A Carbon Microsphere Structure Electromagnetic Wave Absorbing Metamaterial and Its Preparation Method and Application

Abstract

The present invention relates to a carbon microsphere structure electromagnetic wave absorbing metamaterial and its preparation method and application. The present invention uses a coprecipitation in-situ self-assembly technique and prepares a Fe3O4 electromagnetic wave absorbing metamaterial with carbon microsphere arrays filled inside through high-temperature calcination. Specifically, an iron source, a dispersant, and polymer microspheres are added to deionized water. After stirring, a precipitating agent is added to the solution, and then a magnetic Fe3O4 sol is obtained through ultrasonic stirring. Then, the sol is subjected to vacuum filtration. After the filter cake is washed, dried, and ground, the Fe3O4 and the polymer microspheres are self-assembled to obtain a metamaterial precursor. The metamaterial precursor is placed in a high-temperature tube furnace for calcination, and after cooling, a carbon microsphere structure electromagnetic wave absorbing metamaterial is obtained. This material has a strong loss function for electromagnetic waves in the frequency band of 1 to 18 GHz and meets the characteristics of "thin, light, wide, and strong".

Description

Technical Field

[0001] The present invention relates to the technical field of electromagnetic wave absorbing materials, and particularly to a carbon microsphere structure electromagnetic wave absorbing metamaterial and its preparation method and application. Background Art

[0002] With the development of science and technology in our country, various information transmission and communication tools, computers, and household appliances have entered people's lives in large numbers, and the integration of Internet services and social life has become increasingly deep. According to reports, as of June 2021, the scale of Internet users in our country has reached 1.011 billion, and as many as 1.007 billion of them are mobile Internet users, which is sufficient to prove the huge role of smart phones in the popularization of the Internet. In the rapidly emerging mobile Internet era, while humans enjoy the speed, convenience, comfort brought by modernization and the great benefits brought by information technology, the opportunities to contact and be exposed to the electromagnetic fields generated by various electrical appliances are gradually increasing, and people are being threatened by the potential harm to physical and mental health caused by the deteriorating electromagnetic environment. Electromagnetic wave radiation has been listed by the World Health Organization as the fourth largest environmental pollutant after water source, atmosphere, and noise, becoming an invisible killer endangering human health. Long-term exposure to electromagnetic wave environments in certain harmful frequency bands for the human body will cause dizziness, memory loss, tinnitus and other phenomena. Some electromagnetic waves will damage the immune system, increase the probability of cancer, and even some complete exposures in a short time can be directly lethal. Therefore, controlling electromagnetic pollution and finding a material that can shield and weaken electromagnetic wave radiation has become a major topic in materials science. Electromagnetic wave absorbing materials are a type of material that can absorb or significantly weaken the electromagnetic wave energy received on its surface, thereby reducing electromagnetic wave interference. It can convert electromagnetic energy into heat energy and dissipate it to achieve the purpose of reducing or even absorbing electromagnetic waves. Summary of the Invention

[0003] To solve the above problems, the present invention provides a carbon microsphere structure electromagnetic wave absorbing metamaterial and its preparation method and application. The present invention adopts a co-precipitation in-situ self-assembly technology, and through high-temperature calcination, prepares a magnetite electromagnetic wave absorbing metamaterial with carbon microsphere arrays filled inside. This material has a strong loss function for electromagnetic waves in the frequency band of 1 - 18 GHz, meeting the characteristics of "thin, light, wide, and strong", that is, the material has a thin thickness, light weight, wide wave absorption frequency band, and strong wave absorption intensity. This is a new type of electromagnetic wave absorbing metamaterial, which has good application value and market prospects in the field of electromagnetic radiation protection technology.

