Multispectral camouflage infrared wavelength selection film and preparation method thereof

Abstract

The invention provides a multispectral camouflage infrared wavelength selection thin film and a preparation method thereof, and belongs to the technical field of spectral thermal radiation management, and the preparation method comprises the following steps: screening a material with directional emission in a wave band of 8-14 microns as a directional emission layer material according to an optical constant of a thin film material in the wave band of 3-25 microns; a directional emission layer material is combined with a lossless dielectric material and a metal material to construct a cascaded Fabry-Perot resonant cavity structure; according to the arrangement sequence and the optical constant of each layer of film, taking the thickness of each layer of film as an optimization variable, and utilizing an optimization algorithm taking a quality factor function as a judgment basis to carry out iterative calculation to obtain the optimal thickness of each layer of film; and according to the structure of the multi-layer composite film and the optimal thickness of each layer of film, depositing each layer of film material on the substrate by adopting a magnetron sputtering process to prepare the multi-spectral camouflage infrared wavelength selection film. According to the scheme, the optimization efficiency of the film layer is improved, and efficient thermal management is realized while the multispectral camouflage performance is maintained.

Description

Technical Field

[0001] This invention relates to the field of multilayer thin film structure design and broadband spectral thermal radiation management technology, and particularly to a multispectral camouflage infrared wavelength selective thin film and its preparation method. Background Technology

[0002] As infrared detection technology rapidly evolves from single-band detection (such as mid-infrared 3-5 μm (MWIR) and far-infrared 8-14 μm (LWIR)) to multi-spectral band combined detection, higher demands are placed on infrared camouflage capabilities. Traditional camouflage strategies primarily rely on using low-emissivity materials in a single band (such as mid-infrared 3-5 μm or far-infrared 8-14 μm) to conceal targets. However, these methods struggle to achieve comprehensive protection in multi-spectral detection environments. More seriously, low-emissivity designs significantly suppress the target's radiative heat dissipation capacity, leading to heat accumulation and thermal instability, thus increasing the risk of detection during continuous observation.

[0003] In recent years, radiation-cooling films with spectrally selective modulation capabilities have been considered a feasible approach to resolving the aforementioned contradictions, enhancing heat dissipation while achieving infrared camouflage. However, existing research largely focuses on the mid-infrared and far-infrared atmospheric windows, neglecting the potential of the very long-wave infrared (VLWIR, 14-25 μm) band in thermal management. For high-temperature platforms (such as aircraft engine nozzles, at approximately 950 K, and exhaust pipes, at approximately 740 K), the MWIR / LWIR low emissivity strategy is mainly used to suppress radiation signals. However, for relatively low-temperature platforms (such as ship chimneys, at approximately 680 K), how to utilize the VLWIR band to achieve efficient radiation heat dissipation and synergistic control of infrared camouflage remains a lack of systematic research, thus restricting the overall improvement of infrared stealth and heat dissipation performance across the entire wavelength band. Furthermore, the current optimization process of multilayer film structures largely relies on trial and error or local parameter scanning, lacking a unified and operable optical-thermal co-design basis, resulting in low structural optimization efficiency and difficulty in effectively comparing and analyzing results from different studies. Simultaneously, it neglects the challenge of balancing thermal radiation management and mechanical protection.

[0004] Therefore, there is an urgent need to provide a multispectral camouflage infrared wavelength selective thin film and its preparation method. Summary of the Invention

[0005] This invention provides a multispectral camouflage infrared wavelength selective thin film and its preparation method, which can solve the problems of insufficient multispectral camouflage and heat dissipation performance, poor mechanical properties, and low optimization efficiency of multilayer film structure in existing infrared camouflage technologies.

[0006] In a first aspect, the present invention provides a method for preparing a multispectral camouflage infrared wavelength-selective thin film, the method comprising: The optical constants of different thin film materials in the 3-25 μm band were obtained, and thin film materials with directional emission in the 8-14 μm band were selected as directional emission layer materials based on preset screening conditions. The selected directional emission layer material is combined with non-destructive dielectric material and metallic material to construct a cascaded Fabry-Perot resonant cavity structure to form a multilayer composite film structure. Based on the arrangement order and optical constants of the layers in the multilayer composite film structure, the thickness of each layer is used as the optimization variable. An optimization algorithm based on the constructed quality factor function is used for iterative calculation until the quality factor function value meets the convergence condition, thus obtaining the optimal thickness of each layer. The quality factor function is constructed based on the camouflage requirements of different target wavelengths, including 3-5 μm, 5-8 μm, 8-14 μm, and 14-25 μm. Based on the multilayer composite film structure and the optimal thickness of each layer, the multispectral camouflage infrared wavelength selective film is prepared by sequentially depositing each layer of film material on the substrate using a magnetron sputtering process.

