Light-operated reconfigurable metasurface for full-space terahertz wave beam regulation and control

Abstract

The invention discloses a light-operated reconfigurable metasurface for full-space terahertz wave beam regulation and control, solves the problem of how to provide ubiquitous full-space wave beam coverage for multi-user wireless communication application, and belongs to the field of artificial electromagnetic metamaterials. The super subunit comprises N super subunits which are arranged periodically, each super subunit comprises 4 * 4 identical coding units, corresponding codes are '0' and '1' respectively when illumination exists or not, and the phase response difference of the two coding units at 0.7 THz is 180 degrees. Each super subunit comprises five layers, the third layer is used for switching between reflection and transmission, when vanadium dioxide is in a medium state, the super surface is in a transmission mode, and when vanadium dioxide is in a metal state, the super surface is in a reflection mode. The first layer, the second layer, the fourth layer and the fifth layer are used for controlling the amplitude and the phase of the total-space terahertz wave, the conductivity of the photosensitive silicon pattern is changed under excitation of light with different intensities, the phase of the total-space terahertz wave beam is effectively modulated, and one-bit terahertz information coding is achieved.

Description

Technical Field

[0001] The invention relates to a light-controlled reconfigurable metasurface for full-space terahertz beam regulation, and belongs to the field of artificial electromagnetic metamaterials. Background Art

[0002] The realization of dynamic and flexible control of electromagnetic waves has always been the core pursuit of all fields of modern science and technology, especially in the terahertz band. In recent years, terahertz communication has begun to be gradually deployed in 6G and other applications, which will promote the rapid progress of core devices, signal processing technology and antenna technology, and will also play a strong role in promoting terahertz space communication. The full-space control of electromagnetic waves has become one of the issues that people are increasingly concerned about. Reflection-transmission integration is a solution to achieve ubiquitous full-space service coverage and full-space resource development, but the full-space metasurface that realizes dynamic control of terahertz beams is still extremely challenging. With the rapid development of military high-precision technology, the detection and tracking technologies of various countries are becoming increasingly advanced, which poses a serious threat to the survivability of weapon platforms such as missiles, fighter jets, and satellites, and also puts forward more stringent requirements on the concealment of important military equipment. Therefore, how to effectively ensure the safety of sensitive telepathic equipment and military equipment has become an important issue in maintaining national security. In order to meet this challenge, electromagnetic stealth technology came into being and became the key research direction of many research teams at home and abroad. Taking Unmanned Aerial Vehicle (UAV) as an example, when performing autonomous strike missions in high-threat environments, it requires both full-space communication capabilities and stealth characteristics to cope with electromagnetic wave detection by enemy radars and improve the ability to cope with diverse threats in complex electromagnetic environments. In order to meet these contradictory technical requirements, we need to integrate reconfigurable electromagnetic devices and equipment with multiple electromagnetic wave manipulation functions to handle multiple mission requirements through dynamic switching between different functions. Therefore, in the complex environment of multi-dimensional reconnaissance, it is urgent to have equipment that integrates stealth and communication functions to achieve dynamic modulation of the full-space terahertz beam.

[0003] In 2014, Professor Cui Tiejun proposed digital coding metamaterials, creatively using digital coding to characterize metamaterials and metasurfaces. Digital coding metasurfaces are composed of a finite number of basic units arranged in a certain coding sequence. For example, a 1-bit digital coding metasurface is composed of "0" and "1" units with opposite phases; a 2-bit digital coding metasurface is composed of "00", "01", "10" and "11" units with a phase difference of 90 degrees; and so on for higher bits. This discrete digital coding representation method can be regarded as "digital modulation". By changing the arrangement of the coding sequence, the radiation or scattering characteristics of electromagnetic waves can be efficiently controlled, which can greatly simplify the design process and facilitate optimization of simulation and processing testing. The introduction of the concept of digital coding in metasurfaces is also very suitable for combining adjustable devices or materials such as diodes and MEMS switches to form digital programmable metasurfaces under the control of field programmable gate arrays (FPGAs), realizing dynamic control of electromagnetic waves and real-time switching between different functions. At present, digital coding and programmable metasurfaces have been widely used in beam steering, scattering reduction, holographic imaging, microwave imaging, information processing, and wireless communications. More importantly, digitally encoded metasurfaces build a bridge from the physical world to the digital world.

