A dual-wave dynamic thermal camouflage structure and its optimization method

Abstract

The present invention belongs to the technical field of thermal camouflage materials, and specifically relates to a dual-wave dynamic thermal camouflage structure and an optimization method thereof, including a long-wave infrared phase change film layer, a dielectric layer, a mid-wave infrared phase change film layer, and a reflective layer that are sequentially stacked on a substrate. The long-wave infrared phase change film layer is a chalcogenide phase change material, the mid-wave infrared phase change film layer is a vanadium oxide volatile phase change material, and the thickness of the dielectric layer is greater than or equal to 0. The present invention can separately achieve the adaptive regulation of mid-wave infrared and long-wave infrared, realize dual-wave dynamic thermal camouflage, and improve the camouflage effect.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermal camouflage materials, and particularly relates to a dual-wave dynamic thermal camouflage structure and an optimization method thereof. Background Art

[0002] In recent years, inspired by the dynamic structural color camouflage of cephalopods and chameleons in response to background color changes, adaptive thermal camouflage has attracted great attention. Since most military weapons are equipped with infrared (IR) detectors, enabling people to observe at night like owls, the demand for thermal camouflage in the military field is extremely urgent to conceal targets in infrared cameras. According to the Stefan-Boltzmann law, the intensity of the mid-infrared (MIR) signal emitted by an object is proportional to the fourth power of the surface emissivity (ε) and the absolute temperature (T). There are two intuitive ways to achieve thermal camouflage by adjusting the temperature and emissivity. Some studies focus on achieving the regulation of the real temperature field, especially using some thermal metamaterials to control local heat conduction, and then realizing "thermal elimination" similar to the method achieved by solving optical scattering. However, the effective material parameters (thermal conductivity, mass density, heat capacity) of thermally conductive metamaterials are not easily adjusted, limiting their performance and applications. With the extensive research on optical metamaterials, it is possible to use micro-nano scale microcavities to achieve the regulation of infrared radiation characteristics, and then achieve thermal "visual" camouflage or deception (the real temperature field remains unchanged).

[0003] Existing thermal imaging devices often perceive the temperature information of an object by receiving the infrared radiation energy from a heat source. Therefore, regulating the infrared radiation characteristics of an object can well achieve the purpose of thermal camouflage. Early thermal camouflage methods used some metal materials to achieve a low emissivity in the entire infrared light wave range. With the intelligence of detection means, this static low-radiation characteristic is instead prone to being exposed in a complex and changeable environment and then being accurately identified. The development of micro-nano optics has made it possible to regulate the infrared emissivity adaptively. Through metamaterials, the infrared emissivity can be regulated, and thus adaptive thermal camouflage can be achieved. Currently, Document 1 "D. Liu, H. Ji, R. Peng, H. Cheng, and C. Zhang. Infrared chameleon-like behavior from VO2(M) thin films prepared by transformation of metastable VO2(B) for adaptive camouflage in both thermal atmospheric windows, Solar Energy Materials and Solar Cells (2018)" discloses a method for regulating the adaptive infrared radiation characteristics of a vanadium dioxide nano-film on a glass substrate. Document 2 "X. Jiang, Z. Zhang, H. Ma, T. Du, M. Luo, D. Liu, and J. Yang. Tunable mid-infrared selective emitter based on inverse design metasurface for infrared stealth with thermal management, Optics Express (2022)" discloses a method for achieving adaptive thermal camouflage in the mid-wave infrared by combining surface plasmon polaritons (SPPs) with a phase change material germanium antimony tellurium alloy. Due to the limitation of the atmospheric transparent window, the working wavelengths of thermal imaging devices are mostly in one of the two working wavelength ranges of mid-wave infrared (3 - 5 μm) and long-wave infrared (8 - 13 μm), especially long-wave infrared. This is because long-wave infrared is closely related to human life, and this wavelength range can best meet the temperature measurement requirements for daily use. In existing research, there have been some thermal camouflage solutions for single-wavelength ranges and two-wavelength ranges.Reference 3, "K. Du, Q. Li, Y. Lyu, J. Ding, Y. Lu, Z. Cheng, and M. Qiu. Control over emissivity of zero-static-power thermal emitters based on phase-changing material GST, Light: Science & Applications (2017)", discloses an adaptive camouflage in the long-wave infrared based on an asymmetric Fabry-Perot microcavity structure of germanium antimony telluride alloy. Reference 4, "M. Li, D. Liu, H. Cheng, L. Peng, M. Zu. Manipulating metals for adaptive thermal camouflage, Science Advances (2020)", discloses a technology for simultaneous adaptive regulation in the mid-wave infrared and long-wave infrared based on manipulable deposition of silver nanoparticles. In addition to adaptive thermal camouflage, this structural design can also achieve some dynamic display functions in the infrared wavelength. In particular, the thermal patterns based on this structure show extremely high similarity under a mid-wave infrared thermal imager and a long-wave infrared thermal imager.

