Effects of system parameters and damping on an optimal vibration-based energy harvester

The authors present a comprehensive study of the effects of damping and electromechanical coupling on the power optimality of a vibration-based energy harvester. The harvester under consideration utilizes a piezoceramic element operating in the {33} mode to scavenge mechanical energy emanating from a sinusoidal-base excitation. Under typical operating conditions, the piezoceramic element is subjected to small strains and low electric fields, which allows for the adaptation of the linear small-signal constitutive law to model its behavior. To optimize the harvested power, previous researches neglected the role of mechanical damping. This lead to results suggesting that the optimal-harvesting frequencies are not effected by mechanical damping. However, in this paper, exact expressions for the optimal frequency ratios that account for damping are derived. The results show that mechanical damping affects the optimal frequency ratios and optimal harvested power qualitatively and quantitatively. The effects of the electromechanical coupling coefficient is also explored. It is observed that there is an optimal value of the coupling coefficient beyond which the harvested power decreases. This result breaks the taboo suggesting that larger electromechanical coupling culminates in more efficient energy harvesting devices. Additionally, it is shown that at the optimal frequencies, and optimal load resistance, increasing the electromechanical coupling saturates the harvested power.