Multi-order half-wavelength thick broadband wave-transparent metamaterial and preparation method thereof

Abstract

The invention discloses a multi-order half-wavelength thick broadband wave-transparent metamaterial and a preparation method thereof, and belongs to the field of electromagnetic wave-transparent metamaterials. The material comprises periodically arranged cellular units, each cellular unit comprises a bearing base material with the multi-order half-wavelength thickness and a dielectric gradient layer, and the two parts are made of the same dielectric material and are of a continuous integral structure or a separated structure; hole cavities which are uniform or gradually changed in a gradient manner are distributed in the dielectric gradient layer; the period distribution of the cells is square or hexagonal, and the size and thickness of the cell period can be adjusted according to the wavelength of incident electromagnetic waves; meanwhile, the invention provides a preparation method of the broadband wave-transparent metamaterial of single-phase ceramic, complex-phase ceramic and fiber-reinforced ceramic-based composite materials. According to the invention, the bottleneck of broadband wave-transparent structure design and material preparation of the current multi-order half-wavelength thick wave-transparent structure is solved, and a new technical scheme is provided for the high-temperature-resistant broadband wave-transparent structure.

Description

Technical Field

[0001] The present invention belongs to the field of electromagnetic wave-transmitting metamaterials, and in particular relates to a multi-order half-wavelength thick broadband wave-transmitting metamaterial and a preparation method thereof. Background Art

[0002] The half-wavelength thick wave-transmitting structure is the main application form of the wave-transmitting component of the radar antenna of the reentry vehicle. It is required to integrate high performance requirements such as wave transmission, heat protection, load bearing, and weather resistance. In the half-wavelength thick wave-transmitting structure, the structure thickness value is half of the wavelength of the corresponding frequency electromagnetic wave propagating in the medium. The wave transmission principle is to form an efficient transmission window near the center frequency through the phase destructive effect of the electromagnetic wave, so the wave transmission band is narrow. The corresponding wave-transmitting material must have sufficient high-temperature mechanical properties, good ablation resistance, erosion resistance, and thermal shock resistance, as well as very low dielectric constant (ε≤4) and loss tangent (tanδ≤0.01) to reduce the reflection of the electromagnetic wave on the cover wall and the transmission loss. As the time that the wave-transmitting structure is subjected to high temperature gradually increases and the reentry ablation environment becomes increasingly harsh, the thickness order of the wave-transmitting structure continues to increase, which makes the wave transmittance and wave transmission bandwidth of the wave-transmitting structure rapidly decrease. It is urgent to develop high-temperature resistant broadband wave-transmitting structures and materials for multi-order half-wavelength thick structures.

