On the use of an electret-based wind energy harvester to power a vibration sensor : A feasibility study for the city of Freiburg

Sustainable operation of off-grid sensor networks is quite crucial particularly when safety-related applications come along. These, for instance, may include temperature sensors for fire detection, or vibration sensors for civil structures health monitoring, earthquake or volcanic activity predictions, etc. An interesting approach to achieve a redundant and self-sustainable operation of such sensors is making them nature-driven. In this paper, a small-scale leaf-inspired electret-based wind energy harvester is presented and its applicability and compatibility to drive a seismic vibration sensor is assessed. The leaf-like harvester structure mainly consists of a double-deck cantilever beam that mimics the leaf stalk with a short-span hollow airfoil attached to its free end. It works based on a flapping motion under the effect of fluctuating lift force applied by the wind stream on its tip airfoil. As the installation site, the city of Freiburg, Germany, is chosen and an extensive statistical analysis with 1-hour resolution is performed on its 5-year wind speed data. This helps to evaluate the potentially harvestable energy by the presented harvester throughout the year. Indeed, the output power of the harvester is fluctuating due to the continuously-changing speed of environmental wind. A vibration sensor is then selected which is suitable to measure seismic vibrations in terms of acceleration, amplitude and frequency. By superposing the output power of the harvester (as a function of wind speed) on hourly annual trend of wind speed, a possible operating scenario of the vibration sensor powered by the harvester is then investigated. In the possible scenario, the sensor can periodically operate in a combined mode; full power operation within nearly 62% of the year, and the rest in standby mode.