Infrared radar stealth compatible flexible patch based on photonic crystal and metamaterial

Abstract

The invention provides an infrared radar stealth compatible flexible patch based on a photonic crystal and a metamaterial, and belongs to the technical field of stealth materials and structures, the total thickness is smaller than or equal to 1 mm, and a photonic crystal infrared stealth layer, a metamaterial wave-absorbing film and a radar wave-absorbing patch layer are sequentially stacked from outside to inside; the photonic crystal infrared stealth layer, the metamaterial wave-absorbing film and the radar wave-absorbing patch layer are thin films and can be replaced independently; the photonic crystal infrared stealth layer covers the wave bands of 3-5 microns and 8-12 microns, the metamaterial wave-absorbing film absorbs resonance of the Ku wave band, and the radar wave-absorbing patch layer provides broadband dielectric loss and magnetic loss absorption; the photonic crystal infrared stealth layer, the metamaterial wave-absorbing film and the radar wave-absorbing patch layer are attached through negative pressure to form a flexible whole capable of being attached in a curved surface mode. According to the invention, the survivability of the aircraft and equipment in a complex detection environment can be effectively improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of stealth materials and structures, and particularly relates to an infrared radar stealth compatible flexible patch based on photonic crystals and metamaterials. BACKGROUND

[0002] Infrared and radar detection are two main target detection methods. Infrared detectors usually use the thermal radiation characteristics of targets in the medium wave infrared (3-5 μm) and long wave infrared (8-12 μm) atmospheric window waveband to discover targets. Therefore, in order to reduce the detectability of targets in the infrared waveband, it is necessary to reduce the infrared radiation of targets in the 3-5 μm and 8-12 μm waveband or to improve the reflection of the radiation in this waveband, so as to achieve low detectability. Photonic crystal material is an artificial structure with periodic modulation of dielectric constant, and its special photonic bandgap effect can block the propagation of electromagnetic waves in a specific frequency range. When the forbidden band frequency of the photonic crystal covers the 3-5 μm and 8-12 μm waveband sensitive to the infrared detector, the thermal radiation transmission or emission of these two wavebands can be effectively suppressed, thereby achieving the purpose of infrared stealth. Unlike the principle of traditional metal foil and other infrared shielding materials, the pure dielectric photonic crystal is almost transparent to radar waves, so using photonic crystals for infrared stealth will not significantly affect the transmission of radar waves, which makes it easy to be compatible with radar stealth materials.

[0003] Radar stealth is usually achieved by reducing the radar cross section of the target. One important means is to use electromagnetic wave absorbing materials to absorb and dissipate the radar electromagnetic wave energy incident on the target. Traditional wave absorbing materials are generally divided into two categories according to the loss mechanism: dielectric loss type and magnetic loss type. The dielectric loss type wave absorbing material often uses carbon black, graphite, conductive polymer and other dielectric media to convert electromagnetic energy into heat energy dissipation through conductive loss and polarization loss; the magnetic loss type wave absorbing material uses the magnetic hysteresis loss and resonance absorption mechanism of ferromagnetic materials (such as ferrite, carbonyl iron, etc.) to consume electromagnetic energy. In order to obtain good wave absorbing performance in a wide frequency range, engineers often mix various wave absorbing fillers to make composite wave absorbing materials to cover dielectric and magnetic loss mechanisms at the same time. At present, researchers have compounded graphene, magnetic metals such as iron powder, and conductive high polymers in a certain proportion to form wave absorbing coatings, which are coated on the base fabric to form a flexible wave absorbing layer. When the thickness is less than 1mm, the reflection of 8-12GHz radar waves can be reduced by more than 60%. As a new electromagnetic stealth means, metamaterial wave absorber has received widespread attention in recent years. Metamaterial wave absorber uses subwavelength periodic structure to achieve resonance absorption of specific frequency electromagnetic waves. The resonance characteristics of the basic unit structure of the material give the material special values of equivalent permittivity and permeability, thereby producing nearly full absorption effect in a specific frequency band. Compared with traditional wave absorbing materials, metamaterial wave absorbers can achieve high absorption rate at very thin thickness, but the working bandwidth is relatively narrow. Existing research has designed an ultra-thin wave absorbing structure with a total thickness of only about 0.3mm, with an absorption rate close to 100% at the design frequency point (such as 5GHz, 7GHz). Therefore, combining metamaterial wave absorbing structures with traditional wideband wave absorbing materials is expected to achieve high absorption rate and wideband radar stealth performance.

