Uniform scattering acoustic coding metasurface structure under broadband incidence at any angle

Abstract

The invention provides a uniform scattering acoustic coding metasurface structure under broadband incidence at any angle, which comprises a plurality of primitive structures for coding arrangement based on a directivity function, and each primitive structure comprises a Helmholtz cavity and a rectangular strip group; the Helmholtz cavities are horizontally arranged in parallel; the rectangular strip group is vertically added into the Helmholtz cavity to form an element structure, and the rectangular strip group comprises an upper rectangular strip, a middle rectangular strip, a middle rectangular strip and an end rectangular strip; in the multiple element structures, the number and the pasting positions of the rectangular strips located in the middle are different. According to the acoustic coding metasurface structure, the Helmholtz cavities are arranged horizontally and parallelly instead of vertically, the depth of the acoustic coding metasurface structure is shortened, rectangular strips are added into the acoustic coding metasurface structure to increase the acoustic path distance difference, the size is further reduced, arrangement is conducted through an optimization algorithm, and finally the multi-angle incident broadband scattering effect is achieved. The antenna has the advantages of wide acting frequency band range, multiple acting angles and easy application.

Description

Technical Field

[0001] The present invention belongs to the technical field of acoustic coding metasurfaces, and in particular relates to an acoustic coding metasurface structure with uniform scattering under wide-band and arbitrary-angle incidence. Background Art

[0002] The regulation of wave propagation has always been one of the key topics in the field of acoustic waves, and has potential applications in many fields. By designing functional elements (or unit cells) with microstructures, refractive (transmissive) metasurfaces, reflective metasurfaces, and absorptive metasurfaces are manufactured. Common structures of acoustic metasurfaces include comb-like metasurfaces composed of straight well-like elements, spiral structures with spiral channels, plate-like resonant elements, etc. The reflection phase is changed by changing the acoustic path difference or achieving resonance, but these structures are complex in design and difficult to apply in reality.

[0003] As one of the structures of acoustic metasurfaces, digitally coded acoustic metasurface (ACM) "encodes" several units with different phase differences (same phase difference interval) with Boolean numbers or logic bits, and realizes the target metasurface structure by orderly arranging several units on a two-dimensional or three-dimensional surface. Low-bit digitally coded acoustic metasurfaces require fewer structural units, are easy to process and integrate, and have the advantages of general acoustic metasurfaces.

[0004] Low-bit digitally coded acoustic metasurfaces only require a small number of primitive sample formulas to form. They are easy to design and process, and do not lose the wavefront control capabilities of general metasurface structures. Therefore, they can be widely used in various scenarios, such as acoustic cabin design, acoustic energy collection, target acoustic stealth, etc.

[0005] The structural unit design of traditional acoustic metasurfaces is complex and difficult to apply in reality. The action frequency band is narrow, the action angle is small, and the application is limited. Therefore, digital coding metasurfaces have emerged, which have different structures and arrangements for different functions, effectively overcoming the shortcomings of traditional acoustic metasurfaces. For example: a coding metasurface with a 2-element Helmholtz cavity structure is designed for beam splitting and focusing of transmitted sound waves at vertical incidence, and an adjustable 1-bit coding metasurface composed of a series of rectangular strips is proposed for perfect negative reflection. By pushing up or down, each strip can respond to the logical bit "0" or "1", and by adjusting the coding sequence, perfect negative reflection in different directions can be achieved. However, there are few studies on scattering coding metasurfaces for multi-angle incidence and wide-band action, so digital coding metasurfaces should be studied in depth. Summary of the invention

[0006] The purpose of the present invention is to solve the shortcomings of the prior art that it is unable to cope with multi-angle incidence, and to provide an acoustic coding metasurface structure that scatters uniformly under wide-band arbitrary-angle incidence. The depth of the acoustic coding metasurface structure is shortened by changing the traditional vertical arrangement of the Helmholtz cavity to a horizontal and parallel arrangement. The sound path difference is increased by adding rectangular strips inside the acoustic coding metasurface structure, and the size is further reduced. With the purpose of broadband multi-angle scattering, the structure is arranged through an optimization algorithm to ultimately achieve a multi-angle incident broadband scattering effect. The structure has the advantages of a wide effective frequency band, multiple effective angles and easy application.

