A terahertz reflective coding metasurface based on phase change materials

Abstract

The embodiments of the present application relate to the field of artificial electromagnetic material technology, and in particular to a terahertz reflective coding metasurface based on phase change material, comprising: a plurality of metasurface units distributed in an array; each metasurface unit comprising a metal layer, a patch layer located above the metal layer, and a dielectric substrate located between the metal layer and the patch layer; a phase change material layer is provided on the side of the dielectric substrate near the patch layer, and a groove is provided on the phase change material layer for accommodating the patch layer; a phase change material cover layer is provided on the side of the patch layer and the phase change material layer away from the dielectric substrate, and the phase change material cover layer covers the surface of the patch layer and the phase change material layer away from the dielectric substrate. The embodiments of the present application provide a terahertz reflective coding metasurface based on phase change material, which dynamically controls the reflected amplitude and phase of terahertz waves, thereby achieving full polarization of the coding metasurface and joint amplitude-phase-adjustability.

Description

Technical Field

[0001] The embodiments of the present application relate to the technical field of artificial electromagnetic materials, and in particular to a terahertz reflective coding metasurface based on phase change materials. Background Art

[0002] Artificial electromagnetic surfaces (metasurfaces), two-dimensional structures derived from novel three-dimensional artificial electromagnetic materials (metamaterials), have attracted the attention of researchers due to their advantages over three-dimensional metamaterials, including small size, light weight, low cost, and ease of processing and application. Their novel physical properties, in particular, have become a hot topic of research in fields such as electromagnetism, physics, and materials science. These properties can be used to design various functional electromagnetic devices, such as random surfaces, frequency-selective surfaces, and directional radiating antennas, enabling arbitrary control of electromagnetic waves. These devices have important applications in millimeter-wave communications, high-resolution imaging, and radar.

[0003] For this two-dimensional artificial electromagnetic surface, its units can be designed independently, so that each unit can independently control the amplitude and phase of the electromagnetic wave, thereby obtaining a more complex field distribution result. In the existing technology, digitally coded metasurfaces are used, that is, a controlled sequence is used to encode the "0" and "1" elements representing the 0 and π phase responses respectively (i.e., 1-bit encoding), which can manipulate electromagnetic waves and achieve different functions. However, in the terahertz frequency band, existing coded metasurfaces cannot achieve full polarization and amplitude-phase-joint tunability. Summary of the Invention

[0004] The embodiments of the present application provide a terahertz reflective coding metasurface based on phase change material, which solves the problem that existing coding metasurfaces cannot achieve full polarization and amplitude-phase-joint adjustment in the terahertz frequency band.

[0005] To solve the above technical problems, an embodiment of the present application provides a terahertz reflective coding metasurface based on phase change material, comprising: a plurality of metasurface units distributed in an array; each metasurface unit comprises a metal layer, a patch layer located above the metal layer, and a dielectric substrate located between the metal layer and the patch layer; a phase change material layer is provided on a side of the dielectric substrate close to the patch layer, and a groove for accommodating the patch layer is provided on the phase change material layer; a phase change material cover layer is provided on a side of the patch layer and the phase change material layer away from the dielectric substrate, and the phase change material cover layer covers the surface of the patch layer and the phase change material layer away from the dielectric substrate.

[0006] In some exemplary embodiments, a cross section of the phase-change material layer on a plane perpendicular to a thickness direction of the phase-change material layer is in the shape of a U-shaped triangle.

[0007] In some exemplary embodiments, the cross-section of the patch layer on a plane perpendicular to the thickness direction of the patch layer is a square.

[0008] In some exemplary embodiments, the side length of the patch layer is greater than half the side length of the phase change material layer.

[0009] In some exemplary embodiments, the cross section of the phase-change material capping layer on a plane perpendicular to the thickness direction of the phase-change material capping layer is a square.

[0010] In some exemplary embodiments, a side length of the phase change material cap layer is less than or equal to a side length of the top surface of the dielectric substrate.

[0011] In some exemplary embodiments, a surface of the patch layer away from the dielectric substrate is flush with a surface of the phase change material layer away from the dielectric substrate.

