Radar-transparent infrared-laser stealth film

Abstract

The present application belongs to the field of infrared-laser stealth technology, and discloses a radar wave-transparent infrared-laser stealth film, which comprises, from bottom to top, a substrate, a photonic crystal multilayer film structure and a top surface patterning structure; the photonic crystal multilayer film structure is composed of two kinds of transparent medium materials with high and low refractive indexes alternately stacked and arranged; the top surface patterning structure is used for realizing surface phase control; by using the constructive interference effect of the photonic crystal multilayer film structure on the incident wave with a wavelength near a preset target wavelength, and cooperating with the top surface patterning structure, the reflected wave front can be controlled, and the vertical mirror reflection can be reduced. Based on the photonic crystal high-reflection multilayer film structure, by using the constructive interference effect and cooperating with the phase control pattern structure, the phase control reflected electromagnetic wave front can be controlled, so that the vertically reflected electromagnetic wave is deflected to other directions, the conversion from high mirror reflection to high scattering of 8-14 mu m infrared waves can be realized, and the mirror reflection is inhibited.

Description

Technical Field

[0001] This invention belongs to the field of infrared-laser stealth technology, and more specifically, relates to an infrared-laser stealth film that is radar-transparent. The photonic crystal film structure can meet the requirements of infrared-laser stealth in the temperature range of 35°C to high temperature (such as 500°C) and is also radar-transparent. Background Technology

[0002] With the rapid development of electronic technology, multi-mode composite detection methods are becoming increasingly mature, making multi-spectral stealth technology increasingly important. Multi-spectral stealth requires suppressing target characteristics against multiple detection methods, including infrared, radar, laser, and visible light. Specifically, it requires achieving low emission in the infrared atmospheric window bands (3-5 μm and 8-14 μm), low radar reflection, low laser echo (10.6 μm and 1.06 μm), and visible light color matching. Currently, a relatively mature technical solution involves placing radar-absorbing materials in the lower layer and optical (infrared, laser, and visible light) stealth materials in the upper layer, achieving its own stealth function while also allowing radar wave transmission so that it is absorbed by the radar-absorbing material in the lower layer. However, traditional upper-layer infrared stealth materials are mostly highly conductive materials, and their intrinsic high reflectivity to electromagnetic waves severely hinders radar wave transmission, which is detrimental to radar-infrared compatible stealth. Meanwhile, considering the upper-level infrared-laser stealth requirements, the compatibility of far-infrared 8-14 μm and laser 10.6 μm stealth is a technical challenge. This is because the broadband high reflectivity (low emission) required for infrared stealth contradicts the narrowband low specular reflectivity required for laser stealth in the same band.

[0003] In recent years, the emergence of photonic crystal thin film materials has effectively solved the above-mentioned technical problems. Low conductivity material systems can meet the requirement of perfect radar wave transmission, and photonic bandgap and photonic localization characteristics have achieved compatibility between 8-14 μm broadband high reflectivity and 10.6 μm narrowband low specular reflectivity. However, photonic crystal thin films still have the following problems: First, these films are all high specular reflectivity, and their reflection of external infrared heat sources is extremely strong at low temperatures (such as temperatures not exceeding 35°C), making the surface a thermal radiation bright spot at low temperatures, making it difficult to achieve infrared stealth of the target surface at low temperatures, and thus difficult to achieve infrared stealth across the entire temperature range; Second, to achieve infrared-laser compatible stealth, the overall thickness of the film must exceed 10 μm, thus increasing the cost and difficulty of preparation. To address the first problem, a technical solution has emerged involving depositing photonic crystal thin films on high-roughness fiber substrates. This reduces specular reflection from external infrared heat sources through scattering caused by the rough substrate. However, its infrared emissivity is generally higher than 0.4, resulting in poor infrared stealth performance at high temperatures. To address the second problem, scattering metasurfaces can achieve high scattering (low specular reflection) of 10.6 μm lasers, reducing the precision requirements for fabrication. However, this material system is typically based on metal thin films, making it difficult to achieve radar wave transmission. Currently, no effective control method exists to simultaneously achieve infrared-laser stealth across the entire temperature range (~35 ℃ to ~500 ℃) while maintaining radar wave transmission.

