Rotatable broadband tunable acoustic metasurface

Abstract

The present disclosure provides a rotating broadband adjustable acoustic metasurface, comprising a plurality of unit cells arranged side by side in a horizontal direction, the unit cells are configured as a substantially cubic structure, and the inside of the unit cells defines a resonance cavity in communication with the outside; the side of the resonance cavity facing the sound source is provided with a neck having a rectangular opening, the neck includes a rectangular neck configured to have the same cross-sectional area as the rectangular opening and a tapered neck extending to the inside of the resonance cavity, and the tapered neck is configured with an adjustable first surface; wherein each unit cell is configured to adjust the phase difference of the plane wave sound waves input through the rectangular opening in response to a first included angle formed by the extension direction of the first surface and the horizontal direction, so as to make the sound waves directional reflection or spot focusing.

Description

Technical Field

[0001] At least one embodiment of this disclosure relates to the field of acoustic wave control technology, and more specifically, to an acoustic metasurface. Background Technology

[0002] An acoustic metasurface is a structure used to control the propagation of sound waves, typically composed of a series of periodic or aperiodic unit cells. Unit cells are suitable for controlling the local phase and / or amplitude of sound waves to achieve sound field manipulation and thus realize desired functions. Examples include at least one of the following: directional reflection of sound waves, point-to-point focusing, sound absorption, and sound insulation.

[0003] Currently, based on the type of unit cell, acoustic metasurfaces can be broadly classified into three categories: labyrinth type, Helmholtz resonant cavity type, and membrane type metasurfaces. However, these acoustic metasurfaces can only achieve specific functions for sound waves of specific frequencies, such as directional reflection, point focusing, sound absorption, and sound insulation. Therefore, they cannot meet the sound wave control requirements under different operating conditions.

[0004] Therefore, methods such as adjusting the orientation of the entire metasurface or introducing an external field can be used to partially control the acoustic metasurface. However, adjusting the orientation of the entire metasurface cannot achieve large-scale, continuous control; while introducing an external field increases the complexity and control difficulty of the system. Summary of the Invention

[0005] To address at least one of the aforementioned and other technical problems in the prior art, this disclosure provides an acoustic metasurface. Through the configured adjustable first surface, the equivalent impedance of the unit cell can be changed, thereby affecting the phase difference of the incident sound wave and altering the phase gradient of the acoustic metasurface. This enables the acoustic metasurface to switch between directional reflection and point focusing of sound waves.

[0006] Embodiments of this disclosure provide an acoustic metasurface comprising a plurality of unit cells arranged side-by-side along a horizontal direction, the unit cells being configured in a generally cubic structure, the interior of each unit cell defining a resonant cavity communicating with the exterior; a neck with a rectangular opening is provided on the side of the resonant cavity facing a sound source, the neck comprising a rectangular neck configured to have the same cross-sectional area as the rectangular opening and a tapered neck extending toward the interior of the resonant cavity, the tapered neck being provided with an adjustable first surface; wherein each of the unit cells is configured to adjust the phase difference of a planar waveform sound wave input through the rectangular opening in response to a first angle formed by the extension direction of the first surface and the horizontal direction, so as to cause the sound wave to be directionally reflected or focused at a fixed point.

[0007] According to an embodiment of the present disclosure, the unit cell includes: a frame, configured as a generally cubic structure, the interior of the frame defining at least one resonant cavity, the upper part of the resonant cavity forming the rectangular opening; and a blade pair, including two blades, the two blades being symmetrically disposed on opposite sides of the rectangular opening, the upper surface of the blades serving as the first surface.

[0008] According to an embodiment of the present disclosure, the upper part of the frame is symmetrically provided with protrusions on both sides, which protrude inward toward the inside of the frame and extend along the horizontal direction, and the rectangular opening is formed between the two protrusions.

[0009] According to an embodiment of the present disclosure, the blade is rotatably disposed on the frame and has a rotating state that rotates about a fixed axis relative to the rectangular opening and a fixed state that is stationary relative to the rectangular opening, so as to adjust the angle of the first included angle.

[0010] According to embodiments of this disclosure, the resonant cavity is configured as an axisymmetric structure.

[0011] According to embodiments of this disclosure, the aforementioned unit cell is provided with a plurality of resonant cavities connected in series.

[0012] According to an embodiment of the present disclosure, a plurality of the above-mentioned resonant cavities are stacked along the height direction of the above-mentioned unit cell; wherein, the rectangular opening of the above-mentioned resonant cavity located at the upper part serves as the incident side for inputting the above-mentioned sound waves.

[0013] According to an embodiment of the present disclosure, the rectangular opening is disposed in the middle of the resonant cavity, and the orthographic projections of the plurality of rectangular openings along the height direction of the resonant cavity coincide.

[0014] According to embodiments of this disclosure, the angle of the first included angle formed by the conical neck of each of the resonant cavities in the same unit cell is the same.

