Ultrathin Space-Shift Phase-Coherent Cancellation Metasurface for Broadband Sound Absorption.

A space-shift phase-coherent cancellation acoustic metasurface is developed, which can achieve broadband low-frequency sound absorption via ultra-thin integrated structure composed of multiple units with weak absorption capability. Through a space-shift design of the channel length, the large-size required in the thickness direction for low-frequency absorption is transferred into an extremely ultra-thin space layer. The units with gradient channel length are compactly arranged in an ultra-thin layer through space folding, a coplanar sound absorption metasurface component with working bandwidth exceeding an octave and thickness of only λ/25 to λ/57 is obtained. As the construction of a special double-hole "bridge" layout, even if the elements are sparsely distributed, strong coupling interactions between the units can sustain. When a certain local phase relationship is satisfied, the coherent cancellation of sound energy can be achieved, so as to reduce the sound reflection and scattering, and enhance the absorption performance. Therefore, from the perspective of phase relationship among units, the present work provides more clear physical image and intuitive theoretical explanation for achieving excellent broadband sound absorption through parallel superposition of multiple units with weak absorption capability. The proposed ultra-thin sound absorbing metasurface can satisfy the thickness limitations and absorption performance requirements in most equipment.