[0004] Although there have been preliminary attempts at full-space metasurfaces in the microwave band, it is impossible to use electronic components such as diodes to complete the design of metasurfaces in the terahertz band. For traditional electrical control methods, physical wires are usually used to directly connect the metasurface to an external power supply and control circuit. This method is prone to crosstalk between DC and microwave signals, affecting the performance of the metasurface, and also increasing the volume of the entire system. The real-time dynamic control capability is weak. Therefore, the lack of dynamic tunability is an obstacle to the development of terahertz coding metasurfaces, and also limits the development of terahertz metasurfaces towards practical application. In practical applications, it is often necessary to integrate different electromagnetic wave control functions at the same time. Therefore, it is still extremely challenging to achieve dynamic modulation of full-space terahertz beams, especially multifunctional metasurfaces with both communication and stealth functions. Summary of the invention

[0005] In order to solve the problem of how to provide ubiquitous full-space beam coverage for multi-user wireless communication applications, the present invention provides a light-controlled reconfigurable metasurface for full-space terahertz beam regulation.

[0006] The present invention discloses a light-controlled reconfigurable metasurface for full-space terahertz beam regulation, comprising N periodically arranged super subunits, each of which comprises 4×4 identical coding units, the corresponding codes when there is light and when there is no light are "0" and "1", respectively, the phase responses of the two coding units differ by 180° at the operating frequency, and each super subunit is a 1-bit unit.

[0007] Preferably, each coding unit comprises 5 layers arranged in sequence, the first layer comprises a first metal pattern layer, a first active material photosensitive silicon mixed layer, and a first dielectric layer arranged in sequence; the second layer comprises a second metal pattern layer and a second dielectric layer arranged in sequence; the third layer comprises a third metal pattern layer and a vanadium dioxide mixed layer arranged in sequence; the fourth layer comprises a fourth metal pattern layer and a third dielectric layer arranged in sequence; the fifth layer comprises a fourth dielectric layer, a fifth metal pattern layer, and a second active material photosensitive silicon mixed layer arranged in sequence.

[0008] Preferably, when the vanadium dioxide in the third layer is in a dielectric state, the metasurface is in a transmission mode, and when the vanadium dioxide mixed layer is in a metallic state, the metasurface unit is in a reflection mode;

[0009] The 1st, 2nd, 4th and 5th layers are used to control the amplitude and phase of the full-space terahertz wave. Specifically, the conductivity of the metal pattern layer changes under the excitation of light of different intensities, and the phase of the full-space terahertz beam is modulated to achieve one-bit terahertz information encoding.

[0010] Preferably, the first to fourth dielectric layers are all made of polyimide material with a dielectric constant of 3.5, a tangent loss of 0.0027, and a thickness of 10 um.

[0011] Preferably, the operating frequency of the metasurface is the same when it is in reflection mode and transmission mode, both of which are 0.7 THz.

[0012] Preferably, the method for encoding the metasurface comprises:

[0013] S1. Initialize the period and super surface parameters of the super subunit;

[0014] S2. randomly generating an initial population, wherein the individuals in the initial population are random coding sequences of the optically controllable reconfigurable metasurface for full-space terahertz beam control;

[0015] S3, calculate the objective function value under the corresponding coding sequence of each individual in the current population, and determine whether the termination condition is met. If it is met, output the optimal coding sequence and end; otherwise, go to S4; the objective function is set to 360° and 90° are the azimuth angle θ and the elevation angle range, represents the far-field scattering of the coding sequence under normal incidence;

[0016] S4: Perform selection, crossover and mutation operations on the population and transfer to S3.

[0017] Preferably, the metasurface can realize dual-beam and multi-beam control in reflection mode and transmission mode at the operating frequency, and a multi-mode OAM beam is constructed by dynamically modulating the quantized code distribution on the metasurface.

[0018] Preferably, the distribution of quantized codes on the metasurface is dynamically modulated by wireless optical control. The beneficial effects of the present invention are that the present invention has the characteristics of simple structure, easy design, polarization insensitivity, low cost, etc., has great application potential, and promotes the development of electromagnetic metasurfaces. The present invention realizes the regulation of the terahertz beam in the whole space by changing the state of vanadium dioxide, improves the utilization efficiency of the electromagnetic space resources by the metasurface, and is expected to be applied to the next generation of multifunctional, highly integrated, reconfigurable terahertz functional devices in the future. The present invention reversely designs the coding array through genetic algorithm to achieve RCS reduction in the terahertz band, so that the proposed metasurface has a stealth function. The reconfigurable full-space metasurface proposed in the present invention adopts a wireless optical control scheme, which can enrich the control method of the dynamic metasurface, and provides a certain reference significance for the design of multi-physics field metasurfaces, and the optical control-based method has an ultra-fast response time and has the advantage of no contact. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic diagram of the structure of a light-controlled reconfigurable multifunctional full-space metasurface unit according to an embodiment of the present invention. The dielectric layer is polyimide, with a dielectric constant of 3.5, a tangent loss of 0.0027, and a thickness of 10um;

