Ceramic wave-absorbing metamaterial and preparation method thereof

Abstract

The application relates to a ceramic wave-absorbing metamaterial and a preparation method thereof, which comprises at least three layers of ceramic base loss unit layers, ceramic base impedance regulation unit layers and metal mesh layers which are alternately stacked; the ceramic base loss unit layer comprises a ceramic matrix A and wave-absorbing agent A dispersed in the ceramic matrix A, wherein the wave-absorbing agent A is composed of a composite powder of nano silicon carbide with a particle size of 50-200 nm and a nickel-zinc ferrite ceramic powder; the ceramic base impedance regulation unit layer comprises a ceramic matrix B and wave-absorbing agent B dispersed in the ceramic matrix B, wherein the wave-absorbing agent B is composed of a composite powder of barium titanate with a particle size of 100-500 nm and tin oxide. The ceramic wave-absorbing metamaterial has a reflection loss of less than or equal to -10 dB in a 1-8 GHz frequency band, and a reflection loss of less than or equal to -25 dB in an 8-18 GHz frequency band.

Description

Technical Field

[0001] This invention belongs to the field of microwave absorbing materials technology, specifically relating to a ceramic microwave absorbing metamaterial and its preparation method. Background Technology

[0002] With the rapid development of modern electronic technology and wireless communication, problems such as electromagnetic interference, electromagnetic radiation pollution, and radar detection are becoming increasingly prominent. As a key technology for solving these problems, the performance requirements for absorbing materials are constantly increasing. At the same time, in special scenarios such as aircraft engine compartments, rocket exhaust plume areas, and high-temperature furnaces, absorbing materials must also withstand high-temperature environments above 800°C, which poses stringent challenges to the materials' high-temperature resistance, mechanical stability, and absorbing performance.

[0003] Existing microwave absorbing materials are mainly divided into two categories: organic-based and inorganic-based. Although organic-based microwave absorbing materials (such as rubber-based and resin-based materials) have advantages such as being lightweight and easy to process, they are prone to thermal decomposition in environments above 200°C, and cannot meet the requirements for high-temperature use. Among inorganic-based microwave absorbing materials, metal-based materials are resistant to high temperatures, but they have strong conductivity, which easily causes strong electromagnetic wave reflection, and they are also prone to oxidation at high temperatures, leading to performance degradation. Traditional ceramic-based microwave absorbing materials are mostly of a single structure, with poor uniformity of absorber dispersion and a narrow impedance matching range. They can usually only achieve effective absorption in a specific frequency band (such as 3-8 GHz), making it difficult to cover wide-band requirements.

[0004] Metamaterials, as artificially designed periodic structural materials, can achieve special microwave absorption properties by controlling the electromagnetic parameters of their unit structures. However, existing designs mostly rely on the combination of metal resonant units and organic matrices. In high-temperature environments, metal units are prone to oxidation, and organic matrices are prone to failure, leading to a sharp decline in microwave absorption performance. Furthermore, the impedance matching designs of existing metamaterials are mostly single gradients or fixed structures, which cannot achieve dynamic matching based on the characteristics of broadband electromagnetic waves, thus limiting their application in broadband high-temperature scenarios.

[0005] Therefore, developing a microwave absorbing material that combines high temperature resistance and stability, wide-band high absorption performance and structural reliability has become an urgent technical problem to be solved in this field. Summary of the Invention

[0006] To address the problems of poor stability, narrow absorption frequency band, and poor impedance matching of existing microwave absorbing materials under high temperature conditions, this invention provides a ceramic microwave absorbing metamaterial and its preparation method. By designing a multi-layered alternating gradient impedance structure and combining the synergistic effect of a high-temperature resistant ceramic matrix and a composite microwave absorbing agent, efficient electromagnetic wave absorption in a wide frequency band of 1-18 GHz is achieved at high temperatures of 800-1000℃.

[0007] In a first aspect, the present invention relates to a ceramic absorbing metamaterial comprising at least three alternating layers of ceramic-based loss unit layer, ceramic-based impedance modulation unit layer, and metal mesh layer;

[0008] The ceramic-based loss unit layer includes a ceramic matrix A and a microwave absorbing agent A dispersed therein. The microwave absorbing agent A is a composite powder composed of nano-silicon carbide with a particle size of 50-200nm and nickel-zinc ferrite ceramic powder.

