Infrared / microwave compatible stealth metamaterial composite fabric and method of making same

Abstract

This invention discloses a metamaterial composite fabric with infrared / microwave compatible stealth, which is composed of a metamaterial resonant unit layer, an interface control layer, a fabric dielectric layer, and a highly conductive fabric reflective layer stacked sequentially. This invention also discloses a method for preparing the metamaterial composite fabric with infrared / microwave compatible stealth, comprising the following steps: Step 1, preparing the interface control layer; Step 2, constructing the metamaterial resonant unit layer; Step 3, performing pretreatment on the fabric dielectric layer by cutting the fabric dielectric layer to the required size, treating it in a constant temperature water bath, and then drying it in an oven; Step 4, bonding the fabric together using a hot-pressing process to obtain the finished metamaterial composite fabric. This invention belongs to the field of functional textile materials technology and solves the problem that existing metamaterial structures cannot meet the requirements for infrared / radar compatible stealth.

Description

Technical Field

[0001] This invention belongs to the field of functional textile materials technology, and relates to metamaterial composite fabrics with infrared / microwave compatible stealth. This invention also relates to a method for preparing the finished metamaterial composite fabric with infrared / microwave compatible stealth. Background Technology

[0002] With the development of multimodal reconnaissance technologies such as infrared thermal imaging and microwave radar detection, single-band stealth materials are no longer sufficient to meet the target protection requirements in complex battlefield environments. Infrared / microwave compatible stealth materials typically need to possess both low infrared emissivity and high microwave absorption performance to reduce the target's thermal radiation characteristics and radar echo, respectively. However, low infrared emissivity usually requires the material surface to have strong reflectivity to infrared radiation, while efficient microwave absorption requires reducing surface reflection and promoting electromagnetic wave dissipation within the material. These two aspects present certain contradictions in structural design and electromagnetic parameter control, thus achieving infrared / microwave compatible stealth remains a significant challenge. Constructing infrared / microwave compatible stealth materials using fabric as a substrate can endow the material with good flexibility, cutability, and surface fit, making it valuable for applications in military equipment skinning, camouflage materials, protective tents, and wearable protection. Compared to traditional rigid substrate materials, fabric substrates help overcome limitations such as poor flexibility and insufficient adaptability to complex curved surfaces. Compared with lightweight porous materials such as aerogel and foam, fabric substrates have advantages in mechanical durability, sewing processability and practical service adaptability.

[0003] Currently, infrared / microwave compatible stealth fabrics mainly achieve synergistic suppression of infrared and radar bands through material composite modification, multi-layer structure design, and metamaterial structure control. However, existing technologies still generally suffer from problems such as large material thickness, increased areal density due to the introduction of magnetic components, limited microwave absorption bandwidth, insufficient multi-spectral synergistic control effect, and low functional integration. While the Chinese patent "A Method for Preparing a Fabric with Both Infrared and Radar Stealth Properties" (Publication No. CN120350556A, Publication Date 20250722) can achieve a certain degree of infrared and radar microwave stealth effect, it still cannot simultaneously meet the comprehensive requirements of lightweight, broadband microwave absorption, flexible adaptability, and multiple functional protection, limiting its further application in complex service scenarios such as military equipment skins, camouflage materials, and protective tents. To address the aforementioned issues, existing technologies disclose an MXene-based composite metamaterial microwave absorber, as described in the literature "Design and Performance of MXene-Based Composite Metamaterial Microwave Absorbers Inspired by Antheraea pernyi Microstructures, 2026.2.14, Laser&PhotonicsReviews". This literature discloses a method for constructing a metamaterial microwave absorbing structure by screen printing MXene ink onto a cotton fabric substrate, achieving good microwave absorption performance in the X-band and verifying the feasibility of constructing a metamaterial microwave absorbing structure on a fabric substrate surface. However, this technical solution still mainly focuses on the control of single microwave absorption performance and has not yet achieved a synergistic match between low infrared emission and microwave absorption performance, making it difficult to meet the requirements of infrared / radar compatible stealth applications. Furthermore, during the printing process of MXene ink on cotton fabric surfaces, it is susceptible to the effects of fiber capillary action and the porous structure of the fabric, resulting in wicking and lateral diffusion along the fibers and between fiber pores. This leads to reduced ink utilization, blurred pattern boundaries, and decreased structural accuracy, thereby affecting the stability of the metamaterial's microwave absorption performance.

