Experimental Evidence of High-frequency Complete Elastic Bandgap in Pillar-based Phononic Slabs

International audience; We present strong experimental evidence for the existence of a complete phononic bandgap,for Lamb waves, in the high frequency regime (i.e., 800MHz) for a pillar-based phononic crystal(PnC) membrane with a triangular lattice of gold pillars on top. The membrane is composed of analuminum nitride film stacked on thin molybdenum and silicon layers. Experimental characterizationshows a large attenuation of at least 20dB in the three major crystallographic directions of the PnClattice in the frequency range of 760 MHz–820MHz, which is in agreement with our finite elementsimulations of the PnC bandgap. The results of experiments are analyzed and the physics behind theattenuation in different spectral windows is explained methodically by assessing the type of Blochmodes and the in-plane symmetry of the displacement profile