[0004] One of the purposes of the present invention is to provide a preparation method of a carbon microsphere structure electromagnetic wave absorbing metamaterial, and this method specifically includes the following steps:

[0005] (1) Dissolve a certain mass of dispersant in an appropriate amount of deionized water and stir evenly;

[0006] (2) Add a certain mass of iron source and polymer microspheres to the solution obtained in step (1). After stirring evenly at room temperature, solution A is obtained. Add a certain amount of precipitant to solution A and control the dropping rate. While dropping the precipitant, perform ultrasonic stirring to prepare magnetic Fe3O4 sol. After stirring the sol evenly, use diatomite as the filtration medium to perform vacuum filtration on the sol. Among them, Fe3O4 nanocrystals and polymer microspheres self-assemble and arrange to form a metamaterial structure. Wash the filter cake obtained after filtration successively with deionized water and ethanol. Then place the washed filter residue precipitate in a vacuum drying oven and dry it at 40 - 60 °C for 1 - 3 h. After drying, grind the obtained solid material to obtain a metamaterial precursor for standby;

[0007] (3) Put the metamaterial precursor obtained in step (2) into a high-temperature tube furnace. Under the protection of N2 atmosphere, calcine it at 400 - 500 °C for 4 - 6 h. Then cool it to room temperature to obtain a black magnetic powder. Grind the black magnetic powder and pass it through a 200-mesh sieve. The black magnetic powder after sieving is the carbon-containing microsphere structure electromagnetic wave absorption metamaterial.

[0008] Further, in step (1), the dispersant includes one or more of sodium carboxymethyl cellulose, hydroxyethyl cellulose, polyvinylpyrrolidone, polyethylene glycol 400, polyethylene glycol 2000, polyethylene glycol 4000, etc.;

[0009] Further, in step (2), the iron source includes Fe 2+ iron source, Fe 3+ iron source, and the molar ratio of Fe 2+ iron source to Fe 3+ iron source is 1:1.8;

[0010] Further, in step (2), the mass fraction of the iron source in solution A is 2 - 5%, the mass fraction of the dispersant is 10 - 20%, and the mass fraction of the polymer microspheres is 2 - 5%;

[0011] Further, in step (2), the molar ratio of the precipitant to the iron source is 2:1;

[0012] Further, in step (2), Fe 2+ the iron source includes one or more of ferrous chloride, ferrous sulfate, ferrous nitrate; Fe 3+ the iron source includes one or more of ferric chloride, ferric sulfate, ferric nitrate;

[0013] Further, in step (2), the precipitant includes one or more of a potassium hydroxide solution with a concentration of 0.5 mol·L -1 and a 10% ammonia water by mass;

[0014] Further, the dropping rate of the precipitating agent in step (2) is 30 - 60 drops per minute;

[0015] Further, the time of ultrasonic stirring in step (2) is 10 - 30 min;

[0016] Further, the polymer microspheres in step (2) are one or more of polystyrene, polystyrene / methacrylic acid, polystyrene / methyl acrylate, and polystyrene / methyl methacrylate microspheres;

[0017] Further, the polymer microspheres in step (2) have a smooth and pore-free surface and a particle size of 200 - 1000 nm.

[0018] Further, the polymer microspheres with a smooth and pore-free surface in step (2) are self-made, and the preparation method is as follows:

[0019] Preparation of polystyrene microspheres: Measure 20 mL of styrene monomer and transfer it to a 250 mL separatory funnel. Wash it 3 - 4 times with a 5% by mass sodium hydroxide solution and then wash it 6 - 7 times with distilled water. After measuring that the pH of the styrene monomer in the separatory funnel is neutral, transfer it to a three-necked flask. Then add 150 mL of distilled water to the three-necked flask, heat it in a water bath at 50 - 70 °C, and at the same time, introduce nitrogen and magnetically stir the solution in the three-necked flask. After introducing nitrogen for 10 min, weigh 0.108 g of ammonium persulfate and dissolve it in 10 mL of distilled water, and slowly add the ammonium persulfate solution to the above three-necked flask with a pipette. After the addition is completed, introduce nitrogen for another 10 min. It can be seen that the solution in the three-necked flask turns blue and then becomes milky white. Stop the reaction after 7 - 9 h. Centrifuge the solution in the three-necked flask, wash the precipitate obtained by centrifugation with distilled water, collect the precipitate obtained by centrifugation and place it in an oven to dry at 50 - 60 °C for 2 - 3 days. The dried solid is ground to obtain polystyrene microspheres.