[0015] According to embodiments of this disclosure, the first included angle formed by the conical neck of at least a portion of the resonant cavities in the same unit cell is configured to be different from the first included angle formed by the conical neck of other resonant cavities.

[0016] According to the acoustic metasurface provided in this disclosure, the angle of the first included angle can be continuously adjusted through the configured adjustable first surface. The impedance and / or phase difference of the unit cell change in response to the angle of the first included angle, thereby changing the phase gradient of the acoustic metasurface to realize the functional switching of the acoustic metasurface for directional reflection and fixed-point focusing of sound waves. Attached Figure Description

[0017] Figure 1This is a cross-sectional view of an acoustic metasurface according to an illustrative embodiment of the present disclosure;

[0018] Figure 2 yes Figure 1 A partial enlarged view of a unit cell in the schematic embodiment shown;

[0019] Figure 3 yes Figure 1 The finite element equivalent model of the unit cell element of the illustrative embodiment shown; Figure 3 'a' is the finite element model used in solving the impedance and phase difference of a unit cell using the transmission and reflection coefficient method. Figure 3 b is the mesh used in the finite element model; Figure 3 c is a graph showing the relationship between the equivalent impedance of a unit cell with four resonant cavities and the first included angle θ, illustrating the comparison between the finite element simulation solution and the theoretical solution; Figure 3 c is a graph showing the relationship between the phase difference of a unit cell with four resonant cavities and the first included angle θ, illustrating the comparison between the finite element simulation solution and the theoretical solution;

[0020] Figure 4 This is a phase difference diagram showing the directional reflection of a vertically incident sound wave by an acoustic metasurface according to an illustrative embodiment of the present disclosure.

[0021] Figure 5 It is aimed at Figure 4 The schematic embodiment shown is a finite element simulation of the directional reflection of a vertically incident sound wave by an acoustic metasurface.

[0022] Figure 6 It is aimed at Figure 4 The energy flow distribution diagram of the scattered sound field of the acoustic metasurface of the schematic embodiment shown in the figure, which directionally reflects a vertically incident sound wave.

[0023] Figure 7 This is a cross-sectional view of an acoustic metasurface according to another illustrative embodiment of the present disclosure;

[0024] Figure 8 It is aimed at Figure 7 A schematic diagram illustrating the manipulation of sound waves by an acoustic metasurface in an exemplary embodiment; Figure 8 'a' is the sound field time-domain plot, showing the contour plot at 11.36ms; Figure 8 b is the frequency domain sound field obtained from the simulation at 1436Hz;

[0025] Figure 9 A phase difference diagram illustrating the point-focusing of a vertically incident sound wave using an acoustic metasurface according to an illustrative embodiment of the present disclosure.

[0026] Figure 10 It is aimed at Figure 9 The finite element simulation diagram illustrating the illustrative embodiment of the acoustic metasurface focusing a vertically incident sound wave at a specific point; and

[0027] Figure 11 It is aimed at Figure 9 The diagram illustrates the distribution of energy of the scattered sound field along the horizontal cross section of the focal point when the acoustic metasurface of the schematic embodiment focuses a vertically incident sound wave at a specific point.

[0028] In the accompanying drawings, the meanings of the reference numerals are as follows:

[0029] 1. Framework;

[0030] 11. Resonance cavity;

[0031] 111. Rectangular opening;

[0032] 112. Rectangular neck;

[0033] 113. Conical neck;

[0034] 12. Neck; and

[0035] 2. Leaves. Detailed Implementation

[0036] To make the objectives, technical solutions and advantages of this disclosure clearer, the following detailed description is provided in conjunction with specific embodiments and the accompanying drawings.

[0037] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0038] All terms used herein, including technical and scientific terms, have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0039] When using expressions such as "at least one of A, B, and C," the meaning should generally be interpreted according to the understanding of someone skilled in the art. For example, "a system having at least one of A, B, and C" should include, but is not limited to, systems having A alone, having B alone, having C alone, having A and B, having A and C, having B and C, and / or having A, B, and C. Similarly, when using expressions such as "at least one of A, B, or C," the meaning should generally be interpreted according to the understanding of someone skilled in the art. For example, "a system having at least one of A, B, or C" should include, but is not limited to, systems having A alone, having B alone, having C alone, having A and B, having A and C, having B and C, and / or having A, B, and C.

[0040] Figure 1 This is a cross-sectional view of an acoustic metasurface according to an illustrative embodiment of the present disclosure.

