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 source's 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.