[0004] The infrared stealth principle adopted by Chinese patent application CN117470028A is to use a high-reflectivity ITO (indium tin oxide) conductor layer of a metalloid, which has a high reflectivity in the mid-infrared and far-infrared wave bands due to its free carrier characteristics, thereby significantly reducing the infrared emissivity of the material. The essence of its infrared stealth method is to use the high infrared reflectivity of the low-resistance ITO microstructure to reduce the infrared emissivity. In the current multispectral stealth scheme, there has been a design that combines a photonic crystal infrared stealth film with a radar wave absorbing layer. The principle of photonic crystal infrared stealth is that due to the photonic band structure caused by the periodic structure, the photonic crystal completely suppresses propagation in the forbidden band, and the transmission rate ≈ 0, while it can be well transmitted in the passband. Its transmission spectrum is highly frequency-selective, and a common one-dimensional photonic crystal is designed to achieve near-zero transmission in a specific infrared window. Photonic crystals exhibit extremely high reflectivity in their forbidden bands. By designing the periodic structure, high reflectivity can be achieved in the 3-5μm and 8-14μm atmospheric windows. Due to the nearly 100% reflectivity in the designed band gap, there is almost no absorption, so the emissivity is extremely low, and significant infrared radiation suppression can be achieved, realizing infrared stealth.

[0005] Chinese patent application CN112273747A proposes a multi-band stealth clothing structure based on photonic crystal thin film material, including a photonic crystal optical infrared composite stealth layer and a flexible radar wave-absorbing base cloth layer. In this scheme, the photonic crystal stealth layer is subdivided into near-infrared, mid-infrared, far-infrared, etc. sub-layers, which are prepared by vacuum coating; the radar wave-absorbing base cloth layer is formed by coating graphene, iron powder, polyaniline, etc. wave-absorbing materials on non-woven fabric, and the absorption attenuation of 8-12GHz radar waves is more than 60% under the thickness of less than 1mm. This stealth clothing design has both infrared camouflage pattern effect and certain radar stealth ability, and has important significance in the field of camouflage. However, the above scheme still has some deficiencies:

[0006] 1. The radar wave-absorbing layer mainly relies on a single layer of broadband wave-absorbing coating, which has a wide frequency band but needs to improve the absorption efficiency of specific frequency bands (such as Ku-band higher frequency radar waves).

[0007] 2. The photonic crystal layer and the wave-absorbing layer are simply stacked on the base cloth, and the combination method may affect the durability and replaceability of the material, which is not conducive to long-term service on aircraft and other equipment.

[0008] 3. The radar wave-absorbing material attached has a simple structure and is easy to process, but the absorption rate is only 60%, which cannot meet the requirements of the increasingly severe combat environment for high absorption performance.

[0009] Therefore, it is necessary to provide an improved multi-band stealth structure to realize comprehensive stealth for infrared and different radar bands with more concise and efficient hierarchical combination and more firm pasting method, and have good mechanical properties and convenient use and maintenance. SUMMARY

[0010] To solve the above technical problems, the present application provides an infrared and radar stealth compatible flexible patch based on photonic crystals and metamaterials, which combines photonic crystal infrared stealth layer, metamaterial wave-absorbing layer and broadband wave-absorbing composite layer organically, realizes efficient stealth for 3-5μm and 8-12μm infrared bands and multiple radar frequency bands under the premise of maintaining extremely thin structure thickness (≤1mm). The present application is flexible in design, each layer is modularly designed, combined by negative pressure adhesion technology, and the position and material ratio of each layer can be adjusted according to needs, which has the advantages of easy processing, installation and maintenance, and is suitable for various equipment with infrared and radar stealth requirements.