[0007] To achieve the above purpose, the technical solution provided by the present invention is:

[0008] A uniformly scattering acoustic coding metasurface structure under wide-band arbitrary angle incidence, comprising: a plurality of elementary structures, a hard acoustic wave reflecting substrate for vertically placing the elementary structures, wherein the plurality of elementary structures are arranged in coding based on a directivity function;

[0009] Each of the elementary structures comprises: a Helmholtz cavity and a rectangular bar group, wherein the Helmholtz cavity is arranged in a horizontal row and in parallel; the rectangular bar group is vertically added inside the Helmholtz cavity to form the elementary structure, and the rectangular bar group is used to increase the sound path difference;

[0010] The propagation characteristics of sound waves are the same in a two-dimensional structure and a three-dimensional structure with the same cross-section as the two-dimensional structure. Therefore, the cross-section and two-dimensional design of the elementary structure in the acoustic coding metasurface structure are as follows:

[0011] Each of the elementary structures is placed perpendicular to the long side of the hard sound wave reflecting substrate, and the rectangular strip group includes an upper rectangular strip, a middle rectangular strip, a middle rectangular strip and an end rectangular strip; the long side of the upper rectangular strip is placed parallel to the sound wave reflecting substrate, the long side of the middle rectangular strip is placed perpendicular to the center of the upper rectangular strip, and the short side is placed parallel to the sound wave reflecting substrate, and the two form a T-shaped structure; the middle rectangular strip is divided into two groups perpendicular to the upper rectangular strip and parallel to the middle rectangular strip, a plurality of the middle rectangular strips are located on both sides of the middle rectangular strip, and the end rectangular strips are located at both ends of the long side of the sound wave reflecting substrate;

[0012] The rectangular strips attached to the hard sound wave reflective substrate form a Helmholtz cavity and a labyrinth structure, and the middle rectangular strips and the middle rectangular strips are fixed to form a mountain-like structure;

[0013] In the various elementary structures, the number and application positions of the rectangular strips located in the middle of the hard sound wave reflecting substrate are different.

[0014] As a further limitation of the present invention, corresponding to different frequency ranges, the number of multiple end rectangular strips and the distance between the end rectangular strips are adjusted, thereby adjusting the phase response of the elementary structure, so that the phase response difference of the multiple elementary structures at f=4000Hz~8000Hz is π / 2.

[0015] As a further limitation of the present invention, there are 4 kinds of primitive structures, and the number of each kind of primitive structures is 9;

[0016] After the 36 primitive structures are coded and arranged based on the directivity function, they are arranged perpendicular to the hard sound wave reflecting matrix.

[0017] As a further limitation of the present invention, the size of the elementary structure is set according to one tenth to one fifth of the required wavelength of the sound wave;

[0018] In the rectangular strip group, the width of the upper rectangular strip is 17 mm and the thickness is 1 mm; the height of the middle rectangular strip is 5 mm and the width is 1 mm; the height of the middle rectangular strip is 4 mm and the width is 1 mm; the height of the end rectangular strip is 6 mm and the width is 1 mm;

[0019] The length of the hard sound wave reflecting matrix is ​​23 mm, the width is 6 mm, and the thickness is 10 mm. The hard sound wave reflecting matrix has the same cross-sectional dimensions.

[0020] As a further limitation of the present invention, there are four types of primitive structures, which are divided into a first primitive structure, a second primitive structure, a third primitive structure and a fourth primitive structure from small to large corresponding to the phase;

[0021] In the uniformly scattering acoustic coding metasurface structure under broadband arbitrary angle incidence, the arrangement of the elementary structures is as follows:

[0022] The first primitive structure, the second primitive structure, the second primitive structure, the second primitive structure, the first primitive structure, the third primitive structure, the first primitive structure, the fourth primitive structure, the fourth primitive structure, the first primitive structure, the fourth primitive structure, the fourth primitive structure, the third primitive structure, the fourth primitive structure, the second primitive structure, the first primitive structure, the second primitive structure, the third primitive structure, the third primitive structure, the second primitive structure, the first primitive structure, the fourth primitive structure, the third primitive structure, the second primitive structure, the fourth primitive structure, the first primitive structure, the third primitive structure, the third primitive structure, the fourth primitive structure, the first primitive structure, the third primitive structure, the third primitive structure, the fourth primitive structure, the first primitive structure, the third primitive structure, the third primitive structure, the fourth primitive structure, the first primitive structure, the third primitive structure, the third primitive structure, the fourth primitive structure, the first primitive structure, the third primitive structure, the third primitive structure, the fourth primitive structure, the first primitive structure, the third primitive structure, the fourth primitive structure, the first primitive structure, the third primitive structure.

[0023] As a further limitation of the present invention, the side edges of the elementary structure are perpendicular to its bottom edge;

[0024] The elementary structures are aligned and closely arranged respectively and are perpendicular to the bottom edge of the hard sound wave reflecting substrate and parallel to the side edges.

[0025] As a further limitation of the present invention, the rectangular strip group and the hard sound wave reflecting substrate are both made of aluminum material;

[0026] The density of the rectangular strip group and the hard sound wave reflecting matrix is ​​2.7 g / m 3 , Young's modulus is 70GpPa, and the speed of sound is 6300m / s.

[0027] As a further limitation of the present invention, the acoustic coding metasurface structure is uniformly scattered under wide-band and arbitrary-angle incidence, and the frequency of f=4000Hz to 8000Hz and the sound waves incident at multiple angles are regulated to make the reflected waves uniformly scattered.

