Astronavigation-level terahertz stealth thermal control film and preparation method thereof

Abstract

The invention discloses an astronavigation-level terahertz stealth thermal control film and a preparation method thereof, and relates to the field of spacecraft functional materials, the stealth thermal control film comprises an ITO resonance layer, a base material layer and a reflecting layer which are arranged from outside to inside, the base material layer is a polymer flexible film (such as PI or P46), the reflecting layer is a metal coating (such as aluminum and silver), and the ITO resonance layer, the base material layer and the reflecting layer are arranged from outside to inside. And the ITO resonance layer is an ITO array with a hollow pattern. The preparation method comprises the following steps: plating a metal reflecting layer on one surface of a base material layer, pasting a proper mask on the other surface of the base material layer, carrying out resonance layer coating treatment, cutting, and removing the mask to obtain the invisible thermal control film. The thin film is simple and reasonable in structure, thin in thickness and wide in wave absorbing frequency band, the flexible thin film is suitable for large-area manufacturing, the surface of a satellite structure is flexibly wrapped with the thin film, the sealing edge with holes is arranged, the thin film has excellent thermal control performance, meanwhile, the surface radar scattering cross section can be effectively reduced, and the thin film can be widely applied to the fields of spacecraft terahertz radar stealth, electromagnetic shielding, electromagnetic protection and the like.

Description

Technical Field

[0001] The present invention relates to the field of spacecraft functional materials, and in particular to a space-grade terahertz stealth thermal control film and a preparation method thereof. Background Art

[0002] Terahertz waves refer to electromagnetic waves with a frequency range of 0.1THz to 10THz, which are located in the transition frequency band between microwaves and infrared. Compared with microwaves and millimeter waves, terahertz waves have shorter wavelengths and wider bandwidths, and have the advantages of strong information transmission capabilities and high detection accuracy. They have important application value in high-resolution imaging and fine identification of targets. Compared with infrared and laser, terahertz wave radar has a wider detection field of view and better search capabilities, and can be used for combat in complex environments and detection of high-speed moving targets in space. At the same time, terahertz radars have strong anti-interference capabilities and small functional device sizes. Highly integrated, miniaturized, and arrayed terahertz radar systems have become one of the important development directions for the next generation of space-based high-resolution detection radars. Therefore, it is necessary to improve the satellite's stealth capability in the terahertz band and reduce its detectability in orbit.

[0003] The surface of a satellite is usually covered with multiple layers of thermal insulation. Under vacuum conditions, the reflective layer can reflect multiple times to improve the thermal resistance of radiation heat transfer, which can achieve efficient thermal insulation and keep the instruments and equipment in the satellite at a suitable temperature level. The thin-film secondary surface mirror on its outer surface is vacuum-plated with aluminum or silver on a flexible film to form a reflector. The flexible thin-film secondary surface mirror can be prepared and used on a large scale, and is suitable for curved and shaped surfaces of satellites. It is the thermal control material with the largest range of uses in satellites. It usually has an extremely high radar cross-section (RCS) and is very easy to detect or track. Commonly used thin-film secondary surface mirrors include F46 silver-plated and polyimide aluminum-plated secondary surface mirrors, etc., which are composed of multi-layer thermal insulation components in the form of multi-layer composites to achieve the thermal control function of the satellite.

[0004] With the development of space target detection systems, the demand for satellite stealth is becoming increasingly stronger. It is necessary to develop a satellite secondary surface mirror with low surface RCS. Chinese patent application publication number CN106336128A discloses a flexible OSR secondary surface mirror thermal control coating and its preparation method and use, but does not have terahertz stealth function. Chinese patent announcement number CN112501559B proposes a method for preparing a perforated antistatic polyimide film aluminum-plated secondary surface mirror, which does not have terahertz stealth function. Chinese patent application publication number CN117977223A proposes a broadband and incident angle stable optically transparent terahertz stealth body, without considering thermal control function. A secondary surface mirror that has both satellite thermal control and terahertz stealth functions has not been reported. Summary of the invention

[0005] In view of this, the purpose of the present invention is to provide a space-grade terahertz stealth thermal control film and a preparation method thereof. The stealth thermal control film has thermal control properties of low solar absorption ratio and high emissivity, can achieve efficient wave absorption in the terahertz band, and reduce the risk of satellites being detected by radar in orbit.

