There has been considerable research on the design of vibration based energy harvesters in the last decade exploring the potential of autonomous power supply for miniaturized electronic systems. Nonlinear energy harvesting mechanisms are in general perceived as more robust than linear harvester designs owing to the broadband resonance dynamics which allow for efficient energy transduction over a diverse range of input vibrations. In particular, geometrically bi-stable composites with embedded piezoelectric elements have been investigated as a scalable and bio-compatible design with a strong potential for harvesting energy from the high-amplitude interwell oscillations encompassing both the statically stable states of the harvester. Significant research effort has been devoted to devise efficient strategies for shifting between the co-existing stable solution configurations of bi-stable harvesters, thus allowing to consistently maintain the high-amplitude inter-well oscillations favorable for energy harvesting. However, analysis of the compatibility of conventional linear mode shape based harvester designs to harness the complete potential for energy harvesting from nonlinear solution configurations of bistable harvesters has received lesser attention. This study presents an experimental analysis of the operational deformation shapes associated with the intra-well and inter-well response regimes of bi-stable energy harvesters. A qualitative comparison of the operational deformation shapes characterizing the nonlinear response of the harvester with the linear design mode shapes is presented. The results indicate that operational deformation shapes differing significantly from the linear mode shapes are active in the nonlinear response regime of the harvester. The aforementioned deformation shapes, while influencing the mechanical response of the harvester, may not result in any significant contribution to the harvested power as they are essentially excluded in the linear mode shape based harvester design envelop. The presented experimental results essentially highlight the need for considering the operational deformation shapes associated with the nonlinear response regime while designing for the dimensions and the position of the piezoelectric elements on bi-stable composites to ensure that the complete potential for energy conversion across all of the dynamical regimes is harnessed adequately.
Vibration energy harvesters have been proposed as an autonomous power source for meeting the limited power requirements of present-day sensors and electronics that find extensive usage in structural health monitoring systems. Recent research reveals that nonlinear energy harvesters outperform their linear counterparts, designed to operate on the principle of resonance, owing to their wide frequency bandwidth which allows for better performance in realistic operational environments. Particularly, bi-stable energy harvesters designed to exploit piezoelectricity to achieve the mechanical to electrical energy conversion have been widely investigated in literature. Additionally, several investigations have been also proposed to enhance power conversion in linear harvesters by introducing nonlinear circuits, e.g. based on synchronized switching (SS). In this respect, unveiling the effects on the bandwidth and coexisting solutions in the response of strongly nonlinear electrical SS shunts interacting with multi-stable structures requires further investigation. In particular, synchronized switch harvesting on inductor (SSHI) circuits, when connected in parallel with bi-stable energy harvesters, facilitate an increase in the harvested voltage, thus allowing for higher power generation as compared to a standard shunt load. This paper investigates the effects of utilizing a SSHI circuit for enhancing the power output in the different dynamical regimes of a bi-stable energy harvester. In particular, we present a comprehensive study of the efficiency of the SSHI circuit when the response configuration of the system is shifted between coexisting dynamical states of the bi-stable harvester. The herein presented semi-analytical and numerical results show that the qualitative performance of the SSHI circuit is quite robust in terms of superiority over the standard load circuit. However, the quantitative nature of the increase in power harvested by the SSHI circuit is sensitive to the optimal load in the circuit, which in turn varies with the dynamical state of the system.
In this study, the dynamics of a lattice of bistable elements connected by linear springs are investigated with emphasis on the spatial dependence of the response profiles created by the nonlinear transition wave. We address the difficulty in creating a permanent-form transition wave in real-world settings even though such a solution theoretically exists and explain how to utilize the speed difference in wave propagation to minimize this undesirable behavior through numerical investigations. We further introduce dissipative elements along with asymmetric on-site potentials to the baseline lattice and show that almost perfect response invariance can be achieved, where the response is not only spatially independent but also input-independent.
Energy harvesting employing non-linear systems offers considerable advantages over linear systems given the broadband resonant response which is favorable for applications involving diverse input vibrations. In this respect, the rich dynamics of bi-stable systems present a promising means for harvesting vibrational energy from ambient sources. Harvesters deriving their bi-stability from thermally induced stresses as opposed to magnetic forces are receiving significant attention as it reduces the need for ancillary components and allows for bio- compatible constructions. However, the design of these bi-stable harvesters still requires further optimization to completely exploit the dynamic behavior of these systems. This study presents a comparison of the harvesting capabilities of non-magnetic, bi-stable composite laminates under variations in the design parameters as evaluated utilizing established power metrics. Energy output characteristics of two bi-stable composite laminate plates with a piezoelectric patch bonded on the top surface are experimentally investigated for variations in the thickness ratio and inertial mass positions for multiple load conditions. A particular design configuration is found to perform better over the entire range of testing conditions which include single and multiple frequency excitation, thus indicating that design optimization over the geometry of the harvester yields robust performance. The experimental analysis further highlights the need for appropriate design guidelines for optimization and holistic performance metrics to account for the range of operational conditions.
