Emissivity-scattering combined regulation of water-based stealth transparent metasurface and design method

Abstract

The application discloses emissivity-scattering joint regulation of water-based stealth transparent super surface and a design method, and belongs to the technical field of electromagnetic stealth. The super surface comprises four transparent units: a high emissivity (ε1) unit A0 which is composed of a 45°-inclined I-shaped ITO-PET pattern, a PMMA medium, a calcium-sodium glass water storage cavity and an ITO-PET reflection plate, a low emissivity (ε2) unit B0 which is provided with an ITO square patch array with micron slits on both sides of the pattern, and A0 and B0 with a phase of φ1 and B0 with a phase of φ2 which are obtained by rotating A0 and B0 by 90°. 90 90 The method is based on digital image processing to arrange infrared emissivity, uses an analog annealing algorithm to optimize microwave phase coding, and switches the stealth state by charging and discharging the water in the cavity. In the empty state of the water storage cavity, 6.2-15 GHz electromagnetic waves are diffusely scattered, and 3-14 μm realizes infrared imaging. After the water storage cavity is filled with water, 5-20 GHz wide frequency is realized within 10 dB RCS reduction through water medium loss and layer height optimization, and 3-14 μm is in a low radiation state. The application realizes visible light, infrared and radar integrated reconfigurable compatible stealth based on the water-based regulation strategy.​

Description

Technical Field

[0001] This invention relates to the field of electromagnetic stealth technology, specifically to a water-based stealth transparent metasurface and its design method that combines emissivity-scattering regulation. Background Technology

[0002] Stealth technology is a core technology of modern optoelectronic countermeasures. With the increasing prevalence of radar-infrared composite detection systems, single-band stealth materials can no longer meet application requirements, making multi-spectral compatible stealth metasurfaces a research hotspot. Existing traditional metasurfaces are mostly passive metasurfaces with fixed structures and no dynamic control. After fabrication, their scattering, absorption, and infrared radiation characteristics cannot be switched, and optical transparency is difficult to achieve. The emergence of water-based metasurfaces has alleviated this problem to some extent; however, existing water-based stealth solutions still have significant shortcomings: First, they are functionally limited, mostly only achieving microwave absorption and failing to simultaneously achieve infrared camouflage, resulting in poor multi-spectral compatibility; second, infrared array arrangement and microwave phase array are designed separately, lacking an integrated collaborative design approach; third, the water-based loss absorption mechanism can only achieve high-frequency microwave stealth effects, failing to address the needs of low-frequency stealth control; and fourth, at the infrared level, only basic radiation suppression stealth is achieved, lacking infrared imaging deception and camouflage capabilities. Therefore, there is an urgent need to construct a reconfigurable transparent water-based multi-spectral stealth metasurface that integrates microwave RCS reduction and infrared imaging to address the technical shortcomings of existing solutions in multi-band collaborative control and dynamic camouflage. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of existing reconfigurable multi-spectral technologies and provide a water-based stealth transparent metasurface and design method with joint emissivity-scattering control. Based on reconfigurable water medium, it combines infrared emissivity control, RCS reduction technology, digital image processing and simulated annealing algorithm technology to achieve infrared-radar dynamic compatible stealth. At the same time, it uses visible light transparent materials to achieve multi-band compatible stealth, solving the problems of existing metasurfaces such as single function, lack of controllability and poor multi-spectral performance coordination.

[0004] An emissivity-scattering co-regulated water-based stealth transparent metasurface is disclosed. This metasurface comprises four metasurface units: a high emissivity ε1 unit A0, composed of a 45° angled "I"-shaped ITO-PET pattern layer, a PMMA dielectric layer, a calcium-sodium glass water storage cavity, and an ITO-PET reflector layer stacked from top to bottom; a low emissivity ε2 unit B0 with the same structure as unit A0, but with added frequency selective surfaces (FSS) composed of an array of ITO square patches with micron-sized slits on both sides of the "I"-shaped pattern; and unit A0 and unit B0 with phase φ1, rotated 90° to obtain unit A0 with phase φ2. 90 and Unit B 90 ;;

[0005] When the water storage cavity is emptied, electromagnetic wave diffuse scattering in the 6.2~15 GHz frequency band can be achieved by using phase arrangement; a preset image can be generated by using high and low emissivity unit arrangement; when the water storage cavity is filled with liquid, the water medium in the cavity introduces electromagnetic loss to absorb electromagnetic waves, achieving a 10 dB RCS reduction in the 5~20 GHz wide frequency range, and the overall temperature of the metasurface is reduced, resulting in a low radiation state in the 3~14 μm band.

[0006] Furthermore, the ITO-PET pattern layer of unit A0 includes a PET substrate and an ITO patch disposed on top. The ITO patch pattern includes a rectangle placed at a 45° angle and two semicircles disposed at both ends of the rectangle with a diameter equal to its width.

[0007] Unit A 90 Obtained by rotating unit A0 by 90°;

[0008] Based on unit A0, unit B0 is provided with a frequency selective surface FSS consisting of an array of n×n uniform square ITO patches. This array is equally divided into two along the diagonal and arranged on both sides of the "I"-shaped pattern.

[0009] Unit B 90 This is in unit A. 90 Based on this, a frequency selective surface (FSS) consisting of an array of n×n uniform square ITO patches is set up. This array is divided into two equal parts along the diagonal and arranged on both sides of the "I"-shaped pattern.

[0010] Furthermore, the structural parameters of the metasurface unit are determined by parameter scanning using CST electromagnetic simulation software, with the unit period side length being p = 15 mm; the top layer “I”-shaped pattern is composed of a rectangle plus two semicircles with diameters equal to its width, rotated counterclockwise by 45°, with the rectangle having a length of l = 9 mm and a width of w = 4.5 mm;

[0011] The frequency selective surface (FSS) is composed of an array of square ITO patches with micron-level slits. The square ITO patch period is a = 0.35 mm, and the square ITO patch width is b = 0.3 mm. The thickness of the ITO-PET pattern layer and the ITO-PET reflector layer is h1 = 0.125 mm. The thickness of the PMMA dielectric layer is h2 = 3.3 mm. The height of the water storage cavity is h3 = 0.5 mm, and the thickness of the upper and lower calcium-sodium glass covers of the water storage cavity is h3 = 0.2 mm.

