阅读说明：本技术 一种兼容热致变发射率和频率选择散热的红外隐身超结构 (Infrared stealth superstructure compatible with thermotropic emissivity and frequency selective heat dissipation ) 是由 方菲 赵越超 于 2021-06-04 设计创作，主要内容包括：本发明公开了一种兼容热致变发射率和频率选择散热的红外隐身超结构,包括设置于衬底上呈周期排列的若干电磁谐振单元,各电磁谐振单元均分别包括由下至上依次叠设的发射率调控层和介电层,以及周期排布于介电层之上的若干金属柱；发射率调控层是通过在叠设于衬底之上的金属层中嵌入相变材料制得。本发明能够实现在大气透射窗口：3-5μm和8-14μm调制发射率,同时增强大气吸收波段5-8μm的热辐射来主动散热,且具有较宽的发射率调控范围,能够适应多种红外隐身场景。(The invention discloses an infrared stealth superstructure compatible with thermotropic emissivity and frequency selective heat dissipation, which comprises a plurality of electromagnetic resonance units arranged on a substrate in a periodic manner, wherein each electromagnetic resonance unit respectively comprises an emissivity control layer, a dielectric layer and a plurality of metal columns periodically arranged on the dielectric layer, wherein the emissivity control layer and the dielectric layer are sequentially overlapped from bottom to top; the emissivity modulating layer is made by embedding a phase change material in a metal layer overlying the substrate. The invention can realize the following effects in an atmosphere transmission window: emissivity is modulated by 3-5 mu m and 8-14 mu m, meanwhile, heat radiation of atmospheric absorption wave band 5-8 mu m is enhanced to actively dissipate heat, and the emissivity control range is wide, so that the infrared invisible scene can be adapted to various infrared invisible scenes.)

1. An infrared stealth superstructure compatible with thermotropic emissivity and frequency selective heat dissipation is characterized by comprising a plurality of electromagnetic resonance units which are arranged on a substrate in a periodic manner, wherein each electromagnetic resonance unit comprises an emissivity control layer, a dielectric layer and a plurality of metal columns which are periodically arranged on the dielectric layer, wherein the emissivity control layer and the dielectric layer are sequentially overlapped from bottom to top; the emissivity control layer is made by embedding a phase change material in a metal layer stacked on the substrate.

2. The infrared stealth superstructure according to claim 1, wherein said metal pillars are made of a noble metal.

3. The infrared stealth superstructure according to claim 2, characterized in that said metal pillars have cross-sectional dimensions of 1-2 μm, a height of 50-300nm and a pitch of 3-5 μm.

4. The infrared stealth superstructure according to claim 1, wherein said dielectric layer is made of an insulating material.

5. The infrared stealth superstructure according to claim 4, wherein the insulating material from which said dielectric layer is made comprises zinc sulfide, polyimide and silicon nitride.

6. The infrared stealth superstructure according to claim 4 or 5, characterized in that said dielectric layer has a thickness of 50-200 nm.

7. The infrared stealth superstructure according to claim 1, wherein said phase change material is capable of changing its physical properties depending on the temperature of the stealth object; the metal layer is made of noble metal.

8. The infrared stealth superstructure according to claim 7, wherein said phase change material is selected from vanadium dioxide, zinc oxide or antimony doped tin dioxide.

9. The infrared stealth superstructure according to claim 7 or 8, characterized in that said phase change material has a width of 10-20 μm, a thickness of not less than 80nm, not more than 200 nm; the width of the metal layer is 15-25 μm, and the thickness is 120-200 nm.

10. The infrared stealth superstructure according to claim 1, wherein said substrate is made of a material capable of absorbing energy transmitted by said emissivity control layer.

11. The infrared stealth superstructure according to claim 10, wherein said substrate is made of SiO material₂Or Si₃N₄And the thickness of the substrate is not less than 50 μm.

Technical Field

The invention belongs to the technical field of infrared stealth, and particularly relates to an infrared stealth superstructure compatible with thermotropic emissivity and frequency selective heat dissipation.

