Computer-aided design broadband stealth phase recovery method and carpet stealth device

Abstract

The invention belongs to the technical field of metasurface electromagnetic regulation and control, and particularly relates to a computer-aided design broadband stealth phase recovery method and a broadband carpet stealth device. The broadband carpet stealth device is specifically represented as a triangular split platform with the inclination angle phi, and the surface of the broadband carpet stealth device is formed by periodically arranging M * N metasurface units. The broadband stealth phase recovery method is based on a gradient descent method and a root search algorithm, and relates to two phase regulation and control modes. Firstly, M / 2 unit structure parameters are determined based on a gradient descent method, and each unit is composed of an upper-layer multi-mode metal resonator loaded with a variable capacitance diode, a middle-layer F4B dielectric plate and a lower-layer metal floor; and secondly, searching voltages required in three application scenes point by point in a broadband range through a root seeking algorithm, and outputting the voltages in real time by adopting a field programmable gate array so as to accurately recover a scattering electromagnetic wave phase, so that a broadband electromagnetic illusion function is realized. The carpet hiding device works under linear polarized waves, and has the advantages of being high in efficiency, easy to process, programmable and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of electromagnetic multifunctional metasurfaces, and particularly relates to a broadband stealth phase recovery method assisted by computer-aided design and a carpet stealth device. Background Art

[0002] With the rapid development of technology, stealth has gradually evolved from a simple and primitive visual deception method to a precise and systematic modern technology system. By designing reasonable electromagnetic parameters, new electromagnetic wave stealth technologies can flexibly control the propagation and scattering of electromagnetic waves, thereby reducing the detectability of the stealth object. Currently, researchers are attempting to use metasurface electromagnetic regulation technology to achieve a "cloaking device" with a simple structure, low profile, and easy deployment. By simulating the effect of a specific object on the electromagnetic wavefront, target stealth and camouflage can be achieved. In the initial stage, researchers mainly focused on passive metasurfaces, that is, designing the stealth function by adjusting the size of the metal structures on the metasurface. However, once a passive stealth device is fabricated, its size and structure are fixed, and its electromagnetic function is also correspondingly determined, making it impossible to switch according to the actual scenario. To address this problem, programmable metasurfaces have been proposed, which are composed of semiconductor components such as diodes and CMOS transistors, as well as passive metasurfaces. Among them, the semiconductor components are fixed at specific positions on the metasurface metal structure through a precise welding process. Different from traditional passive metasurfaces, programmable metasurfaces can control the equivalent electrical parameters (resistance, capacitance, inductance) of semiconductor components in the form of bias voltage and current, thereby achieving the regulation of the amplitude, phase, polarization, and frequency of spatial electromagnetic waves. They have the advantage of flexibly regulating electromagnetic waves and can achieve specific electromagnetic functions for any scenario, showing broad application prospects in the fields of communication, sensing, and even national defense. Therefore, studying the electromagnetic wave regulation of programmable metasurfaces has important academic value and practical engineering significance.

[0003] However, due to the lack of an effective computer-aided design broadband stealth phase recovery method, the active reconfigurable characteristics of programmable metasurfaces are difficult to play a role, especially the lack of a method for extracting the voltage of gradient unit semiconductor devices point by point, which severely restricts the development of broadband carpet stealth devices. Therefore, there is an urgent need to invent an adaptive broadband stealth phase recovery method. Summary of the Invention

[0004] The present invention designs and studies a programmable metasurface based on a computer-aided design method and incorporating varactor diodes, which has the advantages of easy processing, small profile, reconfigurability, and high efficiency. Such metasurfaces can output a low-frequency reverse bias voltage through an FPGA to control the equivalent capacitance value of the varactor diodes, complete the phase regulation of the emitted y-polarized electromagnetic waves, and achieve dynamic adjustment of the electromagnetic illusion function.

[0005] The present invention discloses a broadband stealth phase recovery method for computer-aided design. The broadband stealth phase recovery method for computer-aided design includes the following steps:

[0006] Step 1, design of broadband carpet stealth device and metasurface unit;

[0007] The broadband carpet stealth device is a three-dimensional triangular wedge platform composed of M*N metasurface units loaded with varactor diodes arranged in an equidistant periodic extension;

[0008] The metasurface unit includes a three-layer structure. The top layer structure includes an H-shaped metal strip and two rectangular metal patches; the middle layer is a dielectric plate, and the bottom layer is a metal floor;

[0009] Step 2, calculation of structural parameters and voltage;

[0010] Construct a three-dimensional triangular wedge platform of a programmable metasurface with a platform tilt angle of 30° and two programmable metasurfaces vertically symmetric; through the broadband stealth phase recovery method, calculate the structural parameters and reverse bias voltage required for the design of the broadband carpet stealth device;

[0011] Step 3, determine the topological structure of the broadband carpet stealth device according to the structural parameters of the metasurface unit.

