Variable infrared emissivity device compatible with radar wave absorption

Abstract

This invention discloses a radar-absorbing variable infrared emissivity device, comprising a periodic array of structural units. Each structural unit includes an infrared-transparent radar-absorbing layer and an electrovariable emissivity layer located below the infrared-transparent radar-absorbing layer. The infrared-transparent radar-absorbing layer includes an infrared-transparent substrate and a metamaterial absorbing structure on the infrared-transparent substrate. The electrovariable emissivity layer includes a carbon-based variable emissivity composite film and an electrode circuit board. The infrared emissivity of the carbon-based variable emissivity composite film is changed by the electrode circuit board. This invention achieves radar-absorbing performance compatibility for electrovariable emissivity devices, effectively solving the problem that electrovariable emissivity devices lack radar stealth capabilities.

Description

Technical Field

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

[0002] Traditional infrared stealth methods mainly employ low emissivity coatings or thermal insulation to reduce the infrared radiation of targets. However, stealth methods based on single emissivity and fixed thermal insulation are insufficient to meet the infrared stealth requirements of moving targets in complex and changing terrain backgrounds and climatic conditions.

[0003] With the continuous maturation of multi-band, high-precision detection technologies such as infrared detection, radar detection, visible light and laser detection, various devices may face threats from multi-band reconnaissance devices simultaneously. Therefore, the field is constantly researching multi-band compatible stealth technologies that can simultaneously counter the detection of multiple instruments.

[0004] Analysis of current contributions to target detection effectiveness reveals that the primary security threats to equipment come from radar and infrared detection. Therefore, infrared-compatible radar stealth technology has become a key research area in this field. Developing adaptive infrared stealth technology with radar stealth capabilities will better meet practical needs and improve the equipment's camouflage and survivability. Summary of the Invention

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

[0006] The technical solution of this invention is: a radar-compatible variable infrared emissivity device, composed of a periodic array of structural units, each structural unit including an infrared transparent radar absorbing layer and an electrovariable 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 electrovariable 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 electrovariable emissivity layer is located below the infrared transparent substrate.

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

[0008] Furthermore, the metamaterial absorbing structure can be square, circular, rhomboid, square ring, or circular ring in shape; the material can be ITO, silver nanowires, or random metal mesh.

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

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

[0011] Furthermore, infrared antireflection coatings are deposited on both sides of the infrared transparent substrate to increase the transmittance of the infrared transparent substrate. The infrared antireflection coating material is ThF4, MgF2, HfO2 or GeO2.

[0012] Furthermore, the carbon-based variable emissivity composite film comprises an upper carbon nanofilm layer, a porous membrane 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 and lower carbon nanofilm layers through an electrode circuit board to achieve changes in the infrared emissivity of the infrared emissivity modulation layer.

[0013] Furthermore, the carbon nanofilm materials of the upper and lower carbon nanofilm layers are graphene, semiconductor carbon nanotubes, or multi-walled carbon nanotubes.

[0014] Furthermore, the porous membrane layer is made of one or more of the following materials: polyethylene, polypropylene, polyvinylidene fluoride-co-hexafluoropropylene, polyimide, and glass fiber.

[0015] Furthermore, the cation in the ionic liquid is one or more of the following: 1-hexyl-3-methylimidazolium cation, 1-butyl-3-methylimidazolium cation, 1-ethyl-3-methylimidazolium cation, and diethylmethyl-(2-methoxyethyl)ammonium cation; and the anion is one or more of the following: bis(trifluoromethanesulfonyl)imide ion, hexafluorophosphate ion, tetrafluoroborate ion, dinitrileamine 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 thin film with a sheet resistance of 12Ω / sq and a square ring shape. The material is ITO, the array period is a = 8mm, the inner diameter of the square ring is b = 2.5mm, the outer diameter of the square ring is c = 3.5mm, the thickness of the infrared transparent substrate is d = 2mm, and the infrared transparent substrate material is ZnS. The thickness of the carbon-based variable emissivity composite film is 50-80μm, which includes an upper carbon nanofilm layer, a porous membrane filled with ionic liquid, and a lower carbon nanofilm layer. Both the upper and lower carbon nanofilm layers are made of carbon nanotubes. The porous membrane is made of a mixture of polyethylene and polypropylene, and the porous membrane is impregnated with 1-ethyl-3-methylimidazolium diimide salt ionic liquid.