Background

Most biological and working instruments have a surface temperature between 20-900 c and the peak of the thermal radiation will be distributed between 3-14 μm according to wien's displacement law (λ T ═ b, where λ is the wavelength, T is the temperature, b is the wien constant, and b ═ 0.002897m · K). However, the 3-5 μm and 8-14 μm bands are atmospheric transmission windows in which infrared radiation is readily transmitted through the atmosphere to be detected by the thermal camera. When there is a difference in radiation intensity between the target and the surrounding environment, the target can be identified in thermal imaging by radiation contrast. It is a great challenge in infrared imaging to fuse the target with the surrounding environment to avoid infrared thermal detection. Infrared stealth generally avoids infrared detection by reducing the difference in thermal radiation intensity of the target and the background. Since most targets have a radiation intensity higher than background, low emissivity materials are typically used on the target to reduce the radiation intensity of the target. Various materials having low emissivity in a 3-14 μm band, such as noble metals, semiconductive materials, biomaterials, inorganic/organic composite materials, etc., have been widely studied. However, conventional low emission materials face challenges of thermal stability and lack of emissivity modulation capability.

The low emissivity of the whole wave band can block the heat radiation of the target object, and the long-time use can cause the temperature of the target object to rise, but can cause higher infrared radiation, which is contrary to the infrared stealth principle. Since the infrared signal of the atmospheric absorption waveband of 5-8 microns can be absorbed by the atmosphere and cannot be detected, the heat dissipation window can be opened in the atmospheric absorption waveband. At present, the periodic metal cylinder-dielectric layer-metal layer superstructure is widely researched, and as the periodic metal cylinder-dielectric layer-metal layer superstructure can have lower emissivity at two infrared detection bands of 3-5 microns and 8-14 microns so as to realize infrared stealth, and can have higher emissivity at an atmospheric absorption band so as to realize heat dissipation, the contradiction between infrared stealth and heat dissipation is well solved.

However, when environmental conditions change, such as temperature, humidity, solar intensity and the like, the infrared radiation characteristics of the environment change, and the low-emissivity film or superstructure only has fixed emissivity, so that the target is easily exposed under dynamic background conditions, and the stealth is disabled. Therefore, the infrared stealth device compatible with self-adaptive infrared stealth and active heat dissipation is constructed, and the application prospect is great.

Disclosure of Invention

The invention aims to solve the two problems of poor thermal stability and lack of emissivity modulation capability of the traditional low-emissivity material, and combines a metal resonant metamaterial and VO (volatile organic compounds)₂Etc. ofThe material is changed, and the material composition of each medium layer of the metamaterial is designed and the structure size is controlled, so that the infrared stealth metamaterial surface device compatible with the thermotropic emissivity and the frequency selective thermal emission is provided. The invention can realize the emissivity modulation in the atmospheric transmission window (3-5 μm and 8-14 μm), and simultaneously enhance the heat radiation of atmospheric absorption band (5-8 μm) to actively dissipate heat.

In order to achieve the purpose, the invention adopts the following technical scheme:

the invention provides an infrared stealth superstructure compatible with thermotropic emissivity and frequency selective heat dissipation, which is characterized by comprising a plurality of electromagnetic resonance units which are arranged on a substrate in a periodic manner, wherein each electromagnetic resonance unit comprises an emissivity control layer, a dielectric layer and a plurality of metal columns which are arranged on the dielectric layer in a periodic manner from bottom to top in sequence; the emissivity control layer is made by embedding a phase change material in a metal layer stacked on the substrate.