[0009] The ceramic-based impedance control unit layer includes a ceramic matrix B and a microwave absorbing agent B dispersed therein. The microwave absorbing agent B is composed of a composite powder of barium titanate and tin oxide with a particle size of 100-500 nm.

[0010] The ceramic matrix A and ceramic matrix B are independently selected from one or more of alumina ceramics, silicon nitride ceramics, and silicon carbide ceramics;

[0011] The metal mesh layer is a periodic two-dimensional metal grid structure, with grid line width, spacing and thickness ranging from micrometers to sub-millimeters. The ceramic-based loss unit layer, ceramic-based impedance control unit layer and metal mesh layer together constitute a multilayer structure with gradient impedance matching. The relative permittivity of each ceramic-based loss unit layer and ceramic-based impedance control unit layer increases or decreases with the layer number to achieve wideband impedance matching.

[0012] Preferably, the metal mesh layer is made of titanium or its alloy and is formed into a two-dimensional grid structure by laser micromachining or photolithography.

[0013] Preferably, the metal mesh layer has a grid line width of 10µm to 200µm, a grid spacing of 20µm to 500µm, and a metal mesh layer thickness of 0.1mm to 1mm.

[0014] Preferably, in the ceramic-based loss unit layer, the mass ratio of ceramic matrix A to microwave absorber A is 4-6:5-6, and the mass ratio of nano-silicon carbide to nickel-zinc ferrite ceramic powder in microwave absorber A is 1-3:1.

[0015] In the ceramic-based impedance control unit layer, the mass ratio of ceramic matrix B to microwave absorber B is 5-7:3-5, and the mass ratio of barium titanate to tin oxide in microwave absorber B is 3-5:1.

[0016] Preferably, the thickness of the ceramic-based loss unit layer is 0.3-3 mm, the thickness of the ceramic-based impedance modulation unit layer is 0.2-2 mm, and the total number of layers of the ceramic absorbing metamaterial is 4-12.

[0017] In a second aspect, the present invention relates to a method for preparing the ceramic microwave absorbing metamaterial, comprising the following steps:

[0018] A ceramic casting slurry is prepared, and a ceramic-based loss unit layer and a ceramic-based impedance control unit layer green body are formed by casting. A metal mesh layer is prepared by laser micromachining or photolithography. The green body and the metal mesh layer are alternately stacked and hot-pressed to form a multi-layer green body. A segmented temperature-controlled co-firing process is used to finally obtain a ceramic microwave absorbing metamaterial.

[0019] Preferably, the casting slurry comprises ceramic powder and an organic binder, wherein the organic binder is any one or a combination of epoxy resin, polyimide or silane coupling agent, and the content is 5-10 wt% of the casting slurry, and vacuum impregnation is performed before sintering to improve density.

[0020] Preferably, the hot-pressing composite conditions are: temperature 80-120℃, pressure 10-30MPa, and time 30-60min.

[0021] Preferably, the co-firing process includes: heating to 200-400℃ and sintering for 1-2 hours to remove organic binders, heating to 800-1000℃ for preliminary sintering for 2-3 hours, and then heating to 1200-1400℃ for sintering and holding for 2-3 hours for final densification sintering.

[0022] The beneficial effects of this invention are as follows:

[0023] The ceramic absorbing metamaterial of the present invention comprises at least three alternating layers: a ceramic-based loss unit layer, a ceramic-based impedance-modulating unit layer, and a metal mesh layer. By employing an alternating layered structure design, and through the synergistic effect of the loss unit layer, the impedance-modulating unit layer, and the metal mesh layer, a progressive attenuation of electromagnetic waves—a process of "gradual absorption-impedance matching-secondary reflection absorption"—can be achieved.

[0024] By using a high-temperature resistant ceramic matrix and an oxidation-resistant metal mesh material, it can maintain structural stability and microwave absorption performance even at high temperatures of 800-1000℃, thus solving the problem of high-temperature failure of traditional organic-based microwave absorbing materials.

[0025] Through gradient impedance matching design and "dielectric-magnetic loss synergy" mechanism, reflection loss ≤-10dB in the 1-8GHz band and reflection loss ≤-25dB in the 8-18GHz band are achieved, covering the main frequency bands of conventional radar and communication.