[0004] Therefore, there is an urgent need for a stealth material that can simultaneously meet the requirements of 8-14 μm broadband low emission, 8-14 μm (including 10.6 μm) low specular reflection, perfect radar wave transmission, and ideal infrared low radiation on the target surface from 35°C to high temperature range (e.g., 500°C). Summary of the Invention

[0005] To address the aforementioned deficiencies or improvement needs of existing technologies, the present invention aims to provide an infrared-laser stealth film with radar transparency. This film utilizes two transparent dielectric materials with different refractive indices (high and low) and alternately stacks them to form a photonic crystal high-reflectivity multilayer thin film structure. This photonic crystal multilayer thin film structure provides high reflectivity for wavelengths within a predetermined target wavelength range. The incident waves in the vicinity exhibit constructive interference (e.g., the refractive indices of the two materials). n ,thickness d With the wavelength of the center of action Relationships are especially satisfying The constructive interference condition is optimal for high reflection of incident electromagnetic waves (the wavelength of the incident electromagnetic wave does not need to be strictly equal to the wavelength of the incident electromagnetic wave). ,exist (Applicable to all nearby frequency bands) Pre-set to meet 8-14μm, it can achieve high specular reflection of 8-14 μm infrared waves; further combined with phase-modulated pattern structure, it can deflect the vertically reflected electromagnetic waves to other directions by phase-modulating the reflected electromagnetic wave front, thereby realizing the conversion from high specular reflection to high scattering of 8-14 μm infrared waves and suppressing specular reflection.

[0006] To achieve the above objectives, according to one aspect of the present invention, an infrared-laser stealth film with radar transmittance is provided, characterized in that it comprises, from bottom to top, a substrate, a photonic crystal multilayer thin film structure, and a top surface patterned structure, all of which are made of dielectric materials and do not affect radar wave transmission; wherein,

[0007] The photonic crystal multilayer thin film structure is composed of two transparent dielectric materials with different refractive indices in the infrared band, stacked alternately.

[0008] The patterned structure on the top surface uses a shape that can cover the entire plane as a repeating unit. The repeating units are covered on the top surface. At the same time, any two repeating units that share a side use the top surface material in one case and not in the other case, thus forming a patterned structure to achieve surface phase control.

[0009] By utilizing the constructive interference effect of the photonic crystal multilayer thin film structure on incident waves with wavelengths near a preset target wavelength, and in conjunction with the patterned top surface structure, the wavefront of the reflected wave can be modulated to reduce specular reflection in the vertical direction; the preset target wavelength is the pre-selected center wavelength of the infrared band or the center wavelength of the laser.

[0010] As a further preferred embodiment of the present invention, in the photonic crystal multilayer thin film structure, the refractive index of the component with the higher refractive index is denoted as... n H The refractive index of the lower refractive index is denoted as . n L Furthermore, let the thickness of each layer of the structure composed of a higher refractive index material be denoted as . d H The thickness of each layer of the structure, which is composed of a high refractive index material, is d L ,but,

[0011]

[0012]

[0013] in, The center wavelength of the infrared band or the center wavelength of the laser is selected in advance;

[0014] The photonic crystal multilayer thin film structure is used to target wavelengths in... The constructive interference effect of the nearby incident waves, combined with the patterned structure on the top surface, can modulate the wavefront of the reflected wave and reduce specular reflection in the vertical direction.

[0015] As a further preferred embodiment of the present invention, for the photonic crystal multilayer thin film structure, the dielectric material with a higher refractive index is selected from germanium, silicon, and tellurium, and the dielectric material with a lower refractive index is selected from zinc sulfide, zinc selenide, magnesium fluoride, and ytterbium fluoride.

[0016] Furthermore, the imaginary part of the refractive index of both the medium material with a higher refractive index and the medium material with a lower refractive index is 0.

[0017] As a further preferred embodiment of the present invention, for the photonic crystal multilayer thin film structure, the dielectric material with a higher refractive index is germanium (Ge), and the dielectric material with a lower refractive index is zinc sulfide (ZnS).

[0018] As a further preferred embodiment of the present invention, for the aforementioned photonic crystal multilayer thin film structure, The thickness of a single Ge layer is 8-12 μm, the thickness of a single Ge layer is 500-750 nm, and the thickness of a single ZnS layer is 909-1363 nm.

