Multifunctional tunable metasurface using VO2 phase change material

Abstract

The progress of the metamaterial promotes the development of programmable metamaterials. At a low wave frequency, the diode or the variable capacitance diode can be used for programming the on-state and off-state of the unit cell of the metamaterial. However, they are no longer applicable at terahertz wave frequencies. A metasurface using a phase change material, such as vanadium dioxide (VO2), has been proposed for use in the terahertz frequency range. However, these metasurfaces are challenged in that, without changing their physical structure, the unit cells may not be adjustable between on and off states, and the unit cells may be difficult to induce a phase change by an external stimulus. Some embodiments herein relate to tunable metasurfaces that can be used at terahertz frequencies, the metasurfaces including unit cells having a physical structure. The structure of the metasurface may also access the plurality of cells by an external stimulus to induce a phase change.

Description

TECHNICAL FIELD

[0001] The present application relates to metasurfaces and metamaterials, and in particular embodiments, to tunable or programmable metasurfaces and metamaterials including vanadium dioxide (VO2). BACKGROUND

[0002] Metamaterials are synthetic engineered materials whose molecular structure enables them to exhibit properties that natural materials do not possess. For example, metamaterials can be designed to have a negative refractive index, which can facilitate the realization of perfect or superlenses, or optical camouflage. Due to their precisely designed structures, metamaterials can also be used to manipulate electromagnetic (EM) radiation, for example, to block, absorb, enhance, or bend EM waves in ways that are not possible with conventional materials.

[0003] Thus, one area in which metamaterials have great potential is the telecommunications field, as almost all telecommunications involve the transmission of electromagnetic (EM) radiation from a transmitter to a receiver. Other areas in which metamaterials can be very useful include wearable devices, infrastructure such as walls or eyeglasses, and the like.

[0004] Metamaterials typically include multiple layers of stacked material layers, and thus, metamaterials can be difficult to manufacture using methods such as nanofabrication. For some applications, a metasurface, defined as a single layer of metamaterial, can be created to eliminate some of the complexities associated with creating metamaterials. SUMMARY

[0005] Advances in the field of metamaterials have facilitated the development of digital or programmable metamaterials, which borrow the concept of bits to produce metamaterials that can exhibit different properties depending on how they are “programmed.” A bit or binary digit is the smallest increment of data on a computer that can hold one of two values (1 or 0), which respectively correspond to an on or off state, or true or false state. Digital metamaterials can be composed of one or more lattices of unit cells that can exhibit a 1 or 0, or an “on” state or an “off’ state. Depending on which unit cells on the surface of the metamaterial are programmed to be in an “on” state and which unit cells are programmed to be in an “off’ state, a single material can be used to manipulate EM radiation in different ways. For example, configuring a metamaterial to have different sequences of encoding of its unit cells (e.g., in one configuration, having consecutive unit cells alternating between the encoding sequence 01010101…, and in another configuration, having the encoding sequence 00110011…) can result in differences in the angle of the beam of reflected EM radiation. Thus, it will be appreciated by those skilled in the art that by programming the unit cells to be arranged in different sequences of encoding, metamaterials can be used for a variety of applications, such as beam steering.

[0006] The tuning of the unit cells between the “on” state and the “off’ state can be implemented using field-programmable gate array (FPGA) hardware. For example, a unit cell with a metallic component can be connected to an electrically controlled diode or varactor diode, which in turn is connected to the FPGA hardware. The FPGA hardware can provide a current to the diode or varactor diode, thereby “turning on” the unit cell. If no current is provided, the unit cell can be in the “off’ state.

[0007] The unit cells can be designed to have a physical structure that results in a difference between the phase response of the unit cell in its on state and off state that is substantially pi. This is because for EM waves, the maximum phase difference between waves is pi (or 180 degrees), and it will be appreciated by those skilled in the art that this phase difference pi between the “on” state and the “off’ state of the unit cell can correspond to a “0” state or a “1” state, respectively.

[0008] At microwave or millimeter (mm) wave frequencies, e.g., EM waves with frequencies less than 300 gigahertz (GHz), diodes or varactor diodes can be used to program or tune the unit cells of a metamaterial between an on state and an off state. However, at wave frequencies in the terahertz (THz) range, diodes or varactor diodes can no longer be suitable as they do not function properly at such high frequencies of EM waves.

[0009] In the field of telecommunications and others, higher frequencies are increasingly being considered and valued. For example, EM radiation with frequencies in the THz range can result in properties such as greater communication capacity, increased resistance to interference due to narrower beams, and good beam directionality, compared to waves with frequencies in the microwave range. Therefore, there is a need for digital metamaterials that can operate at THz frequencies.

[0010] It has previously been proposed to use phase change materials such as vanadium dioxide (VO2) for metasurfaces for use at THz frequencies. VO2 can undergo a phase change between an insulating state and a conductive state in response to an external stimulus, and can therefore be used as part of a unit cell to allow the unit cell to switch between a “0” state and a “1” state without the need for a diode or varactor diode. Therefore, VO2 can be incorporated into the structure of a unit cell structure to create a digital metasurface. However, these proposed metasurfaces using vanadium dioxide face several problems.

[0011] In the proposed metasurfaces using VO2, the physical structure of the unit cells must vary depending on whether the unit cells are intended to be in an "on" state or an "off state. For example, the size (e.g., length or width) or position of the vanadium dioxide used for the unit cells can need to be different between unit cells in an "on" state and unit cells in an "off state, resulting in unit cells having different physical structures. Then, the required programming configuration (e.g., whether the encoding sequence of the unit cells is 101010..., 010101..., or 11001100..., etc.) must be determined in advance before the metamaterial or metasurface is manufactured. Once the metamaterial is manufactured, its physical structure cannot be changed, and therefore, the encoding sequence of the unit cells cannot be changed. Thus, in order to have different encoding sequences, for example, for use in beam steering applications, a brand new metamaterial or metasurface with the new required configuration must be manufactured, which makes the use impractical in such cases.

[0012] Furthermore, the proposed metasurfaces using VO2 do not provide a simple or practical way to induce phase transition of VO2. For example, the design of the proposed metasurfaces is to induce insulator-metal phase transition of the VO2 components on multiple unit cells of the metasurface, each unit cell must be individually accessed by an external stimulus, as the VO2 elements of consecutive unit cells are not connected to each other. Thus, the external stimulator for inducing the insulator-metal phase transition must have a connection device (e.g., a wire) to each individual unit cell.

[0013] Therefore, there is a need for tunable metasurfaces for THz frequencies, which are easier to adjust to have different encoding sequences.

[0014] Some embodiments herein relate to a tunable metasurface or metamaterial. For simplicity, the term "metasurface" is used hereinafter, which can be used to refer to both a metasurface and a metamaterial made of layers of the metasurface.

[0015] The tunable metasurface can include an arrangement of unit cells, each unit cell structure including a phase change material, for example, VO2. The unit cells can have one single physical structure and can be programmed to be in an "on" state or an "off state. Furthermore, the VO2 elements between consecutive unit cells along a particular direction can be physically connected, allowing manipulation of multiple unit cells by an external stimulus applied to one of the multiple unit cells.

[0016] The tunable metasurface can enable applications that require reflection and / or transmission of EM radiation. For example, reflection of EM radiation enabled by the tunable metasurface can be useful in applications that require beam steering, and transmission of EM radiation enabled by the tunable metasurface can be useful in applications that require beam filtering. The tunable metasurface can also enable for EM radiation at lower frequencies, for example, instead of using diodes or varactors.