[0006] The objective of the present invention is achieved through the following technical solutions:

[0007] <First aspect>

[0008] The present invention provides a space-grade terahertz stealth thermal control film, comprising an ITO resonance layer, a substrate layer and a reflective layer arranged from the outside to the inside, wherein the substrate layer is a polymer flexible film, the reflective layer is a metal plating layer, the ITO resonance layer is an ITO array with a hollow pattern, and holes are opened on the edge sealing.

[0009] As an embodiment, the substrate layer is a PI film or a F46 film.

[0010] As an embodiment, the reflective layer is an aluminum coating or a silver coating.

[0011] As an embodiment, the substrate layer has a thickness of 25 to 200 μm.

[0012] As an embodiment, the thickness of the reflective layer is 120-300 nm.

[0013] As an embodiment, the thickness of the ITO resonance layer is 30-50 nm.

[0014] As an embodiment, the sheet resistance of the ITO resonance layer is 1 to 1.5 kΩ / □.

[0015] As an embodiment, the ITO resonance layer is an array composed of a plurality of resonance units.

[0016] In some embodiments, the substrate layer is a PI film with a thickness of 150 μm, the reflective layer is an aluminum coating with a thickness of 160 nm, and the ITO resonance layer is an ITO pattern layer with a thickness of 50 nm and a square resistance of 1 kΩ / □.

[0017] In some embodiments, the overall size of the resonance unit is 25 mm×25 mm.

[0018] As an embodiment, the stealth thermal control film further includes a perforated edge seal provided on the edge of the multilayer structure.

[0019] <Second Aspect>

[0020] The present invention provides a method for preparing a space-grade terahertz stealth thermal control film, comprising the following steps:

[0021] S1, plating a metal reflective layer on one side of the substrate layer;

[0022] S2, pasting a mask on the other side of the substrate layer;

[0023] S3, performing resonance layer coating on the side of the substrate layer on which the mask is attached;

[0024] S4, cutting the thermal control film, removing the mask, and obtaining the stealth thermal control film.

[0025] As an embodiment, in step S1, the reflective layer coating parameters are: vacuum degree is not less than 10 -4 Pa.

[0026] As an embodiment, in step S2, the mask is made of a material that is homogeneous with the substrate layer;

[0027] As an embodiment, in step S2, it can be temporarily attached to the substrate layer.

[0028] As an embodiment, in step S2, the mask is a hollow pattern array with a connected structure.

[0029] In some embodiments, in step S2, the mask has a backing adhesive.

[0030] As an embodiment, in step S2, the mask is prepared by laser cutting.

[0031] In some embodiments, in step S2, the laser cutting is carbon dioxide laser cutting.

[0032] As an implementation scheme, in step S2, the laser cutting uses a power of 10-50% and a cutting speed of 700-900 mm / s.

[0033] In some embodiments, in step S2, the laser cutting parameters are: laser band 10.6 μm, total power 30 W, use power 20%, and cutting speed 800 mm / s.

[0034] As an implementation scheme, in step S2, the mask is cut by laser cutting to form a hollow pattern that is complementary to the resonance unit.

[0035] As an embodiment, in step S3, the parameters of the resonance layer coating are: the vacuum degree before coating is not less than 10 -4 Pa, the oxygen content is controlled at 2% to 5% during coating, the power is 0.6 to 1kW, and the temperature does not exceed 250°C.

[0036] In some embodiments, in step S3, the oxygen content is controlled to be 3%, the power is 1 kW, and the temperature is 200° C. during coating.

[0037] As an embodiment, in step S3, the resonant layer coating area should be significantly larger than the mask coverage area.

