Flexible cross-band compatible electromagnetic camouflage metasurface and preparation method thereof

Abstract

The invention provides a flexible cross-band compatible electromagnetic camouflage metasurface and a preparation method thereof, and the metasurface achieves high-absorptivity electromagnetic camouflage of visible-infrared bands through a micro-nano feature structure formed by a metal-dielectric material, and achieves high transmittance in a microwave band through the design of gaps of periodic patterns. The preparation method comprises the following steps: preparing the cross-band compatible electromagnetic camouflage structure on a hard substrate, and transferring the cross-band compatible electromagnetic camouflage structure to a flexible substrate through wet stripping or laser stripping and other processes. According to the invention, a visible-infrared wave-absorbing structure and a microwave transmission structure are organically integrated to form a cross-band compatible electromagnetic camouflage function layer, and the cross-band compatible electromagnetic camouflage function layer can be transferred to a flexible substrate to realize conformal fitting of complex curved surfaces such as a radome.

Description

Technical Field

[0001] This invention relates to the field of flexible electronics technology, specifically to a flexible cross-band compatible electromagnetic camouflage metasurface and its preparation method. Background Technology

[0002] LiDAR, with its advantages of high detection accuracy and strong tracking capabilities, has been widely used in the field of aircraft detection and tracking. Correspondingly, the design and fabrication methods of electromagnetic camouflage metasurfaces for LiDAR have also received considerable attention. Furthermore, LiDAR can be used in conjunction with traditional infrared radar for joint detection, driving the development of existing electromagnetic camouflage metasurfaces towards cross-band compatible electromagnetic camouflage.

[0003] Currently, it is possible to design electromagnetic camouflage materials or structures compatible with visible-laser-infrared-radar electromagnetic camouflage. For example, Chinese patent document CN114716148B discloses a glass-ceramic material that meets the aforementioned cross-band compatibility requirements, achieving absorption in all designed wavebands. Chinese patent document CN112111720B discloses a laser, infrared, and microwave compatible electromagnetic camouflage material, its preparation method, and its application. This material achieves low reflectivity in three commonly used lidar wavebands and high reflectivity in most infrared wavebands within the 3-5μm and 8-14μm ranges by stacking dielectric materials of different refractive indices in a one-dimensional photonic crystal. Below the one-dimensional photonic crystal is a radar-absorbing material layer used to achieve high absorption in the 2-18GHz microwave band. However, aircraft radomes or communication modules need to achieve both visible-infrared (including lidar wavebands) electromagnetic camouflage and high transmittance in the microwave band, and currently, there are few designs and preparation methods for such cross-band compatible electromagnetic camouflage metasurfaces. Furthermore, metallic material layers or micro / nano structures are often used in the design of absorbing metasurfaces in the visible-near-infrared band. Since microwave wavelengths are significantly longer than visible-near-infrared wavelengths, metallic material layers or micro / nano structures severely reduce microwave transmittance. Therefore, a universal, cross-band compatible metasurface design method is needed to enable visible-near-infrared metasurfaces to maintain high microwave transmittance. In addition, the surfaces of components such as radomes are complex curved surfaces, necessitating the fabrication of cross-band compatible electromagnetic camouflage metasurfaces on flexible substrates before laminating them onto the curved surfaces.

[0004] In summary, the surfaces of components such as aircraft radomes need to have high absorption electromagnetic camouflage characteristics in the visible-infrared band, but high transmittance characteristics are required in the microwave band. Therefore, there is an urgent need to design flexible electromagnetic camouflage metasurfaces with such cross-band compatible characteristics. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a flexible, cross-band compatible electromagnetic camouflage metasurface and its preparation method.