[0017] In some embodiments, a unit cell for a metasurface or metamaterial is provided. The unit cell can also be referred to as an adjustable unit cell or a programmable unit cell. The unit cell can include a substrate including a top layer and a bottom layer. The top layer can be provided with a vanadium dioxide first top layer strip and a vanadium dioxide second top layer strip spaced apart from the vanadium dioxide first top layer strip, the vanadium dioxide first top layer strip and the vanadium dioxide second top layer strip each including a first side and an opposite second side. The first side of the first top layer strip can face the first side of the second top layer strip, the opposite second side of the first top layer strip can face away from the second top layer strip, and the opposite second side of the second top layer strip can face away from the first top layer strip. The opposite second side of the first top layer strip and the opposite second side of the second top layer strip each have a plurality of spaced apart vanadium dioxide protrusions protruding therefrom. The top layer can also be provided with a plurality of top layer metal strips spaced apart from each other, each of the plurality of top layer metal strips extending from the first side of the first top layer strip to the first side of the second top layer strip. The bottom layer can be provided with a vanadium dioxide first bottom layer strip and a vanadium dioxide second bottom layer strip spaced apart from the vanadium dioxide first bottom layer strip, the vanadium dioxide first bottom layer strip and the vanadium dioxide second bottom layer strip each including a first side and an opposite second side. The first side of the first bottom layer strip can face the first side of the second bottom layer strip, the opposite second side of the first bottom layer strip can face away from the second bottom layer strip, and the opposite second side of the second bottom layer strip can face away from the first bottom layer strip. The bottom layer can also be provided with a plurality of vanadium dioxide bottom layer strips spaced apart from each other, each of the plurality of vanadium dioxide bottom layer strips extending from the first side of the vanadium dioxide first bottom layer strip to the first side of the vanadium dioxide second bottom layer strip. The bottom layer can also be provided with a plurality of bottom layer metal strips spaced apart from each other and interposed between the first side of the vanadium dioxide first bottom layer strip and the first side of the vanadium dioxide second bottom layer strip. Each of the plurality of bottom layer metal strips can also be spaced apart from the vanadium dioxide first bottom layer strip, the vanadium dioxide second bottom layer strip, and the plurality of vanadium dioxide bottom layer strips.

[0018] In some embodiments, a metasurface having a repeating pattern of unit cells is provided. Each unit cell can include a substrate including a top layer and a bottom layer. The top layer of each unit cell can be provided with a vanadium dioxide first top layer strip and a vanadium dioxide second top layer strip spaced apart from the vanadium dioxide first top layer strip, the vanadium dioxide first top layer strip and the vanadium dioxide second top layer strip each including a first side and an opposite second side. The first side of the first top layer strip can face the first side of the second top layer strip, the opposite second side of the first top layer strip can face away from the second top layer strip, and the opposite second side of the second top layer strip can face away from the first top layer strip. The opposite second side of the first top layer strip and the opposite second side of the second top layer strip each have a plurality of spaced apart vanadium dioxide protrusions projecting therefrom. The top layer of each unit cell can also be provided with a plurality of top layer metal strips spaced apart from one another, each of the plurality of top layer metal strips extending from the first side of the first top layer strip to the first side of the second top layer strip. The bottom layer of each unit cell can be provided with a vanadium dioxide first bottom layer strip and a vanadium dioxide second bottom layer strip spaced apart from the vanadium dioxide first bottom layer strip, the vanadium dioxide first bottom layer strip and the vanadium dioxide second bottom layer strip each including a first side and an opposite second side. The first side of the first bottom layer strip can face the first side of the second bottom layer strip, the opposite second side of the first bottom layer strip can face away from the second bottom layer strip, and the opposite second side of the second bottom layer strip can face away from the first bottom layer strip. The bottom layer of each unit cell can also be provided with a plurality of vanadium dioxide bottom layer strips spaced apart from one another, each of the plurality of vanadium dioxide bottom layer strips extending from the first side of the vanadium dioxide first bottom layer strip to the first side of the vanadium dioxide second bottom layer strip. The bottom layer of each unit cell can also be provided with a plurality of bottom layer metal strips spaced apart from one another and interposed between the first side of the vanadium dioxide first bottom layer strip and the first side of the vanadium dioxide second bottom layer strip. Each of the plurality of bottom layer metal strips can also be spaced apart from the vanadium dioxide first bottom layer strip, the vanadium dioxide second bottom layer strip, and the plurality of vanadium dioxide bottom layer strips.

[0019] Technical advantages of some embodiments can include the ability to adjust or program a single metasurface having an arrangement (e.g., a lattice or grid) of unit cells (e.g., a crystal lattice) to different configurations (e.g., different code sequences) using an external stimulus device. The different configurations that can be achieved using a single metasurface can result in the metasurface being able to reflect or transmit beams according to a desired application, and also being able to reflect beams having different angles for beam steering and other applications. Furthermore, the physical contact between some of the phase change material elements in the continuous tunable unit cells can allow for manipulation of multiple continuous unit cells (e.g., a column of unit cells) by an external stimulus applied to only one of the multiple unit cells, making it easier and more cost effective to adjust the unit cells of the metasurface. BRIEF DESCRIPTION OF DRAWINGS

[0020] Embodiments will be described, by way of example only, with reference to the drawings, in which:

[0021] Figure 1 A top view of the tunable unit cell is shown in accordance with some embodiments;

[0022] Figure 2 A bottom view of the tunable unit cell is shown in accordance with some embodiments; Figure 1

[0023] Figure 3 Reflection amplitude of electromagnetic (EM) radiation reflected by the tunable unit cell in the first reflective state and the second reflective state as a function of various frequencies of incident EM radiation is shown in accordance with some embodiments; Figure 1

[0024] Figure 4 Reflection amplitude of electromagnetic (EM) radiation reflected by the tunable unit cell in the first reflective state and the second reflective state as a function of various frequencies of incident EM radiation is shown in accordance with some embodiments; Figure 3

[0025] Figure 5 Phase response exhibited by the tunable unit cell in the first reflective state and the second reflective state as a function of various frequencies of incident EM radiation is shown in accordance with some embodiments; Figure 3

[0026] Figure 6 Transmission amplitude exhibited by the tunable unit cell in the transmissive state as a function of various frequencies of incident EM radiation is shown in accordance with some embodiments; Figure 3

[0027] Figures 7 to 9 Various configurations of a tunable metasurface comprising a lattice of tunable unit cells is shown; Figure 3

[0028] Simulated reflective far-field scattering pattern of the metasurface of Figure 10 Figure 7 Simulated reflective far-field scattering pattern of the metasurface of

[0029] Figure 11 Simulated reflective far-field scattering pattern of the metasurface of Figure 8

[0030] Simulated transmissive far-field scattering pattern of the metasurface of Figure 12 Figure 9 DETAILED DESCRIPTION

[0031] For illustrative purposes, specific embodiments are described herein with reference to the accompanying figures.

[0032] Figure 1 and Figure 2 ​​​​​​​​A top view and a bottom view of a unit cell 100 are shown, respectively, in accordance with some embodiments. As shown, the unit cell 100 includes a substrate 102 having a top surface 103 and a bottom surface 113. In one preferred embodiment, the substrate 103 can be polyimide. In some embodiments, the substrate 103 can be another material, for example, sapphire.

[0033] Various elements are disposed on the top surface 103 and the bottom surface 113 of the unit cell 100. Specifically, on the top surface 103, a plurality of strips 104, a plurality of protrusions 106, and a plurality of bands 108 can be disposed. On the bottom surface 113, a plurality of strips 114, a plurality of bands 116, and another plurality of bands 118 can be disposed. It should be noted that the terms "band" and "strip" can be used interchangeably. The use of two different terms is merely for ease of explanation, for example, strips along one direction are referred to as "strips" and strips along another direction are referred to as "bands."

[0034] The plurality of strips 104 and the plurality of protrusions 106 disposed on the top surface 103, and the plurality of strips 114 and the plurality of bands 116 disposed on the bottom surface 113 can be composed of a phase change element. In one preferred embodiment, the phase change element can be vanadium dioxide (V02).

