Transmission type multifunctional nonreciprocal unit structure metasurface

Abstract

The invention discloses a transmission type multifunctional non-reciprocal unit structure metasurface which comprises a plurality of unit structures, the unit structures are arranged from left to right in the-z direction, each unit structure comprises metal layers and dielectric layers, the metal layers and the dielectric layers are alternately arranged at intervals, every two adjacent metal layers at intervals comprise orthogonally-prevented open square rings, and the open square rings are connected with the metal layers at intervals. Wherein the phase change material is embedded into one of the open square rings. According to the transmission type multifunctional non-reciprocal unit structure metasurface, non-reciprocal regulation and control of electromagnetic waves can be achieved through a simple structural design without an external magnetic field, the metasurface can perform different control effects on the electromagnetic waves which are incident in different directions and are in different polarization states, and the metasurface is high in practicability. The material has multiple functions of polarization conversion, wave absorption and the like, and the performance of the material can be dynamically regulated and controlled without depending on an external magnetic field.

Description

Technical Field

[0001] The present invention relates to the technical field of electromagnetic metasurfaces, and in particular to a transmission-type multifunctional non-reciprocal unit structure metasurface. Background Art

[0002] In recent years, metasurface technology has made significant progress in electromagnetic wave manipulation. By precisely designing the geometry and arrangement of microstructure units, metasurfaces can effectively control the polarization, amplitude, phase and resonance of electromagnetic waves on a subwavelength scale. These unique capabilities of metasurfaces have made them widely used in many fields such as optics, wireless communications, radar, and sensors. According to the Lorentz reciprocity principle, in a system with symmetrical dielectric constant and permeability tensors, time-invariant and linear properties, exchanging the positions of the source and detector will not change the electromagnetic field generated by the source at its original position. Therefore, most metasurfaces usually exhibit reciprocal properties: regardless of the direction of the incident wave, the transmission and reflection characteristics remain unchanged. However, in practical applications such as imaging, communication, and sensing, breaking reciprocity has become the key to solving many problems. For example, breaking reciprocity can effectively avoid boundary backscattering, reduce signal loss, and improve system performance and reliability. Therefore, the study of non-reciprocal metasurfaces is of great significance for expanding their applications in high-end communications, stealth technology, nonlinear optics, and other fields.

[0003] Although non-reciprocal metasurfaces have made significant progress in recent years, they still face some technical challenges and have certain functional limitations. For example, some non-reciprocal metasurfaces require an external magnetic field to break the symmetry, which limits their application in compact devices; others require high-intensity incident waves to achieve the non-reciprocal effect, which limits their applicability in practical environments. In addition, problems such as poor integration and high power consumption have also restricted the further development and application of non-reciprocal metasurfaces to a certain extent. Summary of the invention

[0004] In view of the above-mentioned defects of the prior art, the technical problem to be solved by the present invention is that the existing non-reciprocal metasurfaces have complex structures and single functions, and usually require an external magnetic field or high-intensity incident waves to play their role. Moreover, these structures are complex and difficult to meet the requirements of structural indirectness and versatility in practical applications. The present invention provides a transmission-type multifunctional non-reciprocal unit structure metasurface, which can achieve non-reciprocal regulation of electromagnetic waves through a simple structural design without an external magnetic field. The metasurface can perform different control effects on electromagnetic waves of different polarization states incident from different directions, has multiple functions such as polarization conversion and wave absorption, and can dynamically regulate its performance without relying on an external magnetic field.

[0005] To achieve the above-mentioned purpose, the present invention provides a transmission-type multifunctional non-reciprocal unit structure metasurface, comprising a plurality of unit structures arranged periodically, the unit structures being arranged from left to right along the -z direction, the unit structures comprising a metal layer and a dielectric layer, wherein the metal layer and the dielectric layer are arranged alternately at intervals, wherein two adjacent metal layers at intervals comprise orthogonally prevented open square rings, and a grating, and another metal layer is configured to be embedded with a phase change material.

[0006] Furthermore, the unit structure includes 7 layers, of which 4 are metal layers and 3 are dielectric layers.