[0012] In some exemplary embodiments, the dielectric substrate is a square dielectric substrate.

[0013] In some exemplary embodiments, the cross-section of the dielectric substrate on a plane perpendicular to the thickness direction of the dielectric substrate is square or rectangular.

[0014] In some exemplary embodiments, the phase change material is one of vanadium oxide and zinc oxide.

[0015] The technical solution provided by the embodiments of the present application has at least the following advantages:

[0016] The embodiments of the present application address the problem that existing coding metasurfaces cannot achieve full polarization and amplitude-phase-joint tunability in the terahertz frequency band. The embodiments of the present application provide a terahertz reflective coding metasurface based on phase change material, the metasurface structure including multiple metasurface units distributed in an array; each metasurface unit includes a metal layer, a patch layer located above the metal layer, and a dielectric substrate located between the metal layer and the patch layer; a phase change material layer is provided on the side of the dielectric substrate close to the patch layer, and a phase change material cover layer is provided on the side of the patch layer and the phase change material layer away from the dielectric substrate, and the phase change material cover layer covers the surface of the patch layer and the phase change material layer away from the dielectric substrate. The coding metasurface provided by the embodiments of the present application is composed of a metasurface array of multiple metasurface units; because the embodiments of the present application perform periodic dynamic control of the digital coding of the metasurface, the embodiments of the present application have higher design freedom and more flexible and powerful control capabilities for electromagnetic waves; compared with coding metasurfaces with only phase or only amplitude coding, programmable amplitude-phase-joint tunable information metasurfaces have greater freedom in electromagnetic wave processing. Therefore, the embodiments of the present application have the advantages of high programmability and flexibility, and can cope with complex practical application requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] One or more embodiments are exemplarily described by the pictures in the corresponding drawings. These exemplifications do not constitute limitations on the embodiments. Unless otherwise stated, the pictures in the drawings do not constitute proportional limitations.

[0018] Figure 1a A schematic structural diagram of a terahertz reflective coding metasurface based on phase change material provided in one embodiment of the present application;

[0019] Figure 1b A top view of a terahertz reflective coding metasurface based on phase change material provided in one embodiment of the present application;

[0020] Figure 2a A schematic diagram of the reflection amplitude of a vanadium dioxide metasurface at different conductivities provided in one embodiment of the present application;

[0021] Figure 2b A schematic diagram of the reflectivity of a vanadium dioxide metasurface at different conductivities provided in one embodiment of the present application;

[0022] Figure 2c A schematic diagram of the reflection phase of a vanadium dioxide metasurface at different conductivities provided in one embodiment of the present application;

[0023] Figure 3a A model diagram of a terahertz reflective coding metasurface based on phase change material provided in one embodiment of the present application;

[0024] Figure 3b The far-field pattern of the coded metasurface provided in one embodiment of the present application is obtained under the conditions that the left half is illuminated by a low-intensity spot, the right half is illuminated by a high-intensity spot, and the incident wave is right-handed circularly polarized;

[0025] Figure 3c An embodiment of the present application provides a left-hand circular polarization pattern of the coded metasurface under the conditions that the left half is illuminated by a low-intensity spot, the right half is illuminated by a high-intensity spot, and the incident wave is right-hand circularly polarized;

[0026] Figure 3d Another embodiment of the present application provides a left-hand circular polarization pattern of the coded metasurface under the condition that the left half is illuminated by a low-intensity spot and the right half is illuminated by a high-intensity spot, and the incident wave is right-hand circularly polarized;

[0027] Figure 3e An embodiment of the present application provides a planar pattern of a coded metasurface under the conditions that the left half is illuminated by a low-intensity spot, the right half is illuminated by a high-intensity spot, and the incident wave is right-handed circularly polarized;

[0028] Figure 4 The far-field pattern of the coded metasurface provided in one embodiment of the present application is obtained under the conditions of low-intensity spot illumination on the left half and medium-intensity spot illumination on the right half, with the electric field being an x-direction plane wave incident;

[0029] Figure 5a The far-field pattern of the coded metasurface provided in one embodiment of the present application is obtained when the left half is illuminated by a medium-intensity spot, the right half is illuminated by a high-intensity spot, and the electric field is incident on a plane wave in the x-direction.

