Modeling, Simulation and Design of Piezoelectric Micro-Hydraulic Transducer Devices O. Yaglioglu * , Y.H. Su ** , D.C. Roberts * , J. Carretero * and N. W. Hagood * * Active Material and Structures Laboratory, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Rm. 37-315, Cambridge, MA 02139, onnik@mit.edu ** State University of New York, Stony Brook, NY ABSTRACT This paper reports on modeling, simulation and design considerations for piezoelectric Micro-Hydraulic Transducer (MHT) systems, focusing on power generation applications. Since these devices are complex fluid and structural systems, comprehensive simulation tools are needed for effective design. A system level simulation tool has been developed using Simulink TM , by integrating models for different energy domains, namely fluids, structures, piezoelectrics and circuitry. The simulation allows for the monitoring of important parameters such as chamber pressure, flowrate, and various structural component deflections and stresses. Using the simulation, the operation of the system is analyzed and important design considerations are evaluated. Results indicate that system efficiency is highly dependent on compliances within the device structure and the type of piezoelectric material used. Keywords: microhydraulic, power generation, piezoelectric 1 CONFIGURATION AND OPERATION Piezoelectric Micro-Hydraulic Transducers are compact high power density transducers, which can function bi- directionally as actuators/micropumps and/or power generators. These devices are comprised of a main pumping chamber, two actively controlled valves, a low-pressure reservoir and a high-pressure reservoir (Figure 1) [1]. Figure 1: Device layout for power generator configuration. Top and bottom packaging pyrex layers not shown. The active valves regulate fluid flow from the reservoirs into and out of the main chamber, which houses a piezoelectrically driven tethered piston. When operating as a pump, the electrical signal applied to the piezoelectric element results in pressure fluctuations inside the main chamber. When operating as a power generator, pressure fluctuations within the main chamber are converted to an electrical signal, which is rectified and stored in a battery. These devices are designed to generate 0.5-1W power at frequencies of ~15-20kHz, resulting in high power densities approaching 500-1000W/kg. This paper primarily focuses on modeling simulation and design considerations for MHT devices used as power generators. A prototype MHT device consists of a 9-layer stack of pyrex and silicon micromachined layers (Figure 2). Sealing of the piston in the main chamber is provided by annular tethers which are created through Deep Reactive Ion Etching (DRIE) of a SOI wafer. The tether thickness (~10_m) is defined by the SOI device layer, and the buried oxide acts as an etch stop. All glass layers are patterned by conventional diamond core drilling. Piezoelectric cylinders are core drilled from piezoelectric substrate plates, onto which Ti-Pt-AuSn-Au multilayer film is sputter-deposited for eutectic bonding. The device assembly is accomplished through anodic bonding of the glass layers to the silicon layers at 300 o C, a process which also enables the AuSn eutectic alloy to melt. Upon cooling, the alloy solidifies, bonding the piezoelectric cylinders to the silicon layers. [2]. Figure 2: (a) 5-layer device for subcomponent testing (b) Complete 9-layer device (c) SEM of micromachined tethered piston structure. 2 MODELING This section focuses on the development of a system level model to capture the behavior of the main chamber