[0004] Although some solutions for thermal camouflage have been proposed in both the mid-wave infrared and long-wave infrared, there are few reports on how to achieve discrete dynamic thermal camouflage in these two bands. The research on this dual-wave dynamic thermal camouflage structure can, on the one hand, solve the problem of multi-band adaptive thermal camouflage, and on the other hand, this dual-wave dynamic thermal camouflage structure is expected to achieve encryption of infrared thermal information and infrared sub-band display technology. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a dual-wave dynamic thermal camouflage structure and its optimization method, which can discretely achieve adaptive regulation in the mid-wave infrared and long-wave infrared, realize dual-wave dynamic thermal camouflage, and improve the camouflage effect.

[0006] An embodiment of the present invention provides a dual-wave dynamic thermal camouflage structure, including a long-wave infrared phase change film layer, a dielectric layer, a mid-wave infrared phase change film layer, and a reflective layer that are sequentially stacked on a substrate. The long-wave infrared phase change film layer is a chalcogenide phase change material, the mid-wave infrared phase change film layer is a vanadium oxide volatile phase change material, and the thickness of the dielectric layer is greater than or equal to 0.

[0007] When the thickness of the dielectric layer in the present invention is equal to 0, that is, there is no dielectric layer, and there are only a long-wave infrared phase change film layer, a mid-wave infrared phase change film layer, and a reflective layer.

[0008] The two waves in the present invention are mid-wave infrared (3 - 5 μm) and long-wave infrared (8 - 13 μm). The substrate includes, but is not limited to, materials such as organic polymer materials, silicon wafers, quartz substrates, metal surfaces, etc. The long-wave infrared phase change film layer, dielectric layer, mid-wave infrared phase change film layer, and reflective layer of the present invention can be deposited on the substrate material by methods such as magnetron sputtering, electron beam evaporation, pulsed laser deposition, etc.

[0009] In the embodiments of the present invention, the chalcogenide phase change material is an alloy material containing at least one chalcogenide element, mostly composed of some semiconductor elements in Groups 13 - 16 of the periodic table, mainly divided into four categories: binary, ternary, quaternary, and quinary alloys. Binary alloys mainly include: germanium telluride and antimony telluride; ternary alloys mainly include germanium antimony telluride and silicon antimony telluride, etc.; quaternary alloys mainly include nitrogen or oxygen-doped germanium antimony telluride and silver indium antimony telluride, etc.; there are only a few quinary alloys such as germanium or vanadium-doped silver indium antimony telluride. Preferably, it is Ge2Sb2Te5, Ge3Sb2Te6, Ge2Sb2Se4Te1, Ge x Sb 1–x or GeTe.

[0010] In the embodiments of the present invention, the vanadium oxide-based phase change material is a vanadium oxide with thermally induced phase change properties, such as VO2 or V2O3, and doped vanadium oxides, such as W or Mo-doped vanadium oxides. Preferably, it is W or Mo-doped VO2, and more preferably VO2, W x V 1-x O2 or Mo x V 1-x O2.

[0011] In the embodiments of the present invention, the dielectric layer is an infrared dielectric material, preferably ZnS, ZnSe, Ge, SiO2, Si, or BaF2.

[0012] In the embodiments of the present invention, the reflective layer is a metal material, such as metal materials like gold, silver, copper, chromium, tungsten, titanium, etc., for reflecting electromagnetic waves that may be received.

[0013] Preferably, the material of the long-wave infrared phase change film layer A is Ge2Sb2Te5, and the thickness h1 is preferably 100 nm; the material of the dielectric layer B is germanium, and the thickness h2 is preferably 50 nm; the material of the mid-wave infrared phase change film layer C is vanadium dioxide, and the thickness h3 is preferably 300 nm. The material of the reflective layer D is gold, with the chemical formula Au, and the thickness h4 is 100 nm; the material of the substrate is silicon, with the chemical formula Si.