[0030] Figure 5b An embodiment of the present application provides a far-field pattern of a coded metasurface under the condition that the right half is illuminated by a high-intensity light spot. DETAILED DESCRIPTION

[0031] As can be seen from the background technology, the currently available coding metasurfaces cannot achieve full polarization and amplitude-phase-joint adjustment in the terahertz frequency band, and cannot meet complex practical needs.

[0032] Electromagnetic metamaterials are artificial structures with extraordinary electromagnetic properties that do not exist in nature, created through artificial microstructures. A metasurface is a two-dimensional metamaterial composed of a periodic arrangement of unit structures (such as metasurface units) on a two-dimensional plane. It consists of subwavelength inclusions in an ultrathin medium. It utilizes the phase and amplitude variations of electric and magnetic fields on either side of the unit structure to control the phase and amplitude distribution of electromagnetic waves in space. By accumulating these changes on a two-dimensional plane, it can arbitrarily manipulate electromagnetic waves to obtain the desired reflection, transmission, or scattering pattern. It has the advantages of being easy to design and manufacture, with low loss and a small size.

[0033] Related technologies have proposed a digitally coded metasurface that uses a controlled sequence to encode the "0" and "1" elements representing the phase responses of 0 and π, respectively (i.e., 1-bit encoding), which can manipulate electromagnetic waves and achieve different functions. The introduction of digitally coded metasurfaces has opened a bridge connecting the physical world and the digital information world. Another related technology, based on the digitally coded metasurface, proposed a 1-bit coded metasurface to achieve anomalous reflection and scattering of terahertz waves. By using a 1-bit coded metasurface, low reflection and scattering in a wide frequency range (0.77THz to 1.38THz) were achieved, and a specific coding sequence was used to generate various terahertz far-field reflection and scattering patterns. In addition, broadband multi-angle terahertz wave beam steering can be achieved by designing a 2-bit coded metasurface. Although the above-mentioned metasurface structures can manipulate electromagnetic waves and achieve different functions, none of the above-mentioned metasurface structures can achieve full polarization and amplitude-phase-joint tunability in the terahertz frequency band.

[0034] To address the above technical issues, the present invention provides a reflective coding metasurface based on phase change materials, comprising: a plurality of metasurface units arranged in an array; each metasurface unit comprises a metal layer, a patch layer located above the metal layer, and a dielectric substrate located between the metal layer and the patch layer; a phase change material layer is provided on the side of the dielectric substrate adjacent to the patch layer, with a slot provided in the phase change material layer for accommodating the patch layer; a phase change material cap layer is provided on the side of the patch layer and the phase change material layer distal from the dielectric substrate, with the phase change material cap layer covering the surface of the patch layer and the phase change material layer distal from the dielectric substrate. The present invention utilizes multiple metasurface units, forming a metasurface array composed of multiple metasurface units. By periodically and dynamically controlling the digital encoding of the metasurface, the metasurface has greater design freedom and more flexible and powerful control capabilities for electromagnetic waves. Compared to metasurfaces that encode only phase or only amplitude, programmable amplitude-phase-jointly adjustable information metasurfaces offer greater freedom in electromagnetic wave processing. The present invention is programmable and highly flexible, capable of addressing complex practical application requirements and possesses promising application prospects.

[0035] The following detailed description of the various embodiments of the present application is provided in conjunction with the accompanying drawings. However, those skilled in the art will appreciate that many technical details are provided in the various embodiments of the present application to facilitate a better understanding of the present application. However, even without these technical details and the various variations and modifications based on the following embodiments, the technical solutions claimed in the present application can still be implemented.

