also threatens human health. Therefore, the development of high-performance electromagnetic shielding materials is of great significance for the protection of electromagnetic hazards. At the same time, information and communication, aerospace, military, civil and other electromagnetic protection fields need lightweight electromagnetic shielding materials to reduce energy consumption, and lightweight high-performance electromagnetic shielding composite materials are urgently needed in the future.

The performance of traditional shielding materials mainly depends on the perfection and conductivity of the conductive network. In order to obtain good electrical conductivity, it is often necessary to add a high content of conductive fillers (such as graphene, carbon nanotubes, carbon black, metals, etc.). These conductive fillers will not only cause the impedance mismatch between the surface of the composite material and the air, but also cause a large number of incident electromagnetic waves to be reflected (>90%), causing serious secondary electromagnetic radiation pollution problems. In order to tune the contradiction between high shielding performance and low reflection characteristics, investigated methods include building porous structures inside composites, but existing porous structures require complex preparations such as freeze-drying, chemical foaming, expanded microsphere foaming, etc. There are problems such as expensive equipment, environmental pollution, and high material cost. Therefore, developing a lightweight polymer electromagnetic shielding material with both low reflection characteristics and high shielding performance, simplifying its technological process, and realizing its low-cost standardized preparation has become an urgent technical problem to be solved.

SUMMARY OF THE INVENTION

In order to overcome the defects of the prior art, one of the purposes of the present invention is to provide a method for preparing an electromagnetic shielding composite material with an asymmetric structure. The low-temperature impregnation of supercritical fluid and the foaming of high-temperature supercritical fluid form a uniform cell structure, so that the composite The material has low reflection properties.

The second purpose of the present invention is to provide an electromagnetic shielding composite material with an asymmetric structure, which is prepared by the preparation method of the present invention. The internal porous structure and the surface metal layer cooperate to make the composite material have excellent electromagnetic shielding performance.

At the same time, the present invention also provides an electromagnetic shielding device, which is prepared by using the electromagnetic shielding composite material with the asymmetric structure provided by the present invention.

In order to achieve the above object, the technical scheme adopted in the present invention is as follows:

A method for preparing an electromagnetic shielding composite material with an asymmetric structure, comprising first preparing a magnetic conductive polymer matrix, and then performing foaming treatment on the magnetic conductive polymer matrix; wherein the foaming treatment includes firstly preparing the magnetic conductive polymer matrix in a supercritical state. Impregnating at low temperature in the fluid under pressure, and then rapidly foaming with supercritical fluid at the foaming temperature after decompression to obtain a porous structure polymer matrix; coating a conductive metal electromagnetic shielding layer on the surface of one side of the porous structure polymer matrix; wherein The pressure of low temperature holding pressure impregnation is higher than the foaming pressure.

Optionally, the magnetic conductive polymer matrix is prepared by compounding conductive fillers, magnetic particles and high molecular polymers; the mass and dosage ratio of the conductive fillers, magnetic particles and high molecular polymers is 1:1:100.

As an example, in some embodiments of the present invention, the conductive filler is carbon fiber, carbon nanotube, graphene, carbon nanofiber, nanographite sheet, graphite, carbon black or fullerene; more preferably carbon nanotube The magnetic particles are reduced graphene oxide-loaded triiron tetroxide; the macromolecular polymer is polypropylene, polyethylene, polylactic acid, silicone rubber, thermoplastic polystyrene elastomer, thermoplastic polyolefin elastomer, thermoplastic copolymer Polyester elastomer, thermoplastic polyamide elastomer or thermoplastic polyurethane elastomer; further preferably thermoplastic polyurethane elastomer.

Preferably, the pressure of the low-temperature pressure-holding impregnation is 20Mpa, the temperature is 40°C, the pressure-holding time is 2 hours, and the pressure-releasing rate is 5MPa/s.

Further preferably, the specific process of rapidly foaming with a supercritical fluid at the foaming temperature after depressurization includes maintaining pressure, dipping and depressurizing, quickly taking out the sample and placing it in a reaction kettle whose internal temperature reaches the foaming temperature, and feeding the pre-pressure The heated supercritical fluid is pressure-relieved after a certain period of time.

Further preferably, the foaming temperature is 100° C.; the temperature of the preheated supercritical fluid is 90° C.; the pressure holding time is 10 min; and the pressure relief rate is 5 MPa/s.