[0020] Figure 2 are the amplitude and phase responses corresponding to the 1-bit light-controlled reconfigurable multifunctional full-space metasurface unit, where (a) is the simulation result of the reflection amplitude of the 1-bit light-controlled reconfigurable multifunctional full-space metasurface subunit in the frequency band of 0.4 to 1 THz, (b) is the simulation result of the reflection phase of the 1-bit light-controlled reconfigurable multifunctional full-space metasurface subunit in the frequency band of 0.4 to 1 THz, (c) is the simulation result of the transmission amplitude of the 1-bit light-controlled reconfigurable multifunctional full-space metasurface subunit in the frequency band of 0.4 to 1 THz, and (d) is the simulation result of the transmission phase of the 1-bit light-controlled reconfigurable multifunctional full-space metasurface subunit in the frequency band of 0.4 to 1 THz;

[0021] Figure 3is a three-dimensional far-field pattern, wherein (a) is a three-dimensional far-field pattern (reflection mode and transmission mode) generated by a dual-beam control coding sequence (00110011 ...) at an operating frequency of 0.7 THz; (b) is a three-dimensional far-field pattern (reflection mode and transmission mode) generated by a three-beam control coding sequence (000111000111 ...) at an operating frequency of 0.7 THz; (c) is a three-dimensional far-field pattern (reflection mode and transmission mode) generated by a four-beam control coding sequence (chessboard coding) at an operating frequency of 0.7 THz;

[0022] Figure 4 Figure 1 is the process and effect diagram of the encoding method, where (a) is the genetic algorithm flow chart; (b) is the RCS curve corresponding to the encoding sequence reversely designed by the genetic algorithm;

[0023] Figure 5 are phase distribution diagrams, where (a) is the phase distribution diagram of the vortex wave of the OAM mode l=-2 (reflection mode and transmission mode), (b) is the phase distribution diagram of the OAM mode l=-1 (reflection mode and transmission mode), (c) is the phase distribution diagram of the OAM mode l=+1 (reflection mode and transmission mode), and (d) is the phase distribution diagram of the OAM mode l=+2 (reflection mode and transmission mode). DETAILED DESCRIPTION

[0024] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0026] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, but they are not intended to limit the present invention.

[0027] In this embodiment, a light-controlled reconfigurable metasurface for full-space terahertz beam control includes N periodically arranged super subunits, each of which includes 4×4 identical coding units. The corresponding codes when there is light and when there is no light are "0" and "1", respectively. The phase responses of the two coding units at 0.7 THz differ by 180°, and each super subunit is a 1-bit unit.

[0028] like Figure 1As shown, each coding unit includes 5 layers arranged in sequence, the first layer includes the first metal pattern layer and the first active material photosensitive silicon mixed layer and the first dielectric layer arranged in sequence; the second layer includes the second metal pattern layer and the second dielectric layer arranged in sequence; the third layer includes the third metal pattern layer and the vanadium dioxide mixed layer arranged in sequence; the fourth layer includes the fourth metal pattern layer and the third dielectric layer arranged in sequence; the fifth layer includes the fourth dielectric layer, the fifth metal pattern layer and the second active material photosensitive silicon mixed layer arranged in sequence. Specifically, the metal pattern layer and the active material photosensitive silicon mixed layer are composed of 0.5mm thick photosensitive silicon and metal, the dielectric layer is polyimide, its dielectric constant is 3.5, the thickness is d=10μm, and the unit period p=100mm. The dielectric constant of photosensitive silicon is 11.5, and the radius is r=10mm. The conductivity of the adjustable material photosensitive silicon will change with the pump light energy. When the illumination energy increases, the carrier concentration in the semiconductor will also increase, thereby achieving the purpose of regulating the conductivity. The relationship between the conductivity σ of photosensitive silicon and the pump light power I is σ = 4.863×10 -4 ×I 2 +0.1856×I+1.569. When there is no pump excitation, the conductivity of photosensitive silicon is 0; when the pump light power is 790μJ / cm 2 When the conductivity is 5.0×10 5 S / m.