[0003] Ceramic wave-transmitting materials have the characteristics of high melting point, good high-temperature mechanical properties, low linear expansion coefficient and excellent dielectric properties. They are the main candidate materials for high-temperature wave-transmitting structures. Commonly used high-temperature wave-transmitting ceramics mainly include low-dielectric oxides, phosphates, nitride ceramics and their composite ceramics, as well as continuous fiber-reinforced ceramic-based composites. The thermal shock resistance and overall toughness of fiber-reinforced ceramic-based composites are better than those of ceramics and composite ceramics, but their high-temperature performance is limited by the temperature resistance of the reinforcing fibers, and the long-term load-bearing temperature is difficult to exceed 1100°C. The high-temperature mechanics of ceramics and composite ceramics depends on the high-temperature softening temperature, and the high-temperature bending strength is better than that of fiber-reinforced ceramic-based composites. Among them, nitride ceramics and their ceramic-based composites are the material systems with the most development potential. Broadband wave-transmitting structures mainly include thin-walled structures, sandwich structures, gradient structures, etc. Among them, the thickness of the thin-walled structure is usually less than 1 / 10 to 1 / 20 of the wavelength, and can only be used in occasions where the mechanical properties are not required. A sandwich, B sandwich, C sandwich, and gradient structures have relatively good mechanical properties. Both the A and B sandwiches are three-layer structures. The former is composed of two dense high-dielectric constant thin surface layers and a low-dielectric constant, low-density core layer, while the latter is composed of two low-dielectric constant, low-density surface layers and a high-dielectric constant, high-density core layer. The A sandwich structure can achieve good power transmission when the incident angle of the electromagnetic wave is small, and has good application prospects in high-temperature broadband wave-transmitting structures, but the antenna phase distortion is small, but it is very sensitive to polarization. The surface mechanical properties of the B sandwich structure are weak. The dielectric constant of the outer layer material of the B sandwich structure is approximately the mean square value of the middle layer, similar to a 1 / 4 wavelength impedance matcher, but because the surface layer is a porous material, it cannot be used in a high thermal environment. The C sandwich structure is a five-layer structure composed of two layers of A sandwich structures. It has good electromagnetic wave transmittance and can obtain higher transmission performance within a larger range of incident angles, but the difficulty of preparing ceramic materials is significantly increased. The gradient structure can be regarded as a multilayer dielectric material composed of a series of dielectric constants and the matching bonding of multilayer structures. The impedance matching design is used to achieve broadband wave transmission. Porous silicon nitride ceramics are usually used as the material for different dielectric constant layers. It is expected to be used in high-temperature resistant broadband wave-transparent components. However, the difficulty lies in how to control the microscopic composition and porosity of the material to achieve serialized dielectric constants and matching bonding of multilayer structures.

[0004] In summary, there are few research reports on broadband wave-transmitting technology for multi-stage large-thickness load-bearing structures. The application of sandwich structures and multi-layer gradient structures in high-temperature resistant broadband wave-transmitting structures is still greatly limited. On the one hand, the preparation of multi-layer structures is difficult. When the total thickness is small, the thickness and dielectric constant of each layer of materials are very accurate, and the matching and bonding between multiple layers are very difficult. On the other hand, the mechanical strength of each layer of materials is highly dispersed, the mechanical strength of the low dielectric constant layer is usually low, and there is a serious thermal mismatch between different layers. There are obvious weak nodes when subjected to high-temperature mechanical loads, so it is difficult to meet the requirements of long-term high-temperature loads. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a multi-order half-wavelength thick broadband wave-transparent metastructure material and a preparation method in view of the deficiencies in the above-mentioned prior art, so as to avoid the problems of difficult preparation of multi-layer high-precision materials, difficult matching between layers and poor high-temperature mechanical bearing performance existing in sandwich structures and gradient structures, solve the bottlenecks of broadband wave-transparent structure design and material preparation of current multi-order half-wavelength thick wave-transparent structures, and provide a new technical solution for high-temperature resistant broadband wave-transparent structures.

[0006] In order to solve the above technical problems, the following technical solutions are provided:

[0007] A multi-order half-wavelength thick broadband wave-transmitting metamaterial, comprising periodically arranged cellular units, wherein the cellular units comprise a multi-order half-wavelength thick supporting substrate and a dielectric gradient gradient layer, wherein the two parts are made of the same dielectric material and are a continuous integral structure or a separate structure; uniform or gradient cavities are distributed inside the dielectric gradient gradient layer; the periodic distribution of the cellular units is in a square or hexagonal shape, and the periodic size and thickness of the cellular units can be adjusted according to the wavelength of the incident electromagnetic wave;

[0008] When the dielectric gradient layer adopts a structure with two layers with different equivalent dielectric constants and thicknesses, the equivalent dielectric constants of the two layers are ε1 and ε2 respectively, and the thicknesses are t1 and t2 respectively, and the optimization calculation is performed in the following space;

[0009] ε1∈[1,(ε r ) 1 / 3 ]

[0010] ε2∈[1,(ε r ) 2 / 3 ]

[0011]

[0012] When the dielectric gradient layer adopts a structure of two layers with different equivalent dielectric constants and thicknesses, both layers are in the shape of cylindrical holes or square holes, and the pore volume contents P1 and P2 are calculated by the equivalent dielectric constants ε1 and ε2 according to the following formula, thereby determining the diameter or side length of the pores;

[0013]

[0014] When the dielectric gradient gradient layer adopts a continuously gradient equivalent dielectric constant, the interior thereof is a continuously gradient cavity, the total volume content of the cavity is the sum of P1 and P2, and the shape of the cavity includes a conical shape, a parabolic shape or an exponential shape.

