A conventional piezoelectric energy harvester suffers from narrow bandwidth and uni-directional harvesting. This paper presents a U-shaped multi-modal bi-directional piezoelectric energy harvester to overcome the above issues. The U-shaped structure, composed of a main beam and two identical side beams, can be fabricated by bending a beam into a U shape with both ends clamped. The theoretical model of the U-shaped piezoelectric energy harvester is developed and validated with experimental results. This U-shaped piezoelectric energy harvester demonstrates the capability of harvesting vibration energy in both the vertical and horizontal directions, which are the transverse direction of the main beam and that of the side beams, respectively. Parametric studies are conducted to investigate the influence of the aspect ratio of the U-shaped structure on the modal frequencies and voltage output. It is shown that the first two horizontal modal frequencies can be tuned close to each other by shortening the side beams or extending the main beam. The ratio between the horizontal and vertical modal frequencies can also be adjusted to fit the vibration sources by altering the side beams or the main beam. Published by AIP Publishing.
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