Cantilevered piezoelectric energy harvesters have been studied extensively in recent years. Numerous techniques have been investigated to achieve optimal power output. However, the extraction of electrical energy from mechanical vibration leads to a reduction of the vibration magnitude of the harvester because of the electromechanical coupling effect, and so a model considering constant vibration magnitude input is no longer valid. Thus, an energy harvesting model excited with a constant force or acceleration magnitude has been adopted to take into account the damping effect induced by the energy harvesting process. This paper extends this model to the effect of energy harvesting on the fixed host structure (mechanical to mechanical coupling). Theoretical developments are presented as a dynamic problem of an electromechanically coupled two-degree-of-freedom (TDOF) spring–mass–damper system. Then, experimental measurements and computations based on finite element modeling (FEM) are carried out to validate theoretical predictions. It is shown that the extracted power obtained from the TDOF model would reach a maximal value by tuning the mass ratio between the host structure and the harvester and optimizing the electric load. The mechanical to mechanical coupling effect due to the harvester leads to a trade-off between the mechanical energy of the host structure and the harvested energy. When the harvester mass to host structure mass ratio is around 10−3, the maximal power is obtained and the host structure then has a sudden displacement reduction due to the strong mechanical to mechanical coupling. Experimental measurements have been performed for a mass ratio of around 0.02, with which the harvester effect is not negligible on the host structure behavior as the host structure displacement shows a decrease of more than 3 dB. In addition, the harvested power calculated with the TDOF model is about two times less than with a single-degree-of-freedom (SDOF) model under a constant acceleration magnitude as the SDOF model does not consider the backward damping effect due to mechanical to mechanical coupling and thus overestimates the power output.
This paper presents a new approach for modeling a piezoelectric harvester using a nonlinear technique under an arbitrary, including broadband and random, force excitation. Hence it extends and generalizes previous works on monochromatic force excitation to more practical and realistic applications. In the nonlinear technique, a switching device is connected in parallel with the piezoelectric element. Though its nonlinear nature together with broadband and random input suggests a numerical step-by-step analysis, this gives less insight than more analytically based methods which are difficult to conduct and have, until now, been absent. In this paper, the switching device is assumed to be turned on periodically at any chosen frequency. The concept of switching-induced self-sampling and self-aliasing is therefore introduced into the modeling. The modeling is then applied to several well-known excitation cases to validate the theory and demonstrate the effectiveness of the model. The effect of different switching frequencies when the system is subjected to a random force excitation is discussed. It is shown that the harvester gives maximum harvested power when the switching frequency is slightly less than twice the resonance of the harvester.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.