Preparation method of flexible broadband absorption metamaterial film

Abstract

The application relates to a preparation method of a flexible broadband absorption metamaterial film, and relates to a preparation method of an electromagnetic absorption metamaterial. The application aims to solve the technical problems of narrow effective absorption bandwidth and difficult deformation processing of the existing metamaterial film. The preparation method of the application comprises the following steps: 1, preparing a PVB binder; 2, adding graphene and carbonyl iron powder into anhydrous ethanol, ball milling, drying to obtain a composite absorber; 3, adding the composite absorber into the PVB binder to prepare a slurry; 4, casting the slurry on a glass substrate and drying to obtain a film; and 5, using a laser engraving machine to engrave periodic units on the surface of the film to obtain the flexible broadband absorption metamaterial film. The effective absorption bandwidth of the film covers 14.039GHz-26.985GHz under the thickness of 1.5mm, and the maximum reflection loss can reach-21.127dB. The preparation method is simple, can be mass-produced, is easy to deform and process, and can be used in the field of electromagnetic absorption.

Description

Technical Field

[0001] This invention relates to a method for preparing electromagnetic absorbing metamaterials. Background Technology

[0002] With the rapid development of next-generation wireless communication technologies, radio electromagnetic radiation has seriously exceeded standards. To effectively resist external electromagnetic interference and minimize its outward propagation, it is necessary to consider novel electromagnetic absorbing materials with a wider coverage band. Metamaterials, in particular, achieve electromagnetic wave attenuation by increasing the absorption of electrical and magnetic resonances between array units, thus realizing a higher level of control. Current metamaterial absorbers have fixed resonant frequencies, and their narrow absorption bandwidth limits their practical applications. Using composite materials can effectively improve the impedance matching performance of the materials. Since periodic structures are difficult to maintain in complex electromagnetic environments, and the precision of deformation processing needs improvement, novel absorbing metamaterials that combine wide bandwidth, thinness, and ease of processing have become a research hotspot.

[0003] Chinese patent CN101840735A, entitled "A Broadband Microwave Absorber Based on Dendritic Structure Metamaterial," describes a metamaterial absorber with a sandwich structure design, consisting of a hexagonal metal dendritic array unit, a double-layer dielectric substrate, and a metal thin film. This absorber is fabricated using circuit board etching technology and achieves high absorption in the X-band. However, the high cost of metal material preparation, the numerous structural parameters, and the limited effective absorption bandwidth of only 4GHz affect its stable use in complex electromagnetic environments and hinder the large-scale production and processing of metamaterials in the field of electromagnetic absorption. Summary of the Invention

[0004] The present invention aims to solve the technical problems of narrow effective absorption bandwidth and difficulty in deformation processing of existing metamaterials with thin thickness, and provides a method for preparing flexible broadband absorption metamaterial thin films.

[0005] The preparation method of the flexible broadband absorbing metamaterial thin film of the present invention is carried out according to the following steps:

[0006] 1. Dissolve polyvinyl butyral (PVB) powder in anhydrous ethanol and stir with a magnetic stirrer until transparent under water bath heating at 70-80°C to obtain PVB binder.

[0007] 2. Mix graphene and carbonyl iron powder in a mass ratio of (35-37):1, add anhydrous ethanol, put the mixture into a ball mill and ball mill at a speed of 400-500 rpm for 22-24 hours, and dry it to obtain a composite absorbent.

[0008] 3. Pour the composite absorbent obtained in step 2 into the PVB binder obtained in step 1, add the plasticizer dibutyl phthalate (DBP) and the dispersant tributyl phosphate (TBP) in sequence, disperse in a vacuum planetary mixer for 30-40 minutes and perform vacuum defoaming to obtain the slurry.

[0009] 4. After spraying the release agent onto the glass plate, place it in a drying oven at 160-170℃ and heat for 15-20 minutes, then let it cool to room temperature; then cast the slurry obtained in step 3 onto the glass substrate with a scraper at a speed of 10-15 mm / s, and dry it to obtain a film with a thickness of 0.2-0.3 mm.

[0010] 5. Stack multiple layers of the film obtained in step 4 to achieve a thickness of 1-1.5 mm. Use a laser engraving machine to engrave periodic units on the surface of the film. The periodic units are regular hexagonal prism-shaped through holes with a side length of 4.25-5 mm. The periodic units are spaced 10-20 mm apart to obtain a flexible broadband absorbing metamaterial film.

