CN111489732B - Acoustic super-surface and design method thereof and acoustic device - Google Patents
Acoustic super-surface and design method thereof and acoustic device Download PDFInfo
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Abstract
The invention provides an acoustic super surface, a design method thereof and an acoustic device, wherein the acoustic super surface comprises a back cavity structure, the back cavity structure comprises a bottom sound insulation plate and side wall sound insulation plates which are arranged on one side surface of the bottom sound insulation plate and enclose a plurality of cavities; and the cover plates are covered on one side of the side wall sound insulation plate, which is away from the bottom sound insulation plate, are perforated plates, and the cover plates and the cavities form single cells in one-to-one correspondence. From the above, it can be seen that the acoustic super surface provided by the present invention designs and determines the reflection coefficient of each unit cell and the spatial distribution of the phase difference composed of the phase differences of the unit cells according to the expected functional requirements; and further, according to the spatial distribution and reflection coefficient of the phase difference, the arrangement mode of the unit cell array and the parameters of each unit cell are determined, so that the acoustic super-surface meets the expected functional requirement, and the purpose of modulating the acoustic wave phase by the acoustic super-surface is realized. The acoustic super-surface provided by the invention has a simple structure and low cost.
Description
Technical Field
The present invention relates to the field of acoustic technology, and more particularly, to an acoustic super surface, a design method thereof, and an acoustic device.
Background
Sound waves are the propagation of vibrations generated by a sound source in air or other media. As a propagation mode of information and energy, the method has very wide application in the technical field of engineering and production and living. Such as: in the medical field, ultrasonic lithotripsy can be realized by accurately controlling the field intensity distribution of ultrasonic waves and focusing energy to the position of a human body calculus; in the military field, an underwater vehicle can absorb sound waves from sonar through a special acoustic surface, so as to achieve a stealth effect. It can be seen that effectively controlling the amplitude, phase, propagation direction and path of sound waves, and the energy distribution of the sound field, is the technological basis for implementing a range of engineering applications.
The acoustic super surface (Acoustic Metasurface) is a new method of modulating acoustic waves proposed in recent years. The method mainly utilizes a microstructure with elaborate design to realize the phase control of reflected or transmitted sound waves, and further realizes a series of functions which are not possessed by the traditional acoustic surface, such as abnormal reflection, negative refraction, focusing, self-bending and the like of plane sound waves. At present, the microstructures used in acoustic subsurface designs mainly include three types of curled spaces, helmholtz resonators, and resonant thin films. However, the existing acoustic super-surface structure is complex, difficult to process and high in preparation cost.
Disclosure of Invention
In view of the above, the invention provides an acoustic super-surface, a design method thereof and an acoustic device, which effectively solve the technical problems existing in the prior art, and the acoustic super-surface has a simple structure and low cost.
In order to achieve the above purpose, the technical scheme provided by the invention is as follows:
an acoustic subsurface, comprising:
the back cavity structure comprises a bottom sound insulation plate and side wall sound insulation plates which are arranged on one side surface of the bottom sound insulation plate and enclose a plurality of cavities; the cover plates are perforated plates and correspond to the cavities one by one to form single cells, and the reflection coefficient of the single cells is not less than 0.7;
the arrangement mode of the unit cell array formed by the unit cells and the parameter of each unit cell are determined according to the space distribution of the reflection coefficient and the phase difference; the spatial distribution of the reflection coefficient and the phase difference is determined according to the expected functional requirements of the acoustic super-surface; wherein the phase difference is the phase difference between the incident sound wave and the reflected sound wave of the unit cell, and the parameters of the unit cell at least comprise the porosity of the cover plate and/or the plate thickness of the cover plate.
Optionally, the width of a unit cell formed by the cover plate and the cavity is not more than lambda/3, and lambda is the wavelength of the incident sound wave.
Optionally, the shapes and sizes of the plurality of cavities are the same.
Optionally, the cover plate and the back cavity structure are detachably fixed.
Optionally, the cover plate is made of a metal material or a non-metal material.
Alternatively, the desired functional requirement is to regulate the propagation path of the acoustic wave or the energy distribution of the acoustic wave along the propagation path.