[0012] Further, in Step 1, the three-dimensional triangular wedge platform of the broadband carpet stealth device is symmetric on both sides of the central xoz plane, and the M / 2 units in the y-axis direction respectively have metasurface units with different structural parameters, and N metasurface units with the same structural parameters in the x-axis direction are arranged in an equidistant periodic extension.

[0013] Further, in Step 1, the period p of the metasurface unit is 28 mm; the width w of the H-shaped metal strip is 0.6 mm, and there is a 0.2 mm gap in the middle for loading the varactor diode; the gap width g between the H-shaped metal strip and the rectangular metal patch is 0.4 mm, and the initial length a of the metal patch is 25.4 mm; in the top-layer multimode metal resonator structure, the rectangular metal patch and the H-shaped metal strip form a multimode metal resonator structure, which can further expand the phase coverage range and operating bandwidth.

[0014] Further, in Step 2, the following steps are also included:

[0015] Step 21, calculate the discretized phase distribution of the metasurface carpet stealth cloak by using the ray tracing method;

[0016] Step 22, according to the phase distribution, determine the operating frequency band, metasurface unit structure and reverse bias voltage by using the broadband stealth phase recovery method for computer-aided design.

[0017] Further, in step 21, the following steps are also included:

[0018] Step 211, determine a virtual target and simulate its reflected wavefront, and at the same time set the initial phase on the surface of the virtual target to zero;

[0019] Step 212, calculate the distance from the center of each metasurface unit on its surface to the reference plane according to the actual shape structure of the stealth device;

[0020] Step 213, calculate the required phase distribution of each metasurface unit, that is, the spatial phase distribution.

[0021] Further, in step 213, the required phase distribution of the metasurface unit is:

[0022]

[0023] In the formula, p(y) represents the vertical distance between the center of the metasurface unit on the physical surface of the invisibility cloak and the ground plane, v i (y) represents the vertical distance between the selected i virtual target surfaces and the ground plane, k 0 = 2π / λ 0 is the free-space wave vector, λ 0 is the wavelength corresponding to the operating frequency, θ is the incident angle of the electromagnetic wave relative to the ground plane, and π represents the phase mutation caused by the reflection of the electromagnetic wave incident on the ground plane.

[0024] Further, in step 22, based on the phase distribution of the metasurface unit and the computer-aided design wideband stealth phase recovery method, determine the operating frequency band and the metasurface unit structure. The wideband stealth phase recovery method includes the following steps:

[0025] Step 221, establish a large database including frequency, structural parameters, equivalent capacitance value, and reflection phase. The structural parameter is the length of the metal patch; and initialize its parameters to 1.9 GHz, 20 mm, 0.31 pF, and 0° respectively;

[0026] Step 222, calculate the required phase for the electromagnetic illusion function and set the objective function and its threshold according to this phase, and continuously obtain all the structural parameters and equivalent capacitance values that meet the conditions at different frequencies based on the gradient descent method. If the final value is empty, update the step size for the next calculation until all the structural parameters and equivalent capacitance values that meet the function in the large frequency range are found, and confirm the structural parameter size and the operating bandwidth;

[0027] Step 223, after determining the structural parameters, calculate the reverse bias voltage required for the function in multiple application scenarios by the root-finding algorithm frequency by frequency within the operating bandwidth, and finally the relationship between the required reverse bias voltage, frequency, and unit number.

[0028] Furthermore, in step 3, an initial gradient phase is formed based on the structural parameters of the metasurface unit; according to the reverse bias voltage required for the stealth function retrieved in the second step, an FPGA outputs a low-frequency reverse bias voltage to control the equivalent capacitance value of the varactor diode.

[0029] A broadband carpet stealth device is also provided. The broadband carpet stealth device is a three-dimensional triangular wedge platform, which is symmetric on both sides of the central xoz plane. M / 2 units in the y-axis direction respectively have metasurface units with different structural parameters, and N metasurface units with the same structural parameters are arranged in an equidistant periodic extension in the x-axis direction.

[0030] The metasurface unit includes a three-layer structure. The top layer structure includes an H-shaped metal strip and two rectangular metal patches; the middle layer is a dielectric plate, and the bottom layer is a metal floor.

[0031] The period p of the metasurface unit is 28 mm, the width w of the H-shaped metal strip is 0.6 mm, and a 0.2-mm slit is opened at the center to load the varactor diode; the slit width g between the H-shaped metal strip and the rectangular metal patch is 0.4 mm, and the length of the metal patch and the reverse bias voltage of the varactor diode are calculated based on the phase distribution corresponding to the position of the metasurface unit.

[0032] Furthermore, the phase distribution is as follows:

[0033]

[0034] p(y) represents the vertical distance between the center of the metasurface unit on the physical surface of the invisibility cloak and the ground plane, v i (y) represents the vertical distance between the selected i virtual target surfaces and the ground plane, k 0 = 2π / λ 0 is the free-space wave vector, λ 0 is the wavelength corresponding to the operating frequency, θ is the incident angle of the electromagnetic wave relative to the ground plane, and π represents the phase mutation caused by the reflection of the electromagnetic wave incident on the ground plane.

