Broadband non-dispersive acoustic vortex generator based on acoustic artificial structure and design method thereof

Abstract

The application discloses a broadband non-dispersive acoustic vortex generator based on acoustic artificial structures and a design method thereof. The acoustic vortex generator comprises coaxial multi-layer annular structures, and an axially-through hollow channel is formed between adjacent annular structures and in the center of the innermost annular structure. A plurality of partitions are uniformly distributed in the circumferential direction on the axis of the multi-layer annular structures, and the other end of the partition extends radially outward to the outer side surface of the outermost annular structure, thereby dividing each annular structure into a plurality of fan-shaped acoustic artificial structures. A plurality of circular-arc-shaped resonant cavities and a cavity are distributed in the axial direction on the inner side surface of the fan-shaped acoustic artificial structure. The resonant cavities and the cavity are all connected with the corresponding hollow channel. The resonant cavities and the cavity of different fan-shaped acoustic artificial structures on the same layer annular structure are in one-to-one correspondence in the axial position. The coupling resonance effect between the mixed resonances of different resonant cavities is accurately adjusted by using the cavity, so that a broadband non-dispersive linear phase response is achieved. The application has the advantages of compact structure size and wide working frequency band.

Description

TECHNICAL FIELD

[0001] The present application relates to acoustic devices, in particular to a generator capable of generating broadband non-dispersive acoustic vortices based on acoustic artificial structures, and a design method of the acoustic vortex generator. BACKGROUND

[0002] Acoustic vortices have an additional orbital angular momentum manipulation degree of freedom, which not only has important research value in academia, but also has extremely important application value in non-contact particle trapping, manipulation, underwater acoustic communication systems, etc.

[0003] At present, the generator for generating acoustic vortices by using passive acoustic artificial structures includes a metasurface structure and a diffraction structure. In the metasurface structure generator, the acoustic artificial structure often introduces a resonance unit, which will cause strong dispersion characteristics of the acoustic artificial structure, and further affect the working bandwidth of the acoustic vortex generator. Although the diffraction structure generator can generate broadband acoustic vortices, the volume of the generator is often several times the wavelength of the acoustic wave, which greatly limits the miniaturization and integration of the device. SUMMARY

[0004] The first object of the present application is to provide a broadband non-dispersive acoustic vortex generator based on acoustic artificial structures, which has a compact structure size (sub-wavelength size) and can efficiently convert broadband plane waves into high-purity acoustic vortices. The second object of the present application is to provide a design method of the acoustic vortex generator.

[0005] Technical scheme: The first aspect of the present application provides a broadband non-dispersive acoustic vortex generator based on acoustic artificial structures, which includes at least two coaxial ring structures, and an axially through hollow channel is formed between adjacent ring structures and the center of the innermost ring structure. At least four partitions are uniformly distributed along the circumference on the axis of the ring structure, and the other end of the partition extends radially outward to the outer side of the outermost ring structure. Each ring structure is divided into at least four fan-shaped acoustic artificial structures.

[0006] A plurality of resonant cavities and a cavity in the form of a circular arc are distributed along the axis on the inner side of each fan-shaped acoustic artificial structure, the resonant cavities are connected to the corresponding hollow channel through the cavity hole in the form of a circular arc, and the cavity is an open structure connected to the corresponding hollow channel. The resonant cavities and cavities of different fan-shaped acoustic artificial structures on the same ring structure correspond to each other in axial position.

[0007] The coupling resonance effect between the mixed resonances of different resonant cavities is precisely adjusted by using the cavity, so as to achieve broadband non-dispersive linear phase response.

[0008] The non-dispersive acoustic wave regulation effect realized by the different layers of the fan-shaped acoustic artificial structure between two adjacent partitions is the same, and the linear response of the fan-shaped acoustic artificial structure between different partitions has an equal phase interval.

[0009] It should be noted that the broadband non-dispersive acoustic vortex generator of the present application is not limited to forward propagation, and when backward propagation (i.e., the sound wave enters the acoustic vortex generator from the exit end) occurs, an acoustic vortex of order-m can be generated without redesigning the geometric structure parameters, where m is the order of the acoustic vortex generated by the theoretical design of the device.

