Microwave absorber compatible with microwave, infrared camouflage and optical transparency

Abstract

The invention discloses a microwave absorber compatible with microwave, infrared camouflage and optical transparency, and relates to the technical field of multi-spectrum compatibility and artificial intelligence. A first PET film is arranged on the top surface of a PMMA dielectric layer, an ITO square ring patch is arranged on the top surface of the first PET film, and an opening is formed in the ITO square ring patch; meanwhile, an ITO square patch with a cross-shaped gap is embedded in the top surface of the first PET film; the ITO square patch serves as a resistive film to realize microwave loss, the ITO square patch, the first PET film and the PMMA dielectric layer form a three-interlayer microwave absorber, meanwhile, the space radiation characteristic of infrared band electromagnetic waves is regulated and controlled by changing the size of the ITO square patch, and the ITO patch, the first PET film and the PMMA dielectric layer are all made of optical transparent materials to realize transparency of visible light band electromagnetic waves; the structure of the invention realizes compatible design of a microwave band, an infrared band and a visible light band at the same time, and can be widely applied to full-band camouflage of equipment.

Description

Technical Field

[0001] The present invention relates to the field of multi-spectrum compatibility and artificial intelligence technology, and in particular to a microwave absorber compatible with microwave, infrared camouflage and optical transparency. Background Art

[0002] As a two-dimensional form of metamaterial, metasurface is composed of artificially designed sub-wavelength scale structural units, and has powerful functions such as electromagnetic wave manipulation, spectrum camouflage, image coding, and wavefront control. Based on the outstanding regulation ability of electromagnetic waves, metasurfaces can modulate the phase, amplitude, polarization, propagation mode and other characteristics of electromagnetic waves in a more flexible and effective way. Therefore, the application of functional devices composed of metasurfaces has been effectively expanded, providing new and effective methods in abnormal reflection, scattering cancellation, focusing, multi-spectrum camouflage, etc. With the development of multi-sensor detection technology, current reconnaissance and detection technology has put forward higher requirements for the camouflage and stealth of scattering targets. Therefore, multi-spectrum camouflage technology has attracted widespread attention, especially for metasurfaces.

[0003] At present, there are two typical camouflage implementation ideas for multi-spectrum detection technology; one is to combine different spectral camouflage methods with the same material system; integrate microwave absorbing materials and low-emissivity infrared materials with optical transparency into multi-layer metasurfaces to achieve compatible camouflage. This can effectively reduce detectability under multi-spectrum, but also increase the complexity of production; to solve this problem, some wavefront modulation characteristics of metasurfaces are used to simplify functional layers, such as polarization conversion to reduce backscattering, leaky cavity mode to consume electromagnetic waves, these microwave properties can be achieved with only one layer, which provides space for inserting other spectral functional materials; the second solution is to build a selective camouflage system according to the different requirements of different spectra; through the reflection splitting effect and infrared plasma resonance, different coatings can match the required multi-band spectra, have excellent radiation heat control capabilities, and significantly reduce the visual temperature under thermal imagers; coatings with visible transparency and radiation cooling can be used for thermal management; in addition, phase change materials are widely used in switchable absorbers to adapt to changing environments; however, these methods are mainly used in laser and infrared bands.

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

[0005] Therefore, it is difficult for current camouflage materials to achieve compatibility with microwave bands, infrared bands and visible light bands at the same time. Summary of the invention

[0006] The embodiment of the present 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 the current camouflage materials are difficult to simultaneously achieve compatibility with the microwave band, infrared band and visible light band.

[0007] The embodiment of the present invention provides a microwave absorber compatible with microwave, infrared camouflage and optical transparency, comprising a plurality of alternately arranged metasurface units, each of which comprises: a PMMA dielectric layer, a first PET film is arranged on the top surface of the PMMA dielectric layer, an ITO square ring patch is arranged on the top surface of the first PET film, and an opening is arranged on the ITO square ring patch;

[0008] An ITO square patch is arranged in the area on the top surface of the first PET film inside the ITO square ring patch, and a cross-shaped gap is etched on the ITO square patch, and the ITO square patch is divided into four parts;

[0009] The ITO square patch, the first PET film and the PMMA dielectric layer on each of the metasurface units form a three-layer microwave absorber for absorbing electromagnetic waves;

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

[0011] The ITO square patch, the ITO square ring patch, the first PET film and the PMMA dielectric layer are all optically transparent materials, and are 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 plate film is disposed on the bottom surface of the second PET film.

