All-metal retroreflection metamaterial structure for target recognition enhancement

Abstract

The invention discloses an all-metal retroreflection metamaterial structure for target recognition enhancement, and belongs to the technical field of electromagnetic shielding. The all-metal retroreflection metamaterial structure comprises a bottom-layer supercell structure arranged below a middle-layer supercell structure; the upper-layer supercell structure is arranged above the middle-layer supercell structure; design domains in the bottom-layer supercell structure, the middle-layer supercell structure and the upper-layer supercell structure are discretized into a plurality of grid units for arranging reflection units; the grid unit is coded by adopting a one-dimensional vector X, and each element xi in the vector X is a binary variable 0 or 1 and is used for representing whether the reflection unit is placed at the corresponding sub-grid position or not; the periodic structures of the bottom-layer supercell structure, the middle-layer supercell structure and the upper-layer supercell structure are constructed by repeatedly arranging the supercell structures in a two-dimensional plane, so that a periodic reflecting surface is formed; the structure is simple in process and high in raw material utilization rate, and the reliability in a complex electromagnetic environment is remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of target recognition enhancement for electromagnetic shielding chambers, and relates to an all-metal retroreflective metamaterial structure for target recognition enhancement. Background Technology

[0002] With the development of intelligent sensing and target recognition technologies, traditional shielded enclosure structures face higher functional requirements beyond electromagnetic shielding: while suppressing external electromagnetic interference, they need to enhance the perception and recognition of specific target signals. Retroreflection is a special mechanism that reflects incident wave energy back along its original path. Compared to conventional specular reflection, it exhibits higher accuracy and energy utilization in directional reflection control, making it particularly suitable for applications such as target recognition enhancement in complex environments. This paper proposes introducing a three-dimensional metamaterial retroreflective structure on its upper surface to enhance the echo signal of the shielded enclosure under external radar illumination, thereby improving the enclosure's ability to be recognized by radar systems.

[0003] In the field of target recognition enhancement in electromagnetically shielded chambers, existing retroreflective metamaterial technologies mainly rely on the design of regular phase gradient metasurfaces based on the generalized Snell's law. This method has significant drawbacks: low design freedom, difficulty in overcoming periodic structural constraints, resulting in limited improvement in retroreflection efficiency; limited functionality, unable to flexibly adapt to varying incident angles or control the distribution of reflected energy; and the design process relies on empirical trial and error and parameter optimization, which is inefficient and prone to getting trapped in local optima. Summary of the Invention

[0004] To solve the above problems, the technical solution adopted by the present invention is: an all-metal retroreflective metamaterial structure for target recognition enhancement, comprising a bottom supercell structure, a middle supercell structure and an upper supercell structure; The bottom supercell structure is disposed below the middle supercell structure; The upper supercell structure is disposed above the middle supercell structure; The design domains in the bottom supercell structure, the middle supercell structure and the top supercell structure are all discretized into several grid elements for arranging reflection elements. The grid cell is encoded using a one-dimensional vector X, where each element x in vector X is... i It is a binary variable, 0 or 1, used to indicate whether a reflection unit is placed at the corresponding subgrid position; The periodic structure of the bottom layer supercell, the middle layer supercell, and the top layer supercell is constructed by repeatedly arranging the supercell structure in a two-dimensional plane, thereby forming a periodic reflective surface.

[0005] Furthermore: the bottom layer supercell structure, the middle layer supercell structure, and the top layer supercell structure have the same width and length; the bottom layer supercell structure and the top layer supercell structure both have a height of 3mm, and the single cell height of the middle layer supercell structure is 4mm.

[0006] Furthermore, the optimization process for the bottom layer supercell structure, the middle layer supercell structure, and the top layer supercell structure is the same, as follows: The reflection performance of the reflective array in different directions is evaluated, and the reflection intensity in each direction is described by the bistatic radar cross section using the far-field scattering characteristics of the array. Define the pitch angle scanning range. (X; () indicates the direction of the pitch angle. At that time, the bistationary RCS value corresponding to the supercell structure coding sequence X; By comparing the RCS value of the target direction of the reflective array with the total reflected power over the entire elevation angle scan range, and constructing an optimization objective function, the proportion of the reflected power in the target direction in the total reflected energy is maximized.

[0007] Furthermore, the expression for the optimization objective function of the metamaterial structure is as follows:

[0008] in: Design a variable vector, representing the set of parameters that need to be optimized; : No. Each design variable may represent the thickness, material type, and arrangement order of each layer; The total number of design variables, which is the number of layers or parameters; The objective function needs to be maximized. : Directivity function, representing the radiation intensity at direction θ and frequency f0; : Specific target direction; Operating frequency; In direction Radiation intensity on; : Lower limit of integration angle; : Integral limit angle; In direction The absolute value of the radiation intensity on the surface; Threshold; : Physical quantity array aperture; : The upper limit of this physical quantity.

