Acoustic focusing by coiling up space

TLDR

The authors design a gradient‑index acoustic lens by coiling space, offering a direct alternative to prior approaches. The lens consists of curled‑channel metamaterial units that allow free wave propagation while enabling phase delay through unit size adjustment. Simulations demonstrate that the structure emulates a high‑index gradient lens with excellent transmission, suggesting new opportunities for acoustic lens design.

Abstract

We report the design of a gradient index acoustic lens by coiling up space, an entirely different, yet more direct approach compared with previous designs. The proposed model comprises a series of acoustic metamaterial units with curled channels. Acoustic waves propagate freely within the channels but their propagating phases can be delayed at will by adjusting the size of the units. The numerical results show that the designed acoustic metamaterial can mimic an acoustic gradient index lens with arbitrarily large refractive index and considerably high transmission efficiency. This may provide possibilities for the design and application of acoustic lenses.