Interaction of Love waves with coupled cavity modes in a 2D holey phononic crystal

Highlights: • Pillar-containing cavity for Love waves is first demonstrated. • A coupling of the cavity mode to the localized pillar mode is created. • Pillars improves the flatness of the cavity mode and introduces quasi-flat defect modes. • Cavity efficiency is significantly improved with a 240 times greater Q factor without increasing the crystal size. -- Abstract: The interaction of Love waves with square array of pillars deposited on a cavity defined in a 2D holey phononic crystal is numerically investigated using Finite Element Method. First, the existence of SH surface modes is demonstrated separately for phononic crystals that consist of square arrayed holes, or rectangular arrayed Ni pillars, respectively in, or on, a SiO₂ film deposited on a ST-cut quartz substrate. The coupling between SH modes and torsional mode in pillars induces a transmission dip that occurs at a frequency located in the range of the band-gap of the holey phononic crystal. Second, a cavity is constructed by removing lines of holes in the holey phononic crystal and results in a transmission peak that matches the dip. The optimal geometrical parameters enable us to create a coupling of the cavity mode and the localized pillar mode by introducing lines of pillars into the cavity, which significantly improved the efficiency of the cavity without increasing the crystal size. The obtained results will pave the way to implement advanced designs of high-performance electroacoustic sensors based on coupling modes in phononic crystals.