Auxetics: P-wave mode conversion at a solid-vacuum interface

Abstract

An acoustic P-wave being reflected at the solid-vacuum interface, may exhibit mode conversion into reflected shear S-wave without the formation of reflected P-waves. This phenomenon takes place, when the incident P-wave hits the interface at some critical angle, which depends upon Poisson’s ratio. It is also known that for large Poisson’s ratio values no mode conversion exists. Herein, apparently for the first time, the mode conversion is studied for materials with negative Poisson’s ratio (auxetics), revealing that for any negative Poisson’s ratio (i) mode conversion exists; (ii) there are exactly two angles of incidence at which mode conversion occurs; and, (iii) vanishing Poisson’s ratio implies that mode conversion occurs at the oblique incidence of P-wave.