[0006] A flexible, cross-band compatible electromagnetic camouflage metasurface according to the present invention is characterized by comprising: Flexible substrate; and A cross-band compatible electromagnetic camouflage structure disposed on the flexible substrate; The cross-band compatible electromagnetic camouflage structure includes visible-infrared band absorbing units and a gap structure that allows microwaves to pass through. The visible-infrared absorbing unit is composed of a micro-nano feature structure made of metal-dielectric materials, which is used to achieve a high absorption rate of incident light in the 350nm-20μm band. The microwave-transmitting gap structure is composed of visible-infrared band absorbing units arranged laterally with a certain gap, used to achieve high microwave signal transmittance in the 300MHz~300GHz band.

[0007] Preferably, the flexible cross-band compatible electromagnetic camouflage metasurface is characterized in that the micro-nano feature structure of the visible-infrared absorbing unit is a one-dimensional photonic crystal structure formed by longitudinally arranging multiple layers of continuous thin films of metal or dielectric material, or a resonant structure containing discrete micro-nano patterns; the micro-nano feature structure of the visible-infrared absorbing unit absorbs incident light through interlayer interference, surface plasmon resonance, or surface lattice resonance.

[0008] Preferably, in the flexible cross-band compatible electromagnetic camouflage metasurface, the microwave-transmittable gap structure includes a pattern shape that is one or more combinations of circles, polygons, and rings.

[0009] The present invention provides a method for preparing a flexible, cross-band compatible electromagnetic camouflage metasurface, comprising the following steps: Step S1: The micro-nano feature structures for high absorption in the visible-infrared band are patterned with a certain lateral gap so that they have high transmittance in the designed microwave band while maintaining their high absorption capacity in the visible-infrared band, forming a cross-band compatible electromagnetic camouflage structure. Step S2: The cross-band compatible electromagnetic camouflage structure is fabricated on a rigid substrate using micro-nano fabrication technology; Step S3: Transfer the cross-band compatible electromagnetic camouflage structure prepared on a rigid substrate to a flexible substrate to obtain a flexible cross-band compatible electromagnetic camouflage metasurface.

[0010] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention creatively solves the contradictory technical requirements of achieving high absorption rate electromagnetic camouflage in the visible-infrared band and high transmittance in the microwave band by integrating specially designed micro-nano feature units and gap structures with larger feature sizes in the same structural layer.

[0011] 2. The cross-band compatibility of this invention stems from the ingenious design of a single composite structural layer, rather than a simple stacking of multiple materials. This integrated structure reduces the overall thickness of the functional layer, which helps improve the mechanical durability and environmental reliability of the functional structure on a flexible membrane substrate, making it more suitable for weight-sensitive platforms such as aircraft.

[0012] 3. This invention successfully fabricates precise micro / nano structures on flexible substrates using a fabrication strategy of "first preparing on a rigid substrate, then transferring to a flexible substrate." The resulting flexible metasurface can conform to the complex curved surfaces of equipment such as radomes and antenna covers, achieving conformal coverage. Without altering the original aerodynamic shape or affecting the normal operation of the microwave antenna, it significantly enhances the visible-infrared electromagnetic camouflage capability of the platform, greatly expanding its application scenarios. Attached Figure Description

[0013] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a schematic diagram of the process for preparing the flexible cross-band compatible electromagnetic camouflage metasurface and its preparation method in an embodiment of the present invention; Figure 2 This is a schematic diagram of a cross-band compatible electromagnetic camouflage structure that is compatible with microwave band high transmittance, formed by arranging visible-infrared band absorbing electromagnetic camouflage structures at certain intervals in an embodiment of the present invention. Figure 3 This is a schematic diagram illustrating the working effect of the flexible cross-band compatible electromagnetic camouflage metasurface being attached to the radome surface in an embodiment of the present invention.