Heterogeneity in a lattice system has gained continued attention from researchers due to its ability to support interesting localized dynamics and engineering applications. Most studies on the influence of the defects have been done in a one-dimensional monoatomic chain with both linear and nonlinear interactions. However, analysis of defect dynamics in a lattice under on-site potential is still a rare finding. Recently, extreme wave propagation has been demonstrated theoretically and experimentally on a bi-stable lattice with magnetic inter-site force, featuring quartic on-site potential. In this work, the nonlinear dynamics of introducing engineered defects in the form of mass impurities and inter-site forcing disparities on lattices of bi-stable elements are studied. We investigate the effect of the defect presence on the local wave propagation speed and identify the critical conditions that governs the stable propagation of transition waves. With the control of damping, we further observe a special satellite region, where stable transition of wave with intermediate jumps between the stable states of the local unit cell occurs.
Tailless airplanes with swept wings rely on variations of the spanwise lift distribution to provide controllability in roll, pitch and yaw. Conventionally, this is achieved utilizing multiple control surfaces, such as elevons, on the wing trailing edge. As every flight condition requires different control moments (e.g. to provide pitching moment equilibrium), these surfaces are practically permanently displaced. Due to their nature, causing discontinuities, corners and gaps, they bear aerodynamic penalties, mostly in terms of shape drag. Shape adaptation, by means of chordwise morphing, has the potential of varying the lift of a wing section by deforming its profile in a way that minimizes the resulting drag. Furthermore, as the shape can be varied differently along the wingspan, the lift distribution can be tailored to each specific flight condition. For this reason, tailless aircraft appear as a prime choice to apply morphing techniques, as the attainable benefits are potentially significant. In this work, we present a methodology to determine the optimal planform, profile shape, and morphing structure for a tailless aircraft. The employed morphing concept is based on a distributed compliance structure, actuated by Macro Fiber Composite (MFC) piezoelectric elements. The multidisciplinary optimization is performed considering the static and dynamic aeroelastic behavior of the resulting structure. The goal is the maximization of the aerodynamic efficiency while guaranteeing the controllability of the plane, by means of morphing, in a set of flight conditions.
Nonlinear harvesting devices have been shown to maintain large amplitude oscillations over a wider range of frequencies than their linear counter parts. Central to exploiting the dynamic behaviour for harvesting is the understanding of the cross-well oscillations which involve constant snap-through between the stable states of such systems. Yet the phenomena involving the dynamics of snap-through and their impact in the harvesting characteristics have not been studied in detail. In this paper, the relevant response characteristics for dynamically triggered snap-through of bi-stable composite laminates for energy harvesting are investigated. A nonlinear model for the dynamics of the bi-stable composites is used to study the relation between the properties of the laminate and the acceleration level required for causing snap-through. In particular, the effect of varying the induced stress level on the dynamic response is investigated. The obtained relations provide a tool for designing the excitation level for which broad-band response bi-stable systems is obtained, aiding the design of harvesting devices based on such structures.
Recently, the idea to exploit nonlinearity to achieve broadband energy harvesting has been introduced. Bi-stable systems have been used to realise broadband energy harvesting devices. Amongst these, harvesters constructed with bi-stable composites show great potential due to their rich dynamic behaviour. This paper studies a novel cantilevered configuration for a piezoelectric bi-stable composite device for broadband energy harvesting. The cantilevered configuration allows to exploit high strains developed close to the clamped root, further enhancing the harvesting characteristic of bi-stable composites. Furthermore, the desired broadband dynamics are obtained for lower input amplitudes when compared to previous designs constituting a significant improvement for energy harvesting applications. Several cross-well dynamic behaviours are obtained over a relatively wide range of frequencies with the proposed design. In addition, the performance of the developed concept is investigated using a switching shunt harvesting circuit suitable for conversion of broadband oscillations resulting from the cross-well dynamics exhibited by bi-stable composite laminates showing very good results.