[0007] Preferably, the optical constants include the optical constants refractive index and extinction coefficient.

[0008] Preferably, the preset screening conditions are: the intersection of the refractive index curve and the extinction coefficient curve is located in the 8-14μm band, the extinction coefficient tends to be 0 in the 3-5μm band, and the peak value of the extinction coefficient curve is not less than 0.5 in the 14-25μm band.

[0009] Preferably, the material of the directional emission layer is at least one of Al2O3, SiO, SiO2, AlN, or TiO2.

[0010] Preferably, the lossless dielectric material is Ge material, and the cascaded Fabry-Perot resonator structure includes at least two resonator cavities made of Ge material of different thicknesses.

[0011] Preferably, the metallic material is Mo or Ta, used to achieve high emissivity in the 5-8μm band.

[0012] Preferably, the optimal thickness of each film layer is determined by the following method: The thickness of each film layer was used as the optimization variable, and the arrangement order and optical constants of each film layer in the multilayer composite film structure were input into the multiphysics simulation software to iteratively calculate the absorption rate of each film layer at different angles in the 3-25μm band. In each iteration, the quality factor function value is calculated based on the absorption rate of each film at different angles in the 3-25μm band, and the thickness of each film is adjusted in reverse using the quality factor function until the calculated quality factor function value is minimized, so as to output the optimal thickness of each film.

[0013] Preferably, the quality factor function F min It is determined by the following formula: In the formula, A(λ) is the integral difference between the actual emissivity and the target emissivity in the mid-infrared band, 5-8μm band, far-infrared band and ultra-long infrared band within the 3-25μm spectral range; B(λ) is the emissivity weighted value at the center wavelength of the detector; 0.1 and 0.9 are the weighting coefficients for the integral difference between the actual emissivity and the target emissivity and the emissivity weighted value at the center wavelength, respectively; and α(λ) is the actual emissivity at the simulated output wavelength λ.

[0014] Preferably, the process parameters for magnetron sputtering are as follows: sputtering power of 80~130W, applied bias voltage of -110V~-10V, sputtering gas pressure of 0.5~1Pa, sputtering time of 1~10nm / min, and substrate rotation speed of 10~15rad / min.

[0015] Secondly, embodiments of the present invention also provide a multispectral camouflage infrared wavelength selective film, which is prepared by any of the preparation methods described in the first aspect above.

[0016] Preferably, from the incident surface to the substrate, the infrared wavelength selective film sequentially includes a first directional emission region, a first resonant region, a second directional emission region, a selective absorption region, a second resonant region, and a reflective region; wherein: the first directional emission region and the second directional emission region each contain at least two directional emission layers with different refractive indices; the first resonant region and the second resonant region each contain a Fabry-Perot resonant cavity made of Ge; the selective absorption region contains a coupling layer and a metal layer; and the reflective region contains a reflective layer.

[0017] More preferably, from the incident surface to the substrate, the infrared wavelength selective thin film structure is as follows: the first layer is composed of Al2O3 or AlN, with a thickness of 150-250nm or 120-320nm; the second layer is composed of SiO or SiO2, with a thickness of 60-140nm; the third layer is Ge, with a thickness of 550-750nm; the fourth layer is composed of SiO or SiO2, with a thickness of 60-140nm; the fifth layer is composed of TiO2 or Al2O3, with a thickness of 350-550nm or 150-250nm; the sixth layer is ZnS, with a thickness of 50-250nm; the seventh layer is composed of Mo or Ta, with a thickness of 8-12nm or 6-10nm; the eighth layer is Ge, with a thickness of 250-400nm; the ninth layer is TiO2, with a thickness of 200-400nm; and the tenth layer is composed of Ag or Al, with a thickness of 150-250nm.