[0036] See Figure 1a An embodiment of the present application provides a terahertz reflective coding metasurface based on phase change material, comprising: a plurality of metasurface units 10 distributed in an array; each metasurface unit 10 comprises a metal layer 1, a patch layer 3 located above the metal layer 1, and a dielectric substrate 2 located between the metal layer 1 and the patch layer 3; a phase change material layer 4 is provided on a side of the dielectric substrate 2 close to the patch layer 3, and a groove is provided on the phase change material layer 4 for accommodating the patch layer 3; a phase change material cover layer 5 is provided on a side of the patch layer 3 and the phase change material layer 4 away from the dielectric substrate 2, and the phase change material cover layer 5 covers the surface of the patch layer 3 and the phase change material layer 4 away from the dielectric substrate 2.

[0037] The terahertz reflective coding metasurface based on phase-change materials provided in the embodiments of the present application can be used to design beam-steering devices for terahertz communications. By varying factors such as light intensity, voltage, temperature, or electric field strength on the phase-change material, the embodiments of the present application can achieve transitions between an insulator, an intermediate state, and a metal, thereby adjusting the resonant frequency of the metasurface unit. When the phase-change material is in the metallic and insulating states, the unit reflection amplitude is large, the loss is low, and the reflection phase differs by π. In the intermediate state, the reflection amplitude is small, and there is no need to consider the reflection phase, thus achieving amplitude-phase-joint coding.

[0038] The embodiments of the present application utilize the phase change characteristics of the conductivity of the phase change material that changes with light, electricity, temperature, electric field or force to achieve dynamic control of the amplitude and phase of the terahertz wave reflection, so as to achieve full polarization of the coded metasurface and amplitude-phase-joint tunability. Since many phase change materials have phase change characteristics from semiconductor phase to metal phase, such as zigzag zinc oxide nanoribbons that achieve phase change from metal to semiconductor under external stress induction, vanadium dioxide can undergo reversible phase change under thermal excitation, optical excitation and electrical excitation, and its conductivity and other properties change significantly before and after the phase change, achieving a reversible phase change from insulator to metal. The embodiments of the present application utilize the phase change characteristics of the phase change material that can achieve the conversion between insulator and metal, and achieve amplitude-phase joint coding. This phase change time is very short, close to the nanosecond level. The symmetrical unit structure enables the control of fully polarized electromagnetic waves, and the programmability enables it to flexibly respond to complex practical needs. These good properties make phase change materials a very promising revolutionary material.

[0039] In some embodiments, the phase change material may be one of vanadium oxide and zinc oxide. The phase change material in the embodiments of the present application is explained by taking vanadium dioxide as an example.

[0040] Vanadium dioxide is a common temperature-controlled phase-change material. Its morphology can switch between an insulator and a metal as the temperature changes, acting as an insulator at room temperature and a metallic conductor above 68 degrees Celsius. This is because its atomic structure can transform from a room-temperature crystal structure to a metallic structure above 68 degrees Celsius. This transformation occurs in less than a nanosecond and is reversible. These excellent properties make vanadium dioxide a very promising revolutionary material.

[0041] Therefore, the terahertz reflective coding metasurface based on phase change materials provided in the embodiments of the present application can be a terahertz reflective coding metasurface based on a vanadium dioxide thin film. The coding metasurface includes multiple metasurface units, which form a metasurface array. By periodically and dynamically regulating the digital coding of the metasurface, it has a higher degree of design freedom and a more flexible and powerful control capability for electromagnetic waves. Compared with metasurfaces that are only phase-encoded or only amplitude-encoded, programmable amplitude-phase-jointly adjustable information metasurfaces have greater degrees of freedom in electromagnetic wave processing.