[0011] To achieve the above purpose, the present application adopts the following technical scheme:

[0012] An infrared radar stealth compatible flexible patch based on photonic crystals and metamaterials, the total thickness is less than or equal to 1mm, and the photonic crystal infrared stealth layer, the metamaterial wave absorbing film and the radar wave absorbing patch layer are stacked from outside to inside; the photonic crystal infrared stealth layer, the metamaterial wave absorbing film and the radar wave absorbing patch layer are all thin films and can be replaced independently; the photonic crystal infrared stealth layer covers 3-5um and 8-12um bands, the metamaterial wave absorbing film resonates and absorbs Ku band, and the radar wave absorbing patch layer provides wide frequency dielectric loss and magnetic loss absorption; the photonic crystal infrared stealth layer, the metamaterial wave absorbing film and the radar wave absorbing patch layer are formed into a flexible whole through negative pressure fitting to be attached to a curved surface.

[0013] Further, the photonic crystal infrared stealth layer is a one-dimensional multilayer film of Ge / Si and SiO2 / MgF2 deposited alternately.

[0014] Further, the metamaterial wave absorbing film is composed of a polyimide substrate and a copper foil periodic resonance unit array on the surface of the substrate.

[0015] Further, the radar wave absorbing patch layer is based on epoxy resin or silicone rubber, and is filled with two or more of graphite, carbon black, carbon nanotubes, carbonyl iron powder and Fe3O4 particles.

[0016] Further, the positions of the metamaterial wave absorbing film and the radar wave absorbing patch layer are interchangeable, and after interchanging, the total thickness of the infrared radar stealth compatible flexible patch is still less than or equal to 1mm.

[0017] Further, the thickness of the photonic crystal infrared stealth layer is 30-80 microns.

[0018] Further, the thickness of the metamaterial wave absorbing film is 0.1-0.3mm.

[0019] Further, the thickness of the radar wave absorbing patch layer is 0.3-0.5mm.

[0020] Further, the copper foil periodic resonance unit array is a rectangular open ring.

[0021] Further, the copper foil periodic resonance unit array is a resistance-loaded circular ring.

[0022] Beneficial effects:

[0023] The three-in-one infrared and radar stealth structure of the present application combines the infrared stealth photonic crystal film, the narrow-band high-efficiency absorbing metamaterial layer and the wide-band absorbing radar wave absorbing layer, overcomes the limitations of single stealth means, and has the following remarkable advantages:

[0024] (1) Good multi-band stealth compatibility:

[0025] The application effectively suppresses 3-5 mu m and 8-12 mu m infrared radiation through the photonic crystal layer, and combines the metamaterial and the composite material to realize efficient absorption of millimeter wave and centimeter wave radar signals. In particular, the metamaterial absorbing film provides a strong absorption peak for a key radar frequency band (such as the Ku band), and the composite absorbing layer ensures overall absorbing coverage from a lower frequency to a higher frequency, so that the structure has excellent stealth performance in the optical / infrared and radar wave bands.

[0026] (2) thin thickness, light weight and flexible adhesion:

[0027] The total thickness of the application is not more than 1 mm, which is greatly thinned compared with the conventional absorbing material and thermal insulation coating with a thickness of several millimeters to several tens of millimeters, which is beneficial to reduce the total weight of the equipment and maintain the aerodynamic shape. Each layer is in the form of a film, which is formed into a flexible laminated structure by vacuum negative pressure adhesion, and can be adapted to curved surface adhesion without affecting the surface shape of the carrier. At the same time, the film structure can bend with the deformation of the carrier in use, and is not easy to crack and peel off, and has strong environmental adaptability.

[0028] (3) flexible structure combination, easy to manufacture and maintain:

[0029] In the application, the photonic crystal layer, the metamaterial layer and the absorbing patch layer are physically combined, the materials and structure parameters of each layer can be independently designed and optimized, and have strong combination flexibility. When manufacturing, they can be prepared and assembled respectively, and have high yield; the structure can be easily adjusted according to different application requirements, the metamaterial unit design or the different absorbing filler formula is replaced, so as to improve the stealth effect of specific threat frequency band, and the stealth effect requirement of different positions of the equipment can be locally strengthened by adjusting the formula. The modular design idea makes it have high engineering practical value.

