Honeycomb concrete wave-absorbing structure based on all-dielectric phase gradient metasurface

Abstract

The application is a honeycomb concrete wave-absorbing structure based on a full-dielectric phase gradient metasurface, which is composed of a base fiber honeycomb concrete and a top full-dielectric phase gradient metasurface structure. The base fiber honeycomb concrete is divided into a multi-layer structure by different contents of wave-absorbing agents, the impedance matching is adjusted by changing the content and type of the wave-absorbing agents, and the function of maximum absorption of electromagnetic waves is achieved. The fiber wave-absorbing honeycomb woven by wave-absorbing fibers enables the concrete to have good toughness and strength, and achieves the dual effect of synergistic enhancement of wave-absorbing and mechanical properties. The size and shape of the micro units in the full-dielectric phase gradient metasurface can be flexibly adjusted, different micro units are combined, electromagnetic waves produce different phases, and the purpose of flexibly adjusting the electromagnetic wave-absorbing performance of different frequency bands is achieved. Through the combination of 3D fiber honeycomb structure, multi-layer wave-absorbing structure and metasurface and other factors, the optimal electromagnetic wave-absorbing structure is prepared, and the requirements of thin, light, wide and strong of the electromagnetic wave-absorbing material are met.

Description

Technical Field

[0001] This invention relates to a honeycomb concrete microwave absorbing structure based on an all-dielectric phase gradient metasurface. Background Technology

[0002] With the popularization and development of electronic technology, electromagnetic waves have become the most important and ubiquitous carrier of information dissemination, and have been widely used in telecommunications, medical devices, home appliances, and military equipment. However, the ubiquitous electromagnetic radiation can interfere with the operation of electronic devices, threaten the security of civilian and military information, and even seriously endanger human health. Therefore, electromagnetic wave absorption has attracted the attention of researchers in the field of building structures. Research on wave absorption performance can be conducted from the aspects of structural form, type of absorbing agent, and materials. In terms of structure, honeycomb structure and porous structure can be adopted. Traditional honeycomb structure mainly uses honeycomb sheets as the main body, and an absorbent is attached to the inner wall of the honeycomb pores through impregnation, thereby obtaining wave absorption performance. Porous structure can cause multiple reflections of electromagnetic waves inside concrete, accelerating the consumption of electromagnetic waves. In terms of the type of absorbing agent, the main method is to add absorbing agents to the matrix to enhance the electromagnetic attenuation performance of the matrix. In terms of materials, a rapidly developing topic in recent years is metamaterials and metasurfaces. Metamaterials are a new type of artificially synthesized electromagnetic materials, while metasurfaces are extremely thin metamaterials, a new type of two-dimensional metamaterials, with the advantages of smaller thickness and lighter volume. It exhibits relatively low loss and is easier to manufacture compared to traditional metamaterials. Phase-gradient metasurfaces are a type of metasurface. When electromagnetic waves reach a phase-gradient metasurface, different amplitude and phase changes occur in different unit structures. By adjusting the structure of the unit structures, the phase and amplitude of the incident electromagnetic waves can be controlled.

[0003] However, all of the above methods have drawbacks. First, the main honeycomb sheet material of the honeycomb structure does not have microwave absorption properties. The microwave absorbing agent is mainly attached to the honeycomb pore walls through impregnation, which can lead to uneven distribution of the agent and thus unsatisfactory microwave absorption performance. Second, simply adding microwave absorbing agents to the matrix does not achieve the desired absorption effect. Numerous studies have shown that the content of the microwave absorbing agent and the material's microwave absorption performance are not linearly related; there is a peak value. When the microwave absorbing agent content is low, the absorption rate of the material is correspondingly low; when the content is too high, it will cause uneven dispersion, leading to a decrease in absorption rate. Third, the porous structure of concrete has the disadvantages of low strength and easy cracking. Fourth, traditional metasurfaces are metal structures. Although the application prospects of metal-based metasurfaces have been verified in many fields, the performance of metasurfaces is usually limited by the very high inherent ohmic loss of metal materials. Fifth, all of the above methods use a single approach to improve the microwave absorption performance of the material, which cannot meet the requirements of "thin, light, wide, and strong" microwave absorbing materials. Summary of the Invention

[0004] The present invention aims to overcome the above-mentioned shortcomings of the prior art and provide a honeycomb concrete microwave absorbing structure based on an all-dielectric phase gradient metasurface.

