Acoustic beam manipulator based on double-kink topological valley boundary state and preparation and manipulation method thereof

Abstract

This invention discloses an acoustic beam modulator based on double-knot topological valley boundary states, comprising a top layer, a bottom layer, and an intermediate layer. The intermediate layer includes an inverted acoustic cell array structure. The acoustic cell array comprises a plurality of acoustic cells with S-graphene crystal structures arranged periodically in the x and y directions, and the acoustic cells exhibit asymmetry in either the x or y direction. The intermediate layer is further configured to communicate with air only in the x direction, and to have bearded and zigzag boundaries arranged in the y direction. Furthermore, this invention provides a method for fabricating and controlling the aforementioned acoustic beam modulator. This invention can realize double-knot topological valley boundary states with different morphologies at different boundaries. Furthermore, by exciting the two excitation sound sources at a single frequency at the boundary and adjusting the phase difference between the two excitation sources, collimated and split beams into two obliquely emitted beams can be obtained, respectively.

Description

Technical Field

[0001] This invention belongs to the field of acoustic beam control technology, and specifically relates to an acoustic beam controller based on double-knot topological valley boundary states and its preparation and control method. Background Technology

[0002] Over the past few decades, two-dimensional graphene and graphene-like materials have attracted widespread attention due to the linearly degenerate Dirac points in their band structures. With in-depth research into Dirac physics, concepts such as topological half-metals and topological insulators have been extensively developed. By breaking time-reversal symmetry, spatial-reversal symmetry, and constructing spin-orbit coupling, the degeneracy of the Dirac point is opened, thereby creating a band gap. This leads to the quantum Hall effect, valley Hall effect, and quantum spin Hall effect, respectively. The topological states generated by these effects enrich the degrees of freedom for wave manipulation, opening up new application areas by utilizing defect-independent topological states to transmit information.

[0003] The valley Hall effect, which relies solely on broken spatial inversion symmetry, offers local extrema for storing and carrying information and is easily constructed experimentally, making it a highly sought-after technology. Valley states located between crystal domain walls can be constructed based on the valley Hall effect, requiring the two crystals used to construct these states to have opposite valley Chern numbers. Due to valley momentum locking, valley states suppress inter-valley scattering and exhibit robustness when passing through sharp corners. These properties demonstrate the immense potential of valley states in practical applications, such as valley filters and topological antennas for information selection and transmission. Beams formed by exciting valley states and coupling them to the outside air exhibit collimation in air and can be received from a specific direction without interference from background noise in other directions. Beamforms formed by this type of topological acoustic antenna provide a new avenue for sound control and are ideal for practical multi-functional applications.

[0004] However, the formation of valley states currently relies primarily on a pair of Dirac points, resulting in only one excitation mode. This limits the application of valley degrees of freedom and the number of channels when used in acoustic topology antennas. Traditional valley states propagate between two crystal domains with different valley-Chern numbers, requiring two complete crystals to be joined together, which restricts the size of the fabricated devices. Furthermore, current acoustic topology antennas can only excite a beam in a specific direction at the same frequency, failing to enable selection of beams in different directions.

[0005] Therefore, the search for a more compact tunable acoustic beamformer with more valley degrees of freedom, more excitable valley modes, and greater flexibility has become a research focus. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides an acoustic beam modulator based on double-knot topological valley boundary states. It employs an acoustic unit cell with an S-graphene crystal structure and constructs different hard boundaries in the y-direction of the inverted array. This allows for the realization of double-knot topological valley boundary states with different morphologies at different boundaries. Furthermore, by exciting the beams at a single frequency on the boundaries and adjusting the phase difference between the two excitation sources, collimated beams and beams split into two oblique beams can be obtained, respectively. Furthermore, this invention also provides a method for fabricating and controlling the aforementioned acoustic beam modulator.

