An underwater phononic crystal based on valley Hall-induced topological corner states

Abstract

The present invention relates to the field of acoustic technologies, and discloses an underwater phononic crystal based on valley Hall-induced topological corner states. The phononic crystal has a two-dimensional honeycomb hexagonal structure. A number of scatterers are rotatably provided within the hexagonal structure. A central column is further provided at the center of the hexagonal structure. Each of the scatterers is evenly distributed around the central column, and the rotation angles formed by each scatterer and the central column are all the same. The present invention solves the problem that existing two-dimensional phononic crystal structure devices lack flexibility in switching and selection, and has the characteristic that the boundary modes related to pseudospin have strong robustness to defects.

Description

Technical Field

[0001] The present invention relates to the field of acoustic technologies, and more particularly, to an underwater phononic crystal based on valley Hall-induced topological corner states. Background Art

[0002] In recent years, the discoveries of the quantum Hall effect (QHE), quantum spin Hall effect (QSHE), quantum anomalous Hall effect (QAHE), topological insulator (TI), etc. have attracted increasing attention to the abstract topological concepts in mathematics, opening up a new chapter for the research of topological insulators in condensed matter physics. The novel topological properties provide great flexibility for manipulating robust edge states, and it is possible to develop a new generation of low-power transistors and electronic devices, thus promoting the progress of information technology. Introducing the concept of topology into classical wave systems such as light waves, mechanical waves, and sound waves is a hot research field currently, which can achieve topologically protected edge states and many novel functions.

[0003] The topological transport of topological insulators is topologically protected. A remarkable feature of topological transport is its immune defect effect, and it can maintain the original transport state at the defective position with almost no reflection. The topological states in topological insulators have many novel features, such as: unidirectional transport boundary states, no backscattering, etc.

[0004] The discovery of phononic crystals further enriches the research of topological insulators and opens up a broader research field for them. In the bulk-edge correspondence, the dimension of the boundary states of phononic crystals in the same dimension is lower than that of the boundary states of first-order topological insulators. In the bandgap of phononic crystals, there are not only edge states that open the energy gap, but also zero-dimensional corner states or one-dimensional hinge states in the opened energy gap, and the existence of edge states is topologically protected, can exist stably, and has strong robustness.

[0005] In addition to the two degrees of freedom of charge and spin, solid materials also have valley degrees of freedom. Valley refers to a quantum state with an energy extreme value in momentum space. The angular momentum of the wave function at the unequal valley produces an opposite magnetic moment, thereby producing the quantum valley Hall effect. Valley degrees of freedom can be used as a new information carrier to mark discrete energy extreme states in momentum space. They are widely found in conventional semiconductors and the currently popular two-dimensional crystals graphene and molybdenum disulfide, and can be used in the design of future electronic devices. In acoustic systems, like spin in spin electronics, valley degrees of freedom are called pseudospins. The concept of valley states is introduced into phononic crystals, which are directly excited by external sound fields of specific frequencies, and have edge states that support topological protection. Most of the Dirac points in pseudospin acoustic topological insulators are generated by high symmetry. Dirac points can be formed by constructing a hexagonal honeycomb lattice structure with special symmetry, and then topological inversion is achieved by changing the angle of the scatterer. This vortex-locked valley transport will provide people with a completely new way of acoustic wave manipulation, such as rotational manipulation of microparticles, valley-selective excitation, boundary turning anti-reflection, etc. Using valley degrees of freedom for information processing has the advantages of less information loss, fast processing speed, low energy consumption, high integration, and long transmission distance.

[0006] As longitudinal waves, underwater sound waves have no polarization characteristics in the fluid and do not have a "spin" state. Existing acoustic topological isolators mainly study the propagation of sound in the air, which is relatively easy to obtain. In addition, previous studies on the acoustic pseudospin Hall effect have mainly focused on scatterer-dielectric matrix structures and dielectric plate-hole structures, or the use of annular airflow design to achieve acoustic topological insulators. High-order topological boundary states are connected to specific corners or hinges, lacking the flexibility of switching and selection.

