Method for realizing acoustic vortex tunneling transmission on metasurface based on topology

Abstract

The invention provides an acoustic vortex tunneling transmission method based on topology pairing metasurfaces, and the method comprises the steps: respectively arranging an absorption type metasurface and an emission type metasurface which have opposite topological charges at an inlet and an outlet of a tunneling channel, forming a pair of topology pair TPMs structures, and forming a vortex tunneling system together with a sub-wavelength channel; mode conversion between vortex waves and plane waves is achieved through multi-period fan-shaped grooves etched in the angular direction and the radial direction, and the transmission efficiency is enhanced through Fabry-Perot resonance in a sub-wavelength channel. When the length of the tunneling channel meets specific conditions, periodical adjustment of transmissivity and perfect tunneling can be achieved, and the tunneling structure has high OAM mode coupling and transmission efficiency while guaranteeing the compact structure and low material cost. The metasurface designed by the invention supports diversified acoustic vortex tunneling transmission along a straight line and a curve, and shows excellent flexibility and stability.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of acoustic wave regulation, and particularly relates to a method for realizing acoustic vortex tunneling transmission based on topological super surface. BACKGROUND

[0002] With the progress of science and technology, the performance of materials required for high-end device manufacturing gradually improves, and natural materials have been unable to meet the development of society. Super materials have emerged as the times require, which usually refer to artificial structures with physical properties different from natural materials. In the field of acoustics, the proposal of acoustic metamaterials has broadened the scope of acoustic research and enriched people's manipulation and application of sound waves. However, due to the need for periodic arrangement of artificial cells for conventional metamaterials to realize their functions, the disadvantages such as large volume and large loss cannot be ignored, and it is particularly important to make the material light and thin. Therefore, the concept of super surface is proposed, which is described as a sub-wavelength acoustic manipulator and can be regarded as a two-dimensional counterpart of metamaterials. In recent years, research in the field of acoustic super surface has made great progress.

[0003] On the other hand, efficient tunneling of matter or energy is a research topic with far-reaching significance, covering multiple physical fields from quantum mechanics to astrophysics. In classical wave systems, the regulation of light or acoustic wave tunneling through narrow environments has attracted widespread attention and has given rise to a series of potential applications such as mode filtering, energy harvesting, emission enhancement, nonlinear sensing and wavefront control. In order to realize wave tunneling effect, many different strategies such as super coupling and evanescent wave resonance have been proposed and studied. However, the above methods still face many challenges, including large volume, inherent loss and narrow bandwidth. In addition, although these tunneling mechanisms can effectively solve the impedance mismatch problem through sub-wavelength channels, they are mainly suitable for simple plane waves, and still face great obstacles when applied to complex wave fields with higher degrees of freedom, such as orbital angular momentum (OAM) wave field.

[0004] OAM mode is a vortex field with a helical wave front and a phase singularity. Unlike spin angular momentum with only two discrete states, the eigenstate carrying OAM has infinitely many. These unique properties significantly broaden the scope of classical wave research and open up new avenues in fundamental physics and advanced applications, including optical tweezers, microscopic imaging, and high-capacity communication. In practical scenarios, vortex fields inevitably suffer scattering and obstruction from environmental particles and large obstacles during propagation, which can cause problems such as mode crosstalk and efficiency reduction, thus weakening the application of OAM-based technology. Therefore, achieving stable transmission of vortex signals in a narrow space and accurately manipulating the propagation path are the key to overcoming these limitations, thereby enhancing the practical application ability of OAM-based technology in complex scattering environments. In view of the above problems, it is necessary to realize OAM tunneling in acoustics and design an acoustic vortex tunneling method based on this. SUMMARY

[0005] The application provides a method for realizing acoustic vortex tunneling transmission based on topological pair metasurfaces, an absorbing metasurface and a transmitting metasurface are respectively constructed at the entrance and exit of the tunneling channel, and the whole composed of the two metasurfaces and the subwavelength channel is called a topological pair TPM.

[0006] The application provides a method for realizing acoustic vortex tunneling transmission based on topological pair metasurfaces, an absorbing metasurface and a transmitting metasurface are respectively constructed at the entrance and exit of the tunneling channel, and the whole composed of the two metasurfaces and the subwavelength channel is called a topological pair TPM.

