Harvesting vibration energy by branch structures and amplified inertial force acting on piezoelectric sheets

To improve the efficiency of ambient vibration energy harvesting, a novel vibration energy harvester with branch structures is proposed, which primarily generates electric output through dynamic force rather than deflection. When excited, the branch can amplify the inertial force and acts on piezoelectric sheets perpendicularly. This capability allows the harvester to generate a substantial output without undergoing excessive deflection. Theoretical models are established, and corresponding dynamic equations are derived using the Lagrange equation. The simulation results show that there exists super-harmonic resonance in the response. The validation experiments were carried out, in which the excitation types were chosen as the sweeping-frequency, harmonic and random types sequentially. The experiment results for sweeping-frequency and harmonic excitations demonstrate the occurrence of super-harmonic vibration and resonance in the response. These phenomena lead to a significant increase in output voltages. The experiments involving stochastic excitations demonstrate the harvester's capability to generate large outputs under weak random excitations, with a piezoelectric material with dimensions of 10 × 10 × 0.2 mm³. The root mean square of output power could reach 46.24 μW under the excitation of power spectrum density of 0.06 g²/Hz, about 80 % higher than the classical inverted-beam harvester.