The invention has the characteristics and beneficial effects that:

the invention discloses an infrared stealth surface device compatible with thermotropic emissivity and frequency selective thermal emission, which comprises the following components in part by weight: the designed metal column-dielectric layer-metal layer structure can form antiparallel current to cause magnetic resonance, and the antiparallel current is absorbed by infrared radiation resonance of a stealth object and then is dissipated to the atmosphere. The resonance wave band can be dissipated through the wave band of 5-8 μm by adjusting the size of the metal column, so that the heat radiation cannot be detected by the thermal camera and the infrared stealth performance of the device is not influenced; in addition, the phase-change material is periodically distributed in the metal layer, incident heat radiation is influenced by the phase-change material when passing through the phase-change material, and when the phase-change material is in a semiconductor state, the heat radiation penetrates through the phase-change material and is absorbed by the substrate due to the existence of an energy gap, so that high emissivity is caused; when the phase-change material is in a metal state, the energy gap disappears, the heat radiation is reflected, and a lower emissivity is generated. Therefore, the emissivity of the superstructure in the wave bands of 3-5 μm and 8-14 μm can be changed by changing the temperature of the phase-change material, and self-adjusting infrared stealth is realized. The infrared stealth superstructure provided by the embodiment of the invention has the heat radiation performance 3 times that of the traditional low-emissivity material, has a wider emissivity regulation range of 0.1-0.41, and can adapt to various infrared stealth scenes.

Drawings

Fig. 1 is a schematic structural diagram of an infrared stealth superstructure according to an embodiment of the present invention.

Fig. 2 is a cross-sectional view of a resonant cell in an infrared cloaking superstructure of an embodiment of the invention.

FIG. 3 is a spectral characterization of an infrared cloaking superstructure in accordance with an embodiment of the present invention; wherein (a) and (b) are heating and cooling VO, respectively₂An emissivity spectrum of the in-process superstructure; (c) is an emissivity change curve of a 12 mu m wave band in the heating-cooling process; (d) is the emissivity change curve of 6.27 mu m wave band in the heating-cooling process.

FIG. 4 is an electromagnetic physical property of the resonance absorption behavior of an infrared stealth superstructure of an embodiment of the present invention; wherein, (a) and (b) are the magnetic field distribution and the electric field distribution of the metal column-dielectric layer-metal layer in the 6.27 mu m wave band respectively; (c) and (d) the magnetic field distribution and the electric field distribution of the metal column, the dielectric layer and the metal layer in the wave band of 12 microns respectively.

FIG. 5 is an electromagnetic physical property of the emissivity modulation capability of an infrared cloaking superstructure of an embodiment of the invention; wherein (a) and (b) are respectively metal column-dielectric layer-VO₂Magnetic field distribution and electric field distribution in the 6.27 μm electric band; (c) and (d) are respectively metal column-dielectric layer-VO₂Magnetic field distribution and electric field distribution in the 12 μm band.

Fig. 6 (a) and (b) are respectively the resonance absorption peak and the fitting relationship thereof according to the embodiment of the present invention with the change of the diameter of the metal pillar.

Fig. 7 shows an infrared stealth structure with multiple resonance peaks and spectral characteristics according to an embodiment of the present invention.

Fig. 8 is a comparison of the heat dissipation performance of an infrared stealth structure according to an embodiment of the present invention and a conventional infrared stealth material.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be described in detail below with reference to the accompanying drawings and examples. It should be noted that the embodiments and features of the embodiments in the present application may be arbitrarily combined with each other without conflict.

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, however, the present invention may be practiced otherwise than as specifically described herein, and thus the scope of the present invention is not limited by the specific embodiments disclosed below.

The infrared stealth superstructure of the embodiment of the invention has thermal variable emissivity and frequency selective thermal emission performance, and has a structure shown in figure 1, and comprises a plurality of electromagnetic resonance units which are arranged on a substrate 5 in a periodic arrangement, wherein each electromagnetic resonance unit comprises an emissivity control layer and a dielectric layer 2 which are sequentially overlapped from bottom to top, and a plurality of metal columns 1 which are periodically arranged on the dielectric layer 2; wherein the emissivity controlled layer is made by embedding a phase change material 4 in a metal layer 3 stacked on a substrate 5. The metal column 1, the dielectric layer 2 and the metal layer 3 can form antiparallel current, and can generate magnetic resonance with a corresponding thermal radiation waveband, so that the thermal radiation is absorbed to dissipate heat outwards, and the thermal radiation waveband generating the resonance can be regulated and controlled through the diameter of the metal column; when the incident heat radiation passes through the phase change material 4, when the phase change material is in a semiconductor state, the heat radiation can be absorbed by the substrate 5 through the phase change material 4 due to the existence of the energy gap, so that high emissivity is caused, and when the phase change material 4 is in a metal state, the energy gap disappears, and the heat radiation is reflected by the phase change material 4, so that low emissivity is generated.