[0012] A design method for a water-based stealth transparent metasurface with joint emissivity-scattering modulation is also provided. The design method for a water-based stealth transparent metasurface with joint emissivity-scattering modulation includes the following steps:

[0013] Step 1: Introduce a high emissivity unit A0 with both polarization conversion and absorption characteristics into the metasurface, and determine the unit parameters based on the polarization-absorption rate of the unit.

[0014] Step 2, introduce the low emissivity unit B0 of the surface FSS selected for loading frequency into the metasurface;

[0015] Step 3: Based on digital image processing, decompose the infrared camouflage pattern pixels and initially delineate the high emissivity units A0 / A0. 90 and low emissivity unit B0 / unit B 90 Arrangement position;

[0016] Step 4: With RCS reduction as the objective, the phase array arrangement is iteratively optimized using the simulated annealing algorithm to obtain the optimal diffuse scattering configuration. The elements A0 / B0 with phase φ1 and element A with phase φ2 are initially defined. 90 Unit B 90 Arrangement position;

[0017] Step 5: Combining the infrared camouflage arrangement and microwave RCS reduction array design results, comprehensively determine the four elements A0, B0, and A1 within the metasurface array. 90 Unit B 90 The final arrangement.

[0018] Furthermore, in step 1, the polarization conversion rate, absorptivity, and polarization-absorptivity of the metasurface unit's water storage cavity under liquid-filled conditions are:

[0019] Polarization conversion rate = , where r yx This represents the cross-polarization reflection amplitude;

[0020] Absorption rate = Where R is the reflectivity of the unit cell, T is the transmittance of the unit cell, and r xx For the same polarization reflection amplitude, since the bottom layer of the unit cell has a 2 Ω / sq ITO reflective ground plane, T ≈ 0, therefore the absorptivity = ;

[0021] Polarization-absorption rate = Absorption rate + Polarization conversion rate = + = 1 ;

[0022] Based on the thickness h of the water medium w Among different absorptivity, polarization conversion rate, and polarization-absorptivity ranges from 0.1 to 1 mm, the water medium thickness with the optimal polarization-absorptivity was selected.

[0023] Furthermore, in step 2, to achieve good infrared imaging results, considering both the infrared emissivity design requirements and the consistency of microwave reflection amplitude and phase, high emissivity units A0 and A1 are designed based on digital imaging principles. 90 and low emissivity elements B0 and B0 of the surface FSS with frequency selected at the top layer. 90 ;

[0024] Emissivity calculation formula:

[0025] ;

[0026] and These represent the infrared emissivity of ITO and PET, respectively. and These represent the duty cycles of ITO and PET, respectively, satisfying... + = 1, and < , =0.1, = 0.9;

[0027] The duty cycles of ITO and PET were used to calculate the values ​​of cell A0 and cell A. 90 Unit B0 and Unit B 90 The corresponding emissivity are ε1 = 0.69 and ε2 = 0.26, respectively.

[0028] Furthermore, in step 3, firstly, a preset tank is selected as the target pattern to be camouflaged, and grayscale operation is performed on the original color image to remove color channel information and convert the image pixels into a grayscale matrix in the range of 0~255.

[0029] Secondly, a fixed grayscale threshold is set to complete global binarization segmentation, dividing all pixels into two types of regions. After binarization, one type of region corresponds to the high infrared emissivity deployment area, which is used to arrange high emissivity units, and the other type of region corresponds to the low infrared emissivity deployment area, which is used to arrange low emissivity units.

[0030] Finally, the binarized image size is normalized to an m×m pixel matrix that matches the metasurface array, so that each pixel corresponds to a unit position in the array. The initial coordinate distribution of the two types of units inside the array is determined by mapping row by row and column by column, thus completing the pre-arrangement of the 1-bit high and low emissivity encoded array that matches the preset infrared camouflage imaging effect.

[0031] Furthermore, in step 4, the simulated annealing algorithm process includes:

[0032] First, initialize the algorithm parameters by setting the initial temperature T, temperature decay coefficient α, and minimum termination temperature T.min The main loop iteration count is capped at `limit`, and the inner loop iteration count is 20 × N, where N is the number of elements in the metasurface array. The iteration count variable `count1` is then set to zero. Subsequently, a random 1-bit phase encoding is assigned to the m × m array to generate the initial phase arrangement scheme. The target fitness function is then constructed. In the formula The RCS reduction value of the array is used as the optimization target, with an RCS reduction of more than 10 dB in the 5~15 GHz range. The fitness value corresponding to the current code is calculated, and the code and fitness value are assigned as the optimal code. best Optimal fitness P best ;

[0033] Next, the outer main loop is checked, and the loop execution condition is that the current temperature T is greater than the termination temperature T. min Optimal fitness P best If the convergence threshold is not reached and the iteration count (count1) does not exceed the set upper limit, the inner loop is entered if the conditions are met. The total number of iterations in the inner loop is set to 20 × N. In the inner loop, the phase code of a certain cell in the array is randomly flipped to generate a new arrangement scheme and the corresponding fitness P' is recalculated. The difference between the old and new fitness is calculated as Δ = P' - P. If Δ < 0, it means that the new arrangement has a better optimization effect, so the optimal code and the optimal fitness are updated. If Δ ≥ 0, the random number rand < e is used according to the probability criterion. -Δ / T Determine whether to accept the inferior solution. If the probability condition is met, update the encoding; otherwise, retain the original phase arrangement.

[0034] After all iterations of the inner loop are completed, the temperature decay operation T = T×ɑ is executed, the iteration count1 is incremented, and the outer main loop condition judgment is checked again. The iteration is repeated until the main loop judgment condition is no longer met. The algorithm terminates and outputs the optimal m×m binary phase arrangement matrix.

