A new understanding for characterizing acoustic rectangular-rod waveguides and 3D discontinuities

Our investigation on the full finite-element analysis has been extended to precise discussions on the vector-modal behavior of uniform rectangular waveguides, and has found some specific vector-modal behavior in the fundamental mode of the pseudo-longitudinal, flexural and torsional waves. As an example, we show here, for the first time, that the modal behavior of the fundamental flexural mode on a 3D rectangular waveguide can be discussed well by the behavior of the fundamental Lamb mode on the correspondingly approximated 2D elastic-plate waveguide. This new understanding is then applied to develop a novel 2D Lamb-mode-waveguide model for analyzing the transmission characteristics of double-step discontinuities (or a resonator cavity) on a 3D acoustic rectangular waveguide.