[0005] The present invention addresses the above-mentioned shortcomings by employing the following technical solution:

[0006] A honeycomb concrete microwave absorbing structure based on an all-dielectric phase gradient metasurface is disclosed, comprising a 3D fiber honeycomb concrete substrate and an all-dielectric phase gradient metasurface structure on top; the honeycomb is a 3D fiber microwave absorbing honeycomb structure woven from microwave absorbing fibers; the raw materials of the concrete include cement, fly ash, water, water-reducing agent, and microwave absorbing agent; the array structure of the all-dielectric phase gradient metasurface consists of a silica substrate and a geometry made of silicon nanorods on the substrate.

[0007] The fabrication process of the absorbing structure is as follows:

[0008] Step 1: Using microwave-absorbing fibers as raw materials, weave on a loom according to the structural pattern of the 3D fiber microwave-absorbing honeycomb. Select the straight-through method for threading the heddles, then introduce the weft and beat the weft. After several cycles of interlacing, a 3D fiber microwave-absorbing honeycomb is woven.

[0009] Step 2: Premix cement, fly ash, and microwave absorber evenly in a dry container to obtain a uniform powder. Then, transfer the uniform powder to a mixing tank, add water and water-reducing agent to the mixing tank, and mix evenly.

[0010] Step 3: Repeat step 2 according to different amounts of absorbing agent to obtain absorbing concrete with different amounts of absorbing agent.

[0011] Step 4: Pour the prepared microwave-absorbing concrete with different microwave-absorbing agent contents into the 3D fiber microwave-absorbing honeycomb obtained in step 1 in layers, with the microwave-absorbing agent content gradually increasing.

[0012] Step 5: Fabricate a semi-infinite silicon substrate using an etching process. Deposit a silicon film on the silicon dioxide substrate using low-pressure chemical vapor deposition. Spin-coat ZEP520A photoresist onto the silicon film. Then deposit a thin layer of chromium as a resist. Obtain silicon nanorods by electron beam lithography. Finally, remove the photoresist using a removal agent and plasma to obtain an all-dielectric phase gradient metasurface.

[0013] Step 6: Combine the all-dielectric phase gradient metasurface obtained in Step 5 with the honeycomb concrete obtained in Step 4 to obtain a honeycomb concrete microwave absorbing structure based on the all-dielectric phase gradient metasurface.

[0014] The cement used in the concrete is silicate cement or sulfoaluminate cement, the fly ash is siliceous fly ash or calcareous fly ash, the water-reducing agent is lignin sulfonate or naphthalene sulfonate formaldehyde polymer, and the microwave absorbing agent is at least one of graphite, graphene, and carbon nanotubes; the fibers used in the woven honeycomb are carbon fibers, silicon carbide fibers, polycrystalline iron fibers or polypropylene fibers with microwave absorbing properties, so that the honeycomb structure itself has microwave absorbing properties, the microwave absorbing agent is evenly distributed, and the electromagnetic wave absorption capability of the material is improved.

[0015] The substrate is divided into multiple layers based on the varying content of the absorbing agent, with the absorbing agent content increasing sequentially from top to bottom. The substrate has 2, 3, or 4 layers, each with the same thickness, resulting in a total thickness of 15–25 mm. When the multilayer structure has 2 layers, the absorbing agent content in each layer is 0.5%–1.3% and 1.3%–2.5%, respectively; when the multilayer structure has 3 layers, the absorbing agent content is 0.5%–1.2%, 1.2%–1.9%, and 1.9%–2.5%, respectively; and when the multilayer structure has 4 layers, the absorbing agent content is 0.5%–0.8%, 0.8%–1.3%, 1.3%–1.9%, and 1.9%–2.5%, respectively. By changing the absorbing agent concentration, the impedance of each layer is adjusted, thus regulating impedance matching and maximizing the absorption of electromagnetic waves.

[0016] The silicon nanorods are made into hexagonal, frustum, conical, or cylindrical shapes; the micro-units are selected from two or more geometric shapes and combined according to the operating wavelength.

[0017] The silica substrate has a height of 4–7 mm; the silicon nanorods have a height of 3–5 mm and a bottom width or diameter of 3–5 mm. By changing the size, type, and arrangement of the unit structure, the phase is controlled, generating a continuous phase gradient, thereby achieving the modulation of electromagnetic waves and improving the electromagnetic absorption performance of the electromagnetic protection structure.