[0035] Based on the phase distribution, the proposed computer-aided design broadband stealth phase recovery method is used to determine the operating frequency band, the metasurface unit structure, and the reverse bias voltage.

[0036] The beneficial effects achieved by the present invention are as follows:

[0037] Based on the broadband stealth phase recovery method and the broadband metasurface unit design, the present invention realizes the design of a broadband carpet stealth device, and solves the problem that it is difficult for current gradient metasurface devices to achieve broadband operation.

[0038] The present invention adopts a broadband stealth phase recovery method that simultaneously uses the gradient descent method and the root-finding algorithm to accurately calculate the structural parameters and voltages required for the function, and is a broadband stealth phase recovery method with stronger applicability. Description of the Drawings

[0039] Figure 1 It is a functional schematic diagram of a broadband carpet stealth device.

[0040] Figure 2 It is the metasurface unit in the broadband carpet stealth device and the simulation results obtained using CST commercial simulation software. (a) Overall structure and top-layer multimode metal resonator structure, (b) Curve of the corresponding relationship between reverse bias voltage and the equivalent capacitance value of the varactor diode, (c) Relationship between reflection phase and amplitude and frequency when the outgoing electromagnetic wave changes with the reverse bias voltage under the incidence of y-polarized wave, (d) Relationship between reflection phase and amplitude and reverse bias voltage when the outgoing electromagnetic wave changes with the incident angle under the incidence of y-polarized wave, (e) Relationship between reflection phase and amplitude and structural parameters when the outgoing electromagnetic wave changes with the incident angle under the incidence of y-polarized wave.

[0041] Figure 3 It is a specific flowchart of a computer-aided design method including the gradient descent method and the root-finding algorithm.

[0042] Figure 4 It is a graph of the relationship between reflection phase and frequency and reverse bias voltage. The eight unit structural parameters finally determined by the gradient descent method are (a) 20.5 mm, (b) 22 mm, (c) 23.5 mm, (d) 25 mm, (e) 25.2 mm, (f) 26 mm, (g) 26.4 mm, (h) 27 mm.

[0043] Figure 5 It is the relationship between the reverse bias voltage values required to achieve electromagnetic illusion and frequency and unit number in three application scenarios: (a) simulated ground under normal incidence, (b) simulated ground under 15° oblique incidence, and (c) simulated trapezoid under normal incidence.

[0044] Figure 6 It is the simulation results of the near-field electric field and far-field pattern of the electromagnetic illusion function when simulating the ground under normal incidence obtained by CST commercial simulation software. (a) Two-dimensional near-field electric field distribution maps of the metal triangular wedge in the y-polarized channel at five frequency points in the operating frequency range of 1.9 - 3.1 GHz, (b) Two-dimensional near-field electric field distribution maps of the metal plate in the y-polarized channel at five frequency points in the operating frequency range of 1.9 - 3.1 GHz, (c) Two-dimensional near-field electric field distribution maps of the carpet stealth cloak in the y-polarized channel at five frequency points in the operating frequency range of 1.9 - 3.1 GHz, (d) Two-dimensional far-field patterns of the three objects in the y-polarized channel at five frequency points in the operating frequency range of 1.9 - 3.1 GHz.

[0045] Figure 7 These are the simulation results of the near-field electric field and far-field pattern of the electromagnetic illusion function under 15° oblique incidence obtained by the CST commercial simulation software for the simulated ground. (a) Two-dimensional near-field electric field distribution diagrams of the metal triangular wedge at five frequency points in the 1.9 - 3.1 GHz operating frequency range for the y-polarized channel, (b) Two-dimensional near-field electric field distribution diagrams of the metal plate at five frequency points in the 1.9 - 3.1 GHz operating frequency range for the y-polarized channel, (c) Two-dimensional near-field electric field distribution diagrams of the carpet cloak at five frequency points in the 1.9 - 3.1 GHz operating frequency range for the y-polarized channel, (d) Two-dimensional far-field pattern diagrams of the three objects at five frequency points in the 1.9 - 3.1 GHz operating frequency range for the y-polarized channel.

[0046] Figure 8 These are the simulation results of the near-field electric field and far-field pattern of the electromagnetic illusion function under normal incidence for the simulated trapezoid obtained by the CST commercial simulation software. (a) Two-dimensional near-field electric field distribution diagrams of the metal triangular wedge at five frequency points in the 1.9 - 3.1 GHz operating frequency range for the y-polarized channel, (b) Two-dimensional near-field electric field distribution diagrams of the metal plate at five frequency points in the 1.9 - 3.1 GHz operating frequency range for the y-polarized channel, (c) Two-dimensional near-field electric field distribution diagrams of the carpet cloak at five frequency points in the 1.9 - 3.1 GHz operating frequency range for the y-polarized channel, (d) Two-dimensional far-field pattern diagrams of the three objects at five frequency points in the 1.9 - 3.1 GHz operating frequency range for the y-polarized channel.

