Tunable broadband visible-infrared multilayer stealth structure and preparation method

Abstract

The invention discloses a tunable broadband visible-infrared multilayer stealth structure and a preparation method, and belongs to the field of electromagnetic multi-spectrum stealth. From top to bottom, the first layer and the second layer are visible light camouflage functional areas, the third layer is an infrared regulation and control absorption functional area, and the fourth layer is a metal substrate; specifically, a ZnS layer, a Ge layer, a GST layer and a metal substrate layer Ag are sequentially arranged from top to bottom. Visible light camouflage and infrared stealth are achieved, and dynamic reversible switching between stealth and non-stealth is achieved by changing the phase state of the functional layer Ge2Sb2Te5. The multi-layer thin film structure is wide in functional area coverage range, has a dynamic tunable function, is simple in structure and has polarization insensitivity.

Description

TECHNICAL FIELD

[0001] The application provides a wide-band tunable visible-infrared dual-band compatible stealth design method, and belongs to the field of electromagnetic multi-spectrum stealth. BACKGROUND

[0002] With the continuous progress of science and technology, infrared detection technology has developed rapidly and been widely applied. Infrared radiation signals of targets can be accurately captured at night, in bad weather and under low light conditions, and the infrared detection technology is widely applied to reconnaissance of enemy personnel and facility deployment. However, a traditional infrared stealth device is based on fixed material and structure design, and its performance is affected by factors such as structure parameters, material types and arrangement modes. After manufacturing, the performance is basically fixed, and the working frequency domain is fixed in a certain wave band, which is difficult to meet the requirements of dynamic regulation and control in complex environments. At the same time, the enemy often uses multiple detection technologies to search and track targets. Single-band stealth technology is difficult to cope with complex detection methods, which urgently requires the development of technology that can achieve stealth in the visible light and infrared wave bands at the same time.

[0003] For infrared detection, water vapor and carbon dioxide in the atmosphere can absorb infrared radiation of certain specific wavelengths, and the signal is attenuated during transmission, affecting the detection result. At present, the main infrared detection window for detecting targets is 3-5 μm and 8-14 μm, and the signal source is the thermal radiation of the target itself. According to the Kirchhoff's law of thermal radiation, the absorption rate of a material is equal to its emission rate. Therefore, in the detection window, the structure should achieve low absorption rate in the infrared wave band, and achieve stealth effect by suppressing the radiation signal. In order to maintain the reasonable working temperature of the equipment, radiation heat dissipation needs to be carried out in the non-detection wave band.

[0004] The existing multi-band stealth technology has the following deficiencies: (1) the working frequency domain is relatively narrow, and cannot cover the entire infrared detection window; (2) the emission rate is high, and the stealth effect is poor; (3) the structure function is single, and it is difficult to cope with complex environments; (4) the preparation process is complex, and the structure is difficult to mass-produce. SUMMARY

[0005] The application aims to provide a multilayer film design method of a tunable wide-band (visible-infrared) multilayer stealth structure. In view of a narrow working frequency domain, the application sets a visible light and infrared dual-band working area, and can realize visible light camouflage and infrared stealth at the same time, and the two do not affect each other. In view of high emissivity and poor stealth effect, the application is based on the principle of multilayer film interference theory, and uses the finite difference time domain method to analyze the structure, realizes perfect absorption and perfect stealth in the detection window. In view of single function and difficulty in facing complex situations, the application can realize dynamic reversible switching of stealth and non-stealth by changing the phase state of the functional layer Ge2Sb2Te5. The multilayer film structure of the application has a wide coverage range of functional areas, has a dynamic tunable function, and has a simple structure and polarization insensitivity.

[0006] A tunable wide-band visible-infrared multilayer stealth structure, characterized in that, from top to bottom, the first layer and the second layer are visible light camouflage functional areas, the third layer is an infrared regulation and absorption functional area, and the fourth layer is a metal substrate.

[0007] Specifically, from top to bottom, they are ZnS layer, Ge layer, GST layer and Al, Cu, Pb, Zn, Mo, Au, Ag and other metal substrate layers, and Ag is preferably selected.

[0008] The thickness of the first layer ZnS is 100nm-260nm, and different colors of visible light camouflage are realized according to different thicknesses; with the gradual increase of the thickness, the color appears in a cycle of green-yellow-orange-purple-blue-green, and the specific thickness and color relationship is as shown in Figure 7 .

[0009] Further, ZnS has a wide transmission band of 0.3-14μm, covering the visible light band and part of the infrared band, and can effectively transmit or reflect light in a wide band. Usually combined with ITO, Ge, Ag grating and other materials, used to realize a multi-band compatible camouflage structure, and the application selects ZnS and Ge as the visible light camouflage functional area. The thickness of the Ge layer is 100nm.