[0038] As an implementation scheme, between steps S3 and S4, the surface sheet resistance of the non-masked area is measured, and if the sheet resistance is 1-1.5 kΩ / □, step S4 is performed.

[0039] As an embodiment, after step S4, the method further includes installing the stealth thermal control film on the surface of the part to be installed and then performing edge sealing treatment on the edge sealing material with holes.

[0040] In some embodiments, the substrate layer is a PI film, the reflective layer is an aluminum coating, and the resonant film layer is an ITO layer.

[0041] <Third Aspect>

[0042] The present invention provides an application of a space-grade terahertz stealth thermal control film.

[0043] The stealth thermal control film is suitable for application on the structural surface of a spacecraft.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] 1) The stealth thermal control film provided by the present invention has a simple and reasonable structure, small additional weight, strong feasibility, and the flexible film is suitable for large-area manufacturing and can be flexibly applied to the surface of satellite structures. It has thermal control performance with low solar absorption ratio and high emissivity, and at the same time has terahertz stealth function, which can effectively reduce the radar scattering cross-section of the satellite surface.

[0046] 2) The stealth thermal control film provided by the present invention has a thin thickness, a wide absorption bandwidth, and is insensitive to the polarization direction of the incident electromagnetic wave. Different resonant unit structures can be designed according to the radar detection band, and efficient absorption can be achieved in different scenarios through parameter control.

[0047] 3) The stealth thermal control film provided by the present invention can be widely used in the fields of spacecraft terahertz radar stealth, electromagnetic shielding, electromagnetic protection, etc., and has strong compatibility with existing thermal control systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0049] Figure 1 This is a schematic diagram of the side structure (excluding edge sealing) of the stealth thermal control film of Example 1 of the present invention;

[0050] Figure 2 This is a schematic diagram of the planar structure of the stealth thermal control film of Example 1 of the present invention when viewed from the resonance layer side;

[0051] Figure 3 This is a schematic diagram of the preparation process of the stealth thermal control film according to Example 2 of the present invention;

[0052] Figure 4 Schematic diagram of the structure of a hollow pattern in the mask in Example 2 of the present invention. DETAILED DESCRIPTION

[0053] The present invention is described in detail below in conjunction with embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, some adjustments and improvements can also be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0054] For ease of understanding, let us first explain the English terms mentioned below:

[0055] PI film: polyimide film;

[0056] F46 film: FEP film;

[0057] ITO: Indium Tin Oxide.

[0058] Example 1

[0059] This embodiment provides a space-grade terahertz stealth thermal control film, such as Figure 1 and Figure 2 As shown, it includes a substrate layer 1, a reflective layer 2 and an ITO resonant layer 3. The substrate layer 1 is a polymer flexible film (such as PI, F46) with high visible light transmittance and good adaptability to space environment. The reflective layer 2 is a metal coating (such as aluminum, silver) arranged on one side of the film substrate and has a high reflection coefficient. The ITO resonant layer 3 is an ITO hollow pattern array arranged on the other side of the film substrate. Terahertz stealth is achieved through impedance matching and multi-mode resonance. At the same time, ITO has high transmittance in the visible light band and does not affect the thermal control performance.

[0060] Furthermore, the thickness of the substrate layer 1 is 25-200 μm, the thickness of the reflective layer 2 is 120-300 nm, the thickness of the ITO resonance layer 3 is 30-50 nm, and the sheet resistance is 1-1.5 kΩ / □.

[0061] The ITO resonance layer is an array composed of a plurality of resonance units 4 .

[0062] When in use, the stealth thermal control film serves as the outermost film of the multi-layer thermal insulation component, with the ITO resonance layer facing outer space, and is entirely covered on the surface of the satellite structure, realizing the satellite surface thermal control function and terahertz stealth function, and is suitable for large-scale manufacturing and use.

[0063] The stealth thermal control film, when used as the outermost film of a multi-layer thermal insulation component, also includes a perforated edge seal, which is arranged at the edge of the multi-layer structure of the stealth thermal control film to release residual gas inside the multi-layer component to ensure the thermal insulation effect.