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

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

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

[0016] Preferably, the thickness of the first PET film and the second PET film are both 0.05 mm, and the dielectric constant is 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 base plate film, the ITO square patch and the ITO square ring patch are all 200 nm, and the square resistance is 10Ω / sq.

[0018] The embodiment of the present invention provides a microwave absorber that is compatible with microwave, infrared camouflage and optical transparency. Compared with the prior art, the beneficial effects thereof are as follows:

[0019] The present invention provides a first PET film on the top surface of a PMMA dielectric layer, an ITO square ring patch is provided on the top surface of the first PET film, an opening is provided on the ITO square ring patch, and an ITO square patch with a cross-shaped gap is embedded in the top surface of the first PET film; the ITO square patch is used as a resistance film to achieve microwave loss, and forms a three-layer microwave absorber with the first PET film and the PMMA dielectric layer; at the same time, the size of the ITO square patch is changed to adjust the spatial radiation characteristics of electromagnetic waves in the infrared band, and the ITO patch, the first PET film and the PMMA dielectric layer are all optically transparent materials to achieve transparency of electromagnetic waves in the visible light band; the structure of the present invention simultaneously achieves compatible design of microwave band, infrared band and visible light band, and can be widely used in equipment full-band camouflage. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0022] Figure 3 A schematic diagram of the architecture design and dimensions of a microwave absorber compatible with microwave, infrared camouflage and optical transparency provided by an embodiment of the present invention;

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

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

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

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

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

[0028] Fig. 9 A schematic diagram of the same-polarization reflection performance of three micro-units with different infrared emissivity of a microwave absorber compatible with microwave, infrared camouflage and optical transparency provided by an embodiment of the present invention;

[0029] Fig.10 A schematic diagram of the absorptivity, cross-polarization reflectivity and co-polarization reflectivity of a micro-unit of meta-atom I of a microwave absorber compatible with microwave, infrared camouflage and optical transparency provided in an embodiment of the present invention;

[0030] Fig.11 A schematic diagram of the absorptivity, cross-polarization reflectivity and co-polarization reflectivity of a micro-unit of a meta-atom II microwave absorber compatible with microwave, infrared camouflage and optical transparency provided in an embodiment of the present invention;

[0031] Fig.12 A schematic diagram of the absorptivity, cross-polarization reflectivity and co-polarization reflectivity of a micro-unit of a meta-atom III microwave absorber compatible with microwave, infrared camouflage and optical transparency provided in an embodiment of the present invention;

[0032] Fig.13 A schematic diagram showing a comparison of far-field 3D scattering energy distribution between a microwave absorber compatible with microwave, infrared camouflage and optical transparency provided by an embodiment of the present invention and a common ITO film under the condition that two electromagnetic waves are perpendicular;

[0033] Fig.14 A schematic diagram showing a comparison of far-field 3D scattering energy distribution of a microwave absorber compatible with microwave, infrared camouflage and optical transparency provided by an embodiment of the present invention and a common ITO film under the condition of electromagnetic wave incidence at 30°;

[0034] Fig.15 A schematic diagram comparing the experimental value and the result value of the scattering size of microwaves at a vertical incident angle for a microwave absorber compatible with microwave, infrared camouflage and optical transparency provided by an embodiment of the present invention;

[0035] Fig.16 A comparison chart of experimental values ​​and result values ​​of microwave scattering magnitude at incident angles of 15 degrees and 30 degrees for a microwave absorber compatible with microwave, infrared camouflage and optical transparency provided by an embodiment of the present invention;

[0036] Fig.17 A schematic diagram of infrared imaging of samples at different temperatures of a microwave absorber compatible with microwave, infrared camouflage and optical transparency provided by an embodiment of the present invention;

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

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

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

[0040] Fig.21 A schematic diagram showing the actual camouflage effect of a microwave absorber that is compatible with microwave, infrared camouflage and optical transparency 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 DESCRIPTION

[0042] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific embodiments disclosed below.

[0043] In the description of the present invention, it is to be understood that the terms “center”, “longitudinal”, “lateral”, “length”, “width”, “thickness”, “up”, “down”, “front”, “back”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inside”, “outside”, “clockwise”, “counterclockwise”, “axial”, “radial”, “circumferential”, etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0044] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0045] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0046] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

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

[0048] See also Figures 1-2 An embodiment of 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, the present invention designs an absorbing micro-unit with polarization conversion and electromagnetic loss functions. The micro-unit consists of five layers. The top layer is a functional layer with an open square ring, which is an indium tin oxide (ITO) film with a square resistance of 10Ω / sq. ITO is attached to a dielectric constant of 3.0 (1-j0.06) The middle dielectric layer is polymethyl methacrylate (PMMA), with a dielectric constant of 2.25. (1-j0.001) ; The bottom is ITO with 10Ω / sq; the bottom and the dielectric layer are attached by PET; the thickness of PET and ITO is fixed, and the corresponding processing technology is 0.05mm and 200nm.