[0007] The existing patent has a dual-band acoustic wave beam splitting device based on the acoustic valley Hall effect, including a matrix whose medium is air and a scatterer whose medium is an acoustic rigid material. A graphene-like honeycomb two-dimensional phononic crystal structure device is used to simulate the quantum valley Hall effect in acoustics. Because the phononic crystal unit cell structure maintains C6 symmetry, there are two linear Dirac degenerate points at the same time at the K point in the Brillouin zone. The band structure of the two-dimensional honeycomb phononic crystal is obtained using commercial simulation software, and the symmetry in the phononic crystal is adjusted to obtain the extreme point in the energy band - the valley, as a carrier of information. Then, two phononic crystal waveguide structures with different topological states are combined to realize a boundary state with the characteristics of suppressing backscattering and unidirectional transmission, and the unidirectionality of the boundary state is used to realize a dual-band acoustic wave beam splitter device.

[0008] Existing graphene-like honeycomb two-dimensional phononic crystal structure devices lack the flexibility of switching and selection. How to invent a new type of phononic crystal that can perform pure geometric manipulation of non-chiral scatterers and realize pseudospin topological states and higher-order topological states is a problem that needs to be urgently solved in this technical field. Summary of the invention

[0009] In order to solve the problem that existing two-dimensional phononic crystal structure devices lack the flexibility of switching and selection, the present invention provides an underwater phononic crystal based on valley Hall-induced topological corner states, which has the characteristic that the boundary modes related to pseudospin are highly robust to defects.

[0010] To achieve the above object of the present invention, the following technical solutions are adopted:

[0011] An underwater phononic crystal based on valley Hall-induced topological corner states, wherein the phononic crystal has a two-dimensional honeycomb hexagonal structure; several scatterers are rotatably arranged in the hexagonal structure; a central column is further provided at the center of the hexagonal structure; each of the scatterers is uniformly distributed around the central column, and the rotation angles formed by each scatterer and the central column are the same.

[0012] The present invention realizes the pure geometric manipulation of achiral scatterers by designing a two-dimensional honeycomb hexagonal structure and rotatably arranging several scatterers in the hexagonal structure, realizes pseudospin topological states and higher-order topological states, and improves the robustness of the boundary modes related to pseudospin to defects.

[0013] Preferably, the scatterer is a crescent-shaped scatterer.

[0014] Further, the mouth of the crescent of the crescent-shaped scatterer faces clockwise.

[0015] Furthermore, 3 crescent-shaped scatterers are rotatably arranged in the hexagonal structure; the 3 crescent-shaped scatterers are rotatably arranged in the hexagonal structure around the central column with C 3 symmetry.

[0016] Furthermore, in the initial unrotated state, the positions of the 3 crescent-shaped scatterers in each hexagonal structure respectively correspond to the 3 corners of the hexagonal honeycomb unit.

[0017] Furthermore, the rotation angle formed by the scatterer and the central column, that is, the angle between the line connecting the tangent point of the inner arc of the crescent-shaped scatterer and the center point of the hexagonal structure and the line connecting the adjacent vertex of the hexagonal structure and the center, is denoted as θ.

[0018] Furthermore, the distance between two opposite sides of the hexagonal structure is a preset value, denoted as the lattice constant, which is represented as a. The crescent-shaped scatterer is formed by stacking two circles with a radius of 0.1*a with a distance of b between the centers. The distance between two opposite sides of the hexagonal structure is a preset value, denoted as the lattice constant, which is represented as a. The crescent-shaped scatterer is formed by stacking two circles with a radius of 0.1*a with a distance of b between the centers.

[0019] Furthermore, the material of the central column is steel.

[0020] Furthermore, the material of the scatterer is rubber.

[0021] Furthermore, the substrate of the hexagonal structure is water.

[0022] The beneficial effects of the present invention are as follows:

[0023] By designing a two-dimensional honeycomb hexagonal structure and rotatably arranging a plurality of scatterers in the hexagonal structure, the present invention realizes the pure geometric manipulation of achiral scatterers, realizes the pseudo-spin topological state and the high-order topological state, and improves the robustness of the boundary mode related to the pseudo-spin against defects. The present invention thus solves the problem of the lack of flexibility in switching and selection in existing two-dimensional phonon crystal structure devices. Description of the Drawings

[0024] Figure 1 is a schematic structural diagram of an underwater phonon crystal based on the valley Hall-induced topological corner state of the present invention.

[0025] Figure 2 is the first Brillouin zone of an underwater phonon crystal based on the valley Hall-induced topological corner state of the present invention.

[0026] Figure 3 is the energy band diagram of an underwater phonon crystal based on the valley Hall-induced topological corner state of the present invention when the rotation angle θ of the scatterer is -4.57°.

[0027] Figure 4 is the energy band diagram of an underwater phonon crystal based on the valley Hall-induced topological corner state of the present invention when the rotation angle θ of the scatterer is -33.4°.