[0017] The advantages of this invention compared to existing technologies are as follows: By selecting an infrared-transparent medium and designing a low-duty-cycle ITO resonant structure, a metamaterial absorbing structure with high infrared transmittance (greater than 85%) and wide-band radar absorption is achieved. Combined with the infrared-transparent metamaterial absorbing structure designed above, the radar absorption performance of electrovariable emissivity devices is made compatible, solving the problem that electrovariable emissivity devices lack radar stealth capabilities. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of a radar-compatible variable infrared emissivity device according to one embodiment of the present invention.

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

[0020] Figure 3 This is a schematic diagram of the structural units of one embodiment of the present invention;

[0021] Figure 4 This is a diagram showing the reflectivity and absorptivity of a structural unit according to one embodiment of the present invention. Detailed Implementation

[0022] To better understand the technical solution of the present invention, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0023] A radar-compatible variable infrared emissivity device is composed of structural units in a periodic array, see [link to relevant documentation]. 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] Carbon-based variable emissivity composite films reflect almost all incident microwaves. Therefore, by constructing a microwave-absorbing metamaterial with a metal / dielectric / metal sandwich structure on top of the carbon-based variable emissivity composite film, it is possible to absorb radar in specific frequency bands and achieve camouflage and stealth that is compatible with microwave absorption and variable infrared characteristics.

[0025] In this embodiment, the metamaterial absorbing structure 11 adopts a specific sheet resistance ITO film design. Since the ITO film does not have infrared transmittance, the metamaterial absorbing structure 11 needs to be designed with a pattern with the smallest possible duty cycle to reduce the impact on infrared transmission. Infrared transparent ZnS is selected as the infrared transparent substrate 12, with a dielectric constant of 8.3 (1+0.0001i), which can transmit both infrared light and microwaves. The infrared transmittance of ZnS can be further improved by depositing an antireflection coating, thereby enhancing the infrared modulation capability of the overall device. The carbon-based variable emissivity composite film 21 on the substrate acts as a reflective layer, which can enhance the radar absorption intensity. The carbon-based variable emissivity composite film 21 consists of an upper carbon nanofilm layer, a porous membrane filled with ionic liquid, and a lower carbon nanofilm layer. The upper carbon nanofilm layer is an infrared emissivity modulation layer. See [link to documentation]. Figure 2 By applying different voltages to the upper and lower carbon nanofilm layers, the infrared emissivity of the infrared emissivity modulation layer (i.e., the upper carbon nanofilm layer) is varied. Specifically, the electrode circuit board 22 has two electrode strips connected to the upper and lower carbon nanofilm layers respectively. The two electrode strips are connected to the voltage input port. The circuit board can be a flexible polyimide circuit board or a rigid epoxy resin circuit board.

[0026] Based on electromagnetic simulation design, and taking into account the pattern area duty cycle of the resonant absorption structure, the sheet resistance variation of the electrovariable layer, and the radar absorption bandwidth, an optimized metamaterial structural unit is obtained as follows: Figure 3 As shown, the metamaterial absorbing structure 11 is a square ring structure. The array period a = 8 mm, the inner diameter of the square ring b = 2.5 mm, the outer diameter of the square ring c = 3.5 mm, the thickness of the infrared transparent substrate 12 d = 2 mm, and the sheet resistance of ITO is 12 Ω / sq. The duty cycle of the pattern area of ​​this ITO resonant structure is only 9.375%. The simulation results of the reflectivity and absorptivity of the metamaterial absorbing structure are as follows. Figure 4 As shown, the solid line represents reflectivity, and the dashed line represents absorptivity. The absorptivity is greater than 90% in the 9.6-15.5 GHz band, with an effective absorption bandwidth of 5.9 GHz, and two absorption peaks at 10.9 GHz and 14.3 GHz.

[0027] The initial ZnS window has an average infrared transmittance of approximately 70% in the 8-14 μm range. After double-sided antireflection coating, the average transmittance reaches 92%. Subsequently, an ITO conductive film is deposited on the antireflection film. Due to the presence of the ITO conductive film, the ZnS dielectric substrate cannot transmit infrared light. The excess ITO conductive film is etched away using a femtosecond ultraviolet laser, finally obtaining the designed square ring structure. Because the conductive film is etched away, the ZnS dielectric substrate still maintains a high infrared transmittance, with an overall transmittance greater than 85%.