[0010] The ZnS layer adopts a complete and uniform thin film structure or a grating structure; when the grating structure is used, the thickness of the ZnS layer is 180nm, the grating width L is 500nm-1000nm, and the grating spacing d is 500nm-1200nm.

[0011] The optical properties of liquid crystal and graphene can be changed by voltage, and the introduction of such functional materials into the application can achieve dynamic regulation. Phase change materials can also change optical constants through external excitation, and even the changed phase state can exist stably at room temperature without additional energy maintenance. The combination of phase change materials and metamaterials also achieves dynamic regulation function, so the application uses phase change material Ge2Sb2Te5 as a functional layer GST layer. The thickness of the GST layer is 350 nm.

[0012] Metal materials such as Au and Ag have good electrical conductivity and thermal conductivity, high refractive index and good mechanical properties, and are commonly used in infrared absorber reflection layers. The application preferably uses Ag as a metal substrate. The thickness of the substrate is 150 nm.

[0013] Further, the above selected materials are used to design unit structures, and are designed as a multilayer thin film structure. When infrared waves are incident on the multilayer thin film, reflection and refraction occur on the upper and lower surfaces of each thin film layer. These reflected and refracted lights interfere with each other between different thin film layers, thereby realizing light wave absorption, as shown in the schematic diagram. Figure 1

[0014] The first two layers are visible light camouflage functional areas, from top to bottom are ZnS layer and Ge layer respectively, the third layer is an infrared regulation absorption functional area, which is a GST layer. The fourth layer is a silver metal substrate.

[0015] The application is a multilayer thin film structure, in which a physical vapor deposition method is commonly used to prepare high-purity thin film materials. A magnetron sputtering device can be used to uniformly deposit the target material on the substrate by high-energy ion bombardment to form a thin film.

[0016] The application has the following advantages:

[0017] The application provides a wide-band tunable visible-infrared dual-band compatible stealth multilayer thin film design method, which has the following advantages: (1) a dual-band (visible light and infrared light) stealth structure is developed, which has independent adjustment function. That is, changing the visible light color does not affect the infrared stealth function of the structure, and vice versa. (2) The structure can realize dynamic switching between stealth and non-stealth, and the absorption rate can be as high as 99.4% when perfectly absorbing, and the average emission rate of the entire infrared waveband is only 2.1%, which can realize perfect stealth. (3) A wide range of color changes are realized in the visible light waveband, and green-yellow-orange-purple-blue-green color cycles are obtained with the increase of the thickness of ZnS. (4) The structure has polarization angle insensitivity and small-angle incidence insensitivity, and the substrate material and surface structure can be adjusted according to the requirements. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 ​: The schematic diagram of the four-layer thin film structure of wideband tunable visible-infrared dual-band compatible stealth. ZnS / Ge / Ge2Sb2Te5(GST) / Ag.

[0019] Figure 2 : The absorption rate map of the structure with different thickness of GST.

[0020] Figure 3 : The absorption rate map of the structure in the infrared band range with different phase of GST.

[0021] Figure 4 : The energy loss distribution map of the structure in the infrared band range with different phase of GST.

[0022] Figure 5 : The energy loss distribution map of the structure in the visible band range with different phase of GST.

[0023] Figure 6 : The absorption rate map of the structure in the visible band range with different thickness of top layer ZnS.

[0024] Figure 7 : The corresponding CIE1931 chromaticity diagram and the corresponding visible color of the structure with different thickness of top layer ZnS.

[0025] Figure 8 : The absorption rate map of the structure in the infrared band range with different thickness of top layer ZnS.

[0026] Figure 9 : The absorption rate map with the change of incident angle when the incident wave is TE wave and TM wave respectively.

[0027] Figure 10 : The schematic diagram and the absorption rate map of the structure when the top layer is grating.

[0028] Figure 11 : The absorption peak position and the absorption rate of the structure with different substrates. DETAILED DESCRIPTION

[0029] It should be noted that the following detailed description is exemplary in nature and is intended to provide further description of the application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0030] Specific Example 1:

[0031] An infrared and visible light compatible stealth structure, the materials of the films from top to bottom are zinc sulfide, germanium, germanium antimony tellurium, and silver. The thicknesses are 180nm (which can be from 100nm to 260nm), 100nm, 350nm, and 150nm, respectively. The structure is prepared as a whole with a length and width of 10000nm.