[0018] Compared with the prior art, the present invention has at least the following beneficial effects: In this invention, materials with directional emission characteristics in the 8-14μm band are first selected as directional emission layers based on the optical constants of the thin film materials. Then, the selected directional emission layer materials are combined with lossless dielectric materials and metal materials to construct a cascaded Fabry-Perot resonator structure. Based on the determined arrangement order and optical constants of the multilayer composite film structure, the thickness of each film layer is used as the optimization variable, and an optimization algorithm based on the quality factor function criterion is used for iterative calculation. This optimization process combines simulation optimization with physical mechanism guidance. By analyzing the resonance conditions of the Fabry-Perot resonator, the arrangement and thickness of key layers are initially determined. During the iterative process, different camouflage requirements in the 3-5μm, 5-8μm, 8-14μm, and 14-25μm bands are comprehensively considered. A multi-objective optimization criterion with a quality factor function as its core is constructed to finely adjust the resonator structure and thickness until convergence conditions are met, thereby obtaining the optimal thickness of each film layer. This method, combining physical mechanism and simulation optimization, not only significantly improves design efficiency but also ensures that the optimization results achieve a balance of multispectral band performance while adhering to optical principles. Finally, magnetron sputtering is used to sequentially deposit each film material on the substrate, resulting in an infrared wavelength selective film that maintains multispectral camouflage performance while achieving efficient thermal management. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 The absorption curve is for an ideal multispectral compatible structure provided in an embodiment of the present invention; wherein the blue curve is atmospheric transmittance, the orange curve is normal incident (0°) emissivity, and the black curve is high-angle (80°) emissivity. Figure 2 A fracture microstructure of a multispectral camouflage infrared wavelength selective thin film provided in an embodiment of the present invention; Figure 3 The present invention provides simulated and measured emissivity curves of a multispectral camouflage infrared wavelength-selective thin film at different angles, as shown in the embodiments of the present invention. Figure 4 An infrared emissivity curve of a multispectral camouflage infrared wavelength-selective film in the 8-14 μm band is provided for an embodiment of the present invention. Figure 5 The thermal radiation camouflage effect of a multispectral camouflage infrared wavelength selective film at different temperatures is shown in the embodiments of the present invention. Figure 6 This invention provides a displacement variation curve of a multispectral camouflage infrared wavelength selective film in different regions under different loading forces, as shown in the embodiment of the invention. Figure 7 This invention provides a diagram showing the hardness and modulus of different regions in a multispectral camouflage infrared wavelength-selective thin film, as part of an embodiment of the invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0022] As mentioned earlier, most existing studies focus on the mid-infrared and far-infrared atmospheric windows, neglecting the potential of the ultra-long-wave infrared band in thermal management. Considering that the ultra-long-wave infrared band is more compatible with the radiation peak region of low-temperature targets and has high emissivity characteristics in non-atmospheric windows, it can provide an additional heat dissipation path for platforms such as ships. However, the relevant design theory and experimental verification are still lacking.

[0023] Therefore, embodiments of the present invention provide a method for preparing a multispectral camouflage infrared wavelength-selective thin film, the method comprising: The optical constants of different thin film materials in the 3-25 μm band were obtained, and thin film materials with directional emission in the 8-14 μm band were selected as directional emission layer materials based on preset screening conditions. The selected directional emission layer material is combined with non-destructive dielectric material and metallic material to construct a cascaded Fabry-Perot resonant cavity structure to form a multilayer composite film structure. Based on the arrangement order and optical constants of each layer in the multilayer composite film structure, the thickness of each layer is used as the optimization variable. An optimization algorithm based on the quality factor function is used for iterative calculation until the quality factor function value meets the convergence condition, thus obtaining the optimal thickness of each layer. The quality factor function is constructed based on the camouflage requirements of different target wavelengths, including 3-5 μm, 5-8 μm, 8-14 μm, and 14-25 μm. Based on the multilayer composite film structure and the optimal thickness of each layer, the multispectral camouflage infrared wavelength selective film is prepared by sequentially depositing each layer of film material on the substrate using a magnetron sputtering process.

