Characterization of challenges in asymmetric nonlinear vibration energy harvesters subjected to realistic excitation

With an explosion of the internet of things (IoT), vibration energy harvesting provides an environmentally friendly solution to replace consumable batteries in powering IoT wireless sensors. Yet, when implemented in practice, ambient vibration input energy is much less periodic than assumptions adopted in previous studies. This becomes especially important given that asymmetries are inevitable in nonlinear device platforms. This research sheds light on these complex challenges of practical vibration energy harvesting by developing and exploring an analytical model based on equivalent linearization. The modeling approach provides an opportunity to understand influences of asymmetry, nonlinearity, and combined excitation response on the DC power delivery of energy harvesters. In the analytical model, a weighted Gaussian joint distribution is utilized to approximate the influences caused by the random excitation. Combined with numerical and experimental validation, the analysis indicates that with the increase of stochastic base acceleration, two outcomes are possible. A first outcome involves an enhancement of DC power by way of triggering large amplitude nonlinear oscillations. A second outcome corresponds to a loss of high power delivery since the noise interferes with the attainment of the snap-through dynamic. Either reducing asymmetry or increasing harmonic excitation component is found to be favorable to induce the power-enhancing dynamics and inhibit the occurrence of the second case. Although with the simplified Gaussian distribution, the analytical framework cannot reproduce exact details of the dynamic responses in every case, the results show that the statistical trends of the analysis are overall borne out in simulation and experiment. This indicates the new modeling of this research may help guide attention to design and deployment techniques for nonlinear vibration energy harvesters in practical combined excitation environments, where limitations on precise manufacture or placement may introduce structural asymmetry.