A microwave absorber compatible with microwave, infrared camouflage, and optical transparency.

Abstract

This invention discloses a microwave absorber compatible with microwave, infrared camouflage, and optical transparency, relating to the fields of multi-spectral compatibility and artificial intelligence. The invention comprises a first PET film disposed on the top surface of a PMMA dielectric layer, an ITO square ring patch disposed on the top surface of the first PET film with an opening, and an ITO square patch with a cross-shaped slit embedded within the top surface of the first PET film. The ITO square patch acts as a resistive film to reduce microwave loss and forms a three-layer microwave absorber with the first PET film and the PMMA dielectric layer. Furthermore, by changing the size of the ITO square patch, the spatial radiation characteristics of infrared electromagnetic waves can be controlled. Since the ITO patch, the first PET film, and the PMMA dielectric layer are all optically transparent materials, transparency to visible light electromagnetic waves is achieved. This allows the structure of this invention to achieve compatibility with microwave, infrared, and visible light bands, enabling wide application in full-band camouflage of equipment.

Description

Technical Field

[0001] This invention relates to the fields of multi-spectral compatibility and artificial intelligence technology, and in particular to a microwave absorber that is compatible with microwave, infrared camouflage, and optical transparency. Background Technology

[0002] Metasurfaces, as two-dimensional forms of metamaterials, are composed of artificially designed subwavelength-scale structural units and possess powerful functions such as electromagnetic wave manipulation, spectral camouflage, image encoding, and wavefront control. Based on their outstanding ability to modulate electromagnetic waves, metasurfaces can more flexibly and effectively modulate the phase, amplitude, polarization, and propagation mode of electromagnetic waves. Therefore, the application of functional devices composed of metasurfaces has been effectively expanded, providing new and effective methods in areas such as anomalous reflection, scattering cancellation, focusing, and multispectral camouflage. With the development of multi-sensor detection technology, current reconnaissance and detection technologies have placed higher demands on the camouflage and stealth of scattering targets. Therefore, multispectral camouflage technology has attracted widespread attention, especially for metasurfaces.

[0003] Currently, there are two typical approaches to camouflage for multispectral detection technology. The first is to combine different spectral camouflage methods with the same material system; integrating microwave-absorbing materials and optically transparent low-emissivity infrared materials into multilayer metasurfaces achieves compatible camouflage. This effectively reduces detectability in the multispectral range but also increases fabrication complexity. To address this, some wavefront modulation properties of metasurfaces are utilized to simplify functional layers, such as polarization conversion to reduce backscattering and cavity modes to dissipate electromagnetic waves. These microwave properties can be achieved with just one layer, providing space for inserting other spectral functional materials. The second approach is to construct selective camouflage systems based on the different requirements of different spectra. Through reflection splitting effects and infrared plasmon resonance, different coatings can match the required multi-band spectra, exhibiting excellent radiative thermal control capabilities and significantly reducing the apparent temperature under thermal imagers. Coatings with visible transparency and radiative cooling can be used for thermal management. Furthermore, phase change materials are widely used in switchable absorbers to adapt to constantly changing environments. However, these methods are primarily used in the laser and infrared bands.

[0004] However, in the current complex infrared background with multiple emissivity, camouflage materials are difficult to be compatible with microwave and visible light bands; secondly, infrared design is difficult to customize according to user or background environment, especially the coupling with microwave response, because customized infrared design will affect the microwave performance of single functional layer; in addition, for complex infrared background, infrared devices with single low infrared radiation characteristics or high infrared radiation characteristics are difficult to effectively achieve camouflage.

[0005] Therefore, current camouflage materials cannot simultaneously achieve compatibility with microwave, infrared, and visible light bands. Summary of the Invention

[0006] This invention provides a microwave absorber that is compatible with microwave, infrared camouflage, and optical transparency, which can solve the problem in the prior art that current camouflage materials are difficult to simultaneously achieve compatibility with microwave, infrared, and visible light bands.

[0007] This invention provides a microwave absorber compatible with microwave, infrared camouflage, and optical transparency, comprising multiple alternating metasurface units. Each metasurface unit includes a PMMA dielectric layer, a first PET film disposed on the top surface of the PMMA dielectric layer, an ITO square ring patch disposed on the top surface of the first PET film, and an opening provided on the ITO square ring patch.