[0004] Therefore, there is an urgent need to develop an infrared / microwave compatible stealth composite fabric based on a combination of interface control and metamaterial structure control, so as to achieve a synergistic improvement in infrared stealth and microwave absorption performance while maintaining the fabric's lightweight flexibility, thinness and adaptability to complex curved surfaces, and further meet the comprehensive needs for multi-functional protection and safety adaptability in complex service environments. Summary of the Invention

[0005] The purpose of this invention is to provide a metamaterial composite fabric with infrared / microwave compatible stealth, which solves the problem that existing metamaterial structures are insufficient in terms of coordinated control of low infrared emission and microwave absorption, making it difficult to simultaneously meet the requirements of infrared / radar compatible stealth, lightweight and thin design, and multiple functional protection in complex service environments.

[0006] Another objective of this invention is to provide a method for preparing a metamaterial composite fabric with infrared / microwave compatible stealth properties. This method solves the problem that existing MXene water-based inks are easily affected by capillary action when printed on cotton fabrics, resulting in wicking and lateral diffusion along fibers and interfiber channels, leading to ink waste, blurred pattern boundaries, and reduced structural precision, which in turn affects the stability of the metamaterial's microwave absorption performance.

[0007] The technical solution adopted in this invention is a metamaterial composite fabric with infrared / microwave compatible stealth, which is composed of a metamaterial resonant unit layer, an interface control layer, a fabric dielectric layer and a highly conductive fabric reflective layer stacked in sequence.

[0008] Another technical solution adopted in this invention is a method for preparing a metamaterial composite fabric with infrared / microwave compatible stealth, which is implemented according to the following steps: Step 1: Prepare an interface control layer by introducing polyvinyl alcohol containing a large number of polar hydroxyl groups onto the surface of the polytetrafluoroethylene nanofiber membrane for surface modification. Step 2: Construct a metamaterial resonant unit layer. Based on the resonant pattern designed according to the target microwave absorption frequency band, transfer the pattern to the interface modulation layer by screen printing. Step 3: Perform pretreatment of the fabric medium layer. Cut the fabric medium layer to the required size, place it in a constant temperature water bath for treatment, and then place it in an oven to dry. Step 4: The composite material is formed into a single unit through a hot-pressing process to obtain the finished metamaterial composite fabric.

[0009] The beneficial effects of the present invention include the following aspects: 1) This invention uses fabric as a flexible substrate. By introducing surface intercalation and interface modulation, a stable interface modulation layer is constructed on the fabric surface. Combined with metamaterial structural design, an infrared / microwave compatible stealth composite fabric is prepared. This composite fabric can simultaneously achieve low infrared emissivity and high microwave absorption performance within the same flexible structural system. It can reduce the infrared thermal radiation characteristics of the target and weaken radar microwave reflection echoes, thereby effectively reconciling the mechanistic contradiction between infrared stealth and radar stealth.

[0010] 2) This invention uses fabric as the medium substrate, which overcomes the problems of traditional rigid stealth materials such as heavy weight, poor flexibility and insufficient fit to complex curved surfaces. The resulting composite fabric has the characteristics of being lightweight, soft, flexible and highly adaptable to deformation, and can meet the application needs of military equipment skin, camouflage and covering materials, protective tents and wearable protection.

[0011] 3) This invention effectively suppresses the wicking diffusion and lateral penetration of conductive ink in the fabric fibers by introducing an interface control layer between the fabric substrate and the metamaterial resonant structure, thereby improving the boundary clarity and processing accuracy of the resonant pattern. Simultaneously, this interface control layer has good universality across different fabric surfaces, eliminating the need to re-formulate the ink system for each fabric and reducing process complexity.

