A temperature-controlled reconfigurable polarization converter based on VO2 phase transition

Abstract

The present invention relates to a reconfigurable polarization converter, and particularly to a temperature-controlled reconfigurable polarization converter based on VO2 phase change. It includes a bottom metal reflector, an intermediate dielectric layer, and a top resonator unit layer arranged in sequence from bottom to top. The top resonator unit layer includes a plurality of square open metal rings, and the plurality of square open metal rings are periodically arranged in an M×N form on the intermediate dielectric layer to form a periodic array. A phase change material is coated at the opening of each square open metal ring; the phase change material is obtained by dispersing VO2 nano-powder in a PVP matrix. The present invention has strong tunability, frequency flexibility, and the potential to be easily extended to the terahertz and even optical bands. It has great application value in the field of dynamic electromagnetic wave regulation such as antenna radiation and radar cross-section reduction. The preparation process is simple, the requirements for equipment are low, the usage scenarios are wide, and it is easy to promote and use.

Description

Technical Field

[0001] The present invention relates to a reconfigurable polarization converter, and more particularly to a temperature-controlled reconfigurable polarization converter based on VO2 phase change. Background Art

[0002] With the rapid development of electronic countermeasure and communication technologies, the demand for electromagnetic wave regulation is becoming increasingly strong. Polarization state is an important vector characteristic of electromagnetic waves. The polarization of a plane wave refers to the oscillation direction of the electric field in the electromagnetic wave propagation plane. The regulation of polarization state has wide applications in the fields of optical waves, microwave communication, and radar anti-jamming, and has become an important topic in the field of electromagnetic research. Traditional polarization regulation means such as gratings and dichroic crystals have disadvantages such as complex structures, large sizes, and narrow working frequency bands, which limit their applications in practical engineering. The metamaterial surface composed of sub-wavelength unit structures has opened up a new way to solve these problems.

[0003] Metamaterials (MMs), also known as artificial materials, have many peculiar properties that natural media do not possess and can achieve flexible regulation of electromagnetic waves. They are a new type of artificial composite material with at least one of the permittivity or permeability being negative, and generally composed of periodic structures. Based on these strange properties, many devices and materials with special functions have been prepared, such as perfect absorbers, filtering surfaces, and polarization conversion surfaces (Polarization Conversion Metasurface, PCM), etc. Using metamaterials for polarization regulation of electromagnetic waves is mainly divided into transmission type and reflection type. The transmission type polarization converter has disadvantages such as large loss and narrow frequency band, while the reflection type has great improvements in these two aspects. However, the narrow working frequency band is still the main reason restricting its engineering applications. Using multi-point resonance to broaden its working frequency band is a research direction. Zhang Linbo et al. designed a broadband and wide-angle reflection polarization converter in the microwave region, and a polarization conversion bandwidth of more than 75% can be obtained under normal incidence from 7.6 to 15.5 GHz and 45° incidence from 7.8 to 13.0 GHz. In 2017, Jing Cheng Zhao et al. proposed a simple design of an ultra-wideband and efficient reflection linear polarization converter. The linearly polarized wave can be converted into an orthogonal polarization after reflection, and the polarization conversion rate is above 90% in the frequency range of 5.1 to 12.1 GHz, with a relative bandwidth as high as 78.6%.

[0004] The designability of metamaterials itself provides the possibility for reconfigurable polarization converters. Reconfigurable metamaterials overcome the characteristics of traditional materials that cannot be changed after forming, can further broaden the working frequency band of metamaterials, and reduce the material quality. The existing implementation methods of tunable metamaterials can be divided into two types. One is to directly use dielectric materials with adjustable electromagnetic parameters, such as graphene, liquid crystal, indium antimonide, etc. The other is to actively change the electromagnetic structure of metamaterials, such as varactor diodes, variable resistance devices, and MEMS components, etc. Compared with the first method, the latter method has the advantages of simple processing, high modulation depth, and easy simulation design. However, electronic components limit the overall size of the polarization converter and cannot scale the design results proportionally to high-frequency fields or even optical wave fields. Using materials with phase change characteristics to replace variable electronic components, such as vanadium dioxide, can perfectly solve the above problems.