[0028] As a further limitation of the present invention, the directivity function includes the angle and frequency of the incident sound wave, the angle and frequency are known quantities, and the phase information of the coded arrangement is an unknown quantity; the angle is 0°, 30°, 45°, 60°, 70°, and the frequency is 4kHz-8kHz;

[0029] The directivity function is used as the objective function and maximized, and the surface of the hard sound wave reflecting substrate is divided into 36 blocks, and each of the primitive structures has 9 data as a constraint function;

[0030] The plurality of primitive structures are temporarily placed on the surface of the hard sound wave reflecting substrate in an unknown arrangement, and the directivity function is used to obtain the optimal coding arrangement of the plurality of primitive structures.

[0031] As a further limitation of the present invention, the directivity function comprises:

[0032]

[0033]

[0034] In the formula, θ represents the elevation angle of the scattered wave, represents the azimuth of the scattered wave, θ i represents the elevation angle of the incident sound wave, represents the azimuth of the incident sound wave, represents the directivity function of the scattered wave, represents the far-field scattering amplitude, represents the directivity function of the coding metasurface, represents the directivity function of an unstructured smooth surface of the same size, σ R represents the diffusion performance of the coded metasurface compared to the ordinary smooth surface, σ R The larger the value, the better the scattering effect. The elevation angle of the scattered wave is defined as The calculation formula of the scattering coefficient is:

[0035]

[0036] Where D represents the scattering coefficient, L i Represents the sound pressure level value of the far field in different directions, M represents the total number of selected angles, and i represents the selected direction.

[0037] The advantages of the present invention are:

[0038] The present invention shortens the depth of the acoustic coding metasurface structure by changing the traditional vertical arrangement of Helmholtz cavities to horizontal and parallel arrangement, increases the sound path difference by adding rectangular strips inside the acoustic coding metasurface structure, and further reduces the size. With the purpose of broadband multi-angle scattering, the arrangement is performed through an optimization algorithm to ultimately achieve a multi-angle incident broadband scattering effect, which has the advantages of a wide effective frequency band, multiple effective angles and easy application.

[0039] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0041] Figure 1 : Illustrations of four elementary structures of a uniformly scattering acoustic coding metasurface structure under wide-band and arbitrary-angle incidence provided by the present invention;

[0042] Figure 2 : A schematic diagram of a hard sound wave reflecting substrate, an upper rectangular strip, a middle rectangular strip and an end rectangular strip in a basic structure provided by the present invention;

[0043] Figure 3 :The present invention provides Figure 2 Dimensional diagram of the middle number;

[0044] Figure 4 : Schematic diagram of phase response of four basic unit structures provided by the present invention at f=4000Hz~8000Hz;

[0045] Figure 5 : Schematic diagram of the phase response of the four basic unit structures provided by the present invention when the finite element software is used to simulate the basic unit structure at f=5000Hz;

[0046] Figure 6 : Schematic diagram of the phase encoding arrangement of four basic element structures provided by the present invention;

[0047] Figure 7 : A schematic diagram comparing the scattering effects of a flat plate and a coded metasurface provided by the present invention at incident sound wave frequencies of 4.6kHz and 8.4kHz and an incident sound wave angle of 0°;

[0048] Figure 8 : A schematic diagram comparing the scattering effects of a flat plate and a coded metasurface provided by the present invention at incident sound wave frequencies of 4.2kHz and 5.7kHz and an incident sound wave angle of 30°;

[0049] Fig. 9 : A schematic diagram comparing the scattering effects of a flat plate and a coded metasurface provided by the present invention at incident sound wave frequencies of 4.6kHz and 6.3kHz and an incident sound wave angle of 45°;

[0050] Fig.10 : A schematic diagram comparing the scattering effects of a flat plate and a coded metasurface provided by the present invention at incident sound wave frequencies of 4.7kHz and 6kHz and an incident sound wave angle of 60°;

[0051] Fig.11 : A schematic diagram of the comparison of the scattering coefficients of a flat plate and a coded metasurface with frequency at a frequency of 4000 Hz to 10000 Hz when the incident sound wave angle is 0° provided by the present invention;

[0052] Fig.12 : A schematic diagram showing the comparison of the scattering coefficients of a flat plate and a coded metasurface with frequency at a frequency of 4000 Hz to 10000 Hz and an incident sound wave angle of 30° provided by the present invention;

[0053] Fig.13 : A schematic diagram showing the comparison of the scattering coefficients of a flat plate and a coded metasurface with frequency at a frequency of 4000 Hz to 10000 Hz and an incident sound wave angle of 45° provided by the present invention;

[0054] Fig.14 : A schematic diagram showing the comparison of the scattering coefficients of a flat plate and a coded metasurface with frequency at a frequency of 4000 Hz to 10000 Hz and an incident sound wave angle of 60° provided by the present invention;

[0055] In the figure: 10 - elementary structure; 20 - rectangular strip group; 21 - upper rectangular strip; 22 - middle rectangular strip; 23 - end rectangular strip; 30 - hard sound wave reflecting matrix. DETAILED DESCRIPTION

[0056] Embodiments of the present invention are described in detail below. The embodiments are exemplary and intended to be used to explain the present invention, but should not be construed as limiting the present invention.