[0019] Preferred, The thickness is 10.6 μm, the thickness of a single Ge layer is 662.5 nm, and the thickness of a single ZnS layer is 1204.5 nm.

[0020] As a further preferred embodiment of the present invention, the top surface patterned structure can be equilateral triangles, squares, or regular hexagons that can cover the entire plane.

[0021] As a further preferred embodiment of the present invention, for the patterned structure on the top surface, the shape that can cover the entire plane is preferably a square, with a side length of 8-28 μm and a height of 1500-2500 nm; more preferably, the side length of the square is 16 μm or 18 μm and the height is 1800 nm.

[0022] As a further preferred embodiment of the present invention, the refractive index of the top surface material is less than the refractive index of the material with the higher refractive index in the photonic crystal multilayer thin film structure. n H );

[0023] Preferably, the top surface material is one of zinc sulfide, zinc selenide, magnesium fluoride, and ytterbium fluoride; more preferably, it is zinc sulfide.

[0024] As a further preferred embodiment of the present invention, the substrate is a rigid substrate or a flexible substrate, wherein the rigid substrate is one or more of quartz (SiO2), sapphire (Al2O3), silicon wafer, and ceramic, and the flexible substrate is one or more of polyimide (PI), polyethylene terephthalate (PET), fiber cloth, and rubber patch.

[0025] Preferably, the substrate is a flexible polyimide substrate or a rigid quartz substrate.

[0026] As a further preferred embodiment of the present invention, the substrate is a substrate material having a smooth surface.

[0027] Compared with the prior art, the scattering photonic crystal thin film for infrared-laser stealth in this invention mainly includes: a substrate, a photonic crystal multilayer thin film structure disposed on the surface of the substrate, and a phase modulation pattern structure on the surface. The substrate primarily serves to support the film layers. The photonic crystal multilayer thin film structure primarily achieves high specular reflection of 8-14 μm infrared waves, comprising high and low refractive index materials. When the high and low refractive index materials are superimposed with a thickness equal to one-quarter of the center wavelength, the reflected beams at different interfaces have the same phase, resulting in constructive interference and achieving a reflection intensity with a reflectivity close to 1. The phase modulation pattern structure primarily functions to deflect the vertically reflected electromagnetic wave to other directions by modulating the wavefront of the reflected electromagnetic wave, thereby achieving a conversion from high specular reflection to high scattering of 8-14 μm infrared waves and suppressing specular reflection.

[0028] The photonic crystal multilayer thin film structure of this invention consists of alternating stacks of two dielectric materials with different refractive indices, one high and one low. All dielectric materials are transparent in the infrared band, and their imaginary refractive index is 0. When both high and low refractive index materials are stacked with a thickness equal to one-quarter of the center wavelength, the reflected beams at different interfaces have the same phase, resulting in the most significant constructive interference effect. This increases the reflectivity, achieving a broadband high-reflectivity effect, which is optimal for high reflection of incident electromagnetic waves. Furthermore, the more stacking periods, the higher the reflectivity. Taking the construction of a photonic crystal multilayer thin film structure using Ge and ZnS as an example (these two materials have excellent lattice and stress matching properties, which can enhance the mechanical properties of the prepared multilayer thin film), Ge has a refractive index of 4 in the infrared band (corresponding to...). n H ZnS has a refractive index of 2.2 in the infrared band (corresponding to...). n L ), and the corresponding thickness of each Ge layer (i.e., d H ) and the thickness of each ZnS layer (i.e., d L They respectively satisfy:

[0029]

[0030]

[0031] when When pre-set to meet the center wavelength of 8-14 μm, this photonic crystal multilayer thin film structure can achieve high specular reflection in the infrared 8-14 μm band (especially including 10.6 μm laser wavelength), enabling infrared stealth at high temperatures, while also being compatible with radar wave transmission.