[0011] Furthermore, the mass percentage concentration of the PVB adhesive mentioned in step one is 8% to 10%.

[0012] Furthermore, in step two, the graphene and carbonyl iron powder are first sieved and then mixed.

[0013] Furthermore, in step three, the mass ratio of the composite absorbent, PVB binder, dibutyl phthalate and tributyl phosphate is (10-12):1:(1-1.2):(1.8-2).

[0014] Furthermore, the epoxy resin release agent described in step four is heated and dried uniformly for 15–20 minutes.

[0015] To further specify, the drying process described in step four involves natural drying at room temperature for 24–30 hours.

[0016] The flexible broadband absorbing metamaterial thin film of this invention exhibits excellent stability and can be folded according to design requirements. The effective absorption bandwidth of the metamaterial thin film covers 14.039 GHz to 26.985 GHz, and its maximum reflection loss reaches -21.127 dB. The overall structural thickness is 1–1.5 mm. The preparation method of this invention is simple, can be mass-produced, and is easy to deform and process. Attached Figure Description

[0017] Figure 1 This is a photograph of the flexible broadband absorbing metamaterial thin film prepared in Example 1;

[0018] Figure 2 This is a schematic diagram of the unit structure of the flexible broadband absorbing metamaterial thin film prepared in Example 1;

[0019] Figure 3 This is a simulated reflection loss diagram of the flexible broadband absorbing metamaterial thin film prepared in Example 1;

[0020] Figure 4 These are simulated reflection loss diagrams of flexible broadband absorbing metamaterial thin films with different prism radii prepared in Examples 1-5;

[0021] Figure 5 This is an electric field distribution diagram of the unit structure simulated at 16.82 GHz using the software CST Studio for the flexible broadband absorbing metamaterial thin film of Example 1;

[0022] Figure 6 This is an electric field distribution diagram of the unit structure simulated at 20.52 GHz using the software CST Studio for the flexible broadband absorbing metamaterial thin film of Example 1;

[0023] Figure 7 This is an electric field distribution diagram of the unit structure simulated at 25.39 GHz using the software CST Studio for the flexible broadband absorbing metamaterial thin film of Example 1;

[0024] Figure 8 This is a surface current distribution diagram of the unit structure simulated at 20.52 GHz using the software CST Studio for the flexible broadband absorbing metamaterial thin film of Example 1;

[0025] Figure 9 This is a surface current distribution diagram of the unit structure simulated at 25.39 GHz using CST Studio software for the flexible broadband absorbing metamaterial thin film of Example 1;

[0026] Figure 10 These are simulated reflection loss diagrams of the flexible broadband absorbing metamaterial thin films prepared in Comparative Examples 1-3;

[0027] Figure 11 The above are simulated reflection loss diagrams of the flexible broadband absorbing metamaterial thin films prepared in Comparative Examples 4 and 5. Detailed Implementation

[0028] The beneficial effects of the present invention will be verified using the following examples.

[0029] Example 1: The preparation method of the flexible broadband absorbing metamaterial thin film in this example is carried out according to the following steps:

[0030] 1. Dissolve 35.12g of polyvinyl butyral (PVB) powder in 400mL of anhydrous ethanol, and stir with a magnetic stirrer for 2h in an 80℃ water bath heating environment to obtain a transparent PVB adhesive with a mass percentage concentration of 8.07%.

[0031] 2. Mix 54g of carbonyl iron and 1.5g of graphene powder evenly, add 160-180mL of anhydrous ethanol, and then put it into a ball mill and ball mill at 500rpm for 24h. After drying at 80℃ for 5h, the composite absorbent is obtained.

[0032] 3. Pour 50g of the composite absorbent obtained in step 2 into 50mL of the PVB binder obtained in step 1, add 1.2mL of plasticizer dibutyl phthalate (DBP) and 2mL of tributyl phosphate (TBP) in sequence, disperse for 30min using a vacuum planetary mixer, and perform vacuum defoaming to obtain a uniform slurry.

[0033] 4. After spraying epoxy resin release agent onto the glass plate, place it in a 170℃ drying oven and heat for 15 minutes. After cooling to room temperature, cast the slurry obtained in step 3 onto the glass substrate with a scraper at a speed of 10 mm / s. Let it dry naturally at room temperature for 24 hours to obtain a film with a thickness of 0.3 mm, a length of 18 mm, and a width of 18 mm.

