A method for controlling acoustic energy flow using binary coded metamaterials

Abstract

The present invention discloses a method for realizing acoustic energy flow control by using binary coded metamaterials, wherein the two coding units of the binary coded metamaterials are composed of a subwavelength 5×5 non-uniform Mie resonance unit array. When a plane wave is incident vertically onto one side of the coded metamaterial, it can control the transmission path of the sound wave inside its structure while ensuring a high sound wave transmission efficiency. The present invention utilizes the directivity control characteristics of the non-uniform Mie resonance structure on the sound wave in a dipole-like resonance mode, so that the sound wave can propagate along a specified path inside the coded metamaterial, and realizes diversified acoustic energy flow control by arranging and combining the two groups of coding units.

Description

Technical Field

[0001] The present invention relates to the use of binary-coded metamaterials to construct an acoustic system with acoustic energy flow control function. When the unit size of the metamaterial is much smaller than the wavelength of the sound wave, the dipole-like characteristics of the non-uniform Mie resonance unit are used to realize a coding system with controllable acoustic energy flow path, thereby realizing diversified control of the sound wave transmission path. Background Art

[0002] Arbitrary and efficient processing and regulation of sound waves is a long-standing important problem and strong desire in the field of acoustics. The emergence of acoustic metamaterials, including periodic crystal structures with subwavelength artificial structures, has greatly promoted the development of sound wave manipulation technology. Based on the generalized Snell's law, the introduction of abrupt phase can freely regulate the transmitted and reflected sound fields. In addition to regulating the phase alone, the amplitude and phase of the sound wave can be decoupled and modulated by introducing additional energy loss, giving the metamaterial complete control over the sound field. Many exotic transmission and reflection phenomena based on acoustic metamaterials have been revealed, such as anomalous reflection / refraction, acoustic holograms, asymmetric transmission, etc.

[0003] The 21st century is the era of digital information. Digital information transmission methods have injected endless vitality into the development of communication and electronic technology. The continuous parameter characterization method of traditional metamaterials can be classified as "analog modulation", which makes it difficult to be compatible with digital information technology and difficult to implement at the hardware level, thus greatly limiting its application in practical scenarios. Against this background, the concept of coded metamaterials was proposed as a digital version of metamaterials. Coded metamaterials were originally created to efficiently control the radiation and scattering characteristics of electromagnetic waves and simplify the design process of metamaterials. In recent years, they have been successfully expanded to the field of acoustics. Acoustic coded metamaterials have been rapidly proposed and received continuous attention. Unlike traditional acoustic metamaterials that require complex structures to simulate the continuous distribution of equivalent parameters, coded metamaterials control sound waves in a similar way to digital circuits. They innovatively use binary or higher-order coding forms to characterize metamaterials. Different coding sequences represent different acoustic responses, and discrete digital coding sequences are used to control sound waves. However, the coding units of most coded metamaterials are usually constructed from units of different sizes or shapes, and the state of a single coding unit ("0" and "1") cannot be dynamically switched between "0" and "1" on demand. In practical application scenarios, it is usually required that a single coding unit of a metamaterial can dynamically switch between different states. This can not only further simplify the design process of metamaterials, but also adjust and reconfigure the functions of programmed metamaterials in real time, improve the utilization rate of related acoustic prototype devices, and reduce equipment costs. Summary of the invention

[0004] Purpose of the present invention: In order to overcome the deficiencies in the prior art, the present invention uses a non-uniform Mie resonance unit to construct a binary coded metamaterial. The present invention uses the dipole-like characteristics of the non-uniform Mie resonance structure to construct coding units "0" and "1" by flipping the Mie resonance unit left and right. The coding units "0" and "1" are mirror images of each other, so they can be switched dynamically in real time. By dynamically switching the codes corresponding to each coding unit in the coded metamaterial, the propagation path of the sound waves inside the structure can be dynamically configured in real time.

[0005] The technical solution adopted by the present invention is: a method for realizing acoustic energy flow control using binary coded metamaterials, comprising the following steps:

[0006] S1: First find out the characteristic frequency of the designed non-uniform Mie resonance unit, including the frequencies corresponding to the monopole, dipole and other resonance modes, and focus on analyzing the working state of the non-uniform Mie resonance unit at the dipole resonance frequency. The simulation results show that in the dipole state, the non-uniform Mie resonance unit has a directional effect on the transmission of sound waves, but the radiation efficiency is low. Based on this characteristic, the present invention seeks a dipole-like frequency point near the dipole frequency, so that the non-uniform Mie resonance unit can take into account both the directional propagation of sound waves and the higher sound radiation efficiency at this frequency point, thereby realizing the function of regulating the sound energy flow.