[0010] The present application solves the problems of narrow band and large scale of existing acoustic vortex generators, has a compact structure and a wide working frequency band; at the same time, the present application has a flat shape at both ends, which is beneficial to the compact and small application of the broadband acoustic vortex device; in addition, the present application does not need additional circuit regulation, but relies on its own structural characteristics to achieve the above effects.

[0011] Further, the number of layers of the ring structure and the radius of the broadband non-dispersive acoustic vortex generator are determined by the working frequency band.

[0012] Further, the several resonant cavity structures on the same fan-shaped acoustic artificial structure are completely the same.

[0013] Further, the non-dispersive acoustic wave regulation within the working frequency band is realized by changing the structural parameters of the fan-shaped acoustic artificial structure.

[0014] The structural parameters include the height h1 of the hollow channel at the resonant cavity position, the width w3 of the resonant cavity, the width w2 of the resonant cavity hole, the width w of the cavity, the distance d of the cavity from the exit end of the acoustic vortex generator, the height h of the hollow channel at the cavity position, and the number n of resonant cavities. c c c

[0015] The fan-shaped acoustic artificial structure introduces more design freedom by using the cavity, so as to realize precise adjustment of the coupling resonance effect between different resonant cavities in the acoustic artificial structure, and achieve the effect of broadband non-dispersive linear phase response.

[0016] ​​​Furthermore, the wall thickness of the partition and the fan-shaped acoustic artificial structure is greater than or equal to 0.01λ0, where λ0 is the wavelength of the sound wave at the center frequency. This eliminates the mutual coupling between different fan-shaped acoustic artificial structures, resulting in better acoustic vortex generation.

[0017] Furthermore, the height of the hollow channel is 0.01 to 0.08λ0, where λ0 is the wavelength of the sound wave at the center frequency.

[0018] Furthermore, the width and height of all resonant cavities in the fan-shaped acoustic artificial structure are less than 0.12λ0, where λ0 is the wavelength of the sound wave at the center frequency.

[0019] Furthermore, the acoustic impedance of the fan-shaped acoustic artificial structure and the partition material is at least 100 times that of air acoustic impedance.

[0020] Furthermore, the fan-shaped acoustic artificial structure and partitions are made of organic plastic or metal.

[0021] A second aspect of the present invention provides a design method for a broadband nondispersive acoustic vortex generator based on acoustic artificial structures, comprising:

[0022] Design an ideal linear phase curve and objective function.

[0023] in Linear phase curve designed for theory, For the transmission phase results in the numerical simulation, f L f is the upper cutoff frequency of the operating frequency band. U This is the lower cutoff frequency of the operating frequency band;

[0024] By calculating the difference between the phase response of the theoretically designed phase and the phase curve obtained from numerical simulation, one or more sets of structural parameters that minimize the objective function are found among the randomly generated structural parameters.

[0025] Structural parameters include the height h1 of the hollow channel at the resonant cavity location, the width w3 of the resonant cavity, the width w2 of the resonant cavity aperture, and the width w of the hollow cavity. c The distance d between the cavity and the output end of the acoustic vortex generator c The hollow channel is located at the height h of the cavity. c And the number of resonant cavities, n.

[0026] This invention designs a broadband nondispersive acoustic vortex generator based on an integrated resonant unit. This subwavelength structural unit can generate a high-transmittance and nondispersive acoustic wave response within a designed bandwidth, exhibiting a linear phase curve of the transmitted sound wave over a broadband range, thus enabling the construction of a broadband nondispersive acoustic vortex generator. Furthermore, by designing fan-shaped acoustic artificial structures with different numbers of layers and structural parameters, broadband acoustic vortices of arbitrary order can be generated.