[0041] According to the acoustic metasurface provided in this disclosure, such as Figure 1 As shown, the system includes multiple unit cells arranged side-by-side along a horizontal direction, with each unit cell defining a resonant cavity 11 that communicates with the outside. A neck 12 with a rectangular opening 111 is provided on the side of the resonant cavity 11 facing the sound source. The neck 12 includes a rectangular neck 112 configured to have the same cross-sectional area as the rectangular opening 111 and a tapered neck 113 extending inwards towards the resonant cavity 11. The tapered neck 113 is provided with an adjustable first surface. Each unit cell is configured to adjust the phase difference of a planar waveform sound wave input through the rectangular opening 111 in response to a first angle formed by the extension direction of the first surface and the horizontal direction, thereby causing the sound wave to be directionally reflected or focused at a specific point.

[0042] In this implementation, the acoustic metasurface, through its adjustable first surface, can continuously adjust the angle of a first included angle. This change in the angle causes a change in the equivalent bulk modulus and / or equivalent mass of the resonant cavity. Consequently, the impedance and / or phase difference of the unit cell change in response to the angle of the first included angle, thereby altering the phase gradient of the acoustic metasurface and enabling the acoustic metasurface to switch between directional reflection and point-to-point focusing of sound waves.

[0043] In one illustrative embodiment, if the sound wave of the input planar waveform is directionally reflected at a specific angle, according to the generalized Snell's law, the phase gradient of the acoustic metasurface must satisfy the following equation (1):

[0044]

[0045] In Equation 1, θ r Characterized by the reflection angle, θ i The incident angle is represented by λ, and the wavelength of the sound wave is represented by λ. The phase gradient function is represented by dx, the lattice constant of the unit cell is represented by dφ, and the phase difference between two adjacent unit cells is represented by dφ.

[0046] Where, θ i And λ can be obtained based on the sound wave to be reflected, θ r and dx (i.e., the width of a single cell, such as...) Figure 2 The d0 shown is a preset value. Therefore, the phase difference dφ between adjacent unit cells of the acoustic metasurface used for directional reflection of sound waves can be obtained.

[0047] Furthermore, based on COMSOL Multiphysics and MATLAB software, a finite element simulation model of the unit cell can be established, and the equivalent impedance of the unit cell with the corresponding configuration can be calculated accordingly.

[0048] Figure 3 yes Figure 1 The finite element method of the equivalent model of the unit cell element in the illustrative embodiment shown; Figure 3 'a' is the finite element model used in solving the impedance and phase difference of a unit cell using the transmission and reflection coefficient method. Figure 3 b is the mesh used in the finite element model (where the frequency of the sound wave is configured to 1000Hz, and the mesh is a free triangular mesh); Figure 3 c is a graph showing the relationship between the equivalent impedance of a unit cell with four resonant cavities and the first included angle θ, illustrating the comparison between the finite element simulation solution and the theoretical solution; Figure 3 c is a graph showing the relationship between the phase difference of a unit cell with four resonant cavities and the first included angle θ, illustrating the comparison between the finite element simulation solution and the theoretical solution.

[0049] In one illustrative embodiment, reference is made to... Figure 3 The figure shows a unit cell finite element model built using the pressure acoustics module of COMSOL Multiphysics. The boundaries of the unit cells are replaced with acoustic hard boundaries, and the remaining material is air with a density of 1.21 kg / m³. 3 The speed of sound is 343 m / s.

[0050] For details, refer to Figure 3 As shown in Figure a, the Floquet continuity boundary conditions are set for boundaries CE and C1E1 in the above finite element model; plane wave radiation conditions are set for boundary CC1 to simulate an infinite domain; and a plane wave background pressure field p with the wave vector direction perpendicularly downward exists in the air domain. b The pressure amplitude is set to 1 Pa.

[0051] Furthermore, refer to Figure 3As shown in b, the air domain in the above finite element model uses a free triangular mesh, with the largest element size being one-fifteenth of the wavelength, generating a total of 1647 domain elements, 373 boundary elements, and 192 vertex elements.

[0052] For the above finite element model, calculate the total pressure field data in the air domain, denoted as p. t The background pressure field is denoted as p. b (As a known quantity), therefore, the scattering pressure field p s Can be derived from p t -p b get.

[0053] In COMSOL, the time term of the phase is positive, therefore the expression for the incident sound pressure field with the wave vector pointing vertically downwards is:

[0054]

[0055] The direction of the scattered sound pressure field is opposite to that of the incident sound pressure field, and is vertically upward, as expressed in the following expression:

[0056]

[0057] The total sound pressure field is the superposition of the background sound pressure field and the scattered sound pressure field, and its expression is:

[0058]

[0059] Since there may be high-order mode falloff waves on the surface of periodic materials, in order to avoid the influence of high-order modes on the calculation results, the above embodiment does not directly extract the sound pressure at the boundary EE1 between the unit cell and the external air domain. Instead, it extracts the sound pressure at a distance from the upper surface of the unit cell and uses the phase relationship to infer the sound pressure at the upper surface boundary EE1 of the unit cell. The specific method is as follows:

[0060] An averaging operator is set at line segment DD1 to extract the average sound pressure of the background sound pressure field and the scattered sound pressure field at that point, denoted as variable p respectively. b_D and p s_D Assuming the distance between line segments DD1 and EE1 is dy, the incident sound pressure at EE1 can be obtained according to the phase difference relationship:

[0061] p b_E =p b_D e (-ikdy) (Equation 2.3)

[0062] The reflected sound pressure at boundary EE1:

[0063] p s_E =p s_D e (ikdy) (Equation 2.4)

[0064] The reflection coefficient (complex form) at the EE1 boundary can be obtained through the following transformation:

[0065]

[0066] The argument of the reflection coefficient is the phase difference between the incident and reflected sound waves caused by the unit cell at interface EE1, and its expression is as follows:

[0067] Δφ=arg(R) (Equation 2.6)

[0068] The expression for the impedance of a single cell is:

[0069]

[0070] Based on equation (1) and equations (2.1) to (2.7), the relationship between the first angle θ formed by the first surface and the horizontal direction and the phase difference dφ of the two adjacent unit cells can be obtained, and the angle of the first angle can be configured by the phase difference of the two adjacent unit cells.

[0071] Reference Figure 3 As shown in c and d, the calculation results of the equivalent impedance and phase difference of the unit cell and the theoretical solution and the finite element simulation solution of the unit cell adjustable parameter θ are compared. In the simulation, parametric scanning was used to solve θ. The range of the first included angle θ is [45°, 160°], and the step size of the parametric scanning is 0.1°.

[0072] In this implementation, when the first included angle is within the aforementioned range (i.e., θ ranges from [45° to 160°]), the simulation solution and the theoretical solution can match well. Therefore, to achieve directional reflection of sound waves of the corresponding frequency, the first included angle θ can be configured within the aforementioned range. It should be understood that the embodiments of this disclosure are not limited thereto. The aforementioned first included angle, responding to the frequency and / or incident angle of the incident sound wave, can be configured to other angles to preferably meet the requirements for directional reflection of the corresponding sound wave.

[0073] Figure 2 yes Figure 1 A partially enlarged view of a unit cell in the schematic embodiment shown.

[0074] According to embodiments of this disclosure, such as Figure 1 and Figure 2 As shown, the unit cell includes a frame 1 and a pair of blades. The frame 1 is constructed in a generally cubic structure, and the interior of the frame 1 defines at least one resonant cavity 11, with a rectangular opening 111 formed at the top of the resonant cavity 11. The pair of blades includes two blades 2, which are symmetrically arranged on opposite sides of the rectangular opening 111, and the upper surface of the blades 2 serves as the first surface.

[0075] According to embodiments of this disclosure, such as Figure 1 and Figure 2 As shown, the upper part of the frame 1 has symmetrical protrusions on both sides that protrude inwards and extend horizontally, forming a rectangular opening 111 between the two protrusions.

[0076] According to embodiments of this disclosure, such as Figure 1 and Figure 2 As shown, the blade 2 is rotatably mounted on the frame 1, having a rotating state that rotates about a fixed axis relative to the rectangular opening 111, and a fixed state that is stationary relative to the rectangular opening 111, so as to adjust the angle of the first included angle.

[0077] In this embodiment, the blade is rotatably disposed on the protrusion. The phase difference between the adjacent unit cells is obtained according to the function to be achieved by the acoustic metasurface unit. Based on the phase difference, the blade is adjusted in a rotating state, and the blade is kept in a fixed state when a preset first included angle is reached, thereby realizing the functional adjustment of the acoustic metasurface.

[0078] According to embodiments of this disclosure, such as Figure 1 and Figure 2 As shown, the resonant cavity 11 is constructed as an axisymmetric structure.

[0079] According to embodiments of this disclosure, such as Figure 1 and Figure 2 As shown, the unit cell contains multiple resonant cavities 11 connected in series.

[0080] According to embodiments of this disclosure, such as Figure 1 and Figure 2 As shown, multiple resonant cavities 11 are stacked along the height direction of the unit cell. The rectangular opening 111 of the upper resonant cavity 11 serves as the incident side for the input sound wave (e.g., Figure 1 and Figure 2 (as shown on the upper side).

[0081] According to embodiments of this disclosure, such as Figure 1 and Figure 2 As shown, a rectangular opening 111 is disposed in the middle of the resonant cavity 11, and the orthographic projections of multiple rectangular openings 111 along the height direction of the resonant cavity 11 coincide.

[0082] According to embodiments of this disclosure, such as Figure 1 and Figure 2 As shown, the angle of the first included angle formed by the conical neck 113 of each resonant cavity 11 in the same unit cell is the same.

[0083] In one illustrative embodiment, such as Figure 1 and Figure 2As shown, each unit cell of the acoustic metasurface is configured with four resonant cavities. It should be understood that the embodiments of this disclosure are not limited thereto.