[0007] Arrange 25 non-uniform Mie resonance units into a 5×5 array. The incident wave is incident from the left side of the array and the frequency is near the dipole resonance frequency. At this time, the sound wave is emitted from directly above the array, achieving directional propagation of the sound wave in the upward direction. In the present invention, this kind of array is named coding unit "0". In addition, coding unit "1" can be obtained by flipping the non-uniform Mie resonance unit in coding unit "0" left and right. For coding unit "1", when the sound wave is incident from the left side, the sound wave is emitted from directly below the array, achieving directional propagation of the sound wave in the downward direction.

[0008] S2: Combining the two coding units "0" and "1" obtained above, arrange them in the x and y directions to construct a binary coded metamaterial. By changing the arrangement and combination of coding units, the incident sound wave can propagate along different paths in the coded metamaterial. For example, V-shaped, straight-line, and triangle shapes. The transmission efficiency during sound wave propagation will be related to the number of units that the sound wave passes through. Therefore, in order to ensure a high sound transmission efficiency, an appropriate number of coding units can be selected.

[0009] Preferably, the working frequency of the binary coded metamaterial of the present invention is selected as the dipole-like frequency point 1127 Hz, that is, the frequency of the incident sound wave is maintained at 1127 Hz. At this frequency, the sound wave incident vertically from the left end can be emitted from the upper direction of the coding unit after passing through the coding unit "0", and radiate to the outer space perpendicular to the emission surface in the upper direction, and the sound wave radiation efficiency is high. For the coding unit "1", the sound wave is emitted from the lower direction of the coding unit, and radiates to the outer space perpendicular to the emission surface in the lower direction, and the sound wave radiation efficiency is high.

[0010] Preferably, the circular non-uniform Mie resonant structure consists of four sector-shaped parts with different proportions, two of which occupy 1 / 3 of the entire circle, and the other two occupy 2 / 3 of the entire circle. Each sector-shaped part is composed of a zigzag channel with the same slit width t=0.36cm, air inlet width w=0.42cm, wall thickness d=0.2cm and curl number N=4. The radii of the outer circle and inner circle of the Mie resonant structure are R=3cm and r=0.58cm respectively. The wall of the non-uniform Mie resonator is made of epoxy resin. The background medium is air, and the mass density and velocity of air are ρ0=1.21kg / m 3 And c0=343m / s.

[0011] Preferably, the coding unit mentioned in the present invention is a 5×5 array composed of 25 identical non-uniform Mie resonance structures, coding unit "0" and coding unit "1" are mirror images of each other, and the non-uniform Mie resonance structures inside them have the same structure and size.

[0012] Preferably, the coding units in the coded metamaterial designed by the present invention are arranged in a 2×2 array, with a total of 4 coding units. Each coding unit contains 25 non-uniform Mie resonance units, and the entire coded metamaterial requires a total of 100 non-uniform Mie resonance units. By arranging and combining these coding units, sound waves can be propagated along different paths.

[0013] Beneficial effects: The present invention adopts an acoustic coding metamaterial composed of two coding units to achieve efficient regulation of the sound wave propagation path. The proposed metamaterial coding unit is composed of a non-uniform Mie resonator array, which has a dipole-like acoustic directivity characteristic while taking into account high radiation efficiency. Based on the directional response characteristics of the dipole Mie resonance, the present invention realizes the regulation of the sound propagation path by rationally designing the xy plane coding sequence distribution. Three special metamaterial coding modes are designed and simulated, and the three modes correspond to three different sound wave propagation trajectories. By combining the dipole-like characteristics in the coding metamaterial, the results given in this article show important value in the application of sound wave propagation and wavefront processing. The device has a simple structure, small size, and universal principle. By encoding, while realizing the regulation of the sound energy flow, the flexibility of the sound energy flow regulation of the coding metamaterial is significantly improved. The present invention paves a way for the design of acoustic metamaterials and is expected to design intelligent acoustic devices with exciting reconfigurable and programmable applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a structural diagram of a single non-uniform Mie resonance unit.

[0015] Figure 2a , 2b is a functional schematic diagram of the monopole mode and dipole mode of the non-uniform Mie resonance unit.

[0016] Figure 2c , 2d is a functional diagram of the monopole mode and dipole mode of the equivalent unit.

[0017] Figure 3a shows the relationship between the normalized scattered sound pressure amplitude and the frequency of the incident wave on the left.

[0018] FIG3 b is the normalized scattered sound pressure amplitude distribution on the upper boundary in the left illustration of FIG3 a .

