Evidence of a large elastic band gap in a one-dimensional phononic crystal

The aim of this work is to study the mechanisms of enlargement of band gaps in phononic strips and to present the characterization of such a structure. Indeed, to our knowledge, the gap-to-midgap ratio of the PC strips used for applications in literature does not exceed 45%. Yet, large band gaps generally imply better performances for phononic devices and a stronger robustness to fabrication tolerances. Using three different structures based on tungsten pillars fixed on a tailored silicon strip, we show that large band gaps can be obtained by coupling Bragg scattering and local resonances. Optical measurements made on a structure of few millimeters show good agreement with numerical calculations. The three periods phononic strip exhibits a main band gap with a gap-to-midgap ratio close to 100% and a maximum attenuation of -40 dB.