A smart metasurface integrating terahertz beam detection and control

Abstract

The present invention discloses an intelligent metasurface integrating terahertz beam detection and control, comprising a sapphire substrate, a metal structure and a vanadium dioxide microbridge grown on the upper surface of the sapphire substrate, a metal grounding surface grown on the lower surface of the sapphire substrate, and thermally conductive silicone grease for optimizing thermal contact between the metal grounding surface and a heating copper plate. The present invention also discloses a method for preparing the intelligent metasurface integrating terahertz beam detection and control, and a test system for adaptive beam control based on the intelligent metasurface integrating terahertz beam detection and control. The intelligent metasurface of the present invention has both terahertz detection and control functions, and has the characteristics of small size, high integration, and programmable customization of functions.

Description

Technical Field

[0001] The present invention belongs to the technical field of terahertz metasurfaces, and specifically relates to an intelligent metasurface integrating terahertz beam detection and control and a test system for adaptive control built on the intelligent metasurface, and particularly relates to an integrated detection and control array element based on vanadium dioxide, a preparation method and a test system for a terahertz intelligent metasurface based on programmable metamaterials (also called metasurfaces, artificial electromagnetic media, etc.) and terahertz detection technology. Background Art

[0002] With the development of next-generation wireless communication technologies, the demand for intelligent beamforming and electromagnetic information processing technologies is growing. Reconfigurable Intelligent Surface (RIS) provides a solution for reconstructing the electromagnetic wave propagation environment by controlling the reflection / transmission coefficient of each array element in RIS. RIS shows great potential in many wireless communication application scenarios such as coverage expansion, physical layer security enhancement, and cell edge signal hotspot creation. The current implementation of RIS is often based on programmable metasurfaces. In the microwave band, programmable metasurfaces are usually composed of resonant structure arrays with integrated semiconductor switches, and each array element can achieve independent regulation of electromagnetic wave parameters such as amplitude, phase or polarization. In recent years, intelligent metasurfaces have been proposed as an upgraded version of programmable metasurfaces. By integrating sensors into programmable metasurfaces, intelligent metasurfaces that can adaptively adjust according to the surrounding environment can be constructed. Intelligent metasurfaces have shown strong capabilities in the adaptive regulation of electromagnetic waves, such as adaptive stealth, intelligent beam steering, and vital sign monitoring. Due to technical limitations, most intelligent metasurfaces currently work in the microwave frequency band.

[0003] Terahertz communication has attracted widespread attention due to its abundant spectrum resources and support for large-capacity data communication. In order to overcome the serious path loss of terahertz waves in the atmosphere, terahertz communication urgently needs to develop intelligent terahertz beam control technology. In the terahertz frequency band, programmable metasurfaces can be realized by integrating tunable materials (such as semiconductors, phase change materials, liquid crystals, and graphene) into resonant structures. However, the development of terahertz smart metasurfaces faces technical challenges due to the lack of low-cost detectors and the complexity of the integration process. Summary of the invention

[0004] Technical problem: In view of the defects of the above-mentioned prior art, the present invention proposes an intelligent metasurface that integrates terahertz beam detection and control, which has the functions of terahertz detection and control, and has the characteristics of small size, high integration, and programmable customization of functions, providing a new design idea for the intelligent metasurface. At the same time, based on the intelligent metasurface, the present invention has built a test system for adaptive control of terahertz beams, demonstrating the ability of the device to adaptively control the beam without human intervention, providing a possibility for the application of intelligent metasurfaces in unmanned environments.

[0005] Technical solution: The first technical solution proposed by the present invention is a smart metasurface integrating terahertz beam detection and control, comprising a sapphire substrate, a metal structure and a vanadium dioxide microbridge grown on the upper surface of the sapphire substrate, a metal ground plane grown on the lower surface of the sapphire substrate, and thermal conductive silicone grease between the metal ground plane and the heating copper plate for optimizing thermal contact. The metal structure on the upper surface of the substrate is preferably a metal butterfly antenna array.

[0006] The second technical solution provided by the present invention is a beam adaptive control test system built based on the above-mentioned intelligent supersurface with integrated terahertz beam detection and control, including a host computer, a programmable controller, and the above-mentioned intelligent supersurface with integrated terahertz beam detection and control.

