  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.