[0014] Explanation of reference numerals in the attached figures: 1. Visible-near-infrared absorbing micro / nano features; 2. Cross-band compatible electromagnetic camouflage structure; 3. Flexible substrate; 4. Radar radome; 5. Microwave radar. Detailed Implementation

[0015] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0016] This invention provides a flexible, cross-band compatible electromagnetic camouflage metasurface, the core of which is a composite microstructure attached to a flexible substrate 3. This structure is not a single-function uniform coating, but a specially designed "cross-band compatible electromagnetic camouflage structure." Figure 3 As shown, the final form of the metasurface is a flexible film covering the curved surface of the target (such as radome 4), and its basic structure consists of a flexible substrate 3 and a cross-band compatible electromagnetic camouflage structure 2 attached thereto.

[0017] The key to this structure lies in its physical integration of two functional units: a visible-infrared absorbing structure and a microwave-transmitting gap structure. Specifically: Visible-infrared absorbing structure: This unit is realized by a micro-nano feature structure composed of metal and dielectric materials. Its function is to efficiently absorb incident visible to infrared light, with an operating wavelength range covering 350 nm to 20 μm.

[0018] Microwave band transmittance gap structure: This unit consists of a patterned array of visible-infrared absorbing structures arranged with certain gaps. The design principle is to ensure that the feature size of the patterned units is greater than 50 μm, and the gap between units is greater than 5 μm. This design allows longer wavelength microwaves (operating band covering 300 MHz to 300 GHz) to pass through the gaps between units, thus achieving high transmittance.

[0019] These two functional units are not stacked independently, but are designed by arranging and patterning micro-nano feature materials used to achieve visible-infrared absorption in a discrete pattern that is conducive to microwave transmission, thereby integrating the two functions on a single structural layer to form the cross-band compatible electromagnetic camouflage structure 2.

[0020] In a preferred embodiment, the absorbing unit is a one-dimensional photonic crystal structure, which is essentially a multilayer film structure formed by alternating stacks of various metals or dielectric materials in the form of continuous thin films in a direction perpendicular to the substrate. For example, a feasible material combination is an alternating arrangement of metal layers and dielectric layers. This structure mainly relies on the interference effect between the film layers to achieve strong absorption of light waves in a specific wavelength range. By rationally selecting the refractive index, extinction coefficient, and physical thickness of each layer, the high absorption wavelength range can be designed within the target range of 350nm-20μm.

[0021] In another preferred embodiment, the absorbing unit is a resonant structure comprising discrete micro / nano patterns. For example, metallic nanoparticles, nanopores, or other subwavelength-scale periodic patterns are fabricated on a substrate surface. This structure primarily utilizes physical mechanisms such as surface plasmon resonance or surface lattice resonance. When the incident light wavelength matches the resonant wavelength of the structure, the light energy is localized on the structure surface and efficiently converted into heat or other forms of energy, thereby achieving absorption. By designing the shape, size, period, and surrounding medium of the discrete micro / nano patterns, their resonant absorption peak can be precisely controlled to be located in the desired wavelength band.

[0022] To achieve high transmittance in the microwave band, the aforementioned absorbing material layer or structure needs to be "discretized," and the discretized pattern is arranged at certain intervals. The specific shape of this pattern can be diverse, such as circular, polygonal, cross-shaped, or annular geometric shapes, or combinations of these shapes. The specific shape of the pattern can be selected based on ease of processing or compatibility with the absorbing unit.

[0023] The characteristic dimensions of the discrete pattern units (side length for squares, diameter for circles, etc.) need to be greater than 50 μm, and the spacing between adjacent pattern units needs to be greater than 5 μm. This size range is crucial to ensuring that microwaves can pass through effectively. The wavelength of microwaves (e.g., for microwaves at GHz frequencies, the wavelength is on the order of centimeters) is much larger than this size and spacing, so microwaves will primarily view these discrete units as sparse scattering points, and most of the energy can pass through the gaps.

[0024] The method for preparing a flexible cross-band compatible electromagnetic camouflage metasurface of the present invention mainly includes three steps, the core idea of ​​which is "hard first, soft later", that is, first prepare a fine structure on a flat hard substrate, and then transfer it to a flexible substrate 3.