[0035] Furthermore, in step 5, the four metasurface units are combined into a 2-bit code corresponding to two sets of phases and two sets of emissivity:

[0036] Code 00 corresponds to high emissivity ε1, phase φ1 element A0; code 01 corresponds to rotating high emissivity ε1, phase φ2 element A. 90 Code 10 corresponds to low emissivity ε2, phase φ1 element B0; code 11 corresponds to rotating low emissivity ε2, phase φ2 element B. 90 This enables a two-degree-of-freedom 2-bit mapping rule consisting of 1-bit infrared emissivity encoding and 1-bit microwave phase encoding.

[0037] Based on the high and low emissivity arrangement of the infrared pre-arrangement and the microwave 1-bit phase distribution obtained by simulated annealing optimization, the coding matching of each grid position in the m×m array is performed, and the global 2-bit coding matrix is ​​generated by integrating the design requirements of the two arrays.

[0038] The beneficial effects achieved by this invention are:

[0039] Based on optical transparency, this invention can dynamically switch between infrared camouflage imaging and low infrared radiation modes in the infrared band. At the same time, the microwave band of 6.2~15 GHz / 5~20 GHz can achieve 10 dB RCS reduction and reconfigurable control. The whole structure does not require additional functional layers, has a compact structure and strong spectrum compatibility, and naturally meets the requirements for integrated reconfigurable stealth use in the visible light-infrared-microwave three bands.

[0040] This invention uses water as a reconfigurable control medium and achieves global state switching by filling and draining the metasurface: When the water storage cavity is empty, diffuse scattering is achieved in the 6.2~15 GHz microwave range, resulting in a 10 dB RCS reduction, and customized tank camouflage imaging is formed in the 3~14 μm infrared band by arranging high and low emissivity units; when the water storage cavity is filled, electromagnetic waves are efficiently absorbed due to the loss of the water medium, and combined with scattering, a 10 dB RCS reduction can be achieved in the 5~20 GHz wideband range, and the 3~14 μm infrared band becomes a low-emissivity state due to the decrease in temperature.

[0041] The infrared array arrangement of this invention relies on digital image processing technology to pixelate and match the camouflage pattern. The microwave phase array uses simulated annealing algorithm to iteratively optimize the binary phase distribution, which specifically meets the requirements of infrared imaging camouflage and microwave diffuse scattering RCS reduction. This solves the defects of traditional metasurface microwave and infrared arrays being designed separately, with mutual performance constraints and difficulty in coordinating the arrangement, resulting in higher overall stealth control precision.

[0042] The overall transparency of the metasurface in this invention is achieved through the selection of high-transmittance materials and process optimization, eliminating the need for an additional visible light stealth coating and simplifying the structural design.

[0043] The preparation method of this invention adopts mature processes such as laser etching, with controllable parameters, good repeatability, and is suitable for mass production. It can be widely used in fields such as weaponry and optical windows. Attached Figure Description

[0044] Figure 1 This is a schematic diagram illustrating the development history of the water-based metasurface of the present invention, the emissivity-scattering joint regulation of the water-based stealth transparent metasurface unit structure, the final array arrangement, and the functions of the water storage cavity in two states: empty and filled.

[0045] Figure 2For water medium, the real part (a) and imaginary part (b) of the dielectric constant in the temperature range of 2~40 GHz within the temperature range of 0~100 ℃ were numerically calculated based on the Debye model.

[0046] Figure 3 The illustration shows the transmission and reflection amplitudes of the 2 Ω / sq ITO resistive film selected in this invention in the microwave band of 2~40 GHz (wavelength 0.75~15 cm) and the infrared band of 3~14 μm (frequency 20~100 THz). The inset shows the dielectric constant of ITO in the 3~14 μm range calculated numerically using the Drude model.

[0047] Figure 4 The emissivity of the 2 Ω / sq ITO resistive film selected for this invention, and the designed units A0 and B0 in the range of 3~14 μm.

[0048] Figure 5 The amplitudes of co-polarization and cross-polarization reflections within 2–20 GHz are given by the basic unit A0 water storage cavity under liquid-filled conditions.

[0049] Figure 6 The absorptivity, polarization conversion rate, and polarization-absorption rate within 2–20 GHz of the basic unit A0 water storage cavity designed for the emissivity-scattering joint regulation of the water-based stealth transparent metasurface of this invention are measured in liquid state.

[0050] Figure 7 Here are schematic diagrams of water-based metasurface unit models: (a) Model 1 with only a water layer, upper and lower glass covers and a reflective floor; (b) Complete structural model 2 with unit A0 in the empty state of the water storage cavity; (c) Complete structural model 3 with unit A0 in the liquid-filled state of the water storage cavity.

[0051] Figure 8 (a) Absorption rate, (b) polarization conversion rate, and (c) polarization-absorption rate for models 1, 2, and 3 in the range of 2–20 GHz.

[0052] Figure 9 The absorptivity, polarization conversion rate, and polarization-absorptivity of unit A0 at different water layer heights within the range of 2–20 GHz under the condition of a liquid-filled water storage cavity.

[0053] Figure 10 The four basic units A0, A10, and A20 used in this invention 90 B0, B 90 Top view.

[0054] Figure 11 The cross-polarization reflection amplitudes of the four basic units are 2–20 GHz.

[0055] Figure 12The cross-polarization reflection phase of the four basic units is 2~20 GHz.

[0056] Figure 13 Design flow and RCS curves of water-based reconfigurable multi-spectral compatible stealth metasurface arrays; (a) Design flow and final arrangement of high and low emissivity unit arrays based on digital image processing; (b) Iterative optimization flow and final arrangement of microwave phase array distribution based on simulated annealing algorithm; (c) Top view of the four basic units and their emissivity and phase encoding; (d) Final arrangement of the four basic units of the metasurface; (e) RCS reduction curves of the designed metasurface in the range of 5-20 GHz in the water-filled and emptied states of the water storage cavity.

[0057] Figure 14 The far-field scattering patterns of the cross-polarized metasurface at 7, 10, 15, and 18 GHz are shown in the water-filled state of (a) and (b) of the water-filled cavity. Detailed Implementation

[0058] The present invention will be further described below with reference to specific embodiments, and the advantages and features of the present invention will become clearer as a result. However, these embodiments are merely exemplary and do not constitute any limitation on the scope of the present invention. Those skilled in the art should understand that modifications or substitutions can be made to the details and form of the technical solutions of the present invention without departing from the spirit and scope of the present invention, but all such modifications and substitutions fall within the protection scope of the present invention.