[0020] Preparation of polystyrene / methacrylic acid, polystyrene / methyl acrylate, and polystyrene / methyl methacrylate microspheres: Measure 20 mL of styrene monomer and transfer it to a 250 mL separatory funnel. Wash it 3 - 4 times with a 5% sodium hydroxide solution by mass and then wash it 6 - 7 times with distilled water. After measuring that the pH of the styrene monomer in the separatory funnel is neutral, transfer it to a three-necked flask. Then, add 4 mL of the second monomer and 150 mL of distilled water to the three-necked flask. Heat it in a water bath at 50 - 70 °C, while introducing nitrogen and magnetically stirring the solution in the three-necked flask. After introducing nitrogen for 10 min, weigh 0.108 g of ammonium persulfate and dissolve it in 10 mL of distilled water. Slowly drip the ammonium persulfate solution into the above three-necked flask with a pipette. After the dripping is completed, introduce nitrogen for another 10 min. It can be seen that the solution in the three-necked flask turns blue and then becomes milky white. Stop the reaction after 7 - 9 h. Centrifuge the solution in the three-necked flask, wash the precipitate obtained by centrifugation with distilled water, collect the centrifuged precipitate and place it in an oven to dry at 50 - 60 °C for 2 - 3 days. The dried solid is ground to obtain polymer microspheres. When the second monomer is methacrylic acid, methyl acrylate, or methyl methacrylate respectively, the prepared polymer microspheres are polystyrene / methacrylic acid microspheres, polystyrene / methyl acrylate microspheres, and polystyrene / methyl methacrylate microspheres respectively.

[0021] Another object of the present invention is to provide a carbon-containing microsphere structure electromagnetic wave absorbing metamaterial prepared by the above method and the application of the carbon-containing microsphere structure electromagnetic wave absorbing metamaterial as an electromagnetic wave absorbing material in the field of electromagnetic radiation protection technology.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) For the carbon-containing microsphere structure electromagnetic wave absorbing metamaterial prepared by the present invention, in its microscopic structure, magnetite nanocrystals are distributed around the array formed by self-assembly of carbonized polymer microspheres, forming a magnetic metamaterial. Magnetite has the characteristics of high density, ferromagnetism, and high magnetic permeability; carbon microsphere particles have the characteristics of low density, antioxidant property, and strong dielectric loss. The present invention periodically assembles and arranges these two dielectric materials with different refractive indices to prepare a magnetic metamaterial. The magnetic loss of magnetite nanocrystal particles and the electrical loss of carbon microsphere particles act synergistically to optimize impedance matching; the self-assembly forms a periodic internal structure, which is conducive to achieving electromagnetic wave transparency and presenting broadband absorption. In the frequency sweep range of 1 - 18 GHz, at the same matching thickness, the reflectivity of the incident electromagnetic wave can reach below -20 dB, having excellent electromagnetic wave absorption effect and presenting a broadband absorption effect.

[0024] (2) The electromagnetic wave absorbing metamaterial with a carbon microsphere structure prepared by the present invention adopts an in-situ self-assembly technique, using magnetic iron tetroxide to clone polymer microspheres with an opal photonic crystal structure. By changing the particle size of the polymer microspheres in the opal template, the morphology and distribution of the iron tetroxide nanocrystals and carbon microsphere particles in the metamaterial structure are changed, and the resistivity and electromagnetic parameters are adjusted, so that the regulation of the wave absorption band and good electromagnetic wave absorption effect can be achieved.