[0007] Furthermore, the material used for the metal butterfly antenna array and the metal ground plane is gold.

[0008] The metal butterfly antenna serves as an electrode for applying electrical bias, and the conductivity of the vanadium dioxide microbridge connected to it can be changed by adjusting the bias voltage; as a detection unit, the conductivity change of the vanadium dioxide microbridge caused by terahertz radiation can be converted into an output voltage at both ends of the electrode, thereby realizing the detection function of terahertz waves.

[0009] The third technical solution adopted by the present invention is a method for preparing the intelligent metasurface integrating terahertz beam detection and control, comprising the following steps:

[0010] 1. Growth of vanadium dioxide film: Clean the sapphire substrate and deposit a vanadium dioxide film on the surface of the sapphire substrate using laser pulse deposition

[0011] 2. Spin-coating photoresist: Spin-coating photoresist on the upper surface of the sapphire substrate on which vanadium dioxide has been grown and baking;

[0012] 3. UV exposure and development: Place the sapphire substrate with spin-coated photoresist on the photolithography machine and align it with the mask. The structure of the mask used is a periodic rectangular micro-bridge. After exposure, develop it with a positive photoresist developer and then post-bake it.

[0013] 4. Etching the vanadium dioxide film: Use reactive ion etching to etch periodic rectangular microbridges on the vanadium dioxide film, clean the remaining photoresist with acetone, clean it with alcohol and deionized water, and then dry it;

[0014] 5. Spin coating two layers of photoresist: Spin coating two layers of photoresist on the sapphire substrate in sequence;

[0015] 6. Repeat step (3), but use a metal mask;

[0016] 7. Evaporating a layer of metal on the photoresist and the exposed sapphire substrate, and then stripping off the remaining photoresist and the layer of metal on the photoresist, and finally obtaining a metal butterfly antenna array structure;

[0017] 8. Evaporate a layer of metal on the lower surface of the sapphire substrate to form a metal grounding surface.

[0018] Beneficial effects: The present invention discloses an intelligent metasurface that integrates terahertz beam detection and control. The beam control and detection functions are integrated in the array element at the same time. Compared with the traditional intelligent metasurface, it does not need to integrate an external detector, so it has the advantages of small size and high integration. In addition, each array element of the metasurface can be independently programmable and controlled, which greatly increases its potential in applications such as wireless communications. The beam adaptive control test system constructed by the present invention has the advantages of low cost and easy construction because it does not need to integrate an external terahertz detector. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A schematic diagram of the structure of a sub-array element in an array element of an intelligent metasurface with integrated terahertz beam detection and control according to the present invention;

[0020] Figure 2 The schematic diagram of the structure of the intelligent metasurface integrating terahertz beam detection and control of the present invention is a 1×48 array, and each array element is composed of 90×2 sub-array elements;

[0021] Figure 3 It is a schematic diagram and a cross-sectional diagram of some array elements of the intelligent metasurface integrating terahertz beam detection and control of the present invention;

[0022] Figure 4 The reflection coefficient amplitude-frequency curves when the conductivity of vanadium dioxide is 6000S / m and 250000S / m respectively.

[0023] Figure 5 The reflection coefficient phase-frequency curves when the conductivity of vanadium dioxide is 6000S / m and 250000S / m respectively.

[0024] Figure 6These are the spatial beam distribution diagrams when the phase coding sequences are / 000… / , / 00001111… / , / 0011000111… / and / 0011… / , and the operating frequency is 0.425THz.

[0025] Figure 7 Schematic diagram of the test system for realizing adaptive beam control for the above-mentioned intelligent metasurface with integrated terahertz beam detection and control.