[0084] For example, each unit cell can be configured with one, two, three, five, or other numbers of resonant cavities.

[0085] In this implementation, by configuring different numbers of resonant cavities, the following can be adjusted: Figure 2 The number of boundaries A (i.e., the boundary formed by the rectangular neck 112) and B (i.e., the boundary formed by the conical neck 113) is shown. This allows for adjustment of the compression effect of air movement at boundary A on the gas within the resonant cavity, the compression effect of air movement at boundary B on the gas within the resonant cavity, the mutual radiation between boundaries A and B, and the self-radiation effect of boundaries A and B. This, in turn, affects the resonance of the air within the unit cell, causing the sound wave to undergo a phase change from -π to π, thereby improving the acoustic metasurface's adaptability to sound waves.

[0086] Figure 4 This is a phase difference diagram showing the directional reflection of a vertically incident sound wave by an acoustic metasurface according to an illustrative embodiment of the present disclosure. Figure 5 It is aimed at Figure 4 The schematic embodiment shown is a finite element simulation of the directional reflection of a vertically incident sound wave by an acoustic metasurface. Figure 6 It is aimed at Figure 4 The diagram illustrates the energy flow distribution of the scattered sound field when an acoustic metasurface of a schematic embodiment directionally reflects a vertically incident sound wave.

[0087] In one illustrative embodiment, the acoustic metasurface is configured with 40 unit cells arranged side-by-side in a horizontal direction. Specifically, each unit cell is provided with 4 resonant cavities.

[0088] Furthermore, such as Figure 2 As shown, the height (h0) of each unit cell is configured to be 102 mm; the width (d0) of each unit cell is configured to be 34 mm; the wall thickness of each unit cell is configured to be 2 mm; the height (h) of each resonant cavity is configured to be 22 mm; and the thickness (d) of each resonant cavity is configured to be 30 mm. Furthermore, the blade length is configured to be 7.5 mm, and the height of the rectangular neck (i.e., the thickness of the protrusion) is configured to be 3 mm.

[0089] Based on the acoustic metasurface unit in the above embodiments, sound waves with frequencies of 1000Hz, 4000Hz, and 2500Hz are reflected at a 30° angle, and sound waves with a frequency of 2500Hz are reflected at a 45° angle. In detail, for the above four types of directional reflections (hereinafter referred to as functions 1 to 4), the phase difference required for the arrangement of two adjacent unit cells is calculated according to equation (1) and equations (2.1) to (2.7).

[0090] Function 1 (i.e., directional reflection of sound waves with a frequency of 1000Hz at a 30° angle), the phase difference between two adjacent unit cells needs to be configured as π / 10;

[0091] Function 2 (i.e., directional reflection of sound waves with a frequency of 4000Hz at a 30° angle) requires the phase difference between two adjacent unit cells to be configured as 2π / 5.

[0092] Function 3 (i.e., directional reflection of a 2500Hz sound wave at a 30° angle), requires the phase difference between two adjacent unit cells to be configured as π / 4; and

[0093] Function 4 (i.e., directional reflection of sound waves at a frequency of 2500Hz at a 45° angle), the required phase difference between two adjacent unit cells is configured as follows:

[0094] Based on the phase difference configured according to functions 1 to 4 above, the first included angle θ is configured accordingly (including, for example, ...). Figure 2 The values ​​θ1 to θ4 shown are for simplified calculation of the same unit cell configuration (θ1 = θ2 = θ3 = θ4). The specific angles of the first included angle are detailed in Table 1 below:

[0095] Table 1. Angle configuration for the first included angle of directional reflection for an acoustic metasurface with 40 unit cells.

[0096]

[0097]

[0098] In Table 1 above, the rows represent the simulation experiments corresponding to functions 1 to 4; the columns represent the angles (i.e., θ) corresponding to the first angles of the 40 unit cells. r The reflection angle is represented by the sound wave. The table shows the angle of the first angle in response to the frequency of the sound wave and the specific reflection angle. In the table, the unit cell located on the left side of the acoustic metasurface is numbered 1, the unit cell located on the left side of the acoustic metasurface is numbered 40, and the unit cells in between are numbered sequentially according to 2, 3, 4...37, 38, 39.

[0099] In the sound field simulation, the material boundary of the unit cell is used as the acoustic hard boundary, and the rest of the computer is made of air; the density is 1.21 kg / m3, and the sound speed is 343 m / s; the mesh is a free triangular mesh; the maximum element size is set to one-fifteenth of the wavelength.

[0100] Reference Figures 4 to 6 (in, Figures 4 to 6 The top left image corresponds to function 1, the top right image corresponds to function 2, the bottom left image corresponds to function 3, and the bottom right image corresponds to function 4.