Correspondingly, the invention also provides a design method of the acoustic super surface, which is used for designing the acoustic super surface and comprises the following steps:
establishing a database of reflection coefficients of unit cells with different parameters and phase differences between incident sound waves and reflected sound waves;
calculating the arrangement mode of a single cell array of the acoustic super surface to be designed and the spatial distribution of phase differences formed by the phase differences of each single cell in the single cell array based on the expected functional requirement of the acoustic super surface to be designed, and controlling the reflection coefficient of the single cell to meet engineering requirements;
and determining parameters of each unit cell in the unit cell array in the database according to the calculation result, and arranging according to the calculated arrangement mode of the unit cell array to obtain an acoustic super surface.
Optionally, determining parameters of the unit cells of the acoustic super surface in the database further comprises:
and performing functional verification on the acoustic super surface.
Correspondingly, the invention also provides an acoustic device, which comprises the acoustic super-surface.
Compared with the prior art, the technical scheme provided by the invention has at least the following advantages:
the invention provides an acoustic super surface, a design method thereof and an acoustic device, wherein the acoustic super surface comprises a back cavity structure, the back cavity structure comprises a bottom sound insulation plate and side wall sound insulation plates which are arranged on one side surface of the bottom sound insulation plate and enclose a plurality of cavities; the cover plates are perforated plates and correspond to the cavities one by one to form single cells, and the reflection coefficient of the single cells is not less than 0.7; the arrangement mode of the unit cell array formed by the unit cells and the parameter of each unit cell are determined according to the space distribution of the reflection coefficient and the phase difference; the spatial distribution of the reflection coefficient and the phase difference is determined according to the expected functional requirements of the acoustic super-surface; wherein the phase difference is the phase difference between the incident sound wave and the reflected sound wave of the unit cell, and the parameters of the unit cell at least comprise the porosity of the cover plate and/or the plate thickness of the cover plate.
From the above, it can be seen that the acoustic super surface provided by the present invention designs and determines the reflection coefficient of each unit cell and the spatial distribution of the phase difference composed of the phase differences of the unit cells according to the expected functional requirements; and further, according to the spatial distribution and reflection coefficient of the phase difference, the arrangement mode of the unit cell array and the parameters of each unit cell are determined, so that the acoustic super-surface meets the expected functional requirement, and the purpose of modulating the acoustic wave phase by the acoustic super-surface is realized. The acoustic super-surface provided by the invention has a simple structure and low cost.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required to be used in the embodiments or the description of the prior art will be briefly described below, and it is obvious that the drawings in the following description are only embodiments of the present invention, and that other drawings can be obtained according to the provided drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram of an acoustic subsurface according to an embodiment of the present invention;
FIG. 2 is a cut-away view of the AA' direction of FIG. 1;
FIG. 3 is a flow chart of a method for designing an acoustic subsurface according to an embodiment of the present invention;
FIG. 4 shows a finite element model (a) for calculating phase changes and reflection coefficients and incident and reflected wavefields (b-c) provided by an embodiment of the invention;
FIG. 5 shows the phase change (a) and the reflection coefficient (b) of the unit cell according to the variation of the plate thickness T and the porosity sigma provided in the embodiment of the present invention;
FIG. 6 is a graph showing the results of numerical experiments on an abnormally reflected acoustic subsurface having a reflection angle of 30 according to an embodiment of the present invention;
FIG. 7 is a schematic diagram of a numerical experiment result of an abnormal reflection acoustic super surface with a reflection angle of 45 ° and 60 ° according to an embodiment of the present invention;
FIG. 8 is a graph showing the results of numerical experiments on an acoustic subsurface for regular reflection focusing provided by an embodiment of the present invention;
FIG. 9 is a schematic diagram of the numerical experimental results of an acoustic super-surface with arbitrary point reflection focusing provided by an embodiment of the present invention;
fig. 10 is a schematic diagram of a numerical experiment result of an acoustic super surface of a self-bending beam according to an embodiment of the present invention.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
As described in the background, acoustic super-surfaces (Acoustic Metasurface) are a new approach to acoustic modulation that has been proposed in recent years. The method mainly utilizes a microstructure with elaborate design to realize the phase control of reflected or transmitted sound waves, and further realizes a series of functions which are not possessed by the traditional acoustic surface, such as abnormal reflection, negative refraction, focusing, self-bending and the like of plane sound waves. At present, the microstructures used in acoustic subsurface designs mainly include three types of curled spaces, helmholtz resonators, and resonant thin films. However, the existing acoustic super-surface structure is complex, difficult to process and high in preparation cost.