[0024] In this embodiment of the invention, materials with directional emission characteristics in the 8-14μm band are first selected as directional emission layers based on the optical constants of the thin film materials. Then, the selected directional emission layer materials are combined with lossless dielectric materials and metal materials to construct a cascaded Fabry-Perot resonator structure. Based on the determined arrangement order and optical constants of the multilayer composite film structure, the thickness of each film layer is used as the optimization variable, and an optimization algorithm based on the quality factor function criterion is used for iterative calculation. This optimization process combines simulation optimization with physical mechanism guidance. By analyzing the resonance conditions of the Fabry-Perot resonator, the arrangement and thickness of key layers are initially determined. During the iterative process, different camouflage requirements in the 3-5μm, 5-8μm, 8-14μm, and 14-25μm bands are comprehensively considered. A multi-objective optimization criterion with a quality factor function as its core is constructed to finely adjust the resonator structure and thickness until convergence conditions are met, thereby obtaining the optimal thickness of each film layer. This method, combining physical mechanism and simulation optimization, not only significantly improves design efficiency but also ensures that the optimization results achieve a balance of multispectral band performance while adhering to optical principles. Finally, magnetron sputtering is used to sequentially deposit each film material on the substrate, resulting in an infrared wavelength selective film that maintains multispectral camouflage performance while achieving efficient thermal management.

[0025] According to some preferred embodiments, the optical constants include the optical constants refractive index and extinction coefficient; the preset screening conditions are: the intersection of the refractive index curve and the extinction coefficient curve is located in the 8-14μm band, the extinction coefficient tends to be 0 in the 3-5μm band, and the peak value of the extinction coefficient curve is not less than 0.5 in the 14-25μm band.

[0026] According to some preferred embodiments, the directional emission layer material is at least one of Al2O3, SiO, SiO2, AlN, or TiO2.

[0027] To achieve the camouflage requirements in the 8-14 μm band, this invention analyzes the optical constants of different thin film materials and sets dual screening conditions based on the refractive index (n) and extinction coefficient (k) of each material. The intersection of the n and k curves is required to be within the 8-14 μm range, utilizing the strong dispersion and absorption characteristics of the material in this region to achieve directional emission at different angles. Simultaneously, k is required to approach 0 within the 3-5 μm range to ensure the low emissivity requirement of this band is not affected, and a high extinction coefficient is required in the 14-25 μm band to guarantee sufficient intrinsic absorption and heat dissipation. Furthermore, in addition to meeting the above optical characteristics, the mechanical properties of the materials are further considered, placing thin film materials with higher mechanical properties on the top layer to ensure the overall structural durability. This quantitative, multi-dimensional screening method not only improves the efficiency and accuracy of thin film material selection but also lays the foundation for the subsequent construction of a Fabry-Perot resonator structure with excellent optical performance and mechanical stability.

[0028] According to some preferred embodiments, the lossless dielectric material is Ge material, and the cascaded Fabry-Perot resonator structure includes at least two resonator cavities composed of Ge materials of different thicknesses; the metallic material is Mo material with a wetting angle greater than 5 μm, used to achieve high emissivity in the 5-8 μm band.

[0029] Considering the synergistic requirements and fabrication feasibility of various bands in multispectral camouflage, in this embodiment of the invention, Ge material is selected as the non-destructive dielectric material, and Mo material is selected as the metallic material. They are then combined with the directional emission layer material obtained above according to their refractive index in a gradient manner to jointly construct a cascaded Fabry-Perot resonant cavity. Mo material has a high absorption rate in the 5-8 μm band, thereby ensuring a high emissivity (emissivity greater than 0.5) in the 5-8 μm band. In addition, the selection of Mo material with a high wetting angle ensures the surface smoothness and compactness during the film formation process, which is beneficial to ensuring the stability of the optical performance of the infrared wavelength selective thin film material and the repeatability of the process.

[0030] According to some preferred embodiments, the optimal thickness of each film layer is determined as follows: The thickness of each film layer was used as the optimization variable, and the arrangement order and optical constants of each film layer in the multilayer composite film structure were input into the multiphysics simulation software to iteratively calculate the absorption rate of each film layer at different angles in the 3-25μm band. In each iteration, the quality factor function value is calculated based on the absorption rate of each film at different angles in the 3-25μm band, and the thickness of each film is adjusted in reverse using the quality factor function until the calculated quality factor function value is minimized, so as to output the optimal thickness of each film.