[0035] V02 is an element that can undergo a fast insulator-metal phase transition in response to an external stimulus (e.g., a stimulus of light, electrical, or thermal nature). This is due to a change in its crystal structure at approximately 67 degrees Celsius (152.6 degrees Fahrenheit). Specifically, below this threshold temperature, V02 exhibits the properties of an insulator, while above this threshold temperature, V02 exhibits the properties of a conductor. It will be appreciated by those skilled in the art that V02 is capable of reflecting electromagnetic radiation when it is in its conductive state, and is capable of transmitting electromagnetic radiation when it is in its insulating state.

[0036] The plurality of bands 108 disposed on the top surface 103 and the plurality of bands 118 disposed on the bottom surface 113 can be composed of a metallic element. In one preferred embodiment, the metallic element can be gold. In some other embodiments, the metallic element can be another metal, for example, chromium.

[0037] The plurality of strips 104, the plurality of protrusions 106, the plurality of bands 108, the plurality of strips 114, the plurality of bands 116, and the plurality of bands 118 can be disposed onto the top surface 103 or the bottom surface 113 of the unit cell 100 using known manufacturing methods, for example, printing or deposition.

[0038] In one preferred embodiment, as shown in FIG. 1, the plurality of strips 104 and the plurality of protrusions 106 are disposed on the top surface 103 of the unit cell 100. The plurality of strips 114 and the plurality of bands 116 are disposed on the bottom surface 113 of the unit cell 100. The plurality of bands 108 disposed on the top surface 103 and the plurality of bands 118 disposed on the bottom surface 113 are composed of a metallic element, for example, gold. Figure 1As shown, the top face 103 of the unit cell 100 can be provided with two spaced-apart vanadium dioxide strips 104, five spaced-apart vanadium dioxide protrusions 106 protruding opposite the outer sides (e.g., the“second sides”) of each vanadium dioxide strip 104, and five spaced-apart gold strips 108 each extending between and connected to the inner sides (e.g., the“first sides”) of the vanadium dioxide strips 104.

[0039] In a preferred embodiment, as shown, the bottom face 113 of the unit cell 100 can be provided with two spaced-apart vanadium dioxide strips 114, three spaced-apart vanadium dioxide strips 116 each extending between and connected to the inner sides (e.g., the“first sides”) of the vanadium dioxide strips 114, and three spaced-apart gold strips 118 provided between the inner sides of the vanadium dioxide strips 114 but not connected thereto. Each of the three gold strips 118 can also be spaced apart from the three spaced-apart vanadium dioxide strips 116. Figure 2

[0040] For ease of reference, dimensions associated with the unit cell 100 can be described below with respect to the x-y-z axes shown. Specifically, the“length” of a component refers to a measurement along the y-direction, the“width” of a component refers to a measurement along the x-direction, and the“height” or“thickness” of a component refers to a measurement along the z-direction.

[0041] In some embodiments, the length of the unit cell 100 can be 100 um, the width can be 100 um, and the thickness can be 35 um. Relative to the top face 103, the two VO2 strips 104 can be substantially parallel to each other and substantially parallel to the length edges of the unit cell 100. The VO2 protrusions 106 protruding opposite each of the two VO2 strips and the gold strips 108 can be substantially perpendicular to the two VO2 strips 104, substantially parallel to each other, and substantially parallel to the width edges of the unit cell 100. The length of each of the two VO2 strips 104, i.e., across the entire length of the unit cell, can be 100 um, the width can be 10 um, and the thickness can be 0.2 um. The length of each VO2 protrusion 106 can be 10 um, the width can be 15 um, and the thickness can be 0.2 um. The length of each gold strip 108 can be 10 um, the width can be 40 um, and the thickness can be 0.2 um.

[0042] ​With respect to the bottom surface 113, two strips of VO2 114 can be substantially parallel to each other and substantially parallel to the length edges of the unit cell 100. Three bands of VO2 116 and three bands of gold 118 can be substantially perpendicular to the two strips of VO2 114, substantially parallel to each other, and substantially parallel to the width edges of the unit cell 100. Each of the two strips of VO2 114 can have a length of 100 um, a width of 5 um, and a thickness of 0.2 um. Each of the three bands of VO2 can have a length of 5 um, a width of 80 um, and a thickness of 0.2 um. Each of the gold bands 118 can have a length of 5 um, a width of 60 um, and a thickness of 0.2 um.

[0043] Figure 3 Unit cells 100 in different reflective and transmissive states are shown in accordance with some embodiments. Specifically, Figure 3 Example A shows a unit cell 100 in a first reflective state 100A, Example B shows a unit cell 100 in a second reflective state 100B, and Example C shows a unit cell 100 in a transmissive state 100C. The physical structure of the unit cell 100 is the same in the unit cells in the first reflective state 100A, the second reflective state 100B, and the transmissive state 100C. The only difference between the states 100A, 100B, and 100C is whether the vanadium dioxide components are in a conductive state or an insulating state.

[0044] When in the first reflective state 100A, all of the VO2 elements on the top surface 103 of the unit cell 100, i.e., the VO2 strips 104 and the VO2 protrusions 106, are in a conductive state. Similarly, all of the VO2 elements on the bottom surface 113 of the unit cell 100, i.e., the VO2 strips 114 and the VO2 bands 116, are in a conductive state. When in the second reflective state 100B, all of the VO2 elements on the top surface 103 are in an insulating state, while all of the VO2 elements on the bottom surface 113 are in a conductive state. When in the transmissive state 100C, all of the VO2 elements on the top surface 103 and the bottom surface 113 are in an insulating state.

[0045] As previously mentioned, the VO2 elements of the unit cell can be switched between their conductive and insulating states using an external stimulus. In some embodiments, this external stimulus can be provided using a field-programmable gate array (FPGA) controller (not shown). The FPGA controller can be connected to the unit cell 100 using one or more control lines (not shown). In some embodiments, the one or more control lines can be copper wires. In some embodiments, for example, both the top VO2 strips 104 and the bottom VO2 strips 114 can be connected to the FPGA controller via corresponding control lines. As will be appreciated by those skilled in the art, the FPGA controller can send electrical signals through the control lines that can excite the vanadium dioxide and induce a phase change from its insulating state to its conductive state. For example, switches can be toggled between an on mode and an off mode to control whether electrical signals are sent through the corresponding control lines. In this way, all of the VO2 elements of the unit cell can be programmed or tuned between their conductive and insulating states using four control lines.

[0046] For Figures 1 to 3 As shown for the unit cell 100, since there are two VO2 strips 104 on the top surface 103 and two VO2 strips 106 on the bottom surface 113, the FPGA controller can be connected to the unit cell 100 using four control lines. Since each top VO2 tab 106 is in physical contact with one of the top VO2 strips 104 and each VO2 strip 116 is in physical contact with two of the VO2 strips 114, the phase change of all of the VO2 elements of the unit cell 100 can be affected using four control lines (i.e. two control lines can be used to induce phase changes in the VO2 strips 104 and the VO2 tabs 106 on the top surface 103 and the other two control lines can be used to induce phase changes in the VO2 strips 114 and the VO2 strips 106 on the bottom surface 113).

[0047] Figures 4 to 6 Plots of the reflection amplitude, phase response, or transmission amplitude of the unit cell 100 in its different reflection and transmission states are shown. Amplitude or phase response measurements can be simulated using electromagnetic field simulation software such as CST Studio Suite®, or physically measured using a vector signal analyzer.

