Manipulation of acoustic wavefront by transmissive metasurface based on pentamode metamaterials**Project supported by the National Natural Science Foundation of China (Grant Nos. 61571222 and 11474160), the Natural Science Foundation of Jiangsu Province, China (Grant No. BK20161009), and the Six-Talent Peaks Project of Jiangsu Province, China.

Abstract

An underwater acoustic metasurface with sub-wavelength thickness is designed for acoustic wavefront manipulation. In this paper, a pentamode lattice and a frequency-independent generalized acoustic Snellʼs law are introduced to overcome the limitations of narrow bandwidth and low transmittance. The bulk modulus and effective density of each unit cell can be tuned simultaneously, which are modulated to guarantee the achievement of refractive index profile and high transmission. Here, we actualize anomalous refraction, generation of non-diffracting Bessel beam, sub-wavelength flat focusing, and surface wave conversion by constructing inhomogeneous acoustic metasurface. This design approach has potential applications in medical ultrasound imaging and underwater acoustic communications.