Technology Development for Electromechanical Acoustic Liners

This paper presents two key technology components required for the development of a self-powered, wireless, active acoustic liner system. The envisioned system consists of a tunable Helmholtz resonator for acoustic impedance boundary condition modification and an acoustic energy reclamation module as a system power supply. The common electroacoustic element for both of these components is an electromechanical Helmholtz resonator (EMHR) with the standard rigid backplate replaced by a compliant piezoelectric composite diaphragm. The acoustic impedance of the resonator is adjusted and additional degrees of freedom (DOF) added by coupling the EMHR to a passive electrical shunt network. Acoustic energy harvesting is achieved by connecting the EMHR to an energy reclamation circuit that converts the ac voltage signal across the piezoceramic to a conditioned dc signal. Experimental results for a non-optimized device in a normal incidence plane wave tube demonstrate ~9% impedance tuning range for resistive and capacitive shunts. An inductive load results in a three-DOF system and an enhanced tuning range of over 20%. Energy harvesting experiments yield 20–30 mW continuous power for an incident SPL of 151 dB . Such levels are sufficient to power a variety of low power electronic devices.