[0048] Figure 4A plot 400 of the reflected amplitude of EM radiation reflected by the unit cell 100 in the first and second reflective states 100A, 100B is shown. In some embodiments, EM radiation of various frequencies (i.e., different wavelengths) is directed at the unit cell 100 in the first and second reflective states 100A, 100B, and the amplitude of the radiation reflected by the unit cell 100 is measured. For example, in the plot 400, the frequency range of the EM radiation is between 0.5 THz and 0.9 THz. The plot 400 shows a high reflectivity of the curves 410, 420 due to the fact that in both the first and second reflective states 100A, 100B, at least some of the VO2 elements are in the conductive state.

[0049] Figure 5 A plot 500 of the phase response of the unit cell 100 in the first and second reflective states 100A, 100B is shown. In some embodiments, EM radiation of various frequencies is directed at the unit cell 100 in the first and second reflective states 100A, 100B, and the phase of the reflected radiation is measured. In the plot 500, the frequency range of the EM radiation is between 0.5 THz and 0.9 THz, where the plot 500 shows the reflected phase of the unit cell 100 in the first reflective state 100A by the curve 510, and the reflected phase of the unit cell 100 in the second reflective state 100B by the curve 520. In the illustrated example, at a frequency of 0.68579 THz, the measured phase response of the reflected EM radiation between the unit cell 100 in the first reflective state 100A and the unit cell 100 in the second reflective state 100B differs by substantially pi, or about 180 degrees. More generally, in the frequency range between approximately 0.65 THz and 0.9 THz, a substantially pi difference in the measured phase response between the unit cell 100 in the first reflective state 100A and the unit cell 100 in the second reflective state 100B can be observed. It should be noted that the term “substantially pi” as used herein is intended to mean that the phase difference is generally or close to pi, but not necessarily exactly pi, e.g., there can be + / - 40 degrees of variation. For example, in the plot 500, the phase difference at 0.9 THz is about 215 degrees. Those skilled in the art will appreciate that such a substantially pi phase difference effectively allows the unit cell in the first reflective state 100A to exhibit a “1” or “on” state, and the unit cell in the second reflective state 100B to exhibit a “0” or “off’ state. Such a substantially pi phase difference can allow for the desired constructive and / or destructive interference effects between the beams of reflected radiation by the metasurface of the present application, for applications such as beam steering. Figure 5

[0050] ​In practice, in some embodiments, the structure of the aforementioned unit cell 100, including the size of the unit cell 100, the specific elements used (e.g., VO2 and gold), the number of vanadium dioxide strips 104 and protrusions 106 and gold strips 108 to be placed on the top surface 103, and the number of vanadium dioxide strips 114 and 116 and gold strips 118 to be placed on the bottom surface 113, as well as their sizes and spacing relative to each other, can be specifically selected to generate a phase difference of substantially pi between the unit cell in the first reflection state 100A and the unit cell in the second reflection state 100B. In some embodiments, the structure of the unit cell 100, such as the elements, the size of the elements, the spacing between the elements, etc., can be adjusted in different proportions to still achieve a phase difference of substantially pi between the first reflection state 100A and the second reflection state 100B. Therefore, Figure 1 and Figure 2 The specific structure shown is merely one embodiment, and the exact structure shown is not required. For example, to achieve the goal of a phase difference of substantially pi between the first and second reflection states, the number of strips and / or bands and / or protrusions, and / or their size, and / or their spacing relative to each other, can be varied. Variations in the structure can also be provided, or alternatively, that may not result in a phase difference of substantially pi, but can still function appropriately well, depending on the scenario. For example, the phase difference may not be close to pi, but it may be significant enough to still function appropriately well.

[0051] As mentioned earlier, when in the transmission state 100C, all VO2 elements of cell 100 are in the insulating state. Therefore, compared with cell 100 in the first reflection state 100A and the second reflection state 100B, cell 100 can transmit EM radiation better. Figure 6 A graph 600 shows the transmission amplitude of EM radiation reflected by cell 100 in transmission state 100C. EM radiation of various frequencies was directed to cell 100 in transmission state 100C, and the amplitude of the transmitted radiation was measured. As shown, the amplitude of the transmitted EM radiation remains relatively high across the entire frequency range of EM radiation between 0.5 THz and 0.9 THz.

[0052] Figures 7 to 9 Various configurations of a tunable metasurface 700 comprising a lattice or grid of tunable cells 100 are shown. The metasurface 700 typically comprises an arrangement of M x N cells 100, where M and N are integers greater than 0, and M may or may not be equal to N. Figures 7 to 9 The metasurface 700 in the figure is shown as an 8x8 lattice comprising tunable unit cells 100, but this is merely an example. Larger lattices can be deployed in implementations, depending on the application. (See figure.) Figures 7 to 9The metasurface 700 comprises an array of continuous unit cells 100 in rows and columns. In some embodiments, the substrate 102 may be a continuous layer (e.g., made of polyimide) sized to accommodate the required number of unit cells, and the necessary VO2 and gold elements may be printed or deposited on the top and bottom surfaces of the substrate 102. For example, for Figures 7 to 9 The metasurface 700 in the design can have a substrate with dimensions of 800 μm in length, 720 μm in width, and 39 μm in thickness. The metasurface dimensions may vary depending on the application. For example, for smartphone applications, the length and width of the metasurface could be between 1 mm and 1 cm.

[0053] Brief Review Figures 1 to 3 On the top surface 103 of unit cell 100, VO2 stripes 104 extend the entire length of the unit cell, so each VO2 strip 104 reaches both edges of the top surface 103 along the y-direction, while the VO2 protrusions 106 do not extend along the x-direction to reach either edge of the top surface 103. Similarly, on the bottom surface 113 of unit cell 100, VO2 stripes 114 extend along the y-direction to reach both edges of the bottom surface 113, while the VO2 stripes 116 do not extend along the x-direction to reach either edge of the bottom surface 113. Therefore, when unit cells 100 are arranged to form a metasurface, for example, Figures 7 to 9 In the case of the metasurface 700, the physical structure of the metasurface allows each of the two VO2 stripes 104 in a particular cell 100 along the y-direction to be physically connected to the corresponding VO2 stripe 104 of the cell immediately above that particular cell, and also physically connected to the corresponding VO2 stripe 104 of the cell immediately below that particular cell. For the first and last cells 100 in each column, each VO2 stripe 104 is physically connected only to the corresponding VO2 stripe immediately below or immediately above, respectively. Therefore, the top surface VO2 stripe 104 and the bottom surface VO2 stripe 114 of the cells 100 along the metasurface column can form a continuous line extending along the full length of the metasurface.

[0054] This configuration of the connection lines of the VO2 strips 104 on the top surface of the metasurface 700 and the connection lines of the VO2 strips 114 on the bottom surface of the metasurface 700 can advantageously allow multiple unit cells to be adjusted simultaneously between the first reflective state 100A, the second reflective state 100B, and the transmissive state 100C. For example, if an FPGA controller with control lines is used to adjust the unit cells between the various states, the entire column of unit cells 100 can be adjusted simultaneously using the control lines required to adjust a single unit cell 100. For example, as previously described, four control lines can be used to adjust a single unit cell 100, with a first control line connected to one of the VO2 strips 104, a second control line connected to another of the VO2 strips 104, a third control line connected to one of the VO2 strips 114, and a fourth control line connected to another of the VO2 strips 114. Since on the bottom surface 113 of the unit cell, the VO2 strips 114 are also physically connected to the VO2 strips 116, in some embodiments, three control lines can be used to adjust the unit cell 100, as the bottom surface can use only one control line instead of two. In a preferred embodiment, four control lines can be used. Using two control lines instead of one for the bottom layer of VO2 strips 114 can be used to improve the performance of the external stimulator, for example, making the adjustment of the unit cell more robust. Due to the conductive ability of vanadium dioxide, if the control lines are connected to the VO2 strips 104, 114 of the bottom-most unit cell 100 of a column of the metasurface, the electrical signal sent by the FPGA controller can communicate with all of the unit cells 100 in that column of the metasurface through the continuous lines of the VO2 strips 104, 114. If some of the VO2 elements between subsequent unit cells in a column of the metasurface do not have this connection, each unit cell in the metasurface can require four control lines, which can be impractical when the metasurface includes many unit cells.