[0057] See also Figure 1The embodiment of the present invention provides a uniformly scattering acoustic coding metasurface structure under wide-band arbitrary angle incidence, including four elementary structures and a hard acoustic wave reflecting substrate for vertically placing the elementary structures, and the four elementary structures are arranged in coding based on directivity functions; each elementary structure includes: a Helmholtz cavity and a rectangular strip group, wherein:

[0058] The Helmholtz cavity of the embodiment of the present invention is changed from the traditional vertical arrangement to the horizontal arrangement in parallel, thereby shortening the depth of the structure; the acoustic path difference is increased by adding a rectangular bar group inside the Helmholtz cavity, thereby further reducing the size of the structure.

[0059] The propagation characteristics of sound waves are the same in a two-dimensional structure and a three-dimensional structure with the same cross section as the two-dimensional structure. Therefore, the cross section and two-dimensional design of the elementary structure in the acoustic coding metasurface structure are as follows:

[0060] The dimensions of the upper rectangular strip in the embodiment of the present invention are: length 17mm, width 1mm, and its long side is placed parallel to the sound wave reflecting substrate; the dimensions of the middle rectangular strip are: length 5mm, width 1mm, the middle rectangular strip is placed perpendicular to the center of the upper rectangular strip, and its short side is placed parallel to the sound wave reflecting substrate; the dimensions of the end rectangular strips are: length 4mm, width 1mm, and its short side is placed parallel to the sound wave reflecting substrate, and the dimensions of the sound wave reflecting substrate are: length 23*6mm, thickness 10mm.

[0061] The rectangular bar group of the embodiment of the present invention includes upper rectangular bars, middle rectangular bars, middle rectangular bars and end rectangular bars; further, corresponding to different frequency ranges, the number of multiple end rectangular bars and the distance between the end rectangular bars are adjusted, and then the phase response of the elementary structure is adjusted, so that the phase response difference of the multiple elementary structures at f=4000Hz~8000Hz is π / 2.

[0062] The rectangular strip group of the embodiment of the present invention is affixed to a hard sound wave reflecting substrate, and the upper rectangular strips, the middle rectangular strips and the middle rectangular strips are correspondingly affixed to the upper and middle parts of the hard sound wave reflecting substrate, the upper rectangular strips and the middle rectangular strips are perpendicular to each other and form a T-shaped structure (the long side of the middle rectangular strip is perpendicular to the center of the upper rectangular strip, and the short side is parallel to the sound wave reflecting substrate, and the two form a T-shaped structure), the middle rectangular strip is divided into two groups of perpendicular upper rectangular strips and parallel middle rectangular strips, a plurality of middle rectangular strips are located on both sides of the middle rectangular strips, and the end rectangular strips are located at both ends of the long side of the sound wave reflecting substrate.

[0063] Furthermore, in the embodiment of the present invention, the effect of the interaction between the Helmholtz cavity and the maze structure is formed between the rectangular strip groups applied to the hard sound wave reflecting substrate, and the rectangular strips in the middle position and the middle rectangular strips are fixed to form a mountain-like structure; in the various elementary structures, the number and application positions of the rectangular strips located in the middle position on the hard sound wave reflecting substrate are different.

[0064] Please continue reading Figure 1 , there are 4 kinds of elementary structures in the embodiment of the present invention, and the number of each elementary structure is 9; after the 36 elementary structures are coded and arranged based on the directivity function, they are arranged perpendicular to the hard sound wave reflecting matrix, and the arrangement method is as follows Figure 6 As shown, the four colors blue, red, orange and green correspond to four basic structures with phases from small to large. The encoding of the embodiment of the present invention is based on the arrangement obtained by the optimization algorithm under the premise of the best scattering effect of the far-field scattering amplitude under wide-band multi-angle incidence.

[0065] For further information, see Figure 6 There are four types of primitive structures in the embodiment of the present invention, and the corresponding phases are divided from small to large into: the first primitive structure, the second primitive structure, the third primitive structure and the fourth primitive structure; in the acoustic coding metasurface structure with uniform scattering under wide-band arbitrary angle incidence. The embodiment of the present invention arranges four primitives through directivity functions, each with 9 primitives, a total of 36 primitives are encoded and arranged perpendicular to the sound wave reflection matrix according to the encoding results, which can achieve the effect of uniform scattering under multi-angle incidence under wide-band conditions. Preferably, the arrangement of the elementary structures of the embodiment of the present invention is: the first elementary structure, the second elementary structure, the second elementary structure, the second elementary structure, the first elementary structure, the third elementary structure, the first elementary structure, the fourth elementary structure, the fourth elementary structure, the first elementary structure, the fourth elementary structure, the fourth elementary structure, the third elementary structure, the fourth elementary structure, the second elementary structure, the first elementary structure, the second elementary structure, the third elementary structure, the third elementary structure, the second elementary structure, the first elementary structure, the fourth elementary structure, the third elementary structure, the second elementary structure, the fourth elementary structure, the first elementary structure, the third elementary structure, the third elementary structure, the third elementary structure, the fourth elementary structure, the first elementary structure, the third elementary structure, the third elementary structure, the fourth elementary structure, the first elementary structure, the third elementary structure, the third elementary structure, the fourth elementary structure, the first elementary structure, the third elementary structure, the third elementary structure, the fourth elementary structure, the first elementary structure, the third elementary structure. The embodiment of the present invention makes the phase response of the four elementary structures in a wider frequency band present a 2^2 discrete gradient distribution in a 2π period, and the acoustic wave reflection phase difference is π / 2 through a simple structural design of the elementary structure.

