On the minimum coupling required for maximum theoretical power capture from vibration energy harvesters

Abstract

The minimum transducer coupling to enable maximum theoretical power capture from vibration energy harvesters is derived, leading to the simple conclusion that the product of the transducer coupling coefficient and resonance quality factor must be greater than two. Maximum theoretical power capture is experimentally demonstrated on a micromachined piezoelectric energy harvester comprised of a 20 μm thick epitaxial silicon cantilever with 800 nm thick lead-zirconate-titanate along the top surface and a bulk silicon mass at the tip. The coupling of these structures, although small (κ2=0.0033), is entirely sufficient to enable maximum theoretical power capture owing to light damping (Q=906).