[0008] An ITO square patch is provided on the top surface of the first PET film in the area inside the ITO square ring patch, and a cross-shaped slit is etched on the ITO square patch, dividing the ITO square patch into four equal parts.

[0009] Each of the metasurface units has an ITO square patch, a first PET film, and a PMMA dielectric layer forming a three-layer microwave absorber for absorbing electromagnetic waves.

[0010] The size of the ITO square patch on each metasurface unit is different, which is used to control the spatial radiation characteristics of infrared electromagnetic waves.

[0011] The ITO square patch, ITO square ring patch, first PET film, and PMMA dielectric layer are all optically transparent materials used to make electromagnetic waves in the visible light band transparent.

[0012] Preferably, a second PET film is disposed on the bottom surface of the PMMA dielectric layer, and an ITO base film is disposed on the bottom surface of the second PET film.

[0013] Preferably, the ITO square ring patch has a side length of 6mm, a width of 0.5mm, and an opening width of 1.8mm on the ITO square ring patch.

[0014] Preferably, the side length of the ITO square patch is 1mm to 5mm, and the width of the cross-shaped slit etched on the ITO square patch is 0.1mm.

[0015] Preferably, the PMMA dielectric layer has a thickness of 3.6 mm and a dielectric constant of 2.25. (1-j0.001) , j represents the imaginary unit of the imaginary part of the dielectric constant.

[0016] Preferably, both the first PET film and the second PET film have a thickness of 0.05 mm and a dielectric constant of 3.0.(1 -j0.06) , j represents the imaginary unit of the imaginary part of the dielectric constant.

[0017] Preferably, the thickness of the ITO substrate film, the ITO square patch, and the ITO square ring patch are all 200 nm, and the sheet resistance is 10 Ω / sq.

[0018] This invention provides a microwave absorber that is compatible with microwave, infrared camouflage, and optical transparency. Compared with the prior art, its advantages are as follows:

[0019] This invention comprises a first PET film disposed on the top surface of a PMMA dielectric layer, an ITO square ring patch disposed on the top surface of the first PET film with an opening, and an ITO square patch with a cross-shaped slit embedded in the top surface of the first PET film. The ITO square patch acts as a resistive film to reduce microwave loss and forms a three-layer microwave absorber with the first PET film and the PMMA dielectric layer. Furthermore, by changing the size of the ITO square patch, the spatial radiation characteristics of infrared electromagnetic waves can be controlled. Since the ITO patch, the first PET film, and the PMMA dielectric layer are all optically transparent materials, transparency to visible light electromagnetic waves can be achieved. This allows the structure of this invention to achieve compatibility across microwave, infrared, and visible light bands, enabling its wide application in full-band camouflage of equipment. Attached Figure Description

[0020] Figure 1 A schematic diagram of the overall structure of a microwave absorber compatible with microwave, infrared camouflage, and optical transparency, provided for an embodiment of the present invention;

[0021] Figure 2 A functional schematic diagram of a microwave absorber compatible with microwave, infrared camouflage, and optical transparency, provided for an embodiment of the present invention;

[0022] Figure 3 The present invention provides an architectural design and dimensional schematic diagram of a microwave absorber that is compatible with microwave, infrared camouflage, and optical transparency.

[0023] Figure 4 A schematic diagram of the Bayesian neural network architecture and auxiliary design process used in a microwave absorber that is compatible with microwave, infrared camouflage, and optical transparency, provided for an embodiment of the present invention.

[0024] Figure 5 A schematic diagram of the Euclidean distance distribution of a microwave absorber compatible with microwave, infrared camouflage, and optical transparency before and after cleaning, provided for an embodiment of the present invention;

[0025] Figure 6A schematic diagram of the neural network optimization process for a microwave absorber compatible with microwave, infrared camouflage, and optical transparency, provided for an embodiment of the present invention;

[0026] Figure 7 A schematic diagram of the error distribution of the final model of a microwave absorber compatible with microwave, infrared camouflage, and optical transparency, provided for an embodiment of the present invention;

[0027] Figure 8 A schematic diagram of regression analysis of the final prediction results of a microwave absorber compatible with microwave, infrared camouflage, and optical transparency, provided in an embodiment of the present invention;

[0028] Figure 9 A schematic diagram of the copolarization reflection performance of three micro-units with different infrared emissivity in a microwave absorber compatible with microwave, infrared camouflage, and optical transparency, provided for an embodiment of the present invention.