[0007] To achieve this objective, the present invention includes the following technical solutions:

[0008] The first aspect of the present invention discloses an acoustic beam modulator based on double-knot topological valley boundary states, comprising a top layer, a bottom layer, and an intermediate layer located between the top layer and the bottom layer, wherein the intermediate layer comprises an inverted acoustic cell array structure; the acoustic cell array comprises a plurality of acoustic cells having an S-graphene crystal structure periodically arranged in the x and y directions; each acoustic cell comprises a circular cavity and a coupling tube for connecting the circular cavity, wherein the positional distribution of the circular cavity is consistent with the positional distribution of carbon atoms in the S-graphene crystal structure, and the acoustic cell has asymmetry in the x or y direction; the intermediate layer is further configured to: communicate with air only in the x direction, and have a first hard boundary having a bearded boundary morphology and a second hard boundary having a zigzag boundary morphology arranged in the y direction.

[0009] As an alternative, the acoustic unit cell includes a first circular cavity arranged in a rectangular array in the middle, and a second circular cavity arranged on the outer periphery of the rectangular array at an angle of 30° to the horizontal direction; all the first circular cavities have the same radius, and at least one of the second circular cavities has a different radius than the first circular cavity.

[0010] As an alternative, only one of the cavities in the second cavity has a radius different from that of the first cavity.

[0011] As an alternative, the spacing between adjacent circular cavities in the acoustic unit cell is a, the radius of the first circular cavity is r2 = 0.3a, the radius of the second circular cavity which is different from the radius of the first circular cavity is r1 = 0.45a, and the width of the coupling tube is t = 0.25a; the first hard boundary is constructed as the inverse of a circular cavity with a radius of 0.3a added along the y direction of the acoustic unit cell array.

[0012] As an alternative, the acoustic unit cell has a period greater than 7 in both the x and y directions.

[0013] As an alternative, the thickness of the intermediate layer is 0.5 ± 0.05 cm.

[0014] As an alternative, the acoustic beam modulator can be made of any one of the following materials: photosensitive resin, acrylic, metal, or organic plastic.

[0015] The second aspect of the present invention discloses a method for fabricating an acoustic beam modulator based on a double-knot topological valley boundary state as described in the first aspect and any optional embodiment of the present invention, comprising:

[0016] An acoustic unit cell with an S-graphene crystal structure is constructed, and by adjusting the size parameters of the circular cavity and / or coupling tube, the acoustic unit cell is made asymmetric in the x or y direction to break the degeneracy of two pairs of Dirac points and open the bulk band gap.

[0017] The acoustic unit cell is inverted, the inverted region is stretched in the z direction, and then periodically arranged in the x and y directions respectively. Finally, the first hard boundary and the second hard boundary, as well as the top and bottom layers, are constructed to obtain the drawing of the acoustic beam modulator.

[0018] Based on the prepared blueprints, a sound beam modulator is manufactured using 3D printing technology.

[0019] A third aspect of the present invention discloses a control method for controlling the acoustic beam modulator based on the double-knot topological valley boundary state as described in the first aspect and any optional embodiment of the present invention:

[0020] In the two circular cavities at the center of the acoustic unit cell at one end of the second hard boundary of the beam modulator, when a sound source of any frequency within the preset frequency range excites the W-type double-knot topological valley boundary state along the x-direction, or in the two circular cavities at the center of the acoustic unit cell at one end of the first hard boundary of the beam modulator, when a sound source of any frequency within the preset frequency range excites the M-type double-knot topological valley boundary state along the x-direction, two different valley state modes for realizing acoustic beam modulation can be obtained, namely the symmetric mode and the antisymmetric mode.

[0021] In the two circular cavities at the center of the acoustic unit cell at either the second hard boundary or the first hard boundary of the beam modulator, two sound sources with a phase difference of 0 are used to excite a symmetrical mode, which is then coupled with the air to form a collimated beam.