[0018] The array structure of the all-dielectric phase gradient metasurface uses a 4 mm high silicon dioxide substrate as the substrate. On the substrate, three micro-shapes made of nanorods are combined as a unit and periodically arranged. The height of the hexagon is 4 mm and the bottom width of the hexagon is 4 mm. The height of the cylinder is 4 mm and the bottom diameter of the cylinder is 3 mm. The height of the triangular pyramid is 3 mm and the bottom diameter of the triangular pyramid is 4 mm.

[0019] Alternatively, an array structure of all-dielectric phase gradient metasurfaces can be constructed using a 5mm high silicon dioxide substrate. On the substrate, four micro-shapes made of nanorods—cones, cylinders, hexagonal frustums, and hexagons—are combined as a unit and arranged periodically. The hexagons have a height of 5mm and a base width of 5mm, the cylinders have a height of 4mm and a base diameter of 4mm, the cones have a height of 3mm and a base diameter of 4mm, and the hexagonal frustums have a height of 4mm, a base side length of 5mm, and a surface side length of 3mm.

[0020] The absorption mechanism of the honeycomb concrete microwave absorbing structure based on the all-dielectric phase gradient metasurface is as follows: The 3D fiber honeycomb structure of the substrate is composed of fibers with microwave absorption properties. The 3D structure of the honeycomb causes multiple reflections and scattering of electromagnetic waves, accelerating the loss of electromagnetic waves. The concrete filling the honeycomb pores has a porous structure, which is regarded as a wave-transmitting channel, allowing most of the incident electromagnetic waves to pass through the concrete, thereby enhancing the impedance matching between the matrix and the air. Electromagnetic waves undergo multiple reflections and refractions inside the pores, increasing the transmission distance of electromagnetic waves and thus being absorbed and lost. The thin-walled structure between the pores causes multiple interference and destructive effects of electromagnetic waves, increasing the resonant absorption loss of electromagnetic waves. By changing the amount of microwave absorbing agent, the concrete forms a gradually changing impedance gradient structure, allowing electromagnetic waves to enter the interior of the material. The layers attenuate sequentially, and the interfaces of each layer reflect multiple times, resulting in coherent loss and resonance effects. The top layer of the all-dielectric phase gradient metasurface, on the one hand, controls the size and shape of the micro-units, selects different micro-shapes for combination, and further arranges them periodically to achieve the effect of controllable impedance gradient and electromagnetic wave transmission and absorption mode of the composite structure. On the other hand, electromagnetic waves undergo multiple reflections and scattering in the micro-units of the phase gradient metasurface, increasing the transmission distance of electromagnetic waves while being absorbed and lost. The top layer of the all-dielectric phase gradient metasurface generates electromagnetic waves with different phases, flexibly controlling electromagnetic waves in different frequency bands, so that the three-dimensional absorbing honeycomb structure of the substrate can fully exert its absorption effect in different frequency bands, and can achieve phase changes of any gradient in the range of 0 to 2π.

[0021] Compared with the prior art, the advantages of the present invention are as follows:

[0022] 1. The microwave-absorbing honeycomb structure in this invention is woven from fibers with microwave-absorbing properties, and the microwave-absorbing agent is evenly distributed. This solves the problem of uneven distribution of the microwave-absorbing agent when the traditional method of impregnation is used to attach the microwave-absorbing agent to the honeycomb pore walls. The combination of the microwave-absorbing honeycomb structure with microwave-absorbing properties and concrete can achieve the microwave absorption effect of high microwave-absorbing agent content even when the microwave-absorbing agent content in the concrete is low. This solves the problem that when the microwave-absorbing agent content is low, the absorption rate of the material is also low, and when the microwave-absorbing agent content is too high, it will cause uneven dispersion and lead to a decrease in the absorption rate, thus failing to achieve the ideal microwave absorption effect.

[0023] 2. Fiber honeycomb has excellent toughness and strength. When combined with porous concrete, it provides a skeleton for the concrete as support, enhancing the concrete's strength. On the other hand, the fiber honeycomb encases the concrete, limiting cracking and solving the problem of low concrete strength and easy cracking.

[0024] 3. The use of an all-dielectric phase gradient metasurface solves the problems of high metal structure loss and easy oxidation and corrosion of metal patches in traditional phase gradient metasurfaces. The all-dielectric phase gradient metasurface on the top layer generates electromagnetic waves with different phases, flexibly controlling electromagnetic waves in different frequency bands, so that the three-dimensional absorbing honeycomb structure of the substrate can fully exert its absorption effect in different frequency bands.