[0015] Furthermore, for the resonant frequency f0, the thickness d of the half-wavelength thick supporting substrate of different orders is n , according to the specific order n, the wavelength λ0 of the electromagnetic wave in the air, the dielectric constant ε of the supporting substrate r And the electromagnetic wave incident angle θ is calculated:

[0016]

[0017] Furthermore, when electromagnetic waves are in the frequency range of 8 GHz to 40 GHz and at an incident angle of 0° to 75°, for wave-transmitting materials with a dielectric constant ≤ 7 and a half-wavelength order ≤ 7, the high-efficiency wave-transmitting bandwidth near the corresponding resonant frequency can be effectively improved.

[0018] Furthermore, the supporting substrate and the dielectric gradient layer materials are made of single-phase ceramics, multiphase ceramics or continuous fiber reinforced ceramic-based composites. Single-phase ceramics include porous silicon nitride ceramics, alumina ceramics, nitride multiphase ceramics, etc. Multiphase ceramics include quartz quartz composites, quartz fiber reinforced nitride ceramic-based composites, and nitride fiber reinforced nitride ceramic-based composites.

[0019] At the same time, the present invention also provides a method for preparing a multi-order half-wavelength thick broadband wave-transmitting metastructure material, which comprises the following material preparation steps for a broadband wave-transmitting metastructure of a single-phase ceramic or a multi-phase ceramic:

[0020] ① Slurry preparation: ceramic powder with a certain volume of solid content, sintering aid, polymer dispersant, pH regulator, cross-linking initiator, etc. are uniformly mixed to obtain a slurry with moderate viscosity and fluidity, which is used as the raw material for injection molding; by adding a certain proportion of photocurable resin to the slurry, it can be used as the raw material for photocuring molding of additive manufacturing;

[0021] ② Molding and curing, pouring the above slurry into a cast molding mold, wherein the mold has a uniform or gradient-gradient cavity distributed inside the dielectric gradient gradient layer, and a multi-order half-wavelength thick broadband wave-transmitting metastructure material blank is obtained; when using photocuring molding, a broadband wave-transmitting integrated blank structure containing cavities is directly printed out by a 3D printer, and the size shrinkage caused by ceramic sintering is considered in advance during molding and curing to ensure that a broadband wave-transmitting metastructure material of a predetermined size is finally obtained;

[0022] ③ Debonding and pre-sintering: Place the thick solidified green body structure in a muffle furnace and heat it to 600°C at a heating rate of 1°C / min, and keep it warm for 3-5 hours to burn out the resin additives. Place the green body after debonding in an inert atmosphere protection furnace for high-temperature sintering to obtain a porous ceramic with a broadband wave-transmitting structure;

[0023] ④ Densification treatment: the porous ceramics obtained by pre-sintering are densified through sol-gel, precursor impregnation and cracking processes to obtain dense multiphase ceramics, and the material composition and dielectric constant are adjusted to obtain the multi-order half-wavelength thick broadband wave-transmitting metamaterial of the present invention.

[0024] For a broadband wave-transmitting superstructure of a fiber-reinforced ceramic matrix composite material, the following material preparation steps are included:

[0025] ① Preparation of composite materials: dense fiber-reinforced ceramic matrix composite materials are obtained through sol-gel method, chemical vapor deposition method, precursor impregnation and cracking process, etc. The dielectric constant of the composite material is ε r , the thickness is the sum of the thickness of the supporting substrate layer and the dielectric gradient layer;

[0026] ② Cavity processing: machining the tool according to the size of the cavity in the dielectric gradient layer, and processing the dielectric gradient layer containing periodic gradually changing cavities on the surface of the composite material, thus obtaining the multi-order half-wavelength thick broadband wave-transmitting metamaterial of the present invention.