[0055] The physical structure of the metasurface 700 remains the same between the illustrated diagrams. Figures 7 to 9 The difference is whether the unit cells 100 that make up the metasurface are programmed or adjusted to be in the first reflective state 100A, the second reflective state 100B, or the transmissive state 100C. Specifically, in Figure 7 the metasurface 700 is in the first programmed state 700A; in Figure 8 the metasurface 700 is in the second programmed state 700B; and in Figure 9 the metasurface 700 is in the third programmed state 700C. Thus, advantageously, the physical structure of the metasurface 700 or the unit cells 100 does not need to change to be adjusted to be in the various programmed states.

[0056] As Figure 7As shown, the first programming state 700A includes four consecutive columns of unit cells 100 that are all programmed or adjusted to be in the second reflection state 100B, and four consecutive columns of unit cells 100 that are all adjusted to be in the first reflection state 100A. This type of metasurface configuration, in which all unit cells 100 in a column are uniformly adjusted to be in the first reflection state 100A or the second reflection state 100B, can be called a strip configuration.

[0057] The period T of a metasurface can be described as the number of consecutive unit cells tuned along the x or y direction to be in the same first reflection state 100A or second reflection state 100B. For example, for Figure 7 The metasurface 700 configured in the illustrated embodiment has a period T in the x-direction. x The value is 4.

[0058] In a strip configuration, all cells 100 in a column can be adjusted as described above, for example, by using four control lines connected to the FPGA controller. For Figure 7 In the metasurface 700, for example, for each column of metasurface 700, four control lines can be used, thus a total of 32 control lines can be used to adjust all cells 100 of metasurface 700 in the first programming state 700A. Specifically, in order to adjust a column of cells to be in the second reflection state 100B (e.g., for...), Figure 7 In each of the four left columns, the FPGA controller can send electrical signals via the two control lines connected to the top VO2 strip 104, instead of the two control lines connected to the bottom VO2 strip 114. In this way, an insulator-metal phase transition can be achieved only for the top VO2 strip 104 and VO2 protrusion 106, and not for the bottom VO2 strip 114 and VO2 strip 116, resulting in a change in phase density for each cell in the column. Figure 3 The situation is shown in Example B. To adjust a column of unit cells to be in the first reflection state 100A (e.g., for...) Figure 7 (Each of the four right columns in the column), the FPGA controller can send electrical signals via all four control lines connected to the top VO2 stripe 104 and the bottom VO2 stripe 114. In this way, an insulator-metal phase transition can be achieved for all VO2 elements in the column, resulting in a phase transition for each unit cell in the column. Figure 3 The situation shown in Example A.

[0059] exist Figure 8In the second programming state 700B, the metasurface 700 comprises a 4x4 array of continuous cells all adjusted to the first reflection state 100A, followed by a repeating pattern of a 4x4 array of continuous cells all adjusted to the second reflection state 100B, such that the period T along the x-direction... x The period is 4, and the period along the y-direction is T. y The value is 4. This type of metasurface configuration can be called a cross-tiling configuration.

[0060] In cross-tiling configurations, because not all cells in a column are tuned to the same reflection or transmission state, additional control lines may be needed to correctly program the cells along the column. For example, for Figure 8 With the configuration shown, a period of 4 along the y-direction, four control lines can be used for each sub-column of the four units. Therefore, for a metasurface 700 in the second programming state 700B, a total of 64 control lines can be used to adjust all units 100 on the metasurface. If the metasurface needs to be in a strip-like (e.g., Figure 7 (as shown) and cross tiling (e.g., Figure 8 If the metasurface is programmable between the lines shown, then the metasurface will need to be equipped with the number of control lines required to achieve the cross-tiling configuration.

[0061] In some embodiments, for beam control along the x-direction, the periodicity of the columns along the x-direction is used (e.g., Figure 7 (A strip configuration). In some embodiments, for beam control along the y-direction, the periodicity of rows along the y-direction is used. In some embodiments, for beam control along both the x and y directions, the periodicity of columns along the x-direction and rows along the y-direction is used (e.g., Figure 8 (a cross-tiled configuration), and the periodicity of x and y can be different, even if they are in... Figure 8 The examples shown are the same.

[0062] exist Figure 9 In this configuration, the metasurface 700 in the third programming state 700C comprises all the unit cells 100 of the metasurface 700 that are adjusted to be in the transmission state 100C. This type of metasurface configuration can be referred to as a uniform configuration. Similar to the strip metasurface configuration, since all the unit cells 100 in a column are adjusted to the same state, in this embodiment, the transmission state 100C, each column of the metasurface 700 can use four (or three) control lines, and a total of 32 control lines can be used to adjust all the unit cells 100 of the metasurface 700 in the third programming state 700C.

[0063] Figures 7 to 9The configuration of metasurface 700 in the text is merely an example of possible programming configurations for the metasurface. Because the physical structure of metasurface 700 can remain the same, flexibility and freedom are possible in designing various programming states, for example, with different periods T. x The strip configuration and the different periods T x and / or T y The cross-tile structure, although the greater flexibility in the cross-tile structure will require more control lines. In some embodiments, T x and / or T y The metasurface can be changed once or multiple times throughout the entire metasurface structure; that is, the programming configuration of the metasurface may not be uniformly periodic along the entire x-direction and / or y-direction.

[0064] Figure 10 and Figure 11 They are shown respectively as follows Figure 7 and Figure 8 The simulated far-field scattering patterns of the metasurface 700, configured in different programming states, are shown.

[0065] Figure 10 As shown Figure 7 The diagram shows a simulated far-field scattering pattern of the metasurface 700 in its first programming state 700A. In some embodiments, the incident beam of the EM wave can be directed along the z-direction toward the metasurface 700 in its first programming state 700A. The metasurface 700 in its first programming state 700A can reflect, for example... Figure 10 The EM wave shown has multiple main beam directions 1010, each having a deflection angle relative to the incident beam.

[0066] Figure 11 As shown Figure 8 The diagram shows a simulated far-field scattering pattern of the metasurface 700 in its second programming state 700B. In some embodiments, the incident beam of the EM wave can be directed along the z-direction toward the metasurface 700 in its second programming state 700B. The metasurface 700 can reflect, for example... Figure 11 The EM wave shown has multiple main beam directions 1110, each having a deflection angle relative to the incident beam.

[0067] As in Figure 10 and Figure 11 It is obvious from the diagram that Figure 10 The deflection angle of the main beam direction 1010 and Figure 11 The deflection angles of the main beam direction 1110 are different. This difference in deflection angle may be due to changing the programming configuration of the metasurface 700 from the first programming state 700A to the second programming state 700B, i.e., from... Figure 7 The strip configuration in the middle is changed to Figure 8caused by the cross-tile configuration in FIG. 7. Thus, the metasurface 700 (and, in general, a metasurface composed of any number of unit cells 100) can be programmed to enable control of the reflected beam in a desired direction along both the x-direction and the y-direction.

[0068] In some embodiments, the deflection angle can be manipulated, and the resulting reflected beam can be controlled according to the following equation,

[0069] θ = sin -1 (λ / T),

[0070] where θ is the deflection angle, λ is the wavelength of the incident beam, and T is the period in either the x-direction or the y-direction.

[0071] Figure 12 A simulated transmission far-field scattering pattern of the metasurface 700 in the third programmed state 700C is shown as Figure 9 In some embodiments, an incident beam of EM waves can be directed along the z-direction toward the metasurface 700 in the third programmed state 700C. As Figure 12 indicated, the metasurface 700 can transmit the EM waves in the main beam direction 1210.