The specific implementation modes and principles of each component in the infrared stealth superstructure of the embodiment of the invention are respectively explained as follows:

the metal column 1 is arranged on the dielectric layer 2 and can adopt noble metals with low emissivity (the emissivity is not more than 0.3) such as Au, Ag and the like; the cross section of the metal column 1 is not strictly limited, and can be circular, rectangular, rhombic or other cross section shapes; the diameter or side length, height and spacing of the metal posts 1 influence the resonant wave band, the resonant wave band of the electromagnetic resonance unit of the invention is between 5 and 8 mu m, the reference diameter or side length range of the metal posts 1 is approximately between 1 and 2 mu m, the height is between 50nm and 300nm, and the spacing is between 3 and 5 mu m, and the parameters are influenced by the material performance of the metal posts 1. Within this range, the metal pillar 1 can generate resonance absorption with the dielectric layer 2 and the metal layer 3 in a wavelength band of 5-8 μm.

A dielectric layer 2 stacked on the emissivity control layer and made of ZnS, Polyimide (PI), or SiN_xAnd the like; the thickness of the dielectric layer 2 is influenced by the properties of the material chosen, and in order to obtain resonance in the wavelength band of 5-8 μm, the thickness of the dielectric layer 2 is typically 50-200 nm. The dielectric layer 2 can generate resonance absorption with the metal pillar 1 and the metal layer 3 in a wave band of 5-8 μm.

And the emissivity control layer is stacked on the substrate 5 and is obtained by periodically embedding the phase change material 4 into the metal layer 3. The phase change material 4 is made of a material capable of changing the physical properties of the phase change material according to the temperature of the stealth object, so as to adjust the infrared emissivity of the device, such as VO₂ZnO, antimony-doped tin dioxide (ATO), etc.; the metal layer can be made of metal with low emissivity (emissivity is not more than 0.3) such as Au, Ag and the like, and can be made of metal which is the same as or different from the metal column 1; because the wavelength of incident thermal radiation is in a wave band of 3-14 mu m, in order to ensure that the thermal radiation can penetrate through the phase-change material 4 to realize emissivity regulation, the width of the phase-change material 4 is 10-20 mu m, and the thickness of the phase-change material 4 is not less than 80nm and not more than 200 nm; in order to form antiparallel current to realize resonance absorption, the width of the metal layer 3 is not less than the distance between two adjacent metal pillars 1, and is typically 15-25 μm, and the thickness of the metal layer 3 is between 120-200 nm.

And the substrate layer 5 is used for providing physical support for other structural layers and absorbing energy transmitted by the emissivity control layer. SiO can be used₂、Si₃N₄And the like, and low infrared reflection materials. Since the substrate 5 is intended to absorb infrared radiation, its thickness is generally much higher than the wavelength of the radiation, and the thickness of the substrate layer 5 is not less than 50 μm.