[0031] In this embodiment of the invention, after determining the directional emission layer material, the non-destructive dielectric material, and the metallic material, in order to achieve multiple objectives—low emissivity in the 3-5 μm band, high directional emissivity in the 8-14 μm band, and high emissivity in the 14-25 μm band—a cascaded Fabry-Perot resonator structure is constructed based on physical mechanisms. This structure possesses wavelength selectivity, angle sensitivity, and broadband response capabilities, enabling the intrinsic properties of the material to be transformed into intelligent infrared camouflage performance. Then, based on this initial structure (including the arrangement order of each film layer and the thickness of key films), a geometric model of the multilayer thin film is established in multiphysics simulation software, and the optical constants (n, ...) of each material layer are accurately set. Given k) and the initial thickness, the emissivity of the multilayer thin film at different angles (e.g., 0°, 30°, 60°, 80°) in the 3-25μm band is simulated and calculated. The emissivity output from each simulation is input into the constructed quality factor function to quantify the gap between it and the target performance. The thickness of each layer is automatically adjusted iteratively through an optimization algorithm to find the optimal combination of thicknesses that minimizes the objective function value, thereby completing the precise design of the thin film structure.

[0032] According to some preferred embodiments, the quality factor function F min It is determined by the following formula: In the formula, such as Figure 1 As shown, A(λ) is the integral difference between the actual emissivity and the target emissivity in the mid-infrared band (3~5μm), RC band (5~8μm), far-infrared band (8-14μm), and ultra-long infrared band (14~25μm) within the 3~25μm spectral range; B(λ) is the emissivity weighted value at the center wavelength of the detector; 0.1 and 0.9 are the weighting coefficients for the integral difference between the actual emissivity and the target emissivity and the emissivity weighted value at the center wavelength, respectively; and α(λ) is the actual emissivity at the simulated output wavelength λ.

[0033] In this embodiment of the invention, based on the camouflage and heat dissipation requirements of different target bands (3-5μm, 5-8μm, 8-14μm, and 14-25μm), a method using the quality factor function F is proposed. minThe optimization method used as the basis for judgment constructs two sub-functions, A(λ) and B(λ). Function B(λ) focuses on two key wavelengths at the detector's center wavelength: mid-wave infrared (4 μm) and long-wave infrared (11 μm), requiring extremely low emissivity to ensure camouflage performance. Function A(λ) ensures that, while meeting camouflage performance requirements, the material achieves high emissivity in non-atmospheric windows (5~8 µm and 14~25 µm), thus enabling efficient radiative heat dissipation. Furthermore, by assigning specific weighting coefficients to functions A(λ) and B(λ) according to the optimization objectives, heat dissipation efficiency can be maximized while prioritizing camouflage performance. Thus, the above quality factor function formula can balance the detector's center wavelength with the total emissivity across different bands, enabling the rapid and precise development of multilayer infrared thermal radiation camouflage films integrating wavelength-selective emission, directional thermal radiation, and mechanical protection functions, simultaneously achieving high-temperature infrared camouflage and excellent mechanical protection performance within a wide 3-25 μm band.

[0034] According to some preferred embodiments, the process parameters of the magnetron sputtering are as follows: sputtering power of 80~130W (e.g., 80W, 90W, 100W, 110W, 120W or 130W), applied bias voltage of -110V~-10V (e.g., -110V, -100V, -80V, -50V, -30V, -20V or -10V), sputtering gas pressure of 0.5~1Pa (e.g., 0.5Pa, 0.6Pa, 0.7Pa, 0.8Pa, 0.9Pa or 1Pa), and sputtering time of 1~10nm / min (e.g., 1nm / min). The speeds are 1.2 nm / min, 1.3 nm / min, 1.4 nm / min, 1.8 nm / min, 2.5 nm / min, 3 nm / min, 4 nm / min, 5 nm / min, 6.6 nm / min, 8 nm / min, 8.5 nm / min, 9 nm / min, or 10 nm / min, and the substrate rotation speed is 10 to 15 rad / min (e.g., 10 rad / min, 11 rad / min, 12 rad / min, 13 rad / min, 14 rad / min, or 15 rad / min).