[0009] Furthermore, the process of solving the optimization objective is as follows: Generate a population; In each iteration, the objective function value calculated based on the simulation results is used to update the individual optimal and global optimal solutions, and the position of the qubits is adjusted accordingly to generate a new generation of structural codes for the next round of simulation. When the objective function value corresponding to the best individual in the new generation exceeds the preset threshold T, the optimization process is terminated, and the encoding sequence of the current best individual is output.

[0010] The encoded sequence is then decoded to determine whether a reflection structure unit exists in each discrete grid cell; Finally, based on the decoding results, a three-dimensional metamaterial structure model is reconstructed, thereby achieving efficient retroreflection control of incident electromagnetic waves in a preset direction.

[0011] Furthermore: when reflections in different directions include retroreflection channel reflections and specular reflection channel reflections, the expression for the optimization objective function is as follows:

[0012] Design a variable vector, representing the set of parameters that need to be optimized; : No. Each design variable may represent the thickness, material type, and arrangement order of each layer; : Directional reflection function, which represents the reflection function of a metamaterial in a certain direction when an electromagnetic wave is incident from a certain direction. θ The intensity of reflection on the surface, : The direction of the incident wave of the target detection wave; The direction opposite to the incident direction, i.e., the "retroreflection direction". Ideally, retroreflection will cause the wave to return along its original path; Weighting coefficient; : Reflection intensity in the retroreflection direction; : Directional reflection function within the angular range The integral; The starting angle of the integration interval; The ending angle of the integration interval; : The given threshold; The topology optimization design is carried out with the goal of ensuring that the reflection power in the mirror reflection direction is equal to that in the retroreflection direction, and the weighting factor α = β = 1.

[0013] This invention provides an all-metal retroreflective metamaterial structure for enhanced target recognition. It proposes introducing a retroreflective structure on the surface of a three-dimensional metamaterial to enhance the echo signal of the shielded enclosure under external radar illumination, thereby improving the enclosure's ability to be recognized by the radar system. To achieve high-efficiency retroreflection performance, a retroreflection topology optimization model for the three-dimensional metamaterial shielding structure is constructed based on the generalized Snell's law. The optimization objective is to maximize the proportion of reflected power of the incident wave in its original direction. The proposed topology optimization method has been verified through full-wave simulation and measured data. Furthermore, a structural model with dual-channel adjustable reflection characteristics is proposed, further enhancing the practicality of the proposed topology optimization method. This method can automatically search for non-intuitive optimal topologies within a broad design space, significantly improving retroreflection efficiency and achieving dual-channel energy-tunable retroreflection functionality, effectively overcoming the shortcomings of existing technologies such as poor flexibility, limited performance, and complex design.

[0014] This invention significantly improves the electromagnetic wave retroreflection performance of a shielding chamber in a specific direction through a three-dimensional metamaterial retroreflection topology optimization method based on the generalized Snell's law. Compared with traditional structures, the designed retroreflective metamaterial achieves normalized reflection power ratios of 8.4% and 7.9% in the retroreflection direction at 10 GHz for incident angles of 30° and 50°, respectively, far exceeding the almost non-existent retroreflection capability of randomly arranged structures, effectively enhancing the target's identifiability in radar detection. Furthermore, the proposed dual-channel retroreflection amplitude adjustable design method enables flexible control of reflected energy, further improving the structure's adaptability and practicality. The structure is manufactured using 3D printing, which is simple, utilizes raw materials efficiently, and exhibits good angular and frequency robustness, maintaining stable retroreflection characteristics within a ±4° angular offset and ±0.3 GHz frequency variation range, significantly improving its reliability in complex electromagnetic environments. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of specular reflection and retroreflection on the shielded modular shelter; Figure 2This is a schematic diagram of the supercell design region, where (a) is the upper supercell structure, (b) is the middle supercell structure, and (c) is the bottom supercell structure. Figure 3 These are supercell structures and metamaterial arrays, where (a) is a supercell structure and (b) is a schematic diagram of a metamaterial array; Figure 4 This is a flowchart of the design process for retroreflective metamaterials based on topology optimization; Figure 5 It is a retroreflective metamaterial array with 30° incident angle, where (a) is a reflective unit, (b) is a supercell, and (c) is a metamaterial reflective array; Figure 6 This is a schematic diagram of the reflection characteristics of the retroreflection array under 30° incident conditions, where (a) is the three-dimensional bistatic RCS and (b) is the normalized bistatic RCS. Figure 7 These are randomly generated structures and simulated bistationary RCS diagrams; where (a) is the three-dimensional bistationary RCS and (b) is the normalized bistationary RCS. Figure 8 It is a retroreflective metamaterial array with 50° incident angle, where (a) is the supercell structure and (b) is a schematic diagram of the metamaterial array; Figure 9 The reflection characteristics of the retroreflection array under 50° incident conditions are shown in (a) and (b) are the three-dimensional bistatic RCS and normalized bistatic RCS. Figure 10 These are normalized RCS distribution diagrams of a 30° retroreflective metamaterial at different incident angles and frequencies, where (a) is the normalized RCS distribution diagram at different incident angles and (b) is the normalized RCS distribution diagram at different frequencies. Figure 11 These are the reflection characteristics of a dual-channel retroreflective array (designed for 30° incident light), where (a) is the three-dimensional bistatic RCS and (b) is the normalized bistatic RCS. Figure 12 These are the reflection characteristics of a dual-channel retroreflective array (designed for 50° incident light), where (a) is the three-dimensional bistatic RCS and (b) is the normalized bistatic RCS.