[0027] The effective benefits of the present invention are as follows:

[0028] 1. The present invention proposes a multi-order half-wavelength thick broadband wave-transmitting metamaterial and a preparation method, which uses a metamaterial with periodic cavities to achieve the goal of dielectric gradient change, can effectively improve the wave transmission bandwidth of the half-wavelength thick structure, and the integrated structure has good mechanical bearing performance, which can overcome the difficulty of poor mechanical properties of traditional sandwich and multi-layer structures.

[0029] 2. The present invention proposes a multi-order half-wavelength thick broadband wave-transmitting metastructure material and a preparation method. The supporting substrate layer and the dielectric gradient gradient layer use dielectric materials with the same dielectric constant. Through the relationship between the cavity and the equivalent dielectric constant, the equivalent dielectric constant is converted into a gradient cavity that is easy to form and process. The preparation and processing of the broadband wave-transmitting structure is simpler, there is no need to use a multi-layer structure, and the difficulty of bonding the multi-layer structure is avoided.

[0030] 3. The present invention proposes a multi-order half-wavelength thick broadband wave-transparent metastructure material and a preparation method. The dielectric gradient gradient layer and the cavity are highly designable, the molding method is simple, and the applicable material range is wide. The wave-transparent performance and mechanical properties of the broadband wave-transparent structure can be flexibly adjusted to meet the structural and functional integration requirements such as high temperature resistance, broadband wave transmission, and high load-bearing capacity, and can provide support for the design and development of high-performance wave-transparent components. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic diagram of the structure of a multi-order half-wavelength thick broadband wave-transmitting metamaterial, where (a) is a schematic diagram of the broadband wave-transmitting structure, where: 1-multi-order half-wavelength thick bearing layer; 2-dielectric gradient layer; (b) schematic diagram of the double-layer cylindrical cavity structure in the dielectric gradient layer; (c) schematic diagram of the gradient cavity structure in the dielectric gradient layer.

[0032] Figure 2 This is a wave transmittance curve of a 5th-order thickness flat plate and a broadband wave-transmitting metamaterial under the condition of 45° oblique incidence of electromagnetic waves in Example 1.

[0033] Figure 3 It is the transmittance curve of the 5th-order thick plate in the range of 14.5 GHz to 15.5 GHz at different incident angles in Example 1.

[0034] Figure 4 It is the wave transmittance curve of the broadband wave-transmitting structure B in the range of 14.5 GHz to 15.5 GHz at different incident angles in Example 1.

[0035] Figure 5 The sound absorption coefficient of the corrugated curved sandwich materials with different wall thicknesses at normal pressure varies with frequency in Example 1. DETAILED DESCRIPTION

[0036] The present invention aims to provide a multi-order half-wavelength thick broadband wave-transmitting metamaterial and a preparation method thereof. The design method of electromagnetic metamaterials is adopted to introduce a dielectric gradient gradient layer inside a multi-order half-wavelength thick bearing base layer to generate an equivalent dielectric constant, thereby achieving impedance gradient matching and broadband wave transmission of the overall structure, effectively expanding the wave transmission working bandwidth of the multi-order half-wavelength structure, and avoiding the processing difficulties of the multi-layer structure, thereby providing a new technical solution for high-temperature resistant broadband wave-transmitting structures.

[0037] In order to better understand the present invention, the present invention is explained and illustrated in detail below in conjunction with the accompanying drawings and embodiments.