It should be noted that the supercritical fluid can select any foaming gas known in the prior art, and the type of foaming gas does not affect the performance of the prepared composite material. As an example, the supercritical fluid can select nitrogen, air, helium gas, argon, petroleum ether, methane, ethane, propane, butane, pentane, hexane, heptane, n-pentane, n-hexane, n-heptane, dichloromethane or trichlorofluoromethane.

Optionally, the preparation method of the magnetic conductive polymer matrix includes adding conductive fillers into the organic solvent dispersion of magnetic particles, then adding high molecular polymer particles, heating to the dissolution temperature, stirring and mixing uniformly, and pouring into excess deionized water for flocculation. After precipitation, take out, dry to remove the organic solvent, and hot-press to obtain the magnetic conductive polymer matrix;

It also includes firstly preparing magnetic particles, the preferred magnetic particles of the present invention are graphene-loaded ferric oxide particles, and the preparation method includes slowly adding ferric chloride hexahydrate to the graphene organic solvent dispersion, stirring and mixing uniformly, and then adding NaOH and hydrazine hydrate are heated and reacted and cooled to room temperature to obtain a graphene-loaded ferric oxide composite particle dispersion, which is alternately washed with water and ethanol and dried to obtain reduced graphene oxide-loaded ferric oxide composite particle powder.

The organic solvent used in the above preparation method is selected from ethanol, methanol, isopropanol, ethylene glycol, acetone, hexane, pentane, heptane, octane, aniline, butanone, chloroform, dimethylamine, n-heptanol , tetrahydrofuran, benzene, toluene, xylene, ethylbenzene, butyl acetate, chloroform, formic acid, dimethyl sulfoxide, chlorobenzene, dichlorobenzene, dichloromethane, trichloroethylene or N-methylpyrrolidone, etc.

Optionally, the conductive metal electromagnetic shielding layer is a conductive silver layer; the thickness is 30 mm; the thickness of the porous structure polymer matrix is 2 mm.

An electromagnetic shielding composite material with asymmetric structure is prepared by the above preparation method. The composite material of the present invention can be used to manufacture electromagnetic shielding devices applied in the fields of electronic communication equipment, aerospace, medical care and the like.

In the electromagnetic shielding composite material with asymmetric structure provided by the present invention, a porous structure is first introduced into the magnetic conductive polymer matrix by gas foaming technology, and then a conductive metal electromagnetic shielding layer is coated on the surface of the matrix to form an asymmetric structure with porous structure. The polymer matrix is used as the wave absorbing layer, combined with the conductive metal electromagnetic shielding layer on the surface side, so that the electromagnetic wave goes through the process of "low reflection-absorption-reflection-reabsorption" when incident from the wave-absorbing foam side; The foaming process of the magnetic conductive polymer matrix forms a uniform cell structure inside it, which reduces the reflection of the material to the electromagnetic wave, and the multiple reflection and scattering of the electromagnetic wave at the cell interface prolongs the attenuation path of the electromagnetic wave, making the prepared composite material. With both low reflection characteristics and high electromagnetic shielding performance, it can be used in electronic communication equipment, aerospace, medical care and other fields. The principles include:

(1) The principle of low reflection: the magnetic conductive polymer matrix is rapidly foamed under the conditions of foaming temperature and pressure after immersion at low temperature and high pressure, and pre-heated supercritical fluid is preferably introduced at the foaming temperature. A uniform cell structure is introduced into the conductive polymer matrix to increase impedance matching, so that more electromagnetic waves enter the material instead of being reflected. At the same time, the multiple reflection and scattering of electromagnetic waves are increased, the transmission path of electromagnetic waves is extended, and the absorption of electromagnetic waves is enhanced, thereby endowing the composite material with low reflection characteristics;

(2) Principle of high electromagnetic shielding performance: Due to the composite of dense conductive metal electromagnetic shielding layers, an asymmetric structural composite material based on absorbing foam is constructed, so that electromagnetic waves are incident from the absorbing foam side through "low reflection-absorption-reflection" -Reabsorption" process prolongs its transmission path and enhances electromagnetic wave absorption, thus giving syntactic foam excellent electromagnetic shielding properties.

The preparation method provided by the invention is simple, feasible, low in cost and capable of large-scale production.