[0029] Figure 10 A schematic diagram showing the absorption rate, cross-polarization reflectivity, and co-polarization reflectivity of a micro-unit of a microwave absorber (meta-atom I) compatible with microwave, infrared camouflage, and optical transparency, provided for an embodiment of the present invention.

[0030] Figure 11 A schematic diagram showing the absorption rate, cross-polarization reflectivity, and co-polarization reflectivity of a micro-unit of a microwave absorber (meta-atom II) compatible with microwave, infrared camouflage, and optical transparency, provided for an embodiment of the present invention.

[0031] Figure 12 A schematic diagram showing the absorption rate, cross-polarization reflectivity, and co-polarization reflectivity of a micro-unit of a microwave absorber that is compatible with microwave, infrared camouflage, and optical transparency, provided for an embodiment of the present invention.

[0032] Figure 13 A schematic diagram comparing the far-field 3D scattering energy distribution of a microwave absorber compatible with microwave, infrared camouflage, and optical transparency, and a conventional ITO thin film under two electromagnetic wave perpendicular conditions, provided for embodiments of the present invention.

[0033] Figure 14 A schematic diagram comparing the far-field 3D scattering energy distribution of a microwave absorber compatible with microwave, infrared camouflage, and optical transparency, provided for an embodiment of the present invention, and a conventional ITO thin film under electromagnetic wave incident at 30°.

[0034] Figure 15 A schematic diagram comparing experimental and result values ​​of microwave scattering magnitude at a vertical incident angle for a microwave absorber compatible with microwave, infrared camouflage, and optical transparency, provided for an embodiment of the present invention.

[0035] Figure 16 A comparison of experimental and result values ​​of microwave scattering magnitude at 15° and 30° incident angles provided for an embodiment of the present invention;

[0036] Figure 17 A schematic diagram of infrared imaging of a sample at different temperatures of a microwave absorber that is compatible with microwave, infrared camouflage, and optical transparency, provided for an embodiment of the present invention;

[0037] Figure 18 A schematic diagram illustrating the average infrared emissivity test results of a microwave absorber compatible with microwave, infrared camouflage, and optical transparency, provided for an embodiment of the present invention;

[0038] Figure 19 A schematic diagram of the infrared emissivity spectrum of a microwave absorber compatible with microwave, infrared camouflage, and optical transparency in the 3-14 μm range, provided for an embodiment of the present invention;

[0039] Figure 20 A schematic diagram illustrating the optical transmittance performance test results of a microwave absorber compatible with microwave, infrared camouflage, and optical transparency, provided for an embodiment of the present invention;

[0040] Figure 21 This is a schematic diagram illustrating the actual camouflage effect of a microwave absorber that is compatible with microwave, infrared camouflage, and optical transparency, as provided in an embodiment of the present invention.

[0041] Among them: 1. ITO square patch, 2. ITO square ring patch, 3. First PET film, 4. PMMA dielectric layer, 5. Second PET film, 6. ITO base film. Detailed Implementation

[0042] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0043] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to 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 invention.

[0044] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0045] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0046] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0047] It should be noted that when an element is referred to as being "fixed to" or "set on" another element, it can be directly on the other element or there may be an intervening element. When an element is considered to be "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0048] See Figures 1-2 The present invention provides a microwave absorber that is compatible with infrared camouflage and optical transparency, including an ITO square patch 1, an ITO square ring patch 2, a first PET film 3, a PMMA dielectric layer 4, a second PET film 5, and an ITO base film 6.

[0049] Specifically:

[0050] like Figure 3 As shown, this invention designs a microwave absorbing micro-unit with polarization conversion and electromagnetic loss functions. This micro-unit consists of five layers. The top layer is a functional layer with an open square ring, made of indium tin oxide (ITO) thin film with a sheet resistance of 10 Ω / sq. The ITO is attached to a substrate with a dielectric constant of 3.0. (1-j0.06) The substrate is polyethylene terephthalate (PET); the intermediate dielectric layer is polymethyl methacrylate (PMMA) with a dielectric constant of 2.25. (1-j0.001) The bottom layer is ITO with a strength of 10Ω / sq; the bottom layer and dielectric layer are attached with PET; the thickness of PET and ITO is fixed, and the corresponding processing technology is 0.05mm and 200nm respectively.

