Acoustically coupled MEMS transducer pairs with loss and gain

Abstract

This work investigates the dynamics and experimentally extracts the acoustic coupling between a pair of microelectromechanical ultrasound transducers (MUTs) that are immersed in water and acoustically coupled through the fluid medium. A series of these transducer pairs with varying diameters (and thus resonance frequency) and pitch separation (and thus coupling strength) are fabricated and measured. This work presented here models and quantifies the open-loop coupling between the MEMS transducer pairs and its dependence on pitch. Furthermore, a gain feedback loop is systematically applied to one of the device pair, the dynamics of the acoustically coupled gain-loss system is investigated, and the formation of an exceptional point or of an Hopf bifurcation is equally used to quantify the acoustic coupling coefficient. This work provides an exploration of the formation of exceptional points in acoustically coupled MEMS transducers as well as three experimental means to study acoustic coupling in MUT transducers: via open-loop dynamics, Hopf bifurcation, and the formation of an exceptional point.