A geometric phase-based metasurface device with reconfigurable acoustic field control

Abstract

The present invention discloses a metasurface device with reconfigurable acoustic field control based on geometric phase, which is composed of an array of subwavelength double-layer microstructures; the double-layer microstructure can achieve tunable acoustic geometric phase, and is composed of a cylindrical waveguide and two subwavelength double-layer microstructures with opposite artificial topological charges. ξ The invention is composed of a phase gradient meta-grating PGM, which are PGM-1 and PGM-2 respectively; the double-layer microstructure can realize the adjustment of the linear and continuously changing acoustic geometric phase by rotating the angle θ of PGM-2, satisfying the relationship that the present invention realizes arbitrary adjustment of the transmission phase by rotating the geometric angle of each microstructure, and can realize diversified sound field control functions such as beam deflection, focusing and separation, thereby realizing a new type of reconfigurable acoustic metasurface device; the present invention has great application potential in sound field function control devices.

Description

Technical Field

[0001] The present invention belongs to the technical field of acoustic wave control, and in particular relates to a geometric phase-based acoustic field reconfigurable control metasurface device. Background Art

[0002] With technological advancements, the performance of materials required for high-end device manufacturing has gradually improved. Natural materials are no longer sufficient to meet the demands of society's development. Metamaterials, generally referring to artificial structures with physical properties distinct from those of natural materials, have emerged as a response to this need. In the field of acoustics, the introduction of acoustic metamaterials has broadened the scope of acoustic research and enriched the manipulation and application of sound waves. However, because conventional metamaterials require periodic arrangements of artificial unit cells to achieve their functions, they suffer from significant disadvantages such as bulk and high losses. Therefore, reducing the weight and thickness of these materials is crucial. Consequently, the concept of metasurfaces has been proposed. Metasurfaces are described as subwavelength-scale acoustic wave manipulation devices, which can be considered the two-dimensional counterpart of metamaterials. In recent years, research in acoustic metasurfaces has made significant progress. A range of acoustic wave manipulation metasurfaces, including anomalous refraction, focusing, acoustic cloaking, and acoustic holography, have been designed and implemented. However, most currently designed metasurfaces utilize traditional propagation phase or resonance phase principles, achieving phase modulation by varying the geometric parameters of the unit cells. Therefore, once fabricated, these devices cannot be modified, resulting in poor reconfigurability, which significantly limits their development and application.

[0003] On the other hand, in 1956, Pancharatnam discovered that electromagnetic waves will produce a phase related to the polarization state evolution path during the polarization state transformation process. This phase can be represented by half of the solid angle corresponding to the closed path on the Poincare sphere in the polarization state space. In 1984, Berry proposed the concept of geometric phase. When certain parameters of a quantum system undergo an adiabatic evolution process and return to the starting point of the parameters, a phase related to the evolution path in the system representation will be generated, namely the geometric phase. In the field of optics, as a new phase control method, geometric phase provides unprecedented opportunities for freely controlling the behavior of light, especially on subwavelength metasurfaces. When the incident circularly polarized (spin) light passes through the meta-atom in the spatial direction (θ), it will generate Thanks to this simple phase control method, geometric phase has shown great potential in the design of various metasurface devices. However, since acoustic waves are scalar fields and do not have spin degrees of freedom, it is impossible to control the geometric phase by changing the spin state. Therefore, the research and application of acoustic geometric phase are greatly limited.

[0004] To address the above problems, it is necessary to realize geometric phase in acoustics and design a metasurface with reconfigurable sound field control based on it. Summary of the Invention

[0005] Purpose of the invention: The present invention provides a geometric phase-based acoustic field reconfigurable control metasurface device. By twisting a double-layer microstructure with opposite artificial topological charges, the closed path evolution of orbital angular momentum between the plane wave mode and the evanescent vortex mode is achieved, thereby generating a controllable acoustic geometric phase.