[0047] Figure 9 This is a schematic diagram of the topological structure of the broadband carpet cloak device.

[0048] Figure 10 This is the experimental setup diagram for the verification of the electromagnetic illusion function. (a) Far-field test platform and experimental setup, (b) Near-field test platform and experimental setup.

[0049] Figure 11 These are the two-dimensional far-field pattern test results obtained from the far-field experiment under three application scenarios: (a) simulating the ground under normal incidence, (b) simulating the ground under 15° oblique incidence, and (c) simulating the trapezoid under normal incidence, and they are compared with the corresponding simulation results.

[0050] Figure 12 These are the two-dimensional electric field distribution test results obtained from the near-field experiment under three application scenarios: (a) simulating the ground under normal incidence, (b) simulating the ground under 15° oblique incidence, and (c) simulating the trapezoid under normal incidence. Specific implementation manner

[0051] The present invention will be further described below in conjunction with specific embodiments, and the advantages and features of the present invention will become clearer as the description progresses. However, these embodiments are merely exemplary and do not constitute any limitation to the scope of the present invention. Those skilled in the art should understand that modifications or substitutions can be made to the details and forms of the technical solutions of the present invention without departing from the spirit and scope of the present invention, but such modifications and substitutions all fall within the protection scope of the present invention.

[0052] The design indicators of the embodiment are as follows: in the frequency range of 1.9 - 3.1 GHz, the metasurface unit can gradually adjust the phase of the emitted y-polarized electromagnetic wave by changing the equivalent capacitance value of the varactor diode, so as to realize the dynamic electromagnetic illusion function.

[0053] To implement Figure 1 the wideband carpet invisibility device shown, the wideband carpet invisibility device is a three-dimensional triangular wedge platform with an inclination angle of phi and its surface is covered with a programmable metasurface, and is composed of M*N metasurface units loaded with varactor diodes arranged in an equidistant periodic extension.

[0054] The three-dimensional triangular wedge platform is symmetric on both sides of the central xoz plane. M / 2 units in the y-axis direction respectively have metasurface units with different structural parameters, and N metasurface units with the same structural parameters in the x-axis direction are arranged in an equidistant periodic extension. Among them, the structural parameter is the length of the metal patch in the metasurface unit.

[0055] In this embodiment, the wideband carpet invisibility device has 16*10 metasurface units and can realize the invisibility function in 3 application scenarios. The 3 application scenarios are: simulating the reflected wavefront of the ground when the electromagnetic wave is vertically incident on the invisibility cloak, simulating the reflected wavefront of the ground when the electromagnetic wave is obliquely incident on the invisibility cloak at 15°, and simulating the reflected wavefront of a trapezoid when the electromagnetic wave is vertically incident on the invisibility cloak.

[0056] The wideband invisibility phase recovery method is based on the gradient descent method and the root-finding algorithm, and involves two phase modulation methods of structural parameter change and varactor diode voltage change.

[0057] First, 8 metasurface units with different structural parameters are determined based on the gradient descent method to construct a programmable metasurface to expand the phase coverage range. The programmable metasurface unit is composed of an upper metal structure layer, a middle F4B dielectric board, and a lower metal floor. The topmost metal structure is a multimode metal resonator composed of two symmetrically distributed rectangular metal patches and an "H"-shaped metal strip. The two side metal strips of the "H"-shaped metal strip are arranged along the x-axis, the middle connecting metal strip is arranged along the y-axis at the center, and a gap is opened in the middle of the middle connecting metal strip for loading the varactor diode; the two rectangular metal patches are respectively arranged in the area surrounded by the two side metal strips and the middle connecting metal strip.

[0058] Secondly, the reverse bias voltage required for the stealth function in three application scenarios was retrieved point by point in a wide frequency band through a root-finding algorithm, and the field programmable gate array was used to output the voltage in real time to accurately restore the phase of the scattered electromagnetic wave, realizing a wideband electromagnetic illusion function with a bandwidth of 1.9 - 3.1 GHz and solving the problem that it is difficult for gradient metasurface devices to achieve broadband operation.

[0059] The specific implementation is divided into the following three steps: metasurface unit design, structural parameter and voltage calculation, and dynamic electromagnetic function realization.