[0051] Polarization conversion can reduce co-polarization reflectivity by changing the orthogonal polarization state of the reflected wave; for cross-polarized reflected waves, reflectivity can be reduced by scattering cancellation with a specific phase distribution; in addition, electromagnetic waves can be absorbed by cavity resonance and resistive film loss; in this structure, five parameters a, b, d, l, and h2 are given to form the element absorber, where a is the unit period size, b is the size of the open square ring, d is the width of the open square ring, l is the length of the open square ring, and h2 is the thickness of the dielectric layer; in the CST simulation software environment, the polarization direction of the incident electromagnetic wave is along the diagonal direction of the open square ring, which can excite the polarization rotation performance of the open square ring.

[0052] In this process, when an electromagnetic wave in the microwave band is incident on the top surface of the PMMA dielectric layer 4 at a 45° angle between its polarization direction and the direction of the open ring, the reflected electromagnetic wave undergoes linear polarization cross-polarization rotation. Simultaneously, the ITO square patch 1 and the PMMA dielectric layer 4 work together to absorb the electromagnetic wave and reduce the amplitude of the reflected electromagnetic wave. Rotating the ITO square ring patch 2 by 90° introduces a PB geometric phase into the reflected wave, and the resulting cross-polarized reflection phase forms a 180° phase difference with the cross-polarized reflection phase generated by the structure 2 before rotation. By arranging the micro-units before and after rotation alternately to form an absorber, based on the 0° and 180° reflection phase cancellation mechanism, the resistive film loss mechanism, and the cavity resonance mechanism, efficient scattering reduction in the incident direction of the electromagnetic wave can be achieved, and good stability can be maintained in the range of -30° to +30°.

[0053] Among them, the PMMA dielectric layer 4 has a first PET film 3 on its top surface, and an ITO square ring patch 2 and an ITO square patch 1 with slits on its top surface. The metasurface achieves transparency in the visible light band.

[0054] The customized infrared camouflage design specifically includes:

[0055] The key to infrared camouflage applications lies in the design and adjustment of the material's surface emissivity. Generally, metals have high reflectivity and low emissivity to infrared radiation, and ITO also exhibits high infrared reflectivity and low infrared emissivity. ITO can block infrared light emitted by objects inside the material, making it suitable for self-controlled infrared emissivity. Furthermore, ITO's zero transmission and low absorption characteristics across the entire infrared band demonstrate its superior infrared camouflage performance. The surface emissivity of the micro-unit can be calculated using empirical formulas.

[0056] ε=ε m ·f m +ε d ·(1-f m )

[0057] Where: ε is the total emissivity of the metasurface, ε m The emissivity of ITO is approximately 0.05, ε d The emissivity of PET is approximately 0.9, f m This represents the percentage of the area of ​​the ITO portion.

[0058] The absorber surface has a large number of non-ITO regions, offering broad infrared control potential. By inserting an ITO patch in the middle of the surface, the infrared emissivity can be adjusted from high to low based on the change in the proportion of the ITO patch across the entire surface of the absorber. In other words, the infrared emissivity is adjusted by changing the duty cycle of the ITO patch on the absorber surface. The design process is as follows: Figure 4 As shown, considering the resonant coupling between the ITO patch and the open ring, the size x of the ITO patch is the sixth parameter of the microcell; in order to reduce the impact of the inserted patch on the microwave performance, the patch is cut into four parts, with a gap of 0.1 mm between each part.