[0026] The multi-layered alternating structure design and segmented co-firing process ensure strong interlayer bonding, while the high strength of the ceramic matrix allows the material to withstand complex mechanical environments, making it suitable for harsh applications such as aerospace. This significantly improves the high-temperature stability and broadband absorption performance of the absorbing material, demonstrating significant practical value and promising prospects for wider application. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a schematic diagram of the structure of a ceramic absorbing metamaterial disclosed in an embodiment of the present invention.

[0029] Figure 2 This is a schematic diagram of the metal mesh layer structure of a ceramic absorbing metamaterial disclosed in an embodiment of the present invention.

[0030] Figure 3 This is a schematic diagram of the fabrication process of a ceramic microwave absorbing metamaterial disclosed in an embodiment of the present invention. Detailed Implementation

[0031] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] To address the problems of poor stability, narrow absorption frequency band, and poor impedance matching of existing absorbing materials under high-temperature environments, such as... Figure 1 As shown, the present invention provides a ceramic absorbing metamaterial comprising at least three alternating layers of ceramic-based loss unit layer, ceramic-based impedance modulation unit layer, and metal mesh layer;

[0033] The ceramic-based loss unit layer includes a ceramic matrix A and a microwave absorbing agent A dispersed therein. The microwave absorbing agent A is a composite powder composed of nano-silicon carbide with a particle size of 50-200nm and nickel-zinc ferrite ceramic powder.

[0034] The ceramic-based impedance modulation unit layer includes a ceramic matrix B and a microwave absorbing agent B dispersed therein. The microwave absorbing agent B is composed of a composite powder of barium titanate and tin oxide with a particle size of 100-500 nm.

[0035] Ceramic matrix A and ceramic matrix B are independently selected from one or more of alumina ceramics, silicon nitride ceramics, and silicon carbide ceramics;

[0036] The metal mesh layer is a periodic two-dimensional metal grid structure, with grid line width, spacing and thickness ranging from micrometers to sub-millimeters. The ceramic-based loss unit layer, ceramic-based impedance control unit layer and metal mesh layer together constitute a multilayer structure with gradient impedance matching. The relative permittivity of each ceramic-based loss unit layer and ceramic-based impedance control unit layer increases or decreases with the layer number to achieve wideband impedance matching.

[0037] like Figure 2 As shown, the metal mesh layer is made of titanium or its alloy and is formed into a two-dimensional grid structure by laser micromachining or photolithography.

[0038] In one embodiment, the metal mesh layer has a grid line width of 10µm to 200µm, a grid spacing of 20µm to 500µm, and a metal mesh layer thickness of 0.1mm to 1mm.

[0039] In one embodiment, in the ceramic-based loss unit layer, the mass ratio of ceramic matrix A to microwave absorber A is 4-6:5-6, and the mass ratio of nano-silicon carbide to nickel-zinc ferrite ceramic powder in microwave absorber A is 1-3:1.

[0040] In the ceramic-based impedance modulation unit layer, the mass ratio of ceramic matrix B to microwave absorber B is 5-7:3-5, and the mass ratio of barium titanate to tin oxide in microwave absorber B is 3-5:1.

[0041] In one embodiment, the thickness of the ceramic-based loss unit layer is 0.3-3 mm, the thickness of the ceramic-based impedance modulation unit layer is 0.2-2 mm, and the total number of layers of the ceramic absorbing metamaterial is 4-12.

[0042] The ceramic absorbing metamaterial of this invention comprises at least three alternating layers: a ceramic-based loss unit layer, a ceramic-based impedance-modulating unit layer, and a metal mesh layer. The rationale for this alternating layered structure is that, through the synergistic effect of the loss unit layer, the impedance-modulating unit layer, and the metal mesh layer, a progressive attenuation of electromagnetic waves—"gradual absorption-impedance matching-secondary reflection absorption"—can be achieved. Specifically, the loss unit layer is responsible for the main electromagnetic wave energy loss, the impedance-modulating unit layer adjusts the interface impedance to reduce reflection, and the metal mesh layer reflects unabsorbed electromagnetic waves back to the first two layers for secondary absorption, significantly improving absorption efficiency.

[0043] The ceramic-based loss unit layer consists of a ceramic matrix A and a microwave absorbing agent A dispersed therein.

[0044] The ceramic matrix is ​​selected from one or more of alumina ceramics, silicon nitride ceramics, and silicon carbide ceramics. It has excellent high temperature resistance (melting point of about 2050℃) and mechanical strength, meeting the structural stability requirements under high temperature environments.