[0066] In practical application, the size of the elementary structure of the embodiment of the present invention is set according to one tenth to one fifth of the required acoustic wavelength. The acoustic coding metasurface has an operating range of 4000 Hz to 8000 Hz, corresponding to a wavelength of 42 mm to 85 mm in airborne sound. Figure 3 In the rectangular bar group of the embodiment of the present invention, the width of the upper rectangular bar is 17 mm and the thickness is 1 mm; the height of the rectangular bar in the middle position is 5 mm and the width is 1 mm; the height of the middle rectangular bar is 4 mm and the width is 1 mm; the height of the end rectangular bar is 6 mm and the width is 1 mm; the length of the hard sound wave reflecting matrix is ​​23 mm, the width is 36 mm, and the thickness is 10 mm, and the hard sound wave reflecting matrix has the same cross-sectional size.

[0067] The rectangular strip group and the hard sound wave reflecting substrate of the embodiment of the present invention are preferably made of aluminum material; the density of the rectangular strip group and the hard sound wave reflecting substrate is 2.7g / m 3 , Young's modulus is 70GpPa, and the speed of sound is 6300m / s. The acoustic coding metasurface structure is uniformly scattered under wide-band and arbitrary angle incidence, and the frequency of f=4000Hz~8000Hz and multi-angle incident sound waves are regulated to make the reflected waves uniformly scattered.

[0068] Please continue reading Figure 1 and Figure 2 The side edges of the elementary structures of the embodiment of the present invention are perpendicular to the bottom edges; the elementary structures are aligned and closely arranged, and are perpendicular to the bottom edges of the hard sound wave reflecting substrate, and the side edges are parallel.

[0069] The directivity function of the embodiment of the present invention includes the angle and frequency of the incident sound wave, the angle and frequency are known quantities, and the phase information of the coded arrangement is an unknown quantity; the angles are 0°, 30°, 45°, 60° and 70°, and the frequency is 4kHz-8kHz; the directivity function is used as the objective function and is maximized, and the surface of the hard sound wave reflecting matrix is ​​divided into 36 blocks, and the data of each primitive structure is 9 as a constraint function, and multiple primitive structures are temporarily placed on the surface of the hard sound wave reflecting matrix according to an unknown arrangement, and the directivity function is used to obtain the optimal coding arrangement of multiple primitive structures.

[0070] Specifically, the directivity function in the embodiment of the present invention includes:

[0071]

[0072] In the formula, θ represents the elevation angle of the scattered wave, represents the azimuth of the scattered wave, θ i represents the elevation angle of the incident sound wave, represents the azimuth of the incident sound wave, represents the directivity function of the scattered wave, represents the far-field scattering amplitude, represents the directivity function of the coding metasurface, represents the directivity function of an unstructured smooth surface of the same size, σ Rrepresents the diffusion performance of the coded metasurface compared to the ordinary smooth surface, σ R The larger the value, the better the scattering effect. The elevation angle of the scattered wave is defined as The calculation formula of the scattering coefficient is:

[0073]

[0074] Where D represents the scattering coefficient, L i Represents the sound pressure level value of the far field in different directions, M represents the total number of selected angles, and i represents the selected direction.

[0075] The embodiment of the present invention expresses the far-field scattering amplitude based on array theory, where: θ represents the elevation angle of the scattered wave, represents the azimuth of the scattered wave, θ i is the incident wave elevation angle, is the incident wave azimuth, is a mode function of an element and can be ignored in the calculation process. is an array pattern. Assume that the acoustic coding metasurface structure consists of a x ×N y The array of elements is of size Λ. Φ(n,m) is Φ 00 , Φ 01 , Φ 10 , Φ 11 , represents the reflection phase of the four basic structures. By randomly arranging the four basic structures, a uniform scattering effect can be obtained. The expression is:

[0076]

[0077]

[0078]

[0079] Based on the above calculations, the embodiment of the present invention introduces a directivity function. Specifically, the directivity function of the embodiment of the present invention includes the angle and frequency of the incident sound wave. The angle and frequency are known quantities, and the angles are 0°, 30°, 45°, 60°, 70°, and the frequencies are 4kHz-8kHz; and the phase information of the coded arrangement is an unknown quantity. The directivity function of the embodiment of the present invention expresses the scattering effect of the far-field sound wave. The larger the value, the better the scattering effect. The embodiment of the present invention uses the directivity function as the objective function and maximizes it. The surface is divided into 36 blocks on average, and the number of each primitive structure is 9. The four primitive structures are temporarily placed on the surface according to an unknown arrangement. The optimization algorithm is used to obtain the optimal arrangement of the four primitives, that is, the phase information of the coded arrangement is obtained. Figure 4 shown.