[0027] Beneficial effects: Compared with the prior art, the present application has the following remarkable advantages: compact structure size (sub-wavelength size) and the ability to generate broadband non-dispersive acoustic vortices, which has broad prospects in device miniaturization and integration applications. BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments of the present application are briefly introduced as follows. Obviously, the drawings described below are only the embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0029] Figure 1 is a schematic diagram of the principle of the broadband non-dispersive acoustic vortex generator provided by the embodiments of the present application;

[0030] Figure 2 is a schematic diagram of the structure of the broadband non-dispersive acoustic vortex generator provided by the embodiments of the present application;

[0031] Figure 3 is a cross-sectional view of the fan-shaped acoustic artificial structure in the embodiments of the present application;

[0032] Figure 4 is a broadband non-dispersive acoustic wave response curve of the fan-shaped acoustic artificial structure under a specific structure in the embodiments of the present application, wherein, Figure 4 (a) in FIG. 4 is a structure transmittance and phase curve of the four resonant cavities and the hollow channel without the cavity, Figure 4 (b), (c) and (d) in FIG. 4 are respectively the transmittance and phase curve distribution diagrams of the fan-shaped acoustic artificial structure under different frequency bands after introducing three cavities with different geometric sizes without changing the sizes of the resonant cavities and the hollow channel;

[0033] Figure 5 (a) in FIG. 5 is a transmittance curve of the first layer of the fan-shaped acoustic artificial structure after optimization in the embodiments of the present application, Figure 5 (b) in FIG. 5 is a phase distribution curve of the first layer of the fan-shaped acoustic artificial structure after optimization;

[0034] Figure 6 (a) in FIG. 6 is a three-dimensional acoustic field of the sound wave after passing through the broadband non-dispersive acoustic vortex generator provided by the embodiments of the present application, Figure 6 (b) in FIG. 6 is an acoustic pressure amplitude and phase diagram obtained by numerical simulation and experimental measurement at z=25mm and 75mm under 2187Hz, 2287Hz and 2787Hz respectively;

[0035] Figure 7This is a purity distribution diagram of the acoustic vortex generated at 2187–2787 Hz in the embodiments of this application;

[0036] Reference numerals: 1, ring structure; 2, fan-shaped acoustic artificial structure; 3, partition; 4, resonant cavity; 5, cavity; 6, hollow channel. Detailed Implementation

[0037] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are not all the 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 protection scope of the present invention.

[0038] like Figure 1 As shown, when a broadband plane wave passes through a specific acoustic vortex generator, it will be efficiently converted into a broadband acoustic vortex wave at the exit surface. Figure 1 The direction of the middle arrow indicates the direction of sound wave propagation.

[0039] This application uses a generator that produces first-order broadband nondispersive acoustic vortices as an example to further illustrate the present invention.

[0040] like Figure 2 The diagram shown is a schematic representation of a broadband nondispersive acoustic vortex generator based on an acoustic artificial structure provided in this embodiment of the application. The acoustic vortex generator includes a coaxial three-layer ring structure 1. In this embodiment, the radii of the three ring structures 1 from the inside out are 0.133λ0, 0.233λ0, and 0.334λ0, respectively, where λ0 = 15cm is the wavelength of the sound wave at the center frequency.

[0041] A hollow channel 6 is formed between adjacent annular structures 1 and at the center of the innermost annular structure 1.

[0042] Four partitions 3 are evenly distributed circumferentially along the common axis of the three-layer ring structure 1, with the included angle between adjacent partitions 3 being 90°. The other end of the partition 3 extends radially outward to the outer side of the outermost ring structure 1, and each ring structure 1 is divided into four fan-shaped acoustic artificial structures 2.

[0043] Each sector-shaped acoustic artificial structure 2 has several arc-shaped resonant cavities 4 and a cavity 5 distributed axially on its inner surface. The resonant cavities 4 on the same sector-shaped acoustic artificial structure 2 have identical structures. The number of resonant cavities 4 on the sector-shaped acoustic artificial structure 2 is determined by the following design method.