[0017] Figure 13 These are the reflection characteristics of a dual-channel retroreflective array (designed for 30° incident light), where (a) is the three-dimensional bistatic RCS and (b) is the normalized bistatic RCS. Figure 14 Reflection characteristics of a dual-channel retroreflective array (designed for 50° incident angle), where (a) is the three-dimensional bistatic RCS and (b) is the normalized bistatic RCS. Detailed Implementation

[0018] It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] An all-metal retroreflective metamaterial structure for enhanced target recognition includes a bottom supercell structure, a middle supercell structure, and an upper supercell structure. The bottom supercell structure is disposed below the middle supercell structure; The upper supercell structure is disposed above the middle supercell structure; The design domains in the bottom supercell structure, the middle supercell structure and the top supercell structure are all discretized into several grid elements for arranging reflection elements. The grid cell is encoded using a one-dimensional vector X, where each element x in vector X is... i It is a binary variable, 0 or 1, used to indicate whether a reflection unit is placed at the corresponding subgrid position; The periodic structure of the bottom layer supercell, the middle layer supercell, and the top layer supercell is constructed by repeatedly arranging the supercell structure in a two-dimensional plane, thereby forming a periodic reflective surface.

[0021] Furthermore: the bottom layer supercell structure, the middle layer supercell structure, and the top layer supercell structure have the same width and length; the bottom layer supercell structure and the top layer supercell structure both have a height of 3mm, and the single cell height of the middle layer supercell structure is 4mm.

[0022] Furthermore, the optimization process for the bottom layer supercell structure, the middle layer supercell structure, and the top layer supercell structure is the same, as follows: The reflection performance of the reflective array in different directions is evaluated, and the reflection intensity in each direction is described by the bistatic radar cross section using the far-field scattering characteristics of the array. Define the pitch angle scanning range. (X; () indicates the direction of the pitch angle. At that time, the bistationary RCS value corresponding to the supercell structure coding sequence X; By measuring the RCS value of the reflective array in the target direction (X;-θi) is compared with the total reflected power over the entire pitch angle scan range, and an optimization objective function is constructed to maximize the proportion of the reflected power in the target direction in the total reflected energy.

[0023] Furthermore, the expression for the optimization objective function of the metamaterial structure is as follows:

[0024] Design a variable vector, representing the set of parameters that need to be optimized.

[0025] : No. Each design variable may represent the thickness, material type, and arrangement order of each layer.

[0026] The total number of design variables, which is the number of layers or parameters.

[0027] The objective function needs to be maximized.

[0028] : Directional function, representing the direction θ θ and frequency f0 f Radiation intensity at 0.

[0029] : Specific target direction.

[0030] Operating frequency.

[0031] In direction The radiation intensity on it.

[0032] : Integral lower limit angle.

[0033] : Integral limit angle.

[0034] In direction The absolute value of the radiation intensity on the surface.

[0035] A threshold value that requires the ratio to be greater than or equal to... .

[0036] : Aperture of physical quantity array.

[0037] : The upper limit of this physical quantity.

[0038] Furthermore, the process of solving the optimization objective is as follows: Generate a population; In each iteration, the objective function value calculated based on the simulation results is used to update the individual optimal and global optimal solutions, and the position of the qubits is adjusted accordingly to generate a new generation of structural codes for the next round of simulation. When the objective function value corresponding to the best individual in the new generation exceeds the preset threshold T, the optimization process is terminated, and the encoding sequence of the current best individual is output.

[0039] The encoded sequence is then decoded to determine whether a reflection structure unit exists in each discrete grid cell; Finally, based on the decoding results, a three-dimensional metamaterial structure model is reconstructed, thereby achieving efficient retroreflection control of incident electromagnetic waves in a preset direction.

[0040] Furthermore: when reflections in different directions include retroreflection channel reflections and specular reflection channel reflections, the expression for the optimization objective function is as follows:

[0041] Design a variable vector, representing the set of parameters that need to be optimized.

