Experimental evidence of omnidirectional elastic bandgap in finite one-dimensional phononic systems

We present an experimental demonstration of the occurence of omnidirectional reflection in a finite multilayer of two elastic materials. This property is demonstrated in three different samples consisting of a few periods of Pb∕Epoxy. The effect is fullfiled thanks to the large mismatch between the elastic parameters of the two materials in the multilayer. The thicknesses of the layers were chosen in order to have the omnidirectional gap at a few hundreds of kHz. The theoretical treatment of the phononic band structure of the corresponding superlattice as well as the transmission properties through the finite structures are in good agreement with the transmission measurements.