[0026] Figure 8 The output voltage curve diagram of the detection unit of the intelligent metasurface integrating terahertz beam detection and regulation when the terahertz beam is turned on and off is shown in FIG. 1 , and the operating frequency is 0.425 THz. DETAILED DESCRIPTION

[0027] The present invention designs and manufactures a terahertz beam detection and control integrated intelligent metasurface (metasurface for short) based on vanadium dioxide, which can be used for beam control and detection at the same time. It is a one-dimensional antenna array consisting of 1×48 array elements, each of which consists of 90×2 sub-array elements. The sub-array element structure is as follows: Figure 1 As shown, the overall structure is Figure 2 As shown, the local structure and cross-section are as follows Figure 3 As shown, it is mainly composed of a sapphire substrate, a metal structure, a vanadium dioxide microbridge and a metal ground plane, and the designed operating frequency is in the terahertz frequency band. The present invention selects a butterfly antenna array as a metal structure, and the material used is gold. The vanadium dioxide microbridge after reactive ion etching is located in the middle of the butterfly antenna. The material used for the metal ground plane on the bottom surface of the sapphire substrate is gold, which can effectively block the transmission of terahertz waves. Therefore, the metasurface in the present invention is a reflective metasurface. The specific parameters of the sub-array element are as follows: w1=8μm, l1=5μm, l2=57.5μm, w2=140μm, l3=8μm, d1=160μm, t=400μm.

[0028] The working principle of this intelligent metasurface with integrated terahertz beam detection and control is as follows. Figure 4 As shown, when vanadium dioxide is in an insulating state, the conductivity is 6000S / m and the reflection spectrum is as follows Figure 4 As shown by the dotted line; when a voltage is applied to the vanadium dioxide microbridge through the metal electrode, the Joule heat generated will cause the vanadium dioxide to undergo a phase transition from an insulating state to a metallic state, accompanied by a sharp increase in conductivity. When the conductivity rises to 250,000 S / m, the resonant frequency in the reflection spectrum blue-shifts, as shown in Figure 2. Figure 4 If 0.425THz is selected as the operating frequency, the reflection spectrum of the array element will shift by 180° before and after the phase change (see Figure 5), while the amplitude remains the same, so the two states required for 1-bit encoding can be obtained, marked as "0" and "1" respectively. In addition, when vanadium dioxide is in the insulating-metal phase transition range, the conductivity of vanadium dioxide is extremely sensitive to temperature. The temperature change caused by the incident terahertz wave will change the conductivity of vanadium dioxide. If vanadium dioxide is biased by a constant current, it will cause the output voltage to change. Based on this characteristic, the power detection of terahertz waves can be realized.

[0029] The metasurface of the present invention can change the phase distribution, that is, switch the coding pattern composed of "0" and "1". According to the generalized Snell's law, the terahertz beam can be deflected to a specified angle. We selected thermal conductive silicone grease with a thermal conductivity of 14.3W / (m·K) to improve the heat conduction between the metasurface and the heated copper plate, thereby realizing the crosstalk-free loading of the coding pattern. Figure 6 (a), (b), (c) and (d) show the deflection effect of the prepared smart metasurface on the 0.425THz beam. Figure 6 It can be seen that for an incident electromagnetic wave at an angle of 15°, when the coding sequence of the prepared smart metasurface is / 000... / , its spatial beam points in the direction of the mirror reflection angle between the incident beam and the plane where the array is located. The spatial beam pointing corresponding to the sequences / 00001111... / , / 0011000111... / , and / 0011... / deviates from the mirror reflection angle by about 13°, 22.5°, and 28°, respectively. Therefore, by changing the coding sequence of the smart metasurface, the dynamic beam control function of the terahertz wave can be realized.

[0030] The preparation method of the intelligent metasurface integrating terahertz beam detection and control of the present invention:

[0031] According to Figure 1 The sub-array structural parameters of the designed terahertz beam detection and control integrated intelligent metasurface are actually processed. First, the mask file is drawn using drawing software, and then the mask is made. Then the actual sample processing is carried out according to the following steps:

[0032] 1. Grow a 110nm thick vanadium dioxide film on a sapphire substrate;

[0033] 2. Spin coating AZ1500 photoresist: Spin coating AZ1500 photoresist on the top surface of the sapphire substrate on which vanadium dioxide has been grown and bake, with a pre-rotation speed of 600 rpm and a steady rotation speed of 4000 rpm for 6 seconds and 40 seconds respectively, a baking temperature of 90° C., and a baking time of 5 minutes;

[0034] 3. UV exposure and development: Place the sapphire substrate coated with photoresist and the mask on the photolithography machine and align them. The mask structure is a periodic rectangular micro-bridge. The exposure time is 14 seconds. After exposure, positive photoresist developer is used for development, and the development time is 17 seconds.