[0032] The patterned structure at the top layer uses repeating units of shapes capable of tiling the entire plane. After tiling, one of any two repeating units sharing a side is covered by the top surface material, while the other is not. The top surface material is composed of a low-refractive-index dielectric material, forming a surface phase-modulating pattern structure. Taking a surface phase-modulating pattern structure of alternating cubes arranged in a checkerboard pattern as an example, by controlling the reflection phase, the phase difference between the reflected areas containing cubes and those without cubes is made 180°. When this condition is met, the resulting beam interference effect modulates the wavefront of the reflected wave, causing the synthesized reflected electromagnetic wave to deflect towards a spatial azimuth angle of 45°, thereby reducing specular reflection in the vertical direction. (This will be discussed later.) Figure 1 For example, the arrangement is a checkerboard pattern in two-dimensional space with square blocks as units. The area without square blocks can be named "Area 1" and the area with square blocks can be named "Area 2". The reflection phase difference between "Area 1" and "Area 2" is equal to or close to 180° (in radians, expressed as π, with a specific value of approximately 3.14). Under this condition, the wavefront of the reflected wave can be controlled by the beam interference effect, which can deflect the reflected electromagnetic wave and decompose the vertically incident electromagnetic wave into four reflected waves with azimuth angles of 45°, 135°, 225° and 315° respectively. This suppresses specular reflection and converts strong specular reflection into strong scattering, reducing the laser echo signal by 10.6 μm. Strong scattering is still in a low emission state. While maintaining its own low radiation characteristics, it can avoid specular reflection of external heat source radiation on the target surface at low temperature. Therefore, infrared stealth can be achieved in both low temperature and high temperature states.

[0033] Thus, the overall thin film structure can satisfy:

[0034] The infrared emissivity in the 8-14 μm band is less than 0.1;

[0035] The reflectivity of a 10.6 μm laser mirror is less than 0.1.

[0036] The infrared reflection characteristics in the 8-14 μm band are diffuse reflection;

[0037] The radar wave transmittance in the 2-18 GHz band is higher than 0.95.

[0038] Furthermore, this invention is also applicable to the 35°C to high-temperature range (up to, for example, 500°C), enabling infrared-laser stealth in the 35°C to high-temperature range while maintaining radar wave transmission capability. The substrate can preferably be a flexible polyimide substrate or a rigid quartz substrate, both of which possess excellent high-temperature resistance, meeting the heat resistance requirements for stealth.

[0039] In summary, the present invention can achieve the following beneficial effects:

[0040] (1) This invention achieves infrared-laser stealth by converting strong specular reflection into strong scattering. Through scattering, it can effectively suppress external heat sources, exhibiting low emission in the 8-14 μm infrared band, low specular reflection in the 8-14 μm infrared band, and low specular reflection in the 10.6 μm laser band. This avoids the problems of relatively thick overall thickness (usually more than 10 μm) in the traditional photonic crystal thin film photonic localization design for achieving laser stealth.

[0041] (2) The strong scattering characteristics of the present invention can effectively suppress strong specular reflection of external heat source radiation at low temperature (~35 ℃), and the film itself is still in a low emission state, so infrared stealth can be achieved in the range of 35 ℃ to high temperature.

[0042] (3) The material selected in this invention is a whole dielectric material system. When it is covered on the surface of radar absorbing material, it will not hinder radar wave transmission, which is conducive to the realization of multi-spectral stealth of the target.

[0043] In summary, this invention achieves a stealth material that can simultaneously satisfy broadband low emission of 8-14 μm and low specular reflection of 8-14 μm (including 10.6 μm), perfect transmission of radar waves of 2-18 GHz, and also achieve ideal infrared low radiation of the target surface in the range of 35 ℃ to high temperature (e.g., 500 ℃). Attached Figure Description

[0044] Figure 1 This is a schematic diagram of a scattering photonic crystal thin film structure for infrared-laser stealth provided by the present invention. Figure 1 (a) in the image is a side view. Figure 1 (b) is the top view. Figure 1 (c) in the figure is a three-dimensional schematic diagram.

[0045] Figure 2 The infrared transmission characteristic curve of the photonic crystal multilayer thin film structure in Example 1 is shown.

[0046] Figure 3 The infrared band reflection spectra and reflection phases of the structures in "Region 1" and "Region 2" in Example 1 are shown.

[0047] Figure 4 The simulated infrared 8-14 μm transmission spectrum of the scattering photonic crystal thin film structure for infrared-laser stealth provided in Embodiment 1 of the present invention.