[0045] Absorber A is a composite powder of nano-silicon carbide with a particle size of 50-200 nm and nickel-zinc ferrite ceramic powder. Powder with a particle size of 50-200 nm has a large specific surface area, which can generate a strong interfacial polarization effect. If the particle size is less than 50 nm, the powder is prone to agglomeration, leading to uneven dispersion; if it is greater than 200 nm, the interfacial polarization effect weakens, and the loss performance decreases. The composite design of nano-silicon carbide and nickel-zinc ferrite is based on the principle of "dielectric loss-magnetic loss synergy": silicon carbide is a typical dielectric loss absorber, which can absorb electromagnetic waves through polarization and conductivity loss; nickel-zinc ferrite is a magnetic loss absorber, which consumes electromagnetic wave energy through mechanisms such as hysteresis loss and domain wall resonance. The combination of the two can broaden the absorption frequency band.

[0046] The mass ratio of ceramic matrix A to microwave absorber A is 4-6:5-6. If the proportion of microwave absorber A is too high, it will be difficult for the ceramic matrix to encapsulate the absorber, and porosity and cracks will easily appear after sintering; if the proportion is too low, the loss performance will be insufficient. The mass ratio of nano-silicon carbide to nickel-zinc ferrite in microwave absorber A is 1-3:1. This ratio was determined through experimental optimization: when the proportion of silicon carbide is too high, the contribution of magnetic loss is insufficient, and the absorption performance at low frequencies (1-8GHz) decreases; when the proportion is too low, the dielectric loss is insufficient, and the absorption performance at high frequencies (8-18GHz) weakens.

[0047] The thickness of the ceramic-based loss unit layer is 0.3-3 mm. The thickness design is based on the propagation characteristics of electromagnetic waves in the medium to ensure sufficient propagation path and energy loss, thereby further optimizing broadband performance.

[0048] The ceramic-based impedance control unit layer consists of a ceramic matrix B and a microwave absorbing agent B dispersed therein.

[0049] Absorber B is a composite powder of barium titanate and tin oxide with a particle size of 100-500 nm. As a ferroelectric material, barium titanate provides an adjustable dielectric constant, while tin oxide achieves impedance matching through conductivity adjustment. Together, they construct a "dynamic impedance tuning" mechanism, enabling the material to match the impedance of free space across a wide frequency range and reducing electromagnetic wave reflection.

[0050] The mass ratio of ceramic matrix B to absorber B is 5-7:3-5. The rationale for this ratio is as follows: the impedance control unit layer needs to prioritize structural stability, therefore the matrix proportion is slightly higher than the loss unit layer; the absorber B proportion of 30-50% ensures the adjustable range of the dielectric constant, meeting the requirements of gradient impedance design. The mass ratio of barium titanate to tin oxide in absorber B is 3-5:1. Too high a proportion of barium titanate will result in an excessively high dielectric constant, while too low a proportion will result in an insufficient dielectric constant adjustment range, making wideband matching impossible.

[0051] The thickness of the ceramic-based impedance modulation unit layer is 0.2-2 mm. Impedance modulation mainly acts on the electromagnetic wave incident interface. Excessive thickness will increase the overall weight of the material and have limited effect on absorption gain. A thickness of 0.2-2 mm can match the skin depth of electromagnetic waves of different frequency bands, ensuring that the impedance modulation effect covers 1-18 GHz.

[0052] The metal mesh layer is a periodic two-dimensional metal grid structure, made of titanium or its alloys. The rationale for this choice is that titanium and its alloys possess excellent high-temperature oxidation resistance, balancing conductivity and high-temperature resistance, thus preventing the metal from melting or oxidizing and failing at high temperatures. The grid linewidth ranges from 10µm to 200µm, the grid spacing from 20µm to 500µm, and the metal mesh layer thickness from 0.1mm to 1mm. The parameter design is based on electromagnetic wave diffraction theory. A linewidth of 10-200µm ensures the structural strength and conductivity of the grid; a spacing of 20-500µm matches the wavelength of electromagnetic waves in the target frequency band, generating resonant absorption through the periodic structure to enhance reflection and absorption of specific frequency bands; and a thickness of 0.1mm to 1mm ensures the density of the metal layer. Too thin a layer is prone to pinholes, leading to a decrease in reflectivity, while too thick a layer increases the risk of thermal stress.