Based on the above, the invention provides an acoustic super-surface, a design method thereof and an acoustic device, which effectively solve the technical problems existing in the prior art, and the acoustic super-surface has a simple structure and low cost.
In order to achieve the above objective, the technical solution provided by the present invention is described in detail below with reference to fig. 1 to 10.
Referring to fig. 1 and fig. 2, fig. 1 is a schematic structural diagram of an acoustic super surface provided by an embodiment of the present invention, and fig. 2 is a sectional view along AA' direction in fig. 1, where the acoustic super surface provided by the embodiment of the present invention includes:
a back cavity structure comprising a bottom sound insulation plate 110 and side wall sound insulation plates 120 arranged on one side surface of the bottom sound insulation plate 110 and enclosing a plurality of cavities 130; and a plurality of cover plates 200 covering one side of the side wall sound insulation plate 120 away from the bottom sound insulation plate 110, wherein the cover plates 200 are perforated plates, the cover plates 200 and the cavity 130 are in one-to-one correspondence to form a unit cell, and the reflection coefficient of the unit cell is not less than 0.7.
The arrangement mode of the unit cell array formed by the unit cells and the parameter of each unit cell are determined according to the space distribution of the reflection coefficient and the phase difference; the spatial distribution of the reflection coefficient and the phase difference is determined according to the expected functional requirements of the acoustic super-surface; wherein the phase difference is a phase difference between an incident sound wave and a reflected sound wave of the unit cell, and the parameters of the unit cell include at least the porosity of the cover plate 200 and/or the plate thickness of the cover plate 200.
It can be appreciated that the back cavity structure and the plurality of cover plates provided by the embodiments of the present invention form an acoustic super surface of a cube-shaped structure. The bottom sound-insulating plate and the side wall sound-insulating plate provided by the invention are non-perforated plate structures, are thin plates which almost completely reflect sound waves, and are not particularly limited in material; forming a plurality of sub-wavelength sized cavities through the bottom sound insulation plate and the side wall sound insulation plate; the bottom sound-insulating plate and the side wall sound-insulating plate provided by the invention can be of an integrated structure, and the invention is not particularly limited. The cover plates provided by the invention correspond to the cavities one by one and are covered on the side wall sound insulation plates at the sides of the cavities. The cover plate provided by the invention is a perforated plate, and the perforated plate is a thin plate with a large number of holes penetrating through the plate thickness distributed on the plate surface, and has the advantages of simple structure, easiness in manufacturing, long service life, environmental friendliness and the like; the cut sheet is perforated by a numerical control punch, the aperture is about 1mm, the area porosity is between 0.1% and 10%, and the thickness of the sheet is less than 1 mm. Optionally, the cover plate provided by the invention can be made of a metal material, so that the cover plate has the characteristics of water resistance, fire resistance, high temperature resistance and the like, and can be applied to extreme environments; in addition, the material of the cover plate provided by the invention can be a nonmetallic material, and the invention is not particularly limited. The shape of the holes of the perforated plate is not particularly limited, and the perforated plate is required to be specifically designed according to practical application.
Since the acoustic wave is a periodic vibration, a phase difference between the incident acoustic wave and the reflected acoustic wave (hereinafter, described simply as "phase difference") caused by designing the cover plates having different parameters and the unit cell formed by the cavity in the acoustic super surface should cover a [0,2 pi ] (rad) range. In theory, the phase difference that can be achieved by a single cell is influenced by parameters such as the depth h of the cavity, the aperture a of the cover plate, the plate thickness T of the cover plate, the porosity sigma of the cover plate, and the like. Thus, the acoustic supersurface can be tailored to achieve desired functional requirements by selecting specific back cavity structural dimensions and cover plates with different parameters. The expected functional requirement may be to regulate the propagation path of the acoustic wave or the energy distribution of the acoustic wave along the propagation path within a preset acoustic wave working frequency range, specifically, for example, the acoustic super surface can make the acoustic wave reflect at an angle of 30 degrees after perpendicularly incident on the acoustic super surface, the acoustic super surface can make the acoustic wave realize reflection focusing at a specific position, the acoustic super surface can make the reflected acoustic wave propagate along a specific path, and the like.