[0025] (3) The preparation process of the present invention is convenient and simple. It adopts a one-pot co-precipitation in-situ self-assembly method without nitrogen protection. The operating conditions are easy to control, the product quality is stable, and the yield is relatively high. By controlling the dropping rate of the precipitant and adding an appropriate amount of dispersant, the magnetic Fe3O4 particles and polymer microspheres can be evenly arranged, the particle size of Fe3O4 can be controlled, the dispersibility is good, and the electromagnetic loss is strong.

[0026] (4) In the present invention, the Fe3O4 sol and polymer microspheres are mixed evenly by ultrasonic oscillation stirring at room temperature, which greatly shortens the stirring time, and is also low-carbon and environmentally friendly, with low energy consumption and low production cost, and the comprehensive economic benefits are extremely significant. Description of the Drawings

[0027] Figure 1 SEM image of the polystyrene / methacrylic acid microspheres used in Example 1 of the present invention;

[0028] Figure 2 TEM image of the electromagnetic wave absorbing metamaterial with a carbon microsphere structure prepared in Example 1 of the present invention, where Figure (a) is the TEM image of the electromagnetic wave absorbing metamaterial with a carbon microsphere structure, and Figure (b) is the HRTEM image of the electromagnetic wave absorbing metamaterial with a carbon microsphere structure;

[0029] Figure 3 EDS spectrum of the electromagnetic wave absorbing metamaterial with a carbon microsphere structure prepared in Example 1 of the present invention;

[0030] Figure 4 Electromagnetic wave absorption performance graph of the electromagnetic wave absorbing metamaterial with a carbon microsphere structure prepared in Example 1 of the present invention. Detailed Embodiments

[0031] To better understand the content of the present invention, the following will further elaborate on the present invention in combination with specific examples and drawings. The following examples are implemented based on the technology of the present invention, and detailed implementation methods and operation steps are given, but the protection scope of the present invention is not limited to the following examples.

[0032] The present invention provides a preparation method for an electromagnetic wave absorbing metamaterial with a carbon microsphere structure, which specifically includes the following steps:

[0033] (1) Dissolve a certain mass of dispersant in an appropriate amount of deionized water and stir evenly.

[0034] (2) Add a certain mass of iron source and polymer microspheres to the solution obtained in step (1). After stirring evenly at room temperature, solution A is obtained. Add a certain amount of precipitant to solution A and control the dropping rate. While dropping the precipitant, stir ultrasonically to prepare magnetic Fe3O4 sol. After stirring the sol evenly, use diatomite as the filtration medium to perform vacuum filtration on the sol. Wash the filter cake obtained after filtration with deionized water and ethanol successively. Then place the washed filter residue precipitate in a vacuum drying oven and dry it at 40 - 60 °C for 1 - 3 h. After drying, grind the obtained solid material to obtain the metamaterial precursor for standby.

[0035] (3) Put the metamaterial precursor obtained in step (2) into a high-temperature tube furnace. Under the protection of N2 atmosphere, calcine it at 400 - 500 °C for 4 - 6 h, and then cool it to room temperature to obtain black magnetic powder. Grind the black magnetic powder and pass it through a 200-mesh sieve. The black magnetic powder after sieving is the electromagnetic wave absorbing metamaterial with a carbon microsphere structure.

[0036] In step (1), the dispersant includes one or more of sodium carboxymethyl cellulose, hydroxyethyl cellulose, polyvinylpyrrolidone, polyethylene glycol 400, polyethylene glycol 2000, and polyethylene glycol 4000.

[0037] In step (2), the iron source includes Fe 2+ iron source, Fe 3+ iron source, and the molar ratio of Fe 2+ iron source to Fe 3+ iron source is 1:1.8.

[0038] In step (2), the mass fraction of the iron source in solution A is 2 - 5%, the mass fraction of the dispersant is 10 - 20%, and the mass fraction of the polymer microspheres is 2 - 5%.

[0039] In step (2), the molar ratio of the precipitant to the iron source is 2:1.

[0040] In step (2), Fe 2+ the iron source includes one or more of ferrous chloride, ferrous sulfate, and ferrous nitrate; Fe 3+ the iron source includes one or more of ferric chloride, ferric sulfate, and ferric nitrate.