[0038] The present invention provides a multi-order half-wavelength thick broadband wave-transmitting metamaterial and a preparation method thereof, including: Figure 1 The periodically arranged cellular unit shown in the figure comprises two parts: a supporting substrate with a multi-order half-wavelength thickness and a dielectric gradient gradient layer. The two parts are made of the same dielectric material and can be either a continuous integral structure or a separate structure. The dielectric gradient gradient layer is internally distributed with uniform or gradient cavities. The periodic distribution of the cells is square or hexagonal, and the size and thickness of the cell period can be adjusted according to the wavelength of the incident electromagnetic wave. The multi-order half-wavelength thick broadband wave-transmitting metamaterial of the present invention can effectively improve the high-efficiency wave-transmitting bandwidth near the corresponding resonant frequency for electromagnetic waves in the frequency range of 1GHz to 40GHz and incident angles of 0° to 75°, as well as wave-transmitting materials with a dielectric constant ≤7 and a half-wavelength order ≤7.

[0039] For the resonant frequency f0, the thickness d of the half-wavelength thick supporting substrate of different orders n , according to the specific order n, the wavelength λ0 of the electromagnetic wave in the air, the dielectric constant ε of the supporting substrate r And the electromagnetic wave incident angle θ is calculated:

[0040]

[0041] When the dielectric gradient layer adopts a structure with two layers with different equivalent dielectric constants and thicknesses, the equivalent dielectric constants of the two layers are ε1 and ε2 and the thicknesses are t1 and t2, respectively, and are calculated according to the following formula:

[0042] ε1=(ε r ) 1 / 3

[0043] ε2=(ε r ) 2 / 3

[0044]

[0045]

[0046] The above four parameters are taken as the values ​​obtained by the above calculation, which can increase the working bandwidth near the frequency point while keeping the resonant frequency of the multi-order half-wavelength thick plate unchanged, and at the same time significantly improve the minimum wave transmission of the original structure.

[0047] Respectively in ε1∈[1,(ε r ) 1 / 3 ]、ε2∈[1,(ε r ) 2 / 3 ]、 By performing parameter optimization calculation within a range of , the working bandwidth near the resonant frequency can be further broadened and the minimum wave transmittance value can be improved.

[0048] When the dielectric gradient layer adopts a structure of two layers with different equivalent dielectric constants and thicknesses, both layers are cylindrical or square pores. The pore volume contents P1 and P2 are calculated by the equivalent dielectric constants ε1 and ε2 according to the following formula, and then the diameter or side length of the pore is determined.

[0049]

[0050]

[0051] When the dielectric gradient layer adopts a continuously gradient equivalent dielectric constant, its interior is a continuously gradient pore structure, the total volume content is the sum of P1 and P2, and the shape of the pore includes conical, parabolic, exponential, etc.

[0052] The supporting substrate and the dielectric gradient layer material are made of single-phase ceramics, multiphase ceramics or continuous fiber reinforced ceramic-based composite materials. The former includes porous silicon nitride ceramics, alumina ceramics, nitride multiphase ceramics, etc., and the latter includes quartz quartz composite materials, quartz fiber reinforced nitride ceramic-based composite materials, nitride fiber reinforced nitride ceramic-based composite materials, etc.

[0053] At the same time, the present invention provides a method for preparing a multi-order half-wavelength thick broadband wave-transmitting metastructure material, which comprises the following material preparation steps for a broadband wave-transmitting metastructure of a single-phase ceramic and a multi-phase ceramic:

[0054] ① Slurry preparation: ceramic powder with a certain volume of solid content, sintering aid, polymer dispersant, pH regulator, cross-linking initiator, etc. are uniformly mixed to obtain a slurry with moderate viscosity and fluidity, which is used as the raw material for injection molding; by adding a certain proportion of photocurable resin to the slurry, it can be used as the raw material for photocuring molding of additive manufacturing;

[0055] ② Molding and curing, pouring the above slurry into a cast molding mold, wherein the mold has a uniform or gradient-gradient cavity distributed inside the dielectric gradient gradient layer, and a multi-order half-wavelength thick broadband wave-transmitting metastructure material blank is obtained; when using photocuring molding, a broadband wave-transmitting integrated blank structure containing cavities is directly printed out by a 3D printer, and the size shrinkage caused by ceramic sintering is considered in advance during molding and curing to ensure that a broadband wave-transmitting metastructure material of a predetermined size is finally obtained;

