Low-frequency band gap in cross-like holey phononic crystal strip

A silicon-based cross-like holey phononic crystal (PnC) strip is proposed for the control of elastic waves in the field of micro-electro-mechanical systems (MEMS). The goal is to obtain a broad bandgap at low frequencies with a lightweight structure. In this respect, the effects of varying the in-plane and the out-of-plane geometry parameters are discussed. After design, a gap-to-midgap ratio of 47% is obtained with an intermediate filling fraction of the solid material and a small thickness of the strip. The band gap can be moved to an extremely low frequency range while keeping the strip significantly smaller than previously reported PnC strips. The transmission property through a finite number of periods agrees well with the band structure of the infinite system. The proposed PnC strip could, for instance, be used as an isolating anchor for elastic wave resonators in MEMS.