[0034] 5. Stack the film obtained in step 4 into 5 layers to achieve a thickness of 1.5 mm. Use a laser engraving machine to engrave periodic units on the surface of the film. The periodic units are regular hexagonal prism-shaped holes with a side length of 4.5 mm. The center distance between adjacent periodic units is 15 mm, thus obtaining a flexible broadband absorbing metamaterial film.

[0035] Example 2: This example differs from Example 1 in that the periodic unit in step five has a side length of 4 mm. Everything else is the same as in Example 1, resulting in a flexible broadband absorbing metamaterial film.

[0036] Example 3: This example differs from Example 1 in that the periodic unit in step five has a side length of 4.25 mm. Everything else is the same as in Example 1, resulting in a flexible broadband absorbing metamaterial film.

[0037] Example 4: This example differs from Example 1 in that the periodic unit in step five has a side length of 4.75 mm. Everything else is the same as in Example 1, resulting in a flexible broadband absorbing metamaterial film.

[0038] Example 5: This example differs from Example 1 in that the periodic unit in step five has a side length of 5.0 mm. Everything else is the same as in Example 1, resulting in a flexible broadband absorbing metamaterial film.

[0039] Example 5: This example differs from Example 1 in that the periodic unit in step five has a side length of 5.25 mm. Everything else is the same as in Example 1, resulting in a flexible broadband absorbing metamaterial film.

[0040] A photograph of the flexible broadband absorbing metamaterial thin film obtained in Example 1 is shown below. Figure 1 As shown, from Figure 1 As can be seen, the film is smooth and flat, foldable, and has good stability.

[0041] The unit structure of the flexible broadband absorbing metamaterial thin film prepared in Example 1 is as follows: Figure 2 As shown, this serves as the periodic unit that forms the plane in which the electromagnetic wave is actually incident. From Figure 2 As can be seen, the hexagonal prism-shaped pores are evenly distributed on the surface of the film. This porous structure facilitates the incidence of electromagnetic waves and multiple reflections between and within the layers, thereby increasing the internal relaxation time and extending the propagation path of the electromagnetic waves. This structure has better compressive strength, and the pattern design is simple and easy to engrave. Figure 3 The graph shows the reflection loss curve of the metamaterial thin film prepared in Example 1. This structure achieved effective absorption of 14.109 GHz to 26.935 GHz with a thickness of 1.5 mm, and the maximum reflection loss was -21.127 dB.

[0042] The flexible broadband absorbing metamaterial films obtained in Examples 1-6 were subjected to simulation tests of their absorption performance from 2 to 40 GHz, and the results were as follows: Figure 4 The reflection loss curve is shown. From... Figure 4 It can be seen that the thin film with a prism side length of 4 mm has only one absorption peak. When the prism side length increases from 4 mm to 4.25 mm, in addition to the absorption peak at 16.63 GHz, a new absorption peak appears near 25 GHz, further broadening the effective absorption bandwidth. When the prism side length increases to 5.25 mm, the reflection loss in the range of 20.55 GHz to 24.01 GHz is greater than -10 dB, resulting in a shortening of the original complete absorption bandwidth and a decrease in absorption performance. The absorption peak intensity values ​​of each thin film at 16.63 GHz and 25 GHz are shown in Table 1.

[0043] Table 1. Wave absorption properties of the thin films obtained in Examples 1-5

[0044]

[0045] from Figure 4 As shown in Table 1, as the side length increases from 4.25 mm to 5 mm, the two absorption peaks exhibit varying degrees of blue shift, with a maximum reflection loss of -27.3 dB. The coverage bandwidth reaches a maximum of 12.826 GHz when the radius is 4.5 mm. Within the range of 4.25–5 mm for the side length of the periodic cell, the absorption bandwidth can be effectively broadened.

