The collection of clean power from ambient vibrations is considered a promising method for energy harvesting. For the case of wheel rotation, the present study investigates the effectiveness of a piezoelectric energy harvester, with the application of stochastic resonance to optimize the efficiency of energy harvesting. It is hypothesized that when the wheel rotates at variable speeds, the energy harvester is subjected to on-road noise as ambient excitations and a tangentially acting gravity force as a periodic modulation force, which can stimulate stochastic resonance. The energy harvester was miniaturized with a bistable cantilever structure, and the on-road noise was measured for the implementation of a vibrator in an experimental setting. A validation experiment revealed that the harvesting system was optimized to capture power that was approximately 12 times that captured under only on-road noise excitation and 50 times that captured under only the periodic gravity force. Moreover, the investigation of up-sweep excitations with increasing rotational frequency confirmed that stochastic resonance is effective in optimizing the performance of the energy harvester, with a certain bandwidth of vehicle speeds. An actual-vehicle experiment validates that the prototype harvester using stochastic resonance is capable of improving power generation performance for practical tire application.

Nonlinear energy harvesters are frequently considered in preference to linear devices because they can potentially overcome the narrow frequency bandwidth limitations inherent to linear variants; however, the possibility of variable harvesting efficiency is raised for the nonlinear case. This paper proposes a rotational energy harvester which may be fitted into an automobile tyre, with the advantage that it may broaden the rotating frequency bandwidth and simultaneously stabilise high-energy orbit oscillations. By consideration of the centrifugal effects due to rotation, the overall restoring force will potentially be increased for a cantilever implemented within the harvester, and this manifests as an increase in its equivalent elastic stiffness. In addition, this study reveals that the initial potential well barriers become as shallow as those for a bistable system. When the rotational frequency increases beyond an identifiable boundary frequency, the system transforms into one with a potential barrier of a typical monostable system. On this basis, the inter-well motion of the bistable system can provide sufficient kinetic energy so that the cantilever maintains its high-energy orbit oscillation for monostable hardening behaviour. Furthermore, in a vehicle drive experiment, it has been shown that the effective rotating frequency bandwidth can be widened from 15 km/h–25 km/h to 10 km/h–40 km/h. In addition, it is confirmed that the centrifugal effects can improve the harvester performance, producing a mean power of 61 μW at a driving speed of 40 km/h, and this is achieved by stabilising the high-energy orbit oscillations of the rotational harvester.

Energy harvesting from rotating systems has been developed into an important topic as a promising solution for realizing the powering applications of tire monitoring systems. Because of relatively narrow bandwidth of the efficiently operating response, this paper proposes a principle for optimizing the centrifugal distance for tuning frequency matching between stochastic resonance and the external rotation environments. It can minimize the negative effect of a low energy orbit owing to the optimally stabilized stochastic resonance, particularly over the low frequency range before high energy orbit oscillation. The centrifugal force caused by the behavior of rotation acting on the tip mass of the cantilever changes the equivalent stiffness of the cantilever and thus can tune the variation in the Kramers escape rate. Through the match-able relationship of a non-linear bitable system between the Kramers rate and the external rotation frequency, the expression of the optimally centrifugal distance can be solved by theoretical derivation and numerical analysis. The results of simulations and laboratory experiments simultaneously demonstrate that the centrifugal distance is tuned to be the optimal 6.45 cm as theoretically analyzed, and the effective bandwidth of energy harvesting can be stabilized from 30 rad s ⁻¹ to 50 rad s ⁻¹ . While its maximum root mean square voltage can reach the value of 1.23 V corresponding to a harvesting average power of 45.55 μ W, owing to the high matching relationship between stochastic resonance and external rotation frequencies. Thus, by the theoretical optimization of centrifugal distance, the frequency of stochastic resonance can be tuned for matching the externally rotating environments, and further improving the operating performance of rotating-induced energy harvesting.