[0080] Combination Figure 4 , the elevation angle of the scattered wave is defined as In the following formula represents the directivity function of the coding metasurface, represents the directivity function of an unstructured smooth surface of the same size, σ R It indicates the diffusion performance of the coded metasurface compared to an ordinary smooth surface. The larger the value, the better the scattering effect.

[0081]

[0082]

[0083] According to the coding primitive structure obtained from the above formula, the coding arrangement is arranged and the scattering effect is simulated, such as Figure 7-Figure 14 As shown, where: Fig.11 It can be seen that when the incident sound wave angle is 0°, the scattering coefficient of the coding metasurface structure is improved; Fig.12 It can be seen that when the incident sound wave angle is 30°, the scattering coefficient of the coding metasurface structure is improved. Fig.13 It can be seen that when the incident sound wave angle is 45°, the scattering coefficient of the coding metasurface structure is improved. Fig.14 It can be seen that when the incident acoustic wave angle is 60°, the scattering coefficient of the coded metasurface structure is improved.

[0084] In addition, the embodiment of the present invention introduces a scattering coefficient, and the calculation formula of the scattering coefficient is as follows:

[0085]

[0086] Where, L i It represents the sound pressure level value of the far field in different directions, and M represents the total number of selected angles.

[0087] The magnitude of the scattering coefficient in the embodiment of the present invention reflects the uniformity of the scattered sound field energy. A high scattering coefficient indicates that the sound energy is scattered more uniformly in different directions. On the contrary, if all energy is reflected in one direction by a mirror, the reflection coefficient is 0. In the simulation, the sound pressure level value is selected at an angle interval of 2°, and the value of M is 90.

[0088] In combination with the above-disclosed embodiment of the present invention, a uniformly scattering acoustic coding metasurface structure under wide-band and arbitrary angle incidence is provided, the following embodiments 1-4 are provided:

[0089] Example 1: When the sound wave frequency f=4.6kHz and 8.4kHz, the background medium is air, and the sound wave is incident perpendicular to the metasurface, the metasurface structural parameters and arrangement can be calculated by the directivity function and optimization algorithm, and the simulation calculation is performed using COMSOL Multiphysics software. Figure 7 The figure shows a schematic diagram comparing the scattering effects of a flat plate and a coded metasurface when the incident sound wave frequency is 4.6kHz and 8.4kHz and the incident sound wave angle is 0°. The blue line is the external sound pressure level radiation pattern of the metasurface structure, and the green line is the external sound pressure level radiation pattern of the flat plate structure. Figure 6 It can be seen that the acoustic coding metasurface structure of Example 1 scatters the vertically incident sound waves more evenly. Figure 6 The four colors correspond to Figure 1 The four primitive structures of the four colors blue, red, orange, and green correspond to the four primitives with phases from small to large. Therefore, an embodiment of the present invention is a uniformly scattering acoustic coding metasurface structure under wide-band and arbitrary angle incidence, which can adjust the angle of the reflected sound wave by a simple structure and arranging the structure to change the phase of the reflecting surface.

[0090] Example 2: When the sound wave frequency f=4.6kHz and 8.4kHz, the background medium is air, and the sound wave is incident perpendicular to the metasurface, the metasurface structural parameters and arrangement can be calculated by the directivity function and the optimization algorithm, and the simulation calculation is performed using COMSOL Multiphysics software. Figure 8 The following is a schematic diagram comparing the scattering effects of a flat plate and a coded metasurface when the incident sound wave frequency is 4.6kHz and 8.4kHz and the incident sound wave angle is 30°. The blue line is the external sound pressure level radiation pattern of the metasurface structure, and the green line is the external sound pressure level radiation pattern of the flat plate structure. Figure 8 It can be seen that the acoustic coding metasurface structure of Example 2 scatters the sound waves with an incident angle of 30° more evenly. Therefore, an acoustic coding metasurface structure that scatters evenly under wide-band and arbitrary angle incidence in an embodiment of the present invention achieves the control of the angle of the reflected sound wave through a simple structure and by changing the phase of the reflection surface through the structural arrangement.