[0041] In step (2), the precipitant includes one or more of potassium hydroxide solution and ammonia water.

[0042] In step (2), the dropping rate of the precipitant is 30 - 60 drops per minute.

[0043] In step (2), the time of ultrasonic stirring is 10 - 30 min;

[0044] The polymer microspheres in step (2) are one or more of polystyrene, polystyrene / methacrylic acid, polystyrene / methyl acrylate, and polystyrene / methyl methacrylate microspheres.

[0045] The polymer microspheres in step (2) have a smooth and pore-free surface and a particle size of 200 - 1000 nm;

[0046] Among them, the polymer microspheres with a smooth and pore-free surface in step (2) are self-made, and the preparation method is as follows:

[0047] Preparation of polystyrene microspheres: Measure 20 mL of styrene monomer and transfer it to a 250 mL separatory funnel. Wash it 3 - 4 times with a 5% sodium hydroxide solution by mass and then wash it 6 - 7 times with distilled water. After measuring the pH of the styrene monomer in the separatory funnel to be neutral, transfer it to a three-necked flask. Then add 150 mL of distilled water to the three-necked flask, heat it in a water bath at 50 - 70 °C, and at the same time, introduce nitrogen and stir the solution in the three-necked flask magnetically. After introducing nitrogen for 10 min, weigh 0.108 g of ammonium persulfate and dissolve it in 10 mL of distilled water, and slowly add the ammonium persulfate solution to the above three-necked flask with a pipette. After the addition is completed, introduce nitrogen for another 10 min. It can be seen that the solution in the three-necked flask turns blue and then becomes milky white. Stop the reaction after 7 - 9 h. Centrifuge the solution in the three-necked flask, wash the precipitate obtained by centrifugation with distilled water, collect the precipitate obtained by centrifugation and place it in an oven to dry at 50 - 60 °C for 2 - 3 days. The dried solid is ground to obtain polystyrene microspheres.

[0048] Preparation of Polystyrene / Methacrylic Acid, Polystyrene / Methyl Acrylate, and Polystyrene / Methyl Methacrylate Microspheres: Measure 20 mL of styrene monomer and transfer it to a 250 mL separatory funnel. Wash it 3 - 4 times with a 5% sodium hydroxide solution by mass, and then wash it 6 - 7 times with distilled water. After measuring the pH of the styrene monomer in the separatory funnel to be neutral, transfer it to a three-necked flask. Then, add 4 mL of the second monomer and 150 mL of distilled water to the three-necked flask. Heat it in a water bath at 50 - 70 °C, while introducing nitrogen and magnetically stirring the solution in the three-necked flask. After introducing nitrogen for 10 min, weigh 0.108 g of ammonium persulfate and dissolve it in 10 mL of distilled water. Slowly drip the ammonium persulfate solution into the above three-necked flask with a pipette. After the dripping is completed, introduce nitrogen for another 10 min. It can be seen that the solution in the three-necked flask turns blue and then milky white. Stop the reaction after 7 - 9 h. Centrifuge the solution in the three-necked flask, wash the precipitate obtained by centrifugation with distilled water, collect the precipitate obtained by centrifugation, and dry it in an oven at 50 - 60 °C for 2 - 3 days. The dried solid is ground to obtain polymer microspheres. When the second monomer is methacrylic acid, methyl acrylate, or methyl methacrylate respectively, the polymer microspheres prepared are polystyrene / methacrylic acid microspheres, polystyrene / methyl acrylate microspheres, and polystyrene / methyl methacrylate microspheres respectively.

[0049] The following is a detailed description with specific examples:

[0050] Among them, the polystyrene / methacrylic acid microspheres, polystyrene microspheres, and polystyrene / methyl methacrylate microspheres in Examples 1 - 3 are all polymer microspheres prepared by the above method.

