Gapless dispersion of acoustic line modes with glide-symmetry (article)

The effect of glide-symmetry on the dispersion of acoustic surface waves supported by lines of open-ended holes in acrylic plates is investigated. Two samples are experimentally characterised, each formed of a pair of parallel such lines, one having glide-symmetry. This glide-symmetry removes the condition necessary for the supported ‘even’ and ‘odd’ character acoustic surface waves to form standing-waves at the first Brillouin zone boundary; there is instead one ‘mixed’ even-odd hybrid mode. This evolves continuously with increasing frequency to a far greater in-plane wavevector than possible without the glide condition. This study demonstrates that glide-symmetry opens a new degree of freedom for the design of acoustic metamaterial devices for the control of acoustic energy on a surface.