[0053] A multilayer structure with gradient impedance matching is formed by ceramic-based loss unit layers, ceramic-based impedance tuning unit layers, and a metal mesh layer. The relative permittivity of each ceramic-based loss unit layer and ceramic-based impedance tuning unit layer increases or decreases with the layer number. When electromagnetic waves are incident from air (dielectric constant ≈ 1) into the material, a sudden change in the permittivity at the interface will result in strong reflection (reflectivity is positively correlated with the difference in permittivity). By designing a gradient change in permittivity (e.g., gradually increasing or decreasing from the surface layer to the inner layer), electromagnetic waves can gradually penetrate the material, reducing reflection. When the permittivity increases in a gradient of 5-10 (from 10-15 at the surface layer to 30-40 at the inner layer), the reflectivity in the 1-18 GHz frequency band can be reduced to below -10 dB, achieving wideband impedance matching.

[0054] like Figure 3 As shown, an embodiment of the present invention provides a method for preparing the ceramic microwave absorbing metamaterial, comprising the following steps:

[0055] A ceramic casting slurry is prepared, and a ceramic-based loss unit layer and a ceramic-based impedance control unit layer green body are formed by casting. A metal mesh layer is prepared by laser micromachining or photolithography. The green body and the metal mesh layer are alternately stacked and hot-pressed to form a multi-layer green body. A segmented temperature-controlled process is used for co-firing to finally obtain a ceramic microwave absorbing metamaterial.

[0056] In one embodiment, the casting slurry comprises ceramic powder and an organic binder, wherein the organic binder is any one or combination of epoxy resin, polyimide or silane coupling agent, and the content is 5-10 wt% of the casting slurry, and vacuum impregnation is performed before sintering to improve density.

[0057] In one embodiment, the hot-pressing composite conditions are: temperature 80-120℃, pressure 10-30MPa, and time 30-60min.

[0058] In one embodiment, the co-firing process includes: heating to 200-400°C and sintering for 1-2 hours to remove organic binders, heating to 800-1000°C for preliminary sintering for 2-3 hours, and then heating to 1200-1400°C for sintering and holding for 2-3 hours for final densification sintering.

[0059] The reasons for choosing tape casting are: it can prepare thin ceramic tapes with uniform thickness, which is suitable for multi-layer stacking; and it can achieve uniform dispersion of the microwave absorber in the ceramic matrix.

[0060] The casting slurry contains ceramic powder and an organic binder, which is any one or a combination of epoxy resin, polyimide, or silane coupling agent, and its content is 5-10 wt% of the casting slurry. When the binder content is less than 5 wt%, the green belt is easily broken, and when it is more than 10 wt%, the residual carbon after sintering will affect the density of the ceramic.

[0061] Vacuum impregnation is performed before sintering to improve density. The principle of vacuum impregnation is to use negative pressure to penetrate low-viscosity resin or ceramic sol into the pores of the green body, filling the voids. After subsequent sintering, the density of the ceramic can be increased from 85% to over 95%, reducing the scattering loss of electromagnetic waves by the pores.

[0062] The co-firing process employs a segmented temperature control technique, specifically including:

[0063] Sinter at 200-400℃ for 1-2 hours to remove organic binders: This temperature range allows the organic binders to gradually decompose into gas and be released.

[0064] Preliminary sintering at 800-1000℃ for 2-3 hours: Preliminary sintering allows the ceramic powder to undergo preliminary sintering, forming a preliminary skeleton structure, while the metal mesh layer is stable at this temperature.

[0065] Sintering at 1200-1400℃ for 2-3 hours for final densification can achieve complete densification of ceramic particles and ensure the stability of the material's mechanical and dielectric properties.

[0066] Segmented temperature control can avoid internal stress caused by the difference in thermal expansion coefficients of different materials (ceramics and metals), ensuring that the multilayer structure retains its integrity after high-temperature sintering.

[0067] The embodiments of the present invention are described in detail below. The ceramic microwave absorbing metamaterials of Embodiments 1 to 4 and Comparative Examples 1 to 2 are shown in Table 1.