[0012] 4) This invention utilizes a metamaterial resonant structure to effectively control incident microwaves, achieving excellent microwave absorption even with a relatively thin structure. This reduces reliance on high-density magnetic components and heavy multilayer structures, facilitating the lightweighting and flexibility of stealth materials. Therefore, the composite fabric obtained by this invention has promising applications in flexible skins for military equipment, camouflage coverings, protective tents, and wearable stealth protection. Attached Figure Description

[0013] Figure 1 This is a side view of the main structure of the metamaterial composite fabric of the present invention; Figure 2 This is a cross-sectional view of the main structure of the metamaterial composite fabric of the present invention; Figure 3 This is the metamaterial resonant unit pattern of the present invention; Figure 4 This is the structure of the screen printing plate used in the method of the present invention; Figure 5 The surface state and three-dimensional image of the metamaterial resonant unit layer pattern after printing by the method of the present invention; Figure 6 These are the microwave reflection loss test results for the metamaterial composite structure of this invention; Figure 7 The infrared emissivity test results of the metamaterial composite structure of this invention are shown below. Figure 8 This refers to the peel strength between the layers in the metamaterial composite structure of this invention.

[0014] In the figure, 1. Metamaterial resonant unit layer; 2. Interface control layer; 3. Fabric dielectric layer; 4. Highly conductive fabric reflective layer; 5. Screen printing plate; 6. Squeegee; 7. Ink; 8. Pad; 9. Substrate. Detailed Implementation

[0015] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0016] Reference Figure 1 and Figure 2 The metamaterial composite fabric with infrared / microwave compatible stealth of the present invention has the following main structure: it is composed of a metamaterial resonant unit layer 1, an interface control layer 2, a fabric dielectric layer 3 and a highly conductive fabric reflective layer 4 stacked in sequence.

[0017] The metamaterial resonant unit layer 1 is printed onto the surface of the interface control layer 2 using conductive silver paste through screen printing. The metamaterial resonant unit layer 1 can employ various pattern designs, including but not limited to solid rectangles, solid circles, solid triangles, solid hexagons, or combinations of any of these solid shapes with a line shape. Within the same unit, one or more patterns must be arranged according to a preset rule, such as side-by-side, staggered, or surrounding each other, to form a centrally symmetrical pattern with a rotation order of at least 2, thus constituting the metamaterial resonant unit layer 1. By adjusting the pattern type, unit period size, linewidth, gap, and arrangement in the metamaterial resonant unit layer 1, the resonant response, impedance matching, and electromagnetic absorption frequency band width of the metamaterial composite fabric to incident waves can be controlled. The unit period size of the metamaterial resonant unit layer 1 is no greater than half the free-space wavelength corresponding to its target operating frequency. The selected conductive silver paste has a viscosity of 10000~12000 mPa·s and a surface sheet resistance of no more than 400 Ω / sq; the mesh count of the screen printing process screen ranges from 150 to 300 mesh.

[0018] The interface control layer 2 is obtained by using polytetrafluoroethylene nanofiber membrane as a surface intercalation layer and improving its solid-liquid interface energy through surface modification treatment. Since the polytetrafluoroethylene nanofiber membrane has inherently low surface energy and poor wettability, it is difficult to form a clear resonant unit pattern on the surface. Therefore, it is further subjected to polyvinyl alcohol surface modification treatment to improve its solid-liquid interface energy and enhance the interlayer bonding force.

[0019] The type of fabric dielectric layer 3 is woven or knitted fabric with a dielectric constant ranging from 2.5 to 4.5. The fabric dielectric layer 3 has flame retardant properties and is made of silica fabric, polyimide fabric, aramid fabric or other fabrics that meet the requirements for dielectric and flame retardant properties.

[0020] The highly conductive fabric reflective layer 4 is selected from one of the following: conductive silver fiber fabric, conductive copper fiber fabric, conductive nickel fiber fabric, silver-plated nylon fabric, or copper-nickel-plated polyester fabric, with a surface conductivity greater than or equal to 1.0 × 10⁻⁶. 3 S / m.