[0030] In summary, the three-in-one infrared and radar stealth structure provided by the application has significant advantages in terms of multi-spectral stealth performance, light and thin characteristics and applicability, and can effectively improve the survival ability of aircraft and equipment in complex detection environment. The application has the functions of infrared and radar stealth, and can be widely used in multi-spectral stealth coating or covering layer of manned aircraft, unmanned aerial vehicle, vehicle equipment and fixed facility. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 is a schematic diagram of a flexible patch based on photonic crystal and metamaterial infrared radar stealth compatibility of the application;

[0032] Figure 2 is a schematic diagram of a basic unit of the metamaterial layer.

[0033] Wherein, the figure mark is: photonic crystal infrared stealth layer 1, super material wave absorbing film 2, radar wave absorbing patch layer 3, ITO resistance film 4, PET substrate 5. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical scheme and advantage of the present application more clear, the present application is further described in detail below with the help of drawings and examples. It should be understood that the specific examples described here are only used to explain the present application, and are not used to limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0035] As Figure 1 shown, the present application provides an infrared radar stealth compatible flexible patch based on photonic crystal and super material, which includes photonic crystal infrared stealth layer 1, super material wave absorbing film 2, radar wave absorbing patch layer 3.

[0036] It should be noted that the overall structure is from outside to inside photonic crystal infrared stealth layer 1, super material wave absorbing film 2, radar wave absorbing patch layer 3. The photonic crystal infrared stealth layer is located at the outermost surface of the overall structure of the infrared radar stealth compatible flexible patch, which is used to regulate the radiation characteristics of the target in the mid-infrared (3-5 μm) and long-wave infrared (8-12 μm) band, so as to reduce the probability of being detected by infrared imaging equipment. The photonic crystal infrared stealth layer adopts one-dimensional multilayer film photonic crystal structure, which is formed by alternately depositing high refractive index materials and low refractive index materials to form a periodic structure film. For example, the semiconductor materials with high refractive index such as germanium (Ge), silicon (Si) and telluride can be alternately stacked with medium materials with low refractive index such as silicon dioxide (SiO2), magnesium fluoride (MgF2) and calcium fluoride (CaF2). The specific number of layers and thickness distribution are not limited, but it is required to cover the 3-5 μm and 8-12 μm band by designing photonic band gap, so as to realize the radiation suppression of the two infrared windows.

[0037] The basic principle of photonic crystal film realizing infrared stealth is as follows:

[0038] According to electromagnetic field theory, the propagation of light on the interface of different media follows the law of wave optics. For one-dimensional photonic crystal, its structure can be simplified as a multilayer film system composed of two kinds of dielectric films with high (n H ) and low (n L ) refractive index alternately stacked.

[0039] According to the Stefan-Boltzmann law, the total radiant exitance M(T) per unit surface area of an object at temperature T is:

[0040] (1)

[0041] Wherein, is the spectral emissivity of the object at wavelength λ; T is the thermodynamic temperature of the object; is the Stefan-Boltzmann constant; C1 and C2 are the first and second radiation constants, respectively; exp() represents the exponential function; represents the spectral emissivity.

[0042] As can be seen from equation (1), in the case where the target temperature T is difficult to be greatly reduced, the fundamental way to achieve infrared stealth is to reduce the emissivity of the target at a specific infrared detection wavelength .

[0043] According to the Kirchhoff infrared law, under the condition of thermal equilibrium, the spectral emissivity (λ, T) of an object is equal to its spectral absorptivity α(λ, T). For a non-quasi-equilibrium state, the emissivity and the absorptivity are also proportional. Therefore, the goal of reducing the emissivity can be achieved by reducing the absorptivity. For an opaque object, the energy conservation relationship is:

[0044] (2)

[0045] where, is the spectral reflectivity of the object.

