A broadband acoustic metasurface structure based on electromagnetic control and its application

Abstract

The present invention belongs to the field of acoustics, mechanics and material science and technology, and relates to a broadband acoustic metasurface structure and application based on electromagnetic control, wherein the metasurface structure is composed of a plurality of identical sub-wavelength coding units, and the reflected sound waves of the coding units in the 0 and 1 states present the characteristics of anti-phase, and different acoustic functions are realized by different settings of 0 / 1 anti-phase coding sequences; the main structure of the coding unit includes an irregular air channel, a cavity and a solid sheet; a movable solid sheet is arranged between the cavity and the irregular air channel, and the connection or disconnection between the cavity and the irregular air channel is realized by moving the solid sheet, and the coding state is 1 or 0. The metasurface structure has programmability, high flexibility and simple operation; any coding sequence can be generated in the coding metasurface to form a reconfigurable metasurface structure, and various acoustic functions such as directional beam, acoustic focusing and broadband acoustic slow scattering wall are realized.

Description

Technical field:

[0001] The present invention belongs to the field of acoustics, mechanics and material science and technology, and relates to a broadband acoustic metasurface structure and application based on electromagnetic regulation. The acoustic metasurface is composed of a series of identical coding units, and each coding unit can be freely switched between two different states under the regulation of an electromagnet. The reflected sound waves corresponding to the units in these two states show anti-phase characteristics within a wide frequency range and have a very high reflectivity, thereby realizing rich acoustic functions. Background technology:

[0002] Metasurface is a subwavelength artificial layered material. By designing the structure of subwavelength units and arranging their positions in space, acoustic metasurfaces can customize the sound field, thereby realizing many novel physical phenomena, such as negative refraction, acoustic vortex waves, Schroeder diffusion, acoustic focusing, and beam separation. Acoustic metasurfaces have deep subwavelength device thickness and extraordinary acoustic wave manipulation performance, so they have great application prospects in medical imaging, acoustic communications, particle manipulation and other fields. For example, Chinese patent application CN202110768057.6 discloses a reflective acoustic holographic imaging method based on a metasurface, including a reflective acoustic holographic imaging device, and the method includes: obtaining the operating frequency of the reflective acoustic holographic imaging device, and determining the initial sound wave at the operating frequency; vertically incident the initial sound wave into the reflective acoustic holographic imaging device to obtain a reflected sound wave; inputting the reflected sound wave into a reflected sound wave correction model to obtain a corrected sound wave; reconstructing a target image on the imaging surface of the reflective acoustic holographic imaging device according to the corrected sound wave; and solving the problem that the traditional use of acoustic metasurfaces to directly generate a holographic sound field by designing a unit structure may cause deviations in holographic imaging due to sound wave interference when the holographic imaging is used in special scenarios. Chinese patent application CN202110445288.3 discloses an acoustic communication method and system based on multipath spatial multiplexing of composite distorted acoustic waves. Multipath transmission of composite distorted acoustic waves is used to realize real-time communication with high information density in free space. Without the need for large-scale microphone scanning and complex and time-consuming post-processing, real-time and accurate decoding of information from different channels is achieved through a single-layer metasurface, breaking through the information capacity limitation of existing acoustic communications based on spatial multiplexing.

[0003] However, the traditional metasurface design has low flexibility and narrow bandwidth, which limits its wide practical application. If the metasurface can be adjusted within a wide frequency range, the function of the metasurface will be closer to application. Summary of the invention:

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a multifunctional broadband acoustic metasurface structure based on electromagnetic control and its application. The acoustic metasurface structure can control the reflection phase of the sound wave so that it presents an anti-phase characteristic in a wide frequency range. The metasurface structure is composed of a series of identical sub-wavelength coding units. The reflected sound waves of the coding unit in the 0 and 1 states present an anti-phase characteristic in a wide frequency range and have a high reflectivity.

[0005] In order to achieve the above-mentioned purpose, the present invention provides a broadband acoustic metasurface structure based on electromagnetic regulation, wherein the metasurface structure is composed of a series of identical coding units; the metasurface structure is composed of multiple identical subwavelength coding units, and the reflected sound waves of the coding units in the 0 and 1 states show the characteristics of anti-phase, and different acoustic functions are achieved by different settings of 0 / 1 anti-phase coding sequences; the main structure of the coding unit includes an irregular air channel, a cavity, a solid sheet and a telescopic electromagnet; one end of the irregular air channel is a sound wave incident port, and the other end is connected to the cavity; a movable solid sheet is arranged between the cavity and the irregular air channel, and one end of the solid sheet is fixedly connected to the telescopic electromagnet; the movement of the solid sheet is controlled by the telescopic electromagnet, thereby realizing the connection or disconnection between the cavity and the irregular air channel.

