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We theoretically derive three-dimensional (3D) generalized Snell’s law which is demonstrated by reflected wavefront manipulations based on ultrathin quasi-3D acoustic metasurfaces. Acoustic metasurfaces with a deep subwavelength thickness of λ/10 are constructed with 16 unit cells composed of a straight pipe and two ring-like Helmholtz resonators. Based on the 3D generalized Snell’s law, many fascinating reflected wavefront manipulations in 3D space are realized separately, including anomalous reflections, point focusing, line focusing in two perpendicular directions, non-diffracting Bessel beam and self-bending beam. Our results provide a new design methodology for 3D sound wavefront manipulations and practical applications of 3D sound devices. [ABSTRACT FROM AUTHOR]

We report both experimentally and numerically that a pseudospin-dependent acoustic topological insulator is realized based on airborne triangular-lattice sonic crystals with special gear-like rods. By changing structure parameters of the rods in sonic crystals, accidental double Dirac cones and a band inversion phenomenon are obtained successively. In topological waveguides constructed by two sonic crystals with dissimilar topological phases, the topological one-way transports of pseudospin-dependent edge modes are observed. More importantly, the topologically robust sound propagations against two types of defects are also experimentally demonstrated. Our results open a new venue to design pseudospin-dependent topological insulators with versatile applications. [ABSTRACT FROM AUTHOR]

We present the theoretical, numerical and experimental investigations on the high-efficiency anomalous reflection by a passive-lossless acoustic metasurface (AM). In contrast to the conventional AM, the direction of the reflected waves is controlled by the nonlinear local phase shifts in the passive-lossless AM rather than by the linear modulation. Closed-end tubes are designed to realize the passive-lossless AM. A considerable improvement of 31% in the overall efficiency is confirmed in the passive-lossless AM compared to that based on generalized reflection law when the incident and reflected angles are 0° and 75° respectively. Experimental results are in accord with finite element simulations and theoretical analyses. This advance in the proposed AM may pave a way for realizing more complex functionalities such as focusing, self-bending, and vortex generation. [ABSTRACT FROM AUTHOR]

We report the realization of acoustic energy harvesting for low-frequency sound in a subwavelength system consisting of eight multiple-cavity units. This exotic energy harvesting phenomenon arises from a compound monopole Mie resonance (MMR) induced by mutual coupling between the system structure and the MMR of each unit. More importantly, the center intensity can reach about 9000 Pa2 with the parameter r/r0 of 0.73, providing the feasibility for realizing energy harvesting in a low-energy environment. The proposed system has rich compound Mie resonances, high energy harvesting, and strong robustness, which provides diverse routes to design novel acoustic devices with versatile applications. [ABSTRACT FROM AUTHOR]

We proposed and investigated a solution to the inverse acoustic cloak problem, an anti-stealth technology to make cloaks visible, using the time-lapse reversal (TLR) method. The TLR method reconstructs the image of an unknown acoustic cloak by utilizing scattered acoustic waves. Compared to previous anti-stealth methods, the TLR method can determine not only the existence of a cloak but also its exact geometric information like definite shape, size, and position. Here, we present the process for TLR reconstruction based on time reversal invariance. This technology may have potential applications in detecting various types of cloaks with different geometric parameters. [ABSTRACT FROM AUTHOR]

The tunneling effects of acoustics have been found when the proposed solid–fluid superlattices (SLs) are used to match two fluids with a large impedance mismatch. One of the examples shows that, by embedding a rubber/water SL between air and crude oil, the transmission of acoustic energy reaches 0.97 at 5° at 8.73 kHz. According to the results of theoretical analyses and full-wave simulations, this energy tunneling is attributed to the acoustically resonant states induced by the SL at the interface. The tunneling frequencies can be tuned in real time by varying the interspacing between the solid layers of the SL, which may have wide potential applications in matching two fluids, such as acoustic coupling between air and crude oil during petroleum exploration. [ABSTRACT FROM AUTHOR]