The variation of the phase difference is more sensitive to the variation of the porosity sigma of the parametric cover plate and the plate thickness T of the cover plate and is also more convenient for modulation than the aperture a of the cover plate and the depth h of the cavity. Therefore, the design requirements of technical indexes such as phase difference and reflection coefficient can be realized through the combined design of the porosity sigma of the cover plate and the plate thickness T of the cover plate. Optionally, the shapes and the sizes of the plurality of cavities provided by the embodiment of the invention are the same, and further, only the parameters of the cover plate are required to be optimally designed, so that only back cavity structures with the same size are required to be produced in a production link, the industrial production is facilitated, and the production difficulty and the processing cost are reduced.
Furthermore, the cover plate provided by the embodiment of the invention is positioned on one side of the side wall sound insulation plate, which is away from the bottom sound insulation plate, and the cover plate is detachably fixed with the back cavity structure, so that the cover plates with different parameters can be replaced in a detachable and fixed mode between the cover plate and the back cavity structure, and the application range of the acoustic super surface is improved.
As shown in FIG. 1, the acoustic super surface can be formed by arranging a plurality of unit cells in an array on a two-dimensional plane (x-y plane), and when plane sound waves are incident on the acoustic super surface, a specific phase difference gradient is formed by arranging unit cells formed by the plurality of unit cells in an array mode and designing parameters of each unit cell, so that the acoustic super surface with a corresponding sound adjusting and controlling function can be obtained. The width of the unit cell along the phase difference change direction (such as the x direction) is d, and the length of the unit cell perpendicular to the phase difference change direction (the y direction) can be determined according to the working condition; the width d of the unit cell generally takes a sub-wavelength scale, the smaller the value of the width d of the unit cell is, the higher the phase discrete precision is, the closer the phase difference gradient is to be continuous, and the closer the reflected sound field is to the theoretical predicted sound field; however, the smaller the value of the width d of the unit cell, the higher the preparation cost and difficulty of the acoustic super surface. Therefore, reasonable selection of the width d dimension of the unit cell is beneficial to control of cost while maintaining the accuracy of the acoustic ultrasonic surface, and a large number of numerical experiments prove that when the value of the width d of the unit cell is not more than lambda/3, the reflected sound field is almost consistent with the predicted sound field. Optionally, the width of a unit cell formed by the cover plate and the cavity provided by the embodiment of the invention is not greater than λ/3, where λ is the wavelength of the incident sound wave, and the width is a value in the direction of change of the phase difference between the incident sound wave and the reflected sound wave.
In order to ensure the intensity of reflected sound waves, the loss of unit cells on the acoustic super surface to sound waves is within an engineering acceptable range, wherein the embodiment of the application requires that the reflection coefficient of unit cells formed by the cover plate and the cavity is not less than 0.7 after the incident sound waves are normally incident to the unit cells.
As can be seen from the above, the acoustic super-surface provided by the embodiment of the present invention includes a back cavity structure, where the back cavity structure includes a bottom sound-insulating plate, and side wall sound-insulating plates disposed on a surface of one side of the bottom sound-insulating plate and enclosing a plurality of cavities, where the plurality of cavities are arranged in an array; and the cover plates are covered on one side of the side wall sound insulation plate, which is away from the bottom sound insulation plate, are perforated plates, and the cover plates and the cavities form single cells in one-to-one correspondence. The acoustic super-surface provided by the embodiment of the invention has the advantages of simple structure and low cost on the basis of meeting the expected functional requirements.
Correspondingly, the invention further provides a method for designing an acoustic super surface, and referring to fig. 3, a flowchart of the method for designing an acoustic super surface provided by the embodiment of the invention is shown, where the method for designing the acoustic super surface is used for designing the acoustic super surface, and includes:
s1, establishing a database of reflection coefficients of unit cells with different parameters and phase differences between incident sound waves and reflected sound waves.
In one embodiment of the invention, numerical experiments can be performed on single cells with the porosity sigma of different cover plates and the plate thickness T of the cover plates according to a series of parameter conditions such as the material of the cover plate, the aperture a of the cover plate, the depth h of a cavity, the width d of the single cell and the like selected by working conditions (such as allowable space size of acoustic super-surface pavement, including the characteristics of area and thickness, self-weight of structure, structural strength, fire resistance, high temperature resistance and the like), and a database of the phase differences and reflection coefficients of the single cells with different parameters is established through parameterized scanning.
S2, calculating the arrangement mode of the unit cell array of the acoustic super surface to be designed and the spatial distribution of phase differences formed by the phase differences of each unit cell in the unit cell array based on the expected functional requirement of the acoustic super surface to be designed, and controlling the reflection coefficient of the unit cell to meet engineering requirements.