[0035] 4. Etching the vanadium dioxide film: After development, the vanadium dioxide part needs to be left covered by the photoresist AZ1500, and the vanadium dioxide microbridge structure is etched using the reactive ion etching (RIE) process. The etching conditions are as follows: etching gas CF4, flow rate 40sccm, etching process pressure 3Pa, RF source power 100W, etching time 3 minutes. After etching, clean the remaining photoresist with acetone, clean with alcohol and deionized water, and then dry;

[0036] 5. Spin coating two layers of photoresist: on the sample after step (4), first spin coat a layer of photoresist LOR10B, with a pre-rotation speed of 600 rpm, a steady rotation speed of 4000 rpm, the time is 6 seconds and 40 seconds respectively, and the baking temperature is 150°C for 5 minutes; then spin coat a second layer of photoresist AZ1500, with a pre-rotation speed of 600 rpm, a steady rotation speed of 4000 rpm, the time is 6 seconds and 40 seconds respectively, and the baking temperature is 90°C for 2 minutes;

[0037] 6. Repeat step (3), but use a metal mask;

[0038] 7. Evaporate a layer of metal on the photoresist and the exposed sapphire substrate, then immerse the substrate in an N-methylpyrrolidone solution to remove the remaining photoresist LOR10B and AZ1500, and finally obtain a metal butterfly antenna array structure;

[0039] 8. Evaporate a layer of metal on the lower surface of the sapphire substrate to form a metal ground plane.

[0040] After the above procedures, the Figure 1 The smart metasurface shown integrates terahertz beam detection and control.

[0041] The present invention is based on the test system constructed by the intelligent metasurface with integrated terahertz beam detection and control as shown: Figure 7 The schematic diagram of the test system for the terahertz beam detection and control integrated intelligent metasurface to achieve beam adaptive beam is given. The detailed test steps are as follows:

[0042] 1. Embed a heating copper plate with a size comparable to that of the intelligent metasurface integrated with terahertz beam detection and control on a printed circuit board with an opening in the middle;

[0043] 2. Place the side of the smart metasurface coated with thermal grease close to a heating copper plate of equivalent size;

[0044] 3. Connect the temperature sensing wire and heating wire on the temperature controller to the above-mentioned heating copper plate;

[0045] 4. Use a wire bonding machine to connect 48 control electrodes on the printed circuit board with 48 array elements on the intelligent metasurface with integrated terahertz beam detection and control using aluminum wires with a diameter of 50 μm;

[0046] 5. The terahertz beam detection and control integrated intelligent metasurface fixed on the printed circuit board is fixed at the center of the rotating table of the terahertz continuous wave test optical path, and the terahertz transmitting end is fixed at an incident angle of 15 degrees;

[0047] 6. The 47 control signals of the programmable controller are amplified by the amplifier circuit board and then connected to the 47 control electrodes on the printed circuit board one by one, and the remaining 1 channel on the printed circuit board is directly connected to the lock-in amplifier after the current source provides bias current, that is, the remaining 1 channel is used as a terahertz wave detection unit, and the other 47 channels are used as terahertz wave control units;

[0048] 7. The intelligent metasurface integrating terahertz beam detection and control is biased at 60°C through a temperature control table, and the current source is used to bias the detection unit. The output voltage is demodulated by a lock-in amplifier to obtain a detection value (V d );

[0049] 8. The host computer is based on V d Determine whether to perform beam operation: If V d >V th , V th The host computer sends the coded information to the programmable controller, which controls the control unit of the metasurface. In the system demonstration, the phase coding sequence of the vanadium dioxide metasurface antenna is / 00001111… / , so that the beam is tilted to a specific angle; when V d ≤V th , the host computer turns off the control unit. The detection value of the whole process (V d ) can capture the terahertz wave incident state in real time, such as Figure 8 shown.