[0042] Figure 1a FIG. 1 shows a schematic diagram of the structure of a metasurface unit provided in an embodiment of the present application. Figure 1aAs shown, the metasurface units are arranged from bottom to top in the order of metal layer 1, dielectric substrate 2, patch layer 3 (also called microstrip patch), phase change material layer 4 and phase change material cover layer 5, wherein the phase change material is vanadium dioxide; the patch layer 3 and the phase change material cover layer 5 located on the upper surface of the dielectric substrate 2 are a two-layer structure, the first layer structure is composed of the patch layer 3 and the phase change material layer 4, that is, the first layer structure is composed of the patch layer 3 and the vanadium dioxide film wrapped around the patch layer 3. Figure 1a It can be seen that the patch layer 3 can be a square patch layer, and the vanadium dioxide film is a U-shaped vanadium dioxide film; the second layer structure is a phase change material cover layer 5, and the phase change material cover layer 5 can be a square vanadium dioxide film, and the phase change material cover layer 5 covers the patch layer 3 and the phase change material layer 4 in the first layer structure, that is, the square vanadium dioxide film covers the surface of the patch layer 3 and the surface of the U-shaped vanadium dioxide film). The embodiment of the present application utilizes the phase change characteristics of vanadium dioxide whose electrical conductivity changes with temperature. By selecting a specific light spot intensity to irradiate the vanadium dioxide film, it can be realized that the conversion between the insulator, the intermediate state and the metal can be achieved, thereby adjusting the resonant frequency of the metasurface unit. When vanadium dioxide is in the metallic state and the insulating state, the unit reflection amplitude is large, the loss is small, and the reflection phase difference is π, while in the intermediate state, the reflection amplitude is small, and there is no need to consider the reflection phase, thereby realizing amplitude-phase-joint coding.

[0043] In some embodiments, the cross section of the phase change material layer 4 is in the shape of a Chinese y-square on a plane perpendicular to the thickness direction of the phase change material layer 4. Figure 1a and Figure 1b As can be seen in FIG, the cross section of the phase change material layer 4 is in the shape of a Chinese umbilical cord. In the embodiment of the present application, a Chinese umbilical cord-shaped vanadium dioxide film can be used as the phase change material layer 4.

[0044] In some embodiments, the cross section of the patch layer 3 is a square on a plane perpendicular to the thickness direction of the patch layer 3. Figure 1a and Figure 1b As can be seen in the figure, the cross-section of the patch layer 3 is square. The embodiment of the present application uses a square metal patch as the patch layer 3, which is located in the groove of the phase change material layer 4. In other words, the U-shaped vanadium dioxide film surrounds the patch layer 3 and covers the side walls of the patch layer 3.

[0045] In some embodiments, the side length of the patch layer 3 is greater than half the side length of the phase change material layer 4. When the cross section of the patch layer 3 is a square, the length and width of the patch layer 3 are equal, and the length of the patch layer 3 is generally greater than half the length of the outer periphery of the phase change material layer 4, and the width of the patch layer 3 is generally greater than half the width of the outer periphery of the phase change material layer 4.

[0046] In some embodiments, the cross section of the phase change material cover layer 5 is a square on a plane perpendicular to the thickness direction of the phase change material cover layer 5. Figure 1a and Figure 1b As can be seen in the figure, the phase change material cover layer 5 covers the upper surface of the patch layer 3 and the phase change material layer 4. When the cross section of the patch layer 3 is square and the cross section of the phase change material layer 4 is in the shape of a circle, the cross section of the phase change material cover layer 5 is also square.

[0047] In some embodiments, the side length of the phase-change material cap layer 5 is less than or equal to the side length of the top surface of the dielectric substrate 2. Typically, the side length of the phase-change material cap layer 5 is slightly less than the side length of the top surface of the dielectric substrate 2, that is, the side length of the phase-change material cap layer 5 is slightly less than the side length of the metasurface unit.

[0048] In some embodiments, the surface of the patch layer 3 away from the dielectric substrate 2 is flush with the surface of the phase change material layer 4 away from the dielectric substrate 2 , that is, the thickness of the patch layer 3 may be equal to the thickness of the phase change material layer 4 .