[0046] The electric field distribution and surface current distribution of the flexible broadband absorbing metamaterial thin film of Example 1 were simulated in CST Studio at 16.82 GHz, 20.52 GHz, and 25.39 GHz. Figure 5 ,6 Figures 7 and 8 show the electric field distribution of the unit structure at 16.82 GHz, 20.52 GHz, and 25.39 GHz, respectively. Figures 5-7 It can be seen that at lower frequencies, the electric field is concentrated at the edge of the 4.5mm side length regular hexagonal prism hole. As the frequency increases, the area of ​​the periodic unit structure that responds to the electric field further increases, leading to an increase in the electric field strength. The electric field component of the incident electromagnetic wave excites electric resonance in the structural unit. Figure 8 , 9 The images show the surface current distribution of the unit structure at 20.52 GHz and 25.39 GHz, respectively. Figure 8 It can be seen that the induced current distribution at a frequency of 20.52 GHz is ring-shaped, indicating that the electric field induces an equivalent circulating current around it, and electromagnetic resonance absorption causes strong attenuation of the electromagnetic wave. From Figure 9 It can be seen that when the frequency increases to 25.39 GHz, many dots of varying sizes are evenly distributed on the surface. Larger dots are located at the holes of the regular hexagonal prism, while smaller dots are at the center where they connect; these two locations are where the electromagnetic field mainly concentrates. Regardless of... Figure 8 still Figure 9 All of these studies show a significant increase in the area of ​​electromagnetic resonance, which allows the resulting resonant frequency to support wider bandwidth absorption, thereby converting electromagnetic energy into other forms of energy for dissipation. The flexible broadband absorbing metamaterial thin film in Example 1 consists of periodically distributed hexagonal prism holes with a side length of 4.5 mm on its surface. This structure enables electromagnetic resonance, achieving attenuation of electromagnetic waves through absorption.

[0047] Comparative Example 1: This example differs from Example 1 in that step two is replaced by the following operation: 40g of carbonyl iron and 2.5g of graphene powder are mixed evenly, 150mL of anhydrous ethanol is added, and then the mixture is placed in a ball mill and ball-milled at 500rpm for 24h. After drying at 80℃ for 5h, a composite absorbent is obtained; the rest is the same as in Example 1, and a flexible broadband absorbing metamaterial film is obtained.

[0048] Comparative Example 2: This example differs from Example 1 in that step two is replaced by the following operation: 40g of carbonyl iron is added to 150mL of anhydrous ethanol, and then placed in a ball mill and ball-milled at 500rpm for 24h. After drying at 80℃ for 5h, a composite absorbent is obtained; the rest is the same as in Example 1, and a flexible broadband absorbing metamaterial film is obtained.

[0049] Comparative Example 3: This example differs from Example 1 in that step two is replaced by the following operation: 5g of graphene powder is added to 150mL of anhydrous ethanol, and then placed in a ball mill and ball-milled at 500rpm for 24h. After drying at 80℃ for 5h, a composite absorbent is obtained; the rest is the same as in Example 1, and a flexible broadband absorbing metamaterial film is obtained.

[0050] In the films prepared in Comparative Examples 1, 2, and 3, graphene, as a dielectric material, exhibits very high electrical loss, while carbonyl iron is a typical magnetic loss material. Figure 10 These are reflection loss diagrams of the flexible broadband absorbing metamaterial thin films prepared in Comparative Examples 1-3; from Figure 10 It can be seen that the excessively high dielectric constant of pure graphene leads to poor impedance matching performance, and the reflection loss cannot reach -10dB. While films made with pure iron carbonyl as the absorber show significant high-frequency absorption, the mass and thickness limitations of iron carbonyl make it difficult to meet the performance requirements of "thin, wide, light, and strong." Composite absorbers made by doping graphene into iron carbonyl exhibit both electrical and magnetic losses. With a low graphene content, such as the iron carbonyl to graphene mass ratio of 16:1 in the comparative example, the maximum reflection loss is -14.28dB, and the effective absorption bandwidth is only 6.95GHz, indicating a narrow absorption band. However, in Example 1, the iron carbonyl to graphene mass ratio of 36:1 not only causes strong attenuation of electromagnetic waves but also exhibits excellent absorption performance over a wider frequency band.

[0051] Comparative Example 4: The difference between this example and Example 1 is that in step five, the periodic unit is a regular octagonal prism-shaped hole with a side length of 4 mm and a depth of 1.5 mm. The center distance between adjacent periodic units is 15 mm. The rest is the same as in Example 1, resulting in a flexible broadband absorbing metamaterial film.

[0052] Comparative Example 5: This example differs from Example 1 in that in step five, the periodic unit is a rhomboid columnar hole with a side length of 4mm, and the center distance between adjacent periodic units is 15mm. The rest is the same as in Example 1, resulting in a flexible broadband absorbing metamaterial film.

