Novel Design of High Performance Piezoelectric MEMS Energy Harvesters

Internet of Things (IoT), telemedicine, eHealth and Ambient Assisted Living (AAL) are rapidly advancing technologies. All of them represent strong driving forces in research aimed to improve the quality of life. In order to realize the ubiquitous paradigm, which is the main requisite of the aforementioned technologies, the elements composing the networks should be small, wirelessly connected and autonomous. In particular, power demands are typically satisfied using batteries or super capacitors, but often they do not cover the desired lifetime requirements. This limitation and a drastic reduction of the power consumption due to the wireless communication make the implementation of environmental energy harvesters a viable solution for the energetic requirement of such nodes. There are four different types of energy commonly exploited for scavenging purposes, i.e. thermal, kinetic, Radio Frequency (RF) and light. Among them, the vibrational source attracted much interest due to its abundance in most of the environments. There are three main transduction mechanisms successfully used to convert mechanical into electrical energy: piezoelectric, electromagnetic and electrostatic. In particular, the exploitation of piezoelectric materials as transduction mechanism presents some desirable features as easy integration in common micro fabrication process, a relatively high output voltage and a high output power density, in the order of few mW/cm3 [1]. Furthermore, the output impedance of the piezoelectric material is capacitive and so it could be used in a resonance-based circuit to improve the power extracted [2].