[0049] Please continue to see Figure 1a The metal layer 1 is located at the bottom of the metasurface unit, and the material of the metal layer 1 can be gold; the thickness T1 of the metal layer 1 can be 0.2 μm; the dielectric substrate 2 is located above the metal layer 1, and the dielectric substrate 2 can be a square dielectric substrate; the material of the dielectric substrate 2 can be alumina, and its relative dielectric constant ε r =9.8, loss tangent tanδ=0.001; the length and width (metasurface unit period) P of the dielectric substrate 2 are 1 / 25 of the working wavelength, and the thickness H is 2 / 25 of the working wavelength; the patch layer 3 is a square microstrip patch, and the material of the patch layer 3 can be gold. Figure 1b As shown, the length and width X of patch layer 3 can be 3 / 125 of the operating wavelength, and the thickness is T3. Phase-change material layer 4 can be a U-shaped vanadium dioxide thin film. The length and width W of the outer periphery of phase-change material layer 4 are slightly smaller than the side length of the metasurface unit, that is, the length and width W of the outer periphery of phase-change material layer 4 are slightly smaller than the dimensions of the upper surface of dielectric substrate 2 and the upper surface dimensions of metal layer 1. The length and width W of the outer periphery of phase-change material layer 4 can be 0.0384 of the operating wavelength. The length and width of the inner periphery of phase-change material layer 4 are X, and the thickness of phase-change material layer 4 is T4. Phase-change material cap layer 5 can be a square vanadium dioxide thin film. The length and width of phase-change material cap layer 5 are W, and the thickness is T5.

[0050] It should be noted that the length and width of the phase change material cover layer 5 can be equal to the length and width of the periphery of the phase change material layer 4; the thickness T3 of the patch layer, the thickness T4 of the phase change material layer 4, and the thickness T5 of the phase change material cover layer 5 can be equal to the thickness T1 of the metal layer 1, that is, the thickness T3 of the patch layer 3, the thickness T4 of the phase change material layer 4, and the thickness T5 of the phase change material cover layer 5 can be 0.2μm.

[0051] like Figure 1aAs shown, in some exemplary embodiments, the dielectric substrate 2 is a square dielectric substrate.

[0052] In some exemplary embodiments, the cross-section of the dielectric substrate 2 on a plane perpendicular to the thickness direction of the dielectric substrate 2 is square or rectangular. Figure 1a FIG. 2 shows a schematic diagram of a dielectric substrate 2 being a square dielectric substrate, wherein the surface of the dielectric substrate 2 facing the patch layer 3 and the phase change material layer 4 is square. Figure 1b As shown, the side length of the surface of the dielectric substrate 2 facing the patch layer 3 and the phase change material layer 4 is slightly larger than the outer side length of the phase change material layer 4 (the U-shaped vanadium dioxide film), and the side length of the surface of the dielectric substrate 2 facing the patch layer 3 and the phase change material layer 4 is slightly larger than the side length of the phase change material cover layer 5 (the square vanadium dioxide film); the side surface of the dielectric substrate 2 is rectangular.

[0053] The design principle of the metasurface unit in the embodiment of the present application is to make its surface equivalent to an LC series resonant circuit model, and the resonance formula is shown in the following formula (1):

[0054]

[0055] From formula (1), we can see that near the resonant frequency, the reflection amplitude is small and the phase changes significantly. Reasonable setting of the resonant frequency point can achieve amplitude-phase-joint adjustment. When the light spot is irradiated with low light intensity and the temperature is low, the conductivity of vanadium dioxide is low (σ=10S / m), which is equivalent to a small area s of the capacitor plate. The capacitance determination formula is shown as follows:

[0056]

[0057] From formula (2), we can see that the capacitance C is small, so the resonant frequency is large. As the conductivity of vanadium dioxide increases, the equivalent capacitance increases and the resonant frequency decreases. When high-intensity light spot is used for irradiation, the conductivity of vanadium dioxide is high (σ=10 5 S / m), the unit resonant frequency is small. As an example, the simulation results of the metasurface unit reflection amplitude and reflectivity are as follows Figure 2a and Figure 2b As shown in the figure, when vanadium dioxide is in the insulating and metallic states, the reflection amplitude of the unit is large, with a reflectivity of more than 80% at 0.12 THz; when vanadium dioxide is in the intermediate state (σ = 5000 S / m), the unit resonates near 0.12 THz, with a reflection amplitude of -29 dB. The reflection phase is as follows Figure 2cAs shown, the phase difference between vanadium dioxide in the insulating and metallic states at 0.12 THz is 183°, achieving 1-bit phase encoding with a bandwidth of 0.0027 THz. The simulation results are based on TE wave excitation at the Floquet port. The reflection amplitude and phase of the unit under TM (Transverse Magnetic) wave excitation are consistent with those under TE (Transverse Electric) wave excitation, demonstrating that the symmetry of the metasurface unit structure can achieve the control of fully polarized electromagnetic waves.

