Search

This article presents a probabilistic approach to investigate the effect of parametric uncertainties on the mean power, tip deflection, and tip velocity of linear and nonlinear energy harvesting systems. Recently developed conjugate unscented transformation algorithm is used to compute the statistical moments of the output variables with multidimensional Gaussian uncertainty in parameters. The principle of maximum entropy is used to construct the probability density function of output variables from the knowledge of obtained statistical moments. The probability density functions for mean power were significantly complicated in shape with two and three distinct peaks for the nonlinear monostable and nonlinear bistable harvesters, respectively. Monte-Carlo simulations with N = 8 × 104 samples for monostable harvester and N = 6.5 × 104 samples for bistable harvester were used for validating the probability density functions. It is concluded that conjugate unscented transformation methodology affords a significant computational advantage without compromising accuracy. In addition, using conjugate unscented transformation method, we show that the dependence of mean power on parameters (excitation frequency, excitation amplitude, etc.), when multidimensional uncertainties are present, is decidedly different relative to a purely deterministic trend. The discrepancy in predicted power between the deterministic and uncertain trends for the monostable harvester, for instance, reach a maximum of 100%, 234%, and 110% for base frequency, base acceleration, and magnet gap, respectively. The deterministic trend consistently overestimates the harvested power relative to the uncertain trends. This work, therefore, may have applications in evaluating “worst case scenario” for harvested power. The major advantage of the presented methodology relative to extant techniques in energy harvesting literature is the accurate and computationally effective applicability to multidimensional uncertainty in parameters. [ABSTRACT FROM AUTHOR]

A miniature nonlinear piezoelectric energy harvester is developed to power state of the art leadless cardiac pacemakers from cardiac motions. The energy harvester is integrated in the leadless pacemaker and is connected to the myocardium. The energy harvester converts myocardial motions to electricity to power leadless pacemakers. The energy is stored in a battery or supercapacitor and is used for pacing. The device is composed of a bimorph piezoelectric beam confined in a gray iron frame. The system is assembled at high temperature and operated at the body temperature. The mismatch in the coefficients of thermal expansion of the beam and the frame causes the beam to buckle in body temperature. This intentional buckling makes the beam unstable and improves the power production and robustness of the device. Having high natural frequency is a major problem in microelectromechanical systems energy harvesters. Considering the small size of the energy harvester, 0 . 5 c m 3 , the natural frequency is expected to be high. In our design, the natural frequency is lowered significantly using a buckled beam and a proof mass. Since the beam is buckled, the design is bistable and nonlinear, which could increase the output power. In this article, the device is analytically modeled, and the natural frequencies and mode shapes of the energy harvester are analytically derived. The terms corresponding to geometric nonlinearities are included in the electromechanical coupled governing equations. The simulations show that the device generates sufficient electricity to power leadless pacemakers. [ABSTRACT FROM AUTHOR]

Abstract: A nonlinear piezoelectric rotary transducer is developed that makes compact low speed wind generators realizable. Compact wind generators provide power to sensor nodes in remote or hard to reach locations. Since the locations of the sensor nodes are not optimized in terms of wind speed, the compact wind generators should be able to produce power from low speed wind. At smaller scales piezoelectric transduction becomes more effective than electromagnetic transduction. Therefore one way of realizing the compact wind turbines is by replacing the electromagnetic generator with a piezoelectric transducer. This work presents a novel piezoelectric transducer where the rotation of the blades results in large oscillations of piezoelectric beams. The piezoelectric bimorphs are made bi-stable by incorporation of repelling magnetic force. The Magnetic force is due to interaction of permanent magnets at the tip of the beams with permanent magnets rotating with the blades. Since the magnetic force changes with blade rotation, the dynamics of the beams changes in time and the system is thus parametrically excited. Two configurations are presented one called tangential configuration and the other is radial configuration. An 80 mm × 80 mm × 175 mm nonlinear piezoelectric wind generator can generate milliwatts of power from wind as slow as 2 ms−1. The proposed compact wind generators are experimentally investigated in two steps. First the piezoelectric transducer is examined through constant rotational speed tests. Second wind tunnel experiments are performed to characterize the entire wind generator. An analytical model is developed for the piezoelectric rotational transducer. The model is verified with the experimental results. The nonlinear phenomena captured by the experimental investigations are explained using the analytical model. The model is also used for more case studies identifying specifically the effect of parametric excitations. [Copyright &y& Elsevier]

Linear and nonlinear piezoelectric devices are introduced to continuously recharge the batteries of the pacemakers by converting the vibrations from the heartbeats to electrical energy. The power requirement of a pacemaker is very low. However, after few years, patients require another surgical operation just to replace their pacemaker battery. Linear low frequency and nonlinear mono-stable and bi-stable energy harvesters are designed according to the especial signature of heart vibrations. The proposed energy harvesters are robust to variation of heart rate and can meet the power requirement of pacemakers. [ABSTRACT FROM AUTHOR]

