Experimental and numerical study of evanescent waves in the mini stopband of a 1D phononic crystal

This paper deals with the analysis of the guided evanescent waves in stopbands of a 1D phononic crystal (PC). A new numerical implementation is shown in order to get the complex values of the wavenumbers in a frequency range where a gap occurs. The considered phononic system is an aluminum plate with a one-dimensional sinusoidal grating. For this structure a mode-gap (mini stopband) occurs at low frequency: it involves the two fundamental Lamb modes A0 and S0. The numerical study is performed by using a finite element method (ATILA code). The experiments deal with a finite length grating and evanescent waves are characterized at the vicinity of the mini stopband.

► Guided evanescent waves in stopbands of a 1D phononic crystal have been investigated. ► Real and imaginary parts of the wavenumber of these waves have been computed. ► An aluminum plate with a 1D triangular grating has been experimentally studied. ► Back propagating Bloch modes have been pointed out. ► Evanescent waves have been identified in the case of a mini stopband.