Based on the expected functional requirement of the acoustic super surface to be designed, the arrangement mode of the required unit cell array and the spatial distribution of the phase difference are obtained through theoretical calculation. The phase difference is the phase difference of the incident sound wave and the reflected sound wave of the unit cell, and the spatial distribution of the phase difference is realized by the unit cell, so that the spatial distribution of the phase difference is the arrangement mode of the unit cell array. Meanwhile, the reflection coefficient of the control unit cell meets engineering requirements.
S3, determining parameters of each unit cell in the unit cell array in the database according to a calculation result, and arranging according to the calculated arrangement mode of the unit cell array to obtain an acoustic super surface.
In an embodiment of the present application, according to specific engineering requirements, the accuracy degree of the expected functions, the production cost and the like can be achieved, for example, according to the application environment, the calculated phase difference spatial distribution is subjected to sub-wavelength dispersion of spatial dimensions (that is, discrete data with a spatial distance far smaller than the wavelength are used for replacing continuous phase difference spatial distribution), and the sub-wavelength dispersion is used as a unit cell technical index of the super-surface to be designed.
Searching parameters of each unit cell meeting the conditions in a database according to the obtained phase difference space distribution formed by the phase difference of each unit cell and the reflection coefficient of each unit cell; when a series of parameters such as the material of the cover plate, the aperture a of the cover plate, the depth h of the cavity, the width d of the unit cell and the like are fixed, only the porosity sigma of the cover plate and the plate thickness T parameter of the cover plate can be determined, and then each unit cell is arranged according to the arrangement mode of the unit cell array, so that the acoustic super surface is obtained.
As further shown in fig. 3, in the design method provided by the embodiment of the present invention, after determining parameters of a unit cell of the acoustic super surface in the database, the method further includes:
and S4, performing functional verification on the acoustic super surface.
In an embodiment of the present application, the verification of the acoustic subsurface may utilize data experiments to verify the overall design method, verifying whether it meets the expected functional requirements.
Several specific acoustic supersurfaces provided by the present invention are described in detail below in conjunction with fig. 4-10. The following description will take an example of an incident sound wave having an operating frequency of 1kHz, a wave velocity in air of 343m/s, namely, a wavelength lambda of 0.343m, a hole diameter a of 1.4mm of the perforated plate, and a cavity depth h of 3 cm. The unit cells are arranged from left to right as shown in fig. 1, and are composed of a bottom sound insulation plate, a side wall sound insulation plate and a cover plate, a plurality of cavities in a cuboid shape are enclosed by the side wall sound insulation plate, and the back cavity structure is covered with the cover plate made of a perforated plate. The incident sound wave provided by the invention is normal incident plane sound wave, and the acoustic super-surface design is based on generalized Snell's law, namely:
wherein n is i Is the refractive index of the medium, θ i Is the incident angle of sound wave, θ r Is the reflection angle of the sound wave, λ is the wavelength of the incident sound wave, and phi (x) is the phase difference between the reflected sound wave and the incident sound wave. In air, its refractive index n i For 1, the invention takes normal incidence as an example, namely theta i If 0, then formula (2) can be reduced to:
and then the design flow of the acoustic super surface is combined with the diagram shown in fig. 3, firstly, a numerical experiment is carried out to obtain a database of the phase change and the reflection coefficient of the unit cells, then the phase change parameters of the unit cells are obtained through the formula (2), then the parameters of the unit cells are determined through the database obtained through the numerical experiment, the unit cells are arranged, and the numerical experiment is carried out to verify, so that the acoustic super surface required in engineering can be designed.
The numerical experiment platform for calculating the single cell phase change and the reflection coefficient is shown in fig. 4 (a), and a beam of normal incident sound wave is made to the perforated plate, so that a beam of normal reflected sound wave exists, as shown in fig. 4 (b) and fig. 4 (c), the phases of the incident sound wave and the reflected sound wave are respectively obtained at the point A, and the phase difference phi can be obtained by taking the difference value, wherein the distance between the point A and the perforated plate is lambda/2. Based on the above parameters, as the porosity σ of the cover plate and the plate thickness T of the cover plate change, a phase change as shown in fig. 5 (a) and a reflectance map as shown in fig. 5 (b) can be obtained. As can be seen from FIG. 5 (a), the phase variation range which can be regulated by the unit cell is [0.02 pi, 1.62 pi ], and the parameter value of part of the unit cell adopts an approximate method in the practical application process. In order to be as close as possible to the value at which the phase change should theoretically be achieved, the phase change obtained by the formula (2) is approximated to 1.62 pi when it is within [1.62 pi, 1.82 pi ], and approximated to 0.02 pi when the obtained phase range is within [0,0.02 pi ]. Because of partial approximation in the design process, the numerical experimental result has a certain error compared with the ideal reflected sound field, but can be controlled within the engineering acceptable range. It can be seen from FIG. 5 (b) that the range of reflectance values for the unit cells is [0.7,1], whereas the reflectance of each unit cell is required to be greater than 0.7 when designing an acoustic subsurface, so that the unit cells meet the requirements for designing the subsurface.
