In this paper, we proposed a Bi-directional U-shaped piezoelectric energy harvester that is capable of scavenging vibration energy in two orthogonal directions. The U-shaped harvester is a three-segment beam with piezoelectric layers attached. The harvester is designed to work in its first three resonant frequencies. A theoretical model of the harvester is derived based on the Euler-Bernoulli beam theory. The model is capable of simulating the electromechanical coupling system and obtaining the frequency responses under excitations of two orthogonal directions. The resonant frequencies of the harvester can be tuned by simply altering the length-to-width ratio of the beam structure. It is shown in the simulation that the U-shaped design can effectively harvest vibration energy in two directions of excitations.
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