[0006] Technical solution: The present invention provides a metasurface device with reconfigurable acoustic field control based on geometric phase, which is composed of an array of subwavelength double-layer microstructures; the double-layer microstructure can achieve tunable acoustic geometric phase, and is composed of a cylindrical waveguide and two subwavelength ... ξ The double-layer microstructure can adjust the linear and continuous acoustic geometric phase by rotating the angle θ of PGM-2, satisfying the relationship

[0007] Furthermore, the PGM-1 and PGM-2 have ξ A group of fan-shaped supercells, each group of supercells consists of m circles with a central angle of α=2π / (ml ξ ) is composed of fan-shaped cells, and the phase shift of m cells is φ n =2(n-1)π / m(n=1,2,···,m).

[0008] Furthermore, the metasurface device also includes a rectangular frame located outside the double-layer microstructure, and the side surfaces of the rectangular frame are square.

[0009] Furthermore, the thickness of PGM-1 and PGM-2 is h=0.45λ, the radius is R=0.15λ, and coupling layers with a thickness of d=0.2λ are left on both sides. The thickness of the double-layer microstructure is l=2h+2d=1.3λ.

[0010] Furthermore, the fan-shaped cells are designed by a gradient space folding metamaterial structure.

[0011] Furthermore, the fan-shaped cell includes inner and outer walls, side walls, four pillars connected to the outer and side walls, and three pillars connected to the inner and side walls, which are arranged crosswise; the thickness of the inner and outer walls and the pillars is t = 0.01λ, and the thickness of the side wall is f = 0.0025λ. By changing the pillar height b and the spacing g between two adjacent pillars, a fan-shaped cell with a transmission efficiency higher than 95% and phase shift matching is found.

[0012] Furthermore, the fan-shaped cells are made of an acoustically hard material that is impenetrable by sound waves.

[0013] Beneficial effects: Compared with the prior art, the present invention has the following beneficial effects: In the present invention, by twisting a double-layer microstructure with opposite artificial topological charges, the closed path evolution of orbital angular momentum between the plane wave mode and the evanescent vortex mode is realized, an adjustable acoustic geometric phase is generated, and a sound field reconfigurable control metasurface is further designed; based on the sound field reconfigurable control metasurface, by encoding it (changing the torsion angle of PGM-2 in each microstructure) to achieve the required phase distribution, the expected sound wave manipulation function can be arbitrarily realized, such as abnormal refraction, separation, and focusing of sound waves, providing a new and convenient way for the manipulation of sound waves. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Schematic diagram of the principle of the double-layer microstructure in the present invention;

[0015] Figure 2 Schematic diagram of the principle of PGM-1 in the present invention;

[0016] Figure 3 Schematic diagram of the principle of PGM-2 in the present invention;

[0017] Figure 4 Schematic diagram of the design principle of the fan-shaped cell in the present invention;

[0018] Figure 5 Schematic diagram of the cross section of the fan-shaped cell in the present invention;

[0019] Figure 6 Schematic diagram of the structure of PGM in a specific embodiment of the present invention;

[0020] Figure 7 Graph showing the parameters of each sector cell of the PGM in a specific embodiment of the present invention;

[0021] Figure 8 Schematic diagram of the structure of a double-layer microstructure in a specific embodiment of the present invention;

[0022] Figure 9 is a graph showing the relationship between the phase φ, transmission efficiency T and twist angle θ of the double-layer microstructure in a specific embodiment of the present invention;

[0023] Figure 10 This is a sound field simulation diagram of the metasurface acoustic wave deflection function in a specific embodiment of the present invention;

[0024] Figure 11 This is a simulation diagram of the acoustic field of the metasurface acoustic focusing function in a specific embodiment of the present invention;

[0025] Figure 12 This is a simulation diagram of the sound field in which the metasurface achieves a 49° acoustic beam separation function in a specific embodiment of the present invention;

[0026] Figure 13 This is a simulation diagram of the sound field in which the metasurface realizes the 30° acoustic beam separation function in a specific embodiment of the present invention;

[0027] Figure 14 This is a simulation diagram of the sound field of the full-transmission function of the metasurface in a specific embodiment of the present invention;

[0028] Figure 15 This is a simulation diagram of the sound field of the total reflection function of the metasurface in a specific embodiment of the present invention;

[0029] Figure 16 This is a simulation diagram of the sound field incident on the left side of the asymmetric transmission function of the metasurface in a specific embodiment of the present invention;

[0030] Figure 17 This is a simulation diagram of the sound field incident on the right side of the asymmetric transmission function of the metasurface in a specific embodiment of the present invention. DETAILED DESCRIPTION

[0031] The present invention will be further described in detail below with reference to the accompanying drawings.