[0046] Combining equation (2) with the Kirchhoff law, we obtain:

[0047] (3)

[0048] Equation (3) is the theoretical core of the photonic crystal for achieving infrared stealth. It shows that by increasing the spectral reflectivity of the object at a specific wavelength to close to 1, the spectral emissivity at that wavelength can be close to 0, achieving the effect of infrared stealth.

[0049] In order to achieve high reflectivity, the present application adopts the design of one-dimensional photonic crystal, and the optical properties thereof can be analyzed by the transfer matrix method.

[0050] Consider a periodic structure [H / L] N (indicating that the high refractive index material and the low refractive index material are stacked as one unit, and there are N units, i.e. N is the number of periods). When light is vertically incident, the optical behavior of each period can be described by a characteristic matrix.

[0051] For a single-layer uniform dielectric film, the characteristic matrix M is:

[0052] (4)

[0053] where, is the phase thickness of the thin film, for normal incidence, . is the refractive index of the thin film, is its physical thickness. is the optical admittance of the medium, for TE wave, for TM wave, . i is the imaginary unit, represents the propagation angle of the light ray inside the thin film medium.

[0054] For a periodic unit consisting of high and low refractive index materials (e.g. Ge / SiO2), its characteristic matrix M HL is the product of the two thin film characteristic matrices:

[0055] (5)

[0056] where M H is the characteristic matrix of the high refractive index layer constituting the photonic crystal thin film, and M L is the characteristic matrix of the low refractive index layer constituting the photonic crystal thin film.

[0057] For the entire photonic crystal film system containing N periods, its total characteristic matrix M total is the Nth power of the single period matrix:

[0058] (6)

[0059] where m 11 , m 12 , m 21 , m 22 are the final result coefficients obtained by performing the continuous multiplication operation on the characteristic matrix of each layer of the photonic crystal.

[0060] Finally, the reflectivity R of the entire film system can be calculated by its equivalent optical admittance Y = m 21 / m 11 :

[0061] (7)

[0062] where Y is the optical admittance of the incident medium (usually air). The superscript represents the complex conjugate operation.

[0063] When the thickness of the film layer meets the Bragg reflection condition, i.e. the optical thickness nd of each film layer is one quarter of the center wavelength λ0 (nd = λ0 / 4), the reflected light from the interface of each layer will interfere constructively to form high reflection. Through the analysis of the characteristic matrix, it can be deduced that the width Δg of the photonic band gap (i.e. the relative width of the high reflection region) is closely related to the ratio of the refractive indices of the high and low refractive index materials (n H / n L ). The greater the refractive index ratio, the wider the photonic band gap, and the better the stealth performance.

[0064] According to the working wavelength band of common infrared detectors, the infrared wavelength band that needs to be suppressed is determined, mainly the 3~5µm and 8~14µm atmospheric windows. A combination of materials with high and low refractive indices and small absorption in the wavelength band is selected. For example, germanium (Ge) as a high refractive index material and silicon dioxide (SiO2) as a low refractive index material. According to the target center wavelength (such as 4µm and 11µm), the optical thickness of the high and low refractive index layers is designed to be one quarter of the center wavelength.

[0065] By superimposing two one-dimensional photonic crystal structures with center wavelengths of 4µm and 11µm respectively, a composite structure with high reflectivity (close to 100%) in the 3~5µm and 8~14µm atmospheric windows can be constructed, thereby realizing wide-spectrum infrared stealth.

[0066] The photonic crystal infrared stealth layer can be prepared on the substrate by physical vapor deposition method, and then fixed on the outermost layer of the structure of the application by adhesion or transfer. The thickness of the photonic crystal layer is determined according to the design wavelength, generally in the order of several microns to tens of microns. After being made, the film layer is dense and uniform, and has good environmental adaptability.

[0067] The metamaterial wave-absorbing film is located inside the one-layer photonic crystal infrared stealth layer and is used to absorb electromagnetic waves of a specific radar frequency band. The metamaterial wave-absorbing film is a metamaterial layer composed of a periodically arranged metal-dielectric structure, and the basic unit is much smaller than the working wavelength. Taking a two-dimensional metal-dielectric periodic structure as an example, the basic unit is composed of two parts as shown in Figure 2 , which are symmetrical to each other. The main body is a half hexagon (i.e. the lower half of the hexagon), which is successively reduced from outside to inside to form a three-layer progressive half hexagon frame. In the center of the half hexagon, there is a vertical through rectangular bar that divides the pattern into two symmetrical parts. The line widths are the same. The lower part is a mirror image of the upper part, i.e. the upper part is flipped along the central axis.