[0064] The following is a specific introduction using Example 2, in which the film substrate is a PI film with a thickness of 150μm, the reflective layer is an aluminum coating with a thickness of 160nm, the ITO resonance layer is a stealth thermal control film with a thickness of 50nm, a square resistance of 1kΩ / □, and an overall size of the resonance unit 4 of 25mm×25mm.

[0065] Example 2

[0066] This embodiment provides a method for preparing a space-grade terahertz stealth thermal control film. Figure 3 and Figure 4 As shown, the following steps are included:

[0067] S1, coating an aluminum reflective layer on one side of the PI film;

[0068] S2, pasting a mask on the other side of the PI film;

[0069] S3, performing ITO coating on the side of the PI film with the mask attached;

[0070] S4. Detect the sheet resistance. If it meets the requirement of 1-1.5 kΩ / □, cut the thermal control film, remove the mask, and obtain the stealth thermal control film.

[0071] Furthermore, before step S1, the PI film needs to be inspected before the aluminum reflective layer is plated, and the appearance of the film needs to be checked to confirm that the color is uniform, there is nothing on the surface, no stains, and no obvious defects such as ribs and wrinkles.

[0072] Furthermore, in step S1, in the coating tooling, vacuum is drawn before aluminum plating, and the vacuum degree is not less than 10 -4 Pa, aluminum plating is performed.

[0073] Furthermore, in step S2, a carbon dioxide laser cutting device is used to cut the PI film with adhesive backing to make a mask, with a laser band of 10.6 μm, a total power of 30 W, an operating power of 20%, and a cutting speed of 800 mm / s.

[0074] Furthermore, in step S2, the mask is a hollow pattern array, which is a connected structure with symmetry, and the hollow pattern array is cut out by laser.

[0075] Furthermore, in step S2, the cut mask is pasted on one side of the PI film without the aluminum reflective layer through a positioning tool, preferably on the central area of ​​the PI film, so that the ITO coating area is significantly larger than the mask coverage area, ensuring that the ITO pattern layer is uniform.

[0076] Further, in step S3, the PI film with the mask attached is placed in the coating equipment, and the vacuum degree is not less than 10 -4 Pa, the ITO resonance layer was plated, the oxygen content was set to 3%, the power was 1 kW, and the temperature was 200°C during the plating process.

[0077] Furthermore, in step S4, the PI film after being plated with the ITO resonance layer is taken out, and the surface square resistance is tested using a four-probe resistance meter at the position not covered by the mask. If the requirements are met, the thermal control film is cut and the mask is removed to obtain a terahertz stealth thermal control film with an aluminum-plated reflective layer on one side and an ITO resonance layer on the other side.

[0078] In this embodiment, the PI film has good radiation resistance in space, and the aluminum-plated reflective layer has high reflectivity in the visible light and near-infrared bands. At the same time, it will oxidize in space to form a protective film with stable performance.

[0079] This embodiment provides a method for preparing a space-grade terahertz stealth thermal control film, which also includes using the stealth thermal control film as the outermost film of a multi-layer thermal insulation component, edge sealing the edge sealing material with holes, and installing it on the surface of the part to be installed to ensure the thermal insulation effect of the multi-layer thermal insulation component.

[0080] Detection and analysis

[0081] The terahertz stealth thermal control film prepared in Example 2 was tested for wave absorption performance, thermal control performance and vacuum degassing performance. The terahertz wave absorption performance test was performed using a terahertz time-domain spectrometer, and the absorption rate in the frequency range of 0.38THz to 1.5THz was measured to be better than 90%. The solar absorption ratio was tested to be 0.34 and the hemispherical emissivity was 0.69, which met the satellite thermal control requirements.

[0082] The vacuum degassing performance test was carried out according to the provisions of QJ1558. The total mass loss (TML) and condensable volatile matter (CVCM) of the material in vacuum were calculated to be 0.4203% and 0.0559% respectively, which met the vacuum degassing requirements of aerospace materials.

