Piezoelectric Spring Pendulum Oscillator for Animal/Human Motion Energy Harvesting

Animal/human bodies produce a huge amount of energy while performing daily activities. Harvesting this kind of energy presents a viable way to overcome the battery capacity limitation that constrains the long-time operation of wearable monitoring devices. This paper demonstrated a new spring pendulum device integrated with traditional high performance piezoelectric ceramics. The device has two degrees-of-freedom (DOFs): the swing of pendulum $\pmb{u_{1}}$, and the dynamic deformation of spring $\pmb{u2}$. If the resonant frequencies of the two DOFs are specially designed, the swing of pendulum may lead to the drastic oscillation of the spring, effectively converts the mechanical energy into electrical energy. Moreover, because the value of swinging resonance only depends the length of pendulum $\pmb{l_{0}}$ and the gravity value g, the harvester is very easy to be manufactured to match the low-frequency vibration sources. Experimental results obtained from the designed prototype shows that the harvester can output 5.80 mW electrical power under the excitation of common human motion signals (1.75 Hz, 0.20 g).