[0091] Example 3: When the sound wave frequency f=4.6kHz and 6.3kHz, the background medium is air, and the sound wave is incident perpendicular to the metasurface, the metasurface structural parameters and arrangement can be calculated by the directivity function and optimization algorithm, and the simulation calculation is performed using COMSOL Multiphysics software. Fig. 9 This is a schematic diagram comparing the scattering effects of the flat plate and the coded metasurface when the incident sound wave frequency is 4.6kHz and 6.3kHz and the incident sound wave angle is 45° in Example 3, where the blue line is the external field sound pressure level radiation pattern of the metasurface structure, and the green line is the external field sound pressure level radiation pattern of the flat plate structure. Fig. 9It can be seen that the acoustic coding metasurface structure of Example 3 scatters the sound wave with an incident angle of 45° more evenly. Therefore, an acoustic coding metasurface structure that scatters evenly under wide-band and arbitrary angle incidence in an embodiment of the present invention can control the angle of the reflected sound wave by a simple structure and by arranging the structure to change the phase of the reflection surface.

[0092] Example 4: When the sound wave frequency is f=4.7kHz and 6kHz, the background medium is air, and the sound wave is incident perpendicular to the metasurface, the metasurface structural parameters and arrangement can be calculated by the directivity function and the optimization algorithm, and the simulation calculation is performed using COMSOL Multiphysics software. Fig.10 This is a schematic diagram comparing the scattering effects of the flat plate and the coded metasurface when the incident sound wave frequency is 4.7kHz and 6kHz and the incident sound wave angle is 60° in Example 4, where the blue line is the external field sound pressure level radiation pattern of the metasurface structure, and the green line is the external field sound pressure level radiation pattern of the flat plate structure. Fig.10 It can be seen that the acoustic coding metasurface structure of Example 4 scatters the sound wave with an incident angle of 60° more evenly. Therefore, an acoustic coding metasurface structure that scatters evenly under wide-band and arbitrary angle incidence in an embodiment of the present invention can control the angle of the reflected sound wave by a simple structure and by arranging the structure to change the phase of the reflection surface.

[0093] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be included in the protection scope of the present invention.

Claims

1. A uniformly scattering acoustic coding metasurface structure under wide-band and arbitrary-angle incidence, characterized in that: include: A plurality of elementary structures and a hard sound wave reflecting matrix for vertically placing the elementary structures, wherein the plurality of elementary structures are arranged in a coded manner based on a directivity function; Each of the elementary structures comprises: a Helmholtz cavity and a rectangular strip group, wherein the Helmholtz cavities are arranged in parallel in a horizontal row; The rectangular strip group is vertically added inside the Helmholtz cavity to form the elementary structure, and the rectangular strip group is used to increase the sound path difference; The propagation characteristics of sound waves are the same in a two-dimensional structure and a three-dimensional structure with the same cross-section as the two-dimensional structure. Therefore, the cross-section and two-dimensional design of the elementary structure in the acoustic coding metasurface structure are as follows: Each of the elementary structures is placed perpendicular to the long side of the hard sound wave reflecting substrate, and the rectangular strip group includes an upper rectangular strip, a middle rectangular strip, a middle rectangular strip and an end rectangular strip; the long side of the upper rectangular strip is placed parallel to the sound wave reflecting substrate, the long side of the middle rectangular strip is placed perpendicular to the center of the upper rectangular strip, and the short side is placed parallel to the sound wave reflecting substrate, and the two form a T-shaped structure; the middle rectangular strip is divided into two groups perpendicular to the upper rectangular strip and parallel to the middle rectangular strip, a plurality of the middle rectangular strips are located on both sides of the middle rectangular strip, and the end rectangular strips are located at both ends of the long side of the sound wave reflecting substrate; The rectangular strips attached to the hard sound wave reflective substrate form a Helmholtz cavity and a labyrinth structure, and the middle rectangular strips and the middle rectangular strips are fixed to form a mountain-like structure; In the various elementary structures, the number and application positions of the rectangular strips located in the middle of the hard sound wave reflecting substrate are different.

2. According to claim 1, a uniformly scattering acoustic coding metasurface structure under wide-band and arbitrary-angle incidence, characterized in that: Corresponding to different frequency ranges, the number of multiple end rectangular strips and the distance between the end rectangular strips are adjusted, thereby adjusting the phase response of the elementary structure, so that the phase response difference of the multiple elementary structures at f=4000Hz~8000Hz is π / 2.

3. The acoustic coding metasurface structure with uniform scattering under wide-band and arbitrary-angle incidence according to claim 2, characterized in that: There are 4 kinds of primitive structures, and the number of each kind of primitive structures is 9; After the 36 primitive structures are coded and arranged based on the directivity function, they are arranged perpendicular to the hard sound wave reflecting matrix.