[0083] In summary, the aerospace-grade terahertz stealth thermal control film is an electromagnetic metamaterial absorber that can absorb incident electromagnetic waves at the working wavelength and convert them into ohmic heat or other forms of energy. It is a three-layer structure, with a surface structure composed of periodically arranged ITO resistor film units, an intermediate PI film as a dielectric layer, and a complete metal aluminum coating as a reflective layer. When the input impedance of the surface unit structure matches the air, the electromagnetic wave has no reflection, passes through the dielectric layer, is reflected back by the reflective layer, and interferes with the subsequent incident wave. By adjusting the structural parameters and material properties of the surface resonance unit, the equivalent magnetic permeability and equivalent dielectric constant can be adjusted to achieve maximum absorption of electromagnetic waves. The energy loss of the absorbing thermal control film is mainly concentrated in the ITO film, which relies on ohmic loss to convert electromagnetic waves into other forms of energy to increase the absorption rate of electromagnetic waves. The aerospace-grade terahertz stealth thermal control film is thin, has a wide absorption frequency band, and is insensitive to the polarization direction of the incident electromagnetic wave.

[0084] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A space-grade terahertz stealth thermal control film, characterized in that: The stealth thermal control film includes an ITO resonance layer, a substrate layer and a reflection layer arranged from the outside to the inside, the substrate layer is a polymer flexible film, the reflection layer is a metal plating layer, and the ITO resonance layer is an ITO array with a hollow pattern.

2. The aerospace-grade terahertz stealth thermal control film according to claim 1, characterized in that: It also includes at least one of the following technical features: A. The substrate layer is a PI film or a F46 film; B. The reflective layer is an aluminum coating or a silver coating.

3. The aerospace-grade terahertz stealth thermal control film according to claim 1, characterized in that: It also includes at least one of the following technical features: A. The thickness of the substrate layer is 25 to 200 μm; B. The thickness of the reflective layer is 120 to 300 nm; C. The thickness of the ITO resonance layer is 30 to 50 nm; D. The sheet resistance of the stealth thermal control film is 1 to 1.5 kΩ / □.

4. The aerospace-grade terahertz stealth thermal control film according to claim 1, characterized in that: The stealth thermal control film also includes a perforated edge seal arranged at the edge of the multi-layer structure.

5. The method for preparing the aerospace-grade terahertz stealth thermal control film according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1, plating a metal reflective layer on one side of the substrate layer; S2, pasting a mask on the other side of the substrate layer; S3, performing resonance layer coating on the side of the substrate layer on which the mask is attached; S4, cutting the thermal control film, removing the mask, and obtaining the stealth thermal control film.

6. The method for preparing the aerospace-grade terahertz stealth thermal control film according to claim 5, characterized in that: It also includes at least one of the following technical features: In step S1, the reflective layer coating parameters are: vacuum degree not less than 10 -4 Pa; In step S2, the mask is prepared by laser cutting at a cutting speed of 700 to 900 mm / s; In step S3, the parameters of the resonance layer coating are: the vacuum degree before coating is not less than 10 -4 Pa, the oxygen content is controlled at 2% to 5% during coating, the power is 0.6 to 1kW, and the temperature does not exceed 250°C.

7. The method for preparing the aerospace-grade terahertz stealth thermal control film according to claim 5, characterized in that: It also includes at least one of the following technical features: In step S2, the mask can be temporarily attached to the substrate layer; In step S2, the mask is a hollow pattern array with a connected structure.

8. The method for preparing the aerospace-grade terahertz stealth thermal control film according to claim 5, characterized in that: In step S2, the mask is made of the same material as the substrate layer.

9. The method for preparing the aerospace-grade terahertz stealth thermal control film according to claim 5, characterized in that: Between steps S3 and S4, the surface sheet resistance of the non-masked area is measured. If the sheet resistance is 1 to 1.5 kΩ / □, step S4 is performed.

10. Use of the aerospace-grade terahertz stealth thermal control film according to any one of claims 1 to 4, characterized in that: The stealth thermal control film is applied to the structural surface of the spacecraft.

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