Sound transmission within the Bragg gap via the high-order modes in a waveguide with periodically corrugated walls

摘要

The well-known Bragg resonance in periodic waveguides always leads to the creation of the so-called Bragg gap, within which sound propagations are effectively forbidden. Here we report the possibility of sound energy transmission in the Bragg gap via the high-order transverse modes, which penetrate through the forbidden band due to the interactions between different sound modes in an acoustic duct with periodically corrugated walls. The theoretical analysis indicates that in the waveguides with transverse scales comparable to its period, the guided wave modes can interact with the Bragg gap so that the forbidden band undergoes an abnormal change, giving rise to both a considerable compression in the band width and a sharp descent of the transmission loss on the upper edge of the stopband. The experiment confirms the existence and the significance of the interacting effect, and the measurements of the transmission loss and the radial distribution of sound fields agree quite well with the theoretical predictions.