[0060] Step 1, metasurface unit design

[0061] The metasurface unit disclosed in the present invention is as shown in Figure 2 (a). This unit consists of three layers. Among them, the rectangular metal patch and the "H"-shaped metal strip together form the metal resonance structure of the top layer. The middle layer is an F4B dielectric plate with a thickness h = 4 mm, a dielectric constant of 2.65, and an electric tangent loss of 0.001. The bottom layer is a metal floor used to reflect the space electromagnetic wave. The period p of the metal unit is 28 mm, the width w of the "H"-shaped metal strip is 0.6 mm, and there is a 0.2 mm gap in the center to load the varactor diode. The gap width g between the "H"-shaped metal strip and the rectangular metal patch is 0.4 mm, and the initial length a of the metal patch is 25.4 mm. In the multi-mode metal resonator structure of the top layer, the rectangular metal patch and the "H"-shaped metal strip form a multi-mode metal resonator structure, which can further expand the phase coverage range and the working bandwidth. In microwave circuits, introducing external semiconductor integrated devices to adjust the resistance R, inductance L, and capacitance C in the equivalent circuit will cause changes in the electromagnetic response of microwave devices. In order to achieve a large range of phase control and considering the diode package and price at the same time, this chapter uses a varactor diode of model SMV1430-079LF, which has the advantages of low parasitic resistance, high temperature resistance, and high Q value. By referring to the varactor diode manual of model SMV1430-079LF, some numerical relationships between the reverse bias voltage and the capacitance are obtained, as shown in the table in the upper right corner of Figure 2 (b). Then, in order to obtain a complete and rich numerical correspondence library, the cubic spline function in MATLAB software is used to interpolate the original data. This interpolation function has the advantages of high precision, and finally a smooth relationship curve graph of the reverse bias voltage and the equivalent capacitance can be obtained, as shown in Figure 2 (b). Among them, R = 1.5 Ω, L = 0.7 nH, C = 0.31 - 1.21 pF, and these equivalent electrical parameters can be further imported into the CST simulation software to simulate the actual varactor diode.

[0062] To study its tunable electromagnetic properties, full-wave simulation was carried out on it using CST software. In the simulation settings, the x and y directions were respectively set as the unit cell boundary conditions, and the z direction was set as the open (add space) boundary condition. The final simulation results of the S parameters under the incidence of y-polarized waves are as Figure 2 (c) shown. When the reverse bias voltage changes from 0 V to 30 V, the diode capacitance changes from 0.3 pF to 1.2 pF. The reflection phase of the metasurface unit changes significantly in the range of 1.9 - 3.1 GHz, and the reflection amplitude remains at a relatively high level, meeting the requirement of phase regulation under the condition of constant amplitude. Therefore, assuming the amplitude term as a fixed value, by controlling the voltage across the diode, the reflection phase difference caused by unit dispersion at different frequencies is compensated, and a broadband carpet invisibility device is realized.

[0063] Considering the actual application scenario, the detection wave emitted by the enemy detection radar usually incident on the metasurface at a certain angle. It is of great significance to ensure that the designed metasurface carpet invisibility cloak works properly at a certain incident angle. To avoid the deterioration of unit performance caused by oblique incidence, the angle adaptation ability should be considered when designing the unit. The key index to measure the angle adaptation ability is the phase response difference of the unit when the electromagnetic wave is obliquely incident and vertically incident. The smaller the phase difference, the stronger its adaptation ability. Therefore, full-wave simulation of the metasurface unit was carried out using CST software under different incident angles. Here, the simulation results of the incident angle varying with the reverse bias voltage and structural parameters within 30° are given, as Figure 2 (d) and (e) shown. It can be found that when the incident angle changes within 30°, the amplitude response of the unit to the electromagnetic wave hardly changes, its phase response has certain fluctuations, and the phase difference within the bandwidth of 1.9 - 3.1 GHz is within 22.5°. The above results show that the reflection coefficients of the designed metasurface unit under different incident angle conditions are not much different, and it has strong angle adaptation ability, and can maintain relatively stable phase regulation under the oblique incidence of electromagnetic waves.

[0064] In addition, from Figure 2 (c) the simulation results, it can be seen that if only relying on the varactor diode to regulate the phase, the designed metasurface unit can only achieve nearly 360° full-phase coverage within a relatively narrow bandwidth, and it is difficult to achieve full-phase regulation within a broadband range, which greatly limits the invisibility performance of the carpet invisibility cloak. To solve the above problems and achieve a broadband electromagnetic illusion effect, a design method combining varactor diode voltage change and structural parameter change is proposed. This method realizes broadband invisibility effect through full-phase regulation within a certain bandwidth. By Figure 2(e) It can be seen that the reflection phase of the unit changes with the change of the structural size a and has a large phase coverage range. Therefore, in the design process, by combining the transmission phase mechanism with the electrically tunable method to achieve ultra-wideband and large-range electromagnetic phase control, first, metasurface units with different structural sizes are designed to introduce initial phases at different frequencies, and then the final reflection phase of the metasurface unit is controlled by changing the equivalent capacitance of the diode in relay to meet the phase requirements of the calculated electromagnetic illusion function. The detailed computer-aided design method process is given in Figure 3 given.

[0065] As can be seen from the above simulations, by first designing the structural parameters and then changing the equivalent capacitance value of the varactor diode, precise phase control of the outgoing y-polarized wave can be achieved; at the same time, by using the FPGA to output different reverse bias voltage values in real time, the equivalent capacitance value of the varactor diode can be changed, laying a foundation for the subsequent realization of broadband electromagnetic illusion.