[0021] The present invention provides a method for preparing a finished metamaterial composite fabric with infrared / microwave compatible stealth properties, which is carried out according to the following steps: Step 1: Prepare interface control layer 2. The surface of the polytetrafluoroethylene nanofiber membrane is modified by introducing polyvinyl alcohol containing a large number of polar hydroxyl groups. The specific process is as follows: 1.1) Polyvinyl alcohol (PVA) and solvent were stirred in a constant temperature water bath to prepare a polyvinyl alcohol modified solution; wherein the mass ratio of polyvinyl alcohol to solvent was (1:50) to (1:10); the degree of alcoholysis of polyvinyl alcohol was 98.0% to 99.9%, and the viscosity measured in 4% aqueous solution at 20℃ was 22 to 35 mPa·s; the solvent was deionized water; the stirring speed was 600 to 1500 r / min, the stirring time was 4 to 12 h, and the dissolution temperature was 80℃ to 95℃ until the polyvinyl alcohol was completely dissolved to obtain the polyvinyl alcohol modified solution; 1.2) Take a polytetrafluoroethylene nanofiber membrane (PTFE nanofiber membrane) and hot-press it with the receiving medium to obtain a surface intercalation layer; The polytetrafluoroethylene nanofiber membrane has a pore size of 0.1~7μm and a thickness of 15~80μm; the bonding medium is one of TPU hot melt adhesive, PES hot melt adhesive film, and EVA hot melt adhesive; the hot-pressing conditions are: hot-pressing temperature of 100℃~150℃; hot-pressing pressure of 0.1~0.3MPa; and hot-pressing time of 5~20 seconds. 1.3) The polyvinyl alcohol modified solution is transferred to the surface intercalation layer by spraying or scraping to obtain the interface control layer 2; When using the spraying method, the mass ratio of polyvinyl alcohol to solvent is (1:50) to (1:20); When using a scraping method, the mass ratio of polyvinyl alcohol to solvent is (1:50) to (1:10); The spraying conditions are: spraying air pressure 0.1~0.4mPa, spraying distance 20~30cm; The conditions for blade coating are: blade gap 10~150μm, blade speed 10~30mm / s.

[0022] Step 2: Construct metamaterial resonant unit layer 1, The resonant unit pattern designed according to the target microwave absorption frequency band is transferred to the interface modulation layer 2 by screen printing. The specific process is as follows: 2.1) Design as follows Figure 3 The resonant unit pattern shown is used to create a screen printing plate based on the preset resonant unit pattern; the mesh count of the screen printing plate ranges from 150 to 300 mesh.

[0023] 2.2) Conductive silver paste is selected as ink, and the resonant pattern is transferred to the polyvinyl alcohol-modified side of the interface control layer 2 by screen printing; wherein, the viscosity of the conductive silver paste is 10000~12000mPa·S, and the surface sheet resistance is less than or equal to 400Ω / sq; the screen printing process parameters are: squeegee hardness 60~80 Shore A, squeegee pressure 0.1~0.3mPa, printing speed 50~150mm / s, screen and substrate distance 2.5~5mm, and squeegee angle 50°~80°.

[0024] 2.3) Place the printed interface control layer 2 at room temperature for no less than 30 minutes to allow it to dry and cure fully.

[0025] Step 3: Perform pretreatment of fabric medium layer 3. The specific process is as follows: the fabric medium layer is cut to the required size, placed in a constant temperature water bath for treatment, and then dried in an oven. The dielectric layer is made of woven or knitted fabric with a dielectric constant ranging from 2.5 to 4.5. The dielectric layer has flame-retardant properties and is made of silica fabric, polyimide fabric, aramid fabric, or other fabrics that meet the requirements for dielectric and flame-retardant properties. The constant temperature water bath has a processing temperature of 60~80℃ and a processing time of 2~4h; The oven conditions are: temperature 50~80℃, processing time not less than 2 hours, until completely dry.

[0026] Step 4: Prepare the finished metamaterial composite fabric. The specific process is as follows: the interface control layer 2 with metamaterial resonant unit layer 1 obtained in step 2, the fabric dielectric layer 3 after pretreatment in step 3 and the highly conductive fabric reflective layer 4 are stacked in sequence and combined into one by hot pressing molding process to prepare metamaterial composite fabric. The stacking order from bottom to top is: interface control layer 2 with metamaterial resonant unit layer 1, fabric dielectric layer 3, highly conductive fabric reflective layer 4, with one side of the printed pattern of metamaterial resonant unit layer 1 facing away from fabric dielectric layer 3.

[0027] The hot pressing process conditions are: hot pressing temperature 120℃~180℃, hot pressing pressure 0.3~1mPa, and hot pressing time 5~60 seconds.

[0028] The highly conductive fabric reflective layer 4 is selected from one of the following: conductive silver fiber fabric, conductive copper fiber fabric, conductive nickel fiber fabric, silver-plated nylon fabric, or copper-nickel-plated polyester fabric, with a surface conductivity greater than or equal to 1.0 × 10⁻⁶. 3 S / m.