[0056] ③ Debonding and pre-sintering: Place the thick solidified green body structure in a muffle furnace and heat it up to 600°C at a rate of 1°C / min, and keep it warm for 5 hours to burn out the resin additives. Place the green body after debonding in an inert atmosphere protection furnace for high-temperature sintering to obtain a porous ceramic with a broadband wave-transmitting structure;

[0057] ④ Densification treatment: the porous ceramics obtained by pre-sintering are densified through sol-gel, precursor impregnation and cracking processes to obtain dense multiphase ceramics, and the material composition and dielectric constant are adjusted to obtain the multi-order half-wavelength thick broadband wave-transmitting metamaterial of the present invention.

[0058] For a broadband wave-transmitting superstructure of a fiber-reinforced ceramic matrix composite material, the following material preparation steps are included:

[0059] ① Preparation of composite materials: dense fiber-reinforced ceramic matrix composite materials are obtained through sol-gel method, chemical vapor deposition method, precursor impregnation and cracking process, etc. The dielectric constant of the composite material is ε r , the thickness is the sum of the thickness of the supporting substrate layer and the dielectric gradient layer;

[0060] ② Cavity processing: machining the tool according to the size of the cavity in the dielectric gradient layer, and processing the dielectric gradient layer containing periodic gradually changing cavities on the surface of the composite material, thus obtaining the multi-order half-wavelength thick broadband wave-transmitting metamaterial of the present invention.

[0061] The above is a specific implementation method of the present invention. In the prior art, sandwich structures and multi-layer structures have the limitations of difficult processing of materials of each layer with specific dielectric constants, difficulty in high-precision bonding of multiple layers, and insufficient high-temperature mechanical bearing performance of multi-layer combination structures due to the need to match and combine the multi-layer structures. In addition, there is no targeted design method for multi-order half-wavelength thick structures. The multi-order half-wavelength thick broadband wave-transparent metamaterial and preparation method proposed in the present invention use gradient-varying metaunits to achieve a gradient equivalent dielectric constant, and are an integrated structure, which can effectively overcome the limitations of poor mechanical properties of traditional sandwich and multi-layer structures, meet the requirements of structural functional integration such as high temperature resistance, broadband wave transmission, and high load-bearing capacity, and can provide support for the design and development of high-performance wave-transparent components.

[0062] The multi-order half-wavelength thick broadband wave-transmitting metamaterial proposed in the present invention has a simple structure, readily available raw materials, mature preparation process, and strong parameter designability, so it is highly feasible to implement. A specific embodiment of the present invention is given below.

[0063] Example 1

[0064] The cell side length is 5mm. For the wave-transmitting material with a dielectric constant of 4.0, the electromagnetic wave resonance frequency f0 is 15GHz, the electromagnetic wave wavelength λ0 is 20mm, and when the thickness order of the wave-transmitting structure is 5 and the electromagnetic wave incident angle is 45°, the corresponding thickness d5 of the wave-transmitting structure is 26.73mm. It can be calculated that the equivalent dielectric constant ε1 and thickness t1 of the dielectric gradient gradient layer 1 are 1.59 and 4.78mm, respectively, and the equivalent dielectric constant ε2 and thickness t2 of the dielectric gradient gradient layer 2 are 2.52 and 3.53mm, respectively. Further, based on the equivalent dielectric constant, the volume contents P1 and P2 of the pores can be calculated to be 0.734 and 0.41, respectively. For the hexagonal cell, the diameters of the cylindrical pores can be calculated to be 4.5mm and 3.36mm, respectively. According to the data of the above design parameters, a broadband wave-transmitting structure model (structure A) is established, and the finite element simulation calculation of the periodic structure is performed. The wave transmittance of broadband wave-transmitting structure A within 12 GHz to 18 GHz is as follows: Figure 2 As shown, it can be seen that the bandwidth of broadband wave-transmitting structure A with a wave transmittance greater than 70% near the 15GHz frequency point is basically equivalent to that of the original flat plate, but the minimum wave transmittance in the 12GHz to 18GHz band is increased from 38.4% to 56.7%, and the minimum wave transmittance in the 14.5GHz to 15.5GHz range is increased from 62.9% to 70.0%, and the effect is obvious.