[0028] The carbon-based variable emissivity composite film 21 has a thickness of approximately 50-80 μm. Preferably, it consists of an upper carbon nanotube film, a middle polyethylene-polypropylene separator, and a lower carbon nanotube film. The polyethylene-polypropylene separator is impregnated with a 1-ethyl-3-methylimidazolium diimide salt ionic liquid. The two carbon nanotube films and the Celgard separator with the ionic liquid are respectively laid flat on a flexible electrode circuit board. The two carbon nanotube films are connected to two electrodes, respectively. The interface of the flexible circuit board is connected to an external voltage source. By applying different voltage loads, the radiation characteristics can be modulated. At a voltage load of 3V, the device exhibits a low emissivity of approximately 0.35; at a voltage load of -1.7V, the device exhibits a high emissivity of approximately 0.75, with an infrared emissivity modulation range of approximately 0.4.

[0029] It is understood that this invention has been described through embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of this invention. Furthermore, under the teachings of this invention, these features and embodiments can be modified to adapt to specific circumstances without departing from the spirit and scope of this invention. Therefore, this invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are protected by this invention.

[0030] The contents not described in detail in this specification are common knowledge to those skilled in the art.

Claims

1. A variable infrared emissivity device compatible with radar wave absorption, characterized in that: Each structural unit comprises an infrared transparent radar absorbing layer (1) and an electrochromic emissivity layer (2), the infrared transparent radar absorbing layer (1) comprises an infrared transparent substrate (12) and a metamaterial absorbing structure (11) on the infrared transparent substrate, the metamaterial absorbing structure (11) is an electromagnetic structure made of a conductive film with a certain sheet resistance value and a pattern shape, for a single structural unit, the array period a is 5-15 mm, the pattern area of the metamaterial absorbing structure (11) accounts for 8-15% of the area of the structural unit, and the sheet resistance is 8-30 Ω / sq; the electrochromic emissivity layer (2) comprises a carbon-based variable emissivity composite film (21) and an electrode circuit board (22), and the infrared emissivity of the carbon-based variable emissivity composite film (21) is changed through the electrode circuit board (22); the electrochromic emissivity layer (2) is located below the infrared transparent substrate (12).

2. The radar wave-absorbing and variable infrared emissivity compatible device according to claim 1, characterized in that: The pattern shape of the metamaterial absorbing structure (11) is a square, a circle, a diamond, a square ring or a circular ring; the material is ITO, silver nanowire or random metal mesh.

3. The radar wave-absorbing and variable infrared emissivity compatible device of claim 1, wherein: The metamaterial absorbing structure (11) absorbs microwaves in the frequency band of 8-18 GHz.

4. The radar wave-absorbing and variable infrared emissivity compatible device of claim 1, wherein: The transparent substrate thickness d of the infrared transparent substrate (12) is 1-10 mm, and the material is ZnSe, ZnS, GaF2 or Ge.

5. The variable infrared emissivity device compatible with radar and wave absorption according to any one of claims 1 to 4, characterized in that: The infrared transparent substrate (12) is coated with an infrared anti-reflection film layer on both sides 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.

6. The radar wave-absorbing and variable infrared emissivity compatible device of claim 1, wherein: The carbon-based variable emissivity composite film (21) comprises an upper carbon nanomembrane layer, a porous diaphragm filled with ionic liquid and a lower carbon nanomembrane layer; the upper carbon nanomembrane layer is an infrared emissivity modulation layer, and by applying different voltages to the upper carbon nanomembrane layer and the lower carbon nanomembrane layer through the electrode circuit board (22), the infrared emissivity of the infrared emissivity modulation layer is changed.

7. The radar-absorbent, variable-infrared-emissivity device of claim 6, wherein: The carbon nanomembrane material of the upper carbon nanomembrane layer and the lower carbon nanomembrane layer is graphene, semiconductor carbon nanotube or multi-walled carbon nanotube.

8. The radar wave-absorbing and variable infrared emissivity compatible device of claim 6, wherein: The material of the porous diaphragm layer is one or more of polyethylene, polypropylene, polyvinylidene-co-hexafluoropropylene, polyimide and glass fiber.

9. The radar wave-absorbing and variable infrared emissivity compatible device of claim 6, wherein: The cation in the ionic liquid is 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 anion is one or more of bistrifluoromethanesulfonylimide ion, hexafluorophosphate ion, tetrafluoroborate ion, dicyanamide ion, p-toluenesulfonate ion and thiocyanate ion.

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

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