[0007] Furthermore, the first, third, fifth and seventh layers of the unit structure are metal layers, and the second, fourth and sixth layers are dielectric layers; wherein the first and third layers are orthogonally placed open square rings, the fifth layer is a grating structure, the seventh layer is a double open split ring resonator, and the open square ring in the seventh layer is embedded with phase change material vanadium dioxide.

[0008] Furthermore, the metal material of the first layer, the third layer, the fifth layer and the seventh layer is set to copper, the conductivity is 5.9×10 7 S / m, and the thickness of the metal layer is 0.2 μm.

[0009] Furthermore, the dielectric material of the second layer, the fourth layer and the sixth layer is polyimide, the dielectric constant is 3.5, the thickness of the second layer and the fourth layer is 25 μm, and the thickness of the sixth layer is 35 μm.

[0010] Furthermore, the unit structure is a square, and a unit size p of the unit structure is 100 μm.

[0011] Furthermore, the side length a of the open square ring is 90 μm, the width b of the square ring is 15 μm, and the opening width k is 14 μm.

[0012] Further, the first layer, the second layer, and the third layer form a polarization conversion portion.

[0013] Furthermore, in the grating structure of the fifth layer, the grating width e is 18 μm, and the gap width is 2 μm.

[0014] Furthermore, the double open split ring resonator of the seventh layer is composed of an asymmetric open square ring, the side length c of the asymmetric open square ring is 60μm, the width w is 8μm, the opening width w1 is 5μm, and the other opening part is embedded with vanadium dioxide, wherein the width of the vanadium dioxide is w2 which is 7μm.

[0015] Technical Effects

[0016] The present invention provides a transmission-type multifunctional non-reciprocal unit structure metasurface, which comprises a seven-layer structure and can realize non-reciprocal regulation of electromagnetic waves through a simple design. The metasurface has the advantages of simple structure and easy manufacture, and can realize non-reciprocal regulation without an external magnetic field, which fully meets the requirements of modern communication and sensor technology for efficient and flexible electromagnetic wave control. It has broad application prospects in the fields of duplex communication, non-reciprocal antenna covers and sensors, and can provide a more effective and convenient solution for the regulation of electromagnetic waves.

[0017] The present invention provides a transmission-type multifunctional non-reciprocal unit structure metasurface, which adopts a combination of three functional modules: polarization conversion, grating, and wave absorption. The polarization conversion module is composed of orthogonally placed open square rings and dielectric layers, which can effectively control electromagnetic waves of different polarization states incident from different directions. The wave absorption module is composed of an open square ring and an embedded vanadium dioxide material, and the phase change state of vanadium dioxide can dynamically adjust the wave absorption frequency. In the 0.78-0.98THz frequency band, the metasurface can convert the y-polarized wave incident along the -z direction into the x-polarized wave, and the polarization conversion ratio (PCR) is almost close to 1, and a 97.8% wave absorption effect is achieved in the 1.752THz frequency band. For y-polarized waves incident along the +z direction, when vanadium dioxide is in the metallic state, it achieves a 95.6% absorption effect in the 1.859THz frequency band, while in the dielectric state, it achieves 99.9% and 97.6% absorption effects in the 0.963THz and 1.869THz frequency bands, respectively. In addition, x-polarized waves incident along the +z direction can also achieve polarization conversion in the 0.78-0.98THz frequency band, converting to y-polarized waves.

[0018] The concept, specific structure and technical effects of the present invention will be further described below in conjunction with the accompanying drawings to fully understand the purpose, characteristics and effects of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a structural schematic diagram of a transmission-type multifunctional non-reciprocal unit structure metasurface according to a preferred embodiment of the present invention;

[0020] FIG2( a ) is a transmission coefficient diagram of a transmission-type multifunctional non-reciprocal unit structure metasurface when incident along the -z direction according to a preferred embodiment of the present invention;

[0021] FIG2( b ) is a transmission coefficient diagram of a transmission-type multifunctional non-reciprocal unit structure metasurface when incident along the +z direction according to a preferred embodiment of the present invention;

[0022] FIG3( a ) is a reflection coefficient diagram of a transmission-type multifunctional non-reciprocal unit structure metasurface when incident along the -z direction according to a preferred embodiment of the present invention;

[0023] FIG3( b ) is a reflection coefficient diagram of a transmission-type multifunctional non-reciprocal unit structure metasurface when incident along the +z direction according to a preferred embodiment of the present invention;

[0024] Figure 4 It is a polarization conversion rate (PCR) of a transmission-type multifunctional non-reciprocal unit structure metasurface of a preferred embodiment of the present invention for a y-polarized wave incident along the -z direction and an x-polarized wave incident along the +z direction.

