Piezoelectrically tunable electromagnetic vibration harvester

The presented electromagnetic vibration harvester consists of NdFeB magnets fixed to an elastic suspension in close vicinity to the coil. The suspension is realized with a piezoelectric bimorph cantilever with oppositely polarized layers. If an electric field is applied to that configuration the elastostriction alters the cantilevers bending stiffness. As a consequence the eigenfrequency of the harvester can be tuned up to 20%. This beneficial effect is explained with an analytical model including nonlinear piezoelectric properties. Under tuning operation mode, more than 50 ¿W are scavenged continuously across the entire frequency range.