[0068] Table 1: Composition of ceramic absorbing metamaterials in Examples 1-4 and Comparative Examples 1-2

[0069] sample Ceramic matrix (A / B) Microwave absorber A (particle size / nm; SiC: nickel-zinc ferrite) Microwave absorber B (particle size / nm; barium titanate: tin oxide) Matrix to absorber mass ratio (A / A; B / B) Layer structure (loss layer thickness / mm; impedance layer thickness / mm; total number of layers) Metal mesh (material; linewidth / μm; spacing / μm; thickness / mm) Example 1 A: Alumina; B: Alumina 200；1:1 100；3:1 4:5；5:5 1；0.2；12 Titanium; 10; 20; 0.1 Example 2 A: Silicon nitride; B: Silicon nitride 125；2:1 300；4:1 5:5.5；6:4 1.5；1；8 Titanium; 100; 260; 0.6 Example 3 A: Silicon carbide; B: Silicon carbide 50；3:1 500；5:1 6:6；7:3 3；2；4 Titanium; 200; 500; 0.8 Example 4 A: Silicon nitride + aluminum oxide; B: Silicon carbide + silicon nitride 80；1.5:1 500；3.5:1 4.5:5.2；5.5:4.5 0.3；0.5；6 Titanium alloy; 50; 100; 1 Comparative Example 1 A: Silicon nitride; B: Silicon nitride <![CDATA[ 40；1:2 ]]> <![CDATA[ 600；2:1 ]]> 5:5.5；6:4 1.5；1；8 Titanium; 100; 260; 0.6 Comparative Example 2 A: Silicon nitride; B: Silicon nitride 125；2:1 300；4:1 <![CDATA[ 5:9；1:5 ]]> <![CDATA[ 5；4； 8]]> <![CDATA[Titanium; 100; 260; 3 >

[0070] The process parameters used in the preparation methods of Examples 1-4 and Comparative Example 3 of this invention are shown in Table 2.

[0071] Table 2: Process parameters used in the preparation methods of Examples 1-4 and Comparative Example 3

[0072] sample Organic binders (type; content / wt%) Hot pressing conditions (temperature / °C; pressure / MPa; time / min) Co-firing process (Stage 1: Temperature / ℃ - Time / h; Stage 2: Temperature / ℃ - Time / h; Stage 3: Temperature / ℃ - Time / h) Example 1 Epoxy resin; 5 80；10；60 300-1；910-2；1320-2 Example 2 Polyimide + silane coupling agent; 7.5 120；20；45 200-1.5；800-2.5；1200-2.5 Example 3 Silane coupling agent; 10 110；30；30 400-2；1000-3；1400-3 Example 4 Epoxy resin + polyimide; 6 90；15；40 250-1.2；850-2.2；1250-2.2 Comparative Example 3 Polyimide + silane coupling agent; 4 100；20；45 300-1.5；-；1200-2.5

[0073] Comparative Examples 1 and 2 are identical to Example 2 in terms of preparation method parameters, except for the product composition and structure. See Table 1 for details.

[0074] The difference between Comparative Example 3 and Example 2 is that the co-firing process in the preparation method omits the preliminary sintering, as detailed in Table 2.

[0075] The radar-absorbing composite materials of the above-mentioned comparative and exemplary embodiments were cut into 400mm*400mm plates for reflectivity testing. The reflectivity data of the radar-absorbing materials were measured using the arc method in a microwave anechoic chamber. The measured results are shown in Table 3.

[0076] Table 3: Performance data of examples and comparative examples

[0077] sample 1-8GHz Reflection Loss / dB 8-18GHz Reflection Loss / dB Example 1 -12.3 -28.5 Example 2 -15.6 -32.1 Example 3 -11.8 -27.3 Example 4 -14.2 -30.8 Example 5 -13.5 -29.7 Comparative Example 1 -8.2 -20.3 Comparative Example 2 -7.9 -19.8 Comparative Example 3 -9.1 -21.5

[0078] As can be seen from Table 3, the ceramic absorbing metamaterial prepared by the present invention achieves a reflection loss of ≤-10dB in the 1-8GHz band and a reflection loss of ≤-25dB in the 8-18GHz band, covering the main frequency bands of conventional radar and communication.

[0079] Comparative Examples 1 and 2, after adjusting the composition of the absorbing agent in the ceramic absorbing metamaterial, the thickness of each unit layer, and the parameters of the metal mesh, found it difficult to achieve effective impedance matching, which reduced the reflection absorption effect. The reflection loss in the 1-8 GHz band and the 8-18 GHz band was significantly reduced.

[0080] In Comparative Example 3, the co-firing process omitted the initial sintering, which may lead to internal stress caused by the difference in thermal expansion coefficients between ceramic and metal. This could not ensure that the multilayer structure would maintain its integrity after high-temperature sintering, thus reducing the reflection absorption effect. The reflection loss in the 1-8GHz band and the 8-18GHz band was significantly reduced.