[0072] The above embodiments relate to tunable unit cells having VO2 as part of their structure and tunable metasurfaces comprising a plurality of tunable unit cells. The tunable metasurfaces allow for manipulation of EM radiation having terahertz wave frequencies in various ways without the need to change the physical structure of the metasurface. Further, the structure of the unit cells allows for simultaneous adjustment of multiple unit cells between the first reflective state, the second reflective state, and the transmission state using external stimuli.

[0073] As described above, Figure 1 and Figure 2The particular structure of the unit cell shown is merely an example. More generally, the top layer 103 can include a first top layer strip of phase change material (e.g., VO2) and a second top layer strip of phase change material (e.g., VO2) spaced apart from the first top layer strip, e.g., strip 104. Both the first top layer strip and the second top layer strip can include a first side (e.g., an inner side) and an opposite second side (e.g., an outer side). The first side of the first top layer strip can face the first side of the second top layer strip. The opposite second side of the first top layer strip can face away from the second top layer strip. The opposite second side of the second top layer strip can face away from the first top layer strip. Both the opposite second side of the first top layer strip and the opposite second side of the second top layer strip can each have a plurality of spaced apart VO2 protrusions, e.g., protrusions 106, protruding therefrom. The top layer 103 can also include a plurality of top layer metal strips, e.g., strips 108, spaced apart from one another, each of the plurality of top layer metal strips extending from the first side of the first top layer strip to the first side of the second top layer strip. The bottom layer 113 can include a first bottom layer strip of phase change material (e.g., VO2) and a second bottom layer strip of phase change material (e.g., VO2) spaced apart from the first bottom layer strip, e.g., strip 114. Both the first bottom layer strip and the second bottom layer strip can include a first side (e.g., an inner side) and an opposite second side (e.g., an outer side). The first side of the first bottom layer strip can face the first side of the second bottom layer strip, the opposite second side of the first bottom layer strip can face away from the second bottom layer strip, and the opposite second side of the second bottom layer strip can face away from the first bottom layer strip. The bottom layer 113 can also include a plurality of bottom layer strips of phase change material (e.g., VO2), e.g., strips 116, spaced apart from one another, each of the plurality of bottom layer strips extending from the first side of the first bottom layer strip to the first side of the second bottom layer strip. The bottom layer 113 can also include a plurality of bottom layer metal strips, e.g., strips 118, spaced apart from one another and interposed between the first side of the first bottom layer strip and the first side of the second bottom layer strip. Each of the plurality of bottom layer metal strips can also be spaced apart from the first bottom layer strip, the second bottom layer strip, and the plurality of bottom layer strips.

[0074] In some embodiments, both the first top layer strip, the second top layer strip, the first bottom layer strip, and the second bottom layer strip can extend substantially parallel to a same first axis (e.g., the y-axis). In some embodiments, both the plurality of top layer metal strips, the plurality of bottom layer strips of phase change material, and the plurality of bottom layer metal strips can extend substantially parallel to a same second axis (e.g., the x-axis). In some embodiments, the first axis and the second axis can be substantially perpendicular.

[0075] In some embodiments, each of the plurality of spaced-apart protrusions of phase change material protruding relative to the first top strip can be aligned with a respective one of the plurality of spaced-apart protrusions protruding relative to the second top strip, and can also be aligned with a respective one of the plurality of top metal strips. In some embodiments, the plurality of top metal strips can be equally spaced from each other, the plurality of bottom strips of phase change material can be equally spaced from each other, and the plurality of bottom metal strips can be equally spaced from each other.

[0076] In some embodiments, the first top strip, the second top strip, the first bottom strip, and the second bottom strip can each be in communication with an external stimulus device (e.g., an FPGA controller). In some embodiments, the unit cell can be configured by the external stimulus device to switch between a first reflective state (e.g., the first reflective state 100A), a second different reflective state (e.g., the second reflective state 100B), and a third transmissive state (e.g., the transmissive state 100C). In the first reflective state, the first top strip, the second top strip, the plurality of spaced-apart protrusions, the first bottom strip, the second bottom strip, and the plurality of bottom strips can be in a metallic state, i.e., an electrically conductive state. In the second reflective state, the first top strip, the second top strip, and the plurality of spaced-apart protrusions can be in an insulating state, and the first bottom strip, the second bottom strip, and the plurality of bottom strips can be in a metallic state. In the third transmissive state, the first top strip, the second top strip, the plurality of spaced-apart protrusions, the first bottom strip, the second bottom strip, and the plurality of bottom strips can be in an insulating state.

[0077] In some embodiments, the unit cell can be used to interact with electromagnetic radiation having a frequency between 100 gigahertz and 10 terahertz.

[0078] In some embodiments, the metasurface can have a repeating pattern (e.g., a lattice or grid) of unit cells, each unit cell having a structure as previously described. In some embodiments, for each unit cell: the first top strip, the second top strip, the first bottom strip, and the second bottom strip can each extend substantially parallel to a same first axis (e.g., the y-axis), and the plurality of top metal strips, the plurality of bottom strips, and the plurality of bottom metal strips can each extend substantially parallel to a same second axis (e.g., the x-axis); the first axis and the second axis can be substantially perpendicular; and the repeating pattern of unit cells can include at least one column of a plurality of unit cells having a direction of repetition along the first axis and at least one row of a plurality of unit cells having a direction of repetition along the second axis.

[0079] In some embodiments, for at least one column of the plurality of unit cells having a direction along the first axis (e.g., the y-axis) repeating: the first top layer strip of each unit cell in the at least one column can be connected with the first top layer strip of an adjacent unit cell in the at least one column; the second top layer strip of each unit cell in the at least one column can be connected with the second top layer strip of an adjacent unit cell in the at least one column; the first bottom layer strip of each unit cell in the at least one column can be connected with the first bottom layer strip of an adjacent unit cell in the at least one column; and the second bottom layer strip of each unit cell in the at least one column can be connected with the second bottom layer strip of an adjacent unit cell in the at least one column.

[0080] In some embodiments, each unit cell of the metasurface can be configured by an external stimulus device (e.g., an FPGA controller) to switch between the first reflective state, the second different reflective state, and the third transmissive state, as previously described.

[0081] In some embodiments, a period of unit cells along a direction of the first axis (e.g., the y-axis) can be defined as a number of consecutive unit cells appearing along the direction of the first axis all in a same one of the first reflective state or the second reflective state, and groups of consecutive unit cells along the direction of the first axis can alternate between the first reflective state and the second reflective state according to the period (e.g., T y ). In some embodiments, a period of unit cells along a direction of the second axis (e.g., the x-axis) can be defined as a number of consecutive unit cells appearing along the direction of the second axis all in a same one of the first reflective state or the second reflective state, and groups of consecutive unit cells along the direction of the second axis can alternate between the first reflective state and the second reflective state according to the period (e.g., T x ).

[0082] In some embodiments, for a given wavelength, different periods of unit cells along the direction of the first axis, different periods of unit cells along the direction of the second axis, and different periods of unit cells along the directions of the first and second axes can result in different beam reflection directions.

[0083] In some embodiments, the term “substantially parallel” is used herein, e.g., with reference to strips or bands being “substantially parallel” to an axis. In this context, the word “substantially” is used to indicate that it is intended for the strips or bands to be approximately parallel to the axis, but in practical implementations, there can not be perfect parallelism, e.g., there can be some variation and / or error, e.g., + / - 10%. When multiple strips or bands are referred to as being substantially parallel to the same axis, one, some, or all of the strips or bands can each be approximately parallel to the axis within, e.g., + / - 10% variation. The variation can be different for different strips and / or bands. The above explanation also applies when one or more strips and / or bands and / or protrusions are referred to as being “substantially parallel” to something (e.g., an edge of a unit cell) or “substantially parallel” to each other.