[0035] The process parameters used in sputtering vary depending on the film material. According to some specific implementation methods, when the film material is Al₂O₃, the target is Al, the sputtering gases are argon and oxygen, the argon flow rate is 25-35 sccm, the oxygen flow rate is 1-1.5 sccm, the sputtering power is 95-105 W, the applied bias voltage is -110 to -90 V, the sputtering pressure is 0.8-1 Pa, the sputtering time is 1-1.5 nm / min, and the substrate rotation speed is 10-15 rad / min. When the film material is SiO, Ge, ZnS, Mo, or Ag, the target is SiO, Ge, ZnS, Mo, or Ag respectively, i.e., the film material and target are the same, the sputtering gas is argon, and the argon flow rate is... For the first sputtering operation, the sputtering flow rate is 25~35 sccm, the sputtering power is 100~120W, the applied bias voltage is -30~-20V, the sputtering gas pressure is 0.5~0.7Pa, the sputtering time is 1.0~8.5nm / min, and the substrate rotation speed is 10~15rad / min. For the second sputtering operation, the target material is SiO2 or Ti, the sputtering gas is argon and oxygen, the argon flow rate is 25~35 sccm, the oxygen flow rate is 1.5~3 sccm, the sputtering power is 120~130W, the applied bias voltage is -35~-25V, the sputtering gas pressure is 0.5~0.7Pa, the sputtering time is 1.0~2.0nm / min, and the substrate rotation speed is 10~15rad / min. Furthermore, considering that most related technologies focus on the optical and thermal properties of infrared wavelength-selective thin films, their mechanical properties and durability are often severely insufficient when facing mechanical erosion such as sand erosion and rain erosion in practical application environments, leading to the easy failure of thermal radiation control materials under harsh conditions. Therefore, in this embodiment of the invention, not only are mechanical properties taken into consideration during the above-mentioned optimization of thin film materials, but also, based on the optimized thin film structure and thickness, a bias voltage is applied during the preparation process of magnetron sputtering, and through the coordinated control of various process parameters, not only can the stress distribution between film layers be optimized and the adhesion between the film and the substrate be improved, but it is also conducive to the formation of a dense and uniform thin film layer with excellent mechanical properties. Ultimately, this effectively realizes the coupling of high-temperature camouflage and mechanical protection of infrared wavelength-selective thin films, ensuring their long-term stability in complex environments.

[0036] This invention also provides a multispectral camouflage infrared wavelength selective thin film obtained by any of the above-described preparation methods.

[0037] According to some preferred embodiments, from the incident surface to the substrate direction, the infrared wavelength selective film sequentially includes a first directional emission region, a first resonant region, a second directional emission region, a selective absorption region, a second resonant region, and a reflective region; wherein: the first directional emission region and the second directional emission region each contain at least two directional emission layers with different refractive indices; the first resonant region and the second resonant region each contain a Fabry-Perot resonant cavity made of Ge; the selective absorption region contains a coupling layer and a metal layer; and the reflective region contains a reflective layer.

[0038] According to some preferred embodiments, the infrared wavelength selective thin film structure, from the incident surface to the substrate, is as follows: The first layer is composed of Al₂O₃ or AlN. When the first layer is Al₂O₃, the thickness is 150-250 nm (e.g., 150 nm, 200 nm, or 250 nm); when the first layer is AlN, the thickness is 120-320 nm (e.g., 120 nm, 150 nm, 180 nm, 200 nm, 220 nm, 250 nm, 280 nm, 300 nm, or 320 nm); the second layer is composed of SiO or SiO₂. The first layer has a thickness of 60-140 nm (e.g., 60 nm, 80 nm, 100 nm, 120 nm, or 140 nm); the second layer is Ge with a thickness of 550-750 nm (e.g., 550 nm, 600 nm, 650 nm, 700 nm, or 750 nm); the third layer is SiO or SiO2 with a thickness of 60-140 nm (e.g., 60 nm, 80 nm, 100 nm, 120 nm, or 140 nm); the fourth layer is TiO2 or Al2O3, and when the fifth layer is TiO2, the thickness is 35 nm. The thickness of the fifth layer is 0-550nm (e.g., 350nm, 400nm, 450nm, 500nm, or 550nm). When the fifth layer is Al2O3, the thickness is 150-250nm (e.g., 150nm, 200nm, or 250nm). The sixth layer is ZnS, with a thickness of 50-250nm (e.g., 50nm, 100nm, 150nm, or 250nm). The seventh layer is composed of Mo or Ta, and when the seventh layer is Mo, the thickness is 8-12nm (e.g., 8nm, 9nm, 10nm, 11nm, or 1...). The thickness of the seventh layer is 6-10 nm when it is Ta (e.g., it can be 6 nm, 7 nm, 8 nm, 9 nm or 10 nm); the eighth layer is Ge with a thickness of 250-400 nm (e.g., it can be 250 nm, 300 nm, 350 nm or 400 nm); the ninth layer is TiO2 with a thickness of 200-400 nm (e.g., it can be 200 nm, 300 nm or 400 nm); the tenth layer is composed of Ag or Al with a thickness of 150-250 nm (e.g., it can be 150 nm, 200 nm or 250 nm).