[0059] like Figure 1 As shown, this invention provides a water-based stealth transparent metasurface and its design method for emissivity-scattering joint control. Water is used as the reconfigurable control medium, and a fully transparent material is employed. Four metasurface units with matched electromagnetic and infrared emissivity characteristics are set up. A digital image processing method is used to plan the arrangement of high and low emissivity units, while a simulated annealing algorithm is used to iteratively optimize the microwave phase array distribution. Global state switching is achieved by filling and draining the metasurface: In the empty water-storage cavity state, microwaves in the 6.2–15 GHz band achieve diffuse scattering, resulting in a 10 dB RCS reduction and a relative bandwidth of 83.02%. The 3–14 μm infrared band forms customized camouflage imaging through the arrangement of high and low emissivity units. In the liquid-filled water-storage cavity state, electromagnetic waves are efficiently absorbed due to water medium losses, and combined with scattering, a 10 dB RCS reduction and a relative bandwidth of 120% can be achieved in the 5–20 GHz wideband range. The 3–14 μm infrared band exhibits low-emissivity characteristics due to the decrease in temperature. Figure 1As shown in the lower right corner, the basic unit A0 used in this invention is formed by multiple layers stacked from top to bottom, consisting of a 45° angled "I"-shaped ITO-PET pattern layer, a PMMA dielectric layer, a water storage cavity, upper and lower calcium sodium glass covers of the water storage cavity, and an ITO-PET reflective plate layer. Unit B0 is based on unit A0, with the addition of a frequency selective surface FSS composed of a 21×21 uniform square ITO patch array. This array is equally divided into two parts and arranged diagonally on both sides of the "I"-shaped pattern.

[0060] The parameters of the designed emissivity-scattering jointly regulated water-based stealth transparent metasurface structure are as follows:

[0061] The top-layer "I"-shaped pattern consists of a rectangle plus two semicircles of equal diameter and width, rotated counterclockwise by 45°. The rectangle has a length of l and a width of w. The frequency-selective surface (FSS) is composed of square ITO patches with micron-sized slits. The period of each square ITO patch is a, and the patch width is b. The thickness of both the ITO-PET pattern layer and the base plate is h1. The PMMA dielectric layer has a thickness of h2. The water storage cavity has a height of h. w The thickness of the calcium-sodium glass cover plate for the water-based container is h3, and the unit period size is p.

[0062] According to the design process and method, the structural parameters of the water-based stealth transparent metasurface, which are jointly controlled by emissivity-scattering, are as follows: p = 15 mm, h1 = 0.125 mm, h2 = 3.3 mm, h3 = 0.2 mm, h w = 0.5 mm, l = 9 mm, w = 4.5 mm, a = 0.35 mm, b = 0.3 mm; the resistive film material is 2 Ω / sq ITO, the resistive film substrate is PET, the transparent dielectric substrate is polymethyl methacrylate (PMMA) with a dielectric constant of 2.25 and a loss tangent of 0.001; the dielectric constant of sodium calcium glass is 6.05 and the loss tangent is 0.0157. The complex dielectric constant of water exhibits dispersive characteristics, determined by both frequency and temperature, and can be calculated using the Debye model.

[0063]

[0064] Among them, the parameters (T water ), (T water ) and τ(T water These parameters represent the static dielectric constant, high-frequency dielectric constant, and rotational relaxation time of water, respectively. These Debye parameters are related to the water temperature T. water The relationship between them satisfies the following equation:

[0065]

[0066]

[0067]

[0068] Where a1 = 87.9, b1 = 0.404 K -1 c1 = 9.59 × 10 -4 K -2 d1 = 1.33 × 10 -6 K -3 a² = 80.7, b² = 4.42 × 10 -3 K -1 c2 = 1.37 × 10 -13 Given T1 = 651 ℃ and T2 = 133 ℃, the dielectric constant of water in the temperature range of 2~40 GHz within the temperature range of 0~100 ℃ is calculated using the Debye model. Figure 2 As shown, the real part of the complex permittivity of pure water decreases with increasing frequency; while its imaginary part first decreases with increasing frequency below 50 °C, and then increases with increasing frequency above 50 °C. The imaginary part of the complex permittivity leads to dispersion and energy dissipation. This loss stems from the fact that the orientation polarization of water molecules cannot keep up with the rapidly changing electric field, resulting in energy dissipation as heat. In the radar wave band, this property of water makes it a natural electromagnetic wave absorbing medium. This invention uses the permittivity at room temperature (20 °C) to guide subsequent simulation design.

[0069] The dielectric constant of ITO resistive films in the 3~14 μm infrared band can be represented by the Drude model:

[0070]

[0071] Among them, the dielectric constant of the background = 3.9, plasma frequency Collision frequency The relative permittivity of ITO in the range of 3–14 μm is as follows: Figure 3 As shown in the illustration, the real part is negative, which allows ITO to operate at frequencies below the plasma frequency. The following frequency bands exhibit high reflectivity similar to metals.

[0072] The emissivity-scattering co-controlled water-based stealth transparent metasurface designed in this invention achieves reconfigurable stealth across three frequency bands: visible light, infrared, and microwave. Global state switching is achieved by filling and draining the metasurface: when the water-filled cavity is empty, microwaves from 6.2 to 15 GHz achieve diffuse scattering, resulting in a 10 dB RCS reduction and a relative bandwidth of 83.02%, while the 3–14 μm infrared band utilizes high and low emissivity units to form customized camouflage imaging; when the water-filled cavity is liquid-filled, electromagnetic waves are efficiently absorbed through water dielectric loss, and combined with scattering, a 10 dB RCS reduction can be achieved in the 5–20 GHz range, with a relative bandwidth of 120%, and the infrared spectrum becomes low-emissivity due to the decrease in temperature.

[0073] This invention also provides a design method for a water-based stealth transparent metasurface with combined emissivity-scattering modulation, the design method comprising the following steps:

[0074] Step 1: Introduce unit A0, which has both polarization conversion and absorption properties, into the metasurface.