[0059] The training of the Bayesian network and absorber inversion design is specifically as follows:

[0060] With the development of electromagnetic computing and machine learning, neural networks have become a powerful tool that can help inversely design surface units with specific characteristics. The essence of neural network operation is establishing a mapping relationship between input and output parameters. Hidden layers are key to neural network operation, similar to a gray box system. The activation functions of hidden layers are mainly divided into two types: hyperbolic tangent functions and polynomial transfer functions, which are respectively:

[0061] f(x) = 2 / (1-e 2x )-1

[0062] f(x)=ax 2 +bx+c+k

[0063] The effectiveness of a neural network depends primarily on the training data and its internal logic. Data quality is measured by data size and data validity. The amount of data can be increased through the number of experiments or prior work, while data cleaning can improve data validity. Euclidean distance is used to measure data similarity and eliminate duplicate data; the formula is as follows:

[0064]

[0065] Where: d(A,B) is the Euclidean distance between vectors A and B, A i and B i represents the elements in the vector, and n represents the length of the vector.

[0066] For the internal logic, different training algorithms exist depending on the application scenario, memory, and computing power, such as the Levenberg-Marquardt algorithm, Bayesian regularization algorithm, and conjugate gradient algorithm. Bayesian regularization, as a logic algorithm based on prior probability, exhibits excellent generalization performance on difficult, small, or noisy datasets, making it highly suitable for metamaterial / absorbing-assisted design. The core expressions of a Bayesian network are the total probability formula and the Bayesian probability formula:

[0067]

[0068] Where A and B represent an event, the conditional probability is the probability of event A occurring given that event B has already occurred. The conditional probability is denoted as P(A|B) and read as "the probability of A given B". Bayes' theorem expresses the idea that, based on a certain outcome B, all possible sub-cases can be inferred, and the conditional probability proportion of each sub-case can be inferred from the outcome B, which depends on the joint probability of the sub-case and outcome B.

[0069] To measure training performance, a mean squared error function, also known as the loss function, is defined:

[0070]

[0071] Where: X i It is a predicted value. is the average value, and n is the number of samples. The smaller the variance, the more accurate the trained model.

[0072] To achieve compatibility between microwave absorption and customized infrared camouflage, six parameters of the absorber micro-unit were used as input data, and 25 typical reflectivity curve values ​​from 6 to 18 GHz were extracted as output data. The goal was to find three absorber micro-units with different ITO duty cycles, all of which had reflectivity below -10 dB between 7 and 14 GHz. The entire process was as follows: Figure 4 As shown, 1020 samples were collected, and after data cleaning, 311 valid sample data were used for training and testing the Bayesian network. Figure 5 The Euclidean distance distribution before and after data cleaning effectively removes duplicate data; then 75% of the data is used for training, and the remaining data is used for testing; the detailed iterative process is as follows: Figure 6 As shown; the model error after training is as follows Figure 7 As shown, the errors of the training, test, and validation sets are all within ±0.03, indicating good training accuracy; the regression results of the model training are as follows. Figure 8 As shown, the regression correlation is above 0.95, which further confirms the accuracy of the model training; it shows that after training, three different types of absorber micro-units were obtained; detailed parameters and ITO duty cycles are shown in Table 1; Meta-atom represents the micro-unit of the designed absorber.

[0073] Table 1 Microunit structural parameters and corresponding ITO duty cycles

[0074]

[0075] To verify the training results, the three unit structures were simulated in CST software. The same polarization reflection results are as follows: Figure 9 As shown; in CST, the angle between the polarization direction of the linearly polarized wave and the open-aperture resonant square ring is set to 45 degrees, so that the square ring and the polarization rotator form an effective absorber; the results show that the reflectivity values ​​are all below -8dB in the 6-18GHz range, especially below -10dB in the 7-14GHz range, meeting the design requirements. The co-polarization reflectivity, cross-polarization reflectivity, and absorptivity of the three unit structures are as follows: Figure 10 , Figure 11 and Figure 12 As shown; its polarization conversion rate (PCR) equation is:

[0076]

[0077] Where: r xx =r yy Representing the co-polarization reflectivity, r xy =r yxThe values ​​represent the cross-polarization reflectivity, respectively. The results show that all three types of cells achieved over 90% co-polarization reduction in the 7-14 GHz band, meeting the design objectives. It can also be seen that the efficient co-polarization reduction function of the cells is achieved by the combined effect of polarization rotation and resonant absorption, with the resonant absorption effect accounting for a higher proportion.