[0022] In the two circular cavities at the center of the acoustic unit cell at the second hard boundary or one end of the first hard boundary of the beam modulator, two sound sources with a phase difference of π are used to excite antisymmetric modes, which are then coupled with the air to form a split beam.

[0023] The two sound sources used to excite the symmetric or antisymmetric mode have the same frequency and volume.

[0024] As an optional feature, the preset frequency range is 8.850 to 9.250 kHz, and the volume is between 30 and 100 decibels.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) The acoustic unit cell of the S-graphene crystal structure used in this invention has four different Dirac points, which has more valley freedoms than previous graphene materials and can excite more valley modes, so that the acoustic beam has more adjustable channels.

[0027] (2) The double-knot topological valley boundary states described in this invention exist at the boundaries of the acoustic beam modulator, while the valley states of the past exist in the domain walls formed by splicing two crystals with opposite valley Chern numbers. Therefore, our device is more compact. Furthermore, the two boundaries of the same device of this invention have two different valley boundary states, which makes the device more widely applicable. The research results are of great significance for the design of collimating beams and other related valley devices.

[0028] (3) The control method described in this invention can specifically excite a beam of a certain mode. At the same frequency, the beam can be controlled by adjusting the phase difference between the two sound sources, that is, collimated or split emission. This design not only enriches the research on valley states, but also provides new ways and methods for controlling and applying valley states. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of an acoustic beam modulator based on the double-knot topological valley boundary states. (a) shows the acoustic beam modulator structure, with labels 1, 2, and 3 representing the bottom, middle, and top layers, respectively. Beared and zigzag are the two boundaries in the y-direction. (b) is a magnified view of the acoustic beam modulator after removing the top layer. The top and bottom layers are both long plates with a thickness of h1, and the middle layer is composed of a periodic array of materials with inverted acoustic units, with a thickness of h2. (c) is a magnified top-view view of the acoustic beam modulator after removing the top layer. The air within the black frame represents the acoustic units (represented by gray shading).

[0030] Figure 2 This diagram shows the acoustic unit cell structure of the beam modulator and the calculated band structure. In diagram (a), a represents the cavity spacing, and r and t represent the cavity radius and coupling tube width, respectively. x and a y The basis vector lengths are respectively in the x and y directions. a y =3a; (b) is the volume band diagram along the high symmetry direction of the Brillouin zone calculated from the acoustic unit cell, where k1 / k′1 and k2 / k′2 represent the bands at Γx(k y =0) and MY(k) y =π / ay Two pairs of different Dirac points in the direction of )

[0031] Figure 3 A schematic diagram of the acoustic unit cell periodic array with its boundary constructed is shown.

[0032] Figure 4 This is a schematic diagram of the projected band structure of the valley boundary states in a double-knot topology. In (a), the projected band structure is shown in the x-direction; in (b), 1 represents the sound pressure field intensity (P) distribution of one mode on the M-type valley boundary state formed on the bearded boundary (Max. represents the maximum value of the sound pressure field intensity), and 2 represents two different modes generated along the positive x-direction when the W-type valley boundary state is excited at a frequency of 9 kHz on the zigzag boundary: S represents the mode with a symmetrical field intensity distribution, and AS represents the antisymmetric distribution mode.

[0033] Figure 5 This is a schematic diagram of the simulation results for a beam modulator that utilizes double-twisted valley boundary states to achieve beam collimation and beam splitting. Wherein: (a) Momentum space analysis, the black coil represents the 9kHz isofrequency line in air, the rectangular frame represents the first Brillouin zone, e cut The dashed and solid arrows indicate the shear direction at the boundary, respectively, within the beam manipulator and radiated into the air (k). out (a) shows the wave vector of the symmetric (S) and asymmetric (AS) modes excited by two sound sources (marked with asterisks), respectively. (b) and (c) show the simulated field distribution of the sound pressure level (SPL) for the symmetric (S) and asymmetric (AS) modes excited by two sound sources (marked with asterisks). (Min represents the minimum value of the sound pressure level). Detailed Implementation

[0034] The technical solution of the present invention will now be clearly and completely described with reference to specific embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] In the description of this invention, the use of terms such as "upper," "lower," "left," "right," "inner," "outer," "top," and "bottom," indicating orientation or positional relationships, is based on the orientation or positional relationships shown in the accompanying drawings. These terms are used solely for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "including" and "having," and any variations thereof, are intended to cover non-exclusive inclusion, but rather to include other elements not explicitly listed or inherent to these products or devices.