Since the device is a periodic structure, fig. 2 shows an electromagnetic resonance unit of the superstructure and SiO below the unit₂An embodiment of the substrate 5. In the electromagnetic resonance unit of the embodiment, the metal pillar 1 is made of gold pillar, the power saving layer 2 is made of ZnS, and goldThe metal layer 3 is made of gold, and the phase-change material 4 is VO₂Abbreviated as Au-ZnS-Au/VO₂In order to obtain adjustable emissivity of 3-5 μm and 8-14 μm bands and high emissivity of 5-8 μm bands, the structural size of the embodiment is determined by FDTD simulation. Simulating an electromagnetic resonance unit by using FDTD software, applying a periodic boundary condition and incident electromagnetic waves of 3-14 mu m, and monitoring the reflectivity and the transmissivity of the device; in order to obtain the widest emissivity regulation range and the maximum infrared radiation resonance peak value, the size of the electromagnetic resonance unit is determined as follows: square VO embedded in Au layer with length and width of electromagnetic resonance unit being 18 μm₂Has a width of 12 μm, Au pillars have a diameter of 1.3 μm, a pitch between adjacent Au pillars is 3.0 μm, and thicknesses of the metal pillars 5, the dielectric layer 2, the emissivity control layer, and the substrate 5 are each h₁＝0.1μm，h₂＝0.1μm，h₃＝0.15μm，h₄＝100μm。

Spectral characteristics of the device of this example obtained by FDTD simulation are shown in fig. 3, which simulates heating and cooling of VO₂Emissivity spectrum of the device in the process. When VO is present as shown in FIG. 3 (a)₂When the temperature of the device is increased from 293K to 348K, the emissivity of the device is hardly changed below 336K or above 345K; but when the temperature is increased from 336K to 345K, the temperature is increased due to VO₂The emissivity of the device gradually decreases from the insulating state to the metallic state. At VO₂VO cooled from 345K to 328K₂Returning from the metallic state to the insulating state, the emissivity of the device increases again, as shown in fig. 3 (b). The results show that with VO₂The emissivity of the device can be changed reversibly, and the modulation range is 0.1 to 0.41. Meanwhile, a resonance absorption peak exists in a wave band of 5-8 mu m, and VO is₂The heat radiation of 5-8 μm can not be detected by the thermal camera, so that the heat generated by the stealth target can be radiated in the wave band by the device, and the stealth performance of the device in other wave bands is not influenced. Fig. 3 (c) and (d) respectively characterize the emissivity change in the 12 μm and 6.27 μm wavelength bands during heating-cooling. Due to VO₂The thermal hysteresis characteristic of the device shows hysteresis loop in the emissivity of the device on a wave band of 3-14 mu mLine, hysteresis temperature is about (3-8) K.

The electromagnetic mechanism generated by the variable emissivity characteristic and the resonance absorption characteristic of the device is shown in figure 4. The device can be structurally divided into an Au-ZnS-Au structure and an Au-Zns-VO structure₂Structure, respectively associated with resonant absorption and emissivity modulation. The Au-ZnS-Au structure is a conventional Metal-Insulator-Metal (mim) electromagnetic resonance structure. The distribution of electric and magnetic fields in Au-ZnS-Au when thermal radiation is incident is shown in fig. 4, which characterizes the electromagnetic physical properties of the resonant absorption behavior of the device. As shown in fig. 4 (a), at the 6.27 μm band, a strong magnetic field is captured by the dielectric ZnS layer between the Au layer and the Au pillar, which is mainly caused by the antiparallel current generated between the Au plate and the Au pillar interacting with the magnetic field of the incident light, exciting the magnetic polarizer resonance. Meanwhile, surface plasmon is also excited by the interaction of free electrons of the gold surface with incident light, and an electric field is localized on the surface of the gold pillar and extends into the ZnS layer, as shown in fig. 4 (b). The resonance of the magnetic and electric fields causes a strong absorption of thermal radiation at the 6.27 μm wavelength of the stealth target, resulting in a higher emissivity. When the thermal radiation of the non-resonant band, such as the thermal radiation of 12 μm wavelength, is incident, as shown in fig. 4 (c) and (d), the electromagnetic resonance is rather weak, which indicates that the thermal radiation of the band does not generate the resonant absorption behavior, so that the device can have strong absorption and strong emission in the atmospheric absorption band without affecting the absorption of the thermal radiation of other bands of interest. Because VO is embedded in Au layer of MIM structure₂To further understand the optical properties of the device, Au-ZnS-VO₂The magnetic field and electric field distribution in the structure are shown in (a) and (b) of FIG. 5, Au-ZnS-VO₂The structure produces a resonant absorption behavior with 6.27 μm thermal radiation. Thus, Au-ZnS-Au (MIM) and Au-ZnS-VO were combined₂The device of the structure cannot completely absorb the heat radiation in the frequency band, and the emissivity at 6.27 μm is less than 1, in particular 0.8. Furthermore, although the phase change material VO₂And the third layer of the device is positioned, and the device still shows infrared emissivity modulation capability. As can be seen from FIGS. 5 (c) and (d), the electric field and the magnetic field are applied to the ZnS layer and VO₂Is uniform because the ZnS layer is substantially transparent in the infrared band, the heat radiation of the targetCan enter VO through ZnS layer with small loss₂A film. When VO is present₂In the insulating state, part of incident light is reflected by Au, and the rest passes through the transparent VO₂Insulating film back coated with SiO₂Absorbing and therefore the device has a high emissivity, in particular 0.4. When VO is present₂In the metallic state, most of the heat radiation is radiated by Au and VO₂The film is reflective and the emissivity is as low as 0.1.