4. The acoustic coding metasurface structure with uniform scattering under wide-band and arbitrary-angle incidence according to claim 1, characterized in that: The size of the elementary structure is set according to one tenth to one fifth of the required sound wave wavelength. The acoustic coding metasurface has an operating range of 4000Hz to 8000Hz, corresponding to a wavelength of 42mm to 85mm in airborne sound. The dimensions of a single unit structure are set to: 23 mm in width and 6 mm in thickness, where the thickness is one tenth to one fifth of the wavelength corresponding to the action frequency; In the rectangular strip group, the width of the upper rectangular strip is 17 mm and the thickness is 1 mm; the height of the middle rectangular strip is 5 mm and the width is 1 mm; the height of the middle rectangular strip is 4 mm and the width is 1 mm; the height of the end rectangular strip is 6 mm and the width is 1 mm; The length of the hard sound wave reflecting matrix is ​​23 mm, the width is 6 mm, and the thickness is 10 mm. The hard sound wave reflecting matrix has the same cross-sectional dimensions.

5. The acoustic coding metasurface structure with uniform scattering under wide-band and arbitrary-angle incidence according to claim 1, characterized in that: There are four types of primitive structures, which are divided into a first primitive structure, a second primitive structure, a third primitive structure and a fourth primitive structure from small to large corresponding to the phase; In the uniformly scattering acoustic coding metasurface structure under broadband arbitrary angle incidence, the arrangement of the elementary structures is as follows: The first primitive structure, the second primitive structure, the second primitive structure, the second primitive structure, the first primitive structure, the third primitive structure, the first primitive structure, the fourth primitive structure, the fourth primitive structure, the first primitive structure, the fourth primitive structure, the fourth primitive structure, the third primitive structure, the fourth primitive structure, the second primitive structure, the first primitive structure, the second primitive structure, the third primitive structure, the third primitive structure, the second primitive structure, the first primitive structure, the fourth primitive structure, the third primitive structure, the second primitive structure, the fourth primitive structure, the first primitive structure, the third primitive structure, the third primitive structure, the fourth primitive structure, the first primitive structure, the third primitive structure, the third primitive structure, the fourth primitive structure, the first primitive structure, the third primitive structure, the third primitive structure, the fourth primitive structure, the first primitive structure, the third primitive structure, the third primitive structure, the fourth primitive structure, the first primitive structure, the third primitive structure, the third primitive structure, the fourth primitive structure, the first primitive structure, the third primitive structure, the fourth primitive structure, the first primitive structure, the third primitive structure.

6. The uniformly scattering acoustic coding metasurface structure under wide-band and arbitrary-angle incidence according to claim 1, characterized in that: The side edge of the unit structure is perpendicular to its bottom edge; The elementary structures are aligned and closely arranged respectively, and are perpendicular to the bottom edge of the hard sound wave reflecting substrate and parallel to the side edges.

7. The uniformly scattering acoustic coding metasurface structure under wide-band and arbitrary-angle incidence according to claim 1, characterized in that: The rectangular strip group and the hard sound wave reflecting matrix are both made of aluminum material; The density of the rectangular strip group and the hard sound wave reflecting matrix is ​​2.7 g / m 3 , Young's modulus is 70GpPa, and the speed of sound is 6300m / s.

8. The acoustic coding metasurface structure with uniform scattering under wide-band and arbitrary-angle incidence according to claim 1 or 5, characterized in that: The acoustic coding metasurface structure is evenly scattered under wide-band and arbitrary-angle incidence, and the sound waves with frequencies of f=4000Hz to 8000Hz and incident at multiple angles are regulated to make the reflected waves evenly scattered.

9. The uniformly scattering acoustic coding metasurface structure under wide-band and arbitrary-angle incidence according to claim 1, characterized in that: The directivity function includes the angle and frequency of the incident sound wave, the angle and frequency are known quantities, and the phase information of the coded arrangement is an unknown quantity; the angle is 0°, 30°, 45°, 60°, 70°, and the frequency is 4kHz-8kHz; The directivity function is used as the objective function and maximized, and the surface of the hard sound wave reflecting substrate is divided into 36 blocks, and each of the primitive structures has 9 data as a constraint function; The plurality of primitive structures are temporarily placed on the surface of the hard sound wave reflecting substrate in an unknown arrangement, and the directivity function is used to obtain the optimal coding arrangement of the plurality of primitive structures.

10. The acoustic coding metasurface structure with uniform scattering under wide-band and arbitrary-angle incidence according to claim 9, characterized in that: The directivity function includes: In the formula, θ represents the elevation angle of the scattered wave, represents the azimuth of the scattered wave, θ i represents the elevation angle of the incident sound wave, represents the azimuth of the incident sound wave, represents the directivity function of the scattered wave, represents the far-field scattering amplitude, represents the directivity function of the coding metasurface, represents the directivity function of an unstructured smooth surface of the same size, σ R represents the diffusion performance of the coded metasurface compared to the ordinary smooth surface, σ R The larger the value, the better the scattering effect. The elevation angle of the scattered wave is defined as The calculation formula of the scattering coefficient is: Where D represents the scattering coefficient, L i Represents the sound pressure level value of the far field in different directions, M represents the total number of selected angles, and i represents the selected direction.

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