[0005] Vanadium dioxide is a typical strongly electron-correlated metal oxide. When subjected to external stimuli such as heat, voltage, or light, it can reversibly transform from a low-temperature insulating state (M phase) to a high-temperature semiconductor state (R phase), and the resistivity will have a mutation of 3 - 5 orders of magnitude. It has great application potential in the fields of new storage devices, intelligent electromagnetic protection materials, and terahertz technology.

[0006] However, in the current applications of VO2, thin-film technology mostly uses magnetron sputtering, which has complex preparation processes, high requirements for equipment, limited usage scenarios, and is not easy to promote and use. Summary of the Invention

[0007] The purpose of the present invention is to provide a temperature-controlled reconfigurable polarization converter based on VO2 phase change, which has strong tunability, frequency flexibility, and the potential to be easily extended to the terahertz and even optical bands. It has great application value in the field of dynamic electromagnetic regulation such as antenna radiation and radar cross-section reduction. The preparation process is simple, the requirements for equipment are low, the usage scenarios are wide, and it is easy to promote and use.

[0008] The present invention provides a temperature-controlled reconfigurable polarization converter based on VO2 phase change, which includes a bottom metal reflector, an intermediate dielectric layer, and a top resonance unit layer arranged in sequence from bottom to top. The top resonance unit layer includes a plurality of square open metal rings, and the plurality of square open metal rings are periodically arranged in the form of M×N on the intermediate dielectric layer to form a periodic array. The opening of each square open metal ring is coated with a phase change material; the phase change material is obtained by dispersing VO2 nano-powder in a PVP matrix.

[0009] The present invention realizes the reconfigurability of the polarization converter by coating a phase change material at the opening of the square open metal ring in the top resonance unit layer. The phase change material is obtained by dispersing VO2 nano-powder in a PVP aqueous solution matrix.

[0010] Preferably, the preparation method of the phase change material is as follows: First, prepare an aqueous PVP solution, and then disperse VO2 nanopowder in the aqueous PVP solution.

[0011] Preferably, the preparation method of the phase change material: First, prepare an aqueous PVP solution with a mass fraction of 3%-10%, and then disperse VO2 nanopowder in the aqueous PVP solution. The volume fraction of VO2 in the phase change material is 40-80%. Using this phase change material, the film composition is simple, and the water-based organic material PVP is safer and more environmentally friendly. To ensure the stable electrical performance of the prepared VO2 phase change material, considering the mechanical properties of the composite film and the adhesion to the substrate comprehensively, when preparing the reconfigurable polarization converter, the volume fraction of VO2 in the phase change material is 60%, and the volume fraction of PVP is 40%.

[0012] Preferably, both the square open metal ring and the metal reflector are composed of copper-clad metal, and the conductivity σ of the copper-clad metal used copper = 5.96×10 7 S / m. When the frequency is greater than 1 GHz, the skin depth of the copper-clad metal is less than 2.06 μm, and the thickness of the copper-clad metal is 35 μm.

[0013] Preferably, the intermediate dielectric layer uses a high-frequency PCB circuit board, with a dielectric constant of 3-5 and a loss tangent angle of 0.001-0.0037.

[0014] Preferably, the thickness h2 of the intermediate dielectric layer = 3.0-3.4 mm.

[0015] Preferably, a plurality of the square open metal rings are periodically arranged in a 19×19 form on the intermediate dielectric layer to form a periodic array, and the period p = 9-10 mm.

[0016] Preferably, the square open metal ring includes a square metal ring formed by connecting four metal sides end to end. The side length l of each metal side is 5-6 mm, the width w of each metal side is 0.05-0.2 mm. An opening is provided on each of the two opposite metal sides respectively. Two opposite metal sheets are provided at the opening of each metal side. The metal sheets are perpendicular to the metal sides respectively. A phase change material is coated between the two metal sheets. The width s of the phase change material is 0.05-0.2 mm. The length of the phase change material and the length of the metal sheet are both w1 = 0.3-0.7 mm, and the width s1 of the metal sheet is 0.05-0.2 mm. By adjusting the structural parameters of the resonant unit layer, polarization conversion within a specific frequency band can be achieved, while the intermediate dielectric layer can be used for structural support and adjustment of the working frequency of the overall structure. To increase the contact area between the phase change material and the metal ring and reduce the resistance after the VO2 junction phase change, two opposite metal sheets are provided at the opening of each metal side.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] (1) The present invention uses VO2 nano-powder dispersed in a PVP matrix to obtain a phase change material. The preparation process is simple, the usage scenarios are diverse, and it is easier to promote and use. By using the above VO2 phase change material in a metamaterial structure, the design and fabrication of a temperature-controlled metamaterial are realized. The simulation and experimental results show that when VO2 is in the low-temperature insulating state, due to the resonance effect of the periodic metal structure, cross-polarization reflection can be achieved, while when the material is in the high-temperature metallic state, the metal structure is destroyed, and the material can achieve co-polarization emission.

