Acoustic Energy Harvesting Using an Electromechanical Helmholtz Resonator
Fei Liu - lfeicq@ufl.edu
Mark Sheplak - Sheplak@ufl.edu
Stephen Horowitz - steveh23@ufl.edu
Louis Cattafesta - cattafes@ufl.edu
Department of Mechanical and Aerospace Engineering, University of Florida
Gainesville, Florida 32611-6250, USA
Alex Phipps - adaddyp@ufl.edu
Toshikazu Nishida - nishida@ufl.edu
Department of Electrical and Computer Engineering, University of Florida
Gainesville, Florida 32611-6130, USA
Popular version of paper 2pEAb2
Presented Tuesday afternoon, May 19, 2009
157th ASA Meeting, Portland, OR
Aircraft noise is an inevitable environmental impact of aviation that is mainly generated by the airframe and propulsion systems. Propulsion noise dominates during the take-off (with or without cutback in thrust) and cruise phases of the flight. Airframe noise, on the other hand, is dominant during approach. Acoustic liners are widely used to line the engine nacelle duct to suppress propulsion-related noise. The liners can be passive or active in terms of their noise suppression characteristics. A passive acoustic liner has a structure similar to a conventional Helmholtz resonator, consisting of a solid backplate, perforated face sheet, and honeycomb core. The advantage of the passive liner is its simplicity. However, a passive acoustic liner is most effective over a narrow frequency range around its resonant frequency.
Active liners have attracted attention from researchers due to their potential to broaden the noise suppression frequency range. Active liners typically modify their performance in situ by changing the liner geometry (and thus altering the resonant frequency of the liner) or by using bias flow through the liner. Such a system often requires actuators, sensors, power supply and a controller. Therefore, active liners are generally complex and costly.
A novel acoustic liner system has been investigated at the University of Florida. The primary element of this liner system is an electromechanical Helmholtz resonator (EMHR). The EMHR is essentially a Helmholtz resonator with the standard rigid backplate replaced by a compliant piezoelectric composite diaphragm. The piezoelectric diaphragm provides coupling between the acoustic and electrical energy domains. When working as an acoustic liner to reduce the noise, the resonant frequencies of the EMHR can be adjusted by modifying passive electrical shunt loads (e.g., a set of resistors, capacitors and inductors, or short- and open-circuit) attached to its diaphragm. Furthermore, the EMHR can be used to harvest energy form the high intensity acoustic field. In this case, the shunt loads of the EMHR are replaced by a power conversion circuit. The piezoelectric diaphragm converts mechanical energy into electrical energy via the direct piezoelectric effect. Thus, one possible active acoustic liner system is to use an array of EMHRs to suppress the noise, a group of energy harvesting EMHRs to supply power, a set of low-power microphones for sensing, and a wireless communication transceiver and switching circuitry to set the desired shunt loads.
The feasibility of noise suppression and acoustic energy reclamation using an EMHR was demonstrated in a plane wave impedance tube. When the EMHR was attached to resistive or capacitive electric loads, the tuning range of the resonant frequencies of the EMHR was limited to the short- and open circuit. There is approximately an 8% tuning range of the resonant frequency for the EMHR under investigation. When the EMHR was attached to inductive loads, the tuning range of the resonant frequency was significantly improved. Working as an energy harvester, a rectifier was connected across the piezoelectric diaphragm of the EMHR. A specific converter was then connected to the rectifier to improve load matching. When the EMHR under investigation was exposed to an incident acoustic wave with sound pressure level of 160 dB, approximately 30 mW of output power was harvested. Such a power is sufficient for many low power electronics and sensors.