[0014] The present invention is based on the following principles: In the case of light waves perpendicularly incident on the surface, the long-wave infrared phase change film layer A is used to solve the problem of dynamic regulation of long-wave infrared, and provides an asymmetric Fabry-Perot (F-P) resonant microcavity for long-wave infrared. The intermediate dielectric layer B is used to achieve the phase matching of light waves, and thus better achieve the resonant enhancement of long-wave infrared and mid-wave infrared. The mid-wave infrared phase change film layer C is used to solve the problem of dynamic regulation of mid-wave infrared, and provides a thin film microcavity matching mid-wave infrared, thereby generating a local potential well field. The material of the reflective layer D is a metal material, which is used to reflect the infrared electromagnetic waves that may be received.

[0015] An embodiment of the present invention provides an optimization method for the dual-wave dynamic thermal camouflage structure, including the following steps:

[0016] Determine the initial thickness ranges of the long-wave infrared phase change film layer, the dielectric layer, and the mid-wave infrared phase change film layer; find the optimal spectral characteristic curve within the initial thickness ranges; based on the optimal spectral characteristic curve, determine the optimal thickness values.

[0017] The initial thickness ranges of the present invention can be adjusted according to the amount of calculation. For example, it is set that the thickness h1 of the long-wave infrared phase change film layer A is 10 nm to 100 nm, the thickness h2 of the dielectric layer B is 0 nm to 3000 nm, the thickness h3 of the mid-wave infrared phase change film layer C is 10 nm to 1000 nm, and the thickness h4 of the reflective layer D is 100 nm.

[0018] In an embodiment of the present invention, the method for determining the optimal spectral characteristic curve within the initial thickness ranges is as follows: By using the transfer matrix method, traverse all values within the initial thickness ranges, and calculate the curve of the variation law of the emissivity with the wavelength within the mid-wave infrared window wavelength and long-wave infrared window wavelength ranges, which is the spectral characteristic curve; determine the spectral characteristic curve that meets the emissivity requirements as the optimal spectral characteristic curve.

[0019] The calculation method of the emissivity is as follows: Use the transfer matrix to calculate the electric field of the multi-layer thin film structure to obtain the admittance Y parameter related to the wavelength.

[0020] Calculate the complex reflection coefficient

[0021] The reflectivity R(λ) = γ(λ) × γ * (λ), γ * (λ) is the conjugate of the complex reflection coefficient.

[0022] Since there is a reflective layer at the bottom of the multi-layer thin film, the transmittance can be ignored, and the absorptance A(λ) = 1 - R(λ).

[0023] According to Kirchhoff's effect, the absorptance A(λ) of an object is equal to the emissivity ε(λ).

[0024] In the embodiments of the present invention, the emissivity requirement is that the emissivity satisfies the following optimization model:

[0025]

[0026] λ1 is the starting wavelength of the mid-wave infrared window wavelength, generally 3μm; λ2 is the ending wavelength of the mid-wave infrared window wavelength, generally 5μm; λ3 is the starting wavelength of the long-wave infrared window wavelength, generally 8μm; λ4 is the ending wavelength of the long-wave infrared window wavelength, generally 13μm;

[0027] h1 is the thickness of the long-wave infrared phase change film layer A, h2 is the thickness of the dielectric layer B, and h3 is the thickness of the mid-wave infrared phase change film layer C;

[0028] where ε am , ε ad , ε cd respectively represent the spectral emissivities of three different states of the phase change multi-layer thin film. That is, the first item of the subscript represents the state of the long-wave infrared thin film, the subscript a corresponds to the amorphous (initial) state, and the subscript c corresponds to the crystalline state; the second item of the subscript represents the state of the mid-wave infrared thin film, the subscript d corresponds to the dielectric-like (initial) state, and the subscript m corresponds to the metal-like state.

[0029] Specifically, ε am is the emissivity when the long-wave infrared phase change film layer is in the amorphous state and the mid-wave infrared phase change film layer is in the metal-like state, ε ad is the emissivity when the long-wave infrared phase change film layer is in the amorphous state and the mid-wave infrared phase change film layer is in the dielectric-like state, and ε cd is the emissivity when the long-wave infrared phase change film layer is in the crystalline state and the mid-wave infrared phase change film layer is in the dielectric-like state.

