Strong and weak confinement of parity-time–symmetric acoustic surface wave

A strongly confined acoustic surface wave is an acoustic eigenstate localized on an interface between an ordinary acoustic medium and an acoustic metamaterial with negative effective dynamical mass density. Here we show that there is a new unconventional acoustic surface wave sustained by a parity-time $({\cal{PT}})$ -symmetric acoustic interface system, in which the negative effective dynamical mass density is not required (but the effective mass densities of the two adjacent acoustic media should fulfill the parity-time symmetry). Such an acoustic parity-time symmetry in the effective mass density can be used to manipulate acoustic wave propagation, e.g., it can exhibit both weak and strong confinement of the unusual ${\cal{PT}}$ -symmetric acoustic surface wave, and can offer mechanisms for designing acoustic metamaterial devices that would have specific functions in controlling and guiding acoustic wave, including acoustic field enhancement and extraordinary acoustic transmission