[0051] Example 1:

[0052] (1) Dissolve a certain mass of sodium carboxymethylcellulose in an appropriate amount of deionized water and stir evenly;

[0053] (2) Add a certain mass of ferrous chloride, ferric chloride (where n 氯化亚铁 :n 三氯化铁 = 1:1.8), and polystyrene / methacrylic acid microspheres to the solution obtained in step (1). The mass ratio of the iron source, sodium carboxymethylcellulose, polystyrene / methacrylic acid microspheres, and deionized water is 5:20:2:73. After stirring evenly at room temperature, add an appropriate amount of 10 wt% ammonia water (n 氨水 = 2(n 氯化亚铁 + n 三氯化铁)) Control the dropping rate of ammonia water to 60 drops per minute. While dropping, perform ultrasonic stirring for a total of 20 min to prepare magnetic Fe3O4 sol. After stirring the sol evenly, use diatomite as the filtration medium to perform vacuum filtration on the sol. Wash the filter cake obtained after filtration successively with deionized water and ethanol. Then place the washed filter residue precipitate in a vacuum drying oven and dry it at 40 °C for 3 h. After drying, grind the obtained solid material to obtain a metamaterial precursor for standby;

[0054] (3) Put the metamaterial precursor obtained in step (2) into a high-temperature tube furnace and calcine it at 500 °C for 5 h under the protection of N2 atmosphere. Then cool it to room temperature to obtain black magnetic powder. Grind the black magnetic powder and pass it through a 200-mesh sieve. The black magnetic powder after sieving is the electromagnetic wave absorbing metamaterial with a carbon microsphere structure.

[0055] Using the coaxial method, test the material with a vector network analyzer. The results show that when the matching thickness is 2 mm, in the frequency sweep range of 1 - 18 GHz, two absorption peaks of this material appear at 3.62 GHz and 12.7 GHz, and the reflectivities are -8.9 dB and -41.5 dB respectively. The frequency bandwidth below -5 dB in the S, X, and Ku band ranges is 13.3 GHz, and the frequency bandwidth below -10 dB in the X and Ku bands is 3.3 GHz, indicating that the material has good broadband wave absorption performance.

[0056] Figure 2 This is the TEM image of the electromagnetic wave absorbing metamaterial with a carbon microsphere structure prepared in this example. Among them, Figure (a) is the TEM image of the electromagnetic wave absorbing metamaterial with a carbon microsphere structure, and Figure (b) is the HRTEM image of the electromagnetic wave absorbing metamaterial with a carbon microsphere structure. It can be seen from the figure that the particle size of nano-ferroferric oxide is about 20 - 50 nm, and the particle size of the carbon spheres is about 30 - 100 nm. The carbon particles are embedded between the nano-ferroferric oxide particles to form a conductive network bridge structure.

[0057] Figure 3 This is the EDS energy spectrum diagram of the electromagnetic wave absorbing metamaterial with a carbon microsphere structure prepared in this example. It can be seen from the figure that the sample mainly contains three elements: Fe, O, and C.

[0058] The EDS energy spectrum test results of the electromagnetic wave absorbing metamaterial with a carbon microsphere structure prepared in this example also include the elemental relative content table, as shown in Table 1.

[0059] Table 1 Elemental relative content in the sample

[0060]

[0061] As can be seen from Table 1, the relative mass fractions and relative atomic fractions of the elements contained in the carbon microsphere structure electromagnetic wave absorbing metamaterial prepared in this example indicate that partial oxidation of Fe and C elements in the material has occurred.

[0062] Figure 4 This is the electromagnetic wave absorption performance graph of the carbon microsphere structure electromagnetic wave absorbing metamaterial prepared in this example. As can be seen from the figure, under the same matching thickness, the carbon microsphere structure electromagnetic wave absorbing metamaterial prepared in this example has better wave absorption performance than nano-ferroferric oxide, and it exhibits broadband wave absorption characteristics in the frequency range of 1 - 18 GHz.

[0063] Example 2:

[0064] (1) Dissolve a certain mass of sodium carboxymethyl cellulose in an appropriate amount of deionized water and stir evenly.

