Parameter tuning of piezoelectric-electromagnetic hybrid vibration energy harvester by magnetic force: Modeling and experiment

Traditional piezoelectric-electromagnetic hybrid vibration energy harvesters (HVEH) cannot tune their own characteristics easily once they are manufactured. To overcome this limitation, a novel tunable PE&EM-VEH is reported in this article. It employs a magnetic tuning technique to realize the double tuning ability at the same time including the operating frequency tuning and the coupling effect tuning. The magnetic tuning technique is based on a well-designed closed magnetic circuit instead of the isolated magnet model. Furthermore, a distributed parameter model of an axial tensile forced cantilever beam with a tip mass is set up for calculating the operating frequency as a function of the air gap; meanwhile, a lumped parameter model of a closed magnetic circuit is introduced for computing the nonlinear magnetic attractive force and the equivalent electromagnetic force-current factor as a function of the air gap. To verify the theoretical developments, a tunable HVEH prototype was fabricated and tested. The prototype can achieve a wide operating frequency bandwidth ranging from 25.5 Hz to 62 Hz, a variable dimensionless piezoelectric squared force-voltage factor ranging from 0.031 to 0.135 and a variable dimensionless electromagnetic squared force-current factor ranging from 0.172 to 1.073 by tuning the air gap, which agrees with the theoretical model. In addition, the maximum resonance power output of the prototype is 3.32 mW at the air gap of 12 mm under 0.3 g base acceleration. It also achieves 2.78 mW average power output over the operating frequency range.