[0048] Figure 5 This is a 10.6 μm laser scattering pattern of a scattering photonic crystal thin film structure for infrared-laser stealth provided in Embodiment 1 of the present invention.

[0049] Figure 6 This is a comparison of the overall infrared radiation characteristics as a function of surface temperature for a high-emissivity material (i.e., an ideal blackbody material with an infrared emissivity of 1), a traditional mirror photonic crystal thin film (i.e., a region 1 structure, which is a multilayer thin film without surface square blocks), and the scattering photonic crystal thin film structure for infrared-laser stealth provided in Embodiment 1 of this invention. Figure 6 (a) in the text corresponds to a high emissivity material. Figure 6 (b) in the text corresponds to a traditional mirrored photonic crystal thin film. Figure 6 (c) in the figure corresponds to the scattering photonic crystal thin film for infrared-laser stealth obtained in Embodiment 1 of the present invention.

[0050] Figure 7 The simulated 2-18 GHz radar wave transmission spectrum of the scattering photonic crystal thin film structure for infrared-laser stealth provided in Embodiment 1 of the present invention.

[0051] Figure 8 The simulated infrared 8-14 μm transmission spectrum of the scattering photonic crystal thin film structure for infrared-laser stealth provided in Embodiment 2 of the present invention.

[0052] Figure 9 This is a 10.6 μm laser scattering pattern of a scattering photonic crystal thin film structure for infrared-laser stealth provided in Embodiment 2 of the present invention.

[0053] Figure 10 The graph shows the overall infrared radiation characteristics of the scattering photonic crystal thin film structure for infrared-laser stealth as a function of surface temperature, as provided in Embodiment 2 of the present invention.

[0054] Figure 11 The image shows the infrared radiation test pattern of a scattering photonic crystal thin film prepared according to the parameters of Embodiment 2 of the present invention; wherein, Figure 11 (a) in the figure is the infrared radiation diagram under the condition that the surface temperature is 45°C and there is no external radiation source. Figure 11 (b) is the infrared radiation diagram under the condition of surface temperature 45℃ and external radiation source 80℃. Detailed Implementation

[0055] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0056] like Figure 1 As shown, the scattering photonic crystal thin film for infrared-laser stealth of the present invention mainly includes: a substrate, a photonic crystal multilayer thin film structure disposed on the surface of the substrate, and a phase modulation pattern structure on the surface. Wherein:

[0057] The substrate's main function is to support the film layer. For example, the substrate can be a rigid quartz substrate or a flexible polyimide substrate.

[0058] The primary function of the photonic crystal multilayer thin-film structure is to achieve high specular reflection of long-wave infrared incident waves (i.e., 8-14 μm infrared waves), achieving an average specular reflectivity higher than 0.9. When the optical thicknesses of both the high- and low-refractive-index materials are one-quarter of the corresponding center wavelength, constructive interference occurs, increasing the reflectivity. The higher the number of stacking periods, the higher the reflectivity. Preferably, the high-refractive-index material is germanium, the low-refractive-index material is zinc sulfide, the center wavelength is 10.6 μm, and the number of stacking periods is 4. The simulated infrared transmission characteristic curves of the photonic crystal multilayer thin-film structure are shown below. Figure 2 As shown, the average specular reflectance of the 8-14 μm area was calculated to be 0.90, the average transmittance to be 0.10, and the absorptivity to be 0.

[0059] Phase-modulated pattern structures primarily function to convert high specular reflection of long-wave infrared incident waves into high scattering, thereby suppressing specular reflection. For example... Figure 3 As shown, the scattering effect is best when the reflection intensity of "Region 1" and "Region 2" is the same and the reflection phase difference is 180°, causing the perpendicularly incident electromagnetic wave to deflect and scatter in all directions. Preferably, the phase modulation pattern material is zinc sulfide, and the square block pattern has a side length of 16 μm and 18 μm and a height of 1800 nm.

[0060] In practice, a multilayer thin film structure of photonic crystal is first deposited on the substrate surface using electron beam evaporation, and then a 1800 nm thick zinc sulfide film is deposited on its surface. Finally, the zinc sulfide film is patterned through photolithography and etching processes to obtain the corresponding phase modulation pattern structure.

