Microwatt energy harvesting by exploiting flow-induced vibration

The green technology approaches by harvesting energy from aerodynamic flowinduced vibrations using a flexible square cylinder is experimentally investigated. The practicability of flow-induced vibration system to supply a sufficient base excitation vibration in microwatt scale is evaluated through a series of wind tunnel tests with different velocities. Test are performed for high Reynolds number 3.9 × 103≤ Re 1.4 × 104 and damping ratio ζ = 0.0052. The experiment setup is able to replicate the pattern of vibration amplitude for isolated square cylinder with previous available study. Then, the experimental setup is used to study the effect of vibration cylinder in harvesting the fluid energy. A prototype of electromagnetic energy harvesting is invented and fabricated to test its performance in the wind tunnel test. Test results reveal that the harnessed power is corresponding to vibration amplitude flow pattern, but the power obtained is much lower than the vibration amplitude due to the power dissipation at the resistor. The best condition for harnessing power is identified at UR = 7.7 where the Karman Vortex-Induced Vibration (KVIV) is the largest

Autonomous sensors powered by energy harvesting from von Karman vortices in airflow

In this paper an energy harvesting system based on a piezoelectric converter to extract energy from airflow and use it to power battery-less sensors is presented. The converter is embedded as a part of a flexure beam that is put into vibrations by von Karman vortices detached from a bluff body placed upstream. The vortex street has been investigated by Computational Fluid Dynamics (CFD) simulations, aiming at assessing the vortex shedding frequency as a function of the flow velocity. From the simulation results the preferred positioning of the beam behind the bluff body has been derived. In the experimental characterization the electrical output from the converter has been measured for different flow velocities and beam orientations. Highest conversion effectiveness is obtained by an optimal orientation of the beam, to exploit the maximum forcing, and for flow velocities where the repetition frequency of the vortices allows to excite the beam resonant frequency at its first flexural mode. The possibility to power battery-less sensors and make them autonomous has been shown by developing an energy management and signal conditioning electronic circuit plus two sensors for measuring temperature and flow velocity and transmitting their values over a RF signal. A harvested power of about 650 μW with retransmission intervals below 2 min have been obtained for the optimal flow velocity of 4 m/s