[0075] Unit A0 is formed by stacking multiple layers from top to bottom: an ITO-PET patterned layer, a PMMA dielectric layer, sodium calcium glass, a water storage cavity, and an ITO floor. The top layer, resembling an "I" shape, achieves polarization conversion in the 5–15 GHz range, and its co-polarization and cross-polarization reflection amplitudes in the 2–20 GHz range are as follows: Figure 5 As shown, the cross-polarization amplitude is significantly higher than that of co-polarization within the 5–15 GHz range. To better investigate its polarization conversion and absorption characteristics, the polarization conversion rate, absorptivity, and polarization-absorptivity were calculated for the A0 water-filled storage cavity. Wherein, polarization conversion rate = , where r yx The cross-polarized reflection amplitude; absorptivity = Where R is the reflectivity of the unit cell, T is the transmittance of the unit cell, and r xx For the same polarization reflection amplitude, since the bottom layer of the unit cell has a 2 Ω / sq ITO reflective ground plane, T ≈ 0, therefore the absorptivity = Polarization-absorbance = Absorbance + Polarization conversion rate = + = 1 .like Figure 6 As shown, polarization conversion mainly occurs within 5~10 GHz, while the absorption effect of the water medium is the main factor within 10~20 GHz. Under the combined effect of polarization conversion and absorption, unit A0 can achieve a polarization-absorption rate of over 0.9 within 5~20 GHz.

[0076] To further verify the effect of introducing water-based structures on the modulation gain of polarization conversion and wave absorption performance, three sets of progressive simulation models were established for comparative analysis. The corresponding structural schematic diagrams are shown below. Figure 7 As shown. Among them Figure 7 (a) is Model 1, which consists only of a water layer, upper and lower glass covers and an ITO reflective base plate stacked together; Figure 7 (b) is Model 2, which adds an "I"-shaped ITO pattern layer and a PMMA medium layer to Model 1 to form a complete structure of the water storage cavity emptying state unit A0. Figure 7 (c) is model 3, which is to fill the cavity of model 2 with water medium to obtain the overall structure of the reconfigurable unit A0 of the water storage cavity in liquid state. Figure 8 The figures show the absorptivity, polarization conversion rate, and polarization-absorptivity as a function of frequency for the three models. Figure 8 (a) The absorption rate curves show that Model 1 relies solely on the dielectric loss of pure water to produce a weak absorption effect, resulting in a generally low absorption rate across the entire frequency band; Model 2, under the condition of emptying, has no water dielectric loss, exhibiting only weak resonant absorption at low frequencies, and its high-frequency absorption capability is also limited; Model 3, after being filled with water, significantly enhances its absorption intensity by leveraging the high dielectric and high-loss characteristics of the water medium. Observation Figure 8 (b) The polarization conversion rate curves show that Model 1, without a polarization control structure, consistently exhibits a polarization conversion rate close to 0; Models 2 and 3 both achieve efficient polarization conversion in the 5–10 GHz range, demonstrating that the polarization conversion effect is dominated by the upper elliptical pattern configuration. Combined with… Figure 8 (c) Comprehensive analysis of polarization-absorption rate curves: Under the synergistic effect of polarization conversion and water-based absorption, Model 3 can maintain the overall polarization-absorption rate above 0.9 in the 5~20 GHz wideband range, achieving the integrated effect of broadband efficient polarization control and electromagnetic wave loss absorption.

[0077] To further explore the impact of water layer thickness on the three properties of the unit mentioned above, Figure 9 The thickness h of the water medium is given respectively. w Two-dimensional contour plots of (a) absorptivity, (b) polarization conversion, and (c) polarization-absorptivity at different depths between 0.1 and 1 mm. It can be seen that with increasing water layer thickness, the high-frequency absorptivity gradually increases, while the polarization conversion gradually decreases, and the polarization-absorptivity decreases at different depths (h). w After increasing to 0.5 mm, the thickness gradually stabilized and stopped increasing. On the contrary, due to the effect of absorption, when the water layer thickness is above 0.5 mm, the polarization conversion rate decreases sharply, resulting in a slight decrease in polarization-absorption rate at low frequencies. Therefore, based on the above simulation analysis, the present invention sets the water layer thickness at 0.5 mm.

[0078] Step 2: Introduce a metasurface to the low emissivity unit B0 of the frequency-selective surface FSS.

[0079] First, the emissivity of an ITO resistive film with 2 Ω / sq in the 3~14 μm range was numerically simulated using the Drude model. Figure 4 As shown, its average emissivity is approximately 0.1. According to the emissivity calculation formula... It can be seen that the unit emissivity is mainly related to the ITO duty cycle, where, and These represent the infrared emissivity of ITO and PET, respectively. and These represent the duty cycle, = 0.9 and satisfies + = 1, < The average emissivity of cell A0 can be calculated to be approximately ε1 = 0.69.

[0080] To design a high and low infrared emissivity unit that meets the requirements of infrared camouflage, this invention introduces a unit B0 loaded with an FSS consisting of a 21×21 square ITO patch array. This array is split diagonally in half and arranged on both sides of an "I"-shaped pattern, as shown below. Figure 10 As shown in (b), the period of the square ITO patch is a = 0.35 mm. To maintain consistent emission amplitude within each unit while meeting the 0.05 mm laser processing accuracy requirement, the width of the square ITO patch is selected as b = 0.3 mm. Due to the increase in ITO area, according to the emissivity calculation formula, the average emissivity of unit B0 is ε2 = 0.26, and its emissivity curve as a function of wavelength is shown below. Figure 4 As shown.