[0066] Step 2, Structural parameter and voltage calculation

[0067] Through the design of the unit, the phase coverage range and the working bandwidth are further expanded. However, as can be seen from Figure 2 (c), this unit can only achieve a 360° phase coverage range at some frequency points and cannot meet the true broadband working conditions, severely limiting the performance of the metasurface device. Therefore, the present invention proposes a computer-aided design broadband stealth phase recovery method for accurately calculating the structural parameters and reverse bias voltages required for the design of a broadband carpet stealth device; this device is specifically a three-dimensional triangular wedge platform covered with a programmable metasurface, with a platform tilt angle of 30° and two programmable metasurfaces vertically symmetric.

[0068] Specifically, it includes the following steps:

[0069] Step 21, To achieve the electromagnetic illusion function, the ray tracing method is usually used to calculate the discretized phase distribution of the metasurface carpet cloak. The calculation process is mainly divided into the following 3 steps:

[0070] Step 211, Determine the virtual target and simulate its reflected wavefront, and at the same time set the initial phase on the surface of the virtual target to zero;

[0071] Step 212, Calculate the distance from the center of each metasurface unit on its surface to the reference plane according to the actual shape structure of the stealth device;

[0072] Step 213, Calculate the required phase distribution of each metasurface unit, that is, the spatial phase distribution, according to formula (1).

[0073]

[0074] where \(p(y)\) represents the vertical distance between the center of the metasurface unit on the physical surface of the invisibility cloak and the ground plane, and \(v i (y)\) represents the vertical distance between the selected \(i\) virtual target surfaces and the ground plane; among them, \(v 1 (y)\) and \(v 2 (y)\) represent the virtual ground target and the virtual trapezoidal target respectively, \(k 0 = 2\pi / \lambda 0 is the free-space wave vector, \(\lambda 0 is the wavelength corresponding to the operating frequency, \(\theta\) is the incident angle of the electromagnetic wave relative to the ground plane, and \(\pi\) represents the phase mutation caused by the reflection of the electromagnetic wave incident on the ground plane.

[0075] Step 22, after calculating the phase distribution required for the electromagnetic illusion function according to formula (1), use the proposed computer-aided design broadband invisibility phase recovery method to determine the operating frequency band and the metasurface unit structure, and finally realize the design of the broadband carpet invisibility cloak.

[0076] Among them, the process of the broadband invisibility phase recovery method is as Figure 3 shown, and the specific implementation process is mainly divided into the following three steps:

[0077] Step 221, establish a large database including frequency, structural parameters, equivalent capacitance value and reflection phase, and initialize their parameters to 1.9 GHz, 20 mm, 0.31 pF and 0° respectively.

[0078] Step 222, calculate the phase required for the electromagnetic illusion function and set the objective function and its threshold according to this phase, and continuously obtain the structural parameters and equivalent capacitance values that meet the conditions at different frequencies based on the gradient descent method. If the final value is empty, update the step size of this method for the next calculation until the structural parameters and equivalent capacitance values that meet the function in the largest possible frequency range are found, and confirm the structural parameter size and the operating bandwidth. Finally, the structural parameters of 8 units are determined, and the relationship between their reflection phase and frequency and reverse bias voltage is as Figure 4 shown.

[0079] Step 223, after determining the structural parameters, use the root-finding algorithm to calculate the reverse bias voltage required for the function in three application scenarios frequency by frequency within the operating bandwidth. Finally, the relationship between the required reverse bias voltage and frequency and unit number is as Figure 5 shown, which is used to realize the subsequent dynamic electromagnetic illusion function.

[0080] Step 3, realization of dynamic electromagnetic function

[0081] According to the structural parameters of the metasurface unit obtained in Step 2, determine the topological structure of the broadband carpet invisibility device, as Figure 9As shown, an initial gradient phase is formed. Secondly, according to the reverse bias voltage required for the stealth function retrieved in the second step, an FPGA is used to output a low-frequency reverse bias voltage to control the equivalent capacitance value of the varactor diode, thereby achieving a large-range regulation of the phase of the emitted electromagnetic wave within a wide frequency range. Among them, when the reverse bias voltage changes from 0V to 30V, the diode capacitance changes from 0.3pF to 1.2pF, and the reflection phase of the metasurface unit changes greatly within the range of 1.9 - 3.1GHz.

[0082] To verify its broadband stealth performance, taking five frequency points of 1.9, 2.2, 2.5, 2.8, and 3GHz as examples, the near-field electric field distribution and scattering pattern in the yoz plane of the bare metal target, planar metal plate, and broadband carpet stealth cloak are respectively simulated. During the simulation process, a y-polarized plane wave is used for excitation, and the incident electric field is subtracted from the total field to obtain the final reflected electric field result. The simulation results in the three application scenarios are respectively as Figure 6 、 Figure 7 and Figure 8 shown. The results show that the stealth cloak can not only well simulate the reflected wavefront of the ground and trapezoidal objects, but also has a certain adaptability to the incident angle, proving that the broadband carpet stealth device has excellent electromagnetic wave wavefront regulation ability and achieves perfect stealth for the target covered by the stealth device.