[0068] The metamaterial wave-absorbing film is composed of an ITO resistive film 4 and a PET substrate 5. The ITO resistive film 4 absorbs and dissipates electromagnetic waves through its periodic structure, and the PET substrate 5 serves as a carrier for the ITO resistive film. By designing the shape and size of the metal resonant unit array (such as patches, inductive rings, open resonant rings, etc.) and arranging them periodically on the dielectric substrate, the two-layer metamaterial layer can produce strong electromagnetic resonance at the target radar frequency, thereby efficiently dissipating the radar wave energy at the corresponding frequency. For example, in the Ku band (about 12-18 GHz) radar threat frequency range, a double-layer metal pattern is designed to form a wave-absorbing frequency-selective surface, with an absorption rate of nearly 95% at several frequency points. At the same time, in order to take into account different polarizations and incident angles, symmetric structure resonant units or multiple resonant unit combinations are used to achieve wide-angle, high-absorption-rate stealth in specific frequency bands. The specific structure and arrangement of the metamaterial wave-absorbing film in the present application can be customized according to requirements. For example, in one embodiment, a polyimide film or indium tin oxide (ITO) with stable dielectric constant is selected as the substrate, and a two-dimensional copper foil resonant unit array (such as rectangular open rings, resistance-loaded circular rings, etc.) is fabricated on it through photolithography, electroplating or printing process. The resonant unit period is about one-tenth to several tenths of the working wavelength. The prepared metamaterial film (including the substrate) has a thickness of usually 0.1-0.3 mm and has a certain flexibility, which is convenient for lamination with other layers.

[0069] The radar wave-absorbing patch layer is located at the innermost side of the overall structure (or inside the metamaterial layer) and is used to attenuate and absorb radar signals in a wide frequency range. The radar wave-absorbing patch layer is composed of a base material and a wave-absorbing functional filler to form a whole composite sheet, which has both dielectric loss and magnetic loss mechanisms to cover a wide frequency range. The base material can be selected from polymers or elastomers (such as epoxy resin, silicone rubber, polyimide, etc.) that are relatively transparent to radar waves and have good mechanical properties, to bond and support the wave-absorbing filler and provide structural flexibility. The wave-absorbing functional filler can be selected from dielectric-type wave-absorbing agents such as graphite, carbon black, carbon fibers, carbon nanotubes, titanium dioxide, etc. to absorb electromagnetic energy through conductive loss and dielectric polarization; and magnetic wave-absorbing agents such as carbonyl iron powder, Fe3O4 particles, iron-nickel alloy powder, etc. to absorb microwave energy through magnetic hysteresis and resonance loss. The specific ratio and particle size of the wave-absorbing functional filler can be optimized and designed according to the requirements of the stealth frequency band.