[0078] Specific simulation experiments:

[0079] In the microwave band, rotating the opening direction of the open square ring by 90 degrees changes the phase of the cross-polarized reflected wave from 0 to π. The micro-unit before rotation is called code 0, and the micro-unit after rotation is called code 1. Code 0 and code 1 are arranged alternately to form a piano key metasurface. When electromagnetic waves are incident on the metasurface, the total scattered field is canceled in the normal direction and redirected to both sides of the normal direction. Therefore, the energy of the backscattered radar cross section (RCS) is reduced. Combined with the electromagnetic absorption mechanism, broadband ultra-low RCS can be achieved. In the infrared band, micro-unit absorbers with different proportions can be customized to achieve spatial modulation of infrared emissivity. According to the infrared background environment, high infrared emissivity regions and low infrared emissivity regions can appear simultaneously to form a digital camouflage effect, which can effectively adapt to more complex environments.

[0080] like Figure 13 and Figure 14 As shown, an absorber with both visible light transparency and customized infrared camouflage was designed. In far-field simulations from 0 to 30°, the backscattering characteristics of the absorber and the ITO plate were compared, verifying its backscattering reduction. The three-dimensional scattering results under perpendicular incidence are shown below. Figure 13 As shown, the three-dimensional scattering results under 30-degree oblique incidence are as follows: Figure 14 As shown; in the absorber, the reflected wave is split into two beams, and the energy in the incident direction is significantly reduced. Then, the sample is prepared by magnetron sputtering. In the microwave experiment, the sample is placed on an arched platform, and the receiving and transmitting antennas can be moved on the arched platform to detect the RCS of the sample at different angles. In the above process, as the incident direction increases from 0° to 30°, the RCS value in the incident direction is monitored in 15-degree increments, and the results are as follows. Figure 15 and Figure 16 As shown, the results indicate that the experimental measurement results are basically consistent with the simulation results. The errors are mainly caused by factors such as coating accuracy, noise interference, and antenna loss. Coating accuracy affects the sheet resistance of ITO, while noise and antenna loss interfere with signal acquisition.

[0081] In the infrared experiment, the infrared emissivity of different types of micro-units was measured using a TSS-5X infrared emissivity meter. The infrared probe served as the detector, and the absorber was horizontally fixed on the platform. The absorber was placed on the infrared detector to obtain the infrared emissivity of different regions of the sample. The results are as follows: Figure 17As shown; to further observe its infrared spectral radiation characteristics, the infrared emissivity of three micro-units in the range of 3–14 μm was measured using an infrared spectrometer, and the results are as follows. Figure 18 As shown; data from the infrared emissivity calculated empirically, the infrared spectrometer, and the TSS-5X infrared emissivity meter are collected in Table 2; although the measured values ​​differ somewhat due to limitations in instrument accuracy and interference from the experimental background, the data characteristics are consistent, exhibiting the infrared radiation gradient characteristics of the three micro-units; finally, infrared imaging tests were performed on the samples using an infrared imager (Thermao GEAR), as shown... Figure 19 As shown, due to the spatial distribution characteristics of infrared emissivity, the sample exhibits obvious digital infrared camouflage features; when the temperature increases from 50℃ to 70℃, the sample still retains the digital infrared camouflage features, verifying the temperature robustness of the sample.

[0082] Table 2. Infrared emissivity performance characterization results of the unit

[0083]

[0084] The optical performance of the absorber sample was also verified; firstly, the optical transmittance was measured using testing instruments, such as... Figure 20 As shown; the results indicate that this sample has high visible light transparency, approximately 60%, in the 400-800 nm range; then, two test scenarios were selected to verify the sample's practicality in camouflage, such as... Figure 21 As shown, parts of the leaves were picked and heated on a hot plate for different times to obtain four different temperatures, representing four different infrared radiation characteristics of the protected target. In the thermal imaging, the leaves showed different colors and could be easily distinguished from the background. Next, the leaves were covered on the absorber sample. In the visible light image, the sample had effective transparency and the leaves could be clearly observed, while in the infrared image, the leaves covered by the sample were perfectly hidden, as if they were wearing camouflage.