[0006] The cavity and the irregular air passage are surrounded by the shell.

[0007] The encoding unit also includes a groove for accommodating the telescopic electromagnet.

[0008] The cavity is a rectangular air cavity.

[0009] The irregular air passage is designed by optimizing the genetic algorithm, which is a solution for reversely designing the structural unit according to the demand.

[0010] The working principle of the coding unit is that when the electromagnet is turned off, the solid sheet is between the rectangular air cavity and the irregular air channel, the rectangular air cavity is closed, and the sound wave cannot propagate between the two. At this time, the coding unit is recorded as 0; when the electromagnet is turned on, the solid sheet is located at the left end of the rectangular air cavity or the upper / lower surface of the shell, the rectangular air cavity is opened and connected to the irregular air channel, and the sound wave can propagate freely between the two. At this time, the coding unit is recorded as 1; the phase difference between coding unit 0 and coding unit 1 when reflecting the sound wave is close to 180 degrees, and it remains stable in the wide frequency range of 2.2k-4.4k. By controlling the switch of the electromagnet in each coding unit, different coding sequences can be generated in the metasurface, thereby realizing a variety of broadband fluctuation control capabilities.

[0011] In addition to maintaining the anti-phase reflection feature, the encoding unit also needs to ensure that the reflectivity is greater than 0.75.

[0012] The housing and the groove of the encoding unit are both made of hard solid material by 3D printing.

[0013] The coding unit is programmable, and the switch controlling the electromagnet can open or close the cavity. When the cavity is closed, the coding unit is recorded as 0, and when the cavity is opened, the coding unit is recorded as 1. Each coding unit can automatically switch between 0 / 1 coding. The metasurface can realize various acoustic functions such as directional beam, acoustic focusing, etc. through different settings of 0 / 1 anti-phase coding sequences.

[0014] The number of the coding units is not limited and can be set according to the scale of the coding metasurface. The coding units can be distributed in one-dimensional strips or arranged periodically on a two-dimensional plane; the period refers to the minimum repetitive size along the x and y directions on the horizontal plane.

[0015] The encoding unit of the metasurface structure is arranged according to a certain encoding rule, and can be made into acoustic metasurface structures of different forms to achieve adjustable broadband reflective wavefront control. The encoding arrangement rule determines the form of the acoustic metasurface structure.

[0016] The coding unit in the present invention is obtained through topological optimization, and its unit structure is unprecedented; through the reasonable arrangement of the coding unit, an acoustic focusing lens and a new acoustic antenna can be constructed. The acoustic focusing lens can realize the focusing of sound waves at any position in the near field of the reflected sound field. In the new acoustic antenna, the sound wave radiation angle varies with the frequency, and a fan-shaped scanning area is formed. The acoustic antenna can determine the direction of the obstacle according to the frequency of the echo in the scanning area, and further determine the distance of the obstacle according to the echo time. Therefore, the present invention is realized by reverse design according to the needs, and the designed coding unit is also brand new.

[0017] Compared with the prior art, the present invention has the following advantages and positive effects: (1) The present invention is a multifunctional broadband acoustic metasurface structure based on electromagnetic regulation, which is programmable, highly flexible and easy to operate; (2) Each coding unit can be freely switched between two different states under the regulation of an electromagnet, and the phase difference of the reflected sound waves corresponding to the unit in the two states is close to 180 degrees within a wide frequency range, which remains stable and has a very high reflectivity; (3) By adjusting the switch of the electromagnet, an arbitrary coding sequence can be generated in the coding metasurface, forming a reconfigurable coding metasurface structure, realizing various acoustic functions such as directional beams, acoustic focusing, and broadband acoustic slow scattering walls. Description of the drawings:

[0018] Figure 1 This is a schematic diagram of the overall and internal structure principles of the encoding unit of the multifunctional broadband acoustic metasurface structure based on electromagnetic control according to Example 1 of the present invention, wherein A is the overall structure and B is the internal structure.

[0019] Figure 2 This is a schematic diagram of the internal structure principle of the encoding unit of Example 1 of the present invention after the telescopic electromagnet is opened.