[0032] The present invention discloses a geometric phase-based acoustic field reconfigurable control metasurface device, such as Figure 1 As shown, it consists of an array of subwavelength double-layer microstructures; the double-layer microstructure can achieve tunable acoustic geometric phase, consisting of a cylindrical waveguide and two with opposite artificial topological charges ±l ξ The phase gradient super-grating PGM is composed of PGM-1 and PGM-2 respectively; PGM-1 is fixed and PGM-2 is rotatable. The double-layer microstructure can adjust the linear and continuous acoustic geometric phase by rotating the angle θ of PGM-2, satisfying the relationship

[0033] like Figure 2 and Figure 3 As shown, PGM-1 and PGM-2 have l ξ Each supercell group is composed of m fan-shaped cells, and the central angle of the subunit is α=2π / (ml ξ ), the phase shift of m fan-shaped cells satisfies the phase gradient distribution covering 0 to 2π, that is, φ=2(n-1)π / m(n=1,2,···,m). Since PGM-1 and PGM-2 have opposite topological charges, PGM-2 should be placed in the opposite direction in the double-layer microstructure.

[0034] The specific manifestation of the control of geometric phase in the double-layer microstructure is that the incident plane wave passes through the artificial topological charge +l ξ After the PGM-1, it will stimulate the high-order l=l ξThe evanescent vortex sound field, due to the close arrangement of PGM-1 and PGM-2, will continue to pass through the artificial topological charge of -l without attenuation. ξ The PGM-2 evolves into a plane wave emission with a geometric phase, where the geometric phase is related to the closed path of the evolution of the acoustic vortex state. When the torsion angle θ of the PGM-2 changes, it will lead to a change in the evolution path, and thus carry The geometric phase.

[0035] The above-mentioned double-layer microstructure array is combined into a reconfigurable metasurface, and each double-layer microstructure is encoded separately (i.e., the rotation angle θ is changed) to match the phase shift of the required sound wave control, which can realize a variety of sound field control functions including beam deflection, focusing and separation.

[0036] Example 1: Under the condition of working wavelength λ = 10cm, l ξ =2,m=6PGM-1 and l ξ =-2,m=6PGM-2, reference Figure 6 The length of the PGM is h = 0.45λ, and the radius is R = 0.15λ. Placing two PGMs in a waveguide with T = 0.15λ constitutes a double-layer microstructure. In order to ensure the efficiency of sound wave transmission, the thickness of the coupling layer on both sides of the double-layer microstructure is d = 0.2λ, so the total length is l = 2h + 2d = 1.3λ.

[0037] The fan-shaped cells in PGM are designed by gradient space folding metamaterial structure, such as Figure 4 、 Figure 5 As shown, the fan-shaped cell is a cell whose cross section rotates around the z axis by α=2π / (ml ξ )=30°, the fan-shaped cellular structure includes a fan-shaped cavity, 4 columns connected to the outer wall in the cavity, and 3 columns connected to the inner wall. The 7 columns are alternately and evenly distributed in the center of the cell. The distance between every two adjacent columns is g, the height of the columns is b, the thickness is t=0.01λ, and the thickness of the upper and lower walls is also t=0.01λ. In order to avoid interference between adjacent cells, the fan-shaped cavity has a side wall thickness of f=0.0025λ. The fan-shaped cellular structure material is an acoustically hard medium (that is, sound waves cannot pass through). By changing the column height b and the spacing g between two adjacent columns, a fan-shaped cell with a transmission efficiency higher than 95% and phase shift matching is found to form a PGM; such as Figure 6 As shown, 6 cells ( Figure 6 The marked #1, #2, #3, #4, #5, #6) meet the phase distribution of 0, π / 3, 2π / 3, π, 4π / 3, 5π / 3, and the transmission efficiency is higher than 97%, such as Figure 7 shown.