[0025] 4. This invention utilizes a combination of honeycomb structure, multi-layer concrete, and all-dielectric phase gradient metasurface. These three elements complement and promote each other, enhancing electromagnetic wave absorption performance in multiple ways and meeting the requirements of "thin, light, wide, and strong" for absorbing materials. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of an embodiment of the honeycomb concrete microwave absorbing structure based on an all-dielectric phase gradient metasurface according to the present invention.

[0027] Figure 2 This is a schematic diagram of one embodiment of a top-dielectric phase gradient metasurface.

[0028] Figure 3 This is a schematic diagram of the 3D fiber honeycomb structure of the substrate.

[0029] Figure 4 This is a top view of the base honeycomb concrete structure.

[0030] Figure 5 The diagram shows the structure of different micro-shapes of the all-dielectric phase gradient metasurface. The first from the left is a hexagonal shape, the second from the left is a frustum shape, the third from the left is a cone shape, and the fourth from the left is a cylinder shape. Detailed Implementation

[0031] The present invention will be further explained below with reference to the embodiments and accompanying drawings, but this is not intended to limit the scope of protection of this application.

[0032] Example 1

[0033] This embodiment provides a honeycomb concrete microwave absorbing structure based on an all-dielectric phase gradient metasurface, which is prepared by the following steps:

[0034] Step 1: Premix silicate cement, fly ash, and 0.7% graphene in a dry container for 5 minutes. After that, transfer the uniform powder to a mixing tank, pour water and lignin sulfonate water-reducing agent into the mixing tank and stir for 2 minutes.

[0035] Step 2: Repeat Step 1, except that the graphene content is 1.5%;

[0036] Step 3: Select carbon fiber and weave a wave-absorbing honeycomb with a height of 20mm on a loom;

[0037] Step 4: Pour the microwave-absorbing concrete prepared in Step 1 into the microwave-absorbing honeycomb obtained in Step 3, with a height of 10mm, to obtain the first layer of honeycomb concrete.

[0038] Step 5: Pour the microwave-absorbing concrete prepared in Step 2 into the microwave-absorbing honeycomb containing the first layer of concrete obtained in Step 4, to a height of 10mm, to obtain double-layer honeycomb concrete.

[0039] Step 6: Fabricate a semi-infinite silicon substrate using an etching process. Deposit a silicon film on the silicon dioxide substrate using low-pressure chemical vapor deposition. Spin-coat ZEP520A photoresist onto the silicon film. Then deposit a thin layer of chromium as a resist. Obtain silicon nanorods by electron beam lithography. Finally, remove the photoresist using a removal agent and O2 plasma to obtain a fully dielectric phase gradient metasurface composed of two parts: a silicon dioxide substrate with a height of 4 mm, and three micro-shapes made of nanorods: hexagons (height 4 mm, bottom width 4 mm), cylinders (height 4 mm, bottom diameter 3 mm), and triangular pyramids (height 3 mm, bottom diameter 4 mm).

[0040] Step 7: Combine the all-dielectric phase gradient metasurface prepared in Step 6 with the double-layer honeycomb concrete prepared in Step 5 to obtain a surface protrusion absorbing structure.

[0041] The measured peak reflection loss of the obtained absorbing structure was as low as -49.8dB, the effective absorption bandwidth (RL<-10dB) was 16.64GHz, and the compressive strength was 22.3MPa.

[0042] Example 2

[0043] This embodiment provides a honeycomb concrete microwave absorbing structure based on an all-dielectric phase gradient metasurface, which is prepared by the following steps:

[0044] Step 1: Premix silicate cement, fly ash, and 0.6% carbon nanotubes in a dry container for 5 minutes. After that, transfer the uniform powder to a mixing tank, add water and naphthalene sulfonate formaldehyde polymer water-reducing agent to the mixing tank and stir for 2 minutes.

[0045] Step 2: Repeat Step 1, except that the carbon nanotube content is 1.3%;

[0046] Step 3: Repeat Step 1, except that the carbon nanotube content is 2.0%;

[0047] Step 4: Select polypropylene fibers and weave a wave-absorbing honeycomb with a height of 21mm on a loom;

[0048] Step 5: Pour the microwave-absorbing concrete prepared in Step 1 into the microwave-absorbing honeycomb obtained in Step 4, with a height of 7mm, to obtain the first layer of honeycomb concrete.

