An acoustic metasurface structure unit capable of achieving near-perfect transmission

Abstract

This invention discloses an acoustic metasurface structure unit capable of near-perfect transmission, comprising two parallel side-plate-like materials, with a plurality of symmetrically arranged tooth-like materials on the opposite side of the two side-plate-like materials. During the propagation of sound waves within the metasurface structure unit of this invention, the propagating wave gradually transforms into a quasi-surface wave, and then reverses back into a propagating wave, thereby achieving near-perfect transmission. Furthermore, by adjusting the adjustable parameters in the metasurface structure unit of this invention, full-phase control within a 2π range can be achieved.

Description

Technical Field

[0001] This invention relates to an acoustic metasurface structure unit that can achieve near-perfect transmission. Background Technology

[0002] Acoustic metasurfaces are classified into transmissive metasurfaces, reflective metasurfaces, and full-space surfaces that can simultaneously control both transmitted and reflected sound fields. They are one of the key research topics in sound field control. Taking a transmissive acoustic metasurface as an example, the steps to achieve a target transmitted sound field are as follows: (1) Derive the abrupt phase distribution that the acoustic metasurface needs to provide based on the target transmitted sound field and the incident sound field; (2) Discretize this abrupt phase distribution based on the width of the metasurface structural unit that assembles the acoustic metasurface; (3) Adjust the geometric parameters of each metasurface structural unit in the acoustic metasurface to achieve the required abrupt phase at the corresponding position. It can be seen that an ideal transmissive acoustic metasurface structural unit should have the following characteristics: (1) full transmission; (2) full phase control covering a range of 2π; (3) a width small enough to provide the spatial resolution required to achieve the target transmitted sound field.

[0003] Existing typical structural units for constructing transmissive acoustic metasurfaces include labyrinth structures, Helmholtz resonator structures, thin-film structures, piezoelectric materials, and five-mode structures. However, these structures cannot achieve full transmission due to impedance mismatch or viscous losses inherent in the structure itself. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides an acoustic metasurface structure unit with a simple structure that can achieve near-perfect transmission.

[0005] The technical solution of the present invention to solve the above problems is: an acoustic metasurface structure unit that can achieve near-perfect transmission, comprising two parallel side plate-shaped materials, and a plurality of tooth-shaped materials symmetrically arranged on the opposite side of the two side plate-shaped materials.

[0006] The aforementioned acoustic metasurface structure unit that can achieve near-perfect transmission has all the toothed materials distributed on each side plate-like material in a cone shape. That is, the toothed material located in the middle position is the longest, and the length of the toothed material gradually decreases from the middle position to both ends.

[0007] The overall cross-section of the aforementioned acoustic metasurface structure unit that can achieve near-perfect transmission is rectangular.

[0008] The width of the aforementioned acoustic metasurface structure unit that can achieve near-perfect transmission is 0.2λ-0.3λ, where λ is the wavelength of the incident sound wave.

[0009] The aforementioned acoustic metasurface structure unit, which can achieve near-perfect transmission, has an adjustable length of the tooth-shaped material.

[0010] The aforementioned acoustic metasurface structure unit, which can achieve near-perfect transmission, is placed in a background medium, and the acoustic impedance of the acoustic metasurface structure unit exceeds 100 times the acoustic impedance of the background medium.

[0011] The beneficial effects of this invention are as follows: This invention comprises two parallel side-plate-like materials, with a plurality of tooth-like materials symmetrically arranged on the opposite side of the two side-plate-like materials. When a sound wave propagates from the bottom to the center of the acoustic metasurface structure unit, the propagation constant within the acoustic metasurface structure unit gradually increases from k0 to its maximum value. Here, k0 is the propagation constant of the sound wave in the background medium. Correspondingly, when the sound wave propagates from the center to the top of the acoustic metasurface structure unit, the propagation constant gradually decreases from its maximum value to k0. That is to say, during the propagation process of the sound wave in the metasurface structure unit of this invention, the propagation wave gradually transforms from a propagation wave into a quasi-surface wave, and then from a quasi-surface wave back into a propagation wave, thereby achieving near-perfect transmission. Furthermore, by adjusting the adjustable parameters in the metasurface structure unit of this invention, full-phase control within a 2π range can be achieved. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the acoustic metasurface structure unit of the present invention.