[0042] : No. Each design variable may represent the thickness, material type, and arrangement order of each layer.

[0043] : Directional reflection function. Represents the reflection of the metamaterial in direction θ when an electromagnetic wave is incident from a certain direction. θ The intensity of reflection on the surface.

[0044] : The direction of the incident wave of the target detection wave.

[0045] The direction opposite to the incident direction is called the "retroreflection direction". Ideally, retroreflection will cause the wave to return along its original path.

[0046] Weighting coefficient. Used to balance the reflection intensity of the negative reflection channel and retroreflection.

[0047] : The intensity of reflection in the retroreflection direction.

[0048] : Directional reflection function within the angular range The points.

[0049] : The starting angle of the integration interval.

[0050] : The ending angle of the integration interval.

[0051] : A given threshold.

[0052] The topology optimization design is carried out with the goal of ensuring that the reflection power in the mirror reflection direction is equal to that in the retroreflection direction, and the weighting factor α = β = 1.

[0053] Example 1: The process of analyzing the implementation mechanism of a three-dimensional retroreflector is as follows: By superimposing the reflection phases generated by each supercell unit in a periodic metamaterial (MTM), the direction of the reflected beam can be controlled. When an obliquely incident electromagnetic wave irradiates a conventional reflecting surface, if there is no phase gradient in the tangential direction of the reflecting surface, the reflected wave will propagate along different paths and eventually converge at the same exit point. At this time, the optical path and phase of each path are equal, which is a typical specular reflection phenomenon.

[0054] Figure 1 These are images of specular and retroreflective surfaces on the shielded modular shelter. like Figure 1 As shown, in this case, if we assume the phase gradient of the reflecting surface in the tangential direction is... dФ / d The incident angle and the reflection angle are respectively θ i and θ r Then the two satisfy the generalized law of reflection:

[0055] Considering only the phase gradient along the x-axis and no phase gradient in other directions, substituting this into the above equation yields:

[0056] In the case of specular reflection:

[0057] In the case of retroreflection, that is, satisfying θ i =- θ r At that time, the length of the supercell d Should meet:

[0058] This condition is also known as the Bragg condition. It is predicated on the reflection phase. Φ x It has a linear distribution in the x-axis direction. To achieve a linear distribution, the phase distribution in this direction must remain continuous.

[0059] To suppress sidelobe radiation, reflections from non-target directions (i.e., pseudo-reflections), and traditional specular reflection, and to achieve the optimized target of maximum retroreflection ratio in a preset direction, it is necessary to adjust the arrangement structure of the reflective elements, thereby regulating the electromagnetic response characteristics of the supercell array. When the incident wavelength is... λ 0, angle of incidence is θ i When the supercell size is calculated, the size can be determined using the formula above.

[0060] like Figure 2 As shown, (a) is the upper supercell structure, (b) is the middle supercell structure, and (c) is the bottom supercell structure. The supercell design region is decomposed into three different heights of 2 d × d × h The single-cell design regions correspond to the bottom, middle, and top layers of the supercell structure, respectively. Each single-cell design region is discretized into several grid elements for arranging reflection elements. To characterize different topological structures in the supercell, one-dimensional vectors are used. X The grid state from the bottom unit cell to the top unit cell is encoded. Among them, the vector... X Each element in x i It is a binary variable (0 or 1) used to indicate whether a reflection unit is placed at the corresponding subgrid position.

[0061] Figure 3 These are supercell structures and metamaterial arrays, where (a) is a supercell structure and (b) is a schematic diagram of a metamaterial array; like Figure 3 As shown, the periodic structure of the entire metamaterial is constructed by repeatedly arranging the supercell structure in a two-dimensional plane, thereby forming a periodic reflective surface.

[0062] The reflection performance of the reflective array in different directions was evaluated using the commercial finite element software HFSS. The far-field scattering characteristics of the array were utilized, and the reflection intensity in each direction was described using the bistatic radar cross section (RCS). Let the elevation angle scanning range be denoted as , and define... ( X ; () indicates the direction of the pitch angle. At that time, the supercell structure coding sequence X The corresponding bistatic RCS value. This is obtained by calculating the RCS value in the target direction. ( X ;- θ i The total reflected power is compared with the total reflected power over the entire pitch angle scan range, and an optimization objective function is constructed to maximize the proportion of the reflected power in the target direction in the total reflected energy.

[0063] To further prevent isolated reflective units from breaking away from the overall structure and affecting manufacturing feasibility, a perimeter constraint is introduced to control the connectivity of the reflective region. To reduce simulation computational costs, an error threshold is introduced. T When the optimization objective is less than T When the current structure is considered to meet the design requirements, the optimization iteration can be terminated early. The optimization objective function can then be expressed as:

[0064] Figure 4 This is a flowchart of the design process for retroreflective metamaterials based on topology optimization; the optimization process is as follows: Figure 4 As shown, using the Binary Quantum Particle Swarm Optimization (BQPSO) algorithm as the optimization tool, and controlling and calling the commercial finite element simulation software HFSS through the MATLAB platform, the metamaterials corresponding to different structural codes were simulated, and their RCS distribution curves were calculated.