Description of drawings

1 is a schematic overall flow diagram of a method for preparing an electromagnetic shielding composite material with an asymmetric structure according to an embodiment of the present invention;

Fig. 2 is the scanning electron microscope picture of the reduced graphene oxide supported ferric oxide composite particle prepared by the embodiment of the present invention 1;

3 is a cross-sectional SEM image of the electromagnetic shielding composite material with asymmetric structure prepared in Example 1 of the present invention;

Fig. 4 is the reflection power coefficient comparison diagram of the magnetic conductive polymer matrix prepared by Example 1, Comparative Example 1 and Comparative Example 2 of the present invention before and after foaming in the X-band; wherein (a) is before foaming; (b) is hair after soaking;

5 is a comparison diagram of electromagnetic shielding performance (SSE _T ), absorption power coefficient A, transmission power coefficient T, and reflected power coefficient R before and after the magnetic conductive polymer matrix prepared by Example 1, Comparative Example 1 and Comparative Example 2 of the present invention ; Wherein (a) is before foaming; (b) is after foaming;

Fig. 6 is the absorption efficiency (SE _A ), the total electromagnetic shielding effectiveness ( _SET ), the reflection shielding effectiveness (SE ) of the electromagnetic shielding composite materials with asymmetric structure prepared in Example 1, Comparative Example 1 and Comparative Example 2 of the present invention in the X-band _R ) Comparison diagram; where (a) is the average value; (b) is the variation curve of absorption effectiveness (SE _A ) and total electromagnetic shielding effectiveness ( _SET ) at different frequencies; (c) is the reflection shielding effectiveness ( _SER ) at different frequencies ) change curve;

7 is a comparison diagram of reflected power (R), absorbed power (A), and transmitted power (T) in the X-band of the electromagnetic shielding composite materials with asymmetric structure prepared in Example 1, Comparative Example 1 and Comparative Example 2 of the present invention; wherein (a) is the average value; (b) is the variation curve of reflected power (R) at different frequencies; (c) is the variation curve of absorbed power (A) and transmitted power (T) at different frequencies;

FIG. 8 is a comparison of the average values of absorption effectiveness (SE _A ), total electromagnetic shielding effectiveness ( _SET ) and reflection shielding effectiveness ( _SER ) in the X-band of the electromagnetic shielding composite material with asymmetric structure prepared according to the preparation process provided in Comparative Example 3 picture.

Detailed ways

The technical solutions of the present invention will be described in detail below through specific embodiments.

The overall flow of the preparation method of the electromagnetic shielding composite material with the asymmetric structure provided by the following embodiments is shown in FIG. 1 .

Example 1

The present embodiment provides an electromagnetic shielding composite material with an asymmetric structure, and the specific operation steps of the preparation method are as follows:

S1. Preparation of reduced graphene oxide supported ferric oxide composite particles:

Add 0.28 g of graphene to 140 ml of ethylene glycol and ultrasonically for 30 min to make it uniformly dispersed, then slowly add 2.7 g of ferric chloride hexahydrate under mechanical stirring conditions, and add 2 g of NaOH and 10 ml of hydrazine hydrate after stirring evenly. Subsequently, the homogeneously mixed solution was put into a reaction kettle, placed at 200°C for 12 hours, and then cooled to room temperature naturally to obtain a dispersion liquid of reduced graphene oxide-supported ferric oxide composite particles; the dispersion liquid was mixed with deionized water and ethanol After being alternately centrifuged and cleaned five times, it was dried in an oven at 80 °C to obtain reduced graphene oxide-supported ferric tetroxide composite particle powder. The present embodiment prepares and obtains the reduced graphene oxide supported ferric oxide composite particles without agglomeration and uniform dispersion;

S2. Preparation of Magnetic Conductive Polymer Matrix:

0.15g carbon nanotubes and 0.15g reduced graphene oxide supported ferric oxide composite particle powder prepared in step S1 were ultrasonically dispersed in 200ml N-N dimethylformamide, 15g polyurethane particles were added and stirred at 60°C for 4h, The mixed solution was poured into excess deionized water for flocculation and precipitation, then taken out, dried in an oven at 80 °C for 8 hours to remove the solvent, and then the dried composite material was hot-pressed by a vacuum-assisted hot press to obtain carbon nanotubes/graphite. The alkene-supported triiron tetroxide/polyurethane composite as a magnetic conductive polymer matrix, marked as S-T/C1/MG;

S3. Preparation of electromagnetic shielding composite material with asymmetric structure:

Put the carbon nanotube/graphene supported ferric oxide/polyurethane composite material obtained in step S2 into a 40°C autoclave, inject 20MPa carbon dioxide gas and keep the pressure for 2h, and then release the pressure at a rate of 5MPa/s to normal pressure, quickly take out the sample and put it into another reaction kettle with a temperature of 100 ° C, feed 8 Mpa of carbon dioxide heated to 90 ° C, after 10 minutes, quickly release the pressure at a speed of 5 MPa/s to obtain carbon nanotubes/graphene Loaded ferric oxide/polyurethane composite foam, its thickness is about 2mm, marked as F-T/C1/MG; then use a scraper to coat a layer of conductive silver glue on one side of the composite foam and put it in an 80℃ oven for 10min to cure it , set the distance between the scraper and the surface of the syntactic foam to be 30mm, and obtain the asymmetric structure carbon nanotube/graphene supported ferric oxide/polyurethane composite foam, which is marked as F-T/C1/MG-Ag, as shown in Figure 3 as F-T/ The cross-sectional SEM image of C1/MG-Ag shows that it has a uniform and dense porous structure inside, and the surface is uniformly covered with a conductive silver layer.

Comparative Example 1

This embodiment provides an electromagnetic shielding composite material with an asymmetric structure, the preparation method of which is different from that of Embodiment 1 in that 0.3 g of carbon nanotubes are added in step S2 to obtain a magnetic conductive polymer matrix, which is marked as S-T/C2/ MG; carbon nanotube/graphene supported ferric oxide/polyurethane composite foam with a thickness of 2 mm, marked as F-T/C2/MG; asymmetric structure carbon nanotube/graphene supported triiron tetroxide/polyurethane composite foam, Labeled as F-T/C2/MG-Ag.

Comparative Example 2

This embodiment provides an electromagnetic shielding composite material with an asymmetric structure. The difference between the preparation method and the embodiment 1 is that 0.45 g of carbon nanotubes are added in step S2 to obtain a magnetic conductive polymer matrix, which is marked as S-T/C3/ MG; carbon nanotube/graphene supported ferric oxide/polyurethane composite foam with a thickness of 2 mm, marked as F-T/C3/MG; asymmetric structure carbon nanotube/graphene supported ferric oxide/polyurethane composite foam, Labeled as F-T/C3/MG-Ag.

Comparative Example 3

This comparative example provides a preparation process of an electromagnetic shielding composite material with an asymmetric structure. The carbon nanotube/graphene-supported ferric oxide/polyurethane composite material obtained in step S2 of Example 1 is placed in a reaction kettle with a temperature of 100 °C , the carbon nanotube/graphene supported ferric oxide/polyurethane composite foam was obtained, and the thickness was controlled to 2mm. Finally, one side of the composite foam is coated with a layer of conductive silver glue and then placed in an oven at 80°C for 10 minutes to cure. The distance between the scraper and the surface of the composite foam is set to 30mm, and an asymmetric carbon nanotube/graphene supported tetroxide is prepared. Triiron/polyurethane composite foam, labeled F-T/C1/MG-Ag-N.

Adjust the amount of carbon nanotubes in step S2 according to the same method as Comparative Example 1 and Comparative Example 2, and then follow the same preparation process provided in Comparative Example 3 to prepare asymmetric carbon nanotubes/graphene-supported iron tetroxide/polyurethane composite Foams, labeled as F-T/C2/MG-Ag-N and F-T/C3/MG-Ag-N, respectively.

Test case performance verification

1. Using an electromagnetic shielding tester to measure the reflection power coefficient R of the magnetic conductive polymer matrix prepared in Example 1, Comparative Example 1 and Comparative Example 2 before and after foaming in the X-band, the results are shown in Figure 4; the absorption power coefficient A, transmission Power coefficient T, average reflected power coefficient R, as shown in Figure 5;

The results shown in Figure 4 and Figure 5 show that with the increase of the amount of carbon nanotubes, the reflected power coefficients R of the solids before foaming in Example 1, Comparative Example 1 and Comparative Example 2 are: 0.46, 0.61, and 0.68, respectively; The reflected power coefficients R of the porous foam after foaming are: 0.23, 0.36, 0.42; the absorbed power coefficients A of the solid before foaming are: 0.49, 0.38, 0.32; the absorbed power coefficients A of the porous foam after foaming are: 0.46, 0.48, 0.51; the characteristic shielding properties of the foamed solid are: 11.9, 19.2, 23.9dB cm ³ g ^-1 ; the characteristic shielding properties of the foam after foaming are: 13.2, 21.8, 26.3dB cm ³ g ^-1 ; In the entire X-band, the reflected power coefficients of the solid samples before foaming were greater than those after foaming under different carbon nanotube contents, indicating that the foaming process reduced the reflection of the composite material to electromagnetic waves; with the increase of carbon nanotube content , the reflected power coefficient R value of the solid sample before foaming is greater than the reflected power coefficient R value of the sample after foaming, and the characteristic electromagnetic shielding efficiency after foaming is significantly improved, indicating that the foaming process significantly reduces the reflection of the composite material to electromagnetic waves and improves the shielding properties of the composite material.

