Quanqi Dai

Maximizing direct current power delivery from bistable vibration energy harvesting beams subjected to realistic base excitations

Effective development of vibration energy harvesters is required to convert ambient kinetic energy into useful electrical energy as power supply for sensors, for example in structural health monitoring applications. Energy harvesting structures exhibiting bistable nonlinearities have previously been shown to generate large alternating current (AC) power when excited so as to undergo snap-through responses between stable equilibria. Yet, most microelectronics in sensors require rectified voltages and hence direct current (DC) power. While researchers have studied DC power generation from bistable energy harvesters subjected to harmonic excitations, there remain important questions as to the promise of such harvester platforms when the excitations are more realistic and include both harmonic and random components. To close this knowledge gap, this research computationally and experimentally studies the DC power delivery from bistable energy harvesters subjected to such realistic excitation combinations as those found in practice. Based on the results, it is found that the ability for bistable energy harvesters to generate peak DC power is significantly reduced by introducing sufficient amount of stochastic excitations into an otherwise harmonic input. On the other hand, the elimination of a low amplitude, coexistent response regime by way of the additive noise promotes power delivery if the device was not originally excited to snap-through. The outcomes of this research indicate the necessity for comprehensive studies about the sensitivities of DC power generation from bistable energy harvester to practical excitation scenarios prior to their optimal deployment in applications.

Investigation of direct current power delivery from nonlinear vibration energy harvesters under combined harmonic and stochastic excitations

Leveraging smooth nonlinearities in vibration energy harvesters has been shown to improve the potential for kinetic energy capture from the environment as a transduced, alternating flow of electrical current. While researchers have closely examined the direct current power delivery performance of linear energy harvesters, there is a clear need to quantify the direct current power provided by nonlinear harvester platforms, in particular those platforms having bistable nonlinearities that are shown to have advantages over other smooth nonlinearities. In addition, because real world excitations are neither purely harmonic nor purely stochastic, the influences of an arbitrary combination of such excitation mechanisms on power delivery must be uncovered. To bring needed light to these roles and opportunities for nonlinear energy harvesters to provide direct current electrical power for numerous applications, this research formulates a new analytical approach to characterize simultaneous harmonic and stochastic mechanical and electrical responses of nonlinear harvester platforms subjected to realistic base excitation. Based on the outcomes of analytical, numerical, and experimental studies, it is found that additive stochastic excitation may result in direct current power enhancement via perturbation from a low amplitude state particularly at low frequencies or reduce the direct current power by preventing persistent snap-through response often at higher frequencies. When the noise standard deviation is greater than the harmonic amplitude by approximately two times, the advantages to direct current power generation are more often realized.

Impulsive energy conversion with magnetically coupled nonlinear energy harvesting systems

Magnets have received broad attention for vibration energy harvesting due to noncontact, nonlinear forces that may be leveraged among harvesting system elements. Yet, opportunities to integrate multi-directional coupling among a nonlinear energy harvesting system subjected to impulsive excitations have not been scrutinized, despite widespread prevalence of such excitations. To characterize these potentials, this research investigates an energy harvesting system with magnetically induced nonlinearities and coupling effects under impulsive excitations. A system model is formulated and validated with experimental efforts to reconstruct static and dynamic properties of the system via simulations. Then, the model is harnessed to scrutinize dynamic response of the system when subjected to impulse conditions. This research reveals the clear impulse strength dependence and influence of asymmetries on total electrical energy capture and energy conversion efficiency that are tailored by magnetic force coupling. Asymmetry is found to promote greater impulse-to-electrical energy conversion when compared to the symmetric counterpart system and a benchmark nonlinear energy harvester. The roles of initial conditions exemplify how stored energy in an asymmetric energy harvesting system may be released during nonlinear impulsive response. These results provide insights about opportunities and challenges to incorporate magnetic coupling effects in nonlinear energy harvesting systems subjected to impulses.

Investigating a magnetically coupled vibration energy harvesting system under impulsive excitations

Magnetically coupled energy harvesters have been demonstrated to achieve broad tuning of nonlinear behaviors and multi-directional dynamic response by adjusting the relative spacing among magnets. Such flexibility permits a wide accommodation to diverse ambient base excitations for energy conversion and capture. Yet, the magnetic coupling of an energy harvesting system has not been examined as a useful means to enhance energy harvesting outcomes when the excitation source contains the impulsive excitations commonly encountered in ambient environments. To obtain new understanding on the effectiveness of magnetic coupling, a nonlinear vibration energy harvesting system is devised and studied for the electrodynamic responses and direct current power charging that are enabled by impulsive excitations. By comparing experimental and numerical simulation results, the energy harvesting system model is firstly validated. The studies demonstrate the sensitivity of total energy collection on change in the impulse characteristics. The findings reveal that nonlinear snap-through behaviors induced by bistable nonlinearities with magnetic coupling are effective for DC power charging, so long as an impulsive excitation threshold is met. Results from this research emphasize the importance of accurately quantifying the magnetic coupling effects towards characterizing the sensitivities the energy harvesting system when subjected to impulsive excitations.

Extreme impact mitigation by critical point constraints on elastic metamaterials

A critical transition occurs between pre- and post-buckled configurations of lightly-damped structures where the relative proportions of dissipative and elastic forces may reverse, theoretically giving rise to large effective damping properties. This paper describes computational and experimental studies that investigate such fundamental theory and principles. It is found that impact mitigation capabilities of elastic metamaterials are significantly enhanced by critical point constraints. The results of one-dimensional drop experiments reveal that constrained metamaterials reduce impact force and suppress rebound effects more dramatically than conventional damping methods, while constraints nearer to critical points magnify the advantages. When embedded into distributed structures as in conventional applications, it is found that constrained metamaterials provide superior impact mitigation capabilities than solid dampers applied at the same locations. All together, the results show that critical point con...

Modeling and design of lightweight, hyperdamping metamaterials for large, broadband vibroacoustic energy attenuation

The absorption and dissipation of spectrally broadband vibration and wave energy are long-standing pursuits for researchers and engineers. In vehicular applications, light-weighting demands have led to the common use of flexible structural components that exacerbate concerns of low frequency energy transmission and radiation while joints and geometrical features result in higher frequency vibrations that produce adverse noise fields for occupants. To address the needs for broadband vibroacoustic energy attenuation via a lightweight material solution, this research integrates concepts from recent studies on elastic and poroelastic composite materials and investigates a new idea to cultivate hyperdamping effects in an engineered metamaterial. A finite element (FE) model is developed to identify ways in which to effect hyperdamping properties by virtue of controlled instability mechanisms embedded within the metamaterial. Throughout the design space, the simulations predict numerous design parameter selectio...