[0019] 4a and 4b are transmission sound pressure distribution diagrams of sound waves incident on the 5×5 array coding unit “0” from the left and right sides respectively.

[0020] Figures 4c and 4d are the transmitted sound pressure distribution diagrams when the sound wave is incident on the 5×5 array coding unit "1" from the left and right sides respectively.

[0021] Figure 5a , 5b, 5c are the coding arrangements required to realize triangular, straight, and V-shaped sound propagation paths respectively.

[0022] Figures 5d, 5e, and 5f are simulation diagrams of the triangular, straight, and V-shaped acoustic energy flow control models, respectively. DETAILED DESCRIPTION

[0023] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0024] The sample of the non-uniform Mie resonance unit designed by the present invention is as follows Figure 1 As shown, the sample is used to construct a binary coded metamaterial and apply it to the regulation of acoustic energy flow. The circular non-uniform Mie resonance unit consists of four fan-shaped parts with different proportions, two of which occupy 1 / 3 of the entire circle, and the other two occupy 2 / 3 of the entire circle. Each fan-shaped part is composed of a zigzag channel with the same slit width t=0.36cm, air inlet width w=0.42cm, wall thickness d=0.2cm, and curl number N=4. The radii of the outer and inner circles of the Mie resonator are R=3cm and r=0.58cm, respectively. The wall of the non-uniform Mie resonator (gray) is made of epoxy resin. The background medium (white) is air, and the mass density and velocity of air are ρ0=1.21kg / m 3 And c0=343m / s.

[0025] When the Mie resonance unit operates in the monopole mode, the sound waves radiate in all directions inside the structure. However, when the Mie resonance unit operates in the dipole mode, the sound field presents a bidirectional directional pattern. The acoustic energy flow is mainly concentrated in the fan-shaped interior of the zigzag channel, with the inlet and outlet facing the upper right corner and the lower left corner, and the acoustic energy radiated to the external free space is very limited. We hope that the proposed non-uniform Mie resonance unit has both significant directional response characteristics and high radiation efficiency characteristics. Although the above-mentioned dipole Mie resonance radiates sound waves in a bidirectional mode, the acoustic energy radiated to the external free space is very limited. A trade-off is made between the directional radiation behavior of the dipole Mie resonance and the radiation efficiency of the non-uniform Mie resonance unit array. Theoretical calculations show that a proper deviation from the dipole frequency helps the Mie resonance unit generate more acoustic energy radiated to the free space, thereby obtaining higher quality directivity characteristics.

[0026] In order to verify the effectiveness and feasibility of the invention, the eigenmode and eigenfrequency of the designed single non-uniform Mie resonance unit are first calculated using COMSOL Multiphysics numerical simulation software. Figure 2a and 2b As shown, the non-uniform Mie resonance unit is placed in a square lattice for simulation, where periodic boundary conditions are applied to the upper, lower, left and right boundaries of the square lattice. The numerical results of the monopole and dipole resonance frequencies are 823.84 Hz and 1181.9 Hz, respectively.

[0027] Since the size of the non-uniform Mie resonance unit is designed on a sub-wavelength scale, the non-uniform Mie resonance unit can be equivalent to an equivalent medium with the same shape, and the monopole and dipole modes of the non-uniform Mie resonance unit can be verified by the equivalent medium theory ( Figure 2a and 2b ). The non-uniform Mie resonance unit can be equivalent to Figure 2c and 2d The equivalent medium shown is composed of a perforated rigid cylinder connecting four ultra-low dielectric straight channels with high refractive index. The width and direction of the channel are consistent with the opening of the inhomogeneous Mie resonance unit. The equivalent refractive index of the four ultra-low dielectric straight channels can be defined as:

[0028]

[0029] Where L p is the sound propagation path length in the zigzag channel of each sector, calculated as follows:

[0030]

[0031] From the above formula, we can know that the propagation path of the sound wave in the channel is related to the fold number N and the proportion A of the sector in the circle. Therefore, the refractive index of the zigzag channel in the four sectors of the non-uniform Mie resonance unit is different, which means that the equivalent refractive index in these four ultra-low dielectric straight channels is different. Figure 2c and 2d In the equivalent medium, the equivalent refractive index of the lower left straight channel and the upper right straight channel is n r1 ≈5.2, the equivalent refractive index of the upper left straight channel and the lower right straight channel is n r4 ≈2.48. The eigenfrequencies of the monopole mode and dipole mode obtained by the equivalent medium method are 846 Hz and 1055 Hz, respectively. The corresponding sound pressure field distributions are shown in Figure 2c and 2d As shown. In the monopole mode, the sound waves radiate uniformly through four straight channels in the equivalent medium. In the dipole mode, the sound radiates to the outer space along the straight channels in the upper right corner and the lower left corner. Therefore, the results of the equivalent medium are basically consistent with the results of the specific structural model.