[0030] The beneficial effects of the present invention are that the two types of phase change materials of the present invention are both solids, and their phase change states can be induced and regulated by external electrical, optical, thermal and other means. During the phase change process, the characteristics of the long-wave infrared phase change film layer change from a mid-infrared transparent medium to a mid-infrared low-loss material, thereby realizing the regulation of the mid-infrared absorption characteristics; the characteristics of the mid-wave infrared phase change film layer change from a mid-infrared transparent medium to a mid-infrared high-loss material. When the temperature of the material is higher than the phase change temperature, for example, when the temperature of VO2 is much higher than the phase change temperature (68°C), its mid-infrared characteristics are similar to those of a metal thin film. The characteristic differences between the two materials enable them to perform discrete continuous modulation for different bands of mid-infrared (such as mid-wave infrared and long-wave infrared).

[0031] The present invention can achieve a low emissivity similar to that of traditional static thermal camouflage materials in the initial state (the initial state generally refers to the ad state where the dual-wave infrared emissivity is lower than 0.1). By separately regulating the states of the two phase-change film layers, the medium-wave infrared and long-wave infrared radiation characteristics of the film structure can be separately regulated, providing a new solution for dual-wave dynamic thermal camouflage, infrared encryption and infrared discrete display.

[0032] After the optimization method of the present invention, the thickness of each film layer can be adaptively adjusted through the photoelectric method to adjust the emissivity of the thermal camouflage structure, thereby representing a consistent temperature with the background environment, so that the thermal information display capability is significantly weakened, thermal information camouflage is achieved, and the camouflage effect is improved. The designed stealth material meets the needs of large-area preparation and processing, and reduces costs as much as possible. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A structural diagram of a dual-wave dynamic thermal camouflage structure according to an embodiment of the present invention;

[0034] Figure 2 This is a numerical simulation structure diagram of a dual-wave dynamic thermal camouflage structure according to an embodiment of the present invention;

[0035] Figure 3 It is a dual-wave dynamic thermal camouflage structure optimization flow chart of an embodiment of the present invention;

[0036] Figure 4 This is an infrared absorption spectrum of the dual-wave dynamic thermal camouflage structure of a preferred embodiment of the present invention obtained through electromagnetic simulation.

[0037] Figure 5 This is the infrared absorption spectrum when the thickness of the long-wave infrared phase change film layer A, the dielectric layer B, and the medium-wave infrared phase change film layer C are all 50 nm.

[0038] Figure 6 This is the infrared absorption spectrum of the dual-wave dynamic thermal camouflage structure of Example 3.

[0039] Figure 7 This is the infrared absorption spectrum of the dual-wave dynamic thermal camouflage structure of Example 4. DETAILED DESCRIPTION

[0040] The technical solution of the present invention is further specifically described below in conjunction with the accompanying drawings and specific embodiments.

[0041] Example 1

[0042] See also Figure 1-2 The dual-wave dynamic thermal camouflage structure based on phase change material provided in this embodiment includes a long-wave infrared phase change film layer A, a dielectric layer B, a medium-wave infrared phase change film layer C, and a reflective layer D stacked in sequence from top to bottom.

[0043] The multi-layer thin film can be deposited into various different patterns and structures, depending on the shape of the substrate. Here, we demonstrate a multi-layer thin film structure of phase change material on a disc substrate. In practice, the surface of the multi-layer thin film can extend infinitely in the direction perpendicular to the incident direction of light waves (x direction or y direction).

[0044] The material of the long-wave infrared phase change film layer A is Ge2Sb2Te5, and the thickness h1 is 100 nm: the material of the dielectric layer B is germanium, and the thickness h2 is 50 nm; the material of the mid-wave infrared phase change film layer C is vanadium dioxide, and the thickness h3 is 300 nm, and the material of the reflective layer D is gold, with the chemical formula Au and the thickness h4 is 100 nm: the material of the substrate is silicon, with the chemical formula Si.

[0045] Example 2

[0046] Please refer to Figure 3 , in order to meet the requirements of discrete design absorption frequency bands for mid-wave infrared and long-wave infrared, the optimization method proposes a method and process for optimizing design variables, so as to achieve the goal of enhancing the selectivity of the absorption frequency band.

[0047] Step 1: Select the substrate material and size, and set the electromagnetic numerical simulation environment;

[0048] In this embodiment, the selected substrate material is a silicon substrate, and the size can extend infinitely in the x-axis direction and the positive direction of the z-axis.