[0036] In this invention, when valley boundary states on a specific boundary are excited, two valley state modes with different field distributions can be obtained. Based on these different modes, the collimation or splitting of the sound beam coupled into the air can be achieved by adjusting the phase difference between the two excitation sound sources. This invention successfully achieves the excitation of a collimated beam based on double-knot valley boundary states and also generates a double-slanted beam with a splitting morphology. Furthermore, this collimated beam control device has a simple structure, stable properties, and is easy to control, potentially providing new ideas for the design and application of multi-valley acoustic devices.

[0037] Combination Figure 1 and 3 As shown, Embodiment 1 provides an acoustic beam modulator based on the valley boundary state of a double-knot topology. The modulator includes a bottom layer 1, a middle layer 2, and a top layer 3. Both the bottom layer 1 and the top layer 3 are long plates with a thickness of h1. The bottom layer 1 and the top layer 3 are mainly used to satisfy hard boundary conditions in the z-direction, constructing a sealed environment so that sound mainly propagates in the middle layer (i.e., in the xy-plane). Here, "hard boundary" refers to a rigid boundary, meaning that the normal sound pressure at this point is zero.

[0038] The thickness of intermediate layer 2 is h2, and it is mainly composed of the inverted material of the acoustic unit cell array. Understandably, these three parts are tightly integrated, forming a closed whole in the z-direction, allowing sound to propagate only within the acoustic unit cell array region of intermediate layer 2. Specifically, the acoustic unit cell array region consists of several periodically arranged acoustic unit cells with an S-graphene crystal structure, such as... Figure 3 As shown, its left and right boundaries (x-direction) are connected to the air, and its upper and lower boundaries (y-direction) are hard boundaries with bearded and zigzag boundary morphologies, respectively. The bearded boundary is formed by adding a circular cavity with a radius of 0.3a to the upper boundary in the y-direction.

[0039] It should be noted that the S-graphene crystal unit cell selected in this invention consists of eight carbon atoms and carbon-carbon bonds connecting them, and its band structure has four distinct Dirac points. In contrast, ordinary graphene crystal unit cells contain only two carbon atoms and have only one pair of Dirac points in their band structure. Therefore, the breaking of the two pairs of distinct Dirac points in S-graphene provides more controllable valley degrees of freedom. Furthermore, the resulting acoustic system is stable, easy to control, and readily experimental. Based on this, this invention uses an acoustic unit cell with an S-graphene crystal structure as the basis for constructing an acoustic beam modulator.

[0040] In constructing an acoustic unit cell with an S-graphene crystal structure, this invention uses circular air cavities (i.e., circular cavities) and tubes connecting the air cavities (i.e., coupling tubes) to represent carbon atoms and carbon-carbon bonds connecting carbon atoms, respectively. Therefore, the acoustic unit cell has a total of 8 circular cavities and coupling tubes connecting the cavities. The positional distribution of the circular cavities corresponds to the position of carbon atoms in the S-graphene crystal structure, such as... Figure 2 As shown in (a), we can define it as including six circular cavities arranged in a central rectangular array, and circular cavities on the outer periphery of the rectangular array at an angle of 30° to the horizontal, with a spacing of 'a' between adjacent cavities. It is understandable that the cavities in the acoustic unit cell are connected to the coupling tube (i.e.,...). Figure 3 (The gray area of ​​China Unicom) is where air circulates.