The acoustic subsurface provided by the embodiment of the invention can be an abnormal reflection acoustic subsurface. When designing an abnormal reflection acoustic super-surface, when the abnormal reflection acoustic super-surface is formed by an array of super-cells (namely, a structural combination formed by a plurality of unit cells with different structural sizes in the phase difference changing direction), the width D of the super-cells is the ratio of the wavelength of an incident sound wave to the sine value of a reflection angle, and after the working frequency of the incident sound wave is determined, the wavelength of the incident sound wave is determined, and then the size of the width D of the super-cells depends on the value of the reflection angle. And at the moment, the abnormal reflection acoustic super surface is formed by a super cell array, the width D of the super cells is an integer multiple of the width D of the unit cell, namely d=D/n (n is a positive integer), and the proper n can enable the width D of the unit cell to have a reasonable size.
In particular, in one embodiment of the present invention, sound waves normally incident perpendicularly to a surface are reflected by the surface in a direction opposite to the direction of incidence. The so-called extraordinary reflection super surface can reflect sound waves of normal incidence to a designed direction by phase modulation. Since the phase of the acoustic wave varies periodically between [0,2 pi ], in the abnormally reflected acoustic hypersurface, the phase varies periodically, so that the arrangement of the unit cells is also periodic, the unit cells in each period form a supercell, and the phase difference in each supercell can be found as:
bringing formula (3) into formula (2) has:
in the embodiment of the invention, the invention provides an acoustic super surface which can abnormally reflect normal incidence waves at a 30-degree reflection angle, namely theta r =30°. Given that the wavelength λ of the incident sound wave is 0.343M, the supercell width d=0.686M can be found from formula (4), so that each supercell consists of 8 cells, the width of a cell is 0.08575M, and the numbers defining the cells are denoted from left to right as M, respectively i Wherein i is an integer between 1 and 8. The phase difference was changed to 2pi in one period, and the phase change and the perforation plate parameters distributed to each unit cell after discretizing the phase change are shown in table 1 in combination with the database shown in fig. 5:
TABLE 1
Here, M 7 The phase change of the single cell should be 1.75 pi, which we approximate to 1.62 pi; m is M 8 The change in the phase of the number unit cell should be 2 pi, which we approximate to 0.02 pi. Finally, the invention carries out numerical experiment verification on the acoustic response characteristics of the designed acoustic super surface, and the result is shown in fig. 6. Wherein FIG. 6 (a) shows a reflected sound field, arrow direction meterShowing the propagation direction of the reflected sound wave; fig. 6 (b) shows the total sound intensity. The comparison shows that the reflection angle obtained by the numerical experiment is identical to the reflection angle expected by theory, the correctness of the design is verified, and meanwhile, the fact that the phase change is approximated and the functional requirement of the acoustic super surface is not influenced is also proved.
Furthermore, the invention also designs the abnormal reflection acoustic super surface with other reflection angles, wherein 8 single cells are used to form one super cell, so that the rest parameters are the same as the parameters of the abnormal reflection acoustic super surface with 30 degrees of reflection angle provided by the embodiment of the invention except the width D of the super cell and the D of the single cell. Taking a reflection angle of 45 degrees and a reflection angle of 60 degrees as examples, the known wavelength lambda is 0.343m, and under the condition of normal incidence, the width D of a supercell is 0.485m and the width D of a unit cell is 0.0606m when the reflection angle is 45 degrees can be calculated by the formula (4); the width D of the supercell at 60℃reflection angle is 0.396m and the width D of the unit cell is 0.0495m. Similarly, the numerical experiment of the invention is carried out on the abnormal reflection acoustic super surface of 45 degrees and 60 degrees, and the specific result is shown in fig. 7. Wherein, fig. 7 (a) and fig. 7 (b) are numerical simulation results when the reflection angles are 45 ° and 60 °, respectively, and (i) and (ii) are the reflected sound field and the total sound intensity, respectively. It can be seen that the numerical experimental results of the acoustic super-surface designed by the invention can perfectly correspond to the expected results.