[0065] In each iteration, the objective function value calculated based on the simulation results is used to update the individual optimal (Pbest) and global optimal (Gbest) solutions, and the positions of the qubits are adjusted accordingly to generate a new generation of structure encoding for the next round of simulation. When the objective function value corresponding to the best individual in the new generation exceeds a preset threshold... T When the optimal individual is reached, the optimization process terminates, and the encoded sequence of the current best individual is output. This encoded sequence is then decoded to determine whether a reflective structural unit exists in each discrete grid cell. Finally, the three-dimensional metamaterial structure model is reconstructed based on the decoding results, thereby achieving efficient retroreflection control of incident electromagnetic waves in a preset direction.

[0066] Furthermore, the process of structural design and result analysis is as follows: First, the process of designing the structure of the retroreflective metamaterial is as follows: Based on the above optimization method, a metamaterial structure capable of retroreflecting electromagnetic waves of specific wavelengths and incident angles was designed. The design focused on a retroreflection structure for TE-polarized incident waves with a frequency of f0 = 10 GHz and an incident angle of θi = 30°. The width of the supercell, d = 30 mm, was calculated using equation (4.4), and the planar dimensions of the unit cell were 2d × d = 60 mm × 30 mm. The unit cell design region was discretized into 20 × 10 subgrids, each with dimensions l × l = 3 mm × 3 mm.

[0067] To ensure structural continuity, a 0.2mm overlap is maintained between adjacent reflective units; therefore, the actual planar dimensions of the reflective units are... l × l =3.2mm × 3.2mm. The unit cell height of the first and third layers is 3mm, and the unit cell height of the second layer is 4mm. FR4, with a relative permittivity of 4.4, is used as the substrate for the reflective unit.

[0068] Figure 5 It is a retroreflective metamaterial array with 30° incident angle, where (a) is a reflective unit, (b) is a supercell, and (c) is a metamaterial reflective array; Figure 6 This is a schematic diagram of the reflection characteristics of the retroreflective array under a 30° incident angle, where (a) is the three-dimensional bistatic RCS and (b) is the normalized bistatic RCS; the retroreflective metamaterial array obtained after topology optimization and its corresponding three-dimensional bistatic radar cross section (RCS) are shown below. Figure 6 As shown, (a) exhibits a distinct and narrow reflected beam in the 30° retroreflection direction, indicating that the structure possesses good directional selectivity and strong energy concentration capability. To further quantify its directional characteristics, the obtained RCS data was normalized, as shown in Figure (b). At the pitch angle... The normalized reflected power in the 30° direction is significantly higher than in other directions, accounting for 0.084% of the total reflected energy.

[0069] To verify the effectiveness of the designed retroreflective metamaterial structure, a set of randomly arranged structures was constructed as a control group, and their performance was compared under the same simulation parameter settings.

[0070] Figure 7 These are randomly generated structure and simulated bistatic RCS plots; where (a) is the 3D bistatic RCS and (b) is the normalized bistatic RCS; as shown Figure 7 As shown in (a), under the same operating frequency and polarization conditions as the optimized structure, the randomly arranged metamaterial array is irradiated with an oblique incident wave at an incident angle of θi = 30°, exhibiting specular reflection characteristics. The normalized bistatic RCS is as follows: Figure 7 As shown in (b), the maximum reflected power is concentrated in the direction of θo=-30°, indicating that the randomly arranged structure is difficult to form the expected phase gradient and energy accumulation in the absence of ordered topological control, and therefore does not have the ability to reflect back.

[0071] Figure 8 This is a retroreflective metamaterial array with an incident angle of 50°, where (a) is the supercell structure and (b) is a schematic diagram of the metamaterial array; the incident angle is adjusted to θ. iWhen the metamaterial structure is illuminated at 50°, the width of the supercell is selected as 20 mm according to equation (4.4), and the corresponding supercell and its array arrangement are shown in Figure 8. The planar dimensions of each unit cell are 2d×d = 40 mm × 20 mm. The design area of ​​each unit cell is further discretized into 20 × 10 sub-grid units, and the dimensions of each sub-grid are l × l = 2 mm × 2 mm. To ensure the geometric continuity and fabrication feasibility of the structure, a 0.2 mm overlap area is set between adjacent reflective units. Therefore, the actual planar dimensions of the reflective unit are 2.2 mm × 2.2 mm. The far-field directional reflection performance of the metamaterial array is improved by topologically optimizing the spatial distribution of the reflective units within the sub-grids.

