Microsystem Based Energy Harvesting (EH-MEMS): Powering Pervasivity of the Internet of Things (IoT) - A Review With Focus on Mechanical Vibrations

The paradigm of the Internet of Things (IoT) appears to be the common denominator of all distributed sensing applications, providing connectivity, interoperability and communication of smart entities (e.g. environments, objects) within a pervasive network. The IoT demands for smart, integrated, miniaturised and low-energy wireless nodes, typically powered by non-renewable energy storage units (batteries). The latter aspect poses constraints as batteries have a limited lifetime and often their replacement is impracticable. Availability of zero-power energy-autonomous technologies, able to harvest (i.e. convert) and store part of the energy available in the surrounding environment (vibrations, thermal gradients, electromagnetic waves) into electricity to supply wireless nodes functionality, would fill a significant part of the technology gap limiting the wide diffusion of efficient and cost effective IoT applications. Given the just depicted scenario, the realisation of miniaturised Energy Harvesters (EHs) leveraging on MEMS technology (MicroElectroMechanical-Systems), i.e. EH-MEMS, seems to be a key-enabling solution able to conjugate both main driving requirements of IoT applications, namely, energy-autonomy and miniaturisation/integration. This short review outlines the current state of the art in the field of EH-MEMS, with a specific focus on vibration EHs, i.e. converters capable to convert the mechanical energy scattered in environmental vibrations, into electric power. In particular, the issues in terms of conversion performance arising from EHs scaling down, along with the challenge to extend their operability on a frequency range of vibrations as wider as possible, are going to be discussed in the following.