[0019] (2) The present invention coats a phase change material at the opening of the square open metal ring of the top-layer resonant unit layer. The phase change material is obtained by dispersing VO2 nano-powder in a PVP matrix, realizing the reconfigurability of the polarization converter. The simulation and experimental results show that when the temperature is lower than the phase change temperature of VO2 (68 °C), VO2 is in the insulating high-resistance state (M phase), and the reconfigurable polarization converter of the present invention can convert the incident linear polarization wave into a cross-polarization reflected wave at 8 - 18 GHz, and can achieve a polarization conversion rate (PCR) higher than 90% in the range of 8 - 18 GHz, with a bandwidth reaching 79%, and the working frequency band covering the X and Ku bands. When the temperature is higher than the phase change temperature of VO2, VO2 is in the metallic low-resistance state (R phase), and the polarization conversion rate (PCR) of the reconfigurable polarization converter of the present invention is less than 20% in the range of 9.4 GHz - 18 GHz, and most of the incident waves are co-polarization reflected. Before and after the phase change, in the range of 9.8 GHz - 19.6 GHz, the modulation depth is higher than 90%. The smaller the resistance of VO2, the higher the co-polarization reflection coefficient. When the resistance is less than 10 Ω, the co-polarization reflection coefficient is higher than 80%. When the resistance reaches 1 Ω, a co-polarization reflection higher than 90% can be achieved. When the resistance of VO2 is 188 ohms, impedance matching with air is achieved, and the power consumption in VO2 is the highest. The experimental tests are basically consistent with the simulation results.

[0020] (3) The present invention provides a temperature-controlled reconfigurable polarization converter based on VO2 phase change, which has strong tunability, frequency flexibility, and the potential to be easily extended to the terahertz and even optical bands. It has great application value in the field of dynamic electromagnetic wave regulation such as antenna radiation and radar cross-section reduction, and has a simple preparation process, low requirements for equipment, wide usage scenarios, and is easy to promote and use. Description of the Drawings

[0021] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0022] Figure 1 is the side view of each unit structure of the reconfigurable polarization converter;

[0023] Figure 2 is the top view of each unit structure of the reconfigurable polarization converter;

[0024] Figure 3 is the physical diagram of the top resonance unit layer;

[0025] Figure 4 (a) Design diagram of the phase change material test electrode, (b) Physical diagram of the phase change material test electrode, (c) SEM diagram of the phase change material;

[0026] Figure 5 is the temperature-induced phase change curve of the phase change material coating;

[0027] Figure 6 Temperature-induced phase change curves of composite materials with different VO2 volume fractions (20%, 30%);

[0028] Figure 7 Temperature-induced phase change curves of composite materials with different VO2 volume fractions (70%, 80%);

[0029] Figure 8 Temperature-induced phase change curves of composite materials with different VO2 volume fractions (40%, 60%);

[0030] Figure 9 is the change curve of the resistance and VO2 volume fraction before and after the phase change of the phase change material composite film;

[0031] Figure 10 is the temperature-induced phase change test diagram of the VO2 junction of the unit structure;

[0032] Figure 11 is the temperature-induced phase change curve of the VO2 junction of the unit structure;

[0033] Figure 12 (a) is the polarization rate curve of the reconfigurable polarization converter before the phase change, (b) is the polarization rate curve of the reconfigurable polarization converter after the phase change;

[0034] Figure 13 (a) is the polarization conversion rate of the reconfigurable polarization converter before and after the phase change, (b) is the modulation depth curve of the reconfigurable polarization converter;

[0035] Figure 14 is a sample diagram of a reconfigurable polarization converter;

[0036] Figure 15 is a physical diagram of a sample of a reconfigurable polarization converter;

[0037] Figure 16 is a physical diagram after pasting a polyimide heating film on the bottom metal reflector;

[0038] Figure 17 are the test and simulation reflection coefficient diagrams before and after the VO2 phase change of the reconfigurable polarization converter sample.