[0065] (2) Add a certain mass of ferrous sulfate, ferric nitrate (where n 硫酸亚铁 :n 硝酸铁 = 1:1.8), and polystyrene microspheres to the solution obtained in step (1). The mass ratio of iron source, carboxymethyl cellulose, polystyrene microspheres, and deionized water is 2:10:3:85. After stirring evenly at room temperature, add an appropriate amount of 0.5 mol·L -1 potassium hydroxide solution (n 氢氧化钾 = 2(n 硫酸亚铁 + n 硝酸铁 )) to the resulting solution, control the dropping rate of the potassium hydroxide solution at 30 drops per minute, and perform ultrasonic stirring while dropping. The total ultrasonic stirring time is 10 min to obtain magnetic Fe3O4 sol. After stirring the sol evenly, perform vacuum filtration on the sol using diatomite as the filtration medium. Wash the filter cake obtained after filtration successively with deionized water and ethanol, and then place the washed filter residue precipitate in a vacuum drying oven and dry it at 50 °C for 2 h. After drying, grind the dried solid material to obtain the metamaterial precursor for standby.

[0066] (3) Put the metamaterial precursor obtained in step (2) into a high-temperature tube furnace, calcine it at 400 °C for 6 h under the protection of N2 atmosphere, and then cool it to room temperature to obtain a black magnetic powder. Grind the black magnetic powder and pass it through a 200-mesh sieve. The black magnetic powder after sieving is the carbon microsphere structure electromagnetic wave absorbing metamaterial.

[0067] Using the coaxial method, the material was tested by a vector network analyzer. The results show that when the matching thickness is 2.5 mm, within the frequency sweep range of 1 - 18 GHz, three absorption peaks of this material appear at 2.90 GHz, 9.97 GHz, and 17.54 GHz, with reflectivities of -9.62 dB, -23.48 dB, and -19.68 dB respectively. The frequency bandwidth below -5 dB within the S, C, X, and Ku band ranges is 15.24 GHz, and the frequency bandwidth below -10 dB within the X and Ku bands is 5.04 GHz, indicating that the material has good broadband wave absorption performance.

[0068] Example 3:

[0069] (1) Dissolve a certain mass of polyvinylpyrrolidone in an appropriate amount of deionized water and stir evenly;

[0070] (2) Add a certain mass of ferrous nitrate, ferric nitrate (where n 硝酸亚铁 :n 硝酸铁 = 1:1.8), and polystyrene / methyl methacrylate microspheres to the solution obtained in step (1). The mass ratio of the iron source, polyvinylpyrrolidone, polystyrene / methyl methacrylate microspheres, and deionized water is 4:15:4:77. After stirring evenly at room temperature, add an appropriate amount of 0.5 mol·L -1 potassium hydroxide solution (n 氢氧化钾 = 2(n 硝酸亚铁 + n 硝酸铁 )) while controlling the dropping rate of the potassium hydroxide solution at 50 drops per minute. During the dropping, perform ultrasonic stirring for a total of 30 min to prepare a magnetic Fe3O4 sol. After stirring the sol evenly, perform vacuum filtration on the sol using diatomite as the filtration medium. Wash the filter cake obtained after filtration successively with deionized water and ethanol. Then place the washed filter residue precipitate in a vacuum drying oven and dry it at 60 °C for 1 h. After drying, grind the dried solid material to obtain a metamaterial precursor for standby;

[0071] (3) Put the metamaterial precursor obtained in step (2) into a high-temperature tube furnace and calcine it at 450 °C for 5 h under the protection of an N2 atmosphere, and then cool it to room temperature to obtain a black magnetic powder. Grind the black magnetic powder and pass it through a 200-mesh sieve. The black magnetic powder after sieving is the electromagnetic wave absorbing metamaterial with a carbon microsphere structure.