[0072] Figure 9 The reflection characteristics of the retroreflective array under a 50° incident condition are shown, where (a) is the three-dimensional bistatic RCS and (b) is the normalized bistatic RCS. The optimized retroreflective metamaterial array and its corresponding three-dimensional bistatic radar cross section (RCS) are as follows: Figure 9 As shown in Figure (a), a distinct and narrow reflected beam is formed in the 50° retroreflection direction, indicating that the structure has good directional selectivity and strong energy concentration capability. To further quantify its directional characteristics, the obtained RCS data was normalized, and the results are shown in Figure (b). At the pitch angle... The normalized reflected power in the 50° direction is significantly higher than in other directions, accounting for 0.079% of the total reflected energy.

[0073] Further, sample testing was conducted; Figure 10 Figure 10 shows the normalized RCS distribution of the 30° retroreflective metamaterial under different incident angles and frequencies. (a) shows the normalized RCS distribution at different incident angles, and (b) shows the normalized RCS distribution at different frequencies. The experimental sample and platform are shown in Figure 10. The sample measures 358.2 mm × 362.4 mm and is fabricated by 3D printing using 12 × 6 topology-optimized supercells replicated in a two-dimensional plane. To verify the actual electromagnetic performance of the topology-optimized retroreflective metamaterial structure under 10 GHz incident wave conditions, reflection pattern tests were conducted on a bistatic far-field measurement platform within a microwave anechoic chamber. Wedge-shaped absorbing materials were placed on the four walls of the anechoic chamber and around the platform to suppress stray echoes. The transmitting end is a vertically polarized horn antenna, fixed on a fixed arm with an incident angle θi = 30°. The receiving end is also a vertically polarized horn antenna, mounted on a rotatable robotic arm at -90°. The system scans in 2° increments within a 90° elevation range. Both the transmitting and receiving antennas are connected to a vector network analyzer (VNA), and the measured two-port S-parameters are converted to obtain the reflected power at each angle.

[0074] Figure 11 These are the reflection characteristics of a dual-channel retroreflective array (designed for 30° incident light), where (a) is the three-dimensional bistatic RCS and (b) is the normalized bistatic RCS. Figure 11 The normalized RCS results obtained from the tests are shown. In Figure (a), when the incident angle is 30°, the maximum reflection direction of the designed 30° retroreflective metamaterial structure appears at 28°. When the incident angle is 50°, the designed 50° retroreflective metamaterial was placed in the experimental setting, and the receiving antenna was fixed at 50°. The receiving antenna was rotated in the same manner as described above for testing. In Figure (b), when the incident angle is 50°, the maximum reflection direction of the designed 50° retroreflective metamaterial structure appears at 54°. The experimental results show that the designed retroreflective metamaterial forms a significant main lobe reflection near the target retroreflection direction, and its reflection intensity is significantly higher than in other directions. As the receiving angle deviates from this main lobe direction, the reflection power rapidly decreases, indicating that the structure has excellent directionality and retroreflection capability in the target direction.

[0075] Furthermore, the process of verifying the robustness of metamaterials is as follows: Considering that the incident angle and frequency of electromagnetic waves may deviate to some extent in practical applications, this section presents a systematic simulation test of the reflection performance of the designed retroreflective metamaterial structure under non-ideal incident conditions to evaluate its stability and robustness. The test consists of two parts: changing the incident angle while keeping the incident wave frequency fixed, and analyzing the effect of angle deviation on the reflection characteristics; and changing the incident wave frequency while keeping the incident angle fixed, and evaluating its frequency response characteristics.

[0076] Figure 12 The reflection characteristics of a dual-channel retroreflective array (designed for 50° incident light) are shown, where (a) is the three-dimensional bistatic RCS and (b) is the normalized bistatic RCS. Robustness analysis was performed on the designed retroreflective metamaterial structure with an incident angle of 30° and an incident wave frequency of 10GHz. With the incident frequency fixed at the design frequency (10GHz), the incident angle was gradually increased from 26° to 34°. The simulation results of the corresponding normalized bistatic RCS distribution are shown in Figure (a). As the incident angle increases, the direction of the main reflected beam smoothly transitions from 34° to 27°, exhibiting good angle-following characteristics. Except under the 34° incident condition... Apart from a certain degree of enhanced specular reflection at 35°, the structure maintains a significant retroreflection main lobe at all other incident angles. Furthermore, the scattering intensity in the specular reflection direction is consistently lower than 30% of that in the retroreflection direction, indicating that the structure can still maintain good directional reflection capability under a certain range of angular disturbances.