[0039] Description of reference numerals:

[0040] 1 - top - layer resonant unit layer, 2 - intermediate dielectric layer, 3 - bottom - layer metal reflector, 4 - resistance tester, 5 - temperature sensor, 6 - constant - temperature oven. Detailed implementation manners

[0041] It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs.

[0042] It should be noted that the terms used herein are only for describing specific implementation manners and are not intended to limit the exemplary implementation manners according to the present application. The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0043] Embodiment 1

[0044] A temperature - controlled reconfigurable polarization converter based on VO2 phase change, as Figure 1 shown, includes a bottom - layer metal reflector 3, an intermediate dielectric layer 2, and a top - layer resonant unit layer 1 arranged in sequence from bottom to top. As Figure 2 and Figure 3 shown, the top - layer resonant unit layer 1 includes a plurality of square - opening metal rings. The plurality of square - opening metal rings are periodically arranged in a 19×19 form on the intermediate dielectric layer to form a periodic array, with a period p = 9.2 mm. A phase - change material is coated at the opening of each square - opening metal ring ( Figure 2The VO2 thin film in it is the phase change material after coating). Preparation method of the phase change material: First, prepare an aqueous PVP solution with a mass fraction of 5%, and then disperse a certain amount of VO2 nano powder in the PVP matrix. The volume fraction of VO2 in the phase change material is 60%, and the volume fraction of PVP is 40%.

[0045] As Figure 2 shown, each square open metal ring consists of a square metal ring formed by connecting four metal sides end to end. The side length l of each metal side is 5.5 mm, the width w of each metal side is 0.1 mm. An opening is provided at the middle position of each of the two opposite metal sides respectively. Two opposite metal sheets are provided at the opening of each metal side. The materials of the metal sheets and the metal ring are exactly the same and are made integrally. The metal sheets are perpendicular to the metal sides respectively. A phase change material is coated between the two metal sheets (that is, between the two metal sheets). After drying, a VO2 composite thin film is formed. The VO2 nano particles overlap with each other. The width s of the phase change material is 0.1 mm. The length of the phase change material and the length of the metal sheet are both w1 = 0.5 mm, and the width s1 of the metal sheet is 0.1 mm.

[0046] The square open metal ring (including the metal sheets) and the metal reflector are both composed of copper-clad metal. The conductivity σ of the copper-clad metal used copper = 5.96×10 7 S / m. When the frequency is greater than 1 GHz, the skin depth of the copper-clad metal is less than 2.06 μm, and the thickness of the copper-clad metal is 35 μm. In the research frequency band range of this article, electromagnetic waves cannot penetrate, so the transmittance of the polarization converter is 0. In the research, only the incident port can be studied.

[0047] The intermediate dielectric layer uses the high-frequency PCB board Rogers4350B, with a dielectric constant of 3.48 and a loss tangent angle of 0.0037. The thickness h2 of the intermediate dielectric layer is 3.2 mm.

[0048] Test the phase change material prepared in Example 1:

[0049] First, test the resistance of the VO2 phase change material.

[0050] Use the coating process to coat the prepared VO2 phase change material between two electrodes. The design diagram of the phase change material test electrode is as Figure 4 shown in a. The electrode width is 2 mm, and the spacing is 1 mm. The physical diagram of the phase change material test electrode after the VO2 phase change material coating is dried is as Figure 4 shown in b. Figure 4 Figure c is the SEM characterization diagram of the VO2 phase change material coating after drying. It can be seen from the figure that the VO2 nano particles overlap with each other. The temperature-induced phase change curve of the VO2 phase change material coating is as Figure 5 shown.

[0051] Example 2

[0052] A temperature-voltage controlled reconfigurable reflective polarization converter is provided, which is only different from the example in that the volume fractions of VO2 and PVP in the VO2 phase change material are different.