[0070] It should be noted that the metamaterial wave-absorbing film and the radar wave-absorbing patch layer can be interchanged in position in the present application as needed: that is, either the order of "photonic crystal infrared stealth layer / metamaterial wave-absorbing film / radar wave-absorbing patch layer" can be adopted, arranged from the outside to the inside in turn, or the order of "photonic crystal infrared stealth layer / radar wave-absorbing patch layer / metamaterial wave-absorbing film" can be adopted. In the latter case, the metamaterial wave-absorbing film is at the innermost side, closer to the surface of the stealth equipment, and the composite wave-absorbing layer is in the middle. The two arrangements have respective advantages: when the metamaterial wave-absorbing film is placed in the middle, the radar waves incident from the outside first pass through the photonic crystal (almost transparent to the radar waves), then the specific frequency components are selectively absorbed by the metamaterial wave-absorbing film, and the remaining unabsorbed part continues to be transmitted to the inner broadband radar wave-absorbing patch layer to be further dissipated, so that the overall stealth of the target is achieved in combination of wide frequency and narrow frequency bands; conversely, when the metamaterial wave-absorbing film is placed in the innermost layer, the radar waves first pass through the attenuation of the photonic crystal infrared stealth layer and the broadband radar wave-absorbing patch layer, and then the residual specific frequency components are finally absorbed by the metamaterial wave-absorbing film close to the surface of the equipment. The two structures have little difference in stealth effect, and any one scheme can be selected according to the processing technology and actual application needs. Regardless of which arrangement is adopted, the total thickness of the structure of the present application is controlled to be less than 1 mm, and the thickness of each functional layer can be adjusted according to the performance requirements, for example, the thickness of the photonic crystal infrared layer is several tens of microns, the thickness of the metamaterial layer is about 0.2 mm, and the thickness of the radar wave-absorbing patch layer is about 0.3-0.5 mm, so that the total thickness is much thinner than that of the conventional coated stealth material. This thin-layer design ensures that the stealth structure is light in weight, has little effect on the aerodynamic shape of the carrier, and has a certain flexibility, and can be attached to a curved surface without affecting its performance.

Claims

1. An infrared radar stealth-compatible flexible patch based on photonic crystals and metamaterials, characterized in that: The total thickness is ≤1mm. From the outside to the inside, a photonic crystal infrared stealth layer, a metamaterial absorbing film, and a radar absorbing patch layer are stacked sequentially. The photonic crystal infrared stealth layer, the metamaterial absorbing film, and the radar absorbing patch layer are all thin films and can be replaced independently. The photonic crystal infrared stealth layer covers the 3–5μm and 8–12μm bands, the metamaterial absorbing film is designed for Ku-band resonance absorption, and the radar absorbing patch layer provides broadband dielectric loss and magnetic loss absorption. The photonic crystal infrared stealth layer, the metamaterial absorbing film, and the radar absorbing patch layer are bonded together by negative pressure to form a flexible whole that can be applied to curved surfaces.

2. The infrared radar stealth compatible flexible patch based on photonic crystals and metamaterials according to claim 1, characterized in that: The photonic crystal infrared stealth layer is a one-dimensional multilayer film with alternating deposition of Ge / Si and SiO2 / MgF2.

3. The infrared radar stealth compatible flexible patch based on photonic crystals and metamaterials according to claim 1, characterized in that: The metamaterial absorbing film is composed of a polyimide substrate and an array of periodic resonant units of copper foil on its surface.

4. The infrared radar stealth compatible flexible patch based on photonic crystals and metamaterials according to claim 1, characterized in that: The radar absorbing patch layer uses epoxy resin or silicone rubber as the matrix and is filled with two or more of the following: graphite, carbon black, carbon nanotubes, carbonyl iron powder, and Fe3O4 particles.

5. The infrared radar stealth compatible flexible patch based on photonic crystals and metamaterials according to claim 1, characterized in that: The positions of the metamaterial absorbing film and the radar absorbing patch layer can be interchanged. After the interchange, the total thickness of the infrared radar stealth compatible flexible patch is still ≤1mm.

6. The infrared radar stealth compatible flexible patch based on photonic crystals and metamaterials according to claim 1, characterized in that: The thickness of the photonic crystal infrared stealth layer is 30-80 micrometers.

7. The infrared radar stealth compatible flexible patch based on photonic crystals and metamaterials according to claim 1, characterized in that: The thickness of the metamaterial absorbing film is 0.1–0.3 mm.

8. The infrared radar stealth compatible flexible patch based on photonic crystals and metamaterials according to claim 1, characterized in that: The thickness of the radar absorbing patch layer is 0.3–0.5 mm.

9. The infrared radar stealth compatible flexible patch based on photonic crystals and metamaterials according to claim 3, characterized in that: The copper foil periodic resonant unit array is a rectangular open ring.

10. The infrared radar stealth compatible flexible patch based on photonic crystals and metamaterials according to claim 3, characterized in that: The copper foil periodic resonant unit array is a resistive-loaded circular ring.

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