[0065] In addition, according to the design method proposed in the present invention, ε1, t1, ε2, and t2 are optimized in their respective numerical spaces. When the values ​​of the four parameters are 1.75, 2.0 mm, 1.40, and 4.0 mm, respectively, the following can be obtained: Figure 2 The broadband wave transmittance curve shown in the medium-bandwidth wave-transmitting structure B shows that the bandwidth of the wave transmittance>70% near the 15GHz frequency point is significantly improved compared with the flat plate and broadband wave-transmitting structure A, increasing from 0.766GHz to 1.045GHz, and the bandwidth expansion rate reaches 36.4%. Figure 3 , Figure 4 The figures show the wave transmittances of the flat panel and the broadband wave-transmitting structure B in the range of 15.5 GHz to 16.5 GHz under different incident angles. The corresponding wave transmittance values ​​are statistically shown in Table 1. It can be seen that the broadband wave-transmitting structure B effectively improves the minimum wave transmittance of the flat panel in the range of 15.5 GHz to 16.5 GHz, thereby verifying the effectiveness of the patented design method of the present invention.

[0066] Table 1 Statistical table of wave transmittance values ​​of flat plate and broadband wave-transmitting structure B in the range of 15.5 GHz to 16.5 GHz at different incident angles

[0067]

[0068] like Figure 5The actual material of broadband wave-transmitting structure B, which uses silicon nitride ceramics as the main material and is manufactured by additive manufacturing, photocuring and high-temperature sintering, is given. It can be seen that the additive manufacturing method can effectively prepare silicon nitride ceramics, verifying the feasibility of the preparation process of the patented multi-order half-wavelength thick broadband wave-transmitting metastructure material of the present invention.

Claims

1. A multi-order half-wavelength thick broadband wave-transmitting metamaterial, characterized in that: The invention comprises a periodically arranged cellular unit, wherein the cellular unit comprises a supporting substrate with a multi-order half-wavelength thickness and a dielectric gradient gradient layer, wherein the two parts are made of the same dielectric material and are a continuous integral structure or a separated structure; the dielectric gradient gradient layer is internally provided with uniform or gradient cavities; the periodic distribution of the cellular unit is in the shape of a square or a hexagon, and the periodic size and thickness of the cellular unit can be adjusted according to the wavelength of the incident electromagnetic wave; When the dielectric gradient layer adopts a structure with two layers with different equivalent dielectric constants and thicknesses, the equivalent dielectric constants of the two layers are ε1 and ε2 respectively, and the thicknesses are t1 and t2 respectively, and the optimization calculation is performed in the following space; When the dielectric gradient layer adopts a structure of two layers with different equivalent dielectric constants and thicknesses, both layers are in the shape of cylindrical holes or square holes, and the pore volume contents P1 and P2 are calculated by the equivalent dielectric constants ε1 and ε2 according to the following formula, thereby determining the diameter or side length of the pores; When the dielectric gradient gradient layer adopts a continuously gradient equivalent dielectric constant, the interior thereof is a continuously gradient cavity, the total volume content of the cavity is the sum of P1 and P2, and the shape of the cavity includes a conical shape, a parabolic shape or an exponential shape.

