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

The authors present a comprehensive study of the effects of damping and electromechanicalcoupling on the power optimality of a vibration-based energy harvester. The harvesterunder consideration utilizes a piezoceramic element operating in the {33} mode to scavengemechanical energy emanating from a sinusoidal-base excitation. Under typical operatingconditions, 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 itsbehavior. To optimize the harvested power, previous researches neglected the role of mechanicaldamping. This lead to results suggesting that the optimal-harvesting frequenciesare not effected by mechanical damping. However, in this paper, exact expressions forthe optimal frequency ratios that account for damping are derived. The results show thatmechanical damping affects the optimal frequency ratios and optimal harvested power qualitativelyand quantitatively. The effects of the electromechanical coupling coefficient is alsoexplored. It is observed that there is an optimal value of the coupling coefficient beyondwhich the harvested power decreases. This result breaks the taboo suggesting that largerelectromechanical coupling culminates in more efficient energy harvesting devices. Additionally,it is shown that at the optimal frequencies, and optimal load resistance, increasingthe electromechanical coupling saturates the harvested powe