[0053] By adjusting the ratios of VO2 nanoparticles, PVP and deionized water in the VO2 phase change material, VO2 phase change material composite films with VO2 volume fractions of 10%-90% were prepared, and the sum of the volume fractions of VO2 and PVP is 100%.

[0054] The temperature-induced phase change curves of the composite materials with different VO2 volume fractions are shown in Figures 6 - 8 . It can be seen from the curves in the figure that during the heating and cooling processes of the prepared VO2 coating, near 68°C, its resistance showed a sharp change, indicating that the prepared VO2 coating can undergo temperature-induced phase change under temperature changes. At a low temperature of 30°C, the resistance is 41 KΩ, and at a high temperature of 90°C, the resistance is 320 Ω, and the resistance change rate is higher than 2 orders of magnitude.

[0055] When the VO2 volume fraction is 10%, the VO2 junction resistance is infinite and the device cannot measure it. When the VO2 volume fraction is 20%, the resistance can only be measured when the temperature is higher than 70°C, as shown in Figure 6 . When the resistance is higher than 40%, all samples can exhibit a resistance mutation phenomenon. The heating phase change temperature is near 70°C, and when the temperature is higher than 80°C, the resistance is basically unchanged. According to the analysis of the curve of the resistance versus volume fraction in Figure 8 , the percolation threshold of the VO2 / PVP composite material is 40%. When the VO2 volume fraction in the composite material is higher than 40%, the electrical properties of the material change less.

[0056] The curves of the resistance before and after the phase change of the phase change material composite film versus the VO2 volume fraction are shown in Figure 9 .

[0057] To ensure the stable electrical properties of the prepared VO2 composite material, considering the mechanical properties of the composite film and the adhesion to the substrate, etc., when preparing the reconfigurable polarization converter, the volume fraction of VO2 is selected to be 60%.

[0058] Example 1 is the best example. The following tests are carried out on the reconfigurable polarization converter prepared in Example 1:

[0059] Perform temperature-induced phase change tests on the prepared unit structure VO2 junction, and the test diagram is as shown in Figure 10As shown, a unit structure is placed in an incubator. The set temperature is heated from room temperature to 100 °C and then cooled back to room temperature. During the heating and cooling processes, a resistance tester is used to record the resistance values of the unit structure to obtain a resistance-temperature curve. The test results are as Figure 11 shown.

[0060] Since the two VO2 phase change materials in the unit structure are in a parallel relationship, the low-temperature resistance of a single VO2 phase change material is 12 kΩ, and the high-temperature resistance is 94 Ω. During the actual coating process, there will be a certain error in the resistance of the VO2 junction. In the simulation, the low-temperature M-phase VO2 is set to Res = 12 kΩ, and the high-temperature R-phase VO2 is set to Res = 100 Ω.

[0061] When the external temperature is at room temperature, VO2 is in a high-resistance state. The polarization rate curve of the reconfigurable polarization converter before phase change is as Figure 12 shown in Fig. a. In the frequency band of 7.9 GHz - 17.6 GHz, the cross-polarization rate is greater than 80%, and the co-polarization rate is less than 20%. This indicates that before the phase change of VO2, most of the incident x-polarized waves are converted into y-polarized waves after being reflected by the polarization converter. And there are maxima in the cross-polarization rate and minima in the co-polarization rate at 8.7, 11, 15.4, and 17.6 GHz. Among them, perfect polarization conversion is achieved at the first three frequency points, that is, all x-polarized waves are converted into y-polarized waves. When the temperature is higher than the phase change temperature of VO2, VO2 is converted into the low-resistance R phase, and the reflection coefficient curve is as Figure 12 shown in Fig. b. When the frequency is greater than 8.9 GHz, the cross-polarization rate is less than 20%, and the co-polarization rate is higher than 20%. From Figure 13 Fig. a, it can be known that at low temperature, the polarization conversion rate of the designed structure is greater than 90% in the frequency range of 7.8 - 18 GHz, while at high temperature, when the frequency is higher than 9.4 GHz, the polarization conversion rate is less than 20%. This shows that after the phase change of VO2, only a small amount of electromagnetic waves undergo polarization deflection, and at this time, the metamaterial is a co-polarization reflection surface.

