Determination of the appropriate piezoelectric materials for various types of piezoelectric energy harvesters with high output power

For a type-1 piezoelectric energy harvester (PEH), in which stress develops in the supporting system of the piezoelectric materials, the electromechanical coupling factor (k(ij)) of the piezoelectric materials is important for the output power at the resonance frequency. Therefore, soft-piezoelectric materials are good candidates for these PEHs. For type-2 PEHs, in which stress develops in the piezoelectric material and supporting system, the figure of merit (FOM) of the output power at the resonance frequency is (k(ij)(2) x Q(m))/s(11)(E), where Q(m) and s(11)(E) are the mechanical quality factor and the elastic compliance of piezoelectric materials, respectively. In particular, the effect of Q(m) is very large for these PEHs, indicating that hard-piezoelectric materials are good candidates for type-2 PEHs operating at the resonance frequency. For both type-1 and type-2 PEHs operating at off-resonance frequency, the k(ij)(2) x d(ij) x g(ij) is the FOM of the output power of the PEHs, where g(ij) is a piezoelectric voltage constant. Therefore, soft-piezoelectric materials are also good candidates for both type-1 and type-2 PEHs operating at the off-resonance frequency.