[0084] In some embodiments, the term "substantially perpendicular" is used herein, e.g., with reference to a first axis and a second axis (e.g., x-axis and y-axis) that are perpendicular to each other. In this context, the word "substantially" is used to indicate that it is intended for the two axes to be approximately perpendicular, but in a practical implementation they can not be perfectly perpendicular, e.g., there can be some variation and / or error, e.g., + / - 10%. The above applies when one or more strips and / or bands and / or protrusions are referred to as being "substantially perpendicular" to something (e.g., an edge of a cell) or "substantially perpendicular" to each other.

[0085] It is noted that the expression "at least one of A or B" as used herein is interchangeable with the expression "A and / or B". It refers to a list from which one can choose A, or B, or both A and B. Similarly, "at least one of A, B, or C" as used herein is interchangeable with "A and / or B and / or C" or "A, B, and / or C". It refers to a list from which one can choose: A, or B, or C, or A and B, or A and C, or B and C, or all A, B, and C. The same principle applies to longer lists of the same format.

[0086] While the application has been described with reference to particular features and embodiments, it will be understood that various modifications and combinations can be made to the application without departing from the scope of the application. Accordingly, the description and drawings are to be regarded as illustrative in nature and are not intended as limiting the scope of the application. Therefore, although the application and its benefits have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the application as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily understand, the application can be practiced with processes, machines, manufacture, compositions of matter, means, methods or steps that are different from those described in the specification. Accordingly, the appended claims are intended to include within their scope all processes, machines, manufacture, compositions of matter, means, methods or steps that are equivalent to those described in the specification. Accordingly, the appended claims are intended to include within their scope all processes, machines, manufacture, compositions of matter, means, methods or steps that are equivalent to those described in the specification.

[0087] Furthermore, any module, component, or device that executes the instructions executable in this document may include or otherwise access one or more non-transitory computer / processor-readable storage media for storing information, such as computer / processor-readable instructions, data structures, program modules, and / or other data. A non-exhaustive list of examples of non-transitory computer / processor-readable storage media includes magnetic tape cassettes, magnetic tape, disk storage or other magnetic storage devices, optical discs (e.g., compact disc read-only memory, CD-ROM), digital video discs or digital versatile discs (DVDs), and Blu-ray discs. TM This includes volatile and non-volatile, removable and non-removable media, random-access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory, or other memory technologies implemented in any method or technique. Any such non-transitory computer / processor storage medium can be part of a device or accessible or connected to that device. Any application or module described herein can be implemented using computer / processor-readable / executable instructions that can be stored or otherwise preserved by such non-transitory computer / processor-readable storage media.

Claims

1. A unit cell for metasurfaces or metamaterials, comprising: The substrate includes a top layer and a bottom layer, wherein the top layer has: A first top layer strip of vanadium dioxide and a second top layer strip of vanadium dioxide spaced apart from the first top layer strip of vanadium dioxide. Both the first and second top-layer vanadium dioxide strips include a first side and a corresponding second side. In this configuration, the first side of the first top layer strip faces the first side of the second top layer strip, the opposite second side of the first top layer strip faces away from the second top layer strip, and the opposite second side of the second top layer strip faces away from the first top layer strip. The opposite second side of the first top layer strip and the opposite second side of the second top layer strip each have a plurality of spaced vanadium dioxide protrusions that protrude relative to each other; A plurality of top metal strips spaced apart from each other, each of the plurality of top metal strips extending from a first side of a first top strip to a first side of a second top strip; The underlying layer is provided with: A first bottom layer strip of vanadium dioxide and a second bottom layer strip of vanadium dioxide spaced apart from the first bottom layer strip of vanadium dioxide. Both the first and second bottom vanadium dioxide strips include a first side and a corresponding second side. Wherein, the first side of the first bottom strip faces the first side of the second bottom strip, the opposite second side of the first bottom strip is away from the second bottom strip, and the opposite second side of the second bottom strip is away from the first bottom strip; A plurality of vanadium dioxide underlayer strips spaced apart from each other, each of the plurality of vanadium dioxide underlayer strips extending from the first side of the first vanadium dioxide underlayer strip to the first side of the second vanadium dioxide underlayer strip; A plurality of underlying metal strips, the plurality of underlying metal strips being spaced apart from each other and inserted between the first side of the first vanadium dioxide underlying strip and the first side of the second vanadium dioxide underlying strip, each of the plurality of underlying metal strips being spaced apart from the following: the first vanadium dioxide underlying strip, the second vanadium dioxide underlying strip and the plurality of vanadium dioxide underlying strips.

2. The unit cell according to claim 1, wherein, The first top vanadium dioxide strip, the second top vanadium dioxide strip, the first bottom vanadium dioxide strip, and the second bottom vanadium dioxide strip all extend substantially parallel to the same first axis, and the plurality of top metal strips, the plurality of bottom vanadium dioxide strips, and the plurality of bottom metal strips all extend substantially parallel to the same second axis.

3. The unit cell according to claim 2, wherein, The first axis and the second axis are substantially perpendicular.

4. The unit cell according to any one of claims 1 to 3, wherein, Each of the plurality of spaced-apart vanadium dioxide protrusions protruding relative to the first top layer strip of vanadium dioxide is aligned with a corresponding one of the plurality of spaced-apart vanadium dioxide protrusions protruding relative to the second top layer strip of vanadium dioxide, and is also aligned with a corresponding one of the plurality of top layer metal strips.

5. The unit cell according to any one of claims 1 to 4, wherein, The plurality of top-layer metal strips are equally spaced from each other, the plurality of vanadium dioxide bottom-layer strips are equally spaced from each other, and the plurality of bottom-layer metal strips are equally spaced from each other.

6. The unit cell according to any one of claims 1 to 5, wherein, The first top layer strip of vanadium dioxide and the corresponding second side of the second top layer strip of vanadium dioxide each have five spaced-apart vanadium dioxide protrusions that protrude relative to each other. The plurality of top-layer metal strips include five strips; The plurality of vanadium dioxide bottom strips include three strips; The plurality of underlying metal strips includes three strips.

7. The unit cell according to any one of claims 1 to 6, wherein, The first top vanadium dioxide strip, the second top vanadium dioxide strip, the first bottom vanadium dioxide strip, and the second bottom vanadium oxide strip are all connected to an external stimulation device.

8. The unit cell according to claim 7, wherein, The unit cell can be configured by the external stimulation device to switch between a first reflection state, different second reflection states, and a third transmission state, wherein: In the first reflective state, the first top vanadium dioxide strip, the second top vanadium dioxide strip, the plurality of spaced-apart vanadium dioxide protrusions, the first bottom vanadium dioxide strip, the second bottom vanadium dioxide strip, and the plurality of bottom vanadium dioxide strips are in a metallic state; In the second reflective state, the first top vanadium dioxide strip, the second top vanadium dioxide strip, and the plurality of spaced-apart vanadium dioxide protrusions are in an insulating state, while the first bottom vanadium dioxide strip, the second bottom vanadium dioxide strip, and the plurality of bottom vanadium dioxide strips are in a metallic state. In the third transmission state, the first top vanadium dioxide strip, the second top vanadium dioxide strip, the plurality of spaced-apart vanadium dioxide protrusions, the first bottom vanadium dioxide strip, the second bottom vanadium dioxide strip, and the plurality of bottom vanadium dioxide strips are in the insulating state.

9. The unit cell according to claim 8, wherein, For a given wavelength, the phase difference between the first electromagnetic radiation wave reflected by the cell in the first reflection state and the second electromagnetic radiation wave reflected by the cell in the second reflection state is essentially pi.

10. The unit cell according to any one of claims 1 to 9, wherein, The unit cell is used to interact with electromagnetic radiation with frequencies between 100 GHz and 10 terahertz.