The invention can change the magnetic resonance wavelength of the anti-parallel current by changing the size and the number of the gold posts, and can realize the change of the position and the number of the resonance peaks. As shown in FIG. 6 (a), assuming that the pitch of each Au pillar is 3 μm, as the diameter of the Au pillar increases from 1.1 μm to 1.6 μm, the peak position of the wavelength shifts from 5.8 μm to 6.8 μm, and the peak value of the resonance peak hardly changes. Diameter D of gold pillar and position lambda of absorption peak_pIn a linear relationship, as shown in (b) of FIG. 6, fitting gives D- λ_pThe equation:

λ_P＝4.644×D+0.263

within the smallest unit of a periodic array of Au pillars (3X 3 μm) of the device²) By increasing the number of Au posts, according to lambda_pThe diameter of the Au column is designed according to the relation of-D, the number of resonance absorption peaks can be increased in a wave band of 5-8 mu m, and the heat dissipation capacity of the device is further improved. As shown in (a) and (c) of fig. 7, when two Au pillars, the diameters of which are 1.2 μm and 1.3 μm, respectively, are arranged in one cell, resonance peaks fall at 5.81 μm and 6.3 μm; when three Au pillars were arranged in one cell as shown in (b) and (d) of fig. 7, the diameters were 1.16 μm, 1.26 μm, and 1.36 μm, respectively, and the resonance peaks fell at 5.64 μm, 6.10 μm, and 6.60 μm.

The invention is different from the traditional low-emissivity material in that a heat dissipation window is opened in the wave band of 5-8 mu m, and the heat radiation energy of the device and the common low-emissivity film in the temperature range of 300-400K is compared. The emissivity of existing infrared stealth films is obtained by the reference (Huang Z, Zhu D, Lou F, et al. an application of Au thin-film emissive barrier on Ni alloy [ J ]. Applied Surface Science,2008,255(5): 2619-. As shown in FIG. 8, when the temperature rises from 300K to 336K, the heat radiation energy of the device is increased, the heat radiation energy of the device is reduced after reaching the phase change point, and then the heat radiation energy is increased again along with the temperature rise, so that the whole device is in an N-shaped curve. Meanwhile, the heat radiation energy of the existing infrared stealth film is monotonously increased along with the rise of the temperature. The heat radiation energy of the present invention is higher than that of the conventional film in the whole temperature range. Because the heat radiation energy before phase change mainly comes from the heat radiation of 8-14 μm wave band, the heat radiation energy before phase change does not change with the increase of the resonance peak; the heat radiation energy after the phase change mainly comes from the formants, so the heat radiation energy after the phase change is obviously increased along with the increase of the formants, and the invention can obtain the desired heat dissipation capability by adjusting the number of the Au columns. As can be seen from the figure, when the device has 3 resonance peaks, the heat dissipation performance of the device before phase transition is more than 4 times that of the common thin film, and the heat dissipation performance of the device after phase transition is 2.5 times that of the common thin film.

Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.