Energy harvesting with electromagnetic and piezoelectric seismic transducers: Unified theory and experimental validation

This paper presents a comparative simulation and experimental study on the principal features of time-harmonic vibration energy harvesting with electromagnetic and piezoelectric seismic transducers. The study is based on equivalent lumped parameter models and a consistent formulation of the constitutive electromechanical equations for the two transducers so that a unified energy formulation is derived for the two harvesters. The electromagnetic seismic transducer is formed by a moving ferromagnetic ring and coil assembly, which is elastically suspended on a core magnetic element. The piezoelectric seismic transducer is made of a piezoelectric beam laminate with one end clamped to a base block and the other free-end equipped with a tip block. The two seismic transducers are designed and built in such a way as they have similar weights and similar volumes of the base components, similar weights and similar volumes of the suspended components and about the same fundamental natural frequencies. Both transducers are connected to either a resistive-reactive or a purely resistive harvesting impedance load. The study shows that the peak vibration energy harvested with the two systems is heavily influenced by eddy current losses in the electromagnetic seismic transducer and dielectric losses in the piezoelectric seismic transducer. In general, the electromagnetic seismic harvester is characterised by a rather high damping effect that limits the peak value of the stroke and thus of the power harvested per unit base acceleration. Instead, the piezoelectric seismic harvester is characterised by a relatively smaller damping effect such that the peak value of the stroke and thus of the power harvested per unit base acceleration are comparatively larger. Nevertheless, when the harvested power per unit stroke of the seismic transducers is examined, the behaviour is inverted, also in case the electromagnetic transducer was not affected by eddy currents losses. Finally, in general, the electromagnetic harvester outperforms the piezoelectric harvester when it is operated at off resonance frequencies.