[0028] Figure 5 is the energy band diagram of an underwater phonon crystal based on the valley Hall-induced topological corner state of the present invention when the rotation angle θ of the scatterer is 23°.

[0029] Figure 6 is the eigenfrequency diagram of the two bandgap edges at the K point of the phonon crystal corresponding to different rotation angles θ of an underwater phonon crystal based on the valley Hall-induced topological corner state of the present invention.

[0030] Figure 7 is the dispersion curve diagram of an underwater phonon crystal based on the valley Hall-induced topological corner state of the present invention with different boundary types.

[0031] Figure 8 is the eigen sound pressure field distribution diagram of an underwater phonon crystal based on the valley Hall-induced topological corner state of the present invention in the positive boundary state.

[0032] Figure 9 This is the distribution diagram of the eigen - acoustic pressure field of an underwater phononic crystal based on valley - Hall - induced topological corner states in the negative - type boundary state of the present invention.

[0033] Figure 10 This is the distribution diagram of the acoustic pressure field and the eigen - mode diagram of a finite - quadrilateral supercell composed of an underwater phononic crystal based on valley - Hall - induced topological corner states of the present invention.

[0034] Figure 11 This is the distribution diagram of the acoustic pressure field of a defective finite - quadrilateral supercell composed of an underwater phononic crystal based on valley - Hall - induced topological corner states of the present invention.

[0035] Figure 12 This is a schematic diagram of a spliced two - dimensional bent acoustic waveguide structure composed of underwater phononic crystals based on valley - Hall - induced topological corner states, where some are topologically non - trivial and some are topologically trivial in the present invention.

[0036] Figure 13 This is the eigen - acoustic pressure field diagram of a spliced two - dimensional bent acoustic waveguide structure composed of underwater phononic crystals based on valley - Hall - induced topological corner states, where some are topologically non - trivial and some are topologically trivial in the present invention, under the action of an excitation source with a frequency of 42 kHz. Specific implementation manners

[0037] The following describes the present invention in detail in conjunction with the drawings and specific implementation manners.

[0038] Example 1

[0039] As Figure 1 shown, an underwater phononic crystal based on valley - Hall - induced topological corner states, the phononic crystal has a two - dimensional honeycomb hexagonal structure; several scatterers are rotatably arranged in the hexagonal structure; a central column is also provided at the center of the hexagonal structure; each of the scatterers is evenly distributed around the central column, and the rotation angles formed by each scatterer and the central column are the same.

[0040] In this embodiment, the COMSOL Multiphysics software based on the finite - element method is used to simulate the numerical values of the phononic crystal in the present invention, calculate the band diagram of the primitive cell of this phononic crystal to reflect the two - dimensional crystal properties, apply periodic boundary conditions to the corresponding boundaries of the primitive cell, and by rotating the scatterers around the center, the phononic crystal can have different symmetries.

[0041] Example 2

[0042] As Figure 1As shown, an underwater phononic crystal based on valley Hall-induced topological corner states, where the phononic crystal has a two-dimensional honeycomb hexagonal structure; several scatterers are rotatably arranged within the hexagonal structure; a central column is further provided at the center of the hexagonal structure; each of the scatterers is evenly distributed around the central column, and the rotation angles formed by each scatterer and the central column are the same.

[0043] In a specific embodiment, the scatterer is a crescent-shaped scatterer.

[0044] In a specific embodiment, the mouth of the crescent of the crescent-shaped scatterer faces the clockwise direction.

[0045] In a specific embodiment, 3 crescent-shaped scatterers are rotatably arranged within the hexagonal structure; the 3 crescent-shaped scatterers are rotatably arranged in the hexagonal structure around the central column with C 3 symmetry.

[0046] In this embodiment, the lattice constant of the phononic crystal is a = 2.1 cm, and the crescent-shaped scatterer is formed by stacking two circles with a radius of 0.1*a with a staggering distance of b between the centers.

[0047] In a specific embodiment, in the initial unrotated state, the positions of the 3 crescent-shaped scatterers in each hexagonal structure respectively correspond to the 3 corners of the hexagonal honeycomb unit.

[0048] In a specific embodiment, the rotation angle formed by the scatterer and the central column, that is, the angle between the line connecting the tangent point of the inner arc of the crescent-shaped scatterer and the center point of the hexagonal structure and the line connecting the adjacent vertex of the hexagonal structure and the center, is denoted as θ.

