Manipulating Acoustic Wavefront with Metasurface of Inhomogeneous Impedance

Abstract

This chapter establishes the framework of acoustic wavefront manipulation by resorting to the acoustic metasurface which has specific acoustic impedance (SAI) inhomogeneity and discontinuity, rather than the phase inhomogeneity in terms of wave propagation (Sundar et al., Opt Lett 34(3):374–376, 2009, [1], Yu et al., Science 334(6054):333–337, 2011, [2]). SAI is one of the acoustic properties of materials, which is comparably more possible to be controllable in reality than propagation phase. More specifically, we find out that the inhomogeneous SAI will generally give rise to one ordinary reflection $p_{ro}$ and one extraordinary reflection $p_{re}$, i.e., double reflections. Furthermore, the flat inhomogeneous SAI surface is able to switch on or off $p_{ro}$ without the influence on its direction, but to tweak $p_{re}$ in the manner of our proposed design principle: impedance-governed generalized Snell’s law of reflection (IGSL) in acoustics.