[0062] It can be shown that under the action of temperature, the polarization converter changes from a cross-polarization conversion reflection surface to a co-polarization reflection surface, and the polarization converter is reconfigured. When VO2 is in a high-resistance state, the bandwidth of the cross-polarization reflectivity of the designed polarization converter greater than 90% is 10.2 GHz, the working frequency band covers the X and Ku bands, the relative bandwidth is 79%, and the polarization conversion efficiency is higher than 99% in the frequency range of 8.1 - 17.8 GHz. And from Figure 13 Fig. b, it can be seen that the reconfigurable polarization converter designed in the present invention has a modulation depth greater than 80% in the range of 9.8 GHz - 19.6 GHz and has very good tunability.

[0063] A reconfigurable polarization converter is processed using printed circuit board technology. The sample size is 180mm * 180mm and it consists of 19 * 19 unit structures.

[0064] The process flow for coating the opening of the square split-ring resonator with phase change material is as follows: First, a hollowed polyimide film is fabricated according to the converter structure. Then, the hollowed film is attached to the surface of the converter, aligning the film opening with the opening of the top-layer circular structure of the converter. The previously prepared phase change material is sprayed onto the surface of the polyimide film using spraying technology. After drying, the hollowed film is peeled off, and the phase change material at the hollowed positions remains on the surface of the polarization converter. The physical diagram of the polarization converter is shown in Figure 15 , and the sample diagram is shown in Figure 14 .

[0065] A polyimide heating film is pasted on the bottom metal reflector (physical diagram shown in Figure 16 ) to heat the sample. The anechoic chamber test method is adopted. Two identical standard horn antennas are used to transmit and receive signals, connected to a vector network analyzer (Agilent Technologies N5230A), and tested at 6 - 20 GHz. The sample is placed 3 meters directly in front of the two horn antennas, and an absorbing material is placed on the back of the sample to avoid environmental interference. When the transmitting and receiving antennas are in the same direction, the co-polarization reflection coefficient can be measured. By adjusting the receiving antenna to the vertical state, the cross-polarization reflection coefficient can be measured.

[0066] To study the influence of the VO2 coating on the performance of the polarization converter, simulation tests are carried out. In the simulation, VO2 is simplified as a distributed resistance Res, and by adjusting the resistance value, the state of the VO2 thin film at different temperatures is simulated. The incident electromagnetic wave and the reflected electromagnetic wave can be expressed as The structure designed in the present invention is a corner-symmetric structure, and only the rotation of the incident wave in one direction needs to be studied. Taking the x-direction polarized wave as an example, R yx and R xx respectively represent the reflection coefficients of the x-polarized electromagnetic wave to the y-polarization and x-polarization directions, that is, R yx = E rx / E iy , R xx = E rx / E ix ; The co-polarization rate and the cross-polarization rate are respectively T xx = R xx *R xx and T yx = R yx *R yx . The polarization conversion rate PCR represents the polarization conversion ability of the polarization converter to electromagnetic waves, The modulation performance of VO2 on the polarization conversion of the polarization converter is represented by the modulation depth (MD), and MD = 1 - PCR M / PCR R , where PCR M represents the polarization conversion rate of the polarization converter after the phase change of VO2, and PCR R represents the polarization conversion rate of the polarization converter before the phase change of VO2.

[0067] The comparison curves of the test results and simulation results of the reconfigurable polarization converter sample before and after the phase change of VO2 are shown in Figure 17 . It can be seen from the figure that the test results are basically consistent with the simulation results, and the performance reconstruction of the polarization conversion polarization converter is realized by increasing the sample temperature.