[0049] In a specific embodiment, the distance between two opposite sides of the hexagonal structure is a preset value, denoted as the lattice constant, which is represented as a, and the crescent-shaped scatterer is formed by stacking two circles with a radius of 0.1*a with a distance of b between the centers.

[0050] In a specific embodiment, the material of the central column is steel.

[0051] In a specific embodiment, the material of the scatterer is rubber.

[0052] In a specific embodiment, the base material of the hexagonal structure is water.

[0053] In this embodiment, the material of the crescent-shaped scatterer is soft rubber, and the central steel column is a circle with a radius of 0.1*a.

[0054] In this embodiment, the density ρ of the soft rubber 1 = 1000 kg / m3 , the speed of sound c 1 = 489.9 m / s; the density of steel = ρ 2 : 8000 kg / m 3 , the speed of sound c 2 = 5000 m / s; for water, ρ 0 = 1000 kg / m 3 , c 0 = 1482.9 m / s.

[0055] The Brillouin zone of the primitive cell in the initial non-rotated state is as Figure 2 shown. Through the Brillouin zone of the primitive cell, its corresponding dispersion relation can be obtained; the dispersion relation is as Figure 3 , 4 , 5 shown, where the abscissa is the Brillouin zone, the ordinate represents the characteristic frequency, and the lines are energy bands.

[0056] As Figure 3 shown, when θ = -4.57°, it can be seen that at a frequency of 42.9 KHz, an accidental degenerate Dirac point appears at the high-symmetry point K of the Brillouin zone.

[0057] In a specific embodiment, rotating 3 crescent-shaped scatterers around the central column can generate different crystal symmetries.

[0058] In this embodiment, the scatterers are rotated clockwise by 33.4° and counterclockwise by 23° respectively. Taking the counterclockwise rotation as positive, phononic crystals A and phononic crystal B are obtained respectively. The dispersion relations of crystal A and crystal B are as Figure 4 , Figure 5 shown. Crystal A and crystal B respectively correspond to phononic crystals in topologically non-trivial and topologically trivial states. For phononic crystal A, the Dirac point is opened to form a bandgap with a bandwidth of about 4.1 KHz, generating a valley Hall state; for phononic crystal B, the Dirac point is also opened. Thus, during the rotation process from θ = 23° to θ = -33.4°, two valley Hall phase transitions occur continuously. Its acoustic valley pseudospin state shows opposite chirality similar to the electronic valley state. The process of Dirac point opening - closing - opening occurs at the high-symmetry point K of the Brillouin zone, corresponding to Figure 6 .

[0059] In this embodiment, the valley eigenstate acoustic vortices all have the cell center as the vortex center. Among them, the vortex center direction of the p-state is clockwise, while the q+-state is counterclockwise. Therefore, the corresponding electron spin states can be simulated. Among them, + and - respectively represent the vortex acoustic energy fluxes counterclockwise and clockwise around the center point.

[0060] In this embodiment, considering the second bandgap, for the rotation angles θ with opposite signs, different topological properties appear in the two types of phononic crystals A and B. Although the pressure field distributions of the two eigenstates at the K point also form a bandgap, combining the characteristics of the eigen - acoustic pressure field and the vortex distribution, the corresponding valley eigenstates are reversed, indicating that the energy bands have undergone topological inversion, and the signs of the effective masses m near the corresponding Dirac cones are opposite, that is, m (A) =-m (B) , and the valley Chern numbers of the two types of phononic crystals have different valley Hall phases, enabling valley topological transport. The C 3 symmetry of the phononic crystal satisfies the symmetry of the pseudo - time - reversal operator, thus enabling the realization of the acoustic quantum spin Hall effect.

[0061] In this embodiment, the crescent - shaped scatterer satisfies the spatial rotation symmetry. On the specified type of boundary, the topological boundary states excited by a specific valley will propagate along a fixed direction. The topological water - based phononic crystals with different rotation angles are spliced and combined, and different types of boundaries are respectively defined as positive - type boundaries and negative - type boundaries.

[0062] In this embodiment, the valley Hall waveguide dispersion relation of the spliced structure obtained after splicing and combination is as Figure 7 shown, where the abscissa is the direction of the wave vector k and the ordinate is the eigen - frequency. In the figure, the dotted line in the energy band gap of the bulk energy band represents the boundary state of boundary transmission. The energy bands where points A and B are located respectively represent the topological boundary states transmitted along the negative - type and positive - type boundaries, and their group velocities are opposite. The topological boundary states of the phononic crystal at the interface in the topologically trivial and non - trivial states are as Figure 8 and Figure 9 shown.