[0029] The third layer is used to switch between the reflection and transmission working states ultrafast, and is called the reflection-transmission control layer. When the vanadium dioxide in the reflection-transmission control layer is in the dielectric state, the metasurface is in the transmission mode. When the vanadium dioxide mixed layer is in the metallic state, the metasurface unit is in the reflection mode.

[0030] The 1st, 2nd, 4th and 5th layers are used to control the amplitude and phase of the full-space terahertz wave, which are called the light-controlled terahertz information coding layer. This layer uses the conductivity of the metal pattern layer to change under the excitation of light of different intensities. The phase of the full-space terahertz beam is modulated to achieve one-bit terahertz information encoding, thereby dynamically reconfiguring the function of the metasurface.

[0031] like Figure 2 (a)-(d) show the amplitude and phase response curves corresponding to the 1-bit optically controlled reconfigurable multifunctional full-space metasurface unit simulated by the commercial software CST Microwave Studio.

[0032] The operating frequency of the metasurface in this embodiment is the same when in reflection mode and transmission mode, both of which are 0.7THz. The super subunit arrangement is adopted in the design, that is, 4×4 identical metasurface units form a super subunit. The reconfigurable coded metasurface is designed by designing the arrangement of the coding pattern in space, so as to realize the specified electromagnetic function. Figure 3 (a) is the three-dimensional far-field pattern (reflection mode and transmission mode) generated by the dual-beam steering coding sequence at the operating frequency of 0.7 THz; Figure 3 (b) is the three-dimensional far-field pattern (reflection mode and transmission mode) generated by the three-beam control coding sequence at the operating frequency of 0.7THz; Figure 3 (c) is the three-dimensional far-field pattern (reflection mode and transmission mode) generated by the four-beam regulated coding sequence at the operating frequency of 0.7 THz. The angle of beam deflection can be calculated according to θ=arcsin(λ / Γ), where λ is the free space wavelength and Γ represents the period length of the coding sequence.

[0033] In order to reduce energy consumption, simplify the control system and speed up the response speed, the two states of photosensitive silicon are used to realize 1-bit encoding at 0.7 THz, and the metasurface array encoding is designed using genetic algorithms to achieve the function of RCS reduction. The flowchart of reverse design of metasurface array encoding based on genetic algorithms is shown in the figure. Figure 4 As shown, the method for encoding the metasurface includes:

[0034] Step 1, initializing parameters such as the period of the super subunit and the size of the metasurface array;

[0035] Step 2, randomly generating an initial population, including 50 individuals, the individuals in the initial population are random coding sequences of the optically controlled reconfigurable metasurface for full-space terahertz beam control, and each individual is a 32×32 random coding sequence;

[0036] Step 3: Calculate the objective function value of each individual in the current population under the corresponding coding sequence, and determine whether the termination condition is met, such as reaching the maximum number of iterations of 1500. If so, output the optimal coding sequence and end; otherwise, proceed to step 4;

[0037] The objective function of RCS reduction is set as 360° and 90° are the azimuth angle θ and the elevation angle range, represents the far-field scattering of the coding sequence under normal incidence;

[0038] Step 4: Perform selection, crossover and mutation operations on the population and proceed to step 3.

[0039] This cycle repeats until the set number of iterations is reached, and finally the optimal array coding sequence is output. First, the coding array obtained by reverse design is modeled and simulated in CST to obtain the far-field scattering amplitude. Then the far-field scattering amplitude of the metal plate of the same size as the coding metasurface is calculated in the same way. Finally, the RCS values ​​of the two are compared to obtain the RCS reduction value. Figure 4 As shown, the metasurface optimized by genetic algorithm achieves RCS reduction of more than 10 dB in the range of 0.6-0.78 THz. In summary, the present invention improves RCS reduction by optimizing the metasurface coding and radiation field by using genetic algorithm.

[0040] The metasurface can realize a series of dynamic functions at the working frequency, including dual-beam and multi-beam control in reflection mode and transmission mode. It can also generate electromagnetic waves carrying orbital angular momentum (OAM). By dynamically modulating the quantized code distribution on the metasurface, a reconfigurable multi-mode OAM beam can be constructed. The above operation can be completed by wireless optical control. The coding metasurface generates single vortex beams with different topological charge numbers at 0.7THz. Figure 5 shown. Figure 5 (a)-(d) are Far-field scattering results and phase results when . By observing the phase results, it can be found that when the topological charge number is and When the phase is counterclockwise from 0° to 360°, there are 1 and 2 cycles respectively; when the topological charge number is and When , the phase has 1 and 2 cycles from 0° to 360° in the clockwise direction, which is consistent with the characteristics of the vortex beam.