[0039] In this embodiment of the invention, a cascaded Fabry-Perot resonator structure combined with simulation optimization is used to achieve synergy between camouflage, heat dissipation, and mechanical properties in the obtained multispectral camouflage infrared wavelength selective film. A cascaded resonator structure is constructed using Ge layers of varying thicknesses and directional emission materials. By precisely controlling the optical thickness of each cavity, not only is low emissivity camouflage ensured in the 3-5 μm band, high emissivity heat dissipation in the 14-25 μm band, but also angle-sensitive directional emission in the 8-14 μm band. The Mo and ZnS layers act as selective absorption layers to achieve high emissivity in the 5-8 μm band, and together with the dielectric layer, they form partial reflectors, synergistically ensuring optimized performance in each band. Thus, based on the intrinsic properties of the materials and the synergistic design of the optical structure, a balance between multispectral camouflage, heat dissipation, and mechanical properties is achieved. Meanwhile, by combining magnetron sputtering with bias voltage technology, not only are the excellent optical properties of the thin film ensured, but also the mechanical protection properties of high hardness, strong adhesion and corrosion resistance are achieved, providing a reliable guarantee for the long-term stable operation of the thin film in harsh environments.

[0040] To more clearly illustrate the technical solution and advantages of the present invention, the following examples provide a detailed description of a multispectral camouflage infrared wavelength selective film and its preparation method.

[0041] Example The optimal thin film structure and thickness calculated using the above method, from the incident surface to the substrate, are as follows: the first layer is Al2O3 with a thickness of 200 nm, the second layer is SiO with a thickness of 100 nm, the third layer is Ge with a thickness of 650 nm, the fourth layer is SiO2 with a thickness of 100 nm, the fifth layer is TiO2 with a thickness of 450 nm, the sixth layer is ZnS with a thickness of 50 nm, the seventh layer is Mo with a thickness of 10 nm, the eighth layer is Ge with a thickness of 350 nm, the ninth layer is TiO2 with a thickness of 300 nm, and the tenth layer is Ag with a thickness of 200 nm.

[0042] The Si substrate was cleaned with 99.99% alcohol and ultrasonic cleaning for 15 minutes. Based on the multilayer composite film structure and the thickness of each layer, infrared wavelength selective films were prepared on the Si substrate by magnetron sputtering. The magnetron sputtering process parameters for different film layers are shown in Table 1. Table 1 The fracture microstructure of the infrared wavelength selective thin film prepared above is as follows: Figure 2 As shown, by Figure 2As can be seen, the infrared wavelength selective film prepared in this embodiment exhibits good interlayer bonding and is dense and uniform overall. The radiation performance of this infrared wavelength selective film was tested. Figure 3 As can be seen, this infrared wavelength-selective film exhibits extremely low emissivity (0.07 and 0.15, respectively) in the mid-infrared (4 μm) and long-infrared (11 μm) wavelengths at the detector's center, thus ensuring camouflage performance; high emissivity is achieved in non-atmospheric windows (such as 5.6 μm and 22.5 μm). ).like Figure 4 As shown, the emissivity is >0.8 in the long-wave infrared 8-14μm band and at high angles (75°~85°). Furthermore, as... Figure 5 As shown, in the 3-5 μm band, the surface temperature of the infrared wavelength-selective film is significantly lower than the 500℃ of the heating stage, achieving an all-angle camouflage effect. The infrared wavelength-selective film exhibits directional emission performance in the 8-14 μm band, displaying differentiated thermal characteristics at different observation angles. The surface temperature of the infrared wavelength-selective film at all angles is lower than the 120℃ of the heating stage, exhibiting a directional characteristic of low emission at low angles (<60°) and high emission at high angles (80°). Simultaneously, the mechanical properties of the infrared wavelength-selective film were tested. Figure 6 As can be seen from this, the mechanical properties of the infrared wavelength-selective thin film are uniform across all regions. Figure 7 As can be seen, the overall hardness of the infrared wavelength selective film is 14.8 GPa, which is 48% higher than that of infrared wavelength selective films prepared by traditional processes (evaporation, electroplating, magnetron sputtering or atomic deposition, etc.), effectively realizing the coupling of high-temperature camouflage and mechanical protection.