[0038] Example 2: Figure 8As shown in the figure, the designed PGM is placed in the cylindrical waveguide in the forward direction as PGM-1 and in the waveguide in the reverse direction as PGM-2. The PGM is located in the center of the double-layer microstructure. In order to conveniently combine into an array metasurface, Figure 8 A double-layer microstructure of a rectangular frame is designed. The side of the rectangular frame is a square with a side length of a=λ / 3. The material is an acoustically hard medium and does not affect the regulation of the geometric phase.

[0039] In the double-layer microstructure, by changing the twist angle θ of PGM-2, the transmission phase and transmission efficiency corresponding to different θ values ​​are calculated, as shown in Figure 9 As shown, the designed double-layer microstructure has excellent geometric phase control ability, which meets the requirements of relationship, and can make the transmission efficiency greater than 96%.

[0040] Example 3: Eighteen rectangular double-layer microstructures were closely attached to form a 1×18 one-dimensional array metasurface (length 6λ, width 1.3λ), and its control performance was numerically simulated in COMSOL. (The 1×18 metasurface array is only used as an example in this embodiment; similar to this example, any combination of metasurface arrays has the ability to achieve acoustic wave manipulation.) For ease of description, the six cases of unit cell transmission phases of 0, π / 3, 2π / 3, π, 4π / 3, and 5π / 3 are coded as 1, 2, 3, 4, 5, and 6, respectively.

[0041] The metasurface is encoded as “…1, 2, 3, 4, 5, 6, …”, and the encoding period is p=2λ, that is, the phase distribution satisfies “…0, π / 3, 2π / 3, π, 4π / 3, 5π / 3, …”, as shown in Figure 10 As shown in the figure, the incident Gaussian plane wave on the left side, as predicted by the generalized Snell's law, the sound wave is deflected 30° and emitted, that is, the anomalous refraction function of the sound wave is realized.

[0042] In order to make the acoustic wave focus at 4λ after passing through the metasurface, the metasurface code is matched with the spherical wave emitted at 4λ, and the metasurface code is set to “5, 4, 3, 2, 2, 1, 6, 6, 6, 6, 6, 1, 2, 2, 3, 4, 5”, as shown in Figure 11 As shown, a Gaussian plane wave is incident on the left, and the outgoing sound wave is perfectly converged at a distance of 4λ from the metasurface, realizing the focusing function of the sound wave.

[0043] The metasurface can also realize the function of acoustic wave beam splitting. The metasurface is encoded as “…1, 1, 4, 4, 1, 1, 4, 4…”, and the encoding period is p = 4λ / 3, as shown in the following example: Figure 12 As shown in the figure, the incident Gaussian plane wave on the left side stimulates an acoustic wave beam splitting phenomenon of approximately 49° on the right side of the metasurface; the metasurface coding is changed to “…1, 1, 1, 4, 4, 4, …”, and the coding period is p = 2λ, as shown in the figure. Figure 13 As shown, a 30° acoustic beam splitting phenomenon will be stimulated on the right side of the metasurface.

[0044] Similarly, the full transmission and full reflection functions of sound waves are also verified. The metasurface is encoded as “…1, 1, 1, 1, …”, that is, the phase is all 0, such as Figure 14 As shown in , the transmission function of the sound wave is realized, and the sound wave is not affected by the metasurface and continues to propagate along the original path with high efficiency; for total reflection, the metasurface is encoded as “…1, 4, 1, 4, …”, that is, the phase distribution is “…0, π, 0, π, …”, as shown in Figure 15 As shown in the figure, when the sound wave is incident from the left, it cannot pass through the metasurface and is reflected efficiently. Based on this function, the sound wave can be efficiently turned on and off.

[0045] In addition, asymmetric transmission of acoustic waves can also be realized in metasurfaces. The metasurface is encoded as “…1, 3, 5,…”, with an encoding period of p=λ, that is, the phase distribution is “…0, 2π / 3, 4π / 3,…”. When the left Gaussian plane wave is incident on the metasurface at a direction of 30° to the lower right, as shown in the following example: Figure 16 As shown in the figure, an anomalous refraction phenomenon occurs, and the wave exits at an angle of -30°. However, when the Gaussian plane wave on the right side is incident on the metasurface at a direction of 30° to the upper left, as shown in the figure, Figure 17 As shown, sound waves cannot pass through the metasurface and will stimulate reflected plane waves that return along the original path, realizing asymmetric transmission of sound waves. This function can also be further utilized to make "acoustic diodes".