[0025] Figure 5 It is a schematic diagram of the polarization states of an incident electromagnetic wave and an outgoing electromagnetic wave when a transmission-type multifunctional non-reciprocal unit structure metasurface of a preferred embodiment of the present invention is incident along the -z direction;

[0026] FIG6( a ) is a graph showing the variation of the wave absorption rate of a transmission-type multifunctional non-reciprocal unit structure metasurface in different vanadium dioxide states when a y-polarized wave is incident along the -z direction according to a preferred embodiment of the present invention;

[0027] Figure 6(b) is a graph showing the variation of the wave absorption rate of a transmission-type multifunctional non-reciprocal unit structure metasurface in different vanadium dioxide states when a y-polarized wave is incident along the +z direction according to a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0028] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0029] In the following description, specific details such as specific internal procedures and techniques are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present invention. However, it should be clear to those skilled in the art that the present invention may be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present invention.

[0030] like Figure 1 As shown, an embodiment of the present invention provides a transmission-type multifunctional non-reciprocal unit structure metasurface, including a plurality of unit structures, the unit structure is square, and the unit size p of the unit structure is 100μm. The unit structure is arranged from left to right along the -z direction, and the unit structure includes a metal layer and a dielectric layer, wherein the metal layer and the dielectric layer are alternately arranged, wherein two adjacent metal layers include orthogonally prevented open square rings, and the other metal layer is configured to embed a phase change material.

[0031] In the embodiment of the present invention, the unit structure includes 7 layers, of which 4 are metal layers and 3 are dielectric layers; in the unit structure arranged from left to right along the -z direction, the first, third, fifth and seventh layers are metal layers, and the second, fourth and sixth layers are dielectric layers; wherein the first and third layers are orthogonally placed open square rings, the fifth layer is a grating structure, and the seventh layer is a double open split ring resonator, and the open square ring in the seventh layer is embedded with phase change material vanadium dioxide. The first, second and third layers form a polarization conversion part; the side length a of the open square rings of the first and third layers is 90μm, the width b of the square ring is 15μm, and the opening width k is 14μm.

[0032] Among them, the metal material of the first, third, fifth and seventh layers is set to copper, with a conductivity of 5.9×107S / m, and the thickness of the metal layer is 0.2μm. The dielectric material of the second, fourth and sixth layers is polyimide, with a dielectric constant of 3.5, the thickness of the second and fourth layers is 25μm, and the thickness of the sixth layer is 35μm. In the grating structure of the fifth layer, the grating width e is 18μm and the gap width is 2μm. The double open split ring resonator of the seventh layer is composed of an asymmetric open square ring, the side length c of the asymmetric open square ring is 60μm, the width w is 8μm, the opening width w1 is 5μm, and the other opening part is embedded with vanadium dioxide, where the width of vanadium dioxide is w2 is 7μm. By changing the conductivity of the vanadium dioxide in the seventh layer, the change of vanadium dioxide in the conductor state and the dielectric state can be realized to realize the switching function of the wave absorption frequency.

[0033] The vanadium dioxide material in the terahertz band can be described by the Drude model, and its dielectric constant ε(ω) is expressed as:

[0034]

[0035] where ε ∞ =9,ω p =1.40×10 15 S -1 ,ω d =5.75×10 13 S -1 ,σ0=3×10 5 S / m.

[0036] When the conductivity is σ=10S / m, vanadium dioxide is in the dielectric state. When σ=2×10 5 S / m, vanadium dioxide is in a conductive state.