[0051] Polarization conversion can reduce the co-polarization reflectivity by changing the orthogonal polarization state of the reflected wave; for cross-polarized reflected waves, the reflectivity can be reduced by scattering cancellation of specific phase distribution; in addition, electromagnetic waves can be absorbed through cavity resonance and resistive film loss; in this structure, five parameters a, b, d, l, and h2 are given to constitute 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 stimulate the polarization rotation performance of the open square ring.

[0052] Among them, when the electromagnetic wave in the microwave band is incident on the top surface of the PMMA dielectric layer 4 with the polarization direction forming an angle of 45° with the direction of the open ring, the reflected electromagnetic wave will undergo linear polarization cross-polarization rotation, and the ITO square patch 1 and the PMMA dielectric layer 4 will work together to achieve loss absorption of the electromagnetic wave and reduce the amplitude of the reflected electromagnetic wave; rotating the ITO square ring patch 2 by 90° can introduce a PB geometric phase to the reflected wave, and the resulting cross-polarization reflection phase forms a phase difference of 180° with the cross-polarization reflection phase generated by the structure 2 before rotation; the micro-units before and after the rotation are alternately arranged to form an absorber, and based on the reflection phase cancellation mechanism of 0 and 180°, the resistance 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 at -30°-+30°.

[0053] Among them, the PMMA dielectric layer 4, the top surface of the PMMA dielectric layer 4 is provided with a first PET film 3, the top surface of the first PET film 3 is provided with an ITO square ring patch 2 and an ITO square patch 1 with a slit treatment, and the metasurface realizes transparency in the visible light band.

[0054] Customized infrared camouflage design is as follows:

[0055] The key to the application of infrared camouflage is the design and adjustment of the surface emissivity of the material. Generally speaking, metals have high reflectivity and low emissivity for infrared rays. ITO also exhibits high infrared reflectivity and low infrared emissivity. ITO can block the infrared light emitted by objects inside the material and is suitable for self-control of infrared emissivity. In addition, ITO's zero transmission and low absorption characteristics in the entire infrared band reflect its superior infrared camouflage performance. According to the empirical formula, the surface emissivity of the micro-unit can be calculated:

[0056] ε=ε m ·f m +ε d ·(1-f m )

[0057] Where: ε is the total emissivity of the metasurface, ε m is the emissivity of ITO, about 0.05, ε d is the emissivity of PET, which is about 0.9, f m is the area percentage of the ITO part.

[0058] There are a lot of non-ITO areas on the surface of the absorber, which has a wide infrared control potential. By inserting an ITO patch in the middle of the surface, the infrared emissivity can be adjusted from high to low according to the change of the proportion of the ITO patch on the entire surface of the element, that is, the change of the duty cycle of the ITO patch on the surface of the element adjusts the infrared emissivity. 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 micro unit; in order to reduce the impact of the inserted patch on the microwave performance, the patch is cut into four parts, and the gap between each part is 0.1mm.

[0059] The training of Bayesian network and absorber inversion design is 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 work is to establish a mapping relationship between input parameters and output parameters. The hidden layer is the key to neural work, similar to the gray box system. The activation function of the hidden layer is mainly divided into two types: hyperbolic tangent function and polynomial transfer function, which are:

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

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

[0063] The effectiveness of neural network work mainly depends on the training data and internal logic. The measurement of data quality is data size and data validity. The amount of data can be increased through the number of experiments or the accumulation of previous work. Data cleaning can improve the validity of data. The Euclidean distance is used to measure the similarity of data and eliminate duplicate data. The formula is:

[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 internal logic, there are different training algorithms according to the application scenario, memory and computing power, such as Levenberg-Marquardt algorithm, Bayesian regularization algorithm and conjugate gradient algorithm; Bayesian regularization, as a logic algorithm based on prior probability, has a good generalization effect for difficult, small or noisy data sets, and is very suitable for metamaterial / absorber assisted design; the core expression of the Bayesian network is the total probability formula and the Bayesian probability formula is:

[0067]

[0068] Among them: A and B represent an event, conditional probability is the probability of event A occurring when event B has already occurred, conditional probability is recorded as P(A|B), read as "the probability of A conditional on B", and the Bayesian formula expresses an idea, that is, based on a certain result B, all possible sub-situations can be inferred, and based on result B, the conditional probability ratio of each sub-situation can be inferred, which depends on the joint probability of the sub-situation and effect B.