The acoustic super surface provided by the embodiment of the invention can also be a reflection focusing acoustic super surface, and particularly can be a function of realizing regular reflection focusing. At (0, y) 0 ) The phase distribution expression for the normal reflection focus is:
in the embodiment of the present invention, the regular reflection focusing at (0, 4λ) is taken as an example. The invention selects 30 single cells, the width d of each single cell is 0.1M, and the numbers of the single cells are M from left to right in sequence i Wherein i is an integer between 1 and 30. The phase difference of each unit cell can be calculated by the formula (5) with the known wavelength lambda of 0.343m, and the respective phase differences can be found out by the database shown in FIG. 5The parameters of the perforated plates in the unit cells are shown in Table 2:
TABLE 2
It should be noted that when we calculate the phase change of each unit cell, we choose the coordinates of the midpoint of the unit cell to calculate. In the present embodiment, for M 1 、M 6 、M 16 M is as follows 26 The phase difference of the number unit cells is approximated. Numerical experiment verification is carried out on the designed regular reflection focusing super surface, and the result is shown in fig. 8, wherein fig. 8 (a) is a reflection sound field; fig. 8 (b), fig. 8 (e) is total sound intensity and reflected sound intensity, respectively; FIG. 8 (c), FIG. 8 (d) is the total sound intensity on the transverse and longitudinal cross-section of the overfocal spot, respectively; fig. 8 (f) is the scattered sound intensity on the transverse and longitudinal cross-section of the overfocal spot. It can be seen that the numerical experimental results closely match the results expected in the design of the present invention.
The acoustic super surface provided by the embodiment of the invention can also be a reflection focusing acoustic super surface, and particularly can realize the focusing function at any point. At (x) 0 ,y 0 ) The phase change distribution formula of the reflection focusing is as follows:
taking focusing at (0.5,4 lambda) as an example, 30 single cells are selected, the width d of each single cell is 0.1M, and the numbers of the single cells are M in sequence from left to right i Wherein i is an integer between 1 and 30. Knowing the wavelength λ as 0.343m, the phase difference of each cell can be calculated by equation (6), and the parameters of the perforated plates in each cell can be found out by the database shown in fig. 5, and the specific parameters are shown in table 3:
TABLE 3 Table 3
It should be noted that when we calculate the phase change of each unit cell, we choose the coordinates of the midpoint of the unit cell to calculate. Likewise, M of the present embodiment 2 、M 6 、M 11 M is as follows 21 The phase difference of the number unit cells is approximated. Numerical experiment verification is carried out on the designed arbitrary point reflection focusing super surface, and the result is shown in fig. 9, wherein fig. 9 (a) is a reflection sound field; fig. 9 (b), fig. 9 (e) is total sound intensity and reflected sound intensity, respectively; fig. 9 (c), fig. 9 (d) is the total sound intensity on the transverse and longitudinal cross-section of the overfocal point, respectively; fig. 9 (f) is the scattered sound intensity on the transverse and longitudinal cross-section of the overfocal spot. The numerical experimental results perfectly match the results expected in the design of the invention.
The acoustic hypersurface provided by the embodiment of the invention can also be an acoustic hypersurface of a self-bending beam. In order for the reflected wave to propagate around a semicircle with radius r, the phase difference spatial distribution expression of the hypersurface needs to satisfy:
in the embodiment of the invention, the reflected sound wave is taken as an example to propagate around a semicircle with a radius of 1 m. We choose 30 single cells, each with a width d of 0.1M, the number of single cells being M in sequence from left to right i Wherein i is an integer between 1 and 30. Knowing the wavelength λ as 0.343m, the phase difference of each cell can be calculated by equation (7), and the parameters of the perforated plates in each cell can be found out by the database shown in fig. 5, and the specific parameters are shown in table 4:
TABLE 4 Table 4
Note that we calculate eachAnd when the phase of each unit cell changes, the coordinates of the midpoint of the unit cell are selected for calculation. In the present embodiment, M 5 、M 18 、M 24 M is as follows 29 The phase difference of the number unit cells is approximated. Numerical experiment verification is carried out on the designed arbitrary point reflection focusing super surface, and the result is shown in fig. 10, wherein fig. 10 (a) is a reflection sound field; FIG. 10 (b) is a reflected sound intensity; fig. 10 (c) is the total sound intensity. The numerical experimental results are quite consistent with the expected results in the design of the invention.