[0013] Figure 2 The transmittance and transmission phase of the acoustic metasurface structural unit of the present invention vary with the adjustable parameter w. N The relationship diagram of changes.

[0014] Figure 3 To utilize this invention for negative refraction of sound waves, at incident angles θ i =30° and θ i Simulation diagram of the incident sound field and scattered sound field distribution at a temperature of -30°.

[0015] Figure 4 This is a simulation diagram of the incident sound field and scattered sound intensity distribution when using the present invention for multi-point sound focusing. Detailed Implementation

[0016] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0017] like Figure 1 As shown, an acoustic metasurface structure unit that can achieve near-perfect transmission includes two parallel side plate-like materials, and several tooth-like materials are symmetrically arranged on the opposite side of the two side plate-like materials.

[0018] All the toothed materials distributed on each side plate-like material are conical in shape, with the toothed material in the middle being the longest, and the length of the toothed material gradually decreasing from the middle to both ends.

[0019] The overall cross-section of the acoustic metasurface structure unit is rectangular.

[0020] The width of the acoustic metasurface structure unit is 0.2λ-0.3λ, where λ is the wavelength of the incident sound wave.

[0021] The length of the tooth-shaped material is adjustable.

[0022] The aforementioned acoustic metasurface structure unit, which can achieve near-perfect transmission, is placed in a background medium, and the acoustic impedance of the acoustic metasurface structure unit exceeds 100 times the acoustic impedance of the background medium.

[0023] Figure 1 The geometric parameters are set as follows: the width of the metasurface structural unit is a = 25 mm, and the thickness of the side plate is d. w =0.5mm, the thickness of the toothed material t = 1mm, the spacing of the toothed material g = 2.1mm, the minimum length of the toothed material w1 = 0.25mm, and the length of the side plate, i.e., the length of the metasurface structural unit L = 311mm. The maximum length of the toothed material w N This is an adjustable parameter. It should be noted that... Figure 1 For clarity, the number of toothed materials distributed on a side plate-like material is only 17, while in all embodiments of the acoustic metasurface structure unit of the present invention, the actual number of toothed materials is 101.

[0024] like Figure 2 As shown, the transmittance and transmission phase of the metasurface structural unit of the present invention vary with the adjustable parameter w. N The relationship between the changes in the metasurface structural unit of the present invention and the geometric parameter w can be seen. N With variations in the geometric parameter w, full phase coverage within a 2π range can be achieved. Furthermore, with variations in the geometric parameter w... N Within the same range of variation, the metasurface structural units of the present invention can achieve near-perfect transmission. In the simulation calculations of the transmittance and transmission phase of the metasurface structural units of the present invention, and in the simulation calculations of the acoustic metasurfaces constructed from the metasurface structural units of the present invention—that is, all embodiments of the present invention—the density and elastic modulus of the metasurface structural units of the present invention are set to 8000 kg / m³. 3 The pressure is 160 GPa. The background medium is air, with a density and elastic modulus set to 1.2 kg / m³. 3 and 1.4×10 5 Pa, the working wavelength of the incident sound wave is set to 100mm.

[0025] Based on the metasurface structural units of this invention, acoustic metasurfaces with different phase profiles are constructed, namely: (1) the abrupt phase distribution required by the acoustic metasurface is derived based on the target transmitted sound field and the incident sound field; (2) this abrupt phase distribution is discretized based on the width of the metasurface structural units used to construct the acoustic metasurface; (3) the adjustable parameters of each metasurface structural unit in the acoustic metasurface are adjusted to achieve the required abrupt phase at the corresponding position. Different sound field control functions can be realized, such as negative refraction of sound waves and multi-point focusing of sound.