[0049] The incident light wave is set as a plane wave polarized in P polarization, incident on the surface of the thin film along the positive direction of the z-axis, and the multi-layer thin film structure extends infinitely along the x-axis.

[0050] The propagation matrix method is used to calculate the electric field of the multi-layer thin film structure, and the admittance Y parameter related to the wavelength is obtained, and the complex reflection coefficient is calculated

[0051] Reflectivity R(λ) = γ(λ) × γ *( λ), γ * (λ) is the conjugate of the complex reflection coefficient.

[0052] Since there is a metal thin film at the bottom layer of the multi-layer thin film, the transmittance can be ignored, and the absorptance A(λ) = 1 - R(λ),

[0053] According to Kirchhoff's effect, the emissivity ε(λ) of the object = A(λ) = 1 - R(λ),.

[0054] Step 2: Define the initial design domain of the multi-layer thin film;

[0055] Among them, the long-wave infrared phase-change film layer A is a phase-change material germanium antimony tellurium alloy with the chemical formula Ge2Sb2Te5, and the thickness range is 0 ≤ h1 ≤ 100 nm; the intermediate transition layer B is an infrared dielectric material germanium with the chemical formula Ge, and the thickness range is 0 ≤ h2 ≤ 2000 nm; the mid-wave infrared phase-change film layer C is a volatile phase-change material vanadium dioxide, and the thickness range is 0 ≤ h3 ≤ 300 nm; the metal reflective layer D is gold with the chemical formula Au and the thickness h4 = 100 nm.

[0056] Step 3: Fit and optimize the model, and select the optimal multi-layer film structure

[0057] During the implementation process, the three states of the multi-layer film are quantitatively subjected to electromagnetic numerical simulations respectively, which are: the Ge2Sb2Te5 material is in the amorphous state (a), and the vanadium dioxide is in the metal-like state (m), which is called the am state; the Ge2Sb2Te5 material is in the amorphous state (a), and the vanadium dioxide is in the dielectric-like state (d), which is called the ad state; the Ge2Sb2Te5 material is in the crystalline state (c), and the vanadium dioxide is in the dielectric-like state (d), which is called the cd state.

[0058] Using the transfer matrix method and the calculation method of emissivity, by traversing the possible thicknesses (h1, h2, h3) of the entire design variables, all possible mid-infrared emission spectral parameters in the initial design domain are obtained.

[0059] Give the design optimization model:

[0060]

[0061] Among them, λ1 and λ2 respectively represent the starting and ending wavelengths of the mid-wave infrared window wavelengths, which are set to 3 μm and 5 μm respectively, and λ3 and λ4 respectively represent the starting and ending wavelengths of the long-wave infrared window wavelengths, which are set to 8 μm and 13 μm respectively. Search for the optimal structure that meets the above emissivity requirements in the initial design domain.

[0062] Step 4: Obtain the optimal multi-layer film structure based on the phase-change material

[0063] The optimal multi-layer film structure based on the phase-change material is as Figure 1 、 2 shown. The long-wave infrared phase-change film layer A is a germanium antimony tellurium alloy with the chemical formula Ge2Sb2Te5 and the thickness h1 = 100 nm; the intermediate transition layer B is an infrared dielectric material germanium with the chemical formula Ge and the thickness h2 = 50 nm; the mid-wave infrared phase-change film layer C is vanadium dioxide with the chemical formula VO2 and the thickness h3 = 300 nm; the metal reflective layer D is gold with the chemical formula Au and the thickness h4 = 100 nm; the substrate material is silicon with the chemical formula Si.

[0064] AsFigure 4 As shown, from the preferred multi-layer thin film design results, it can be seen that the gray solid line, black solid line, and black dashed line respectively represent the mid-infrared spectral curves of the multi-layer thin film based on the phase change material when it is in the cd, am, and ad states.

[0065] When the thin film is in the am state, it is a mid-wave infrared emitter with an average emissivity of 0.9, and some thermal information can be displayed in the mid-wave infrared; while in the long-wave infrared spectrum, the average emissivity is 0.3, and the thermal information display ability is weak.

[0066] When the thin film is in the cd state, the average emissivity in the long-wave infrared is 0.4, and the emissivity at the absorption peak is 0.7, enabling color display in the long-wave infrared; while in the mid-wave infrared spectrum, the average emissivity is less than 0.1, without the ability to display thermal information, and thermal information shielding in the mid-wave infrared can be achieved.