[0037] In the embodiment of the present invention, a polarization converter, a sub-wavelength grating, and an absorber are combined together, and the selective transmission of the grating is used to achieve the directional polarization conversion performance of the metasurface. The following will take the transmission performance using the Jones matrix as an example for analysis. The incident wave is represented as a column vector, and the matrix is ​​applied from the left. The Jones matrix of the ideal polarization converter (PC) is represented as:

[0038]

[0039] Here -z and +z represent that the electromagnetic wave is incident along the -z direction or the +z direction. The Jones matrix of the ideal grating structure (SWG) is:

[0040]

[0041] Therefore, the Jones matrix of the metasurface can be obtained by multiplying the Jones matrices of the polarization converter and the grating:

[0042]

[0043] At this time, the relationship between the incident wave and the transmitted wave is:

[0044]

[0045] It can be seen from the above formula that when the y-polarized wave is incident on the metasurface along the -z direction, the y-polarized wave is completely converted into the x-polarized wave and emitted. On the contrary, when the x-polarized wave is incident along the -z direction, the transmittance is 0. Similarly, when the x-polarized waves propagate along the +z direction, they are converted into y-polarized waves and propagate out, while the y-polarized waves cannot pass through the metasurface.

[0046] The embodiment of the present invention uses CST Microwave Studio for simulation, adopts the frequency domain finite element method, uses periodic boundary conditions along the x-axis and y-axis to simulate the infinite periodic array, and uses open boundary conditions along the z-axis. Through these settings, we obtain the S parameters of the metasurface.

[0047] Performance Test Results

[0048] like Figure 2a The figure shows the transmission coefficient diagram of the metasurface of the present invention when incident along the -z direction. The dotted line is the curve of vanadium dioxide in the dielectric state, and the solid line is the curve of vanadium dioxide in the metallic state. When the y-polarized wave is incident, it can be seen that the cross-polarization curve is greater than 0.7 in the 0.78-0.98THz band, and the co-polarization remains at 0, which indicates that the y-polarized wave incident along the -z direction is well converted into the x-polarized wave.

[0049] like Figure 2bThe figure shows the transmission coefficient diagram of the metasurface of the present invention when incident along the +z direction. The dotted line is the curve of vanadium dioxide in the dielectric state, and the actual line is the curve of vanadium dioxide in the metallic state. When the x-polarized wave is incident along the +z direction, it can be seen that the cross-polarization curve is greater than 0.7 in the 0.78-0.98THz band, and the co-polarization is less than 0.2, which indicates that the x-polarized wave incident along the +z direction is converted into a y-polarized wave.

[0050] like Figure 3a The figure shows the reflection coefficient of the metasurface of the present invention when incident along the -z direction, wherein the dotted line is the curve of vanadium dioxide in the dielectric state, and the solid line is the curve of vanadium dioxide in the metallic state.

[0051] like Figure 3b The figure shows the reflection coefficient of the metasurface of the present invention when incident along the +z direction, wherein the dotted line is the curve of vanadium dioxide in the dielectric state, and the solid line is the curve of vanadium dioxide in the metallic state.

[0052] like Figure 4 Shown is the polarization conversion rate (PCR) of the polarization conversion of the y-polarized wave incident along the -z direction and the x-polarized wave incident along the +z direction of the present invention. It can be seen that the PCR is greater than 0.9 in the corresponding frequency band, indicating that the metasurface has completed the polarization conversion very well.

[0053] like Figure 5 The figure shows the polarization states of the incident electromagnetic wave and the outgoing electromagnetic wave along the -z direction of the present invention. It can be seen that for the incident electromagnetic wave, as long as it contains the y-polarized wave component, it is converted into the x-polarized wave, and the larger the y component is, the more parts are converted.

[0054] like Figure 6a Shown is the absorption rate of the y-polarized wave incident along the -z direction and its corresponding Q value of the metasurface, where the Q value represents the frequency selection characteristic of the absorption frequency point. The higher the Q value, the better the selection characteristic. It can be seen that for the y-polarized wave incident along the -z direction, the absorption rate of the metasurface at 1.752 THz is 97.8%, and the Q value reaches 159.2. In addition, the state of the vanadium dioxide on the back side has no effect on its absorption rate.

[0055] like Figure 6b The figure shows the absorption rate of the y-polarized wave incident along the +z direction and its corresponding Q value. For the incident y-polarized wave, when vanadium dioxide is in different states, the metasurface can switch from single-frequency absorption to dual-frequency absorption. When vanadium dioxide is in a metallic state, the absorption rate is 95.6% at 1.859 THz and the Q value is 154.9. When vanadium dioxide is in a dielectric state, the absorption rate of the metasurface at 0.963 and 1.869 THz is 99.9% and 97.6%, respectively, and the corresponding Q values ​​are 66.3 and 196.7, respectively.