[0068] Polarization is an important characteristic parameter of electromagnetic waves. The controllable regulation of electromagnetic polarization has important application values in the fields of antenna radiation, satellite communication, and radar stealth. The present invention designs and prepares a temperature-controlled reconfigurable polarization converter based on the phase change of VO2. The simulation and experimental results show that when the temperature is lower than the phase change temperature of VO2 (68 °C), VO2 is in an insulating high-resistance state (M phase). The reconfigurable polarization converter of the present invention can convert the incident linear polarization wave into a cross-polarization reflected wave at 8 - 18 GHz, and can achieve a polarization conversion rate (PCR) higher than 90% in the range of 8 - 18 GHz, with a bandwidth reaching 79%, and the working frequency band covering the X and Ku bands. When the temperature is higher than the phase change temperature of VO2, VO2 is in a metallic low-resistance state (R phase). The polarization conversion rate (PCR) of the reconfigurable polarization converter of the present invention is less than 20% in the range of 9.4 GHz - 18 GHz, and most of the incident waves are co-polarization reflected. Before and after the phase change, in the range of 9.8 GHz - 19.6 GHz, the modulation depth is higher than 90%. The smaller the resistance of VO2, the higher the co-polarization reflection coefficient. When the resistance is less than 10 Ω, the co-polarization reflection coefficient is higher than 80%. When the resistance reaches 1 Ω, a co-polarization reflection higher than 90% can be achieved. When the resistance of VO2 is 188 ohms, impedance matching with air is achieved, and the power consumption in VO2 is the highest. The experimental tests are basically consistent with the simulation results. The designed structure has great application values in the fields of electromagnetic wave dynamic regulation such as antenna radiation and radar cross-section reduction.

[0069] The temperature-controlled reconfigurable polarization converter based on the phase change of VO2 provided by the present invention has many advantages, has strong tunability, frequency flexibility, and the potential to be easily extended to the terahertz and even optical bands, has a simple manufacturing process, low cost, and has great application values in the fields of electromagnetic wave dynamic regulation such as antenna radiation and radar cross-section reduction.

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A temperature-controlled reconfigurable polarization converter based on VO2 phase transition, characterized in that: It includes a bottom metal reflector, an intermediate dielectric layer, and a top resonant unit layer arranged in sequence from bottom to top. The top resonant unit layer includes a plurality of square open metal rings. The plurality of square open metal rings are periodically arranged on the intermediate dielectric layer in the form of M×N to form a periodic array. A phase change material is coated at the opening of each square open metal ring; the phase change material is obtained by dispersing VO2 nano-powder in a PVP matrix. The preparation method of the phase change material is as follows: First, prepare a PVP aqueous solution with a mass fraction of 3%-10%, and then disperse VO2 nano-powder in the PVP aqueous solution. The volume fraction of VO2 in the phase change material is 40%-80%.

2. The temperature-controlled reconfigurable polarization converter based on VO2 phase transition according to claim 1, wherein: The volume fraction of VO2 in the phase change material is 60%, and the volume fraction of PVP is 40%.

3. The temperature-controlled reconfigurable polarization converter based on VO2 phase transition according to claim 1, wherein: Both the square open metal ring and the metal reflector are composed of copper-clad metal, and the conductivity σ of the copper-clad metal used copper = 5.96×10 7 S / m. When the frequency is greater than 1 GHz, the skin depth of the copper-clad metal is less than 2.06 μm, and the thickness of the copper-clad metal is 35 μm.

4. The temperature-controlled reconfigurable polarization converter based on VO2 phase transition according to claim 1, wherein: The intermediate dielectric layer uses a high-frequency PCB circuit board with a dielectric constant of 3-5 and a loss tangent angle of 0.001-0.0037.

5. The temperature-controlled reconfigurable polarization converter based on VO2 phase transition according to claim 4, wherein: The thickness h2 of the intermediate dielectric layer is 3.0-3.4mm.

6. The temperature-controlled reconfigurable polarization converter based on VO2 phase transition according to claim 1, characterized in that: The plurality of square open metal rings are periodically arranged on the intermediate dielectric layer in the form of 19×19 to form a periodic array, and the period p is 9-10mm.

7. The temperature-controlled reconfigurable polarization converter based on VO2 phase transition according to claim 6, wherein: The square open metal ring includes a square metal ring formed by connecting the four metal sides end to end. The side length l of each metal side is 5-6mm, the width w of each metal side is 0.05-0.2mm. An opening is provided on each of the two opposite metal sides respectively. Opposite metal sheets are provided at the opening of each metal side. The metal sheets are perpendicular to the metal sides respectively, and the phase change material is coated between the two metal sheets.

8. The temperature-controlled reconfigurable polarization converter based on VO2 phase transition according to claim 7, characterized in that: The width s of the phase change material is 0.05-0.2mm. The length of the phase change material and the length of the metal sheet are both w1 = 0.3-0.7mm, and the width s1 of the metal sheet is 0.05-0.2mm.

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