3. Use an electromagnetic shielding tester to measure and calculate the absorption efficiency (SE _A ), the total electromagnetic shielding efficiency ( _SET ), Reflection shielding effectiveness (SE _R ), as shown in Figure 6, with the increase of the amount of carbon nanotubes, the absorption efficiency SE _A of the asymmetric structure electromagnetic shielding composite materials prepared in Example 1, Comparative Example 1 and Comparative Example 2 are respectively : 88.9dB, 95dB, 102.7dB.; the total shielding effectiveness SE _T is 89.2dB, 95.5dB, 103.5dB; the average reflection shielding effectiveness SE _R of the X-band is 0.24dB, 0.5dB, 0.83dB respectively; in the entire X-band , the average reflection shielding effectiveness (SER ), absorption effectiveness (SE _A ) and total electromagnetic shielding effectiveness ( _{SET )} of the asymmetric structure electromagnetic shielding composites increased with the increase of carbon nanotube content, indicating that the electromagnetic wave reflection is not effective. increase, and the SE _A curve almost overlaps with the SE _T , which means that the increase of the total shielding performance SE _T is mainly due to the increase of the absorption loss SE _A , which proves that the composite material prepared by the present invention is mainly based on the absorption loss realized by the unique porous structure. electromagnetic shielding mechanism.

4. Use an electromagnetic shielding tester to measure and calculate the reflected power (R), absorbed power (A) and transmitted power (T) of the electromagnetic shielding composite materials with asymmetric structures prepared in Example 1, Comparative Example 1 and Comparative Example 2 in the X-band ), as shown in Figure 7, with the increase of the amount of carbon nanotubes, the average reflected power coefficients (R) of the asymmetric structural composite foams prepared in Example 1, Comparative Example 1 and Comparative Example 2 are: 0.05, 0.11, 0.17 , the absorption power coefficient (A) values are: 0.95, 0.89, 0.83, and the T values are: 2.73545×10 ^-9 , 3.76084×10 ^-10 , 9.41558×10 ^-11 ; The reflected power coefficient R of the electromagnetic shielding composites with asymmetric structure prepared in Example 1 and Comparative Example 2 increased with the increase of carbon nanotube content, and the absorbed power coefficient A and transmission power coefficient T both increased with the increase of carbon nanotube content. decreased, but due to the asymmetric structure design, the R value remained extremely low in the entire X-band range; when the carbon nanotube mass in Example 1 was 1% of the polyurethane mass, and the asymmetric structure syntactic foam was at 10.9GHz, the reflection The minimum peak value of the power coefficient R value is 0.001, and the maximum peak value of the absorption power coefficient A value is 0.999, indicating that 99.9% of the electromagnetic waves are absorbed.

5. An electromagnetic shielding tester was used to measure and calculate the absorption effectiveness (SE _A ), total electromagnetic shielding effectiveness ( _SET ) and reflection shielding effectiveness of the electromagnetic shielding composite material with asymmetric structure prepared according to the preparation process described in Comparative Example 3 in the X-band. (SE _R ), as shown in Fig. 8, with the increase of the amount of carbon nanotubes, the absorption efficiency SE _A of the prepared asymmetric structure electromagnetic shielding composite material is: 77.9dB, 81.5dB, 84.1dB. The total shielding The effectiveness SE _T is 80.3dB, 85.6dB, 91.3dB respectively; the average reflection shielding effectiveness SE _R of the X-band is 2.4dB, 4.1dB, 7.2dB, respectively, the composite materials prepared in Comparative Example 1, Comparative Example 1 and Comparative Example 2 , after omitting the low temperature and high pressure impregnation process, the electromagnetic shielding performance of the composite material is greatly reduced.