[0007] (1) The tunneling channel radius R0 satisfies R0 < λ, and λ is the working wavelength, that is, the tunneling channel is a subwavelength channel;

[0008] (2) An absorbing metasurface and a transmitting metasurface are respectively constructed at the entrance and exit of the tunneling channel, and the whole composed of the two metasurfaces and the subwavelength channel is called a topological pair TPM;

[0009] (3) The radius of the large cylindrical waveguide connected with the two metasurfaces is R > R0, and the large cylindrical waveguide is used as the incident end and the emitting end, respectively;

[0010] (4) The two metasurfaces are respectively etched with m and n sector cells in an angular direction and a radial direction in a period, each sector cell contains a sector groove and a hard boundary; the sector groove has q periods in the angular direction, and there are q*n*m sector grooves on the end faces of the incident end and the emitting end, and the center of the end face is connected with a small pipeline with a radius of R0;

[0011] (5) The groove structures of the absorbing and emitting topological pair of metasurfaces are arranged in the opposite direction and position, but the same size and shape, so that the two metasurfaces carry opposite topological charges, -q and +q respectively, and the topological charge of the whole topological pair is zero;

[0012] (6) The groove structure design and the topological charge carried on the end face make the conversion of vortex waves in the large waveguide and planar waves in the central subwavelength channel, and the depth d of different sector grooves is controlled ij so that the absorbing surface converts the q-order vortex wave incident in the large waveguide into a planar wave and is absorbed into the small waveguide;

[0013] (7) Considering the wave entering the subwavelength channel as the wave source of the emitting metasurface, the emitting metasurface plays the role of the inverse process of absorption, i.e. converting the planar wave in the subwavelength channel into a vortex wave and propagating it to the large waveguide, and the transmission T of the corresponding vortex mode at the exit port is greater than zero, indicating that the acoustic vortex wave can realize tunneling through the subwavelength channel.

[0014] Further, the angular thickness of each sector cell is and the radial thickness is Further, the sector groove has an angular thickness of Δθ ' and a radial thickness of ΔR ' , and the depth of each sector groove is d ij , and i and j represent the angular and radial serial numbers respectively.

[0015] Further, the angular and radial intervals between the sector grooves are fixed values, w θ = Δθ - Δθ', and w R = ΔR - ΔR'.

[0016] Further, the thickness of the sector region of the two metasurfaces is not greater than 0.5λ, and the total length of the central subwavelength channel is L > λ, so that the total length of the subwavelength channel is greater than the total thickness of the two parts of the metasurface, ensuring that the two parts of the metasurface region do not overlap.

[0017] Further, the material of the sector cell wall and the subwavelength channel wall is an acoustic hard material that cannot be penetrated by acoustic waves.

[0018] Further, the length L of the subwavelength channel satisfies the Fabry-Perot resonance, forming a strong standing wave distribution inside the channel, and realizing maximum transmission.

[0019] Further, the subwavelength channel is a straight path or a curved path.

[0020] Further, the subwavelength channel is filled with lossy and gainy materials, or can be filled with air.

[0021] Advantages: Compared with the prior art, the advantages of the present application: the present application converts the high-order vortex mode incident in the waveguide into a low-order plane wave mode in the subwavelength channel, adjusts the length of the subwavelength channel, can realize perfect transmission of vortex waves through the subwavelength channel, and further realize arbitrary manipulation of the tunneling channel, which provides a new and convenient way for the manipulation of sound waves. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The principle diagram of the topological pair superstructure surface in the present application;

[0023] Figure 2 The principle diagram of the topological pair superstructure surface in the present application;

[0024] Figure 3 The principle diagram of the topological pair superstructure surface in the present application;

[0025] Figure 4 The design principle diagram of the single-sided reflection type loss superstructure surface in the specific embodiment of the present application;

[0026] Figure 5 The cross-sectional schematic diagram of the reflection type loss superstructure surface in the specific embodiment of the present application;

[0027] Figure 6 The analysis of the reflection coefficient of the reflection type loss superstructure surface in the specific embodiment of the present application; The variation graph of the channel length d and the loss γ;