[0101] in, Figure 4 The phase difference between adjacent unit cells is shown to be linear and periodically uniformly distributed; Figure 5 It shows that the reflected sound waves are reflected in a planar waveform at a preset reflection angle; Figure 6 This demonstrates that sound waves form an energy flow of corresponding intensity along a preset reflection angle. This illustrates that the acoustic metasurface corresponding to the above embodiment achieves directional reflection of sound waves at preset frequencies (including 1000Hz, 4000Hz, and 2500Hz) along preset angles (including 30° and 45°).

[0102] Figure 7 This is a cross-sectional view of an acoustic metasurface according to another illustrative embodiment of the present disclosure.

[0103] According to embodiments of this disclosure, such as Figure 7 As shown, the first included angle formed by the conical neck 113 of at least a portion of the resonant cavities 11 in the same unit cell is configured to be different from the first included angle formed by the conical neck 113 of other resonant cavities 11.

[0104] In another illustrative embodiment, such as Figure 7 As shown, the acoustic metasurface is configured with 15 unit cells arranged side by side along the horizontal direction. Specifically, each unit cell is configured with 2 resonant cavities.

[0105] In one illustrative embodiment, such as Figure 7 As shown, the height (h0) of each unit cell is configured to be 102 mm; the width (d0) of each unit cell is configured to be 50 mm; the wall thickness of each unit cell is configured to be 2 mm; the height (h) of each resonant cavity is configured to be 52 mm; and the thickness (d) of each resonant cavity is configured to be 46 mm. Furthermore, the blade length is configured to be 11 mm, the blade thickness is configured to be 3 mm, and the height of the rectangular neck (i.e., the thickness of the protrusion) is configured to be 8 mm.

[0106] Based on the acoustic metasurface unit in the above embodiments, a 45° directional reflection of a 1436Hz sound wave was performed for verification. Furthermore, a corresponding waveguide platform, sound source, microphone, and data acquisition system were configured as a two-dimensional sound field experimental setup for verifying the acoustic metasurface unit.

[0107] The waveguide platform consists of two parts: a rectangle and an isosceles trapezoid. The rectangular part is made of two 95cm*95cm transparent acrylic sheets, each 1cm thick, with a 24mm gap between them. The upper and lower surfaces can be considered acoustic hard boundaries, and the perimeter is filled with sound-absorbing wedges, considered a perfect matching layer. The isosceles trapezoid has an upper base length of 2.8cm, a lower base length of 70cm, and a height of 50cm. Both sides and the upper and lower surfaces are made of 3mm thick acrylic material, which can also be considered acoustic hard boundaries. A loudspeaker (i.e., the sound source) is placed on the upper base, and the lower base is connected to the rectangular waveguide. Furthermore, the sound source is a single 23mm diameter circular full-range loudspeaker. Sound-absorbing cotton is placed behind the loudspeaker to prevent sound wave reflection at the boundary and to isolate external background noise, reducing the impact of reflected waves and background noise from the boundary on the experimental results. Furthermore, the aforementioned two-dimensional sound field experimental setup employs two microphones to simultaneously acquire sound field data. The microphones are connected to a dual-rail stepper motor via two steel rulers and extend into a rectangular waveguide from below via sound-absorbing wedges. As the stepper motor moves, the microphones change position, scanning the time-domain data of the sound field within the test area and inputting it into the data acquisition system. The scanning area is 60*29cm, and the scanning step size is 5mm. The microphone sampling rate is 100,000 times per second, with a sampling duration of 25.60ms per sampling point. The microphone scanning path is S-shaped.

[0108] Figure 8 It is aimed at Figure 7 The schematic diagram illustrates the manipulation of sound waves by an acoustic metasurface in an exemplary embodiment. Figure 8 'a' is the sound field time-domain plot, showing the contour plot at 11.36ms. Figure 8 b is the frequency domain sound field obtained from the simulation at 1436Hz.

[0109] Based on the acoustic metasurface unit in the above embodiment, a 45° directional reflection of a sound wave with a frequency of 1436Hz is achieved.

[0110] Reference Figure 8 As shown in Figure a, the reflected wave at this point (11.36 ms) propagates along a 45° direction. Further, refer to... Figure 8As shown in b, a finite element model of the frequency domain sound field was established using the COMSOL Multiphysics pressure acoustic module. The studied frequency was 1436Hz, which is consistent with the center frequency of the incident signal in the experiment. It can be seen that the results of the finite element model based on the above acoustic metasurface unit are consistent with those of the above two-dimensional sound field experimental device, and the reflected wave achieved 45° directional reflection.

[0111] Based on the above experiments, the specific angle of the first included angle is detailed in Table 2 below:

[0112] Table 2 shows the angle configuration for the first included angle of directional reflection for an acoustic metasurface with 15 unit cells.

