Non-Bragg resonance of surface water waves in a trough with periodic walls

The non-Bragg resonance of surface water waves is investigated, both theoretically and experimentally, in a trough with square-wave corrugated sidewalls. Unlike the familiar Bragg resonances, the non-Bragg resonances occur far from the edges of the Brillouin zone and open additional forbidden bands. The experimental observations confirm the existence of these resonances, and the measurements for the transmission properties showing both Bragg and non-Bragg band gaps agree fairly well with the theoretical predictions obtained by the plane-wave expansion method. It is shown that both Bragg and non-Bragg resonances highly depend on the symmetry of the corrugations on the opposite sidewall. As the relative shift between the two corrugations increases from zero to the half period of the corrugations, the Bragg gap shrinks and vanishes, but the non-Bragg gap varies in the opposite way, reaching its maximum, which is impressively wide and much more efficient in reflecting water waves.