[0041] To break the spatial inversion symmetry of the unit cell, this invention sets different radii for the circular cavities in the acoustic unit cell, such as... Figure 2 As shown in (a), compared to the six circular cavities arranged in a rectangle, the radius of the cavity at the top of the rectangle's outer perimeter can be enlarged, or the radius of the cavity at the bottom of the rectangle's outer perimeter can be enlarged and reduced respectively, or the width of the coupling tube can be adjusted. In short, as long as the acoustic unit cell has asymmetry in the x-direction or y-direction, and the spatial inversion symmetry of the unit cell is broken, the degeneracy of the two pairs of Dirac points can be broken, and the bulk band gap can be opened.

[0042] In Example 1, the cavity spacing of the acoustic unit cell of the acoustic beamsweeper is set to a = 1 cm, and the different cavity radii and coupling tube widths are: r1 = 0.45a, r2 = 0.3a, and t = 0.25a. It is understood that the cavity spacing a, the cavity radii r1 and r2, and the coupling tube width t can all be adjusted to other values ​​as needed, and are not limited to these. For example, the cavity spacing a of the acoustic beamsweeper unit cell can be enlarged or reduced, that is, the acoustic beamsweeper can be enlarged or reduced proportionally.

[0043] The period of the unit cell array in the acoustic beam modulator can also be larger, for example, the number of periods in the x-direction can be 15, 18, 20, etc. The number of periods in the y-direction can be the same or different from the number of periods in the x-direction. Considering the size effect and the stability of the formed valley states, the number of periods in both directions is usually set to be greater than 7. In Example 1, the number of periods in the x and y directions are 13 and 10, respectively.

[0044] Regarding the thickness design, the thickness of the intermediate layer 2 in Example 1 is chosen to be 0.5 ± 0.05 cm. This is calculated to ensure that it does not affect the suitable height of our device. Too thin a layer would be detrimental to the fabrication and use of the device, while too thick a layer would affect the transmission and stability of the valley state. The thickness of the bottom layer 1 and the top layer 3 is 0.2 cm. Their thickness can be adjusted according to actual needs, and this invention does not limit this adjustment.

[0045] In terms of material selection, Example 1 selected photosensitive resin material for 3D printing. Of course, acoustic rigid materials such as acrylic, metal, and organic plastics can also be selected.

[0046] The acoustic beam modulator disclosed in this invention can obtain M-type and W-type double-knot topological valley boundary states at the hard boundaries of the bearded and zigzag boundaries, respectively. Unlike traditional valley states which exist at the domain walls after the splicing of two crystals, the valley states of this device exist on the boundaries, greatly compressing the device structure.

[0047] Example 2 discloses a preparation method for fabricating the acoustic beam modulator based on the double-knot topological valley boundary state described in Example 1. The method mainly includes the following steps:

[0048] Step 1: Construct an acoustic unit cell with an S-graphene crystal structure and adjust its asymmetry in the x or y direction by adjusting the size parameters of the cavity and / or coupling tube.

[0049] Based on the S-graphene crystal structure, air cavities and coupling tubes connecting the cavities replace the carbon atoms and carbon-carbon bonds in the crystal, respectively, resulting in a total of eight cavities with the same positional configuration as the carbon atoms in the S-graphene crystal. To achieve the Valley Hall effect, i.e., breaking its spatial inversion symmetry, the acoustic unit cell can be made asymmetrical in the x or y direction by adjusting the relative size of the cavities and the size of the coupling tubes, such as... Figure 2 As shown in (a), the cavity spacing of the acoustic unit cell is set to a = 1 cm, and the different cavity radii and coupling tube widths are: r1 = 0.45a, r2 = 0.3a, and t = 0.25a, ​​respectively. The bulk band structure of its acoustic unit cell is as follows: Figure 2 As shown in (b), along Γx(k) in the Brillouin zone y =0) and MY(k) y =π / a y The two pairs of Dirac points, k1 / k′1 and k2 / k′2, in the high-symmetry direction are opened, and the bulk band gap is shown in the gray shaded area in the figure. All numerical calculations in this invention were performed using the frequency domain module of pressure acoustics in the finite element software COMSOL. In the calculations, the sound velocity and air density were taken as 345 m / s and 1.25 kg / m³, respectively. 3 Furthermore, the projected band structure can be calculated using a supercell in COMSOL, such as... Figure 4 As shown in (a), W-type and M-type double-knot topological valley boundary states can be generated on the zigzag and beared boundaries, respectively.