[0081] Furthermore, in order to investigate the effect of FSS on the amplitude and phase of cross-polarization reflection of the unit, Figure 10 The designed basic unit A0 and the unit A after rotating 90° are given. 90 Element B0 after loading FSS and its element B rotated 90° 90 The top view. In CST, a full-wave simulation is performed on the four basic units, and the simulation results are as follows. Figure 11 and Figure 12 As shown, it is easy to see that the four basic units A0, A 90 B0, B 90 The cross-polarization reflection amplitudes are essentially identical within the range of 2–20 GHz, where A0 and B0, A 90 With B 90 With the same phase, A0 and A 90 B0 and B 90 The phase difference is 180° for both. Furthermore, in the 3–14 μm infrared band, A0 and A… 90The average emissivity is ε1 = 0.69, B0 and B 90 The average emissivity is ε² = 0.26. Therefore, A0, A 90 B0, B 90 It not only meets the 1-bit phase design requirements for microwave diffuse scattering in the 5~15 GHz range, but also meets the 1-bit emissivity requirements for infrared imaging camouflage in the 3~14 μm infrared band.

[0082] Step 3: Based on digital image processing, the infrared camouflage pattern pixels are decomposed, and the 1-bit high and low emissivity units are arrayed.

[0083] Based on digital image processing, the infrared camouflage pattern is decomposed into pixels, and 1-bit high and low emissivity units are arranged in an array. The specific processing flow is as follows: Figure 13 As shown in (a), a tank outline is selected as the target pattern to be camouflaged. First, grayscale conversion is performed on the original color image to remove color channel information and convert the image pixels into a grayscale matrix in the range of 0~255. Then, a fixed grayscale threshold is set to complete global binarization segmentation, dividing all pixels into two types of regions. After binarization, the blue pixel region corresponds to the high infrared emissivity deployment area, which is used to arrange A0 and A1. 90 The unit, with a white background pixel area corresponding to a low infrared emissivity area, is used to arrange B0 and B... 90 Unit; then the binarized image size is normalized to a 20×20 pixel matrix that matches the metasurface array, so that each pixel corresponds to a unit position in the array. The initial coordinate distribution of the two types of units inside the array is determined by mapping row by row and column by column, and the 1-bit high and low emissivity encoded array pre-arrangement matching the preset infrared camouflage imaging effect is completed.

[0084] Step 4: The phase array is iteratively optimized using the simulated annealing algorithm to obtain the optimal 1-bit phase arrangement for diffuse scattering.

[0085] The phase array is iteratively optimized using a simulated annealing algorithm to obtain the optimal 1-bit phase arrangement for diffuse scattering. The complete iterative process of the algorithm is as follows: Figure 13 As shown in (b). The specific execution process is as follows: First, the algorithm parameters are initialized, and the initial temperature T, temperature decay coefficient α, and minimum termination temperature T are set. min The inner loop iterates 20×N times (N is the total number of units in the metasurface array), with an iteration limit (limit), and the iteration count variable count1 is set to zero. Then, a random 1-bit phase encoding is assigned to the 20×20 array to generate the initial phase arrangement scheme; the target fitness function is then constructed. In the formula The RCS reduction value of the array is used as the optimization target, with an RCS reduction of more than 10 dB in the 6.2~15 GHz range. The fitness value corresponding to the current coding is calculated, and the coding and fitness value are assigned as the optimal coding code. best Optimal fitness P best .

[0086] Next, the outer main loop is checked, and the loop execution condition is that the current temperature T is greater than the termination temperature T. min Optimal fitness P best If the convergence threshold is not reached and the iteration count (count1) does not exceed the set upper limit, the inner loop is entered if the conditions are met. The total number of iterations in the inner loop is set to 20 × N. In the inner loop, the phase code of a certain cell in the array is randomly flipped to generate a new arrangement scheme and the corresponding fitness P' is recalculated. The difference between the old and new fitness is calculated as Δ = P' - P. If Δ < 0, it means that the new arrangement has a better optimization effect, and the optimal code and the optimal fitness are directly updated. If Δ ≥ 0, the random number rand < e is used according to the probability criterion. -Δ / T Determine whether to accept a suboptimal solution. If the probability condition is met, update the encoding; otherwise, retain the original phase arrangement.

[0087] After all iterations of the inner loop are completed, the temperature decay operation T = T×ɑ is executed, the iteration count1 is incremented, and the algorithm jumps back to the outer main loop condition check. This process is repeated until the main loop condition is no longer met. The algorithm then terminates and outputs the optimal 20×20 binary phase arrangement matrix, as shown in the figure. Figure 13 (b) The array diagram in the upper right corner is shown.

[0088] Step 5: Combining the infrared camouflage arrangement and the microwave RCS reduction array design results, the final 2-bit array arrangement of the four basic units is obtained.

[0089] like Figure 13 As shown in (c), this design combines the four types of units with two sets of phases and two sets of emissivity into a 2-bit code: code 00 corresponds to phase φ1 and high emissivity unit A0, and code 01 corresponds to phase φ2 and high emissivity unit A0. 90 Code 10 corresponds to phase φ1 and low emissivity unit B0, and code 11 corresponds to phase φ2 and low emissivity unit B0. 90 This enables a two-degree-of-freedom 2-bit mapping rule that combines 1-bit infrared emissivity encoding with 1-bit microwave phase encoding.

[0090] Based on the high and low emissivity constraints of the infrared pre-arrangement and the microwave 1-bit phase distribution obtained by simulated annealing optimization, the coding matching and assignment of each grid position in the 20×20 array are performed. The global 2-bit coding matrix is ​​generated by fusing the two sets of array design requirements. The final overall array arrangement result is as follows. Figure 13 As shown in (d); Figure 13 In (d), different colored blocks correspond to 2-bit codes: blue blocks are coded as 00, white blocks as coded as 10, light pink blocks as coded as 01, and orange-red blocks as coded as 11. This fused array's spatial arrangement strictly matches the binarized pixel distribution of the tank's infrared camouflage, meeting the camouflage requirements of the 3~14μm band infrared imaging. Simultaneously, its overall phase arrangement fulfills the phase cancellation conditions for microwave diffuse scattering in the 5~20 GHz range, simultaneously achieving a reduction in radar cross-section bandwidth and completing the design of a microwave-infrared multi-spectral compatible stealth integrated array configuration.

