Powering autonomous wireless sensors with miniaturized piezoelectric based energy harvesting devices for NDT applications

IoT (Internet of Things) is driving an intense research activity targeting novel consumer applications. It has also an industrial counterpart, where thousands of sensors can be connected together into a proprietary network, i.e. into a Wireless Sensor Network (WSN). Such Industrial WSN may exhibit various shapes for different kind of applications. It can indeed be used for Structure Health Monitoring (SHM) to survey bridges, railways, avionic or automotive structures, rotating machine maintenance prediction, it can also serve security purposes like fire forest detection, border security, etc. In this paper we presents the architecture of a miniaturized and low-frequency piezoelectric-based vibrational-energy harvesting device (PEH) and its advanced manufacturing process flow. This harvesting technique uses direct piezoelectric effect to transform mechanical vibrations into electrical power. Over the past decade, several MEMS architectures have been built and assessed to harvest such low frequency (50-75Hz) vibrations. MEMS based PEH use thin (<5 mu m) and thick (<50 mu m) piezoelectric films allowing a high degree of integration and miniaturization, but at low frequencies the amount of harvested energy is not enough to power sensing electronics which typically consumes 100 mu W in average during 200ms. To overcome this limitation, we have developed and optimized a thinning process that enable us to use ultra-thin bulk PZT material (<20 mu m) and propose a performant and miniaturized PEH.