Variable infrared emissivity device compatible with radar wave absorption

Abstract

The invention discloses a variable infrared emissivity device compatible with radar wave absorption, which is composed of structural units in a periodic array, and each structural unit comprises an infrared transparent radar wave absorption layer and an electrochromic variable emissivity layer located below the infrared transparent radar wave absorption layer. The infrared transparent radar wave-absorbing layer comprises an infrared transparent substrate and a metamaterial wave-absorbing structure located on the infrared transparent substrate, the electrochromic variable-emissivity layer comprises a carbon-based variable-emissivity composite film and an electrode circuit board, and the infrared emissivity of the carbon-based variable-emissivity composite film is changed through the electrode circuit board. According to the invention, the electrochromic variable-emissivity device is compatible with the radar wave absorbing performance, and the problem that the electrochromic variable-emissivity device does not have the radar stealth capability is effectively solved.

Description

Technical Field

[0001] The invention relates to the field of stealth materials, in particular to a variable infrared emissivity device compatible with radar wave absorption. Background Art

[0002] Traditional infrared stealth methods mainly use low-emissivity coatings or thermal insulation protection to reduce the target's infrared radiation. However, stealth methods with a single emissivity and fixed thermal insulation are difficult to meet the infrared stealth requirements of moving targets under complex and changing terrain backgrounds and climatic conditions.

[0003] With the continuous maturity of multi-band, high-precision detection technologies such as infrared detection technology, radar detection technology, visible light and laser detection technology, various types of equipment may face the threat of multi-band reconnaissance equipment at the same time. Therefore, this field is constantly researching multi-band compatible stealth technology that can simultaneously counter detection by multiple instruments.

[0004] From the current analysis of the contribution to target detection effectiveness, it can be seen that the security threats to the equipment mainly come from radar and infrared detection. Therefore, infrared compatible radar stealth technology has become a key research content in this field. The development of adaptive infrared stealth technology with radar stealth capability will be more in line with actual needs and will help improve the camouflage ability and survivability of the equipment. Summary of the invention

[0005] The technical problem solved by the present invention is to overcome the shortcomings of the prior art, solve the technical problem of infrared and radar compatible stealth, and provide a variable infrared emissivity device compatible with radar absorption.

[0006] The technical solution of the present invention is: a variable infrared emissivity device compatible with radar absorption, which is composed of a periodic array of structural units, each structural unit includes an infrared transparent radar absorbing layer and an electro-variable emissivity layer, the infrared transparent radar absorbing layer includes an infrared transparent substrate and a metamaterial absorbing structure located on the infrared transparent substrate, the electro-variable emissivity layer includes a carbon-based variable emissivity composite film and an electrode circuit board, and the infrared emissivity of the carbon-based variable emissivity composite film is changed by the electrode circuit board; the electro-variable emissivity layer is located below the infrared transparent substrate.

[0007] Furthermore, the metamaterial absorbing structure is an electromagnetic structure made of a conductive film with a certain square resistance value and a graphic shape. For a single structural unit, the array period a is 5 to 15 mm, the graphic area of ​​the metamaterial absorbing structure accounts for 8 to 15% of the structural unit area, and the square resistance is 8 to 30 Ω / sq.

[0008] Furthermore, the graphic shape of the metamaterial absorbing structure is a square, a circle, a diamond, a square ring or a circular ring; and the material is ITO, silver nanowires or a random metal grid.

[0009] Furthermore, the metamaterial absorbing structure absorbs microwaves in the frequency band of 8 to 18 GHz.

[0010] Furthermore, the infrared transparent substrate has a transparent substrate thickness d of 1 mm to 10 mm, and the material is ZnSe, ZnS, GaF2 or Ge.

[0011] Furthermore, infrared anti-reflection film layers are plated on both sides of the infrared transparent substrate to increase the transmittance of the infrared transparent substrate, and the material of the infrared anti-reflection film layer is ThF4, MgF2, HfO2 or GeO2.

[0012] Furthermore, the carbon-based variable emissivity composite film comprises an upper carbon nanofilm layer, a porous diaphragm filled with ionic liquid and a lower carbon nanofilm layer; the upper carbon nanofilm layer is an infrared emissivity modulation layer, and different voltages are applied to the upper carbon nanofilm layer and the lower carbon nanofilm layer through an electrode circuit board to achieve a change in the infrared emissivity of the infrared emissivity modulation layer.

