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Nowadays, environmental energy resources, especially mechanical vibrations, have attracted the attention of researchers to provide energy for low-power electronic circuits. A common method for environmental mechanical energy harvesting involves using piezoelectric materials. In this study, a spiral multimode piezoelectric energy harvester was designed and fabricated. To achieve wide bandwidth in low frequencies (below 15 Hz), the first three resonance frequencies of the beam were designed to be close to each other. To do this, the five lengths of the substrate layer were optimized by the Taguchi method, using an L27 orthogonal array. Each experiment of the Taguchi method was then simulated in ANSYS software. Next, the optimum level of each design variable was obtained. A test rig was then constructed based on the optimum design values and some experimental investigations were conducted. A good correlation was observed between measured and the finite element results. [ABSTRACT FROM AUTHOR]

In this paper, an analytical approach was used to formulate for gathering energy from ambient sources of vibrations. The apparatus consists of a cantilevered beam harvester with a piezoelectric patch. A coupled electromechanical modal model based on Euler–Bernoulli theory is used. The governing equations were extracted using Hamilton’s principle and then were discretized by using the Rayleigh–Ritz approach. The expected value of the electrical power output was obtained for a weakly stationary, Gaussian bandpass with zero mean base excitation. Next, a numerical solution for the beam under band-limited ambient random acceleration as the input was calculated and validated by experiment. The numerical results closely correlated to the experimental data with a deviation of about 10%. [ABSTRACT FROM AUTHOR]

• Energy harvesting from moving harmonic and continuous mass on simply supported beam. • Theoretical and experimental study of energy harvesting from moving mass. • Increase in the harvested power by adding the mass and the speed of the moving part. • Decrease in the harvested power by increasing the length of moving continuous mass. In this paper, energy harvesting from a simply supported beam using piezoelectric materials has been performed. Two different models for the moving objects were considered. First, the passing object was modeled as a concentrated mass with some amount of unbalances. The coupled governing equations of the beam, the piezoelectric patch, and the moving mass were obtained and discretized using assumed mode method. The beam response and the output voltage were calculated for different values of moving mass and unbalances. In the second model, the passing object was studied as a distributed mass. The governing equations of the system were extracted at three stages, namely entrance, main, and exit of the object from the beam. To validate the numerical findings, two test setups were erected, and the beam midpoint deflection and the piezoelectric power were measured experimentally. A good degree of correlation was found between numerical and measured values. [ABSTRACT FROM AUTHOR]

The coupling between polarization and strain gradients is called flexoelectricity. This phenomenon exists in all dielectrics with any symmetry. In this paper, energy harvesting from a Timoshenko beam is studied by considering the flexoelectric and strain gradient effects. General governing equations and related boundary conditions are derived using Hamilton's principle. The flexoelectric effects are defined by gradients of normal and shear strains which lead to a more general model. The developed model also covers the classical Timoshenko beam theory by ignoring the flexoelectric effect. Based on the developed model, flexoelectricity effect on dielectric beams and energy harvesting from cantilever beam under harmonic base excitation is investigated. A parametric study was conducted to evaluate the effects of flexoelectric coefficients, strain gradient constants, base acceleration and the attaching tip mass on the energy harvested from a cantilever Timoshenko beam. Results show that the flexoelectricity has a significant effect on the energy harvester performance, especially in submicron and nano scales. In addition, this effect makes the beam to behave softer than before and also it changes the harvester first resonance frequency. The present study provides guidance for flexoelectric nano-beam analysis and a method to evaluate the performance of energy harvester in nano-dielectric devices. [ABSTRACT FROM AUTHOR]

This paper aims to investigate the amount of energy which can be harvested by a cantilever beam type piezoelectric energy harvester from a bridge vibration. The sources of vibration are vehicles traversing the bridge. Two types of masses are considered as models for traversing vehicles: concentrated and distributed masses. The mass of the harvester is assumed negligible compared to that of the bridge. First, the problem of moving mass travelling with a constant speed over a beam is considered. The formulations for both concentrated and distributed masses are presented. The obtained results are then compared to the data available in the literature, in order to validate the model of a beam with a moving mass. Next, a mathematical model for the harvester is proposed, which is composed of an Euler–Bernoulli beam as a substrate, a tip mass, and a single piezoelectric patch whose electrodes are connected to a changeable resistance. To validate the model, the harvester is fabricated and tested on a shaker. The electroelastic frequency response functions of the system are measured by low-amplitude chirp excitation tests. The optimal resistive load at the resonance frequency, obtained from theory and experiments, are compared. Finally, the acceleration time histories for the beam at mid-span, where the harvester is located, are calculated for two mass types and used as base excitation signals to the harvester. These signals are replayed on an electromagnetic shaker to simulate the bridge vibrations on the fabricated harvester and the experimental results are compared with theoretical ones. Good agreement is observed. [ABSTRACT FROM AUTHOR]