[0028] Figure 7 The incident sound pressure diagram of the reflection type superstructure surface from the left cylindrical waveguide in the specific embodiment of the present application;

[0029] Figure 8 The scattering sound pressure diagram of the reflection type superstructure surface in the left cylindrical waveguide in the specific embodiment of the present application;

[0030] Figure 9 The sound field simulation diagram of the non-Hermite topological pair superstructure surface from the left cylindrical waveguide in the specific embodiment of the present application;

[0031] Figure 10 The sound field amplitude diagram on the circular cross section of the incident end in the specific embodiment of the present application;

[0032] Figure 11 The sound field phase diagram on the circular cross section of the incident end in the specific embodiment of the present application;

[0033] Figure 12 The sound field amplitude diagram on the circular cross section of the incident end in the specific embodiment of the present application;

[0034] Figure 13 for the sound field phase diagram on the exit end circular cross section in the embodiment of the present application;

[0035] Figure 14 for the sound field simulation diagram of the Helmholtz-type topological pair metasurface in the embodiment of the present application;

[0036] Figure 15 for the relationship between the tunneling length and the transmittance and reflectance of the Helmholtz-type topological pair metasurface in the embodiment of the present application;

[0037] Figure 16 for the sound field simulation diagram of the Helmholtz-type topological pair metasurface for long-distance vortex transmission in the embodiment of the present application;

[0038] Figure 17 for the sound field simulation diagram of the Helmholtz-type topological pair metasurface for vortex transmission of a curved tunneling path in the embodiment of the present application. DETAILED DESCRIPTION

[0039] The present application will be further described in detail below with reference to the accompanying drawings.

[0040] The present application discloses a method for realizing acoustic vortex tunneling transmission based on a topological pair metasurface (TPMs), and a topological pair metasurface (TPMs) structure as shown in the figure is composed of a pair of metasurfaces respectively carrying opposite artificial topological charges ±q, connected by a subwavelength channel (with a radius R0 less than the working wavelength λ) in the middle, and large cylindrical waveguides (with a radius R>R0) on both sides as incident and exit ends. Figure 1 Each fan-shaped groove and acoustic hard boundary is contained in each fan-shaped cell, and q×n×m groove units are formed in total, with the center connected to the subwavelength small channel. The groove size and shape of the two metasurfaces are completely consistent, but the angular arrangement directions are opposite, respectively carrying topological charges -q and +q, and the overall topological charge is zero. The left side of the absorbing metasurface is connected to the subwavelength channel through a subwavelength absorber, and the right side of the transmitting metasurface is connected to the subwavelength channel through a subwavelength emitter. ij The q-order vortex wave at the incident end is converted into a plane wave and coupled to the subwavelength channel efficiently, while the transmitting metasurface on the right side performs the reverse process to convert the plane wave into a vortex wave output, realizing vortex tunneling with transmittance T greater than zero. In order to further improve the transmission efficiency, the length L of the center channel is designed to meet the Fabry-Perot resonance condition, so as to form a strong standing wave distribution inside the channel, realizing maximum transmission.

[0041] Due to the complex multimode scattering and increased degrees of freedom in Hermitian systems, obtaining a clear physical mechanism analysis presents significant challenges. Therefore, a non-Hermitian system is first designed, with loss and gain materials filled at opposite ends of the channel. The absorbing metasurface on one side is matched with the gain metasurface on the other side using a time-reversal symmetry approach, such as... Figure 2 As shown, replacing the gain and loss within the channel with air (γ = 0), efficient tunneling can still be maintained as long as the channel length meets the FP resonance condition. Figure 3 As shown, the support of TPMs structure for FP resonance can not only realize vortex wave transmission in straight paths, but also stably maintain orbital angular momentum transmission in longer distances or even curved paths.