[0050] Step 2: Based on the acoustic unit cell of the designed acoustic beam modulator, draw the device schematics using AutoCAD software:

[0051] First draw a length of A rectangle with a width of 3a is drawn; then, acoustic units are drawn within the rectangle; the acoustic units are subtracted from the rectangular region, i.e., the inversion process is performed; then, the inverted region is stretched by 0.5cm in the z-direction; the stretched region is periodically arrayed in the x and y directions for 13 and 10 periods respectively; at the top left of the arrayed region in the y-direction, a length of... is drawn. A rectangle of width *a* is constructed. Two semicircles with a radius of 0.3*a* are subtracted from the two bottom corners of the rectangle, and then stretched by 0.5 cm in the z-direction. A bearded boundary is then constructed by arraying the rectangle along the x-direction for 13 periods. The upper and lower boundaries in the y-direction are then extended by a length of... A long board with a width of 0.2cm and a height of 0.5cm serves as the hard boundary between the bearded and zigzag boundaries. Finally, long boards with the same length, width, and thickness as the middle layer and 0.2cm are added to the bottom and top surfaces, respectively, namely bottom layer 1 and top layer 3.

[0052] Step 3: Export the drawing as a whole, and use 3D printing technology to print the acoustic beam modulator.

[0053] Example 3 provides a method for controlling an acoustic beam modulator, used to control the acoustic beam modulator based on the double-knot topological valley boundary state described in Example 1. The method includes the following three aspects:

[0054] (1) In the two circular cavities at the center of the acoustic unit cell at one end of the beam modulator zigzag boundary, when a sound source of any frequency within the preset frequency range excites a w-type valley state along the positive (or negative) x direction, two valley state modes with different field distributions are obtained, which are named the symmetric mode (S) and the antisymmetric mode (AS), respectively.

[0055] Specifically, when a 9kHz sound source excites a W-type double-knot topological valley boundary state (W-type valley state for short) along the positive x-direction within the two circular cavities at the center of the acoustic unit cell at one end of the zigzag boundary, two valley state modes with different field distributions can be obtained. For example... Figure 4 As shown in (b), two valley state modes with different field distributions are obtained near the k1 and k′2 valleys. The field strengths of these modes are symmetrically and antisymmetrically distributed along the short black line, respectively, and are denoted as S and AS modes. When excited along the negative x direction, the same two different valley state modes, symmetrical mode (S) and antisymmetric mode (AS), can also be obtained, and the acoustic beam can be controlled.

[0056] Understandably, the excitation of valley states at the zigzag boundary of the beamshifter is merely an example of the control method. Similarly, within the two circular cavities at the center of the acoustic unit cell at one end of the beamed boundary, W-type double-knot topological valley boundary states (referred to as M-type valley states) can also be excited to control the beam. That is, when an M-type valley state is excited by a sound source at any frequency within a preset frequency range along the positive (or negative) x-direction of the beamshifter's beamed boundary, two valley state modes with different field distributions can be obtained. Then, by exciting different modes, the acoustic beam can be controlled.

[0057] The preset frequency can be any other frequency within the range of 8.850-9.250kHz, such as 8.9kHz, 9.05kHz, 9.15kHz, etc. Understandably, the volume of the excited sound source is adjustable, and in actual experiments, it can range from 30 to 100 decibels.