[0072] Using the coaxial method, the material was tested by a vector network analyzer. The results show that when the matching thickness is 3 mm, within the frequency sweep range of 1 - 18 GHz, three absorption peaks of this material appear at 2.48 GHz, 8.15 GHz, and 14.74 GHz, and the reflectivities are -9.90 dB, -22.63 dB, and -17.72 dB respectively. The frequency bandwidth below -5 dB within the S, C, X, and Ku band ranges is 16.72 GHz, and the frequency bandwidth below -10 dB within the X and Ku band ranges is 5.24 GHz, indicating that the material has good broadband microwave absorption performance.

[0073] The above are only embodiments of the present invention and do not impose any formal limitations on the present invention. The present invention may also have other forms of embodiments based on the above structure and functions, which will not be listed one by one. Therefore, any person skilled in the art, without departing from the scope of the technical solution of the present invention, any simple modification, equivalent change, and modification made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A preparation method of a carbon microsphere structure electromagnetic wave absorbing metamaterial, characterized in that Specifically, it includes the following steps: (1) Dissolve a certain mass of dispersant in an appropriate amount of deionized water and stir evenly; (2) Add a certain mass of iron source and polymer microspheres to the solution obtained in step (1), stir evenly at room temperature to obtain solution A, add a certain amount of precipitant to solution A and control the dropping rate at 30 - 60 drops per minute. While dropping the precipitant, perform ultrasonic stirring to prepare magnetic Fe3O4 sol. After stirring the sol evenly, use diatomite as the filtration medium to perform vacuum filtration on the sol. Wash the filter cake obtained after filtration successively with deionized water and ethanol. Then place the washed filter residue precipitate in a vacuum drying oven and dry it at 40 - 60 °C for 1 - 3 h. After drying, grind the obtained solid material to obtain a metamaterial precursor for standby; (3) Put the metamaterial precursor obtained in step (2) into a high-temperature tube furnace, calcine it at 400 - 500 °C for 4 - 6 h under the protection of N2 atmosphere, and then cool it to room temperature to obtain a black magnetic powder. Grind the black magnetic powder and pass it through a 200-mesh sieve. The black magnetic powder after sieving is the carbon microsphere structure electromagnetic wave absorption metamaterial; In step (2), the mass fraction of the iron source in solution A is 2-5%, the mass fraction of the dispersant is 10-20%, and the mass fraction of the polymer microspheres is 2-5%; the iron source includes Fe 2+ iron source, Fe 3+ iron source, and Fe 2+ the iron source and Fe 3+ the molar ratio of the iron source is 1:1.8; the molar ratio of the precipitating agent to the iron source is 2:1; the precipitating agent includes one or more of potassium hydroxide solution and ammonia water; the polymer microspheres are one or more of polystyrene, polystyrene / methacrylic acid, polystyrene / methyl acrylate, and polystyrene / methyl methacrylate microspheres; the surface of the polymer microspheres is smooth and pore-free, and the particle size is 200-1000 nm.

2. The preparation method of the carbon microsphere structure electromagnetic wave absorbing metamaterial according to claim 1, characterized in that In step (2), the time of ultrasonic stirring is 10 - 30 min.

3. The preparation method of the carbon microsphere structure electromagnetic wave absorbing metamaterial according to claim 2, characterized in that In step (1), the dispersant includes one or more of sodium carboxymethyl cellulose, hydroxyethyl cellulose, polyvinylpyrrolidone, polyethylene glycol 400, polyethylene glycol 2000, and polyethylene glycol 4000; in step (2), Fe 2+ The iron source includes one or more of ferrous chloride, ferrous sulfate, and ferrous nitrate; Fe 3+ The iron source includes one or more of ferric chloride, ferric sulfate, and ferric nitrate.

4. The carbon microsphere structure electromagnetic wave absorption metamaterial prepared by the preparation method according to any one of claims 1 - 3.

5. Application of the carbon microsphere structure electromagnetic wave absorption metamaterial according to claim 4 as an electromagnetic wave absorption material in the field of electromagnetic radiation protection technology.

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