Dylan J. Morris

A resonant frequency tunable, extensional mode piezoelectric vibration harvesting mechanism

Electrical power for distributed, wireless sensors may be harvested from vibrations in the ambient through the use of electromechanical transducers. To be most useful, the electromechanical transducer should maximize the harvested power by matching its resonant frequency to the strongest vibration amplitude in the sources vibration spectrum. This paper introduces a new frequency tunable mechanism wherein the deformation of the piezoelectric elements is primarily in-plane extension, and bending effects may be neglected. The extensional mode resonator (XMR) is formed by suspending a seismic mass with two piezoelectric sheets. The mechanism is made frequency tunable by an adjustable link that symmetrically pre-tensions both piezoelectric sheets. A prototype XMR has been built and tested that has demonstrated adjustable and repeatable resonant frequency variation from 80 to 235 Hz. The electrical power generated by the XMR is also insensitive to the driving frequency, when the resonant frequency is matched to the driving frequency.

A MEMS-BASED MICRO HEAT ENGINE WITH INTEGRATED THERMAL SWITCH

This work details the effect of top membrane compliance on the performance of a MEMS based micro-heat engine and integrated thermal switch at operating speeds of 20, 40, and 100Hz and heat inputs of up to 60mJ per cycle. The engine consists of two flexible membranes encapsulating a volume of saturated working fluid. A thermal switch is used to intermittently reject heat from the engine to a constant temperature cooling sink. Mechanical work output is measured based on the engine’s top membrane deflection and internal operating pressure. Three top membranes are considered; a 2micron thick silicon membrane, a 300nm thick silicon-nitride membrane, and a 3micron thick corrugated silicon membrane. The engine is shown to produce 1.0mW of mechanical power when operated at 100Hz.

Failure Pzt Thin Films in Mems

Many microelectromechanical systems (MEMS) are based on polysilicon films used for electrostatic actuation. However, piezoelectric films, such as lead zirconate titanate (PZT), can provide the ability to generate high forces at lower strains as actuators [1] or for use in energy conversion applications, bringing a different set of challenges regarding processing and reliability in mechanical applications. These often are used in the form of thin PZT membranes [2], and so this structure is of particular interest for piezoelectric MEMS, among the many possible geometries for this type of material [3]. In this presentation, failure mechanisms in PZT MEMS will be described for both processing requirements and during service.