[0029] The preparation principle of the metamaterial composite fabric of this invention is as follows: This invention achieves high-precision printing of conductive silver paste ink onto a fabric substrate by constructing a metamaterial composite fabric structure based on an interface control layer 2. Specifically, polyvinyl alcohol (PVA) is used as the interface layer modifier. The film-forming properties and hydrophilic properties of PVA improve the interfacial wettability of the PTFE nanofiber membrane surface. Simultaneously, after film formation, PVA fills the pores and capillary channels between fibers, thereby forming a dense and smooth interface control layer 2 on the PTFE substrate surface. This interface control layer 2 effectively inhibits the wicking diffusion and lateral penetration of conductive silver paste in the fibers and interfiber channels during subsequent screen printing, solving the precision problems of blurred pattern boundaries and uncontrolled linewidth caused by ink bleeding in traditional fabric printing. Furthermore, this interface control layer 2 has good universality for fabric substrates of different materials, weave densities, and surface energies, eliminating the need to re-formulate the ink system for each fabric and significantly reducing process complexity.

[0030] Furthermore, this invention utilizes a hot-pressing composite process to construct a metamaterial composite fabric structure capable of achieving infrared and microwave compatible stealth performance, while simultaneously possessing excellent flame-retardant properties. For radar stealth, the standing wave condition and electro- or magnetic resonance effect between the highly conductive fabric reflective layer 4 and the metamaterial resonant unit layer 1 dissipate electromagnetic wave energy. For infrared stealth, low-emissivity conductive silver paste ink is used to construct the metamaterial resonant unit layer 1, and the infrared emissivity is reduced to below 0.5 by adjusting the pattern area ratio. For flame retardancy, the intrinsic high-temperature resistance of the fabric dielectric layer 3 is utilized to form a physical barrier during combustion, inhibiting oxygen transport and heat diffusion, and blocking flame propagation. Thus, this invention simultaneously achieves the integration of microwave absorption, infrared radiation suppression, and flame-retardant properties.

[0031] Example 1 The preparation method of this Example 1 is implemented according to the following steps: Step 1) Preparation of interface control layer 2: 1.1) Take PVA with a degree of hydrolysis of 98.5% and slowly add it to deionized water, pre-stirring with a glass rod to initially disperse it. Then place the mixture in a constant temperature water bath at 90℃ and stir at a stirring speed of 1000 r / min for 5 h until the PVA is completely dissolved to obtain a PVA modified solution. The mass ratio of PVA to deionized water is 1:49.

[0032] 1.2) A PTFE nanofiber membrane was used as the substrate for surface intercalation. The PTFE nanofiber membrane had a pore size of 0.45 μm and a thickness of 50 μm. The PTFE nanofiber membrane was hot-pressed with the TPU hot melt adhesive as the substrate at a temperature of 130℃, a hot-pressing pressure of 0.2 mPa, and a hot-pressing time of 7 s to obtain the surface intercalation.

[0033] 1.3) The above-mentioned PVA modified solution was transferred to the surface intercalation layer by a blade coating process. The blade coating parameters were: blade gap 10 μm, blade coating speed 15 mm / s. After drying, interface control layer 2 was obtained. Based on contact angle testing, the interfacial energy between the solid substrate and the liquid in this interface control layer 2 was calculated to be 22.5 mN·m⁻² before treatment. - ¹ Reduced to 8.9 mN·m after treatment - ¹.

[0034] Step 2) Constructing the metamaterial resonant unit layer 1: 2.1) Design using full-wave electromagnetic simulation software CST, such as Figure 3 The resonant unit pattern shown has a periodic unit size p of 12mm, a side length a of 5mm for the solid rectangle, a gap b between the rectangle and the line of 0.3mm, and a line width c of 0.2mm.

[0035] 2.2) A 200-mesh screen printing plate was selected, and conductive silver paste ink was used as the printing material to transfer the resonant unit pattern to the surface of the interface control layer 2.

[0036] Before screen printing, the screen printing plate needs to be treated. Specifically, a 3mm thick pad 8 is glued to each side of the screen frame to adjust the distance between the screen printing plate 5 and the substrate 9. The treated screen printing plate 5 is shown below. Figure 4 As shown. During the printing process of ink 7, a squeegee 6 with a hardness of 60 Shore A is used, the squeegee pressure is set to 0.2 mPa, the printing speed is 80 mm / s, and the squeegee angle is 60°.