[0013] Furthermore, the carbon nanofilm material of the upper carbon nanofilm layer and the lower carbon nanofilm layer is graphene, semiconductor carbon nanotube or multi-walled carbon nanotube.

[0014] Furthermore, the material of the porous diaphragm layer is a mixture of one or more of polyethylene, polypropylene, polyvinylidene fluoride-co-hexafluoropropylene, polyimide, and glass fiber.

[0015] Furthermore, the cations in the ionic liquid are a mixture of one or more of 1-hexyl-3-methylimidazolium cation, 1-butyl-3-methylimidazolium cation, 1-ethyl-3-methylimidazolium cation, and diethylmethyl-(2-methoxyethyl)ammonium cation; and the anions are a mixture of one or more of bistrifluoromethanesulfonyl imide ion, hexafluorophosphate ion, tetrafluoroborate ion, dinitrile amide ion, p-toluenesulfonate ion, and thiocyanate ion.

[0016] Furthermore, in the structural unit of the periodic array, the metamaterial absorbing structure of each structural unit is made of a conductive film with a square resistance of 12Ω / sq and a graphic shape of a square ring, the material is ITO, the array period a=8mm, the inner diameter of the square ring b=2.5mm, the outer diameter of the square ring c=3.5mm, the transparent substrate thickness d=2mm of the infrared transparent substrate, and the infrared transparent substrate material is ZnS; the thickness of the carbon-based variable emissivity composite film is 50-80μm, including an upper carbon nanofilm layer, a porous diaphragm filled with ionic liquid and a lower carbon nanofilm layer, the upper carbon nanofilm layer and the lower carbon nanofilm layer are both made of carbon nanotubes, the porous diaphragm is made of a mixture of polyethylene and polypropylene, and the porous diaphragm is infiltrated with 1-ethyl-3-methylimidazole diimide salt ionic liquid.

[0017] The advantages of the present invention over the prior art are: by optimizing infrared transparent media and designing a low duty cycle ITO resonant structure, high infrared transmittance is achieved, with a transmittance greater than 85%, and a metamaterial absorbing structure design with radar broadband absorption. Combined with the infrared light transparent metamaterial absorbing structure designed above, the electro-emissivity device is compatible with radar absorbing performance, solving the problem that the electro-emissivity device does not have radar stealth capability. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic diagram of the structure of a variable infrared emissivity device compatible with radar absorption according to an embodiment of the present invention;

[0019] Figure 2 A schematic diagram of the structure of a carbon-based variable emissivity composite film according to an embodiment of the present invention;

[0020] Figure 3 A schematic diagram of a structural unit of an embodiment of the present invention;

[0021] Figure 4 Graph showing the reflectivity and absorptivity of a structural unit according to an embodiment of the present invention. DETAILED DESCRIPTION

[0022] In order to better understand the technical solution of the present invention, the specific implementation mode of the present invention is described in detail below with reference to the accompanying drawings.

[0023] A variable infrared emissivity device compatible with radar absorption is composed of a periodic array of structural units, see Figure 1 Each structural unit includes an infrared transparent radar absorbing layer 1 and an electrovariable emissivity layer 2. The infrared transparent radar absorbing layer 1 includes an infrared transparent substrate 12 and a metamaterial absorbing structure 11 located on the infrared transparent substrate. The electrovariable emissivity layer 2 includes a carbon-based variable emissivity composite film 21 and an electrode circuit board 22. The infrared emissivity of the carbon-based variable emissivity composite film 21 is changed by the electrode circuit board 22. The electrovariable emissivity layer 2 is located below the infrared transparent substrate 12.

[0024] The carbon-based variable emissivity composite film reflects almost all incident microwaves. Therefore, a microwave-absorbing metamaterial with a metal / dielectric / metal sandwich structure is constructed on top of the carbon-based variable emissivity composite film. This material can absorb radars in specific frequency bands and achieve camouflage and stealth that is compatible with microwave absorption and variable infrared properties.