[0049] Step 6: Pour the microwave-absorbing concrete prepared in Step 2 into the microwave-absorbing honeycomb containing the first layer of concrete obtained in Step 5, to a height of 7mm, to obtain double-layer honeycomb concrete.

[0050] Step 7: Pour the microwave-absorbing concrete prepared in Step 3 into the microwave-absorbing honeycomb containing two layers of concrete obtained in Step 6, with a height of 7mm, to obtain three layers of honeycomb concrete.

[0051] Step 8: Fabricate a semi-infinite silicon substrate using an etching process. Deposit a silicon film on the silicon dioxide substrate using low-pressure chemical vapor deposition. Spin-coat ZEP520A photoresist onto the silicon film. Then deposit a thin layer of chromium as a resist. Obtain silicon nanorods by electron beam lithography. Finally, remove the photoresist using a removal agent and plasma to obtain a fully dielectric phase gradient metasurface composed of two parts: a 5mm high silicon dioxide substrate, and a combination and periodic arrangement of cones with a height of 4mm and a bottom diameter of 4mm made of nanorods and cones with a height of 3mm and a bottom side length of 3mm.

[0052] Step 9: Combine the all-dielectric phase gradient metasurface obtained in Step 8 with the three-layer honeycomb concrete obtained in Step 5 to obtain a surface protrusion absorbing structure.

[0053] The measured peak reflection loss of the obtained absorbing structure was as low as -36.2dB, the effective absorption bandwidth (bandwidth of RL<-10dB) was 14.04GHz, and the compressive strength was 25.6MPa.

[0054] Example 3

[0055] This embodiment provides a honeycomb concrete microwave absorbing structure based on an all-dielectric phase gradient metasurface, which is prepared by the following steps:

[0056] Step 1: Premix silicate cement, fly ash, and 0.5% graphite in a dry container for 5 minutes. After that, transfer the uniform powder to a mixing tank, add water and naphthalene sulfonate formaldehyde polymer water-reducing agent to the mixing tank and stir for 2 minutes.

[0057] Step 2: Repeat Step 1, except that the graphite content is 0.9%;

[0058] Step 3: Repeat Step 1, except that the graphite content is 1.5%;

[0059] Step 4: Repeat Step 1, except that the graphite content is 2.0%;

[0060] Step 5: Select silicon carbide fibers and weave a wave-absorbing honeycomb with a height of 24mm on a loom;

[0061] Step 6: Pour the microwave-absorbing concrete prepared in Step 1 into the microwave-absorbing honeycomb obtained in Step 5, with a height of 6mm, to obtain the first layer of honeycomb concrete.

[0062] Step 7: Pour the microwave-absorbing concrete prepared in Step 2 into the microwave-absorbing honeycomb containing the first layer of concrete obtained in Step 6, to a height of 6mm, to obtain double-layer honeycomb concrete.

[0063] Step 8: Pour the microwave-absorbing concrete prepared in Step 3 into the microwave-absorbing honeycomb containing two layers of concrete obtained in Step 7, with a height of 6mm, to obtain three layers of honeycomb concrete.

[0064] Step 9: Pour the microwave-absorbing concrete prepared in Step 4 into the microwave-absorbing honeycomb containing three layers of concrete obtained in Step 8, with a height of 6mm, to obtain four layers of honeycomb concrete.

[0065] Step 10: Fabricate a semi-infinite silicon substrate using an etching process. Deposit a silicon film on the silicon dioxide substrate using low-pressure chemical vapor deposition. Spin-coat ZEP520A photoresist onto the silicon film. Then deposit a thin layer of chromium as a resist. Obtain silicon nanorods by electron beam lithography. Finally, remove the photoresist using a removal agent and plasma to obtain a fully dielectric phase gradient metasurface with a silicon dioxide substrate of 5 mm in height. On the substrate, four micro-shapes made of nanorods are combined as a unit and periodically arranged: cones (3 mm in height, 4 mm in bottom diameter), cylinders (4 mm in height, 4 mm in bottom diameter), hexagonal frustums (4 mm in height, 5 mm in bottom side length, 3 mm in surface side length), and hexagons (5 mm in height, 5 mm in bottom side length).