[0091] Based on the final fused array arrangement, far-field electromagnetic simulation analysis was conducted for two working modes: liquid-filled and empty water storage chambers of the units. The simulation results of the overall array RCS reduction are as follows: Figure 13 As shown in (e), when the water-filled cavity is filled, the array relies on the 1-bit phase arrangement to form an electromagnetic wave diffuse scattering cancellation effect, and relies on the dielectric loss of the water medium to achieve efficient electromagnetic absorption. The two mechanisms work together to achieve an RCS reduction of no less than 10 dB in the ultra-wide frequency range of 5~20 GHz, with a relative bandwidth of 120%. When the water-filled cavity is emptied, there is no water loss medium inside the cavity, and the stealth effect is achieved only by phase-encoded diffuse scattering. It can stably meet the 10 dB RCS reduction target in the frequency band of 6.2~15 GHz, with a relative bandwidth of 83.02%.

[0092] To visually characterize the spatial scattering modulation characteristics of the array's two operating modes, three-dimensional far-field scattering patterns were plotted at four typical frequency points: 7, 10, 15, and 18 GHz. The results are as follows: Figure 14 As shown, where Figure 14 (a) is a three-dimensional scattering pattern of the metasurface array under cross-polarization when the water storage cavity is emptied. Figure 14(b) shows the three-dimensional scattering pattern of the water-filled cavity, with the color changing from blue to red corresponding to the change in scattering field strength from minimum to maximum. Under the condition of an empty water-filled cavity, the 7, 10, and 15 GHz frequency arrays can stably maintain a 180° cross-polarization phase difference between elements, and the backscattering main lobe energy is dispersed throughout space to form a diffuse scattering distribution, achieving radar echo suppression. At a higher frequency of 18 GHz, the cross-polarization reflection amplitude of the elements is attenuated overall, while the phase difference remains at 180°, and the total radiated energy of the overall scattering pattern decreases compared to the first three frequency points. Under the condition of a water-filled cavity, the water medium inside the cavity introduces significant dielectric loss, producing an absorption and attenuation effect on electromagnetic waves. The overall three-dimensional scattering field strength at all four frequency points in the full frequency domain is lower than that under the condition of an empty water-filled cavity. Under the combined effect of loss absorption and diffuse scattering, the backscattering energy is further suppressed, broadening the effective bandwidth for radar stealth.

[0093] The above are merely preferred embodiments of the present invention and do not constitute any limitation on the scope of protection of the present invention; all technical solutions formed by equivalent transformations or equivalent substitutions fall within the scope of protection of the present invention; the parts of the present invention not described in detail are well known to those skilled in the art.

Claims

1. A water-based stealth transparent metasurface with combined emissivity-scattering modulation, characterized in that, The emissivity-scattering jointly regulated water-based stealth transparent metasurface includes four metasurface units: the high emissivity ε1 unit A0 consists of a 45° inclined "I"-shaped ITO-PET pattern layer, a PMMA dielectric layer, a calcium-sodium glass water storage cavity, and an ITO-PET reflector layer arranged from top to bottom; the low emissivity ε2 unit B0 has the same structure as unit A0, but adds a frequency selective surface FSS composed of an array of ITO square patches with micron-sized slits on both sides of the "I"-shaped pattern; unit A0 and unit B0 with phase φ1 are rotated 90° to obtain unit A with phase φ2. 90 and Unit B 90 ;; When the water storage chamber is emptied, electromagnetic wave diffuse scattering in the 6.2~15 GHz frequency band can be achieved by means of phase arrangement; A preset image is generated by arranging high and low emissivity units; when the water storage cavity is filled with liquid, the water medium inside the cavity introduces electromagnetic loss to absorb electromagnetic waves, achieving a 10 dB RCS reduction in the 5~20 GHz wideband range, and the overall temperature of the metasurface is reduced, resulting in a low radiation state in the 3~14 μm band.

2. The emissivity-scattering jointly modulated water-based stealth transparent metasurface according to claim 1, characterized in that, The ITO-PET pattern layer of unit A0 includes a PET substrate and an ITO patch disposed on top. The ITO patch pattern includes a rectangle placed at a 45° angle and two semicircles disposed at both ends of the rectangle with a diameter equal to its width. Unit A 90 Obtained by rotating unit A0 by 90°; Based on unit A0, unit B0 is provided with a frequency selective surface FSS consisting of an array of n×n uniform square ITO patches. This array is equally divided into two along the diagonal and arranged on both sides of the "I"-shaped pattern. Unit B 90 This is in unit A 90 Based on this, a frequency selective surface (FSS) consisting of an array of n×n uniform square ITO patches is set up. This array is divided into two equal parts along the diagonal and arranged on both sides of the "I"-shaped pattern.

3. The emissivity-scattering jointly modulated water-based stealth transparent metasurface according to claim 1, characterized in that, The structural parameters of the metasurface unit were determined by parameter scanning using CST electromagnetic simulation software. The unit period side length is p = 15 mm. The top layer "I"-shaped pattern is composed of a rectangle plus two semicircles with diameters equal to its width, rotated counterclockwise by 45°. The length of the rectangle is l = 9 mm and the width is w = 4.5 mm. The frequency selective surface (FSS) is composed of an array of square ITO patches with micron-level slits. The square ITO patch period is a = 0.35 mm, and the square ITO patch width is b = 0.3 mm. The thickness of the ITO-PET pattern layer and the ITO-PET reflector layer is h1 = 0.125 mm. The thickness of the PMMA dielectric layer is h2 = 3.3 mm. The height of the water storage cavity is h3 = 0.5 mm, and the thickness of the upper and lower calcium sodium glass covers of the water storage cavity is h3 = 0.2 mm.

4. A design method for a water-based stealth transparent metasurface based on the emissivity-scattering joint modulation described in claims 1-3, characterized in that, The design method for water-based stealth transparent metasurfaces with combined emissivity-scattering modulation includes the following steps: Step 1: Introduce a high emissivity unit A0 with both polarization conversion and absorption characteristics into the metasurface, and determine the unit parameters based on the polarization-absorption rate of the unit. Step 2: Introduce the low emissivity unit B0 of the frequency-selective surface FSS into the metasurface; Step 3: Based on digital image processing, decompose the infrared camouflage pattern pixels and initially delineate high emissivity units A0 / unit A. 90 and low emissivity unit B0 / unit B 90 Arrangement position; Step 4: With RCS reduction as the objective, the phase array arrangement is iteratively optimized using the simulated annealing algorithm to obtain the optimal diffuse scattering configuration. The elements A0 / B0 with phase φ1 and element A with phase φ2 are initially defined. 90 Unit B 90 Arrangement position; Step 5: Combining the infrared camouflage arrangement and microwave RCS reduction array design results, comprehensively determine the four elements A0, B0, and A1 within the metasurface array. 90 Unit B 90 The final arrangement.