[0083] On the basis of completing the simulation verification, the sample was also processed. The finished product is as shown in the upper right corner of Figure 10 (b), and it was experimentally tested using a near-field and far-field test platform. The specific settings of the experiment are as shown in Figure 10 . Among them, Figure 10 (b) is the setting of the near-field test platform. A high-gain linearly polarized horn antenna is placed 1.7m directly in front of the center of the sample to ensure that the electromagnetic wavefront reaching the sample is approximately a plane wave. At the same time, a monopole antenna with a length of 3cm is installed as a probe on the stepping motor in the middle position between the sample and the transmitting antenna, and the 500mm×500mm area is scanned with a step size of 25mm to obtain the final electric field distribution information in the yoz plane. At this time, the incident electric field and reflected electric field information will overlap. Therefore, two different tests need to be carried out, and it is ensured that the result of the second test only contains the incident electric field information. Then, the result of the first test is subtracted from the result of the second test to ensure that pure reflected electric field information is obtained.

[0084] Figure 10(a) is the setting of the far-field test platform. A high-gain horn antenna with a smaller aperture is placed 0.7m in front of the center of the sample to approximately meet the far-field conditions, and the receiving antenna is placed on the rotating arm. The final two-dimensional far-field pattern information is obtained through the far-field test platform composed of a motor, a rotating arm and a vector network analyzer. It should be noted that in order to avoid the transmission antenna blocking the reflected electromagnetic wave and causing the pattern to be deformed, the transmitting antenna and the receiving antenna need to be separated by a certain distance in the y direction. This is because the reflected beam has a certain beam width. Although the final result is somewhat different from the true pattern, it does not affect the final directivity result.

[0085] Before the formal test, you still need to use Figure 10 (a) The FPGA control board shown in the lower left corner outputs the reverse bias voltage required for the stealth function to control the equivalent capacitance value of the diode on the metasurface. The far-field and near-field test results are shown in Figure 2. Figure 11 and Figure 12 As shown in the figure, Figure (a) and Figure (b) respectively give the test results of the simulated metal floor under vertical incidence and 15° incidence conditions, and Figure (c) gives the test results of the simulated trapezoidal metal plate under vertical incidence. Since the results at a large number of frequency points are given in the simulation stage, the correctness of the proposed broadband programmable metasurface functional design is proved. Therefore, the test results at 5 frequency points with a step size of 0.3GHz are also given in the experimental stage to verify its actual stealth effect. It can be seen from the results that the carpet stealth device can not only well restore the reflected wavefront and directional pattern that are highly consistent with various virtual targets, but also has a certain angle insensitivity and can work normally under different incident angles, which strongly proves the feasibility of combining multiple phase control strategies.

[0086] The above are only specific steps of the present invention and do not constitute any limitation to the protection scope of the present invention; any technical solutions formed by equivalent transformation or equivalent replacement shall fall within the protection scope of the present invention; some parts not elaborated in detail in the present invention belong to the known technologies of those skilled in the art.

Claims

1. A computer-aided design of a broadband stealth phase recovery method, characterized in that: The computer-aided design of a broadband stealth phase recovery method comprises the following steps: Step 1: Design of broadband carpet stealth device and metasurface unit; The broadband carpet stealth device is a three-dimensional triangular wedge platform composed of M*N metasurface units loaded with varactor diodes arranged at equal intervals and periodically extended; The metasurface unit comprises a three-layer structure, wherein the top layer comprises an H-shaped metal strip and two rectangular metal patches; the middle layer is a dielectric plate, and the bottom layer is a metal floor; Step 2, structural parameters and voltage calculation; Construct a three-dimensional triangular splitting platform of programmable metasurface, with a platform tilt angle of 30° and two programmable metasurfaces vertically symmetrical; calculate the structural parameters and reverse bias voltage required for the design of broadband carpet stealth device through broadband stealth phase recovery method; Step 3: Determine the topological structure of the broadband carpet stealth device based on the structural parameters of the metasurface unit.

2. The computer-aided design broadband stealth phase recovery method according to claim 1, characterized in that: In step 1, the three-dimensional triangular wedge platform of the broadband carpet stealth device is symmetrical along the central xoz plane on both sides, and the M / 2 units along the y-axis direction have metasurface units with different structural parameters, and the N metasurface units with the same structural parameters in the x-axis direction are arranged in an evenly spaced periodic manner.

3. The computer-aided design broadband stealth phase recovery method according to claim 2, characterized in that: In step 1, the period of the metasurface unit p = 28 mm; the width of the H-shaped metal strip w = 0.6 mm, and a 0.2 mm gap is opened in the middle to load the varactor diode; the gap width between the H-shaped metal strip and the rectangular metal patch is g = 0.4 mm, and the initial length of the metal patch is a = 25.4 mm; the rectangular metal patch and the H-shaped metal strip in the top-level multi-mode metal resonator structure form a multi-mode metal resonator structure, which can achieve further expansion of the phase coverage range and the working bandwidth.