[0085] This invention achieves microwave broadband backscatter reduction, customizable infrared digital camouflage, and visible light transparency simultaneously using only a single functional layer. Furthermore, it utilizes a Bayesian neural network to rapidly design three micro-unit structures with different infrared emissivity but the same size. In the microwave band, all three micro-units achieve efficient backscatter reduction in the 7–14 GHz range. Based on the coded metasurface design principle, coded 0 and coded 1 are arranged in a key-like configuration, achieving efficient backscatter reduction under the combined effect of microwave loss mechanisms. In the infrared band, this can be achieved by arranging three micro-units with different infrared emissivity. By controlling the spatial infrared radiation characteristics, a digital camouflage effect is achieved macroscopically. In the visible light band, optically transparent materials ITO and PET were selected as the basic materials to achieve high light transmittance. To verify the performance of the design, samples were fabricated and experiments were conducted in the microwave, infrared, and optical bands. The experimental results were basically consistent with the simulation results. Without reducing microwave performance, the artificially designed infrared digital camouflage pattern can adapt to a variety of infrared background environments, expanding the application range of compatible visible-infrared-microwave camouflage facilities. This invention can be applied to specific scenarios such as transparent windows of off-road vehicles and aircraft cockpit canopies.

[0086] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A microwave absorber compatible with microwave, infrared camouflage, and optical transparency, characterized in that, It includes multiple alternating metasurface units, wherein the alternating arrangement is as follows: in the microwave band, the opening direction of the ITO square ring patch (2) is rotated by 90 degrees, and the phase of the cross-polarized reflected wave changes from 0 to π; the micro-unit before rotation is coded 0, and the micro-unit after rotation is coded 1; coded 0 and coded 1 are arranged alternately to form a piano key metasurface; Each of the metasurface units includes: a PMMA dielectric layer (4), a first PET film (3) is disposed on the top surface of the PMMA dielectric layer (4), an ITO square ring patch (2) is disposed on the top surface of the first PET film (3), and an opening is disposed on the ITO square ring patch (2); An ITO square patch (1) is provided on the top surface of the first PET film (3) in the area inside the ITO square ring patch (2), and a cross-shaped slit is etched on the ITO square patch (1), dividing the ITO square patch (1) into four equal parts. Each of the metasurface units has an ITO square patch (1), a first PET film (3), and a PMMA dielectric layer (4) forming a three-layer microwave absorber for absorbing electromagnetic waves. The size of the ITO square patch (1) on each metasurface unit is different, and the spatial radiation characteristics of the infrared electromagnetic wave can be controlled by changing the size of the ITO square patch (1). The ITO square patch (1), ITO square ring patch (2), first PET film (3) and PMMA dielectric layer (4) are all optically transparent materials used to make electromagnetic waves in the visible light band transparent.

2. A microwave absorber compatible with microwave, infrared camouflage, and optical transparency according to claim 1, characterized in that, The bottom surface of the PMMA dielectric layer (4) is provided with a second PET film (5), and the bottom surface of the second PET film (5) is provided with an ITO substrate film (6).

3. A microwave absorber compatible with microwave, infrared camouflage, and optical transparency according to claim 1, characterized in that, The ITO square ring patch (2) has a side length of 6mm and a width of 0.5mm, and the opening width on the ITO square ring patch (2) is 1.8mm.

4. A microwave absorber compatible with microwave, infrared camouflage, and optical transparency according to claim 1, characterized in that, The side length of the ITO square patch (1) is 1mm to 5mm, and the width of the cross-shaped slit etched on the ITO square patch (1) is 0.1mm.

5. A microwave absorber compatible with microwave, infrared camouflage, and optical transparency according to claim 1, characterized in that, The PMMA dielectric layer (4) has a thickness of 3.6 mm and a dielectric constant of 2.

25. (1-j0.001) , j represents the imaginary unit of the imaginary part of the dielectric constant.

6. A microwave absorber compatible with microwave, infrared camouflage, and optical transparency according to claim 2, characterized in that, Both the first PET film (3) and the second PET film (5) have a thickness of 0.05 mm and a dielectric constant of 3.

0. (1-j0.06) , j represents the imaginary unit of the imaginary part of the dielectric constant.

7. A microwave absorber compatible with microwave, infrared camouflage, and optical transparency according to claim 2, characterized in that, The thickness of the ITO substrate film (6), the ITO square patch (1) and the ITO square ring patch (2) are all 200 nm, and the sheet resistance is 10 Ω / sq.

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