[0063] In this embodiment, the two - dimensional phononic crystals with topologically trivial and non - trivial structures are spliced together, and it is infinite - periodic in the y - direction. It can be seen that the sound field energy is only localized at the splicing boundary, and the sound pressure of the eigen - state of the sound pressure is localized on the boundary, that is, the edge state, and the edge state appears in the bandgap of the bulk state, and the boundary state connects the bulk states. The formation of the boundary state comes from the change of the topological valley Chern numbers of different topological structures on both sides of the boundary; the perturbations of phononic crystal A and phononic crystal B respectively satisfy Δp A <0 and Δp B >0, where Δp represents the geometric perturbation. For the negative - type boundary, since the valley Chern number changes to at the K' point and will be transmitted in the opposite direction at the K point, △C (K‘) =1.

[0064] As can be seen from this embodiment, when the rotation angle of the scatterer is θ = -33.4°, the primitive cell of the phononic crystal is a topologically non-trivial structure; in this embodiment, a finite acoustic structure is constructed using the primitive cell with topologically non-trivial properties. To verify the robustness of the parallelogram supercell, the topologically non-trivial phononic crystal A was assembled into a 10*10 parallelogram phononic crystal supercell, and its eigenmode conditions within the bandgap were calculated; as Figure 10 shown, in the sound pressure eigenfield of the angular state at a frequency of 44.7 kHz, it can be found that there are eigenfrequencies within the complete bandgap. By observing their sound pressure eigenfields, one-dimensional boundary states and zero-dimensional angular states can be found. The shaded area in the figure represents the bandgap range. The finite phononic crystal supercell generates topological boundary states and topological angular states within the bandgap, and robust low-dimensional corner or hinge states appear in the edge gaps of the higher-order topological insulator. The angular state mode can be clearly seen from the sound pressure eigenfield. For the non-trivial supercell composed of phononic crystal A, the sound field energy is significantly concentrated at the lower left corner point, and the sound pressure intensity at other positions is almost zero. The sound pressure eigenfield corresponding to the eigenfrequency outside the bandgap is the bulk state mode, and the sound pressure of the bulk state mode will be distributed over the entire finite acoustic structure.

[0065] In this embodiment, the topological boundary state is not affected by defects. Whether it is a curved boundary or a boundary with defects such as holes and disorder, the topologically protected boundary state can bypass these defects with almost no reflection, so it has strong robustness. A point defect is a defect that deviates from the normal arrangement of the crystal structure at a node or in a neighboring microscopic region. It is the simplest crystal defect. For example, vacancies, interstitial atoms, impurity atoms, etc. are all point defects, which are also called zero-dimensional defects. In the following content, we verified that in the vacancy defect type of this phononic crystal, the topologically protected angular states with different pseudospin states still exist stably.

[0066] Example 3

[0067] More specifically, in this embodiment, the valley topological sound pressure amplitude distribution generated by acoustic excitation is as Figure 11 shown, where the arrow indicates the point sound source, which is located at any point on the interface of the phononic crystal, and the excited sound wave frequency is 44.7 kHz. Figure 10 It shows that when the valley topological phononic crystal has no defect structure, this finite crystal structure can well support the transmission of valley Hall topological sound waves; as Figure 11 shown, the sound source excitation can still bypass the vacancy defect and reach the corner point of the finite quadrilateral structure composed of this phononic crystal, corresponding to Figure 10 shown, the sound source excitation can still bypass the vacancy defect and reach the corner point of the finite quadrilateral structure composed of this phononic crystal,

[0068] The mediocre-non-trivial boundary corresponds to the negative-type boundary, and the valley Chern number changes by △C at the K' point(K‘) =-1, the energy flow rotates clockwise, while at the non-trivial - trivial boundary, the opposite is true. The sound pressure field is mainly concentrated at the topological trivial and non-trivial boundaries and propagates. The energy decays rapidly during the process of propagating from the interface between the two different lattices of phononic crystal A and phononic crystal B to both sides. Since the proposed finite structure can support topological boundary states, we can utilize this unique property to realize new functional waveguide devices.