[0041] The purpose of this embodiment is to propose a light-controlled reconfigurable multifunctional full-space metasurface that integrates three modes: reflection communication, transmission communication, and electromagnetic stealth. It can provide ubiquitous full-space beam coverage for multi-user wireless communication applications and improve the survivability of military equipment on the battlefield. The proposed metasurface has realized a series of dynamic functions, including dual-beam and multi-beam control in reflection mode and transmission mode. The designed reconfigurable metasurface is further used to generate electromagnetic waves carrying orbital angular momentum (OAM). By dynamically modulating the distribution of quantized codes on the metasurface, a reconfigurable multimode OAM beam can be constructed. In the electromagnetic stealth mode, the array arrangement of the coding metasurface is reversely designed using a genetic algorithm, which can achieve the function of reducing the radar cross section.

[0042] Although the present invention is described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. It should therefore be understood that many modifications may be made to the exemplary embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that the various dependent claims and features described herein may be combined in a manner different from that described in the original claims. It should also be understood that features described in conjunction with individual embodiments may be used in other described embodiments.

Claims

1. A light-controlled reconfigurable metasurface for full-space terahertz beam control, characterized in that: It includes N super sub-units arranged periodically, each super sub-unit includes 4×4 identical coding units, the corresponding codes when there is light and when there is no light are "0" and "1" respectively, the phase response of the two coding units at the operating frequency differs by 180°, and each super sub-unit is a 1-bit unit.

2. The light-controlled reconfigurable metasurface according to claim 1, characterized in that: The coding unit includes five layers arranged in sequence, the first layer includes a first metal pattern layer, a first active material photosensitive silicon mixed layer, and a first dielectric layer arranged in sequence; the second layer includes a second metal pattern layer and a second dielectric layer arranged in sequence; the third layer includes a third metal pattern layer and a vanadium dioxide mixed layer arranged in sequence; the fourth layer includes a fourth metal pattern layer and a third dielectric layer arranged in sequence; the fifth layer includes a fourth dielectric layer, a fifth metal pattern layer, and a second active material photosensitive silicon mixed layer arranged in sequence.

3. The light-controlled reconfigurable metasurface according to claim 2, characterized in that: When the vanadium dioxide in the third layer is in the dielectric state, the metasurface is in the transmission mode, and when the vanadium dioxide mixed layer is in the metallic state, the metasurface unit is in the reflection mode; The 1st, 2nd, 4th and 5th layers are used to control the amplitude and phase of the full-space terahertz wave. Specifically, the conductivity of the metal pattern layer changes under the excitation of light of different intensities, and the phase of the full-space terahertz beam is modulated to achieve one-bit terahertz information encoding.

4. The light-controlled reconfigurable metasurface according to claim 3, characterized in that: The first to fourth dielectric layers are all made of polyimide material with a dielectric constant of 3.5, a tangent loss of 0.0027, and a thickness of 10 um.

5. The light-controlled reconfigurable metasurface according to claim 3, characterized in that: The operating frequency of the metasurface in reflection mode and transmission mode is the same, which is 0.7THz.

6. The light-controlled reconfigurable metasurface according to claim 3, characterized in that: Methods for encoding metasurfaces include: S1. Initialize the period and super surface parameters of the super subunit; S2, randomly generating an initial population, where the individuals in the initial population are random coding sequences of the light-controlled reconfigurable metasurface; S3, calculate the objective function value under the corresponding coding sequence of each individual in the current population, and determine whether the termination condition is met. If it is met, output the optimal coding sequence and end; otherwise, go to S4; the objective function is set to 360° and 90° are the azimuth angle θ and the elevation angle range, represents the far-field scattering of the coding sequence under normal incidence; S4: Perform selection, crossover and mutation operations on the population and transfer to S3.

7. The light-controlled reconfigurable metasurface according to claim 3, characterized in that: The metasurface can realize dual-beam and multi-beam control in reflection mode and transmission mode at the working frequency point, and construct a multi-mode OAM beam by dynamically modulating the quantized code distribution on the metasurface.

8. The light-controlled reconfigurable metasurface according to claim 7, characterized in that: Dynamic modulation of the quantized code distribution on the metasurface is accomplished by wireless optical control.

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