Defect Modes in Solid-Liquid Phononic Crystals: Approaches for Acoustic Liquid Sensors Development
In this contribution, we show approaches to the development of acoustic liquid sensors based on the phononic crystals concepts. Phononic crystals, which are made of solid blocks with a periodic structure of cylindrical holes of different symmetries, containing defect (deviations from periodicity) in the form of liquid-filled cylindrical cavity were investigated as a step towards the integration of a phononic crystals with microfluidic elements. We pay attention to acoustic excitation and readout of longitudinal and axisymmetric resonant modes of liquid-filed defect in the center of phononic crystal structure and solve several challenges of mechanical energy losses due to liquid viscosity and acoustic energy radiation, coupling effects between oscillations of liquid and solid systems, as well as between piezoelectric transducers and liquid-filled cavity resonator. Numerical simulation of the propagation of acoustic waves through phononic crystals was carried out in COMSOL Multiphysics Software. Experimental structures of phononic crystals were made of stainless steel with mechanically drilled holes. We show that a tuning of the phononic crystal transparency and solid-liquid vibrational modes coupling is the key to an enhanced sensitivity of the sensor to liquid analyte properties.