[0037] 2.3) After printing, the interface control layer is placed in a natural environment for 2 hours to allow it to fully dry and cure. The pattern of the metamaterial resonant unit layer 1 obtained after printing is as follows: Figure 5 As shown.

[0038] Step 3) Perform pretreatment of fabric medium layer 3: Using silica woven fabric as the medium layer, cut it into 20cm×20cm pieces and place it in a constant temperature water bath at 70℃ for 3 hours. After treatment, remove it and place it in an oven to dry at 60℃ for 3 hours.

[0039] Step 4) Prepare the finished metamaterial composite fabric: The interface control layer 2 with metamaterial resonant unit layer 1 obtained in step 2, the fabric dielectric layer 3 (using silica woven fabric) pretreated in step 3, and the highly conductive fabric reflective layer 4 (using copper-nickel plated polyester fabric) are stacked sequentially from bottom to top; wherein the pattern side of the metamaterial resonant unit layer 1 faces away from the silica woven fabric; the conductivity of the copper-nickel plated polyester fabric is 1.55 × 10⁻⁶. 4 The hot-pressing temperature during the process was 140℃, the hot-pressing pressure was 0.6 MPa, and the hot-pressing time was 25 s. The final metamaterial composite fabric had a thickness of approximately 0.8 mm, was freely bendable, and had an areal density of 770 g / m². 2 .

[0040] Performance testing: 1) The prepared metamaterial composite fabric was tested using an arch-shaped method with a high-precision reflectivity testing module, such as... Figure 6 As shown, the reflection loss achieves effective microwave absorption in the 12.1~18GHz frequency band, with a minimum reflection loss of -25.9dB.

[0041] 2) The average infrared emissivity of the metamaterial composite fabric in the 3–5 μm and 8–14 μm regions was measured to be 0.34 using a Fourier transform infrared spectrometer (FTIR) equipped with an integrating sphere attachment (IntegratIR™, PIKE Technologies, USA). Figure 7 As shown. Its limiting oxygen index is greater than 90% according to GB / T 5454 standard, exhibiting significant non-flammable characteristics.

[0042] 3) Peel strength tests were conducted using a universal testing machine. The peel strength between all functional layers exceeded 16 N / 5 cm. (See attached image) Figure 8 This indicates that the hot-pressing composite process ensures good interlayer bonding strength.

[0043] Example 2 The difference between Example 2 and Example 1 lies in the PVA concentration. Specifically, in Example 2, the mass ratio of PVA to solvent is 1:19. All other steps and parameter settings are the same as in Example 1. Based on contact angle testing, the interfacial energy between the solid substrate and the liquid in the interface control layer 2 is 22.5 mN·m⁻² for the untreated layer. - ¹ Reduced to 5 mN·m after treatment - ¹.

[0044] Tests showed that the metamaterial composite fabric prepared in Example 2 had a minimum reflection loss of -23.5dB in the 12.2~18GHz frequency band, an infrared emissivity of 0.36, and a limiting oxygen index greater than 90%, which was generally comparable to the performance of the finished product prepared in Example 1.

[0045] Example 3 The difference between Example 3 and Example 1 is that the interface control layer 2 is coated by spraying. Specifically, in Example 3, spraying is used, with the following conditions: spraying air pressure 0.2 mPa, spraying distance 23 cm, and other steps and parameters are the same as in Example 1.

[0046] Tests showed that the metamaterial composite fabric prepared in Example 3 had a minimum reflection loss of -27dB in the 11.8~18GHz frequency band, an infrared emissivity of 0.35, and a limiting oxygen index greater than 90%, which is comparable to the performance of the finished product prepared in Example 1.

[0047] Example 4 The difference between Example 4 and Example 1 lies in changing the temperature, time, and pressure of the hot-pressing composite. Specifically, the hot-pressing conditions used in Example 4 are: hot-pressing temperature 160℃, hot-pressing time 10s, and hot-pressing pressure 0.8mPa. All other steps and parameters are the same as in Example 1.

