Vibration Energy Harvesting

The harvesting of ambient energy in the shape of vibrations is considered a key technology to enable self-sustained, long-lasting and free-maintenance wireless electronics. Kinetic energy is abundantly available in industrial plants, transportations, infrastructures and also human activities. However, mechanical vibrations from natural and artificial sources are pretty much weak and sited below few hundreds of hertz.

On the other hand, typical vibration energy harvesters (VEHs) are resonant spring-mass-damper systems that only work efficiently at resonance frequency.

In order to improve the bandwidth of harvesting devices some alternative concepts have been proposed in recent years: self-tuning resonators, piezoelectric cantilevers arrays and mechanical frequency-up conversion systems. Moreover, nonlinear Duffing-like piezoelectric oscillators have already been shown in my PhD Thesis to be advantageous for harvesting energy under random noise and low−frequency vibrations. The conversion of mechanical energy at low frequencies has been also approached via frequency−up conversion techniques. However, while piezoelectric and electromagnetic converters are still quite bulky, electrostatic vibration harvesters are more suitable to be implemented into micro-electromechanical systems (MEMS). Nevertheless, at sub-centimeter dimensions the resonance quickly increases from few hundreds hertz to several kHz depending on the proof mass, thus deteriorating the capability to harvest energy at frequencies below 100 Hz.

My research work is devoted to proposing, studying and implementing innovative dynamical energy harvesting systems with improved power efficiency for vibration capture and transformation into electricity from macro down to nano scale. For instance, in the Marie Curie project NEHSTech, I've proposed a device that exploits a nonlinear multiple degrees of freedom (multi-DOF) oscillating system with impacting masses to implement frequency-up conversion within a silicon-based MEMS electrostatic generator. Although this device measures only 10 x 10 x 0.4 cubic millimiter, it demonstrates a power density up to 140 microWatts per cubic centimeter, an improvement up to ten times in terms of power converted at very low frequency vibrations (10 to 20Hz). In conclusion, the capability of operating at very low frequency (10-60 Hz) for a MEMS harvester makes this micro-VEH potentially suitable for important applications such as peacemaker self-powering from human movements, wearable sensors driven by noise and self-powered wireless sensors for infrastructure and ambient monitoring.