[0058] (2) Two sound sources with a phase difference of 0 are used to excite a symmetric mode (S) in two circular cavities at the center of the acoustic unit cell at one end of the zigzag boundary of the beam modulator. After coupling with the air, a collimated beam is formed.

[0059] In the lower left corner of the beam modulator (i.e., within the two circular cavities at the center of the acoustic unit cell at one end of the zigzag boundary), such as Figure 5 (b) In the S-mode acoustic unit cell within the dashed box, two sound sources with zero phase difference are placed at the two identical asterisk positions, excited by the sound sources at a frequency of 9 kHz. Since this mode is near the k1 energy valley, therefore... Figure 5 (a) As shown in the momentum analysis diagram above, the wave vector in the beamformer has only one branch pointing towards the k1 energy valley along the positive x-direction. To couple the valley state into the air in the y-section device, along the tangential direction (e... cut The wave vector of ) should remain unchanged. Therefore, if we choose to excite the S-mode, k must satisfy y =0, thus obtaining as Figure 5 (b) The simulation results show a collimated beam that exits only along the x-axis.

[0060] (3) Two sound sources with a phase difference of π are used to excite antisymmetric modes (AS) in two circular cavities at the center of the acoustic unit cell at one end of the zigzag boundary of the beam modulator. After coupling with the air, a split beam is formed.

[0061] In the lower left corner of the beam modulator (i.e., within the two circular cavities at the center of the acoustic unit cell at one end of the zigzag boundary), such as Figure 5 In (c), within the dashed box of the AS mode, two sound sources with a phase difference of π are placed at the positions of the two different colored asterisks in the acoustic unit cell, excited by the sound sources at a frequency of 9 kHz. Since this mode is near the k2 valley, therefore... Figure 5(a) As shown in the momentum analysis diagram below, because the k′2 valley has two equivalent Bloch wave vectors at the first Brillouin zone boundary, i.e., k y =±π / a y Therefore, we can obtain the following: Figure 5 (c) The simulation results show that the two cleaved, obliquely exiting beams have refraction angles that satisfy:

[0062] θ = arcsin(k) y / k0) (1)

[0063] Where k0 is the sound wave vector in the air, and the theoretical value of the split refraction angle θ is ±39.71°.

[0064] Understandably, in aspects (2) and (3), the two circular cavities at the center of the acoustic unit cell at one end of the bearded boundary can also be used to form collimated or split beams after coupling with the air by exciting symmetric mode (S) or antisymmetric mode (AS) in the two circular cavities.

[0065] This invention can use two sound sources to excite valley states, and the two sound sources used to excite symmetric or antisymmetric modes have only a phase difference of 0 or π, with completely identical frequencies and volume. Furthermore, when valley states of different modes are coupled into air, the wave vector in the beamformer differs near different valleys, requiring the beams on both sides to be aligned along the tangent direction of the interface (e0). cut The wave vector should remain unchanged, and the refraction angle should satisfy θ = arcsin(k y By using two sound sources ( / k0), different output beams can be obtained. Compared to excitation with a single sound source, it is easier to control the valley state mode of the excitation, thereby achieving our goal of beam manipulation.

[0066] Finally, it should be noted that although the embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments and application fields described above. The specific embodiments described above are merely illustrative and instructive, and not restrictive. Those skilled in the art, guided by this specification, can make many other forms without departing from the scope of protection of the claims of the present invention, and all of these are within the scope of protection of the present invention.

Claims

1. An acoustic beam modulator based on double-knot topological valley boundary states, characterized in that, The system comprises a top layer, a bottom layer, and an intermediate layer between the top and bottom layers. The intermediate layer includes an inverted acoustic cell array. The acoustic cell array comprises a plurality of acoustic cells with an S-graphene crystal structure arranged periodically in the x and y directions. Each acoustic cell includes a circular cavity and a coupling tube for connecting the circular cavity, wherein the positional distribution of the circular cavity corresponds to the positional distribution of carbon atoms in the S-graphene crystal structure, and the acoustic cells are asymmetric in the x or y direction. The intermediate layer is further configured to communicate with air only in the x direction, and to have a first hard boundary with a bearded boundary morphology and a second hard boundary with a zigzag boundary morphology arranged in the y direction.