[0025] Step S1: Structural Design First, determine the initial structure (one-dimensional photonic crystal or resonant structure) of the target visible-infrared absorbing metasurface. Then, discretize and pattern this structure according to a feature size ≥50μm and a spacing ≥5μm. Through simulation optimization, ensure that the structure is optimized for microwave bands (e.g.,...) Figure 3 While ensuring high transmittance in the specified frequency band (300MHz-300GHz) when the medium microwave radar 5 is operating, its high absorption characteristics in the visible-infrared band (350nm-20μm) are preserved as much as possible, thus obtaining the final cross-band compatible electromagnetic camouflage structure.

[0026] Step S2: Fabrication of cross-band compatible electromagnetic camouflage structures on rigid substrates This step enables the fabrication of cross-band compatible electromagnetic camouflage structures on a rigid substrate. The rigid substrate can be a flat and stable material such as glass or sapphire. Micro-nano fabrication techniques such as photolithography deposition, printing, or electroplating can be employed.

[0027] Step S3: Transferring the cross-band compatible electromagnetic camouflage structure to the flexible substrate 3 This step completely transfers the fragile, cross-band compatible micro / nanostructure from the rigid substrate to the flexible substrate 3.

[0028] The flexible substrate 3 can be made of polydimethylsiloxane (PDMS) film, polyimide (PI) film, or polyethylene terephthalate (PET) film, etc. Transfer methods can employ techniques such as wet peeling or laser peeling. The final result is a substrate that can be adhered to complex curved surfaces (such as...). Figure 3 The flexible, cross-band compatible electromagnetic camouflage metasurface of the radar dome 4 in the middle.

[0029] In the description of this application, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0030] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A flexible, cross-band compatible electromagnetic camouflage metasurface, characterized in that, include: Flexible substrate (3); as well as A cross-band compatible electromagnetic camouflage structure (2) is disposed on the flexible substrate (3). The cross-band compatible electromagnetic camouflage structure (2) includes a visible-infrared band absorbing unit and a gap structure that allows microwaves to pass through. The visible-infrared absorbing unit is composed of a micro-nano feature structure (1) made of metal-dielectric material, which is used to achieve high absorption rate of incident light in the 350nm-20μm band. The microwave-transmitting gap structure is composed of visible-infrared band absorbing units arranged laterally with a certain gap, used to achieve high microwave signal transmittance in the 300MHz~300GHz band.

2. The flexible cross-band compatible electromagnetic camouflage metasurface according to claim 1, characterized in that, The micro-nano feature structure (1) of the visible-infrared absorbing unit is a one-dimensional photonic crystal structure formed by longitudinally arranging multiple layers of metal or dielectric material continuous thin films, or a resonant structure containing discrete micro-nano patterns; the micro-nano feature structure (1) of the visible-infrared absorbing unit absorbs incident light through interlayer interference, surface plasmon resonance or surface lattice resonance.

3. The flexible cross-band compatible electromagnetic camouflage metasurface according to claim 1, wherein the microwave-transmittable gap structure comprises a pattern shape that is one or more combinations of circles, polygons, and annulus.

4. A method for preparing a flexible, cross-band compatible electromagnetic camouflage metasurface, characterized in that, Includes the following steps: Step S1: The micro-nano feature structure (1) for high absorption in the visible-infrared band is patterned with a certain lateral gap so that it has high transmittance in the designed microwave band while maintaining its high absorption capacity in the visible-infrared band, forming a cross-band compatible electromagnetic camouflage structure (2). Step S2: The cross-band compatible electromagnetic camouflage structure is fabricated on a rigid substrate using micro-nano fabrication technology (2). Step S3: Transfer the cross-band compatible electromagnetic camouflage structure (2) prepared on a rigid substrate to a flexible substrate (3) to obtain a flexible cross-band compatible electromagnetic camouflage metasurface.

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