High-power piezoelectric acoustic-electric power feedthru for metal walls Xiaoqi Bao 1 , Will Biederman, Stewart Sherrit, Mircea Badescu, Yoseph Bar-Cohen, Christopher Jones, Jack Aldrich and Zensheu Chang Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA ABSTRACT Piezoelectric acoustic-electric power feed-through devices transfer electric power wirelessly through a solid wall using elastic waves. This approach allows for the elimination of the need for holes through structures for cabling or electrical feed-thrus . The technology supplies power to electric equipment inside sealed containers, vacuum or pressure vessels, etc where holes in the wall are prohibitive or may result in significant performance degradation or requires complex designs. In the our previous work, 100-W of electric power was transferred through a metal wall by a small, piezoelectric device with a simple-structure. To meet requirements of higher power applications, the feasibility to transfer kilowatts level power was investigated. Pre-stressed longitudinal piezoelectric feed-thru devices were analyzed by finite element modeling. An equivalent circuit model was developed to predict the characteristics of power transfer to different electric loads. Based on the analytical results, a prototype device was designed, fabricated and successfully demonstrated to transfer electric power at a level of 1-kW. Methods of minimizing plate wave excitation on the wall were also analyzed. Both model analysis and experimental results are presented in detail in this paper. KEYWORD: piezoelectric devices, acoustic wave, electric power supply, wireless power feed, pressure vessels. 1. INTRODUCTION There are many engineering applications where the use of wires to transfer power and communicate data through the walls of a structure is prohibitive or involves a significantly complex design. The use of feed-through wires in such systems may make them prone to leakage of chemicals or gasses, loss of pressure or vacuum, as well as hamper the ability to adequately insulate them thermally or electrically. Various future NASA missions are expected to require transmission of power into sealed solid metallic structures. Such structures may include a sample container providing planetary protection that requires internal power for monitoring, or power a spacecraft or power the space station in rendezvous and docking, as well as support autonomous operations. To address this need the method of acoustic- electric transmission using elastic waves to transmit power was investigated. This transmission device uses the direct and indirect piezoelectric effects as means of generating stress waves that are transmitted through walls where the received wave is converted to an electric power using a piezoelectric transducer and is delivered to an electric load. Potentially, the technology will allow for both power and/or data transfer from either direction. In previous work we demonstrated the transmission of 100 W, at 87-88% efficiency through a 3.4 mm thick titanium plate using two piezoelectric ceramic disks [Bao et. Al. 2007]. In this paper, a 1kW feed though by pre-stressed PZT transducer with 88% efficiency is reported. 2. BACKGROUND Using elastic waves to transfer power through a wall was suggested [Hu et al, 2003]. A system having piezoelectric layers on both sides of a plate, one as a transmitter and the other as a receiver, was investigated. A sinusoidal voltage was applied across the transmitting piezoelectric layer generating an elastic wave that travels through the wall into the receiving piezoelectric transducer where the stress wave generates a sinusoidal voltage. The theoretical problem of a piezoelectric/elastic layer/piezoelectric was solved using 1-D wave equations. An alternative approach based on network equivalent circuits was suggested [Sherrit et al. 2005, 1999] that can be easily modified to account for 1 Correspondence: xbao@jpl.nasa.gov Industrial and Commercial Applications of Smart Structures Technologies 2008, edited by L. Porter Davis, Benjamin Kyle Henderson, M. Brett McMickell, Proc. of SPIE Vol. 6930, 69300Z, (2008) · 0277-786X/08/$18 · doi: 10.1117/12.776473 Proc. of SPIE Vol. 6930 69300Z-1 2008 SPIE Digital Library -- Subscriber Archive Copy