[0032] Further, the structure is simulated by using a finite difference time domain method. In this experiment, the finite difference time domain algorithm (FDTD) in COMSOL is used, and the electromagnetic wave and the frequency domain (ewfd) module are selected. According to the designed structure parameters, two-dimensional and three-dimensional models are constructed, materials are selected, ideal electrical conductors, ports, impedance boundary conditions, periodic boundary conditions, and wave equations are set, the electromagnetic wave frequency domain is set to the infrared frequency range of 3-14μm, and the grid is divided.

[0033] The simulation results obtained by using the finite difference time domain method are shown in Figure 2 When the GST layer thickness is set to 200, 250, 300, 350, 400, and 450nm, respectively, when the GST is in an amorphous state, the emissivity of the structure is low, and the stealth effect is good. With the increase of the thickness, the peak value of the emissivity appears right shift. When the GST is in a crystalline state, with the increase of the thickness, the absorption peak appears right shift. Since the infrared detection window is 3-5μm and 8-14μm, the GST layer thickness is selected to be 350nm, so that high absorption and low emissivity can be achieved in the detection window.

[0034] The absorption rate simulation results of each layer using the optimal thickness are shown in Figure 3 When the GST is in an amorphous state (a-GST), the average absorption rate in the 3-5μm band is 0.72%, and the average absorption rate in the 8-13μm band is 2.6%. The average absorption rate in the entire infrared band is only 2.1%, which means that the emissivity is very low, and therefore the stealth performance is good. When the GST is in a crystalline state (c-GST), the absorption rate in the two infrared detection atmospheric window bands of 3-5μm and 8-14μm reaches the maximum value at 3.66μm and 10.57μm, respectively, which are 99.4% and 95.8%, respectively, which can achieve perfect absorption, and therefore the stealth performance is not good. Therefore, the dynamic switching between stealth and non-stealth can be realized by controlling the GST phase state.

[0035] According to the high contrast of the absorption rate of GST in different phases, the dynamic switching of invisibility and non-invisibility can be realized by regulating the phase of GST. To transform GST from amorphous state to crystalline state, a pulse with small amplitude and long time is needed. The heat generated by the pulse will make the material heat up. Since the pulse time is long enough, the atoms will rearrange into an ordered structure, realizing the transformation from amorphous state to crystalline state. On the contrary, if we want to make GST from crystalline state to amorphous state, we need to give a pulse with large amplitude and very short time, which will make the material heat up instantaneously, and the atoms cannot rearrange, thus forming an amorphous state. At present, the most widely used is ultra-short pulse laser, and the transformation rate only needs tens of nanoseconds. In addition, GST has special non-volatility, that is, when GST is in a certain state, it will remain unchanged for a long time without external stimulation, which means that the structure can exist stably in the "invisibility" and "non-invisibility" states and can realize dynamic switching.

[0036] The power loss density of the structure is analyzed. When the waveband is in the infrared waveband, the GST layer and the Ag layer mainly absorb infrared. When the waveband is in the visible light waveband, the ZnS layer and the Ge layer mainly absorb energy, as shown in Figure 4 and Figure 5 It is shown that the upper and lower functional areas of the structure do not affect each other, and the infrared invisibility and the visible light camouflage are independent of each other.

[0037] The thickness of the top layer ZnS is changed from 100 nm to 260 nm, and the absorption rate of the structure in the visible light range is tested, as shown in Figure 6 It is found that with the gradual increase of the thickness, the color appears green-yellow-orange-purple-blue-green cycle, and the specific thickness and color relationship is shown in Figure 7 Therefore, the visible light camouflage can be realized by stacking ZnS flakes on the top layer of the structure. At the same time, the absorption rate in the infrared range is also tested, as shown in Figure 8 It is found that the change of the structure does not affect the infrared invisibility function.

[0038] Figure 9 The infrared absorption spectrum of the structure is shown when the incident angle changes from 0° to 70°. For TE polarized wave Figure 9 and TM polarized wave Figure 9In the middle (b), the absorption of the structure is affected by the incident angle. For TE wave, the absorption effect is not much different from the normal incidence when the incident angle is less than 60°. The infrared absorbance peak of the structure is still at 3.66 μm and 10.57 μm, and the maximum absorbance at 3.66 μm increases first and then decreases with the increase of the incident angle. When the incident angle is 50°, the maximum absorbance of the structure can reach 99.96%, which is greater than 95.8% under normal incidence. At the second absorption peak, the absorbance still increases and then decreases with the increase of the incident angle, and reaches the maximum value of 11.6% at 60°. The average absorbance is 2.3%. For TM wave, with the increase of the incident angle, the first peak moves slightly to the left, and the absorption rate decreases first and then increases. The maximum absorption is 99.5%, and the minimum absorption is 97.2%. The second absorption peak moves to the left with the increase of the incident angle, and the maximum absorption decreases from 95.8% to 90.4%. The peak wavelength changes from 10.6 μm to 7.25 μm. The maximum absorbance of the other phase structure gradually decreases with the increase of the angle, from 6.28% to 3.23%. The average absorption rate changes little, with the maximum value of 2.11% and the minimum value of 1.5%, corresponding to the average absorption rate at an incident angle of 60°. In summary, the structure is not sensitive to polarization for TE wave and TM wave.