[0053] The reflection loss diagrams of the thin films prepared in Comparative Examples 4 and 5 are shown below. Figure 11 As shown, from Figure 11 It can be seen that the rhomboid periodic unit produces a stronger resonant frequency, but a narrower absorption peak; the absorption peaks of the regular octagonal prism periodic unit are located at 16.63 GHz and 25.14 GHz on the left and right sides, respectively, with a significantly enhanced effective absorption bandwidth, but the difference in absorption loss between the two sides is large. In contrast, Example 1 uses regular hexagonal prism-shaped holes as periodic units, which makes the overall structure exhibit better absorption performance over a wide frequency range, demonstrating the advantages of structural design.

[0054] The flexible broadband absorbing metamaterial thin film prepared by this invention can achieve effective absorption of 14.109 GHz to 26.935 GHz with a thickness of only 1.5 mm. The position of the absorption peak can be adjusted by changing the size of the honeycomb structure. The film preparation process using the casting method is simple and suitable for large-scale production. The film is soft yet tough, with uniform thickness and good physical stability.

Claims

1. A method of making a flexible, broadband, absorptive metamaterial film, the method comprising: The method is carried out according to the following steps: ​ Step one, polyvinyl butyral powder is dissolved in anhydrous ethanol, and is stirred to be transparent by a magnetic stirrer under the condition of heating at 70-80 DEG C water bath, to obtain PVB binder; Step two, carbonyl iron powder and graphene are mixed in a mass ratio of 36:1, and then anhydrous ethanol is added, and the mixture is ball milled in a ball mill at a speed of 400-500 rpm for 22-24 h, and then dried to obtain a composite absorbent; Step three, the composite absorbent obtained in step two is poured into the PVB binder obtained in step one, and then plasticizer dibutyl phthalate and dispersant tributyl phosphate are added, and the mixture is dispersed by a vacuum planetary mixer for 30-40 min and vacuum degassing to obtain a slurry; Step four, after the glass plate is sprayed with a release agent, it is placed in a drying oven at 160-170 DEG C for 15-20 min, and then cooled to room temperature; then the slurry obtained in step three is cast on the glass substrate by a doctor blade at a speed of 10-15 mm / s, dried to obtain a thin film with a thickness of 0.2-0.3 mm; Step five, the thin film obtained in step four is stacked to a thickness of 1-1.5 mm, and a periodic unit is engraved on the surface of the thin film by a laser engraving machine, wherein the periodic unit is a regular hexagonal hole with a side length of 4.25-5 mm, and the distance between the periodic units is 10-20 mm, to obtain a flexible broadband absorption metamaterial film.

2. The method for preparing a flexible broadband absorbing metamaterial thin film according to claim 1, characterized in that, The mass percentage concentration of the PVB binder in step one is 8%-10%.

3. The method of claim 1 or 2, wherein the flexible broadband absorbing metamaterial film is prepared by the steps of: providing a substrate; depositing a first layer of a first material on the substrate; depositing a second layer of a second material on the first layer; and depositing a third layer of a third material on the second layer. In step two, the graphene and carbonyl iron powder are sieved and then mixed.

4. The method of claim 1 or 2, wherein the flexible broadband absorbing metamaterial film is prepared by the steps of: providing a substrate; depositing a first layer of a first material on the substrate; depositing a second layer of a second material on the first layer; and depositing a third layer of a third material on the second layer. In step three, the mass ratio of the composite absorbent, PVB binder, dibutyl phthalate and tributyl phosphate is (10-12):1:(1-1.2):(1.8-2).

5. The method of claim 1 or 2, wherein the flexible broadband absorbing metamaterial film is prepared by the steps of: providing a substrate; depositing a first layer of a first material on the substrate; depositing a second layer of a second material on the first layer; and depositing a third layer of a third material on the second layer. The release agent in step four is an epoxy release agent, which is uniformly dried for 15-20 min under heating.

6. The method of claim 1 or 2, wherein the flexible broadband absorbing metamaterial film is prepared by the steps of: providing a substrate; depositing a first layer of a first material on the substrate; depositing a second layer of a second material on the first layer; and depositing a third layer of a third material on the second layer. The drying in step four is natural drying at room temperature for 24-30 h.

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