2. The acoustic beam modulator as described in claim 1, characterized in that, The acoustic unit cell includes a first circular cavity arranged in a rectangular array in the middle, and a second circular cavity arranged on the outer periphery of the rectangular array at an angle of 30° to the horizontal direction. The first circular cavities all have the same radius, and at least one of the second circular cavities has a different radius than the first circular cavity.

3. The acoustic beam modulator as described in claim 2, characterized in that, The second circular cavity has only one cavity with a radius different from that of the first circular cavity.

4. The acoustic beam modulator as described in claim 3, characterized in that, The distance between adjacent cavities in the acoustic unit cell is a, the radius of the first cavity is r2 = 0.3a, the radius of the second cavity is r1 = 0.45a, which is different from the radius of the first cavity, and the width of the coupling tube is t = 0.25a; the first hard boundary is constructed as the inverse of a cavity with a radius of 0.3a added along the y direction of the acoustic unit cell array.

5. The acoustic beam modulator as described in claim 1, characterized in that, The period of the acoustic unit cell is greater than 7 in both the x and y directions.

6. The acoustic beam modulator as described in claim 1, characterized in that, The thickness of the intermediate layer is 0.5 ± 0.05 cm.

7. The acoustic beam modulator as described in claim 1, characterized in that, The acoustic beam modulator is made of any one of the following materials: photosensitive resin, acrylic, metal, or organic plastic.

8. A preparation method, characterized in that, For fabricating an acoustic beam modulator based on the double-knot topological valley boundary state as described in any one of claims 1 to 7, comprising: An acoustic unit cell with an S-graphene crystal structure is constructed, and by adjusting the size parameters of the circular cavity and / or coupling tube, the acoustic unit cell is made asymmetric in the x or y direction to break the degeneracy of two pairs of Dirac points and open the bulk band gap. The acoustic unit cell is inverted, the inverted region is stretched in the z direction, and then periodically arranged in the x and y directions respectively. Finally, the first hard boundary and the second hard boundary, as well as the top and bottom layers, are constructed to obtain the drawing of the acoustic beam modulator. Based on the prepared blueprints, a sound beam modulator is manufactured using 3D printing technology.

9. A control method, characterized in that, For controlling an acoustic beam modulator based on the double-knot topological valley boundary state as described in any one of claims 1 to 7: In the two circular cavities at the center of the acoustic unit cell at one end of the second hard boundary of the beam modulator, when a sound source of any frequency within the preset frequency range excites the W-type double-knot topological valley boundary state along the x-direction, or in the two circular cavities at the center of the acoustic unit cell at one end of the first hard boundary of the beam modulator, when a sound source of any frequency within the preset frequency range excites the M-type double-knot topological valley boundary state along the x-direction, two different valley state modes for realizing acoustic beam modulation can be obtained, namely the symmetric mode and the antisymmetric mode. In the two circular cavities at the center of the acoustic unit cell at either the second hard boundary or the first hard boundary of the beam modulator, two sound sources with a phase difference of 0 are used to excite a symmetrical mode, which is then coupled with the air to form a collimated beam. In the two circular cavities at the center of the acoustic unit cell at the second hard boundary or one end of the first hard boundary of the beam modulator, two sound sources with a phase difference of π are used to excite antisymmetric modes, which are then coupled with the air to form a split beam. The two sound sources used to excite the symmetric or antisymmetric mode have the same frequency and volume.

10. The control method as described in claim 9, characterized in that, The preset frequency range is 8.850 to 9.250 kHz, and the volume is between 30 and 100 decibels.

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