[0020] Figure 3 This is a schematic diagram of the numerical simulation results of the acoustic focusing lens effect when the coding sequence constructed using the coding unit in Example 2 of the present invention is "1101101110000001".

[0021] Figure 4 This is a schematic diagram of the numerical simulation results of the acoustic antenna effect when the coding sequence constructed using the coding unit in Example 3 of the present invention is "0011001100110011". Specific implementation method:

[0022] The present invention is further described below through specific embodiments in conjunction with the accompanying drawings.

[0023] Embodiment 1:

[0024] The present embodiment relates to a broadband acoustic metasurface structure based on electromagnetic regulation, and the metasurface structure is composed of a series of identical coding units; the main structure of the coding unit includes an irregular air channel 1, a cavity 2, a solid thin sheet 3, a telescopic electromagnet 4, a shell 5 and a groove 6, and the shell 5 contains the irregular air channel 1 and the cavity 2; the groove 6 is fixedly connected to one side of the shell 5; the irregular air channel 1 and the cavity 2 are connected; the cavity 2 is a rectangular air cavity; a movable solid thin sheet 3 is arranged between the cavity 2 and the irregular air channel 1, and one end of the solid thin sheet 3 is fixedly connected to the telescopic electromagnet 4; the end of the irregular air channel 1 away from the solid thin sheet 3 is a sound wave incident port; the movement of the solid thin sheet 3 is controlled by the telescopic electromagnet to realize the opening and closing of the cavity 2, thereby realizing the connection or disconnection between the cavity 2 and the irregular air channel 1.

[0025] The shell 5 of the encoding unit described in this embodiment is made of hard solid material through 3D printing, and the material type is not limited, such as metal, plastic, etc.; the upper and lower surfaces of the shell 5 are closed, and irregular air channels and cavities pass through the left and right sides.

[0026] The groove 6 is made of a hard solid material by 3D printing, and the groove is used to place the telescopic magnet.

[0027] The structural dimensions of the irregular air passage are obtained through optimization design using a genetic algorithm.

[0028] The acoustic wave reflectivity of the encoding unit is greater than 0.75.

[0029] The working principle of the coding unit described in this embodiment is as follows: when the electromagnet is turned off, the solid sheet is between the cavity and the irregular air channel, the cavity is closed, and the cavity 2 and the irregular air channel 1 are completely separated by the solid sheet 3, so that the sound wave cannot propagate between the two, and the sound wave enters from the irregular air channel port and is reflected by the solid sheet, and the coding unit is recorded as 0 at this time; when the electromagnet is turned on, the solid sheet moves to the left side of the cavity, the cavity is opened and connected to the irregular air channel, and the sound wave enters from the irregular air channel port and reaches the cavity area, and is finally reflected by the solid sheet, and the coding unit is recorded as 1 at this time; each coding unit can automatically switch between 0 / 1 coding. The coding unit when the air cavity is closed (recorded as 0) and the coding unit when the air cavity is opened (recorded as 1) have a phase difference of nearly 180 degrees when reflecting the sound wave, and remain stable in the wide frequency range of 2.2k-4.4k.

[0030] In this embodiment, the sound wave enters from the right side of the coding unit, and the reflected sound wave formed after being adjusted by the air channels of the 0 and 1 coding units maintains a stable anti-phase characteristic within a wide frequency range. This characteristic can be used to realize applications such as sound focusing lenses and acoustic antennas.

[0031] The number of the encoding units is not limited.

[0032] The specific geometric dimensions of the encoding unit of this embodiment are: for each unit, the total thickness in the direction of sound wave reflection is L=0.052m, and the width of each unit is W=0.042m; the thickness of the irregular air channel is m=0.04m, the thickness of the cavity is n=0.008m, and the thickness of the solid sheet is t=0.002m.

[0033] Embodiment 2:

[0034] This embodiment involves a simulation experiment of constructing an acoustic focusing lens metasurface structure using the coding units of Embodiment 1. The number of coding units used in the experiment is 16. The 16 coding units are tightly arranged in a row along the width direction. The total length of the formed metasurface structure is 16W, and the total thickness in the sound wave reflection direction is L=0.052m.

[0035] In order to calculate the coding unit sequence for constructing the acoustic focusing lens, in this embodiment, a region containing a number of coding units in the same state (0 code or 1 code) is called a coding region, and adjacent coding regions include the same or different numbers of coding units.