11. The unit cell according to any one of claims 1 to 10, wherein, The plurality of top-layer metal strips and the plurality of bottom-layer metal strips comprise gold.

12. The unit cell according to any one of claims 1 to 11, wherein, The substrate comprises polyimide.

13. A metasurface having a repeating pattern of unit cells, each unit cell comprising: The substrate includes a top layer and a bottom layer, wherein the top layer has: A first top layer strip of vanadium dioxide and a second top layer strip of vanadium dioxide spaced apart from the first top layer strip of vanadium dioxide. Both the first and second top-layer vanadium dioxide strips include a first side and a corresponding second side. In this configuration, the first side of the first top layer strip faces the first side of the second top layer strip, the opposite second side of the first top layer strip faces away from the second top layer strip, and the opposite second side of the second top layer strip faces away from the first top layer strip. The opposite second side of the first top layer strip and the opposite second side of the second top layer strip each have a plurality of spaced vanadium dioxide protrusions that protrude relative to each other; A plurality of top metal strips spaced apart from each other, each of the plurality of top metal strips extending from a first side of a first top strip to a first side of a second top strip; The underlying layer is provided with: A first bottom layer strip of vanadium dioxide and a second bottom layer strip of vanadium dioxide spaced apart from the first bottom layer strip of vanadium dioxide. Both the first and second bottom vanadium dioxide strips include a first side and a corresponding second side. Wherein, the first side of the first bottom strip faces the first side of the second bottom strip, the opposite second side of the first bottom strip is away from the second bottom strip, and the opposite second side of the second bottom strip is away from the first bottom strip; A plurality of vanadium dioxide underlayer strips spaced apart from each other, each of the plurality of vanadium dioxide underlayer strips extending from the first side of the first vanadium dioxide underlayer strip to the first side of the second vanadium dioxide underlayer strip; A plurality of underlying metal strips, the plurality of underlying metal strips being spaced apart from each other and inserted between the first side of the first vanadium dioxide underlying strip and the first side of the second vanadium dioxide underlying strip, each of the plurality of underlying metal strips being spaced apart from the following: the first vanadium dioxide underlying strip, the second vanadium dioxide underlying strip and the plurality of vanadium dioxide underlying strips.

14. The metasurface according to claim 13, wherein, For each unit cell: The first top vanadium dioxide strip, the second top vanadium dioxide strip, the first bottom vanadium dioxide strip, and the second bottom vanadium dioxide strip all extend substantially parallel to the same first axis, and the plurality of top metal strips, the plurality of bottom vanadium dioxide strips, and the plurality of bottom metal strips all extend substantially parallel to the same second axis. The first axis and the second axis are substantially perpendicular; The repeating pattern of the unit cells includes at least one column having a plurality of unit cells repeating along the first axis and at least one row having a plurality of unit cells repeating along the second axis.

15. The metasurface according to claim 14, wherein, For at least one column having multiple unit cells repeating along the first axis: The first top layer strip of vanadium dioxide in each unit cell of the at least one column is connected to the first top layer strip of vanadium dioxide in the adjacent unit cells of the at least one column; The second top layer strip of vanadium dioxide in each unit cell of the at least one column is connected to the second top layer strip of vanadium dioxide in the adjacent unit cells of the at least one column; The first vanadium dioxide bottom layer strip of each unit cell in the at least one column is connected to the first vanadium dioxide bottom layer strip of the adjacent unit cells in the at least one column; The second bottom layer strip of vanadium dioxide in each unit cell of the at least one column is connected to the second bottom layer strip of vanadium dioxide in the adjacent unit cells of the at least one column.

16. The metasurface according to any one of claims 13 to 15, wherein, Each unit cell can be configured by an external stimulation device to switch between a first reflection state, different second reflection states, and a third transmission state, wherein: In the first reflective state, the first top vanadium dioxide strip, the second top vanadium dioxide strip, the plurality of spaced-apart vanadium dioxide protrusions, the first bottom vanadium dioxide strip, the second bottom vanadium dioxide strip, and the plurality of bottom vanadium dioxide strips are in a metallic state; In the second reflective state, the first top vanadium dioxide strip, the second top vanadium dioxide strip, and the plurality of spaced-apart vanadium dioxide protrusions are in an insulating state, while the first bottom vanadium dioxide strip, the second bottom vanadium dioxide strip, and the plurality of bottom vanadium dioxide strips are in a metallic state. In the third transmission state, the first top vanadium dioxide strip, the second top vanadium dioxide strip, the plurality of spaced-apart vanadium dioxide protrusions, the first bottom vanadium dioxide strip, the second bottom vanadium dioxide strip, and the plurality of bottom vanadium dioxide strips are in the insulating state.

17. The metasurface according to claim 16, wherein, The period of a unit cell along the first axis is defined as the number of consecutive unit cells that are in the same state, either the first reflection state or the second reflection state, appearing along the first axis. Each group of consecutive unit cells along the first axis alternates between the first reflection state and the second reflection state according to the period.

18. The metasurface according to claim 16 or 17, wherein, The period of a unit cell along the second axis is defined as the number of consecutive unit cells that are in the same state, either the first reflection state or the second reflection state, appearing along the second axis. Each group of consecutive unit cells along the second axis alternates between the first reflection state and the second reflection state according to the period.

19. The metasurface according to claim 17 or 18, wherein, The metasurface can be configured by the external stimulation device to change the period of the unit cells along the first axis by changing the number of consecutive unit cells in the same state, which are in either the first or the second reflection state, appearing along the first axis.

20. The metasurface according to claim 18 or 19, wherein, The metasurface can be configured by the external stimulation device to change the period of the unit cells along the second axis by changing the number of consecutive unit cells in the same state, which are in either the first or the second reflection state, appearing along the second axis.

21. The metasurface according to claim 20, wherein, For a given wavelength, different periods of the cell along the first axis, different periods of the cell along the second axis, and different periods of the cell along both the first and second axes result in different beam reflection directions.

22. The metasurface according to any one of claims 13 to 21, wherein, For each unit cell: Each of the plurality of spaced-apart vanadium dioxide protrusions protruding relative to the first top layer strip of vanadium dioxide is aligned with a corresponding one of the plurality of spaced-apart vanadium dioxide protrusions protruding relative to the second top layer strip of vanadium dioxide, and is also aligned with a corresponding one of the plurality of top layer metal strips.

23. The metasurface according to any one of claims 13 to 22, wherein, For each unit cell: The plurality of top-layer metal strips are equally spaced from each other, the plurality of vanadium dioxide bottom-layer strips are equally spaced from each other, and the plurality of bottom-layer metal strips are equally spaced from each other.

24. The metasurface according to any one of claims 13 to 23, wherein, For each unit cell: The first top layer strip of vanadium dioxide and the corresponding second side of the second top layer strip of vanadium dioxide each have five spaced-apart vanadium dioxide protrusions that protrude relative to each other. The plurality of top-layer metal strips include five strips; The plurality of vanadium dioxide bottom strips include three strips; The plurality of underlying metal strips includes three strips.

25. The metasurface according to any one of claims 16 to 24, wherein, For a given wavelength, the phase difference between the first electromagnetic radiation wave reflected by the cell in the first reflection state and the second electromagnetic radiation wave reflected by the cell in the second reflection state is essentially pi.

26. The metasurface according to any one of claims 13 to 25, wherein, The metasurface is used to interact with electromagnetic radiation with frequencies between 100 GHz and 10 terahertz.

27. The metasurface according to any one of claims 13 to 26, wherein, For each unit cell: The plurality of top-layer metal strips and the plurality of bottom-layer metal strips comprise gold.

28. The metasurface according to any one of claims 13 to 27, wherein, The substrate comprises polyimide.

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