Optimization of a right-angle piezoelectric cantilever using auxiliary beams with different stiffness levels for vibration energy harvesting

This paper presents experiments and models of a piezoelectric cantilever generator with a right-angle structure. Analysis shows that the extended part provides a large torque to the main beam, which can dramatically smoothen the strain distribution of the main beam. The auxiliary beam was fabricated with half the length of the main beam. When the auxiliary beam has a stiffness which is 0.02 times that of the main beam the piezoelectric element has a highly uniform strain distribution; in addition, its relative utilization efficiency (RUE) is 93% at the initial resonant frequency, whereas it is 50% for a conventional rectangular piezoelectric cantilever. The performances of three right-angle generators with auxiliary beams having different levels of stiffness, but constant-stiffness main beams are studied. The RUE of the piezoelements increases as the auxiliary beam's stiffness decreases. A model based on the Rayleigh-Ritz method is established to demonstrate the principle of the strain-smoothing effect. The voltage and power outputs of the generators are measured. Finite element method simulations are also presented, and the result fits the experiments well.