[0042] To observe the physical phenomena occurring during vortex tunneling more accurately and clearly, a reflective lossy metasurface was designed to achieve perfect absorption of the incident vortex. Under the condition of an operating wavelength λ0 = 10 cm, the incident topological charge is considered to be l. in A vortex wave with q=1 is incident. A lossy reflective metasurface with q=1 is designed first, the specific structure of which is as follows: Figure 4 As shown, a lossy metasurface with q = -1 is considered. The length of the metasurface is d = 0.5λ, and the outer radius is R = 0.4λ. This lossy metasurface has a central channel with radius R0 = 0.1λ0 and length d, which is filled with a lossy material with a refractive index of n. c =1-γi. The channel is surrounded by a fan-shaped slot array, designed with two rows radially and three columns angularly. The angular width of each slot element is Δθ = 2π / 3, where the angular width of the acoustic hard wall is w. θ =0.03Δθ, radial thickness is w R =0.02λ0. To satisfy the nonlocal ITC condition q=-1, the corresponding depth of these 6 grooves is d. 11 =0.641λ0,d 12 =0.211λ0,d 13 =0.174λ0,d 21 =0.306λ0,d 22 =0.148λ0,d 23 =0.220λ0. In the parameter space, The zero values ​​at d = 0.7λ0 and γ = 0.063 indicate that perfect vortex absorption has been achieved, such as... Figure 6 As shown. Figure 7 and Figure 8 Simulation results demonstrate that this design achieves perfect absorption of vortex waves. Figure 8 In the simulation diagram shown, we can clearly observe that the absorption in the subwavelength channel is resonant absorption.

[0043] According to the time reversal law, the corresponding absorption-type reflective metasurface has the opposite groove distribution in the angular direction compared to the absorption-type metasurface, and the gain material in the subwavelength channel is set to correspond to the refractive index The length is d, and such a design ensures that the plane wave incident in the central subwavelength channel can be effectively converted into the corresponding vortex wave. By connecting the two types of reflective metasurfaces, perfect transmission of vortex waves can be achieved, as shown in Figure 9 . Figure 10 to Figure 13 From the phase and amplitude information of the input and output vortices, it can also be seen that perfect vortex wave tunneling occurs.

[0044] In the above process, the channel length d is set to be greater than the groove depth d ij , ensuring that the loss structure and gain structure do not overlap when constructing TPMs. The coupling layer on both sides of the double-layer microstructure has a thickness of d, so the total length is L = 2d.

[0045] As shown in Figure 9 , the typical periodic enhanced field distribution in the channel indicates that the FP resonance is dominant in the subwavelength channel, and at this time the efficiency of the tunneling is dominated by the length of the channel, and the gain and loss in the channel are no longer important for the tunneling result. Therefore, further, by replacing the gain / loss medium in the channel with lossless air (γ = 0) while keeping other geometric parameters unchanged, the vortex tunneling performance of the lossless TPMs is shown in Figure 14 . Since TPMs support Fabry-Perot resonance, this helps to achieve longer tunneling distances. In Figure 15 , the reflectivity and the transmittance are shown as a function of the channel length L, where the subscript indicates the incident vortex mode, the superscript indicates the outgoing mode, and the whole indicates the reflectivity and transmittance of the l in = 1 vortex wave incident when l = 1 mode. The overall effect is that the transmittance T shows a periodic variation with the length L of the subwavelength channel, and the channel lengths of the adjacent two perfect transmissions satisfy ΔL = 0.5λ0. This means that perfect vortex wave tunneling comes from the Fabry-Perot resonance in the channel. In addition, the OAM tunneling case of a longer and curved tunneling path is selected, as shown in Figure 16 and Figure 17 , respectively, and the corresponding tunneling channel length is equal and satisfies the special length in Figure 15 when the transmittance is maximum.

[0046] Of course, the metasurface is not limited to the functions described above. This scheme is universal and can be extended to high-order vortex tunneling. By setting different sector groove depths and central tunneling lengths, different orders of OAM mode tunneling can be achieved by the metasurface designed in this paper.

[0047] The above-described embodiments are merely illustrative of several embodiments of the present application, which are described in more detail and in a specific manner, but should not be construed as limiting the scope of the patent. It should be noted that for those skilled in the art, several modifications and improvements can be made without departing from the concept of the present application, and these are all within the scope of the present application. Therefore, the scope of protection of the patent of the present application should be subject to the appended claims.