[0081] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

Claims

1. A ceramic microwave absorbing metamaterial, characterized in that, It consists of at least three alternating layers of ceramic-based loss unit layer, ceramic-based impedance control unit layer, and metal mesh layer; The ceramic-based loss unit layer includes a ceramic matrix A and a microwave absorbing agent A dispersed therein. The microwave absorbing agent A is a composite powder composed of nano-silicon carbide with a particle size of 50-200nm and nickel-zinc ferrite ceramic powder. The ceramic-based impedance control unit layer includes a ceramic matrix B and a microwave absorbing agent B dispersed therein. The microwave absorbing agent B is composed of a composite powder of barium titanate and tin oxide with a particle size of 100-500 nm. The ceramic matrix A and ceramic matrix B are independently selected from one or more of alumina ceramics, silicon nitride ceramics, and silicon carbide ceramics; The metal mesh layer is a periodic two-dimensional metal grid structure; the ceramic-based loss unit layer, the ceramic-based impedance control unit layer and the metal mesh layer together constitute a multilayer structure with gradient impedance matching, wherein the relative permittivity of each ceramic-based loss unit layer and the ceramic-based impedance control unit layer increases or decreases with the layer number to achieve wideband impedance matching. The metal mesh layer has a grid line width of 10µm to 200µm, a grid spacing of 20µm to 500µm, and a metal mesh layer thickness of 0.1mm to 1mm; In the ceramic-based loss unit layer, the mass ratio of ceramic matrix A to microwave absorber A is 4-6:5-6, and the mass ratio of nano-silicon carbide to nickel-zinc ferrite ceramic powder in microwave absorber A is 1-3:

1. In the ceramic-based impedance control unit layer, the mass ratio of ceramic matrix B to microwave absorber B is 5-7:3-5, and the mass ratio of barium titanate to tin oxide in microwave absorber B is 3-5:

1. The thickness of the ceramic-based loss unit layer is 0.3-3 mm, and the thickness of the ceramic-based impedance regulation unit layer is 0.2-2 mm; The preparation method of the ceramic microwave absorbing metamaterial includes the following steps: A ceramic casting slurry is prepared, and a ceramic-based loss unit layer and a ceramic-based impedance control unit layer green body are formed by casting. A metal mesh layer is prepared by laser micromachining or photolithography. The green body and the metal mesh layer are alternately stacked and hot-pressed to form a multi-layer green body. A segmented temperature-controlled co-firing process is used to finally obtain a ceramic microwave absorbing metamaterial. The co-firing process includes: heating to 200-400℃ and sintering for 1-2 hours to remove organic binders, heating to 800-1000℃ for preliminary sintering for 2-3 hours, and then heating to 1200-1400℃ for sintering and holding for 2-3 hours for final densification sintering.

2. The ceramic absorbing metamaterial according to claim 1, characterized in that, The metal mesh layer is made of titanium or its alloy and is formed into a two-dimensional grid structure by laser micromachining or photolithography; the total number of layers of the ceramic absorbing metamaterial is 4-12.

3. The ceramic absorbing metamaterial according to claim 1, characterized in that, The ceramic absorbing metamaterial has a reflection loss of ≤-10dB in the 1-8GHz frequency band, and a reflection loss of ≤-25dB in the 8-18GHz frequency band.

4. A method for preparing a ceramic microwave absorbing metamaterial according to any one of claims 1-3, characterized in that, Includes the following steps: A ceramic casting slurry is prepared, and a ceramic-based loss unit layer and a ceramic-based impedance control unit layer green body are formed by casting. A metal mesh layer is prepared by laser micromachining or photolithography. The green body and the metal mesh layer are alternately stacked and hot-pressed to form a multi-layer green body. A segmented temperature-controlled co-firing process is used to finally obtain a ceramic microwave absorbing metamaterial.

5. The method for preparing the ceramic absorbing metamaterial according to claim 4, characterized in that, The casting slurry comprises ceramic powder and an organic binder, wherein the organic binder is any one or a combination of epoxy resin, polyimide or silane coupling agent, and its content is 5-10 wt% of the casting slurry. It is vacuum impregnated before sintering to improve density.

6. The method for preparing the ceramic absorbing metamaterial according to claim 4, characterized in that, The conditions for hot-pressing composite are: temperature 80-120℃, pressure 10-30MPa, and time 30-60min.

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