[0061] The following are specific examples:

[0062] Example 1

[0063] In this embodiment, the Ge thickness in the photonic crystal multilayer thin film structure is 662.5 nm, the ZnS thickness is 1204.5 nm, and the stacking period number is 4. The transmission characteristic curve of the photonic crystal multilayer thin film structure is shown below. Figure 2 As shown, the structure achieves high average specular reflectivity and low emissivity in the 8-14 μm wavelength range. The ZnS square blocks in the phase-tuned pattern structure have a side length of 16 μm and a height of 1800 nm. Figure 3 The reflection spectra of region 1 (without the ZnS phase modulation pattern at the top) and region 2 (with the ZnS phase modulation pattern at the top) and the reflection phase comparison diagram of the two are shown. It can be seen that the reflection intensity of the two regions for the same incident wavelength is close, and the reflection phase difference is close to 180° (π), indicating that the scattering effect is the best at this time. Figure 4 The simulated infrared transmission spectrum of the scattering photonic crystal thin film structure for infrared-laser stealth provided in Embodiment 1 of this invention (8-14 μm) shows that the specular reflectivity is below 0.2 at most wavelengths, with an average specular reflectivity of 0.16 at 8-14 μm; the average transmittance at 8-14 μm is below 0.1, indicating an emissivity below 0.1. Simulation results show that 84% of the incident energy is converted into scattering by specular reflection, thus the structure possesses both low specular reflectivity and low emissivity.

[0064] Figure 5 The image shows a 10.6 μm laser scattering pattern of a scattering photonic crystal thin film structure for infrared-laser stealth provided in Embodiment 1 of the present invention. It can be qualitatively seen from the image that the specular reflection intensity of the 10.6 μm laser is very weak, and most of the incident energy is reflected in all directions in the form of scattering. Therefore, the laser specular echo signal is reduced, and laser stealth can be achieved.

[0065] Figure 6 The graphs show the infrared emissivity as a function of surface temperature for three materials: a high-emissivity material, a traditional specular photonic crystal thin film, and a scattering photonic crystal thin film, all under the condition of an external radiation source at 50°C. (Comparison) Figure 6 (a) and Figure 6 As shown in (b), when there is an external radiation source and the target surface temperature is in the low-temperature range of 20-80℃, the radiative output of the traditional mirror photonic crystal film is actually higher than that of the ideal blackbody material. At this time, the traditional mirror photonic crystal film does not have infrared stealth effect. When the surface temperature is higher than 80℃, the radiative output of the traditional photonic crystal film is lower than that of the ideal blackbody material, and it has infrared stealth capability. Figure 6Figure (c) shows the overall infrared radiation characteristics of the scattering photonic crystal thin film structure for infrared-laser stealth provided in Embodiment 1 of the present invention as a function of surface temperature. The figure shows that when the surface temperature exceeds 35 °C, the radiative exitance of the scattering photonic crystal thin film is lower than that of an ideal blackbody material, thus possessing infrared stealth capabilities. Compared to traditional specular photonic crystals, it extends the application temperature range by 45 °C. Simulation results demonstrate that in the presence of an external radiation source, strong scattering can reflect less external radiation energy, effectively suppressing external thermal radiation reflection compared to strong specular reflection. Under the condition that the target surface temperature is not lower than 35 °C, it can exhibit lower infrared radiation than an ideal blackbody at the same temperature, achieving infrared stealth.

[0066] Figure 7 The 2-18 GHz microwave transmission spectrum of the scattering photonic crystal thin film structure for infrared-laser stealth provided in Embodiment 1 of the present invention shows that the average radar wave transmittance of the thin film structure in the 2-18 GHz range is 0.997 (very close to 1), which demonstrates perfect transmission of radar waves. This is beneficial for compatibility with lower-layer microwave stealth, thereby achieving multi-spectral stealth.