[0044] The resonant cavity 4 has an arc-shaped opening on one side facing the axial direction to connect with the corresponding hollow channel 6. The hollow cavity 5 is an open structure and is also connected with the corresponding hollow channel 6. The resonant cavities 4 and cavities 5 on the same layer of the annular structure 1, located in different fan-shaped acoustic artificial structures 2, are axially aligned one-to-one.

[0045] Since the fan-shaped acoustic artificial structures 2 of each ring structure 1 are separated by partitions 3, the mutual coupling between different fan-shaped acoustic artificial structures 2 can be ignored.

[0046] Figure 3 The figure shown is a cross-sectional view of a single fan-shaped acoustic artificial structure 2. In this embodiment, the total height of the single fan-shaped acoustic artificial structure 2 is H = 0.1λ0.

[0047] By changing the geometric parameters of the fan-shaped acoustic artificial structure 2, the coupling effect between the resonant modes inside the fan-shaped acoustic artificial structure 2 can be adjusted, ultimately achieving broadband nondispersive acoustic wave modulation based on an integrated resonance mechanism. There are a total of seven adjustable geometric parameters, including the height h1 of the hollow channel 6 located in the resonant cavity 4, the width w3 of the resonant cavity 4, the width w2 of the cavity aperture of the resonant cavity 4, and the width w of the hollow cavity 5. c The distance d between cavity 5 and the output end of the acoustic vortex generator c The hollow channel 6 is located at the height h of the cavity 5. c And the number n of resonant cavities 4.

[0048] By rationally setting seven geometric parameters, the fan-shaped acoustic artificial structure 2 can achieve non-dispersive acoustic wave modulation within the working frequency band.

[0049] This application also provides a design method for a broadband nondispersive acoustic vortex generator, which first designs an ideal linear phase curve and an objective function. in Linear phase curve designed for theory, For the transmission phase results in the numerical simulation, f L f is the upper cutoff frequency of the operating frequency band. U The lower cutoff frequency of the operating frequency band is then used. By calculating the difference between the theoretically designed phase response and the phase curve obtained from numerical simulation, one or more sets of structural parameters that minimize the objective function are found among the randomly generated structural parameters. These structural parameters are the seven geometric parameters mentioned above.

[0050] The following is a theoretical explanation of the broadband nondispersive acoustic vortex generator provided in the embodiments of this application.

[0051] For a cylindrical device, if the phase boundary condition at the exit surface is satisfied as follows: When the phase difference of the sectorial acoustic artificial structure 2 between two adjacent partitions 3 is a certain value, corresponding acoustic vortices can be generated at the exit surface, where m is the order of the generated acoustic vortex, and N is the number of partitions 3.

[0052] The above formula is extended to a certain operating bandwidth, and the phase boundary condition at the exit surface can be obtained as follows:

[0053] where is the transmission phase curve of the i-th sectorial acoustic artificial structure, m is the order of the theoretically designed acoustic vortex, N is the number of partitions 3, and α is an arbitrary constant. When the sectorial acoustic artificial structure 2 between every two partitions 3 satisfies the linear phase distribution with equal intervals, the device can realize the conversion of wideband plane waves to wideband acoustic vortices.

[0054] Figure 4 The specific effect of the sectorial acoustic artificial structure based on integrated resonance mechanism is shown. As shown in (a) of FIG. 6, Figure 4 the resonant cavity has strong resonance characteristics at a certain frequency, and when the acoustic wave is near the strong resonance frequency, it will exhibit strong nonlinear phase characteristics. By changing the geometric parameters of the cavity of the sectorial acoustic artificial structure 2, the coupling effect between the resonance modes in the sectorial acoustic artificial structure 2 can be adjusted, and finally an integrated resonance state can be formed between two strong resonance modes, thereby realizing a wideband non-dispersive linear phase response, as shown in (b)-(d) of FIG. 6. Figure 4

[0055] By adjusting the structural parameters, the linear phase distribution of the sectorial acoustic artificial structure at different positions can be obtained, and finally a complete wideband acoustic vortex generator can be constructed.

