A tunable and bistable piezoelectric vibrational energy harvester with a compliant ortho-planar spring and buckled H-I structure

This work presents a tunable, magnet-free, and bistable piezoelectric vibrational energy harvester (PVEH) with an enhanced bandwidth. The main structure features a buckled double clamped beam (I-structure) coupled with four cantilever beams (H-structure) and a compliant ortho-planar spring. The PVEH can transition from a monostable to a bistable configuration by buckling the H-I structure. Six bimorph PZT-5H materials, connected in parallel with a 90 kΩ load resistor, were employed as piezoelectric generators. Analytical modelling and experimentation are performed to study the dynamic and electrical characteristics of the harvester. Four configurations of the I-structure, specifically planar, 3.5 mm, 5.5 mm, and 7.5 mm buckled, were tested under sine sweep and random excitation in a non-gravity direction. The analytical and experimental results demonstrate that the 3.5 mm and 5.5 mm configurations show bistable behaviour under sweep excitation (0.6 g, g = 9.8 m/s²) due to a snap-through phenomenon. In contrast, the planar and 7.5 mm configurations reveal nonlinear and monostable behaviour. The former gains a peak power of 3.2 mW (at 10 Hz) under 0.6 g sweep excitation, while the latter shows three peaks in the output power (multi-modal behaviour). The PVEH can be tuned to suit the wide range of ambient vibrations from 7 Hz to 17 Hz. Finally, the 5.5 mm configuration exhibits the largest rms output power of 15.4 μW under 0.84 g rms random excitation (between 6 Hz and 30 Hz), making the harvester suitable for the broad spectrum, low-frequency, and random nature of environmental vibrations.