[0066] Step 11: Combine the all-dielectric phase gradient metasurface obtained in Step 10 with the three-layer honeycomb concrete obtained in Step 5 to obtain a surface protrusion absorbing structure.

[0067] The measured peak reflection loss of the obtained absorbing structure reached a minimum of -57.2dB, the effective absorption bandwidth (bandwidth with RL < -10dB) was 17.03GHz, and the compressive strength was 28.4MPa.

[0068] Comparative Example 1

[0069] The same preparation method as in Example 1 was used, except that the honeycomb structure and all-dielectric phase gradient metasurface structure were not used. The lowest reflection loss value was -12.75dB, the effective absorption bandwidth (bandwidth with RL < -10dB) was 3.02GHz, and the compressive strength was 16.8MPa.

[0070] Comparative Example 2

[0071] The same preparation method as in Example 2 was used, except that the honeycomb structure and all-dielectric phase gradient metasurface structure were not used. The lowest reflection loss value was -18.04dB, the effective absorption bandwidth (bandwidth of RL < -10dB) was 6.03GHz, and the compressive strength was 20.6MPa.

[0072] The peak reflection loss of the absorbing structure obtained by the present invention is not less than -36dB, preferably -45dB to -58dB; the effective absorption bandwidth (RL<-10dB) is 12 to 17 GHz, and the compressive strength is 22 to 30 MPa.

[0073] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0074] Any aspects not covered in this invention are applicable to existing technologies.

Claims

1. A honeycomb concrete microwave absorbing structure based on an all-dielectric phase gradient metasurface, characterized in that, It consists of a 3D fiber-reinforced honeycomb concrete substrate and a top all-dielectric phase gradient metasurface structure; the honeycomb is a 3D fiber-reinforced honeycomb structure woven from microwave-absorbing fibers; the raw materials of the concrete include cement, fly ash, water, water-reducing agent and microwave-absorbing agent; the array structure of the all-dielectric phase gradient metasurface consists of a silica substrate and a geometry made of silicon nanorods on the substrate; The fabrication process of the absorbing structure is as follows: Step 1: Using microwave-absorbing fibers as raw materials, weave on a loom according to the structural pattern of the 3D fiber microwave-absorbing honeycomb. Select the straight-through method for threading the heddles, then introduce the weft and beat the weft. After several cycles of interlacing, a 3D fiber microwave-absorbing honeycomb is woven. Step 2: Premix cement, fly ash, and microwave absorber evenly in a dry container to obtain a uniform powder. Then, transfer the uniform powder to a mixing tank, add water and water-reducing agent to the mixing tank, and mix evenly. Step 3: Repeat step 2 according to different amounts of absorbing agent to obtain absorbing concrete with different amounts of absorbing agent. Step 4: Pour the prepared microwave-absorbing concrete with different microwave-absorbing agent contents into the 3D fiber microwave-absorbing honeycomb obtained in step 1 in layers, with the microwave-absorbing agent content gradually increasing. Step 5: Fabricate a semi-infinite silicon substrate using an etching process. Deposit a silicon film on the silicon dioxide substrate using low-pressure chemical vapor deposition. Spin-coat ZEP520A photoresist onto the silicon film. Then deposit a thin layer of chromium as a resist. Obtain silicon nanorods by electron beam lithography. Finally, remove the photoresist using a removal agent and plasma to obtain an all-dielectric phase gradient metasurface. Step 6: Combine the all-dielectric phase gradient metasurface obtained in Step 5 with the honeycomb concrete obtained in Step 4 to obtain a honeycomb concrete microwave absorbing structure based on the all-dielectric phase gradient metasurface.

2. The honeycomb concrete microwave absorbing structure based on an all-dielectric phase gradient metasurface according to claim 1, characterized in that, The cement used in the concrete is silicate cement or sulfoaluminate cement, the fly ash is siliceous fly ash or calcareous fly ash, the water-reducing agent is lignin sulfonate or naphthalene sulfonate formaldehyde polymer, and the microwave absorbing agent is at least one of graphite, graphene, and carbon nanotubes; the fiber used in the woven honeycomb is carbon fiber, silicon carbide fiber, polycrystalline iron fiber or polypropylene fiber with microwave absorbing properties.