[0069] In order to measure the training performance, the mean square error function is defined, which is called the loss function:

[0070]

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

[0072] In order to achieve the compatibility of microwave absorption and customized infrared camouflage, the six parameters of the absorber microunit are used as input data, and 25 typical reflectivity curve values ​​from 6 to 18 GHz are extracted as output data; the goal is to find three absorber microunits with different ITO duty ratios, whose reflectivity between 7 and 14 GHz is less than -10 dB. The whole process is as follows Figure 4 As shown, 1020 samples were collected. After data cleaning, 311 valid sample data were used for training and testing of the Bayesian network; Figure 5 The Euclidean distance distribution before and after data cleaning is used to effectively remove duplicate data. Then 75% of the data is used for training, and the rest of the data is used for testing. The detailed iterative process is as follows Figure 6 As shown; the model error after training is Figure 7 As shown in the figure, the errors of the training set, test set and validation set are all within ±0.03, and the training accuracy is good; the regression results of the model training are as follows Figure 8 As shown, the regression correlation is above 0.95, which once again confirms the accuracy of the model training; it shows that after the training, three different types of absorber micro-units are obtained; the detailed parameters and ITO duty ratios are shown in Table 1; Meta-atom represents the designed absorber micro-unit.

[0073] Table 1 Micro-unit structural parameters and corresponding ITO duty cycle

[0074]

[0075] In order to verify the training results, the three unit structures were simulated in CST software. The co-polarization reflection results are shown in Fig. 9 As shown; in CST, the angle between the polarization direction of the linear polarized wave and the open-hole 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 ​​in the range of 6 to 18 GHz are all lower than -8 dB, especially in the range of 7 to 14 GHz, the reflectivity values ​​are all lower than -10 dB, which meets the design requirements. The co-polarization reflectivity, cross-polarization reflectivity and absorptivity of the three unit structures are shown as follows: Fig.10 , Fig.11 and Fig.12 As shown; its polarization conversion rate (PCR) equation is:

[0076]

[0077] Where: r xx =r yy They represent the co-polarization reflectivity, r xy =r yxThe results show that all three units have achieved more than 90% co-polarization reduction in the 7-14 GHz frequency band, achieving the design goal; at the same time, it can be seen that the efficient co-polarization reduction function of the unit is achieved due to the combined effect of polarization rotation and resonant absorption, among which the resonant absorption effect accounts for a higher proportion.

[0078] Specific simulation experiment:

[0079] In the microwave band, the opening direction of the open square ring is rotated 90 degrees, and the phase of the cross-polarized reflected wave can be changed 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 the electromagnetic wave is incident on the metasurface, the total scattering field is offset in the normal direction and redirected to both sides of the normal; 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 areas and low infrared emissivity areas can appear at the same time, forming a digital camouflage effect, which can effectively adapt to more complex environments.

[0080] like Fig.13 and Fig.14 As shown in the figure, an absorber with both visible light transparency and customized infrared camouflage is designed; in the 0-30° far-field simulation, the backscattering characteristics of the absorber and the ITO plate are compared, and the backscattering reduction is verified; the three-dimensional scattering results under vertical incidence are shown in Fig.13 As shown, the three-dimensional scattering results under 30-degree oblique incidence are as follows Fig.14 As shown in the figure; in the absorber, the reflected wave is divided 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 the arch platform, and the receiving and transmitting antennas can move on the arch to detect the RCS of the sample at different angles. In the above process, as the incident direction increases from 0° to 30°, with a step of 15 degrees, the RCS value in the incident direction is monitored, and the results are shown in the figure. Fig.15 and Fig.16 As shown in the figure, the experimental measurement results are basically consistent with the simulation results. The existing errors are mainly caused by factors such as coating accuracy, noise interference and antenna loss. The coating accuracy will affect the square resistance of ITO, and noise and antenna loss will 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 was used as a detector, and the absorber was fixed horizontally on the platform. The absorber was placed on the infrared detector to obtain the infrared emissivity of different areas of the sample. The results are shown in Fig.17As shown; In order to further observe its infrared spectral radiation characteristics, the infrared emissivity of three micro-units in the range of 3 to 14 μm was measured using an infrared spectrometer. The results are shown in Fig.18 As shown; the data of the empirically calculated infrared emissivity, infrared spectrometer and TSS-5X infrared emissivity meter are collected in Table 2; although there are certain differences in the measured values ​​due to the limitation of instrument accuracy and the interference of experimental background, the data characteristics are consistent, showing the infrared radiation gradient characteristics of the three micro-units; finally, an infrared imager (Thermao GEAR) is used to perform infrared imaging tests on the samples, as shown Fig.19 As shown; due to the spatial distribution characteristics of infrared emissivity, the sample has obvious digital infrared camouflage characteristics; when the temperature rises from 50℃ to 70℃, the sample still maintains the digital infrared camouflage characteristics, verifying the temperature robustness of the sample.