[0043] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a multispectral camouflage infrared wavelength-selective thin film, characterized in that, The preparation method includes: The optical constants of different thin film materials in the 3-25 μm wavelength range were obtained, and thin film materials with directional emission in the 8-14 μm wavelength range were selected as directional emission layer materials based on preset screening conditions. The optical constants include the refractive index and extinction coefficient. The preset screening conditions are: the intersection of the refractive index curve and the extinction coefficient curve is located in the 8-14 μm wavelength range, the extinction coefficient tends to be 0 in the 3-5 μm wavelength range, and the peak value of the extinction coefficient curve is not less than 0.5 in the 14-25 μm wavelength range. The selected directional emission layer material is combined with non-destructive dielectric material and metallic material to construct a cascaded Fabry-Perot resonant cavity structure to form a multilayer composite film structure. The thickness of each film layer was used as the optimization variable, and the arrangement order and optical constants of each film layer in the multilayer composite film structure were input into the multiphysics simulation software to iteratively calculate the absorption rate of each film layer at different angles in the 3-25μm band. In each iteration, the quality factor function value is calculated based on the absorption rate of each film at different angles in the 3-25μm band, and the thickness of each film is adjusted in reverse by the quality factor function until the calculated quality factor function value is minimized, so as to output the optimal thickness of each film. Wherein, the quality factor function F min It is determined by the following formula: In the formula, A(λ) is the integral difference between the actual emissivity and the target emissivity in the mid-infrared band, 5-8μm band, far-infrared band and ultra-long infrared band within the 3~25μm spectral range; B(λ) is the emissivity weighted value at the center wavelength of the detector; 0.1 and 0.9 are the weighting coefficients of the integral difference between the actual emissivity and the target emissivity and the emissivity weighted value at the center wavelength, respectively; and α(λ) is the actual emissivity at the simulated output wavelength λ. Based on the multilayer composite film structure and the optimal thickness of each film layer, a multispectral camouflage infrared wavelength selective thin film was prepared by sequentially depositing each film layer on the substrate using a magnetron sputtering process. From the incident surface to the substrate, the infrared wavelength selective film sequentially includes a first directional emission region, a first resonant region, a second directional emission region, a selective absorption region, a second resonant region, and a reflective region; wherein: the first directional emission region and the second directional emission region each contain at least two directional emission layers with different refractive indices; the first resonant region and the second resonant region each contain a Fabry-Perot resonant cavity made of Ge; the selective absorption region contains a coupling layer and a metal layer; and the reflective region contains a reflective layer.

2. The preparation method according to claim 1, characterized in that, The directional emission layer material is at least one of Al2O3, SiO, SiO2, AlN, or TiO2.

3. The preparation method according to claim 1, characterized in that, The lossless dielectric material is Ge material, and the cascaded Fabry-Perot resonant cavity structure includes at least two resonant cavities made of Ge material of different thicknesses.

4. The preparation method according to claim 1, characterized in that, The metallic material is Mo or Ta, used to achieve high emissivity in the 5-8μm band.

5. The preparation method according to claim 1, characterized in that, The process parameters for magnetron sputtering are as follows: sputtering power of 80~130W, applied bias voltage of -110V~-10V, sputtering gas pressure of 0.5~1Pa, sputtering time of 1~10nm / min, and substrate rotation speed of 10~15rad / min.

6. A multispectral camouflage infrared wavelength selective thin film, characterized in that, It is prepared by any one of claims 1 to 5.

7. The multispectral camouflage infrared wavelength selective film according to claim 6, characterized in that, From the incident surface to the substrate, the infrared wavelength selective thin film structure is as follows: the first layer is composed of Al2O3 or AlN, with a thickness of 150-250nm or 120-320nm; the second layer is composed of SiO or SiO2, with a thickness of 60-140nm; the third layer is Ge, with a thickness of 550-750nm; the fourth layer is composed of SiO or SiO2, with a thickness of 60-140nm; the fifth layer is composed of TiO2 or Al2O3, with a thickness of 350-550nm or 150-250nm; the sixth layer is ZnS, with a thickness of 50-250nm; the seventh layer is composed of Mo or Ta, with a thickness of 8-12nm or 6-10nm; the eighth layer is Ge, with a thickness of 250-400nm; the ninth layer is TiO2, with a thickness of 200-400nm; and the tenth layer is composed of Ag or Al, with a thickness of 150-250nm.

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