3. The honeycomb concrete microwave absorbing structure based on an all-dielectric phase gradient metasurface according to claim 1, characterized in that, The substrate is divided into multi-layer structures based on the varying content of the absorbing agent, with the absorbing agent content increasing sequentially from top to bottom. The substrate has 2, 3, or 4 layers, each with the same thickness, resulting in a total thickness of 15–25 mm. When the multi-layer structure has 2 layers, the absorbing agent content in each layer is 0.5%–1.3% and 1.3%–2.5%, respectively. When the multi-layer structure has 3 layers, the absorbing agent content in each layer is 0.5%–1.2%, 1.2%–1.9%, and 1.9%–2.5%, respectively. When the multi-layer structure has 4 layers, the absorbing agent content in each layer is 0.5%–0.8%, 0.8%–1.3%, 1.3%–1.9%, and 1.9%–2.5%, respectively.

4. The honeycomb concrete microwave absorbing structure based on an all-dielectric phase gradient metasurface according to claim 1, characterized in that, The silicon nanorods are made into hexagonal, frustum, conical, or cylindrical shapes; the micro-units are selected from two or more geometric shapes and combined according to the operating wavelength.

5. The honeycomb concrete microwave absorbing structure based on an all-dielectric phase gradient metasurface according to claim 1, characterized in that, The silica substrate has a height of 4–7 mm; the geometry made of silicon nanorods has a height of 3–5 mm and a bottom width or diameter of 3–5 mm.

6. The honeycomb concrete microwave absorbing structure based on an all-dielectric phase gradient metasurface according to claim 1, characterized in that, The array structure of the all-dielectric phase gradient metasurface uses a 4 mm high silicon dioxide substrate as the substrate. On the substrate, three micro-shapes made of nanorods are combined as a unit and periodically arranged. The height of the hexagon is 4 mm and the bottom width of the hexagon is 4 mm. The height of the cylinder is 4 mm and the bottom diameter of the cylinder is 3 mm. The height of the triangular pyramid is 3 mm and the bottom diameter of the triangular pyramid is 4 mm. Alternatively, an array structure of all-dielectric phase gradient metasurfaces can be constructed using a 5mm high silicon dioxide substrate. On the substrate, four micro-shapes made of nanorods—cones, cylinders, hexagonal frustums, and hexagons—are combined as a unit and arranged periodically. The hexagons have a height of 5mm and a base width of 5mm, the cylinders have a height of 4mm and a base diameter of 4mm, the cones have a height of 3mm and a base diameter of 4mm, and the hexagonal frustums have a height of 4mm, a base side length of 5mm, and a surface side length of 3mm.

7. The honeycomb concrete microwave absorbing structure based on an all-dielectric phase gradient metasurface according to claim 1, characterized in that, The absorption mechanism of the honeycomb concrete absorbing structure based on the all-dielectric phase gradient metasurface is as follows: the 3D fiber honeycomb structure of the substrate is composed of fibers with wave absorption properties. The 3D structure of the honeycomb causes multiple reflections and scattering of electromagnetic waves, which accelerates the loss of electromagnetic waves. The concrete filling the honeycomb pores has a porous structure, which is regarded as a wave-transmitting channel, allowing most of the incident electromagnetic waves to pass through the concrete, thereby enhancing the impedance matching between the matrix and the air. The electromagnetic waves undergo multiple reflections and refractions inside the pores, increasing the transmission distance of the electromagnetic waves while being absorbed and lost. The thin-walled structure between the pores causes multiple interference cancellation effects on the electromagnetic waves, increasing the resonant absorption loss of the electromagnetic waves. By varying the amount of microwave absorber in concrete, a gradually changing impedance gradient structure is formed. Electromagnetic waves incident into the material are attenuated sequentially, and multiple reflections at the interfaces of each layer produce coherent loss and resonance effects. The top layer of the all-dielectric phase gradient metasurface, on the one hand, achieves the effect of controllable impedance gradient and electromagnetic wave transmission and absorption mode of the composite structure by controlling the size and shape of the micro-units, selecting different micro-shapes for combination and further periodically arranging them. On the other hand, electromagnetic waves undergo multiple reflections and scattering in the micro-units of the phase gradient metasurface, increasing the transmission distance of electromagnetic waves while being absorbed and lost. The top layer of the all-dielectric phase gradient metasurface generates different phases of electromagnetic waves, flexibly controlling electromagnetic waves in different frequency bands, so that the three-dimensional microwave absorbing honeycomb structure of the substrate can fully exert its microwave absorption effect in different frequency bands.

Images