[0082] Table 2 Unit infrared emissivity performance characterization results

[0083]

[0084] The optical performance of the absorber samples was also verified; first the optical transmittance was measured using a test instrument such as Fig. 20 As shown; the results show that the sample has a high visible light transparency of about 60% in the range of 400-800nm; then, two test scenes are selected to verify the practicality of the sample in camouflage, such as Fig.21 As shown; some leaves are picked and heated on a hot plate for different times to obtain 4 different temperatures, representing 4 protected targets with different infrared radiation characteristics; in thermal imaging, the leaves appear in different colors and can be easily distinguished from the background; next, the leaves are covered on the absorber sample; in the visible light image, the sample has effective transparency and the leaves can be clearly observed, while in the infrared image, the leaves covered by the sample are perfectly hidden, just like wearing camouflage.

[0085] The present invention can simultaneously achieve microwave broadband backscatter reduction, customizable infrared digital camouflage and visible light transparency through only a single functional layer; at the same time, three micro-unit structures with different infrared emissivity but the same size are quickly designed by using a Bayesian neural network; in the microwave band, the three micro-units can all achieve efficient backscatter reduction in the range of 7 to 14 GHz; according to the design principle of the coded metasurface, code 0 and code 1 are arranged through piano keys, and under the joint action of the microwave loss mechanism, efficient backscatter reduction is achieved; in the infrared band, three micro-units with different infrared emissivity can be arranged to achieve custom backscatter reduction. The infrared radiation characteristics of space are controlled and regulated to achieve digital camouflage effects from a macro perspective. In the visible light band, optically transparent materials ITO and PET are selected as basic materials to achieve a higher light transmittance. In order to verify the performance of the design, samples were made and experiments were carried out in microwave, infrared and optical bands. The experimental results were basically consistent with the simulation results. Without reducing the microwave performance, the artificially designed infrared digital camouflage pattern can adapt to a variety of infrared background environments, expanding the application scope of compatible visible-infrared-microwave camouflage facilities. The invention can be applied to specific scenarios such as transparent windows of off-road vehicles and aircraft cockpit covers.

[0086] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A microwave absorber compatible with microwave, infrared camouflage and optical transparency, characterized in that: The invention comprises a plurality of alternately arranged metasurface units, each of the metasurface units comprising: a PMMA dielectric layer (4), a first PET film (3) being arranged on the top surface of the PMMA dielectric layer (4), an ITO square ring patch (2) being arranged on the top surface of the first PET film (3), and an opening being arranged on the ITO square ring patch (2); An ITO square patch (1) is arranged in the area on the top surface of the first PET film (3) inside the ITO square ring patch (2), and a cross-shaped gap is etched on the ITO square patch (1), and the ITO square patch (1) is divided into four equal parts; The ITO square patch (1), the first PET film (3) and the PMMA dielectric layer (4) on each of the metasurface units form a three-layer microwave absorber for absorbing electromagnetic waves; The size of the ITO square patch (1) on each metasurface unit is different, and is used to control the spatial radiation characteristics of electromagnetic waves in the infrared band; The ITO square patch (1), the ITO square ring patch (2), the first PET film (3) and the PMMA medium layer (4) are all optically transparent materials and are 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: A second PET film (5) is arranged on the bottom surface of the PMMA medium layer (4), and an ITO base plate film (6) is arranged on the bottom surface of the second PET film (5).

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

4. The 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 1 mm to 5 mm, and the width of the cross-shaped gap etched on the ITO square patch (1) is 0.1 mm.

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

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

6. The microwave absorber compatible with microwave, infrared camouflage and optical transparency according to claim 2, characterized in that: The thickness of the first PET film (2) and the second PET film (5) are both 0.05 mm, and the dielectric constant is 3.0 (1-j0.06) , j represents the imaginary unit of the imaginary part of the dielectric constant.

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

Images