[0067] Example 2

[0068] In this embodiment, the Ge thickness in the photonic crystal multilayer thin film structure is 662.5 nm, the ZnS thickness is 1204.5 nm, and the stacking period is 4. The ZnS square blocks in the phase modulation pattern structure have a side length of 18 μm and a height of 1800 nm. Figure 8 The infrared 8-14 μm simulated transmission spectrum of the scattering photonic crystal thin film structure for infrared-laser stealth provided in Embodiment 2 of the present invention shows that the average specular reflectivity of 8-14 μm is 0.23 and the average transmittance is also less than 0.1, indicating that the emissivity is less than 0.1 and most of the incident energy is scattered back.

[0069] Figure 9 The image shows a 10.6 μm laser scattering pattern of a scattering photonic crystal thin film structure for infrared-laser stealth provided in Embodiment 2 of the present invention. As can be seen from the image, the specular reflection intensity of the 10.6 μm laser is also low, and most of the energy is reflected in all directions in the form of scattering. Therefore, the specular echo signal of the laser is reduced, and laser stealth can be achieved.

[0070] Figure 10The graph shows the overall infrared radiation characteristics of the scattering photonic crystal thin film structure for infrared-laser stealth provided in Embodiment 2 of the present invention against surface temperature. Calculation results show that, in the presence of an external radiation source, when the surface temperature exceeds 38 °C, the radiative exitance of the scattering photonic crystal thin film is lower than that of an ideal blackbody material, thus exhibiting infrared stealth capability. This indicates that strong scattering, compared to strong specular reflection, can effectively suppress external thermal radiation reflection, achieving infrared stealth even at relatively low target surface temperatures.

[0071] Figure 11 The image shows the infrared radiation test result of a scattering photonic crystal thin film prepared according to the parameters of Example 2 of the present invention. Figure 11 (a) in the figure is the infrared radiation diagram under the condition that the surface temperature is 45°C and there is no external radiation source. Figure 11 (b) shows the infrared radiation pattern under the condition of a surface temperature of 45°C and an external radiation source of 80°C. When there is no external heat source, compared to the radiation temperature of 41.3°C for the tape (with an emissivity close to a blackbody), the radiation temperature of the scattering photonic crystal is 24.2°C, and the radiation temperature of the mirror photonic crystal is 20.6°C; both types of photonic crystal films exhibit lower radiation temperatures. Figure 11 As shown in (b), when irradiated by an external heat source at a temperature of 80°C (the black dashed box represents the area irradiated by the external heat source), the radiation temperature of the scattering photonic crystal is 40.8°C, the radiation temperature of the mirror photonic crystal increases to 87.4°C, and the radiation temperature of the tape is 44.5°C. At this time, the scattering photonic crystal exhibits the lowest radiation temperature, indicating that the strong scattering characteristics of the surface can effectively suppress the strong mirror reflection of the surface to the external heat radiation source under low temperature conditions.

[0072] This invention utilizes a photonic crystal all-dielectric material system. Its overall low conductivity ensures that when applied to radar-absorbing materials, it does not impede radar wave transmission, facilitating multi-spectral stealth. Infrared-laser stealth is achieved by converting the strong specular reflection of the photonic crystal thin film into strong scattering, exhibiting low emission (emissivity less than 0.1) in the 8-14 μm infrared band, low specular reflection (average specular reflectivity less than 0.25) in the 8-14 μm infrared band, and low specular reflection (spectral reflectivity less than 0.1) in the 10.6 μm laser band. This avoids the excessively high requirements for film thickness precision in traditional photonic crystal thin film photonic localization designs for laser stealth. Furthermore, the strong scattering characteristics effectively suppress strong specular reflection from external heat sources at lower temperatures, while the film itself remains in a low-emissivity state. Therefore, infrared stealth can be achieved at surface temperatures of 35 °C and above.

[0073] The above embodiments are merely examples. For instance, the side length and height of the square can be flexibly adjusted according to actual needs (for example, the side length can be any value between 8 and 28 μm, and the height can be any value between 1500 and 2500 nm). Different side lengths of the square will result in different angles (scattering angles) between the scattered beam and the vertical direction, and different heights will result in different scattering efficiencies. These can be flexibly adjusted according to actual needs.