[0056] In this embodiment, the generation of wideband non-dispersive acoustic vortices in the frequency band of 2187-2787 Hz is mainly considered, and the radii of the three-layer annular structure 1 from inside to outside are 1.99 cm, 3.49 cm and 5 cm, respectively. Each sectorial acoustic artificial structure 2 is rotated by π / 2 in the angular direction, and the wall thickness of the partition 3 and the acoustic artificial structure 2 is 0.15 cm. The radius and thickness W of the entire acoustic vortex generator are 5 cm and 11.25 cm, respectively.

[0057] Using the above design method, the specific geometric parameters of the acoustic artificial structure of the first-order wideband acoustic vortex generator are shown in Table 1.

[0058] Table 1

[0059]

[0060] If a higher-order acoustic vortex is needed to be generated, only the phase curve with equal phase difference needs to be designed and selected.​

[0061] Figure 5 The simulation results show the high transmittance and linear phase response of the four fan-shaped acoustic artificial structures 2 in the first-layer annular structure 1, and the simulation results of the fan-shaped acoustic artificial structures 2 in other layers are similar.

[0062] Figure 6 Figure (a) shows the numerical simulation results of the three-dimensional sound field of a first-order broadband nondispersive acoustic vortex generator. The results show that at 2287Hz, after the plane sound wave passes through the acoustic vortex generator designed in this invention, the sound field exhibits the typical characteristics of a first-order Bessel sound field. It can be seen that the acoustic vortex remains stable even after passing through 3λ0. In the numerical simulation, all acoustic artificial structures were made of PMMA material. Other materials with acoustic impedance much greater than that of air, such as metals and alloys, can also be used as alternative materials.

[0063] Figure 6 (b) shows the numerical simulation and experimental measurement results of the sound pressure and phase of the emitted sound field at 2187Hz, 2287Hz, and 2787Hz, at distances of z = 25mm and z = 75mm from the output end. The results show that at all three frequencies, the sound pressure and phase distributions exhibit characteristics of a first-order Bessel vortex field: the sound pressure exhibits a concentric circular distribution with a singularity at the center; the phase distribution shows a 2π phase abrupt change around the singularity. The consistency between the numerical simulation and experimental measurement results demonstrates that within the designed operating bandwidth, this invention can effectively achieve the efficient conversion of broadband planar sound waves to broadband acoustic vortices.

[0064] Finally, the purity of the generated acoustic vortex field is calculated using the following formula: Where C m Let be the relative intensity of the m-th order acoustic vortex. Let be the complex sound pressure level on the cross-section, and r be the radius of the cross-section in the propagation direction. Let z be the axial angle of the tangent in the propagation direction, and z be the distance from the emission end. Finally, the relative intensity of the m-order acoustic vortex can be obtained.

[0065] Figure 7 As can be seen, the relative intensity of the first-order acoustic vortex is above 0.9 at most frequencies within the operating frequency band, indicating that the generated broadband acoustic vortex is of very high quality.

[0066] In summary, the wideband non-dispersive acoustic vortex generator based on the acoustic artificial structure provided by the embodiments of the present application has the advantages of subwavelength structure scale, 0.1λ0 transverse resolution and 0.75λ0 propagation thickness, can efficiently generate wideband non-dispersive acoustic vortex while keeping the structure compact, has the advantages of high purity and stability of the generated wideband acoustic vortex, can realize an average acoustic vortex purity of 0.9 in the working frequency band, and still maintains typical acoustic vortex characteristics after propagation for at least 3λ0, and further has the feature of planar shaping, which has important application potential in integrated design.

[0067] It is worth mentioning that the wideband non-dispersive acoustic vortex generator based on the acoustic artificial structure provided by the embodiments of the present application can also be used reversely, that is, a wideband plane wave enters the acoustic vortex generator from one end close to the cavity for reverse propagation, can generate a negative first-order wideband non-dispersive acoustic vortex, and does not need to redesign the geometric structure parameters.