5. The design method for water-based stealth transparent metasurfaces with combined emissivity-scattering modulation according to claim 4, characterized in that, In step 1, the polarization conversion rate, absorptivity, and polarization-absorptivity of the metasurface unit water storage cavity under liquid-filled conditions are: Polarization conversion rate = , where r yx This represents the cross-polarization reflection amplitude; Absorption rate = Where R is the reflectivity of the unit cell, T is the transmittance of the unit cell, and r xx For the same polarization reflection amplitude, since the bottom layer of the unit cell has a 2 Ω / sq ITO reflective ground plane, T ≈ 0, therefore the absorptivity = ; Polarization-absorption rate = Absorption rate + Polarization conversion rate = + = 1 ; Based on the thickness h of the water medium w Among different absorptivity, polarization conversion rate, and polarization-absorptivity ranges from 0.1 to 1 mm, the water medium thickness with the optimal polarization-absorptivity was selected.

6. The design method for water-based stealth transparent metasurfaces with combined emissivity-scattering modulation according to claim 4, characterized in that, In step 2, to achieve good infrared imaging results, considering the design requirements for infrared emissivity and the consistency of microwave reflection amplitude and phase, high emissivity unit A0 and unit A are designed based on digital imaging principles. 90 and low emissivity elements B0 and B0 of the surface FSS with frequency selected at the top layer. 90 ; Emissivity calculation formula: ； and These represent the infrared emissivity of ITO and PET, respectively. and These represent the duty cycles of ITO and PET, respectively, satisfying... + = 1, and < , =0.1, = 0.9; The duty cycles of ITO and PET are used to calculate the values ​​of cell A0 and cell A. 90 Unit B0 and Unit B 90 The corresponding emissivity are ε1 = 0.69 and ε2 = 0.26, respectively.

7. The design method for water-based stealth transparent metasurfaces with combined emissivity-scattering modulation according to claim 4, characterized in that, In step 3, firstly, a tank is selected as the target pattern to be camouflaged. The original color image is then converted to grayscale to remove color channel information and the image pixels are uniformly converted into a grayscale matrix in the range of 0 to 255. Secondly, a fixed grayscale threshold is set to complete global binarization segmentation, dividing all pixels into two types of regions. After binarization, one type of region corresponds to the high infrared emissivity deployment area, which is used to arrange high emissivity units, and the other type of region corresponds to the low infrared emissivity deployment area, which is used to arrange low emissivity units. Finally, the binarized image size is normalized to an m×m pixel matrix that matches the metasurface array, so that each pixel corresponds to a unit position in the array. The initial coordinate distribution of the two types of units inside the array is determined by mapping row by row and column by column, thus completing the 1-bit emissivity encoding arrangement that matches the preset infrared camouflage imaging effect.

8. The design method for water-based stealth transparent metasurfaces with combined emissivity-scattering modulation according to claim 4, characterized in that, In step 4, the simulated annealing algorithm process includes: First, initialize the algorithm parameters by setting the initial temperature T, temperature decay coefficient α, and minimum termination temperature T. min The main loop iteration count is capped at `limit`, and the inner loop iteration count is 20 × N, where N is the number of elements in the metasurface array. The iteration count variable `count1` is then set to zero. Subsequently, a random 1-bit phase encoding is assigned to the m × m array to generate the initial phase arrangement scheme. The target fitness function is then constructed. In the formula The RCS reduction value of the array is used as the optimization target, with an RCS reduction of more than 10 dB in the 5~15 GHz range. The fitness value corresponding to the current code is calculated, and the code and fitness value are assigned as the optimal code. best Optimal fitness P best ; Next, the outer main loop is checked, and the loop execution condition is that the current temperature T is greater than the termination temperature T. min Optimal fitness P best If the convergence threshold is not reached and the iteration count (count1) does not exceed the set upper limit, the inner loop is entered, with a total number of iterations set to 20 × N. In the inner loop, the phase code of a certain cell within the array is randomly flipped, a new arrangement is generated, and the corresponding fitness P' is recalculated. The difference between the old and new fitness Δ = P' - P is calculated. If Δ < 0, it indicates that the new arrangement is more effective, so the optimal code and optimal fitness are updated. If Δ ≥ 0, a random number rand < e is generated according to the probability criterion. -Δ / T Determine whether to accept the inferior solution. If the probability condition is met, update the encoding; otherwise, retain the original phase arrangement. After all iterations of the inner loop are completed, the temperature decay operation T = T×ɑ is executed, the iteration count1 is incremented, and the outer main loop condition judgment is checked again. The iteration is repeated until the main loop judgment condition is no longer met. The algorithm terminates and outputs the optimal m×m binary phase arrangement matrix.

9. The design method for water-based stealth transparent metasurfaces with combined emissivity-scattering modulation according to claim 4, characterized in that, In step 5, the four metasurface units are combined into a 2-bit code corresponding to two sets of phases and two sets of emissivity: Code 00 corresponds to high emissivity ε1, phase φ1 element A0; code 01 corresponds to rotating high emissivity ε1, phase φ2 element A. 90 Code 10 corresponds to low emissivity ε2, phase φ1 element B0; code 11 corresponds to rotating low emissivity ε2, phase φ2 element B. 90 A two-degree-of-freedom 2-bit mapping rule of 1-bit infrared emissivity coding + 1-bit microwave phase coding was constructed. Based on the 1-bit emissivity arrangement of the infrared pre-arrangement and the microwave 1-bit phase distribution obtained by simulated annealing optimization, the coding matching of each grid position in the m×m array is performed, and the design requirements of the two frequency bands are integrated to generate a global 2-bit coding matrix.

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