Correspondingly, the invention also provides an acoustic device, which comprises the acoustic super surface provided by any embodiment.
The invention provides an acoustic super surface, a design method thereof and an acoustic device, wherein the acoustic super surface comprises a back cavity structure, the back cavity structure comprises a bottom sound insulation plate and side wall sound insulation plates which are arranged on one side surface of the bottom sound insulation plate and enclose a plurality of cavities; the cover plates are perforated plates and correspond to the cavities one by one to form single cells, and the reflection coefficient of the single cells is not less than 0.7; the arrangement mode of the unit cell array formed by the unit cells and the parameter of each unit cell are determined according to the space distribution of the reflection coefficient and the phase difference; the spatial distribution of the reflection coefficient and the phase difference is determined according to the expected functional requirements of the acoustic super-surface; wherein the phase difference is the phase difference between the incident sound wave and the reflected sound wave of the unit cell, and the parameters of the unit cell at least comprise the porosity of the cover plate and/or the plate thickness of the cover plate.
From the above, it can be seen that the acoustic super surface provided by the present invention designs and determines the reflection coefficient of each unit cell and the spatial distribution of the phase difference composed of the phase differences of the unit cells according to the expected functional requirements; and further, according to the spatial distribution and reflection coefficient of the phase difference, the arrangement mode of the unit cell array and the parameters of each unit cell are determined, so that the acoustic super-surface meets the expected functional requirement, and the purpose of modulating the acoustic wave phase by the acoustic super-surface is realized. The acoustic super-surface provided by the invention has a simple structure and low cost.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (9)
1. An acoustic subsurface, comprising:
the back cavity structure comprises a bottom sound insulation plate and side wall sound insulation plates which are arranged on one side surface of the bottom sound insulation plate and enclose a plurality of cuboid cavities; the cover plates are perforated plates and correspond to the cavities one by one to form single cells, and the reflection coefficient of the single cells is not less than 0.7; wherein the perforated plate is a plate with a plurality of holes penetrating through the plate thickness distributed on the plate surface, and the area porosity is between 0.1% and 10%;
the arrangement mode of the unit cell array formed by the unit cells and the parameter of each unit cell are determined according to the space distribution of the reflection coefficient and the phase difference; the spatial distribution of the reflection coefficient and the phase difference is determined according to the expected functional requirements of the acoustic super-surface; wherein the phase difference is the phase difference between the incident sound wave and the reflected sound wave of the unit cell, and the parameters of the unit cell at least comprise the porosity of the cover plate and/or the plate thickness of the cover plate.
2. The acoustic super surface according to claim 1, wherein a width of a unit cell formed by said cover plate and said cavity is not more than λ/3, λ being a wavelength of an incident sound wave.
3. The acoustic super surface of claim 1, wherein the plurality of cavities are identical in shape and size.
4. The acoustic super surface according to claim 1, wherein said cover plate is detachably secured to said back cavity structure.
5. The acoustic subsurface of claim 1, wherein the cover plate is a metallic material or a non-metallic material.
6. The acoustic super surface according to claim 1, wherein said desired functional requirement is to regulate the propagation path of sound waves or the energy distribution of sound waves along the propagation path.
7. A method of designing an acoustic subsurface, characterized by comprising:
establishing a database of reflection coefficients of unit cells with different parameters and phase differences between incident sound waves and reflected sound waves;
calculating the arrangement mode of a single cell array of the acoustic super surface to be designed and the spatial distribution of phase differences formed by the phase differences of each single cell in the single cell array based on the expected functional requirement of the acoustic super surface to be designed, and controlling the reflection coefficient of the single cell to meet engineering requirements;
and determining parameters of each unit cell in the unit cell array in the database according to the calculation result, and arranging according to the calculated arrangement mode of the unit cell array to obtain an acoustic super surface.
8. The method of claim 7, further comprising, after determining parameters of a unit cell of the acoustic super surface in the database:
and performing functional verification on the acoustic super surface.
9. An acoustic device comprising the acoustic subsurface of any one of claims 1-6.
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