[0067] When the thin film is in the ad state, its average emissivity in both the dual-wave infrared is less than 0.1, and these two performance indicators can be comparable to the low emissivity of traditional thermal camouflage films.

[0068] In addition, the emissivity of the proposed thin film structure can be continuously adjusted by optoelectronic methods, thus covering most of the average emissivity ranges in the mid-wave and long-wave infrared, that is, the adjustable range of the average emissivity in the mid-wave infrared is 0.1 - 0.9 (when the thin film changes from the ad state to the am state), and the adjustable range of the average emissivity in the long-wave infrared is 0.1 - 0.4 (when the thin film changes from the ad state to the cd state).

[0069] As Figure 5 shown, to illustrate the optimization of the multi-layer thin film structure performance by the optimization model, we give a set of results of an unselected thin film thickness combination for comparison, and the thicknesses of its three layers A, B, and C are all 50 nm. It can be seen from the results that such a multi-layer thin film structure does not have the ability of dynamic thermal camouflage for dual-wave infrared. Especially in the long-wave infrared, all three states show low emission characteristics (the emissivity is less than 0.1). Although this characteristic similar to traditional thermal camouflage has a strong shielding effect on the thermal information of the object, it is easy to expose the target due to the thermal information contrast with the background environment.

[0070] Example 3

[0071] Please refer to Figure 3 , to meet the requirements of discrete design of absorption frequency bands for mid-wave infrared and long-wave infrared, the design method proposes a method and process for optimizing design variables, and further achieves the goal of enhancing the selectivity of the absorption frequency band. When there is no intermediate dielectric layer, this method can also obtain a preferred thin film structure.

[0072] Step 1: Select the substrate material and size, and set the electromagnetic numerical simulation environment;

[0073] In this embodiment, the selected substrate material is a silicon substrate, which can extend infinitely in the x-axis direction and the positive z-axis direction.

[0074] The incident light wave is set as a P-polarized plane wave, which is incident on the film surface along the positive z-axis direction, and the multi-layer film structure extends infinitely along the x-axis.

[0075] The propagation matrix method is used to calculate the electric field of the multi-layer film structure, and the admittance Y parameter related to the wavelength is obtained, and the reflection coefficient is calculated

[0076] The reflectance R(λ) = γ(λ) × γ * (λ), γ * (λ) is the conjugate of the complex reflection coefficient.

[0077] Since there is a metal film at the bottom layer of the multi-layer film, the transmittance can be ignored, and the absorptance A(λ) = 1 - R(λ),

[0078] According to Kirchhoff's effect, the emissivity ε(λ) of the object = A(λ) = 1 - R(λ),.

[0079] Step 2: Define the initial design domain of the multi-layer film;

[0080] Among them, the long-wave infrared phase change film layer A is a phase change material germanium antimony tellurium alloy with the chemical formula Ge2Sb2Te5, and the thickness range is 0 ≤ h1 ≤ 800 nm; the mid-wave infrared phase change film layer C is a volatile phase change material vanadium dioxide, and the thickness range is 0 ≤ h3 ≤ 1000 nm; the metal reflective layer D is gold with the chemical formula Au and the thickness is h4 = 100 nm. Since there is no intermediate dielectric layer B, h2 = 0 nm.

[0081] Step 3: Fit the optimization model and select the optimal multi-layer film structure

[0082] During the implementation process, the three states of the multi-layer film are quantitatively subjected to electromagnetic numerical simulation respectively, namely: the Ge2Sb2Te5 material is in the amorphous state (a), and the vanadium dioxide is in the metal-like state (m), which is called the am state; the Ge2Sb2Te5 material is in the amorphous state (a), and the vanadium dioxide is in the dielectric-like state (d), which is called the ad state; the Ge2Sb2Te5 material is in the crystalline state (c), and the vanadium dioxide is in the dielectric-like state (d), which is called the cd state.

[0083] Using the transfer matrix method and the calculation method of emissivity, by traversing all possible thicknesses (h1, h2, h3) of the design variables, all possible mid-infrared emission spectral parameters in the initial design domain are obtained.