[0048] Tests showed that the metamaterial composite fabric prepared in Example 4 had a minimum reflection loss of -25.5dB in the 12.2~18GHz frequency band, an infrared emissivity of 0.34, and a limiting oxygen index greater than 90%, all of which did not change significantly. The peel strength between each functional layer exceeded 19N / 5cm.

[0049] Example 5 The difference between Example 5 and Example 1 is that the fabric medium layer 3 is made of aramid woven fabric. All other steps and parameters are the same as in Example 1.

[0050] Testing showed that the metamaterial composite fabric prepared in Example 5 exhibited a minimum reflection loss of -15 dB in the 13.7–18 GHz frequency band, an infrared emissivity of 0.35, a limiting oxygen index of 32%, and a peel strength exceeding 24 N / 5 cm between all functional layers. Compared to Example 1, the radar absorption performance decreased after using aramid woven fabric because the lower dielectric constant of aramid fibers weakens the electromagnetic coupling strength between the resonant unit and the dielectric layer. The flame retardant performance decreased after using aramid woven fabric, but still met conventional flame retardant requirements. The infrared emissivity remained almost unchanged because the pattern area ratio of the low-emissivity ink did not change, thus the overall infrared radiation characteristics of the surface were not significantly affected. The peel strength slightly improved because the surface roughness of aramid fabric is higher than that of silica fabric, which facilitates a stronger mechanical interlocking effect of the hot melt adhesive during hot pressing, thereby enhancing the interlayer bonding strength. Example 5 demonstrates that aramid woven fabric can be used as an alternative to silica fabric.

[0051] Example 6 The difference between Example 6 and Example 1 is that the size of the resonant unit layer pattern is changed. The size of the resonant unit layer is adjusted as follows: the side length a of the solid rectangle is 4mm, the gap b between the rectangle and the line is 0.4mm, and the width c of the line is 0.1mm. All other steps and parameters are the same as in Example 1.

[0052] Tests showed that the metamaterial composite fabric prepared in Example 6 had a minimum reflection loss of -30dB in the 9.7~12.8GHz frequency band, an infrared emissivity of 0.4, and a limiting oxygen index greater than 90%.

Claims

1. A metamaterial composite fabric with infrared / microwave compatible stealth, characterized in that, It is composed of a metamaterial resonant unit layer, an interface modulation layer, a fabric dielectric layer, and a highly conductive fabric reflective layer stacked sequentially.

2. The metamaterial composite fabric with infrared / microwave compatible stealth as described in claim 1, characterized in that, The metamaterial resonant unit layer is printed onto the surface of the interface control layer by conductive silver paste using a screen printing process. The metamaterial resonant unit layer adopts a variety of pattern types. Within the same unit, one or more patterns are arranged according to a preset rule to form a centrally symmetrical pattern with a rotation order of at least 2.

3. The metamaterial composite fabric with infrared / microwave compatible stealth as described in claim 1, characterized in that, The interface control layer is obtained by using a polytetrafluoroethylene nanofiber membrane as a surface intercalation layer and improving its solid-liquid interface energy through surface modification treatment.

4. The metamaterial composite fabric with infrared / microwave compatible stealth as described in claim 1, characterized in that, The type of the fabric dielectric layer is woven or knitted fabric, and its dielectric constant ranges from 2.5 to 4.

5.

5. The metamaterial composite fabric with infrared / microwave compatible stealth as described in claim 1, characterized in that, The highly conductive fabric reflective layer is selected from one of the following: conductive silver fiber fabric, conductive copper fiber fabric, conductive nickel fiber fabric, silver-plated nylon fabric, or copper-nickel-plated polyester fabric, with a surface conductivity greater than or equal to 1.0 × 10⁻⁶. 3 S / m.

6. A method for preparing a metamaterial composite fabric with infrared / microwave compatible stealth, characterized in that, Follow these steps: Step 1: Prepare an interface control layer by introducing polyvinyl alcohol containing a large number of polar hydroxyl groups onto the surface of the polytetrafluoroethylene nanofiber membrane for surface modification. Step 2: Construct a metamaterial resonant unit layer. Based on the resonant pattern designed according to the target microwave absorption frequency band, transfer the pattern to the interface modulation layer by screen printing. Step 3: Perform pretreatment of the fabric medium layer. Cut the fabric medium layer to the required size, place it in a constant temperature water bath for treatment, and then place it in an oven to dry. Step 4: The composite material is formed into a single unit through a hot-pressing process to obtain the finished metamaterial composite fabric.

