Two-sided Acoustic Metascreen for Broadband and Individual Reflection and Transmission Control

TL;DR

This work introduces a two-sided acoustic metascreen (TAM) that enables independent amplitude and phase control of both reflected and transmitted waves across a broad band from $4$–$8$ kHz, addressing the single-sided limitation of prior metasurfaces. The TAM uses holey, lossy metamaterial unit cells with slit structures to decouple reflection and transmission control via independent parameters, achieving full $2\pi$ phase coverage on both sides. It demonstrates diffusion and focusing on opposite sides, broadband operation at multiple frequencies, and two-sided acoustic holograms on a $25\times25$ TAM panel using Iterative Angular Spectrum Approach (IASA). These results provide a flexible platform for wavefront engineering with potential applications in communications, imaging, encryption, and architectural acoustics.

Abstract

Acoustic wave modulation plays a pivotal role in various applications, including sound-field reconstruction, wireless communication, and particle manipulation, among others. However, current acoustic metamaterial and metasurface designs typically focus on controlling either reflection or transmission waves, often overlooking the coupling between amplitude and phase of acoustic waves. To fulfill this gap, we propose and experimentally validate a design enabling complete control of reflected and transmitted acoustic waves individually across a frequency range of 4 kHz to 8 kHz, allowing arbitrary combinations of amplitude and phase for reflected and transmitted sound in a broadband manner. Additionally, we demonstrate the significance of our approach for sound manipulation by achieving acoustic diffusion, reflection, focusing, and generating a two-sided 3D hologram at three distinct frequencies. These findings open an alternative avenue for extensively engineering sound waves, promising applications in acoustics and related fields.

Figures (7)

• Figure 1: Schematic diagram of the proposed metascreen for two-sided field modulation in contrast to other metasurfaces. The solid arrow indicates the modulated acoustic fields whereas the dashed arrow represents the non-modulated fields. The schematic diagram on the right illustrates a panel consisting of multiple two-sided acoustic metascreen unit cells, with each square unit representing a single cell.
• Figure 2: Conceptual illustration of the simultaneous modulation on reflection and transmission wave. (a) Schematic diagram of an array of TAM unit cells. (b) A three-dimensional illustration of a unit cell. (c) Cross-section view of a unit cell and its geometrical parameters. The length of the unit cell $L=14.3$ mm, the thickness of the pair of slabs $h_2 = 14.3$ mm, the thickness of solid frames $t=1$ mm, the distance between adjacent thin plates $h_4 = 4$ mm. (d) Broadband simulated reflection and transmission phase responses to the parameters ${h_1}$ and ${w_2}$, respectively.
• Figure 3: At 6000 Hz, the phase and amplitude responses of the TAM unit cell correspond to various configurations: (a) Simulated phase as a function of $h_1$ when $w_2 = 1$ mm (left). Simulated phase as a function of $w_2$ when $h_1 = 28$ mm (right). (b) Simulated amplitude as a function of $w$ when $h_1$ and $w_2$ are fixed as constants.
• Figure 4: The designed TAM array enables acoustic diffusion on the reflection side and acoustic focusing on the transmission side. (a) The phase profiles for the acoustic diffusion and focusing are calculated according to the generalized Snell's law. (b) The corresponding $h_1$ values for the acoustic diffusion function vary with the $x$-coordinates. (c) The corresponding $w_2$ values for the acoustic focusing function vary with the $x$-coordinates. (d) Simulated (left) and measured (right) acoustic intensity at 6000 Hz with plane waves incident from the left side. The insert is a photograph of our 3D-printed TAM array.
• Figure 5: The broadband TAM array design enables acoustic reflection for the reflection side and acoustic focusing for the transmission side across a broadband frequency range. (a) The phase profiles for the acoustic reflection and focusing are calculated according to the generalized Snell's law. (b) The corresponding $h_1$ values for the acoustic reflection function vary with the $x$-coordinates. (c) The corresponding $w_2$ values for the acoustic focusing function vary with the $x$-coordinates. (d) Simulated and measured acoustic intensity at 5500, 6000, and 6500 Hz with plane waves incident from the top side.