Interface states of dipole-like distributions in a quasi-periodic acoustic waveguide

Abstract Interface states of dipole-like distributions are experimentally observed in an acoustic waveguide with designed quasi-periodically corrugated walls. Due to the orthogonality breaking of guided transverse modes induced by the wall corrugations, a type of non-Bragg nature forbidden bands can be generated based on the interactions between different transverse modes. An interface state arises from the non-Bragg gap when we connect the two corrugated ducts to form a mirror structure. It is worth noting that the interface state in non-Bragg gaps exhibits two maximum sound pressures with totally opposite phases near the structure interface, while that in traditional Bragg gaps always has only one maximum. Our experimental measurements and numerical analysis reveal that the observed interface state with different mode characteristics is caused by the interaction of different transverse modes, which has the localization effect and high Q factor.