[0084] Give the design optimization model:

[0085]

[0086] Among them, λ1 and λ2 respectively represent the starting and ending wavelengths of the mid-wave infrared window wavelength, which are set to 3 μm and 5 μm respectively, and λ3 and λ4 respectively represent the starting and ending wavelengths of the long-wave infrared window wavelength, which are set to 8 μm and 13 μm respectively. Search for an optimal structure that meets the above emissivity requirements in the initial design domain.

[0087] Step 4: Obtain an optimal multi-layer thin film structure based on phase change materials

[0088] In the optimal multi-layer thin film structure based on phase change materials, the long-wave infrared phase change film layer A is a germanium antimony tellurium alloy with the chemical formula Ge2Sb2Te5 and a thickness h1 = 170 nm; the mid-wave infrared phase change film layer C is vanadium dioxide with the chemical formula VO2 and a thickness h3 = 410 nm; the metal reflection layer D is gold with the chemical formula Au and a thickness h4 = 100 nm; the substrate material is silicon with the chemical formula Si.

[0089] As Figure 6 shown, the thermal emissivity of the proposed thin film structure has an adjustable range of 0.01 - 0.88 in the mid-wave infrared (when the thin film changes from the ad state to the am state), and an adjustable range of 0.09 - 0.61 in the long-wave infrared (when the thin film changes from the ad state to the cd state).

[0090] Example 4

[0091] Please refer to Figure 3 , in order to meet the requirements for discrete design absorption bands in mid-wave infrared and long-wave infrared, the design method proposes a method and process for optimizing design variables, thereby achieving the goal of enhancing the selectivity of the absorption band. In the other material combinations described, this optimization method can also obtain an optimal dual-wave dynamic thermal camouflage thin film structure.

[0092] Step 1: Select the substrate material and size, and set the electromagnetic numerical simulation environment;

[0093] In this example, the selected substrate material is a silicon substrate, and the size can extend infinitely in the x-axis direction and the positive z-axis direction.

[0094] The incident light wave is set as a P-polarized plane wave, incident on the surface of the thin film along the positive z-axis, and the multi-layer thin film structure extends infinitely along the x-axis.

[0095] Use the propagation matrix method to calculate the electric field of the multi-layer thin film structure, obtain the admittance Y parameter related to the wavelength, and calculate the reflection coefficient

[0096] Reflectivity R(λ) = γ(λ) × γ * (λ), where γ * (λ) is the conjugate of the complex reflection coefficient.

[0097] Since there is a metal thin film at the bottom layer of the multi-layer thin film, the transmittance can be ignored, and the absorptance A(λ) = 1 - R(λ).

[0098] According to Kirchhoff's effect, the emissivity ε(λ) of the object = A(λ) = 1 - R(λ).

[0099] Step 2: Define the initial design domain of the multi-layer thin film;

[0100] Among them, the long-wave infrared phase change film layer A is a phase change material germanium antimony tellurium alloy with the chemical formula Ge2Sb2Te5, and the thickness range is 0 ≤ h1 ≤ 100 nm; the intermediate transition layer B is an infrared dielectric material zinc sulfide with the chemical formula ZnS, and the thickness range is 0 ≤ h2 ≤ 2000 nm; the mid-wave infrared phase change film layer C is a vanadium dioxide which is a volatile phase change material, and the thickness range is 0 ≤ h3 ≤ 1000 nm; the metal reflection layer D is gold with the chemical formula Au and the thickness h4 = 100 nm.

[0101] Step 3: Fit the optimization model and select the optimal multi-layer thin film structure

[0102] During the implementation process, the three states of the multi-layer thin film are quantitatively subjected to electromagnetic numerical simulations respectively, namely: the Ge2Sb2Te5 material is in the amorphous state (a), and the vanadium dioxide is in the metal-like state (m), which is called the am state; the Ge2Sb2Te5 material is in the amorphous state (a), and the vanadium dioxide is in the dielectric-like state (d), which is called the ad state; the Ge2Sb2Te5 material is in the crystalline state (c), and the vanadium dioxide is in the dielectric-like state (d), which is called the cd state.

[0103] Using the transfer matrix method and the calculation method of emissivity, by traversing all possible thicknesses (h1, h2, h3) of the design variables, all possible mid-infrared emission spectral parameters in the initial design domain are obtained.

