Energy harvesting using a flextensional compliant mechanism

This work presents a vibration-based electromagnetic energy harvester that relies on a mechanical motion amplification mechanism. The aim is to convert a small persistent base motion into larger oscillations in order to generate greater amounts of electric power. The device can be used in situations where a small cyclic relative motion occurs between two surfaces, and where a device can be fitted to generate energy from within. Unlike conventional amplification mechanisms that rely heavily on gears, we employ a compliant mechanism of the flextensional type for energy harvesting. Such a mechanism contains few mechanical parts and attains its mobility from the elasticity of the material, thereby reducing excessive clearance, friction, and power losses. To convert the amplified mechanical motion into electrical energy, a permanent magnet is attached to the output end of the mechanism and is designed to oscillate past a stationary coil. A quasi-static model is formulated in conjunction with a finite element model of the mechanism in order to evaluate the amplification ratio, internal stresses in the flexure joints, output voltage, and power in terms of the design parameters of the flextensional mechanism. The results are supported experimentally on a cam-driven polymer flextensional mechanism across a range of operating speeds and load resistance. A parametric study is conducted to investigate the effect of the various design parameters on the system performance. An effort is made to optimize the design parameters to achieve higher output power levels while minimizing the internal stresses generated in the mechanism.