[0113]

[0114] in, Figure 8 The sound field time-domain plot shown in figure a illustrates the contour plot at 11.36 ms. Figure 8 b represents the simulated frequency domain sound field at 1436 Hz. It can be seen that the aforementioned acoustic metasurface, in the configured two-dimensional sound field experimental setup, through... Figure 8 A observed that the reflected wave vector achieved directional reflection according to the preset 45° direction.

[0115] Furthermore, refer to Figure 8 The simulated 1436Hz frequency domain sound field shown in Figure b is consistent with the experimental results above. Therefore, it can be concluded that the above illustrative embodiment achieves the function of directional reflection of sound waves.

[0116] Furthermore, based on the above illustrative embodiments, an implementation method is also provided in which the blades in different resonant cavities of the same unit cell are configured with different first included angles. By configuring the adjustable first included angles of the two resonant cavities, a technical means to regulate the phase difference of adjacent unit cells by configuring different first included angles of the blades is added, thereby enriching the regulation methods of unit cells and improving the ability to regulate sound waves.

[0117] In another illustrative embodiment, the acoustic metasurface is configured with 41 unit cells arranged side-by-side in a horizontal direction. Specifically, each unit cell is configured with 4 resonant cavities.

[0118] In one illustrative embodiment, such as Figure 2As shown, the height (h0) of each unit cell is configured to be 102 mm; the width (d0) of each unit cell is configured to be 34 mm; the wall thickness of each unit cell is configured to be 2 mm; the height (h) of each resonant cavity is configured to be 22 mm; and the thickness (d) of each resonant cavity is configured to be 30 mm. Furthermore, the blade length is configured to be 7.5 mm, and the height of the rectangular neck (i.e., the thickness of the protrusion) is configured to be 3 mm.

[0119] Figure 9 A phase difference diagram illustrating the point-focusing of a vertically incident sound wave using an acoustic metasurface according to an illustrative embodiment of the present disclosure. Figure 10 It is aimed at Figure 9 The schematic embodiment shown is a finite element simulation of an acoustic metasurface focusing a vertically incident sound wave at a specific point. Figure 11 It is aimed at Figure 9 The diagram illustrates the distribution of energy of the scattered sound field along the horizontal cross section of the focal point when the acoustic metasurface of the schematic embodiment focuses a vertically incident sound wave at a specific point.

[0120] Based on the acoustic metasurface unit in the above embodiments, sound waves with frequencies of 2500Hz and 4000Hz are focused at a fixed point at 0.34 meters, and a sound wave with a frequency of 2500Hz is focused at a fixed point at 0.68 meters. Specifically, for the above three types of directional reflections (hereinafter referred to as functions 5 to 7). Furthermore, based on functions 5 to 7, according to the generalized Snell's law, the phase gradient of the acoustic metasurface must satisfy the following equation (3).

[0121]

[0122] In equation (3), x represents the horizontal distance from a point on the acoustic metasurface to the focal point, F represents the vertical distance from the focal point to the boundary of the acoustic metasurface, k represents the wave number of the sound wave, and φ(x) represents the phase gradient function.

[0123] Based on the above equation (3), calculate the phase difference required for the configuration of two adjacent unit cells.

[0124] Function 5 (i.e., pinpoint focusing of a 2500Hz sound wave at 0.34 meters), the required phase difference configuration for two adjacent unit cells is as follows: Figure 9 As shown in the left figure;

[0125] Function 6 (i.e., pinpoint focusing of a 4000Hz sound wave at 0.34 meters) requires the following phase difference configuration between two adjacent unit cells: Figure 9 As shown in the middle figure;

[0126] Function 7 (i.e., pinpoint focusing of a 2500Hz sound wave at 0.68 meters), the required phase difference configuration for two adjacent unit cells is as follows: Figure 9 As shown in the right figure.

[0127] Based on the phase difference configured in functions 5 to 7 above, the first included angle θ is configured accordingly (including, for example, ...). Figure 2 The values ​​θ1 to θ4 shown are for simplified calculation of the same unit cell configuration (θ1 = θ2 = θ3 = θ4). The specific angles of the first included angle are detailed in Table 3 below.

[0128] Table 3 shows the angle configuration for the first included angle of point focusing on an acoustic metasurface with 41 unit cells.

[0129]

[0130]

[0131]

[0132] In Table 3 above, the rows represent the simulation experiments corresponding to functions 5 to 7; the columns represent the angles (i.e., θ) corresponding to the first included angles of the 41 unit cells; and F represents the vertical distance from the focal point to the boundary of the acoustic metasurface. The table shows the angles of the first included angles in response to the frequency of the sound wave and a specific reflection angle. In the table, the unit cells located on the left side of the acoustic metasurface are designated as number -20, the unit cells located in the middle are designated as 0, and the unit cells located on the left side of the acoustic metasurface are designated as number 20. Unit cells numbered -19 to -1 and numbered 1 to 19 are symmetrically arranged on both sides of the unit cell numbered 0.