[0025] In this embodiment, the metamaterial absorbing structure 11 is designed with an ITO film of specific square resistance. Since the ITO film does not have infrared transmittance, the metamaterial absorbing structure 11 needs to be designed into a pattern with a duty cycle as small as possible to reduce the impact on infrared transmittance. Infrared transparent ZnS is selected as the infrared transparent substrate 12, and its dielectric constant is 8.3 (1+0.0001i). It can transmit infrared light and microwaves at the same time, and the infrared transmittance of ZnS can be further improved by coating an anti-reflection film, thereby improving the infrared modulation capability of the overall device. The carbon-based variable emissivity composite film 21 of the substrate acts as a reflective layer, which can enhance the radar absorbing intensity. The upper carbon nanofilm layer, the porous diaphragm filled with ionic liquid, and the lower carbon nanofilm layer in the carbon-based variable emissivity composite film 21, the upper carbon nanofilm layer is the infrared emissivity modulation layer, see Figure 2 . By applying different voltages to the upper carbon nanofilm layer and the lower carbon nanofilm layer, the infrared emissivity of the infrared emissivity modulation layer (i.e., the upper carbon nanofilm layer) is changed. Specifically, there are two electrode strips on the electrode circuit board 22, which are respectively connected to the upper carbon nanofilm and the lower carbon nanofilm. The two electrode strips are connected to the voltage input port, and the circuit board material can be a polyimide flexible circuit board or an epoxy resin hard circuit board.

[0026] Based on electromagnetic simulation design, after comprehensively considering the pattern area duty ratio of the resonant absorption structure, the change in the square resistance of the electrovariable layer, and the radar absorption bandwidth, a metamaterial structural unit is obtained after optimization. Figure 3 As shown, the metamaterial absorbing structure 11 is a square ring structure. The array period a = 8mm, the inner diameter of the square ring b = 2.5mm, the outer diameter of the square ring c = 3.5mm, the transparent substrate thickness d = 2mm of the infrared transparent substrate 12, and the square resistance of ITO is 12Ω / sq. The area duty ratio of the ITO resonant structure pattern is only 9.375%. The simulation results of the reflectivity and absorptivity of the metamaterial absorbing structure are shown in Figure 4 As shown, the solid line is the reflectivity and the dotted line is the absorptivity. In the 9.6-15.5 GHz band, the absorptivity is greater than 90%, the effective absorption bandwidth is 5.9 GHz, and there are two absorption peaks at 10.9 GHz and 14.3 GHz.

[0027] The initial ZnS window has an average infrared transmittance of about 70% in the range of 8-14μm. After double-sided anti-reflection film coating, the average transmittance can reach 92%. Then, an ITO conductive film is coated on the anti-reflection film. Due to the presence of the ITO conductive film, the ZnS dielectric substrate at this time cannot transmit infrared light. The excess ITO conductive film is partially etched away by ultraviolet femtosecond laser, and finally the square ring structure of the above design is obtained. Since the conductive film is etched away, the ZnS dielectric substrate still maintains a high infrared transmittance, and the overall transmittance is greater than 85%.

[0028] The thickness of the carbon-based variable emissivity composite film 21 is about 50-80 μm, and preferably an upper carbon nanotube film, a middle polyethylene polypropylene membrane and a lower carbon nanotube film are used, and the ethylene polypropylene membrane is soaked with 1-ethyl-3-methylimidazole diimide salt ionic liquid. The two layers of carbon nanotube film and the Celgard membrane dripped with ionic liquid are respectively laid flat on the flexible electrode circuit board, and the two layers of carbon nanotube film are respectively connected to the two electrodes. The interface end of the flexible circuit board is connected to the external voltage source, and the radiation characteristics are controlled by loading different voltage loads. When the voltage load is 3V, the device shows a low emissivity of about 0.35, and when the voltage load is -1.7V, the device shows a high emissivity of about 0.75, and the infrared emissivity modulation range is about 0.4.

[0029] It is to be understood that the present invention is described by way of embodiments, and it is known to those skilled in the art that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. In addition, under the teachings of the present invention, these features and embodiments may be modified to adapt to specific circumstances without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and embodiments that can fall within the scope of the claims of this application all fall within the scope protected by the present invention.

[0030] The contents not described in detail in the specification of the present invention belong to the common knowledge of those skilled in the art.

Claims

1. A variable infrared emissivity device compatible with radar absorption, characterized in that: The invention is composed of a periodic array of structural units, each structural unit comprising an infrared transparent radar absorbing layer (1) and an electro-variable emissivity layer (2), the infrared transparent radar absorbing layer (1) comprising an infrared transparent substrate (12) and a metamaterial absorbing structure (11) located on the infrared transparent substrate, the electro-variable emissivity layer (2) comprising a carbon-based variable emissivity composite film (21) and an electrode circuit board (22), the infrared emissivity of the carbon-based variable emissivity composite film (21) being changed by the electrode circuit board (22); and the electro-variable emissivity layer (2) being located below the infrared transparent substrate (12).