Claims

1. A method for realizing acoustic vortex tunneling transmission based on topology-paired metasurfaces, characterized in that, The implementation process is as follows: (1) The tunnel radius R0 satisfies R0<λ, where λ is the working wavelength, that is, the tunnel is a subwavelength channel; (2) An absorptive metasurface and an emissive metasurface are constructed at the entrance and exit of the tunnel channel, respectively. The whole consisting of the two metasurfaces and the subwavelength channel is called the topological pair TPMs. (3) The large cylindrical waveguide connected to the two metasurfaces has a radius of R>R0, which serves as the incident end and the output end, respectively. (4) Two metasurfaces are etched with m and n sector cells in the angular direction and radial direction respectively in one cycle. Each sector cell contains a sector groove and an acoustic hard boundary. The sector groove has q cycles in the angular direction. There are q×m×m sector grooves on the end face of the incident end and the end face of the exit end respectively. A small pipe with a radius of R0 is connected to the center of the end face. (5) The trench structures of the absorbing and emitting metasurfaces of the topological pair are arranged in opposite directions and positions in the angular direction, but have the same size and shape, so that the topological charges carried by the two metasurfaces are opposite, namely -q and +q, and the topological charge of the entire topological pair is zero. (6) The trench structure design on the end face and the topological charge it carries enable the conversion between vortex waves in the large waveguide and plane waves in the central subwavelength pipe, controlling different fan-shaped trench depths d. ij This allows the absorbing surface to convert the q-order vortex wave incident in the large waveguide into a plane wave, which is then absorbed into the small waveguide. (7) Consider the wave entering the subwavelength channel from the absorbing metasurface as the wave source of the emitting metasurface. The role of the emitting metasurface is the reverse process of absorption, that is, converting the plane wave in the subwavelength channel into a vortex wave and propagating it into the large waveguide. The transmittance T of the corresponding vortex mode at the output port is greater than zero, indicating that the acoustic vortex wave can tunnel through the subwavelength channel.

2. The method for realizing acoustic vortex tunneling transmission based on topology-paired metasurfaces according to claim 1, characterized in that, The angular thickness of each sector cell is radial thickness is The interior contains fan-shaped grooves with a angular thickness of Δθ' and a radial thickness of ΔR', each with a depth of d. ij , i and j represent the angular and radial indices, respectively.

3. The method for realizing acoustic vortex tunneling transmission based on topology-paired metasurfaces according to claim 2, characterized in that, The spacing between the fan-shaped grooves in the angular and radial directions is a fixed value, respectively w θ =Δθ-Δθ', w R =ΔR-ΔR'.

4. The method for realizing acoustic vortex tunneling transmission based on topology-paired metasurfaces according to claim 1, characterized in that, The thickness of the sector region of the two metasurfaces is no greater than 0.5λ, and the total length of the central subwavelength channel is L>λ, so that the total length of the subwavelength channel is greater than the sum of the thicknesses of the two metasurfaces, ensuring that the two metasurface regions do not overlap.

5. The method for realizing acoustic vortex tunneling transmission based on topology-paired metasurfaces according to claim 1, characterized in that, The fan-shaped cell wall and the subwavelength channel wall are made of acoustically hard materials that sound waves cannot penetrate.

6. The method for realizing acoustic vortex tunneling transmission based on topology-paired metasurfaces according to claim 1, characterized in that, The subwavelength channel length L satisfies the Fabry-Perot resonance, forming a strong standing wave distribution inside the channel to maximize transmission.

7. The method for realizing acoustic vortex tunneling transmission based on topology-paired metasurfaces according to claim 1, characterized in that, The subwavelength channel can be a straight path or a curved path.

8. The method for realizing acoustic vortex tunneling transmission based on topology-paired metasurfaces according to claim 1, characterized in that, The subwavelength channel has a curved path.

9. The method for realizing acoustic vortex tunneling transmission based on topology-paired metasurfaces according to claim 1, characterized in that, The subwavelength channel is filled with loss and gain materials.

10. The method for realizing acoustic vortex tunneling transmission based on topology-paired metasurfaces according to claim 1, characterized in that, The subwavelength channel is filled with air.

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