[0032] The present invention utilizes the dipole-like characteristics of the non-uniform Mie resonance unit to regulate the acoustic energy flow. The coding unit of the binary coded metamaterial is constructed by a 5×5 non-uniform Mie resonance unit array, and the coding units "0" and "1" are mirror images of each other and can be converted to each other. For coding unit "0", the incident wave enters from the left side of the array, and at the dipole-like frequency, the sound wave is emitted from directly above the array. For coding unit "1", the incident wave enters from the left side of the array, and at the dipole-like frequency, the sound wave is emitted from directly below the array.

[0033] Combining the coding units obtained above, they are connected in parallel to form a meta-material. By changing the arrangement and combination of the coding units in the coding meta-material, the sound waves can be propagated along different paths. For example, V-shaped, straight-line, and triangle, etc. The efficiency of transmission will be related to the number of units that the sound wave passes through. Therefore, in order to ensure high-efficiency transmission, an appropriate number of coding units and basic units can be selected.

[0034] On this basis, the acoustic wave regulation effect of the coding unit "0" and "1" constructed using the non-uniform Mie resonance structure was further simulated and analyzed. The thermoviscous acoustic module and the acoustic-structure coupling module in COMSOL Multiphysics were used, and epoxy resin was selected as the wall material of the Mie resonance unit. The Poisson's ratio, Young's modulus and mass density of epoxy resin are 0.35, 5.08 GPa and 1050 kg / m respectively. 3 . The relationship between the normalized scattered sound pressure amplitude and the frequency of the incident wave on the left is shown in Figure 3a. The sound wave amplitude reaches a peak value of about 0.62 at the near-dipole frequency of 1133 Hz. At this frequency, the scattered sound pressure field of the non-uniform Mie resonance unit array is shown in the right inset of Figure 3a. The designed non-uniform Mie resonance unit array can effectively radiate sound waves into the free space above the array and propagate in a direction slightly deviated from the y-axis. However, as shown in the left inset of Figure 3a, if the frequency is selected as 1127 Hz, the scattered sound pressure amplitude will be slightly reduced (≈0.55), but at this time the sound wave radiates and propagates in the +y direction. Based on this, the present invention selects a dipole-like frequency of 1127 Hz as the operating frequency, and the corresponding sound transmission coefficient at this frequency is about 0.55. Figure 3b is the distribution of the scattered sound pressure amplitude on the upper boundary (left inset of Figure 3a) under the 1127 Hz dipole-like frequency, which is normalized with the amplitude of the incident plane wave. The results show that the peak appears near the middle of the measurement line, which is consistent with the prediction results.

[0035] Figures 4a-4d show the simulated scattered acoustic pressure fields of coding units "0" and "1" induced by left and right incident waves at a dipole-like frequency of 1127 Hz. As shown in Figure 4a, for coding unit "0", when a plane wave is incident from the left and propagates in the +x direction, the transmitted wave (white arrow) propagates in the +y direction, and at the same time, there is a reflected wave (black arrow) in the -x direction. The incident wave hardly undergoes any phase shift after passing through the coding unit, and the output wave is still an approximate plane wave, which is consistent with the original incident wave. For the same coding unit "0" shown in Figure 4b, it is observed that when the incident is emitted from the opposite direction, the transmitted wave propagates in the -y direction. The proposed inhomogeneous Mie resonator can obtain the same structure by horizontal and vertical inversion. Therefore, according to this situation, we present the coding unit "1" by horizontally inverting the Mie resonator in coding unit "0" from left to right, as shown in Figures 4c and 4d. Figures 4c and 4d clearly show that, for both cases, the coding unit “1” exhibits transmitted waves in both upward (+y) and downward (−y) directions, which is very consistent with the prediction.