2. The multi-order half-wavelength thick broadband wave-transmitting metamaterial according to claim 1, characterized in that: For the resonant frequency f0, the thickness d of the half-wavelength thick supporting substrate of different orders n , according to the specific order n, the wavelength λ0 of the electromagnetic wave in the air, the dielectric constant ε of the supporting substrate r And the electromagnetic wave incident angle θ is calculated:

3. A multi-order half-wavelength thick broadband wave-transmitting metamaterial according to claim 1 or 2, characterized in that: When electromagnetic waves are in the frequency range of 8GHz to 40GHz and at an incident angle of 0° to 75°, for wave-transmitting materials with a dielectric constant ≤7 and a half-wavelength order ≤7, the high-efficiency wave-transmitting bandwidth near the corresponding resonant frequency can be effectively improved.

4. The multi-order half-wavelength thick broadband wave-transmitting metamaterial according to claim 3, characterized in that: The bearing substrate and the dielectric gradient layer materials are made of single-phase ceramics, multiphase ceramics or continuous fiber reinforced ceramic-based composites. Single-phase ceramics include porous silicon nitride ceramics, alumina ceramics, nitride multiphase ceramics, etc. Multiphase ceramics include quartz quartz composites, quartz fiber reinforced nitride ceramic-based composites, and nitride fiber reinforced nitride ceramic-based composites.

5. A method for preparing a multi-order half-wavelength thick broadband wave-transmitting metamaterial, characterized in that: The preparation of the multi-order half-wavelength thick broadband wave-transmitting metastructure material as claimed in claim 4, for the broadband wave-transmitting metastructure of single-phase ceramic and multi-phase ceramic, comprises the following material preparation steps: ① Slurry preparation: ceramic powder with a certain volume of solid content, sintering aid, polymer dispersant, pH regulator, cross-linking initiator, etc. are uniformly mixed to obtain a slurry with moderate viscosity and fluidity, which is used as the raw material for injection molding; by adding photocurable resin to the slurry, it is used as the raw material for additive manufacturing photocuring molding; ② Molding and curing, pouring the above slurry into a cast molding mold, wherein the mold has a uniform or gradient-gradient cavity distributed inside the dielectric gradient gradient layer, and a multi-order half-wavelength thick broadband wave-transmitting metastructure material blank is obtained; when using photocuring molding, a broadband wave-transmitting integrated blank structure containing cavities is directly printed out by a 3D printer, and the size shrinkage caused by ceramic sintering is considered in advance during molding and curing to ensure that a broadband wave-transmitting metastructure material of a predetermined size is finally obtained; ③ Debonding and pre-sintering: Place the thick solidified green body structure in a muffle furnace and heat it to 600°C at a heating rate of 1°C / min, and keep it warm for 3-5 hours to burn out the resin additives. Place the green body after debonding in an inert atmosphere protection furnace for high-temperature sintering to obtain a porous ceramic with a broadband wave-transmitting structure; ④ Densification treatment: The porous ceramics obtained by pre-sintering are densified through sol-gel, precursor impregnation and cracking processes to obtain dense multiphase ceramics, and the material composition and dielectric constant are adjusted to finally obtain multi-order half-wavelength thick broadband wave-transmitting metastructure materials.

6. A method for preparing a multi-order half-wavelength thick broadband wave-transmitting metamaterial, characterized in that: The preparation of the multi-order half-wavelength thick broadband wave-transmitting metastructure material as claimed in claim 4, for a broadband wave-transmitting superstructure of a fiber-reinforced ceramic matrix composite material, comprises the following material preparation steps: ① Preparation of composite materials: dense fiber-reinforced ceramic matrix composite materials are obtained through sol-gel method, chemical vapor deposition method, precursor impregnation and cracking process, etc. The dielectric constant of the composite material is ε r , the thickness is the sum of the thickness of the supporting substrate layer and the dielectric gradient layer; ② Cavity processing: machining the tool according to the size of the cavity in the dielectric gradient layer, and processing the dielectric gradient layer containing periodic gradually changing cavities on the surface of the composite material, thus obtaining the multi-order half-wavelength thick broadband wave-transmitting metamaterial of the present invention.

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