Micromachined Piezoelectric Energy Harvesters

date March 1, 2013
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Friday, March 1, 2013 4:00 p.m. in ETC 4.150

Donghwan Kim
Department of Electrical & Computer Engineering
The University of Texas at Austin
http://www.ece.utexas.edu/

Small-scale piezoelectric energy harvesters (PEH) have been the subject of recent investigations.  Previously the power output of MEMS PEHs was considered too small to operate a sensor, but advances in lowering the power demands of small, unattended sensors make PEHs attractive as a power source.  The opportunity to create a maintenance-free remote sensor network is attractive for many applications, including intrusion detection systems and structural health monitoring.  Fundamentally, a PEH utilizes ambient vibration input so that the piezoelectric element on the harvester deforms and produces power.  This technique is most effective near the PEH’s fundamental resonance frequency due to large mechanical deformations.  As one might expect, power output is also proportional to resonance quality factor Q.  Cantilever geometries are popular for this reason.  Designing for maximum power capture at resonance by using high‑Q resonant devices comes at the expense of reducing the PEH’s effectiveness off-resonance.  To overcome this, a broad‑band harvester innovation is proposed.  This presentation will include microfabrication of single-mode piezoelectric cantilever test structures comprised of 20‑µm‑thick silicon beams with bulk silicon tip masses.  The beams are fabricated with 1‑µm‑thick lead zirconate titanate (PZT) films along their top surface.  Testing results are also presented and include demonstration of impedance matching and theoretical maximum power capture.  A discussion of preliminary design considerations for upcoming broadband harvesters is also included.