Claims

1. A smart metasurface integrating terahertz beam detection and control, characterized in that: It includes a sapphire substrate, a metal structure and a vanadium dioxide microbridge grown on the upper surface of the sapphire substrate, a metal ground plane grown on the lower surface of the sapphire substrate, and thermal grease between the metal ground plane and a heating copper plate; each array element of the intelligent metasurface has two functions of terahertz beam detection and regulation: first, each array element can be independently controlled by a programmable controller to achieve reconfigurable distribution of reflection phase, thereby achieving control of beam deflection angle; second, each array element can be used as a bolometer for terahertz wave detection; the metal structure on the upper surface of the sapphire substrate is a butterfly antenna array, the vanadium dioxide microbridge is connected to two metal sheets of the butterfly antenna array, and the two metal sheets serve as electrodes for applying bias; the conductivity of vanadium dioxide is regulated by changing the bias, thereby achieving control of the reflection phase of the terahertz wave; the incident terahertz wave causes the conductivity of vanadium dioxide to change, resulting in a change in the output voltage at both ends of the electrode, thereby achieving detection of the incident power.

2. The intelligent metasurface integrating terahertz beam detection and control according to claim 1, characterized in that: The conductivity of the vanadium dioxide microbridge is sensitive to temperature.

3. The intelligent metasurface integrating terahertz beam detection and control according to claim 1, characterized in that: The thermal conductive silicone grease is used to reduce the thermal resistance between the metal grounding surface and the heating copper plate.

4. A method for preparing the intelligent metasurface integrating terahertz beam detection and control as claimed in claim 1, characterized in that: The method comprises the following steps: (1) growing a vanadium dioxide film: cleaning a sapphire substrate, and depositing a vanadium dioxide film on the upper surface of the sapphire substrate by a laser pulse deposition method; (2) spin coating a photoresist: spin coating a photoresist on the upper surface of the sapphire substrate on which the vanadium dioxide film has been grown, and baking the photoresist; (3) UV exposure and development: placing the sapphire substrate on which the photoresist has been spin-coated on a photolithography machine and aligning it with the mask, wherein the structure of the mask used is a periodic rectangular microbridge, and after exposure, developing is performed with a positive photolithography developer, and then post-baking is performed; (4) Etching the vanadium dioxide film: etching a periodic rectangular microbridge on the vanadium dioxide film using a reactive ion etching process, cleaning the remaining photoresist with acetone, cleaning with alcohol and deionized water, and then drying; (5) Spin coating two layers of photoresist: spin coating two layers of photoresist on the sapphire substrate in sequence; (6) Repeating step (3), wherein the structure of the mask used is a metal butterfly antenna array structure; (7) evaporating a layer of metal on the photoresist and the exposed sapphire substrate, and then stripping off the remaining photoresist and the layer of metal on the photoresist to finally obtain a metal structure; (8) evaporating a layer of metal on the lower surface of the sapphire substrate to form a metal ground plane; (9) Apply thermal conductive silicone grease to the metal ground surface.

5. A beam adaptive control test system, characterized in that: The invention comprises a host computer, a programmable controller, an amplifying circuit and the intelligent metasurface integrated with terahertz beam detection and control as claimed in claim 1, wherein the host computer determines whether to perform beam deflection based on the detection signal of the intelligent metasurface, and the judgment result is sent to the programmable controller in the form of a control instruction, and the programmable controller adjusts the control signal according to the control instruction and the amplifying circuit performs power amplification, and then transmits it to the intelligent metasurface to realize real-time control of the terahertz beam.

6. The beam adaptive control test system according to claim 5, characterized in that: The upper function can adjust the control signal in real time based on the detection signal without human intervention.

7. The beam adaptive control test system according to claim 5, characterized in that: The side of the smart metasurface coated with thermal conductive silicone grease is attached to a heating copper plate, and the array elements of the smart metasurface are connected one by one to the control electrodes of the printed circuit board through aluminum wires of a wire bonding machine.

8. The beam adaptive control test system according to claim 5, characterized in that: The control signal of the programmable controller is amplified by the amplifier circuit board and connected one by one to the array element control electrodes of the printed circuit board, while the remaining one path on the printed circuit board is directly connected to the phase-locked amplifier after the current source provides bias current.

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