[0036] To ensure that the phase difference between adjacent coding regions of the coding metasurface is π, the electromagnet is adjusted to set the coding units of adjacent coding regions to different types of 0 or 1. x ,y=f y ) should satisfy the following formula (1):

[0037]

[0038] in is the distance from the ±i-th region in the metasurface to the focus, r ±i is the coordinate of the center of the ±i-th encoding region on the x-axis, and defines r0=0,; λ=c / f, is the wavelength of the focusing frequency f, and c is the speed of sound in air.

[0039] The length direction of the super surface structure of this embodiment is taken as the x-axis, the center point of the super surface structure is set as the origin of the x-axis, the coding area to which the center point belongs is the 0th coding area, that is, r0=0, and the code of the 0th coding area is set to 1; r1 and r2 are calculated by formula (1) -1 , that is, the coordinate of the center of the first coding region on the x-axis is r1, the code of the first coding region is 0, the coordinate of the center of the -1th coding region on the x-axis is r1, the code of the -1th coding region is 0; and so on, the number of coding regions within the length range of the hypersurface structure is calculated, and then the coding sequence of the hypersurface structure is obtained.

[0040] For example, when the fixed focus position is set to (f x ,f y )=(504mm,400mm), when the focusing frequency is f=4200Hz, according to formula (1), it can be calculated that the metasurface of this embodiment contains 7 coding regions, and the coding sequence of the metasurface is: “1101101110000001”. The acoustic metasurface model of the above coding sequence is imported into COMSOL Multiphysics simulation software to simulate the focusing results. The focusing effect of the sound wave vertically incident on the metasurface is as follows: Figure 3 As shown in FIG. 1 , it is shown that a sound focusing lens can be constructed through a reasonable arrangement of units. The sound focusing lens can achieve sound wave focusing at any position in the near field of the reflected sound field.

[0041] Embodiment 3:

[0042] This embodiment involves a simulation experiment of constructing a new acoustic antenna supersurface structure using the coding units of Embodiment 1. The number of coding units used in the experiment is 16. The 16 coding units are tightly arranged in a row along the width direction. The total length of the formed supersurface structure is 16W, and the total thickness in the sound wave reflection direction is L=0.052m.

[0043] In this embodiment, the coding units that construct the metasurface structure are periodically arranged, that is, 4 coding units (coding sequence is 0011) form one period, and there are 4 periods in total. The overall coding sequence is: "0011001100110011". The coding metasurface modulates the reflected beam into two beams, and the deflection angle of the reflected beam is:

[0044]

[0045] Where λ is the wavelength of the incident sound wave, Γ is the width of the coding unit per cycle, and the unit is m. In this embodiment, Γ is the total width of 4 coding units, that is, Γ=4W. When the frequency of the incident sound wave is different, the deflection angle of the sound wave is also different. The new acoustic antenna metasurface structure model constructed by the above coding sequence is imported into the COMSOL Multiphysics simulation software for acoustic wave scanning simulation. Figure 4 The simulation results are given for incident sound wave frequencies of 2700Hz, 3300Hz, and 4200Hz respectively.

[0046] When the incident wave frequency is swept in the range of 2.2kHz-4.4kHz, the reflection angle can be continuously changed in the range of 68.3° to 27.7°, and the reflection beam angle decreases with the increase of frequency.

[0047] The present invention can construct a new acoustic antenna through the reasonable arrangement of coding units. In the new acoustic antenna, the sound wave reflection angle changes with the incident frequency and forms a fan-shaped scanning area. The acoustic antenna can determine the direction of the obstacle according to the frequency of the echo in the scanning area, and further determine the distance of the obstacle according to the echo time.

[0048] Embodiment 3:

[0049] The present embodiment relates to a broadband acoustic metasurface structure based on electromagnetic control, and the metasurface structure is composed of a series of identical coding units; the main structure of the coding unit is different from that of Example 1 in that: the left side of the air 2 is a closed structure; the solid sheet is between the cavity 2 and the irregular air channel and can move up and down; there is a hole on the upper or lower surface of the shell 5 corresponding to the position of the solid sheet, and the solid sheet can move up and down in the hole, and the connection or blockage between the cavity and the irregular air channel 1 is achieved by moving the solid sheet up and down.

[0050] The up and down movement of the solid sheet can be achieved by the telescopic electromagnet.

