Nonlinear phenomena in magnetic plucking of piezoelectric vibration energy harvesters

This work presents an investigation on the dynamics of a magnetically frequency up-converted piezoelectric energy harvester. The magnetic interaction arises between a tip magnet on a piezoelectric bimorph and a moving magnet. The latter is controlled through a low-frequency shaker at a fixed frequency of 3 Hz. We investigate in detail the effect of increasing velocity interaction between the magnets at the same input frequency, in terms of frequency up-conversion (i.e. migration from slow to fast dynamics). We show that, for increasing velocity of interaction, the frequency of the first bending mode of the piezoelectric bimorph gradually appears. Also material nonlinearities are observed as a frequency shift of the bending mode. The work shows also that the magnetic plucking phenomenon can be reliably simulated by means of a reduced order model that takes into account material nonlinearities.