[0104] Give the design optimization model:

[0105]

[0106] Among them, λ1 and λ2 respectively represent the starting and ending wavelengths of the mid-wave infrared window wavelengths, which are set to 3 μm and 5 μm respectively, and λ3 and λ4 respectively represent the starting and ending wavelengths of the long-wave infrared window wavelengths, which are set to 8 μm and 13 μm respectively. Search for the optimal structure that meets the above emissivity requirements in the initial design domain.

[0107] Step 4: Obtain the optimal multi-layer thin film structure based on phase change materials

[0108] The preferred multi-layer thin film structure based on phase change materials is as Figure 1 , 2 shown. The long-wave infrared phase change film layer A is a germanium antimony tellurium alloy with the chemical formula Ge2Sb2Te5 and a thickness h1 = 100 nm; the material of the dielectric layer B is zinc sulfide with a thickness h2 of 260 nm; the mid-wave infrared phase change film layer C is vanadium dioxide with the chemical formula VO2 and a thickness h3 = 110 nm. The metal reflection layer D is gold with the chemical formula Au and a thickness h4 = 100 nm; the substrate material is silicon with the chemical formula Si.

[0109] As Figure 7 shown, preferably, the thermal emissivity of the thin film structure has a certain modulation ability. In the mid-wave infrared, the adjustable range of the average emissivity is 0.02 - 0.35 (when the thin film changes from the ad state to the am state), and in the long-wave infrared, the adjustable range of the average emissivity is 0.04 - 0.35 (when the thin film changes from the ad state to the cd state).

[0110] Those of ordinary skill in the art should understand that the discussion of any of the above embodiments is only exemplary and is not intended to imply that the scope of protection of this application is limited to these examples; within the concept of this application, the technical features in the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations in different aspects of one or more embodiments of this application as described above, which are not provided in detail for the sake of brevity.

[0111] One or more embodiments of this application are intended to cover all such substitutions, modifications, and variations that fall within the broad scope of this application. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of one or more embodiments of this application shall be included within the scope of protection of this application.

Claims

1. A dual-wave dynamic thermal camouflage structure, characterized in that It includes a long-wave infrared phase change film layer, a dielectric layer, a mid-wave infrared phase change film layer, and a reflective layer that are stacked in sequence from top to bottom on a substrate; The material of the long-wave infrared phase change film layer is Ge2Sb2Te5, the material of the dielectric layer is germanium, and the material of the mid-wave infrared phase change film layer is vanadium dioxide; The thickness of the long-wave infrared phase change film layer is 100 nm; the thickness of the dielectric layer is 50 nm; the thickness of the mid-wave infrared phase change film layer is 300 nm.

2. The double-wave dynamic thermal camouflage structure according to claim 1, characterized in that, The reflective layer is a metallic material.

3. An optimization method for the dual-wave dynamic thermal camouflage structure according to claim 1, characterized in that, It includes the following steps, Determine the initial thickness ranges of the long-wave infrared phase change film layer, the dielectric layer, and the mid-wave infrared phase change film layer; find the optimal spectral characteristic curve within the initial thickness ranges; based on the optimal spectral characteristic curve, determine the optimal thickness values; The method for determining the optimal spectral characteristic curve within the initial thickness ranges is to, through the transfer matrix method, traverse all values within the initial thickness ranges, calculate the curve of the variation law of the emissivity with wavelength within the mid-wave infrared window wavelength and long-wave infrared window wavelength ranges, which is the spectral characteristic curve; determine the spectral characteristic curve that meets the emissivity requirements as the optimal spectral characteristic curve; The emissivity requirements are that the emissivity satisfies the following optimization model, ， λ1 is the starting wavelength of the mid-wave infrared window wavelength, λ2 is the ending wavelength of the mid-wave infrared window wavelength, λ3 is the starting wavelength of the long-wave infrared window wavelength, and λ4 is the ending wavelength of the long-wave infrared window wavelength; h1 is the thickness of the long-wave infrared phase change film layer, h2 is the thickness of the dielectric layer, and h3 is the thickness of the mid-wave infrared phase change film layer; is the emissivity when the long-wave infrared phase-change film layer is in the amorphous state and the mid-wave infrared phase-change film layer is in the quasi-metallic state, is the emissivity when the long-wave infrared phase-change film layer is in the amorphous state and the mid-wave infrared phase-change film layer is in the quasi-dielectric state, is the emissivity when the long-wave infrared phase-change film layer is in the crystalline state and the mid-wave infrared phase-change film layer is in the quasi-dielectric state.

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