[0056] In summary, the transmissive multifunctional non-reciprocal unit structure metasurface of the present invention has the following beneficial effects:

[0057] By combining the polarization conversion part, the grating part, and the wave absorbing part, the metasurface provided by the embodiment of the present invention exhibits different control effects on positively and negatively incident polarized waves, and effectively realizes non-reciprocal transmission through a simple structure without the need for an additional magnetic field.

[0058] The metasurface provided by the present invention converts the y-polarized wave incident along the -z direction into an x-polarized wave in the 0.78-0.98THz band. And the wave absorption rate is 97.8% at 1.71.752THz. For the x-polarized wave incident along the +z direction, it is converted into a y-polarized wave in the 0.78-0.98THz band. For the y-polarized wave incident along the +z direction, as the state of vanadium dioxide changes, different wave absorption effects are achieved at different frequencies. Specifically, when vanadium dioxide is in a metallic state, the wave absorption rate is 95.6% at 1.859THz. When vanadium dioxide is in a dielectric state, the wave absorption rates of the metasurface at 0.963 and 1.869THz are 99.9% and 97.6%, respectively.

[0059] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A transmissive multifunctional non-reciprocal unit structure metasurface, characterized in that: It includes a plurality of unit structures arranged periodically, wherein the unit structures are arranged from left to right along the -z direction, and the unit structures include a metal layer and a dielectric layer, wherein the metal layer and the dielectric layer are arranged alternately at intervals, wherein two adjacent metal layers include orthogonally placed open square rings and a grating, and another metal layer is configured to embed a phase change material.

2. A transmissive multifunctional non-reciprocal unit structure metasurface as claimed in claim 1, characterized in that: The unit structure includes 7 layers, of which 4 are metal layers and 3 are dielectric layers.

3. A transmissive multifunctional non-reciprocal unit structure metasurface as claimed in claim 2, characterized in that: The first, third, fifth and seventh layers of the unit structure are metal layers, and the second, fourth and sixth layers are dielectric layers; wherein the first and third layers are orthogonally placed open square rings, the fifth layer is a grating structure, and the seventh layer is a double open split ring resonator, and the open square ring in the seventh layer is embedded with phase change material vanadium dioxide.

4. A transmissive multifunctional non-reciprocal unit structure metasurface as claimed in claim 3, characterized in that: The metal material of the first layer, the third layer, the fifth layer and the seventh layer is set to copper, and the conductivity is 5.9×10 7 S / m, the thickness of the metal layer is 0.2μm.

5. The transmissive multifunctional non-reciprocal unit structure metasurface according to claim 3, characterized in that: The dielectric material of the second layer, the fourth layer and the sixth layer is polyimide, and the dielectric constant is 3.

5. The thickness of the second layer and the fourth layer is 25 μm, and the thickness of the sixth layer is 35 μm.

6. The transmissive multifunctional non-reciprocal unit structure metasurface according to claim 1, characterized in that: The unit structure is a square, and a unit size p of the unit structure is 100 μm.

7. The transmissive multifunctional non-reciprocal unit structure metasurface according to claim 3, characterized in that: The side length a of the open square ring is 90 μm, the width b of the square ring is 15 μm, and the opening width k is 14 μm.

8. The transmissive multifunctional non-reciprocal unit structure metasurface according to claim 7, characterized in that: The first layer, the second layer, and the third layer form a polarization conversion portion.

9. The transmissive multifunctional non-reciprocal unit structure metasurface according to claim 3, characterized in that: In the grating structure of the fifth layer, the grating width e is 18 μm and the gap width is 2 μm.

10. The transmissive multifunctional non-reciprocal unit structure metasurface according to claim 3, characterized in that: The double open split ring resonator of the seventh layer is composed of an asymmetric open square ring, the side length c of the asymmetric open square ring is 60μm, the width w is 8μm, the opening width w1 is 5μm, and the other opening part is embedded with vanadium dioxide, wherein the width of vanadium dioxide is w2 which is 7μm.

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