[0039] Figure 10 The effect of the top layer structure on the infrared absorption rate is shown. Figure 10 The middle (a) is a three-dimensional schematic diagram of the grating structure, Figure 10 The middle (b) is an absorption curve. L is the width of the grating, and d is the grating pitch. L1=500 nm, d1=1,000 nm; L2=1,000 nm, d2=500 nm; L3=1,000 nm, d3=1,000 nm and L4=1,000 nm, d4=1,200 nm are set respectively. As can be seen from the figure, the width and pitch of the grating will not affect the absorption rate of the structure when GST is in the crystalline state. However, it will slightly increase the emissivity of the structure in the amorphous state. The larger the pitch between the gratings, the more the emissivity increases. The average emissivity corresponding to the four different grating parameters is 1.94%, 2.40%, 2.16% and 2.81% respectively, which still maintains a low value, so the grating structure will not affect the stealth function of the structure.

[0040] Figure 11 In order to change the absorption characteristics of the structure when the substrate (such as Al, Cu, Mo, Au, etc.) is changed. The specific values are shown in the table. The structure still has good absorption in the infrared detection window when c-GST is in the state. At the same time, the structure still realizes low absorption rate when a-GST is in the state. Therefore, the application can select different types of substrate materials according to different application scenarios and needs.

[0041] The above merely describes the preferred embodiments of the present application, and it should be noted that those skilled in the art can obtain other embodiments based on the above disclosure, or by using the knowledge or technology in the related field to make modifications, and the features of each embodiment can be interchanged or replaced, and the modifications and changes made by those skilled in the art do not deviate from the spirit and scope of the present application, and thus should be within the protection scope of the claims of the present application.

Claims

1. A tunable wide-band visible-infrared multi-layer stealth structure, characterized in that: From top to bottom, the first and second layers are visible light camouflage functional areas, the third layer is the infrared control absorption functional area, and the fourth layer is the metal substrate; specifically, from top to bottom, they are ZnS layer, Ge layer, GST layer and Al, Cu, Pb, Zn, Mo, Au, Ag and other metal substrate layers, preferably Ag.

2. A tunable wide-band visible-infrared multi-layer stealth structure according to claim 1, characterized in that: The thickness of the first layer of ZnS is 100nm-260nm, and different colors of visible light camouflage are achieved according to the thickness; as the thickness gradually increases, the colors appear green-yellow-orange-purple-blue-green.

3. A tunable wide-band visible-infrared multi-layer stealth structure according to claim 1, characterized in that: ZnS and Ge are selected as the visible light camouflage functional area, where the thickness of the Ge layer is 100nm.

4. The tunable wide-band visible-infrared multi-layer stealth structure according to claim 1, characterized in that: The ZnS layer adopts a complete and uniform thin film structure or a grating structure; in the grating structure, the grating width L is 500nm-1000nm, the grating spacing d is 500nm-1200nm, and the preferred thickness of the ZnS layer is 180nm.

5. The tunable wide-band visible-infrared multi-layer stealth structure according to claim 1, characterized in that: The phase change material Ge2Sb2Te5 is used as the functional layer GST layer, and the thickness of the GST layer is 350nm.

6. The tunable wide-band visible-infrared multi-layer stealth structure according to claim 1, characterized in that: The thickness of the substrate was 150 nm.

7. The tunable wide-band visible-infrared multi-layer stealth structure according to claim 1, characterized in that: Visible light camouflage and infrared stealth can be achieved without affecting each other. You can choose visible light camouflage and infrared stealth, or visible light camouflage and non-stealth.

8. A tunable wide-band visible-infrared multi-layer stealth structure according to claim 7, characterized in that: Dynamic reversible switching between stealth and non-stealth is achieved by changing the phase state of the functional layer Ge2Sb2Te5.

9. The tunable wide-band visible-infrared multi-layer stealth structure according to claim 1, characterized in that: The physical vapor deposition method is used to prepare high-purity thin film materials. A magnetron sputtering device is used to bombard the target material with high-energy ions, so that it is evenly deposited on the substrate to form a thin film.

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