4. The computer-aided design broadband stealth phase recovery method according to claim 1, characterized in that: In step 2, the following steps are also included: Step 21, using a ray tracing method to calculate the discretized phase distribution of the metasurface carpet cloak; Step 22, according to the phase distribution, a wideband stealth phase recovery method using computer-aided design is used to determine the operating frequency band, metasurface unit structure and reverse bias voltage.

5. The computer-aided design broadband stealth phase recovery method according to claim 4, characterized in that: In step 21, the following steps are also included: Step 211, determining a virtual target and simulating its reflected wavefront, while setting the initial phase on the surface of the virtual target to zero; Step 212, calculating the distance from the center of each metasurface unit on the surface of the actual stealth device to the reference surface according to the actual stealth device appearance structure; Step 213, calculating the required phase distribution of each metasurface unit, that is, the spatial phase distribution.

6. The computer-aided design broadband stealth phase recovery method according to claim 5, characterized in that: In step 213, the phase distribution required for the metasurface unit is: Where p(y) represents the vertical distance between the center of the metasurface unit on the physical surface of the cloak and the ground plane, v i (y) represents the vertical distance between the selected i virtual target surfaces and the ground plane, k0=2π / λ0 is the free space wave vector, λ0 is the wavelength corresponding to the operating frequency, θ is the incident angle of the electromagnetic wave relative to the ground plane, and π represents the phase mutation caused by the electromagnetic wave after being incident on the ground plane and reflected.

7. The computer-aided design of broadband stealth phase recovery method according to claim 4, characterized in that: In step 22, the working frequency band and the structure of the metasurface unit are determined based on the phase distribution of the metasurface unit and the broadband stealth phase recovery method designed by computer aided design. The broadband stealth phase recovery method includes the following steps: Step 221, establishing a large database including frequency, structural parameters, equivalent capacitance value and reflection phase, wherein the structural parameter is the length of the metal patch; and initializing its parameters to 1.9 GHz, 20 mm, 0.31 pF and 0° respectively; Step 222, calculate the phase required for the electromagnetic illusion function and set the objective function and its threshold according to the phase, and continuously obtain all structural parameters and equivalent capacitance values ​​that meet the conditions at different frequencies based on the gradient descent method. If the final value is empty, update the step size for the next calculation until all structural parameters and equivalent capacitance values ​​that meet the function within a large frequency range are found, and confirm the structural parameter size and working bandwidth; Step 223, after the structural parameters are determined, the reverse bias voltage required for the functions in multiple application scenarios is inverted frequency by frequency within the working bandwidth by using a root-finding algorithm, and finally the relationship between the required reverse bias voltage and the frequency and the unit number is obtained.

8. The computer-aided design of broadband stealth phase recovery method according to claim 1, characterized in that: In step 3, an initial gradient phase is formed based on the structural parameters of the metasurface unit; according to the reverse bias voltage required for the stealth function retrieved in the second step, the FPGA is used to output a low-frequency reverse bias voltage to control the equivalent capacitance value of the varactor diode.

9. A broadband carpet stealth device designed according to the broadband stealth phase recovery method designed by computer aided design according to any one of claims 1 to 8, characterized in that: The broadband carpet stealth device is a three-dimensional triangular split platform, which is symmetrical along the central xoz plane on both sides, and the M / 2 units along the y-axis direction have metasurface units with different structural parameters, and the N metasurface units with the same structural parameters in the x-axis direction are arranged in an evenly spaced periodic extension. The metasurface unit comprises a three-layer structure, wherein the top layer comprises an H-shaped metal strip and two rectangular metal patches; the middle layer is a dielectric plate, and the bottom layer is a metal floor; The metasurface unit period p = 28 mm, the width of the H-shaped metal strip w = 0.6 mm, and a 0.2 mm gap is opened in the center to load the varactor diode; the gap width between the H-shaped metal strip and the rectangular metal patch is g = 0.4 mm, and the metal patch length and the reverse bias voltage of the varactor diode are calculated based on the phase distribution corresponding to the metasurface unit position.

10. The broadband carpet stealth device according to claim 9, characterized in that: The phase distribution is: p(y) represents the vertical distance between the center of the metasurface unit on the physical surface of the cloak and the ground plane, v i (y) represents the vertical distance between the selected i virtual target surfaces and the ground plane, k0=2π / λ0 is the free space wave vector, λ0 is the wavelength corresponding to the operating frequency, θ is the incident angle of the electromagnetic wave relative to the ground plane, and π represents the phase mutation caused by the electromagnetic wave incident on the ground plane and reflected; Based on the phase distribution, the proposed computer-aided design wideband stealth phase recovery method is used to determine the operating frequency band, metasurface unit structure and reverse bias voltage.

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