[0036] The coding units "0" and "1" in Figures 4a-4d are compactly arranged in a 2×2 array in the x and y directions to construct a binary coded metamaterial. During the design process, the spatial distribution of the coding units in the metamaterial is determined according to the designed acoustic propagation path. The present invention constructs three acoustically coded metamaterials (modes A, B, and C) to achieve the desired acoustic propagation paths, such as "triangle", "1", and "V". Figure 5a-5c As shown in the figure, when an acoustic plane wave with a dipole-like resonance frequency (1127 Hz) is incident on the coding unit in the upper left corner of the coded metamaterials of modes A, B, and C, respectively, the sound wave propagates along the gray arrows in each coding unit and radiates to the outer space, thereby presenting "triangle", "1", and "V" sound propagation trajectories in modes A, B, and C, respectively. In order to verify the correctness of the design method, a full-wave simulation was performed, and Figures 5d-5f show the sound pressure field distribution of the coded metamaterials with these three modes, respectively. It can be observed that the sound waves in modes A, B, and C propagate along the trajectories of "triangle", "1", and "V", respectively, which is consistent with Figure 5a-5c The predicted trajectory is consistent. According to the measurement, the acoustic transmission coefficients of binary coded metamaterials with propagation trajectories of "triangle", "1" and "V" are approximately 0.35, 0.35 and 0.25, respectively. In addition, other transmission trajectories can be designed by introducing appropriate distributions of coding units "0" and "1" in the xy plane. The above conclusions confirm that the coded metamaterial designed by the present invention can dynamically adjust the propagation trajectory of the acoustic energy flow, which has potential practical value for particle manipulation of arbitrary trajectories in two-dimensional space.

[0037] The present invention proposes to use the dipole-like mode of the non-uniform Mie resonance unit to achieve the regulation of the acoustic energy flow, thereby achieving the regulation effect of the sound propagation path. Due to the simplicity of the encoding unit of this design, different acoustic energy flow regulation effects can be flexibly achieved, not limited to the trajectory propagation of "triangle", "1" and "V" proposed in this design.

[0038] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for realizing acoustic energy flow control using binary coded metamaterials, characterized in that: The following steps are involved: S1: First, find out the characteristic frequency of the designed non-uniform Mie resonance unit, including the frequencies corresponding to the monopole and dipole resonance modes, and focus on analyzing the working state of the non-uniform Mie resonance unit at the dipole resonance frequency; Arrange 25 non-uniform Mie resonance units into a 5×5 array; the incident wave enters from the left side of the array and the frequency is near the dipole resonance frequency. At this time, the sound wave is emitted from the top of the array, realizing the directional propagation of the sound wave in the upward direction; this array is named coding unit "0"; the coding unit "1" is obtained by flipping the non-uniform Mie resonance unit in coding unit "0" left and right; for coding unit "1", when the sound wave is incident from the left side, the sound wave is emitted from the bottom of the array, realizing the directional propagation of the sound wave in the downward direction; S2: Combine the two obtained coding units "0" and "1" and arrange them in the x and y directions to construct a binary coded metamaterial; by changing the arrangement and combination of coding units, the incident sound wave propagates along different paths in the coded metamaterial; the transmission efficiency during the sound wave propagation process will be related to the number of units the sound wave passes through; The circular non-uniform Mie resonance unit is composed of four sector-shaped parts with different proportions, two of which account for 1 / 3 of the entire circle, and the other two account for 2 / 3 of the entire circle; each sector is composed of a zigzag channel, which has the same slit width t=0.36cm, air inlet width w=0.42cm, wall thickness d=0.2cm and curling number N=4; the radii of the outer circle and inner circle of the non-uniform Mie resonance structure are R=3cm and r=0.58cm respectively; the wall of the non-uniform Mie resonance structure is made of epoxy resin; the background medium is air, and the mass density and velocity of the air are ρ0=1.21kg / m 3 And c0=343m / s.

2. The method for realizing acoustic energy flow control using binary coded metamaterials according to claim 1, characterized in that: The operating frequency of the binary coded metamaterial is selected as a dipole-like frequency point of 1127 Hz, that is, the frequency of the incident sound wave is maintained at 1127 Hz; at this frequency, the sound wave incident vertically from the left end passes through the coding unit "0" and then is emitted from the upper direction of the coding unit, and is radiated to the outer space perpendicular to the emission surface in the upper direction, and the sound wave radiation efficiency is high; for the coding unit "1", the sound wave is emitted from the lower direction of the coding unit, and is radiated to the outer space perpendicular to the emission surface in the lower direction, and the sound wave radiation efficiency is high.

3. The method for realizing acoustic energy flow control using binary coded metamaterials according to claim 2, characterized in that: The coding unit is a 5×5 array composed of 25 identical non-uniform Mie resonance structures, and the coding unit "0" and the coding unit "1" are mirror images of each other, and the non-uniform Mie resonance structures inside them have the same structure and size.

4. The method for realizing acoustic energy flow control using binary coded metamaterials according to claim 3, characterized in that: The coding units in the binary coded metamaterial are arranged in a 2×2 array, with a total of 4 coding units; each coding unit contains 25 non-uniform Mie resonance units, and the entire coded metamaterial requires a total of 100 non-uniform Mie resonance units; by arranging and combining these coding units, sound waves are made to propagate along different paths.

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