[0133] refer to Figure 9 As shown, refer to Figures 9 to 11 (in, Figures 9 to 11 The left image corresponds to function 5, the middle image corresponds to function 6, and the right image corresponds to function 7.

[0134] In the sound field simulation, the material boundary of the unit cell is used as the acoustic hard boundary, and the rest of the computer is made of air; the density is 1.21 kg / m3, and the sound speed is 343 m / s; the mesh is a free triangular mesh; the maximum element size is set to one-fifteenth of the wavelength.

[0135] in, Figure 9 The phase difference between adjacent unit cells is shown to be nonlinear and symmetrically distributed with respect to the unit cells located in the middle. Figure 10 It shows that the reflected sound waves are focused at a predetermined focal point at a vertical distance from the boundary of the acoustic metasurface; Figure 11The diagram illustrates the energy distribution of the scattered sound field along the horizontal cross section where the focal point is located, resulting from the acoustic metasurface's pinpoint focusing of a vertically incident sound wave. This demonstrates that the acoustic metasurface corresponding to the above embodiment achieves pinpoint focusing of sound waves at preset frequencies (including 2500Hz and 4000Hz) along preset focal points (including 0.34m and 0.68m).

[0136] It should also be noted that the directional terms mentioned in the embodiments, such as "up," "down," "front," "back," "left," and "right," are only for reference to the directions in the accompanying drawings and are not intended to limit the scope of protection of this disclosure. Throughout the drawings, the same elements are represented by the same or similar reference numerals. Conventional structures or constructions will be omitted where they may cause confusion in understanding this disclosure.

[0137] The embodiments of this disclosure have been described above. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of this disclosure. Although various embodiments have been described above, this does not mean that the measures in the various embodiments cannot be used advantageously in combination. The scope of this disclosure is defined by the appended claims and their equivalents. Various substitutions and modifications can be made by those skilled in the art without departing from the scope of this disclosure, and all such substitutions and modifications should fall within the scope of this disclosure.

Claims

1. A rotary broadband tunable acoustic metasurface, characterized in that, It includes multiple unit cells arranged side by side along the horizontal direction, and the interior of each unit cell defines a resonant cavity (11) that is connected to the outside. The resonant cavity (11) has a neck (12) with a rectangular opening (111) on the side facing the sound source. The neck (12) includes a rectangular neck (112) configured to have the same cross-sectional area as the rectangular opening (111) and a tapered neck (113) extending into the resonant cavity (11). The tapered neck (113) is provided with an adjustable first surface. Each of the unit cells is configured to adjust the phase difference of the acoustic wave of the planar waveform input through the rectangular opening (111) in response to a first angle formed by the extension direction of the first surface and the horizontal direction, so that the acoustic wave is directionally reflected or focused at a fixed point.

2. The metasurface according to claim 1, characterized in that, The unit cell includes: A frame (1) is constructed in a generally cubic structure, the interior of which defines at least one of the resonant cavities (11), the upper portion of which forms the rectangular opening (111); and The blade pair includes two blades (2), which are symmetrically arranged on opposite sides of the rectangular opening (111), and the upper surface of the blades (2) is used as the first surface.

3. The metasurface according to claim 2, characterized in that, The upper part of the frame (1) is symmetrically provided with protrusions on both sides, which protrude into the inside of the frame (1) and extend along the horizontal direction, and the rectangular opening (111) is formed between the two protrusions.

4. The metasurface according to claim 3, characterized in that, The blade (2) is rotatably disposed on the frame (1) and has a rotational state that rotates about a fixed axis relative to the rectangular opening (111) and a fixed state that is stationary relative to the rectangular opening (111) to adjust the angle of the first included angle.

5. The metasurface according to any one of claims 1 to 4, characterized in that, The resonant cavity (11) is constructed as an axisymmetric structure.

6. The metasurface according to any one of claims 1 to 4, characterized in that, The unit cell contains multiple resonant cavities (11) connected in series.

7. The metasurface according to claim 6, characterized in that, Multiple resonant cavities (11) are stacked along the height direction of the unit cell; The rectangular opening (111) of the upper resonant cavity (11) serves as the incident side for inputting the sound wave.

8. The metasurface according to claim 7, characterized in that, The rectangular opening (111) is located in the middle of the resonant cavity (11), and the orthographic projections of the plurality of rectangular openings (111) along the height direction of the resonant cavity (11) coincide.

9. The metasurface according to claim 7, characterized in that, The angle of the first included angle formed by the conical neck (113) of each of the resonant cavities (11) in the same unit cell is the same.

10. The metasurface according to claim 7, characterized in that, The first included angle formed by the conical neck (113) of at least a portion of the resonant cavity (11) in the same unit cell is configured to be different from the first included angle formed by the conical neck (113) of the other resonant cavities (11).

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