[0051] The working principle of the coding unit described in this embodiment is: when the solid thin sheet is between the cavity and the irregular air channel, the cavity is closed, the cavity and the irregular air channel are completely separated by the solid thin sheet, the sound wave cannot propagate between the two, the sound wave enters from the irregular air channel port and is reflected by the solid thin sheet, and the coding unit is recorded as 0 at this time; when the solid thin sheet moves upward or downward so that the lower end or upper end of the solid thin sheet moves to the upper surface or lower surface of the shell, the cavity is opened and connected with the irregular air channel, the sound wave enters from the irregular air channel port and reaches the cavity area, and is finally reflected by the left side wall of the cavity, and the coding unit is recorded as 1 at this time; each coding unit can automatically switch between 0 / 1 coding.

Claims

1. A broadband acoustic metasurface structure based on electromagnetic regulation, characterized in that: The metasurface structure is composed of a plurality of identical sub-wavelength coding units, and the reflected sound waves of the coding units in the 0 and 1 states present an anti-phase characteristic, and different acoustic functions are achieved by different settings of the 0 / 1 anti-phase coding sequence; The main structure of the encoding unit includes an irregular air channel, a cavity and a solid sheet; one end of the irregular air channel is a sound wave incident port, and the other end is connected to the cavity; a movable solid sheet is arranged between the cavity and the irregular air channel, and the connection or disconnection between the cavity and the irregular air channel is achieved by moving the solid sheet, so that the encoding state of the encoding unit is 1 or 0; the solid sheet is connected to a telescopic electromagnet, and the movement of the solid sheet is achieved by controlling the switch of the telescopic electromagnet, so as to achieve the connection or disconnection between the cavity and the irregular air channel; The working principle of the encoding unit is that when the electromagnet is turned off, the solid sheet is between the rectangular air cavity and the irregular air channel, the rectangular air cavity is closed, and the sound waves cannot propagate between the two. At this time, the encoding unit is recorded as 0; when the electromagnet is turned on, the solid sheet is located at the bottom of the rectangular air cavity, the rectangular air cavity is opened and connected to the irregular air channel, and the sound waves propagate freely between the two. At this time, the encoding unit is recorded as 1; the phase difference between encoding unit 0 and encoding unit 1 when reflecting sound waves is 180 degrees, and remains stable within the wide frequency range of 2.2k-4.4k; controlling the switch of the electromagnet in each encoding unit can generate different encoding sequences in the metasurface, thereby realizing a variety of broadband fluctuation control capabilities.

2. The broadband acoustic metasurface structure based on electromagnetic control according to claim 1, characterized in that: The cavity and the irregular air passage are surrounded by the shell.

3. The broadband acoustic metasurface structure based on electromagnetic control according to claim 1, characterized in that: The cavity is a rectangular air cavity; the irregular air channel is obtained by optimizing the design through a genetic algorithm.

4. The broadband acoustic metasurface structure based on electromagnetic regulation according to claim 1, characterized in that: In addition to maintaining the anti-phase reflection feature, the encoding unit also needs to ensure that the reflectivity is greater than 0.

75.

5. The broadband acoustic metasurface structure based on electromagnetic regulation according to claim 1, characterized in that: The number of the coding units is not limited and can be set according to the scale of the coding metasurface. The coding units are arranged in a one-dimensional strip distribution or a two-dimensional planar periodic arrangement.

6. The broadband acoustic metasurface structure based on electromagnetic regulation according to claim 5, characterized in that: The period of the coding unit refers to the minimum repetition size along the x and y directions on the horizontal plane.

7. The broadband acoustic metasurface structure based on electromagnetic regulation according to claim 1, characterized in that: The encoding unit of the metasurface structure is arranged according to certain encoding rules, and can be made into acoustic metasurface structures of different forms to achieve adjustable broadband reflective wavefront control.

8. The broadband acoustic metasurface structure based on electromagnetic regulation according to claim 1, characterized in that: Through the reasonable setting of the encoding unit, the metasurface structure can be used as an acoustic focusing lens and a new acoustic antenna; The acoustic focusing lens can achieve the focusing of the acoustic wave at any position in the near field of the reflected acoustic field; In the new acoustic antenna, the sound wave radiation angle changes with the frequency and forms a fan-shaped scanning area; the acoustic antenna can determine the direction of the obstacle based on the frequency of the echo in the scanning area, and further determine the distance of the obstacle based on the echo time.

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