[0026] Negative refraction of sound waves:

[0027] like Figure 3 The image shows the sound field distribution of the gradient metasurface constructed from the acoustic metasurface structural units of this invention, which achieves negative refraction of sound waves. When the sound wave is incident at an angle θ... i When incident at 30°, the transmission angle θ occurs. t = -30° transmission; when the sound wave is at an incident angle θ i When incident at -30°, the transmission angle θ occurs. t Transmission at 30°. The transmission behavior of the gradient metasurface is given by the generalized Snell's law:

[0028]

[0029] Where k0 = 2π / λ0 is the wave number of air, λ0 = 100 mm is the wavelength in air, and θ t Let θ be the transmission angle. i Angle of incidence Let be the phase gradient of the acoustic metasurface. For a gradient metasurface with a period length of D, the phase gradient has two possible cases: or In this embodiment, a phase gradient is set. And D = λ0, that is Combining this formula with the generalized Snell's law yields the transmission angle values ​​corresponding to different incident angles. Since the period length D = λ0 = 100 mm for the acoustic gradient metasurface in this embodiment, and the width of the metasurface structural unit of this invention is a = 25 mm, one period of this metasurface is composed of four metasurface structural units of this invention. Based on the set phase gradient... The tunable parameters of the four metasurface structural units of this invention within one period in the acoustic gradient metasurface of this embodiment are derived as w. N = 8.27mm, 9.65mm, 2.86mm, 6.19mm. It should be noted that as long as the set phase gradient is met, the negative refraction phenomenon of acoustic waves designed in this embodiment can be achieved. The values ​​of the adjustable parameters listed above are only one set.

[0030] Multi-point sound focusing:

[0031] like Figure 4 The figure shown is a simulation diagram of the incident sound field and scattered sound intensity distribution of the metasurface constructed from the acoustic metasurface structural units of the present invention, achieving multi-point sound focusing. When the sound wave is incident normally on the metasurface from the bottom, two-point sound focusing occurs in the transmitted sound field, i.e., the transmitted sound field is: Where (x1,z1)=(-6λ0,6λ0) and (x2,z2)=(6λ0,4λ0) are the coordinates of the two focal points. k0=2π / λ0 is the wavenumber of air, and λ0=100mm is the wavelength in air. L is the thickness of the metasurface. In this embodiment, 64 [missing information] are used. Figure 1 The acoustic metasurface structural units of the present invention are used to construct this metasurface. The geometric parameters w of each structural unit in the metasurface of this embodiment are derived from the phase distribution of the incident sound field and the target transmitted sound field. N The distribution of is shown in Table 1 below.

[0032] Table 1 shows the geometric parameters w of each structural unit in the metasurface of this embodiment. N Distribution (unit: mm)

[0033]

Claims

1. An acoustic metasurface structure unit capable of near-perfect transmission, characterized in that: The two parallel arranged side plate-shaped materials are symmetrically provided with a plurality of tooth-shaped materials on the opposite sides; All the tooth-shaped materials distributed on each side plate-shaped material are conical as a whole, that is, the tooth-shaped material at the middle position has the longest length, and the length of the tooth-shaped material gradually decreases from the middle position to both ends. The length of the tooth-shaped material is adjustable.

2. The nearly perfectly transmissive acoustic metasurface structure unit of claim 1, wherein: The acoustic metasurface structure unit has a rectangular overall cross section.

3. The nearly perfectly transmissive acoustic metasurface structure unit of claim 1, wherein: The width of the acoustic metasurface structure unit as a whole is , is the wavelength of the incident sound wave.

4. The nearly perfectly transmissive acoustic metasurface structure unit of claim 1, wherein: The acoustic metasurface structure unit is arranged in a background medium, and the acoustic impedance of the acoustic metasurface structure unit exceeds 100 times the acoustic impedance of the background medium.

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