[0068] The above merely illustrates the specific embodiments of the present application, but the protection scope of the present application is not limited thereto, any changes or replacement solutions that can be easily thought of by those skilled in the art within the technical range disclosed by the present application shall be covered in the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. A broadband nondispersive acoustic vortex generator based on an acoustic artificial structure, characterized in that, It includes at least two coaxial ring structures (1), with an axially connected hollow channel (6) formed between adjacent ring structures (1) and at the center of the innermost ring structure (1); at least four partitions (3) are evenly distributed circumferentially on the axis of the ring structure (1), and the other end of the partitions (3) extends outward radially to the outer side of the outermost ring structure (1), and each ring structure (1) is divided into at least four fan-shaped acoustic artificial structures (2). On the inner side of each fan-shaped acoustic artificial structure (2), there are several arc-shaped resonant cavities (4) and a cavity (5) distributed along the axial direction. The resonant cavities (4) are connected to the corresponding hollow channels (6) through arc-shaped cavity holes. The cavity (5) is an open structure that connects to the corresponding hollow channels (6). The resonant cavities (4) and cavities (5) located on different fan-shaped acoustic artificial structures (2) on the same layer of the annular structure (1) are in axial positions that correspond one-to-one. By using the cavity (5) to precisely adjust the coupling resonance effect between different resonant cavities (4) to achieve a broadband non-dispersive linear phase response; The number of layers in the annular structure (1) and the radius of the broadband nondispersive acoustic vortex generator are determined by the operating frequency band; Several resonant cavities (4) on the same fan-shaped acoustic artificial structure (2) have completely identical structures; By changing the structural parameters of the fan-shaped acoustic artificial structure (2), non-dispersive acoustic wave modulation can be achieved in the working frequency band. The structural parameters include the height of the hollow channel (6) located at the position of the resonant cavity (4). The width of the resonant cavity (4) The width of the cavity aperture of the resonant cavity (4) The width of the cavity (5) The distance between the cavity (5) and the output end of the acoustic vortex generator The hollow channel (6) is located at the height of the cavity (5). and the number of resonant cavities (4) .

2. The broadband nondispersive acoustic vortex generator according to claim 1, characterized in that, The wall thickness of the partition (3) and the fan-shaped acoustic artificial structure (2) is greater than or equal to 0.01 mm. , The wavelength of the sound wave at the center frequency.

3. The broadband nondispersive acoustic vortex generator according to claim 1, characterized in that, The hollow channel (6) has a height of 0.01~0.08 meters. , The wavelength of the sound wave at the center frequency.

4. The broadband nondispersive acoustic vortex generator according to claim 1, characterized in that, The width and height of all resonant cavities (4) in the fan-shaped acoustic artificial structure (2) are less than 0.

12. , The wavelength of the sound wave at the center frequency.

5. The broadband nondispersive acoustic vortex generator according to claim 1, characterized in that, The acoustic impedance of the fan-shaped acoustic artificial structure (2) and the partition (3) material is at least 100 times that of the air acoustic impedance.

6. The broadband nondispersive acoustic vortex generator according to claim 1, characterized in that, The fan-shaped acoustic artificial structure (2) and the partition (3) are made of organic plastic or metal.

7. A design method for a broadband nondispersive acoustic vortex generator based on an acoustic artificial structure as described in claim 1, characterized in that, include: Design an ideal linear phase curve and objective function. ; in Linear phase curve designed for theory, This represents the transmission phase result from the numerical simulation. f L This is the upper cutoff frequency of the operating frequency band. f U This is the lower cutoff frequency of the operating frequency band; By calculating the difference between the phase response of the theoretically designed phase and the phase curve obtained from numerical simulation, one or more sets of structural parameters that minimize the objective function are found among the randomly generated structural parameters. Structural parameters include the height of the hollow channel (6) located at the position of the resonant cavity (4). The width of the resonant cavity (4) The width of the cavity aperture of the resonant cavity (4) The width of the cavity (5) The distance between the cavity (5) and the output end of the acoustic vortex generator The hollow channel (6) is located at the height of the cavity (5). and the number of resonant cavities (4) .

Images