Abstract: A unified approximation method is derived to illustrate the effect of electro-mechanical coupling on vibration-based energy harvesting systems caused by variations in damping ratio and excitation frequency of the mechanical subsystem. Vibrational energy harvesters are electro-mechanical systems that generate power from the ambient oscillations. Typically vibration-based energy harvesters employ a mechanical subsystem tuned to resonate with ambient oscillations. The piezoelectric or electromagnetic coupling mechanisms utilized in energy harvesters, transfers some energy from the mechanical subsystem and converts it to an electric energy. Recently the focus of energy harvesting community has shifted toward nonlinear energy harvesters that are less sensitive to the frequency of ambient vibrations. We consider the general class of hybrid energy harvesters that use both piezoelectric and electromagnetic energy harvesting mechanisms. Through using perturbation methods for low amplitude oscillations and numerical integration for large amplitude vibrations we establish a unified approximation method for linear, softly nonlinear, and bi-stable nonlinear energy harvesters. The method quantifies equivalent changes in damping and excitation frequency of the mechanical subsystem that resembles the backward coupling from energy harvesting. We investigate a novel nonlinear hybrid energy harvester as a case study of the proposed method. The approximation method is accurate, provides an intuitive explanation for backward coupling effects and in some cases reduces the computational efforts by an order of magnitude. [Copyright &y& Elsevier]

This paper addresses an issue in energy harvesting that has plagued the potential use of harvesting through the piezoelectric effect at the micro-electro-mechanical systems (MEMS) scale. Effective energy harvesting devices typically consist of a cantilever beam substrate coated with a thin layer of piezoceramic material and fixed with a tip mass tuned to resonant at the dominant frequency of the ambient vibration. The fundamental natural frequency of a beam increases as its length decreases, so that at the MEMS scale the resonance condition occurs orders of magnitude higher than ambient vibration frequencies, rendering the harvester ineffective. Here, we propose a new geometry for MEMS scale cantilever harvesters with low fundamental frequencies. A "zigzag" geometry is proposed, modeled, and solved to show that such a structure would be able to vibrate near resonance at the MEMS scale. An analytical solution is presented and verified against Rayleigh's method and is validated against a macroscale experiment. The analysis is used to provide design guidelines and parametric studies for constructing an effective MEMS scale energy harvesting device in the frequency range common to low frequency ambient vibrations, removing a current barrier. [ABSTRACT FROM AUTHOR]

An analytical electromechanical model is proposed to predict the deflection, voltage, and the power output of a proposed low-frequency micro-harvesting structure. The high natural frequencies of the existing designs of micro-scale vibrational energy harvesters are serious drawbacks. A zigzag design is proposed to overcome this limitation. First, the natural frequencies and the mode shapes of the zigzag structure are calculated. The piezoelectric direct and reverse effect equations, together with the electrical equations, are used to relate the voltage output of the structure to the base vibrations magnitude and frequency. The closed-form solution of the continuous electromechanical vibrations gives the power output as a function of base acceleration spectrum. The usefulness of the design is proved by the significant increase of the power output from the same base accelerations, providing a method of designing a micro-scale harvester with low natural frequency. The optimal mechanical and electrical conditions for power generation are investigated through the case studies. [ABSTRACT FROM AUTHOR]

This research presents an experimental and theoretical energy harvesting characterization of beam-like, uniform cross-section, unimorph structures employing single-crystal piezoelectrics. Different piezoelectric materials, substrates, and configurations are examined to identify the best design configuration for lightweight energy harvesting devices for low-power applications. Three types of piezoelectrics (singlecrystal PMN-PZT, polycrystalline PZT-5A, and PZT-5H-type monolithic ceramics) are evaluated in a unimorph cantilevered beam configuration. The devices have been excited by harmonic base acceleration. All of the experimental characteristics have been used to validate an exact electromechanical model of the harvester. The study shows the optimum choice of substrate material for single-crystal piezoelectric energy harvesting. Comparison of energy scavengers with stainless steel substrates reveals that single-crystal harvesters produce superior power compared with polycrystalline devices. To further optimize the power harvesting, we study the relation between the thickness of the substrate and the power output for different substrate materials. The relation between power and substrate thickness profoundly varies among different substrate materials. The variation is understood by examining the change of mechanical transmissibility and the variations of the coupling figure of merit of the harvesters with thickness ratio. The investigation identifies the optimal thickness of the substrate for different substrate materials. The study also shows that the densities of the substrates and their mechanical damping coefficients have significant effects on the power output. [ABSTRACT FROM PUBLISHER]

This paper investigates the spin resonance of a rattleback subjected to base oscillations which is able to transduce vibrations into continuous rotary motion and, therefore, is ideal for applications in Energy harvesting and Vibration sensing. The rattleback is a toy with some curious properties. When placed on a surface with reasonable friction, the rattleback has a preferred direction of spin. If rotated anti to it, longitudinal vibrations are set up and spin direction is reversed. In this paper, the dynamics of a rattleback placed on a sinusoidally vibrating platform are simulated. We can expect base vibrations to excite the pitch motion of the rattleback, which, because of the coupling between pitch and spin motion, should cause the rattleback to spin. Results are presented which show that this indeed is the case—the rattleback has a mono-peak spin resonance with respect to base vibrations. The dynamic response of the rattleback was found to be composed of two principal frequencies that appeared in the pitch and rolling motions. One of the frequencies was found to have a large coupling with the spin of the rattleback. Spin resonance was found to occur when the base oscillatory frequency was twice the value of the coupled frequency. A linearized model is developed which can predict the values of the two frequencies accurately and analytical expressions for the same in terms of the parameters of the rattleback have been derived. The analysis, thus, forms an effective and easy method for obtaining the spin resonant frequency of a given rattleback. Novel ideas for applications utilizing the phenomenon of spin resonance, for example, an energy harvester composed of a magnetized rattleback surrounded by ferromagnetic walls and a small scale vibration sensor comprising an array of several magnetized rattlebacks, are included. [ABSTRACT FROM AUTHOR]