Broadband acoustic meta-porous layer for reflected wave manipulation and absorption

Reconfigurable and Phase‐Engineered Acoustic Metasurfaces for Broadband Wavefront Manipulation

“…The GSL is then harnessed as a guide of the element arrangement with periodicity, which can be rewritten considering the diffracted wave as [ 53–55,58 ] $$$$\begin{equation} \sin {\theta}_{\mathrm{re}}-\ \sin {\theta}_{\mathrm{in}}=\ m\frac{\lambda}{2\pi}\frac{d\mathrm{\Phi}\left(x\right)}{\textit{dx}} \end{equation}$$$$where m denotes the diffracted order stemming from the periodicity of the structure. Supposing that the metasurface in a period is constructed by arranging the elements in the sequence, that is, elements #1, #2, #3, …, #8, then the factor $$\frac{{d\Phi ( x )}}{{dx}}$$ can be simplified as 2π/ D owing to the linear variation of Φ( x ), in which D is the periodic length of the metasurface.…”

“…In previous studies, numerous metasurfaces designed for acoustic wave manipulation are constructed by the elements with a representative configuration, that is, the cavity-like structure, [52,53] for instance, the uniform cavities varying with heights, [54,55] and the uniform coiled-up channels with diverse internal dimensions. [5,7] The latter can also be regarded as the uniform cavities holding different cross-sectional areas (s 1 ) and heights (l 1 ) by the conversion of incident area (s 0 ), as shown in Figure 1a.…”

“…Moreover, the analytical and numerical results are in good agreement with each other, demonstrating the correctness of the analytical model. The GSL is then harnessed as a guide of the element arrangement with periodicity, which can be rewritten considering the diffracted wave as [53][54][55]58] sin…”

Dual-frequency anti-nonlinear sound-absorbing metasurface via multilayer nested microslit resonators

“…Acoustic metasurface has been widely applied for acoustic focusing [1,2], acoustic cloaking [3], acoustic energy harvesting [4,5], and sound absorption [6][7][8][9][10][11][12][13]. The sound-absorbing metasurface (SM) can achieve effective low-frequency sound absorption on the subwavelength scale, solving the problems of insufficient low-frequency dissipation of traditional porous materials.…”

“…The sound-absorbing metasurface (SM) can achieve effective low-frequency sound absorption on the subwavelength scale, solving the problems of insufficient low-frequency dissipation of traditional porous materials. Helmholtz resonator (HR) [6][7][8][9][14][15][16][17][18], micro-perforated plate (MPP) [19,20], coiling space [8,[10][11][12][13][21][22][23][24] are the representative structures of SM, which can increase the energy density by resonance to enhance low-frequency sound absorption. However, most SM structures have only one quasi-perfect absorption frequency [25][26][27][28], and high sound intensity incidence usually causes nonlinear acoustical effects [29][30][31][32][33][34], i.e., a significant impact on sound absorption.…”