[0074] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A radar-transparent infrared-laser stealth film, characterized in that, From bottom to top, the structure includes a substrate, a multilayer thin-film photonic crystal structure, and a patterned top surface, all made of dielectric materials to avoid affecting radar wave transmission. The photonic crystal multilayer thin film structure is composed of two transparent dielectric materials with different refractive indices in the infrared band, stacked alternately. The patterned structure on the top surface uses a shape that can cover the entire plane as a repeating unit. The repeating units are covered on the top surface. At the same time, any two repeating units that share a side use the top surface material in one case and not in the other case, thus forming a patterned structure to achieve surface phase control. By utilizing the constructive interference effect of the photonic crystal multilayer thin film structure on incident waves with wavelengths near a preset target wavelength, and in conjunction with the patterned top surface structure, the wavefront of the reflected wave can be modulated to reduce specular reflection in the vertical direction; the preset target wavelength is the pre-selected center wavelength of the infrared band or the center wavelength of the laser.

2. The radar-transparent infrared-laser stealth film as described in claim 1, characterized in that, In the aforementioned photonic crystal multilayer thin film structure, the refractive index of the component with the higher refractive index is denoted as . n H The refractive index of the lower refractive index is denoted as . n L Furthermore, let the thickness of each layer of the structure composed of a higher refractive index material be denoted as . d H The thickness of each layer of the structure, which is composed of a material with a low refractive index, is d L ,but, in, The center wavelength of the infrared band or the center wavelength of the laser is selected in advance; The photonic crystal multilayer thin film structure is used to target wavelengths in... The constructive interference effect of the nearby incident waves, combined with the patterned structure on the top surface, can modulate the wavefront of the reflected wave and reduce specular reflection in the vertical direction.

3. The thin film as described in claim 1, characterized in that, For the aforementioned photonic crystal multilayer thin film structure, the dielectric material with a higher refractive index is selected from germanium, silicon, and tellurium, and the dielectric material with a lower refractive index is selected from zinc sulfide, zinc selenide, magnesium fluoride, and ytterbium fluoride. Furthermore, the imaginary part of the refractive index of both the medium material with a higher refractive index and the medium material with a lower refractive index is 0.

4. The film as described in claim 1, characterized in that, For the aforementioned photonic crystal multilayer thin film structure, the dielectric material with a higher refractive index is germanium (Ge), and the dielectric material with a lower refractive index is zinc sulfide (ZnS).

5. The film as described in claim 4, characterized in that, For the aforementioned photonic crystal multilayer thin film structure The thickness is 8-12 μm, the thickness of a single Ge layer is 500-750 nm, and the thickness of a single ZnS layer is 909-1363 nm.

6. The thin film as described in claim 5, characterized in that, For the aforementioned photonic crystal multilayer thin film structure The thickness is 10.6 μm, the thickness of a single Ge layer is 662.5 nm, and the thickness of a single ZnS layer is 1204.5 nm.

7. The thin film as claimed in claim 1, characterized in that, For the patterned structure on the top surface, the shape that can cover the entire plane is an equilateral triangle, a square, or a regular hexagon.

8. The thin film as claimed in claim 1, characterized in that, For the patterned structure on the top surface, the shape that can cover the entire plane is a square, with a side length of 8-28 μm and a height of 1500-2500 nm.

9. The thin film as described in claim 8, characterized in that, The square has a side length of 16 μm or 18 μm and a height of 1800 nm.

10. The thin film according to claim 1, characterized in that, The refractive index of the top surface material is less than the refractive index of the material with the higher refractive index in the photonic crystal multilayer thin film structure. n H ).

11. The thin film as claimed in claim 10, characterized in that, The top surface material is one of zinc sulfide, zinc selenide, magnesium fluoride, and ytterbium fluoride.

12. The thin film as claimed in claim 10, characterized in that, The top surface material is zinc sulfide.

13. The thin film as claimed in claim 1, characterized in that, The substrate is a rigid substrate or a flexible substrate. The rigid substrate is one or more of quartz (SiO2), sapphire (Al2O3), silicon wafer, and ceramic, while the flexible substrate is one or more of polyimide (PI), polyethylene terephthalate (PET), fiber cloth, and rubber patch.

14. The thin film as claimed in claim 13, characterized in that, The substrate is a flexible polyimide substrate or a rigid quartz substrate.

15. The thin film as claimed in claim 1, characterized in that, The substrate is a substrate material with a smooth surface.

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