  The goal of this research is to increase the bandwidth (BW) over which
substantial energy can be harvested using a piezoelectric energy harvester
(PEH). The key innovation is the use of bias-flip (BF) electronics at the
output of a PEH having a large electromechanical coupling coefficient
$\kappa_{e}^{2}$. For a PEH with large $\kappa_{e}^{2}$, the open-circuit
resonance frequency $f_{oc}$ is substantially larger than the short-circuit
resonance frequency $f_{sc}$. Over the intervening range, the reactive part of
the conjugate matched load impedance is small, and can be approximated using BF
electronics in which the BF voltage is sufficiently small and the BF losses are
small. This results in a large BW over which substantial energy can be
harvested. Experimental results using a commercially available PEH are
presented to demonstrate this concept. Design guidelines are provided for
achieving PEHs having increased $\kappa_{e}^{2}$.