To sum up, the composite material prepared with the mass dosage ratio of conductive filler, magnetic particles and high molecular polymer at 1:1:100 has a high electromagnetic shielding performance of 89.2dB and a reflection power coefficient as low as 0.05, and the reflection efficiency SE _R Only 0.24dB, the absorption power coefficient A value is as high as 0.95. Indicates that 99.9999999% of electromagnetic waves are shielded and only 0.5% of electromagnetic waves are reflected. Furthermore, at 10.9 GHz, the minimum reflected power coefficient R value is as low as 0.001, indicating that only 0.1% of the electromagnetic waves are reflected. It shows that the electromagnetic shielding composite material with asymmetric structure prepared by the invention has both low reflection characteristics and high electromagnetic shielding performance, and can be applied to the fields of electronic communication equipment, aerospace, medical care and the like.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, but not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that it can still be The technical solutions described in the foregoing embodiments are modified, or some technical features thereof are equivalently replaced; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims (10)

1. a preparation method of asymmetric structure electromagnetic shielding composite material, is characterized in that, comprises at first preparing magnetic conductive polymer matrix, then carries out foaming treatment to magnetic conductive polymer matrix; Wherein foaming treatment comprises at first magnetic conductive polymer matrix The polymer matrix is immersed in a supercritical fluid under low temperature and pressure, and after the pressure is released, it is rapidly foamed with a supercritical fluid at the foaming temperature to obtain a porous structure polymer matrix; the surface of the porous structure polymer matrix is coated with conductive Metal electromagnetic shielding layer; wherein the pressure of the low temperature holding pressure impregnation is greater than or equal to the foaming pressure. 2 . The method for preparing an electromagnetic shielding composite material with asymmetric structure according to claim 1 , wherein the magnetic conductive polymer matrix is prepared by compounding conductive fillers, magnetic particles and high molecular polymers; the conductive fillers, The mass dosage ratio of magnetic particles and high molecular polymer is 1:1:100. 3. The preparation method of asymmetric structure electromagnetic shielding composite material as claimed in claim 2, it is characterized in that, described conductive filler is carbon fiber, carbon nanotube, graphene, carbon nanofiber, nanographite sheet, graphite, carbon black or fullerene; the magnetic particles are reduced graphene oxide supported triiron tetroxide; the macromolecular polymer is polypropylene, polyethylene, polylactic acid, silicone rubber, thermoplastic polystyrene elastomer, thermoplastic polyolefin elastic polyester, thermoplastic copolyester elastomer, thermoplastic polyamide elastomer or thermoplastic polyurethane elastomer. 4. The preparation method of electromagnetic shielding composite material with asymmetric structure as claimed in claim 3, characterized in that, the pressure of the low-temperature pressure-holding impregnation is 20Mpa, the temperature is 40°C, and the pressure-holding time is 2 hours; the pressure relief rate is 5MPa/ s. 5. the preparation method of the electromagnetic shielding composite material of asymmetric structure as claimed in claim 4, and it is characterized in that, the concrete process of foaming with supercritical fluid under the foaming temperature rapidly after pressure relief comprises pressure-retaining dipping after pressure-relief , quickly take out the sample and put it into the reaction kettle whose internal temperature reaches the foaming temperature, feed the preheated supercritical fluid, and release the pressure after maintaining the pressure for a certain period of time. 6 . The preparation method of the electromagnetic shielding composite material with asymmetric structure according to claim 5 , wherein the foaming temperature is 100° C.; the temperature of the preheated supercritical fluid is 90° C.; the pressure holding time is 10 min; The pressure rate was 5MPa/s. 7. The preparation method of the asymmetric structure electromagnetic shielding composite material according to any one of claims 2 to 6, and characterized in that, the preparation method of the magnetic conductive polymer matrix comprises adding the conductive filler to the magnetic particle organic solvent dispersion, Then add high molecular polymer particles, heat to the melting temperature, stir and mix evenly, pour into excess deionized water for flocculation precipitation, take out, dry to remove the organic solvent, and hot-press molding to obtain a magnetic conductive polymer matrix. 8. The preparation method of the asymmetric structure electromagnetic shielding composite material according to any one of claims 2 to 6, wherein the conductive metal electromagnetic shielding layer is a conductive silver layer; the thickness is 30mm; the porous structure polymer matrix The thickness is 2mm. 9 . An electromagnetic shielding composite material with an asymmetric structure, characterized in that it is prepared by the preparation method according to any one of claims 1 to 8 . 10 . An electromagnetic shielding device, characterized in that, it is made of the electromagnetic shielding composite material with asymmetric structure as claimed in claim 9 .

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