[0077] With a fixed incident angle of 30°, the incident wave frequency was scanned from 9.7 GHz to 10.3 GHz, and the normalized bistatic RCS obtained is shown in Figure (b). It can be observed that the main reflection beam smoothly changes from 33° to 27° with increasing frequency, and is still concentrated near the retroreflection direction. Among them, only at the 9.7 GHz frequency does a certain degree of specular reflection enhancement appear, while significant retroreflection characteristics are exhibited at other frequency points.

[0078] The proposed retroreflective metamaterial structure can still maintain strong directional selectivity and stable control under certain incident angle and operating frequency perturbation conditions, demonstrating good robustness and practical application potential.

[0079] To enhance the adaptability and flexibility of the designed structure in complex application scenarios, in addition to achieving strong directional retroreflection characteristics, additional reflection channels can be introduced in specific directions to realize multi-channel reflection control. In the proposed design method, the directions and reflection intensities of both the retroreflection channel and the specular reflection channel can be flexibly adjusted according to actual needs. The far-field reflection power at various angles of the structure is calculated through numerical simulation, and the reflection intensities in the target specular reflection direction (θr) and retroreflection direction (-θi) are extracted, denoted as D(X;θr) and D(X;-θi), respectively, to quantify the reflection intensities in the two target directions.

[0080] To achieve flexible control over the dual-channel reflection intensity ratio, weighting factors α and β are introduced, corresponding to the importance weights of the specular reflection and retroreflection directions, respectively. By adjusting these two parameters, the reflection energy distribution of the two channels can be dynamically controlled, achieving adjustable dual-channel reflection characteristics. The optimization objective function is set to minimize the difference in weighted reflection power between the two directions, ensuring that the metamaterial structure can achieve reasonable energy distribution in the two target directions.

[0081] Furthermore, to ensure that the designed structure possesses sufficient energy reflection capability and directional control capability in practical applications, a minimum reflection power threshold T is introduced as a minimum reflection intensity constraint for each target reflection direction. When the reflection power in a certain direction is less than the power threshold T, the structural solution is considered impractical. To effectively filter out such "inferior solutions" during the optimization process, a penalty is imposed on the objective function when the reflection intensity constraint is not met, causing it to reach a preset maximum value, thus eliminating it during population updates. The overall optimization is illustrated as follows: (4.6) The topology optimization design is carried out with the goal of equal reflection power in the mirror reflection direction and the retroreflection direction (i.e., weighting factor α = β = 1). At a frequency of 10 GHz, the incident wave is incident on the surface of the structure at an angle of 30°. The optimization goal is to generate dual-channel reflection beams with equal amplitude in both the -30° and 30° directions.

[0082] Figure 13 The reflection characteristics of a dual-channel retroreflective array (designed for 30° incident light) are shown in Figure (a), where (b) is the three-dimensional bistatic RCS and (a) is the normalized bistatic RCS. By optimizing the supercell structure's topology, a supercell structure satisfying the dual-channel reflection target was obtained. This supercell was then horizontally and periodically replicated along the x and y directions in a two-dimensional plane to form a complete metamaterial array, as shown in Figure (a). Simulation analysis of this array yielded the normalized bistatic RCS shown in Figure (b). The reflection amplitude ratio in the two target directions is approximately 0.98:1, close to the design target of 1:1, indicating that the designed structure achieved the expected control effect in terms of dual-channel reflection energy distribution.

[0083] Figure 14 The reflection characteristics of a dual-channel retroreflective array (designed for 50° incident angle) are shown, where (a) is the three-dimensional bistatic RCS and (b) is the normalized bistatic RCS. Similarly, under the conditions of an incident radio frequency of 10 GHz and an incident angle of 50°, the optimization objective is to achieve a dual-channel reflection performance with a reflection amplitude ratio of 1:1 in both the 50° and -50° directions. A supercell structure is obtained through topology optimization design, and horizontal periodic replication is performed along the x and y axes in a two-dimensional plane to construct a metamaterial array. The simulated three-dimensional bistatic RCS distribution and normalized bistatic RCS curves are shown below. Figure 14 As shown, the designed structure produces obvious reflection main lobes in both ±50° directions. The normalized RCS values ​​extracted in the two target directions are D(X;50°) and D(X;-50°). The reflection amplitude ratio in the two directions is approximately 1:0.93, exhibiting clear dual-channel reflection characteristics.

[0084] Through comparative calculations at two different incident angles (30° and 50°), the proposed dual-channel reflection design method is verified to effectively control the reflected energy in the target direction under different incident angles, and has certain directional adaptability and structural stability, proving the feasibility and effectiveness of the proposed design method in a wide angle range.