[0058] The following describes the basic principles of the reflective coding metasurface provided by the embodiments of the present application. Taking a 1-bit reflective coding metasurface composed of M×N units as an example, an FPGA (programmable logic device) outputs M×N control signals to control the phase response of the reflection coefficient of each of the M×N units to switch between 0 and π. When a plane wave is incident vertically on the metasurface, according to traditional phased array antenna theory, the formula for its far-field scattering is:

[0059]

[0060] In formula (3), θ and are the elevation and azimuth angles of the scattered field, is the far-field function of the subarray, and k is the propagation constant, so its directivity function can be given by the following formula:

[0061]

[0062] The present invention provides a fully polarization-amplitude-phase-adjustable terahertz reflective coded metasurface based on a vanadium dioxide thin film. By irradiating the vanadium dioxide film with a light spot of a specific intensity, the vanadium dioxide temperature and conductivity can be precisely controlled. Different spatial arrangements of the coded metasurface units result in different responses to electromagnetic waves.

[0063] The embodiment of the present application uses a coding metasurface composed of 50×50 metasurface units for simulation, such as Figure 3a As shown, the left half is illuminated by a low-intensity spot (σ=10S / m), and the right half is illuminated by a high-intensity spot (σ=10 5 S / m), at this time the reflection loss of the coding metasurface is small. When the right-hand circularly polarized incident wave is vertically incident on the metasurface, the direction pattern of the coding metasurface, the left-hand circularly polarized direction pattern, the right-hand circularly polarized direction pattern and the plane direction pattern are respectively as follows Figure 3b 、 Figure 3c and Figure 3d As shown, the plane direction diagram is as Figure 3e As shown, the reflected electromagnetic wave is left-hand circularly polarized. From the results, we can see that this encoding method realizes the function of polarization conversion.

[0064] When the left half is illuminated by a low-intensity spot and the right half is illuminated by a medium-intensity spot (σ=5000S / m), and the electric field is incident with a plane wave in the x-direction, the radiation pattern of the coding metasurface is as follows: Figure 4 shown.

[0065] In order to verify the influence of the smaller reflection amplitude in the intermediate state of vanadium dioxide (σ = 5000S / m), when the left half is illuminated by a medium-intensity spot and the right half is illuminated by a high-intensity spot, the incident wave is a plane wave with an electric field in the x direction, and the radiation pattern of the coding metasurface is as follows: Figure 5a As shown; Since the reflection amplitude of the unit is small near 0.12THz when vanadium dioxide is in the intermediate state, under the condition of unchanged excitation and boundary conditions, the radiation pattern of the right half of the high-intensity spot is as follows Figure 5b .Depend on Figure 5a and Figure 5b The results show that when vanadium dioxide is in an intermediate state, the unit reflection amplitude is small and the reflection characteristics are less affected.

[0066] Therefore, the embodiment of the present application uses vanadium dioxide as an example, and utilizes the temperature-controlled phase change characteristics of vanadium dioxide to achieve its conversion between insulator and metal, and the phase change time is very short. The embodiment of the present application adjusts its conductivity by selecting a specific intensity spot to irradiate vanadium dioxide and precisely controlling its temperature. When it is in the metallic state or the insulating state, the unit reflection amplitude is large, and the reflection phase difference between the two states is π, achieving 1-bit phase encoding; when it is in a certain state between metal and insulation, the unit reflection amplitude is small, achieving amplitude-phase joint encoding.

[0067] It should be noted that the coding metasurface provided in the embodiment of the present application has a symmetrical structure about the longitudinal center axis of the metasurface, and each metasurface also has a symmetrical structure about the longitudinal center axis of the metasurface unit, so that the coding metasurface can realize the control of incident waves with fully TE or TM electric fields.

