Miniature wind energy harvesters

• Main Author: Sun, Huihui
• Other Authors: Beeby, Stephen
• Published: University of Southampton 2017
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.729770

Energy harvesting is a very attractive technique for a wide variety of self-powered microsystems such as wireless sensors. Airflow induced oscillations have been used as an attractive technique for energy harvesting because of its potential capacity for generating electrical power. The aero-elastic instability phenomenon such as flutter has been suggested especially for small scale energy harvesters. This paper describes the design, simulation, fabrication, measurement and performance of a miniature wind energy harvester based on a flapping cantilevered beam. The wind generator is based on oscillations of a cantilever that faces the direction of the airflow. The oscillation is amplified by interactions between an aerofoil attached on the cantilever and a bluff body placed in front of the aerofoil. To achieve the optimum design of the harvester, both computational simulations and experiments have been carried out to investigate the structure. Simulation is achieved with ANSYS to optimise the structure and predict the power generation for practical design. Both piezoelectric materials and electromagnetic transducers are used for the generator and tested. Three prototypes with the same volume of 37.5 cm3 are fabricated and tested through two aspects of the performance namely the threshold wind speed for operation and the output power. Wind tunnel test results are presented to determine the optimum structure and to characterize the performance of the harvesters. The piezoelectric generator is fabricated by thick-film screen printing technique. The optimized device finally achieved a working wind speed range from 2 m/s to 8 m/s. The power output was ranging from 0.35 to 3.6 μW and the open-circuit output voltage was from 0.6V to 1.9V. The first electromagnetic harvester had a working wind speed range from 1.35 m/s to 6 m/s with a maximum power output of 29.8 μW and a voltage of 293 mV. While for the second generator, the wind speed for operation is form 1.5 m/s to 6.5 m/s. The output power is ranging from 8.9 μW to 41 μW and the output voltage is up to 171 mV. Results verified the harvester can effectively convert wind energy into large amplitude mechanical vibration without strict frequency matching constraints.