[0069] In this embodiment, a two-dimensional bent acoustic waveguide structure is spliced by topological non-trivial and topological trivial lattices. This structure is spliced by phononic crystal A and topological trivial phononic crystal B. The interface contains topological trivial and topological non-trivial primitive cells. Above and below the dashed and solid lines are topological trivial lattices and topological non-trivial lattices respectively, and the interface direction is a bent curve. As Figure 12 shown, the dashed and solid lines are two different types of splicing interfaces. The solid line is a zigzag interface, and the dashed line is an armchair interface. A directional waveguide structure is constructed by splicing two different types of lattices.

[0070] In this embodiment, at the left end of the two-dimensional finite waveguide structure, that is, at the splicing interface of phononic crystal A and phononic crystal B, a point source is placed for eigenfield excitation. Figure 13 This is the excitation sound pressure field diagram of the two-dimensional bent acoustic waveguide structure at an excitation source frequency of 42 kHz. From the sound pressure field distribution, it can be found that due to the existence of topologically protected boundary states at the interface between non-trivial and trivial splices, even though the splicing interface between phononic crystal A and phononic crystal B is in a curved shape, the sound wave can still propagate forward along the interface, and the backscattering is effectively suppressed. On the one hand, it shows that even if there are some uncontrollable bending defects in the waveguide structure, the edge states can still bypass the defects and propagate to the right side of the waveguide, thus indicating that the valley topological acoustic waveguide has good robustness; on the other hand, due to the high transmittance and backscattering-free sound transmission of this phononic crystal structure, based on the propagation characteristics of this phononic crystal waveguide and the utilization of topologically protected interface states, acoustic waveguide transmission devices and materials with specific functions can be designed and constructed.

[0071] The present invention designs a two-dimensional honeycomb hexagonal structure and rotatably arranges a plurality of scatterers within the hexagonal structure, realizing pure geometric manipulation of achiral scatterers, achieving pseudo-spin topological states and higher-order topological states, and improving the robustness of the boundary modes related to pseudo-spin against defects. The present invention theoretically designs a selective higher-order topological corner state using common materials. The corner states are manifested in different geometric corners due to different valley selections, showing topological switchability and valley-point selectivity, providing a theoretical model for the interaction between higher-order topological insulators, valley-selective corner states, and higher-order valley degrees of freedom, and helping to improve the flexibility of selective corners. This selective and robust underwater acoustic topological transmission helps to realize acoustic lossless devices such as topological switches and energy harvesting. The present invention thus solves the problem that the existing two-dimensional phononic crystal structure devices lack flexibility in switching and selection.

[0072] Obviously, the above-mentioned embodiments of the present invention are merely examples for clearly illustrating the present invention, rather than limitations on the implementation manners of the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the claims of the present invention.

Claims

1. An underwater phononic crystal based on valley Hall-induced topological corner states, Characterized in that: The phonon crystal described is a two-dimensional honeycomb hexagonal structure; several scatterers are rotatably arranged within the hexagonal structure; a central column is further provided at the center of the hexagonal structure; each of the scatterers is evenly distributed around the central column, and the rotation angles formed by each scatterer and the central column are the same; the scatterer is a crescent-shaped scatterer; 3 crescent-shaped scatterers are rotatably arranged within the hexagonal structure; the 3 crescent-shaped scatterers are rotatably arranged in the hexagonal structure around the central column with C 3 symmetry. In the initial unrotated state, the positions of the 3 crescent-shaped scatterers in each hexagonal structure correspond to the 3 corners of the hexagonal honeycomb unit; the rotation angle formed by the scatterer and the central column, that is, the angle between the line connecting the tangent point of the inner arc of the crescent-shaped scatterer and the center point of the hexagonal structure and the line connecting the adjacent vertex of the hexagonal structure and the center, is denoted as θ.

2. The underwater phononic crystal based on valley Hall-induced topological corner states according to claim 1, Characterized in that: The mouth of the crescent of the crescent-shaped scatterer faces clockwise.

3. The underwater phononic crystal based on valley Hall-induced topological corner states according to claim 2, Characterized in that: The distance between two opposite sides of the hexagonal structure is a preset value, denoted as the lattice constant, the lattice constant is represented as a, and the crescent-shaped scatterer is formed by stacking two circles with a radius of 0.1*a with a distance of b between the centers.

4. The underwater phononic crystal based on valley Hall-induced topological corner states according to claim 1, Characterized in that: The material of the central column is steel.

5. The underwater phononic crystal based on valley Hall-induced topological corner states according to claim 1, Characterized in that: The material of the scatterer is rubber.

6. The underwater phononic crystal based on valley Hall-induced topological corner states according to claim 1, Characterized in that: The base material of the hexagonal structure is water.

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