Theoretical and experimental study on a self-tuning stretch-mode piezoelectric energy harvester

Abstract

Traditional cantilevered piezoelectric energy harvesters suffer from uneven strain and narrow bandwidth, thereby reducing harvesting efficiency. This study introduces a self-tuning stretch-mode piezoelectric energy harvester featuring a two-segment cantilevered beam that stretches a PVDF film for power generation and a sliding mass for frequency self-tuning. The harvester adapts to excitation frequencies by passively adjusting its resonant frequency through the sliding mass, governed by the interplay of inertial force and gravity. High inertial force enables the sliding mass to shift toward the beam’s free end, thereby lowering the resonant frequency, while low inertial force fails to overcome gravity, causing the sliding mass to shift toward the fixed end, raising the resonant frequency. A theoretical model is developed and validated experimentally. Frequency sweep tests demonstrate the sliding mass’s influence on frequency responses and reveal a significant hardening effect due to geometric nonlinearity. Fixed-frequency tests confirm self-tuning behavior. Under varying excitation amplitudes and frequencies, the motion of the sliding mass can be categorized into four distinct behavior regions. In the region where the frequency response exhibits two energy orbits, the movement of the sliding mass enables a transition from a low-energy to a high-energy state, thereby boosting power output. At 0.5 g excitations, the maximum voltage reaches 28.98 V—1.71 times higher than non-self-tuning stretch-mode nonlinear harvesters—with a bandwidth 1.83 times broader, demonstrating superior performance for energy harvesting applications.