2. The variable infrared emissivity device compatible with radar absorption according to claim 1, characterized in that: The metamaterial absorbing structure (11) is an electromagnetic structure made of a conductive film with a certain square resistance value and a graphic shape. For a single structural unit, the array period a is 5 to 15 mm, the graphic area of ​​the metamaterial absorbing structure (11) accounts for 8 to 15% of the structural unit area, and the square resistance is 8 to 30 Ω / sq.

3. The variable infrared emissivity device compatible with radar absorption according to claim 2, characterized in that: The shape of the metamaterial wave absorbing structure (11) is a square, a circle, a diamond, a square ring or a circular ring; the material is ITO, silver nanowire or a random metal grid.

4. The variable infrared emissivity device compatible with radar absorption according to claim 2, characterized in that: The metamaterial absorbing structure (11) absorbs microwaves in the frequency band of 8 to 18 GHz.

5. The variable infrared emissivity device compatible with radar absorption according to claim 2, characterized in that: The infrared transparent substrate (12) has a transparent substrate thickness d of 1 mm to 10 mm, and is made of ZnSe, ZnS, GaF2 or Ge.

6. The variable infrared emissivity device compatible with radar absorption according to any one of claims 1 to 5, characterized in that: Infrared anti-reflection film layers are plated on both sides of the infrared transparent substrate (12) to increase the transmittance of the infrared transparent substrate. The infrared anti-reflection film layer material is ThF4, MgF2, HfO2 or GeO2.

7. The variable infrared emissivity device compatible with radar absorption according to claim 1, characterized in that: The carbon-based variable emissivity composite film (21) comprises an upper carbon nanofilm layer, a porous diaphragm filled with ionic liquid, and a lower carbon nanofilm layer; the upper carbon nanofilm layer is an infrared emissivity modulation layer, and different voltages are applied to the upper carbon nanofilm layer and the lower carbon nanofilm layer through an electrode circuit board (22) to achieve a change in the infrared emissivity of the infrared emissivity modulation layer.

8. The variable infrared emissivity device compatible with radar absorption according to claim 7, characterized in that: The carbon nanofilm material of the upper carbon nanofilm layer and the lower carbon nanofilm layer is graphene, semiconductor carbon nanotube or multi-walled carbon nanotube.

9. The variable infrared emissivity device compatible with radar absorption according to claim 7, characterized in that: The material of the porous diaphragm layer is a mixture of one or more of polyethylene, polypropylene, polyvinylidene fluoride-co-hexafluoropropylene, polyimide, and glass fiber.

10. The variable infrared emissivity device compatible with radar absorption according to claim 7, characterized in that: The cations in the ionic liquid are a mixture of one or more of 1-hexyl-3-methylimidazolium cations, 1-butyl-3-methylimidazolium cations, 1-ethyl-3-methylimidazolium cations, and diethylmethyl-(2-methoxyethyl)ammonium cations; and the anions are a mixture of one or more of bistrifluoromethanesulfonyl imide ions, hexafluorophosphate ions, tetrafluoroborate ions, dinitrile amide ions, p-toluenesulfonate ions, and thiocyanate ions.

11. The variable infrared emissivity device compatible with radar absorption according to claim 1, characterized in that: In the structural unit of the periodic array, the metamaterial absorbing structure (11) of each structural unit is made of a conductive film with a square resistance of 12Ω / sq and a graphic shape of a square ring, the material is ITO, the array period a=8mm, the inner diameter of the square ring b=2.5mm, the outer diameter of the square ring c=3.5mm, the transparent substrate thickness d=2mm of the infrared transparent substrate (12), and the material of the infrared transparent substrate (12) is ZnS; the thickness of the carbon-based variable emissivity composite film (21) is 50-80μm, and it comprises an upper carbon nanofilm layer, a porous diaphragm filled with ionic liquid, and a lower carbon nanofilm layer, the upper carbon nanofilm layer and the lower carbon nanofilm layer are both made of carbon nanotubes, the porous diaphragm is made of a mixture of polyethylene and polypropylene, and the porous diaphragm is infiltrated with 1-ethyl-3-methylimidazole diimide salt ionic liquid.

Images