[0085] This application addresses the practical needs of shielded enclosures in enhancing target recognition by proposing a three-dimensional metamaterial retroreflection topology optimization method based on the generalized Snell's law. By optimizing the distribution of metamaterial reflective units, incident electromagnetic waves can be efficiently reflected back in their original direction, enhancing the radar identifiability of the shielded enclosure. Taking a 10GHz incident wave as an example, retroreflection examples with incident angles of 30° and 50° were designed, and corresponding three-dimensional metamaterial structures were constructed. Full-wave simulations verified the retroreflection performance in the target direction and a certain degree of structural robustness, while experimental tests further validated the effectiveness of the proposed topology optimization method. Furthermore, a dual-channel retroreflection amplitude adjustable design method is proposed, making the retroreflection response of the structure more flexible, thereby further improving the practicality of the proposed topology optimization method.

[0086] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A target recognition-enhanced all-metal retroreflective metamaterial structure, characterized in that: This includes the bottom supercell structure, the middle supercell structure, and the top supercell structure; The bottom supercell structure is disposed below the middle supercell structure; The upper supercell structure is disposed above the middle supercell structure; The design domains in the bottom supercell structure, the middle supercell structure and the top supercell structure are all discretized into several grid elements for arranging reflection elements. The grid cell is encoded using a one-dimensional vector X, where each element x in vector X is... i It is a binary variable, 0 or 1, used to indicate whether a reflection unit is placed at the corresponding subgrid position; The periodic structure of the bottom layer supercell, the middle layer supercell, and the top layer supercell is constructed by repeatedly arranging the supercell structure in a two-dimensional plane, thereby forming a periodic reflective surface.

2. The all-metal retroreflective metamaterial structure for enhanced target recognition according to claim 1, characterized in that: The bottom, middle, and top supercell structures have the same width and length; the bottom and top supercell structures have a height of 3 mm, and the single cell height of the middle supercell structure is 4 mm.

3. The all-metal retroreflective metamaterial structure for enhanced target recognition according to claim 1, characterized in that: The optimization process for the bottom layer supercell structure, the middle layer supercell structure, and the top layer supercell structure is the same, as follows: The reflection performance of the reflective array in different directions is evaluated, and the reflection intensity in each direction is described by the bistatic radar cross section using the far-field scattering characteristics of the array. Define the pitch angle scanning range. (X; () indicates the direction of the pitch angle. At that time, the bistationary RCS value corresponding to the supercell structure coding sequence X; By comparing the RCS value of the target direction of the reflective array with the total reflected power over the entire elevation angle scan range, and constructing an optimization objective function, the proportion of the reflected power in the target direction in the total reflected energy is maximized.

4. The all-metal retroreflective metamaterial structure for enhanced target recognition according to claim 1, characterized in that: The objective function for optimizing the metamaterial structure is expressed as follows: in: Design a variable vector, representing the set of parameters that need to be optimized; : No. Each design variable may represent the thickness, material type, and arrangement order of each layer; The total number of design variables, which is the number of layers or parameters; The objective function needs to be maximized. : Directional function, representing the direction θ θ and frequency f0 f Radiation intensity at 0; : Specific target direction; Operating frequency; In direction Radiation intensity on; : Lower limit angle of integration; : Integral limit angle; In direction The absolute value of the radiation intensity on the surface; Threshold; : Physical quantity array aperture; : The upper limit of this physical quantity.

5. The all-metal retroreflective metamaterial structure for enhanced target recognition according to claim 1, characterized in that: The process of solving the optimization objective is as follows: Quantum observation generates populations; In each iteration, the objective function value calculated based on the simulation results is used to update the individual optimal and global optimal solutions, and the position of the qubits is adjusted accordingly to generate a new generation of structural codes for the next round of simulation. When the objective function value corresponding to the best individual in the new generation exceeds the preset threshold T, the optimization process is terminated, and the encoding sequence of the current best individual is output. The encoded sequence is then decoded to determine whether a reflection structure unit exists in each discrete grid cell; Finally, based on the decoding results, a three-dimensional metamaterial structure model is reconstructed, thereby achieving efficient retroreflection control of incident electromagnetic waves in a preset direction.

6. The optimization method for an all-metal retroreflective metamaterial structure for enhanced target recognition according to claim 1, characterized in that: When reflections in different directions include retroreflection channel reflections and specular reflection channel reflections, the expression for the optimization objective function is as follows: Design a variable vector, representing the set of parameters that need to be optimized; : No. Each design variable may represent the thickness, material type, and arrangement order of each layer; : Directional reflection function, representing the intensity of reflection of a metamaterial in direction θ when an electromagnetic wave is incident from a certain direction. : The direction of the incident wave of the target detection wave; The direction opposite to the incident direction is called the "retroreflection direction"; ideally, retroreflection will cause the wave to return along its original path. Weighting coefficient; : Reflection intensity in the retroreflection direction; : Directional reflection function within the angular range The integral; The starting angle of the integration interval; The ending angle of the integration interval; : The given threshold; The topology optimization design is carried out with the goal of ensuring that the reflection power in the mirror reflection direction is equal to that in the retroreflection direction, and the weighting factor α=β=1.

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