[0068] Furthermore, in some embodiments, the conductivity of the phase-change material is altered by irradiating the vanadium dioxide with light spots of varying intensities to change its temperature. In other embodiments, the conductivity of the phase-change material can be altered by selectively controlling light, electricity, heat, electric fields, force, or a combination of these.

[0069] In addition, it should be noted that in the embodiment of the present application, only one phase change material, vanadium dioxide, is used to realize a fully polarization amplitude-phase-jointly adjustable terahertz reflective coding metasurface, which is schematic, but the embodiment of the present application is not limited to vanadium dioxide as a phase change material.

[0070] Based on the above technical solution, the embodiments of the present application address the problem that existing coding metasurfaces cannot achieve full polarization and amplitude-phase-joint tunability in the terahertz frequency band, and propose a terahertz reflective coding metasurface based on phase change material. The metasurface structure includes a plurality of metasurface units 10 distributed in an array; each metasurface unit 10 includes a metal layer 1, a patch layer 3 located above the metal layer 1, and a dielectric substrate 2 located between the metal layer 1 and the patch layer 3; a phase change material layer 4 is provided on the side of the dielectric substrate 2 close to the patch layer 3, and a phase change material cap layer 4 is provided on the side of the patch layer 3 and the phase change material layer 4 away from the dielectric substrate 2, and the phase change material cap layer 4 covers the surface of the patch layer 3 and the phase change material layer 4 away from the dielectric substrate 2. The terahertz reflective coding metasurface provided in the embodiments of the present application includes a metasurface array composed of a plurality of metasurface units 10. By periodically and dynamically controlling the digital coding of the metasurface, it has a higher degree of design freedom and a more flexible and powerful control capability of electromagnetic waves. Compared to metasurfaces that are only phase- or only amplitude-encoded, programmable amplitude-phase-jointly tunable information metasurfaces offer greater freedom in electromagnetic wave processing. Therefore, the embodiments of the present application offer the advantages of high programmability and flexibility, enabling them to address complex practical application requirements.

[0071] Those skilled in the art will appreciate that the above-described embodiments are specific examples for implementing the present application, and that in actual applications, various changes in form and detail may be made thereto without departing from the spirit and scope of the present application. Any person skilled in the art may make changes and modifications without departing from the spirit and scope of the present application. Therefore, the scope of protection of the present application shall be subject to the scope defined in the claims.

Claims

1. A terahertz reflective coding metasurface based on phase change material, characterized in that: include: A plurality of metasurface units distributed in an array; Each of the metasurface units includes a metal layer, a patch layer located above the metal layer, and a dielectric substrate located between the metal layer and the patch layer; A phase change material layer is provided on a side of the dielectric substrate close to the patch layer, and a groove for accommodating the patch layer is provided on the phase change material layer; A phase change material cover layer is provided on the side of the patch layer and the phase change material layer away from the dielectric substrate, and the phase change material cover layer covers the surface of the patch layer and the phase change material layer away from the dielectric substrate; On a plane perpendicular to the thickness direction of the phase change material layer, the cross section of the phase change material layer is in the shape of a Chinese y-square; On a plane perpendicular to the thickness direction of the patch layer, the cross section of the patch layer is a square; The dielectric substrate is a square dielectric substrate; On a plane perpendicular to the thickness direction of the dielectric substrate, the cross section of the dielectric substrate is square or rectangular; The phase change material is one of vanadium oxide and zinc oxide.

2. The terahertz reflective coding metasurface based on phase change material according to claim 1, characterized in that: The side length of the patch layer is greater than half of the side length of the phase change material layer.

3. The terahertz reflective coding metasurface based on phase change material according to claim 1, characterized in that: On a plane perpendicular to the thickness direction of the phase change material cover layer, the cross section of the phase change material cover layer is a square.

4. The terahertz reflective coding metasurface based on phase change material according to claim 3, characterized in that: The side length of the phase change material cover layer is less than or equal to the side length of the top surface of the dielectric substrate.

5. The terahertz reflective coding metasurface based on phase change material according to claim 1, characterized in that: The surface of the patch layer away from the dielectric substrate is flush with the surface of the phase change material layer away from the dielectric substrate.

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