Design and Development of Multi-directional Dual-beam Piezoelectric Energy Harvesters

The demand for powering small electronics has stimulated the development of vibration energy harvesting. Among several transduction mechanisms that can convert vibration into electrical energy, piezoelectric transduction has received the most attention. A conventional piezoelectric energy harvester is a cantilever beam with piezoelectric layers attached in a unimorph or a bimorph configuration. The conventional piezoelectric energy harvester has the advantages of compactness and simplicity in design. However, it suffers from a narrow bandwidth and uni-directional sensitivity. The narrow bandwidth indicates that a conventional piezoelectric energy harvester can only scavenge sufficient energy at a specific frequency and the uni-directional sensitivity means that the harvester can only work efficiently when the excitation is in the transverse direction of the beam. These two major issues limit the applications of piezoelectric energy harvesting. To overcome the narrow bandwidth, a V-shaped piezoelectric energy harvester and four magnet-integrated piezoelectric energy harvesters were designed, theoretically modeled, and numerically or experimentally validated. The V-shaped piezoelectric energy harvester is composed of two sections of beam and tip masses attached to the ends of the two sections. An analytical linear model was derived and validated with a finite-element-method model. The results show that the V-shape design can have the first resonant frequencies closer than a conventional design. The angle between the two sections significantly influences the first two resonant frequencies. Besides the linear method, a magnet-integrated dual-cantilever piezoelectric energy harvester was also designed and developed. The dual-cantilever harvester consists of two cantilever beams with magnets attached to couple the two beams. A theoretical model was derived and verified with experimental results. Significant improvement in bandwidth is shown in the result. Moreover, multi-directional energy harvesters were designed and developed to overcome the issue of uni-directional sensitivity. These multi-directional energy harvesters consist of a main piezoelectric beam and one or two auxiliary subsystems. The auxiliary subsystems were theoretically and experimentally proven to enhance the functionality of the harvesters for multi-directional broadband energy harvesting.