[0046] Of course, metasurfaces are not limited to the functions described above. Any function achieved by manipulating the wavefront phase can be realized with the metasurface designed in this article, including but not limited to acoustic holography and the excitation of vortex acoustic beams.

[0047] This invention reveals a mechanism for manipulating the geometric phase of acoustic waves by altering the evolution path of their vortex states. This mechanism pioneers the study and application of geometric phase in acoustic waves. The double-layer microstructure designed based on this mechanism has a tunable geometric phase, enabling the metasurface to achieve arbitrary acoustic wavefront manipulation. Encoding metasurfaces can achieve a wide range of acoustic wave manipulation functions, breaking the limitation of single-function metasurface devices due to fixed geometric structures. This holds great promise for applications in acoustic communications, acoustic computing, and other fields.

[0048] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims, not the foregoing description, and all variations within the meaning and range of equivalents of the claims are intended to be included therein. Any reference sign in a claim should not be construed as limiting the claim to which it relates.

[0049] In addition, it should be understood that although this specification is described according to embodiments, not every embodiment contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A geometric phase-based acoustic field reconfigurable control metasurface device, characterized in that: The metasurface device is composed of an array of subwavelength double-layer microstructures; the double-layer microstructure can achieve tunable acoustic geometric phase, and is composed of a cylindrical waveguide and two subwavelength ... ξ The phase gradient super-grating PGM is composed of PGM-1 and PGM-2, PGM-1 is fixed and PGM-2 is rotatable; the double-layer microstructure can achieve linear and continuous adjustment of the acoustic geometric phase by rotating the angle θ of PGM-2, satisfying the relationship Specifically, the incident plane wave passes through the artificial topological charge +l ξ The PGM-1 will stimulate the high-order l=l ξ The evanescent vortex sound field, due to the close arrangement of PGM-1 and PGM-2, will continue to pass through the artificial topological charge of -l without attenuation. ξ The PGM-2 evolves into a plane wave emission with a geometric phase, where the geometric phase is related to the closed path of the evolution of the acoustic vortex state. When the torsion angle θ of the PGM-2 changes, it will lead to a change in the evolution path, and thus carry The geometric phase.

2. The geometric phase-based acoustic field reconfigurable control metasurface device according to claim 1, characterized in that: The PGM-1 and PGM-2 have l ξ A group of fan-shaped supercells, each group of supercells consists of m circles with a central angle of α=2π / (ml ξ ) is composed of fan-shaped cells, and the phase shift of m cells is φ n =2(n-1)π / m(n=1,2,···,m).

3. The geometric phase-based acoustic field reconfigurable control metasurface device according to claim 1, characterized in that: The metasurface device also includes a rectangular parallelepiped frame located outside the double-layer microstructure, and the side surfaces of the rectangular parallelepiped frame are square.

4. The geometric phase-based acoustic field reconfigurable control metasurface device according to claim 1, characterized in that: The thickness of PGM-1 and PGM-2 is h=0.45λ, the radius is R=0.15λ, and coupling layers with a thickness of d=0.2λ are left on both sides. The thickness of the double-layer microstructure is l=2h+2d=1.3λ.

5. The geometric phase-based acoustic field reconfigurable control metasurface device according to claim 2, characterized in that: The fan-shaped cells are designed by a gradient space folding metamaterial structure.

6. The geometric phase-based acoustic field reconfigurable control metasurface device according to claim 2, characterized in that: The fan-shaped cell includes inner and outer walls, side walls, four pillars connected to the outer and side walls, and three pillars connected to the inner and side walls, which are arranged crosswise; the thickness of the inner and outer walls and the pillars is t = 0.01λ, and the thickness of the side wall is f = 0.0025λ. By changing the pillar height b and the spacing g between two adjacent pillars, a fan-shaped cell with a transmission efficiency higher than 95% and phase shift matching is found.

7. The geometric phase-based acoustic field reconfigurable control metasurface device according to claim 2, characterized in that: The fan-shaped cells are made of an acoustically hard material that is impenetrable by sound waves.

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