7. The method for preparing the metamaterial composite fabric with infrared / microwave compatible stealth as described in claim 6, characterized in that, In step 1, the specific process is as follows: 1.1) Polyvinyl alcohol (PVA) and solvent were stirred in a constant temperature water bath to prepare a polyvinyl alcohol modified solution; wherein the mass ratio of polyvinyl alcohol to solvent was (1:50) to (1:10); the degree of alcoholysis of polyvinyl alcohol was 98.0% to 99.9%, and the viscosity measured in 4% aqueous solution at 20℃ was 22 to 35 mPa·s; the solvent was deionized water; the stirring speed was 600 to 1500 r / min, the stirring time was 4 to 12 h, and the dissolution temperature was 80℃ to 95℃ until the polyvinyl alcohol was completely dissolved to obtain the polyvinyl alcohol modified solution; 1.2) Take a polytetrafluoroethylene nanofiber membrane and hot-press it with a receiving medium to obtain a surface intercalation layer; The polytetrafluoroethylene nanofiber membrane has a pore size of 0.1~7μm and a thickness of 15~80μm; the bonding medium is one of TPU hot melt adhesive, PES hot melt adhesive film, and EVA hot melt adhesive; the hot-pressing conditions are: hot-pressing temperature of 100~150℃; hot-pressing pressure of 0.1~0.3MPa; and hot-pressing time of 5~20 seconds. 1.3) The polyvinyl alcohol modified solution is transferred to the surface intercalation layer by spraying or scraping to obtain the interface control layer. When using the spraying method, the mass ratio of polyvinyl alcohol to solvent is (1:50) to (1:20); When using a scraping method, the mass ratio of polyvinyl alcohol to solvent is (1:50) to (1:10); The spraying conditions are: spraying air pressure 0.1~0.4mPa, spraying distance 20~30cm; The conditions for blade coating are: blade gap 10~150μm, blade speed 10~30mm / s.

8. The method for preparing the metamaterial composite fabric with infrared / microwave compatible stealth as described in claim 6, characterized in that, In step 2, the specific process is as follows: 2.1) Design the resonant unit pattern and create a screen printing plate based on the preset resonant unit pattern; 2.2) Conductive silver paste was selected as the ink, and the resonant pattern was transferred to the interface control layer by screen printing; wherein, the viscosity of the conductive silver paste was 10000~12000mPa·s, and the surface sheet resistance was less than or equal to 400Ω / sq; the screen printing process parameters were: squeegee hardness 60~80 Shore A, squeegee pressure 0.1~0.3mPa, printing speed 50~150mm / s, screen-to-substrate distance 2.5~5mm, and squeegee angle 50°~80°; 2.3) Place the printed interface control layer at room temperature for no less than 30 minutes to allow it to dry and cure completely.

9. The method for preparing the metamaterial composite fabric with infrared / microwave compatible stealth as described in claim 6, characterized in that, In step 3, the specific process is as follows: The fabric interlayer is cut to the required size, treated in a constant temperature water bath, and then dried in an oven. The fabric dielectric layer is made of woven or knitted fabric with a dielectric constant ranging from 2.5 to 4.

5. The constant temperature water bath has a processing temperature of 60~80℃ and a processing time of 2~4h; The oven conditions are: temperature 50~80℃, processing time not less than 2 hours, until completely dry.

10. The method for preparing the metamaterial composite fabric with infrared / microwave compatible stealth according to claim 6, characterized in that, In step 4, the specific process is as follows: The interface control layer with metamaterial resonant unit layer obtained in step 2, the fabric dielectric layer after pretreatment in step 3, and the highly conductive fabric reflective layer are stacked in sequence and combined into one piece by hot pressing molding process to obtain metamaterial composite fabric. The stacking order from bottom to top is: interface control layer with metamaterial resonant unit layer, fabric dielectric layer, highly conductive fabric reflective layer, with one side of the printed pattern of metamaterial resonant unit layer facing away from the fabric dielectric layer. The hot pressing process conditions are: hot pressing temperature 120~180℃, hot pressing pressure 0.3~1mPa, and hot pressing time 5~60 seconds.

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