Rupesh Patel

A geometric parameter study of piezoelectric coverage on a rectangular cantilever energy harvester

This paper proposes a versatile model for optimizing the performance of a rectangular cantilever beam piezoelectric energy harvester used to convert ambient vibrations into electrical energy. The developed model accounts for geometric changes to the natural frequencies, mode shapes and damping in the structure. This is achieved through the combination of finite element modelling and a distributed parameter electromechanical model, including load resistor and charging capacitor models. The model has the potential for use in investigating the influence of numerous geometric changes on harvester performance, and incorporates a model for accounting for changes in damping as the geometry changes. The model is used to investigate the effects of substrate and piezoelectric layer length, and piezoelectric layer thickness on the performance of a microscale device. Findings from a parameter study indicate the existence of an optimum sample length due to increased mechanical damping for longer beams and improved power output using thicker piezoelectric layers. In practice, harvester design is normally based around a fixed operating frequency for a particular application, and improved performance is often achieved by operating at or near resonance. To achieve unbiased comparisons between different harvester designs, parameter studies are performed by changing multiple parameters simultaneously with the natural frequency held fixed. Performance enhancements were observed using shorter piezoelectric layers as compared to the conventional design, in which the piezoelectric layer and substrate are of equal length.

Optimization of piezoelectric cantilever energy harvesters including non-linear effects

This paper proposes a versatile non-linear model for predicting piezoelectric energy harvester performance. The presented model includes (i) material non-linearity, for both substrate and piezoelectric layers, and (ii) geometric non-linearity incorporated by assuming inextensibility and accurately representing beam curvature. The addition of a sub-model, which utilizes the transfer matrix method to predict eigenfrequencies and eigenvectors for segmented beams, allows for accurate optimization of piezoelectric layer coverage. A validation of the overall theoretical model is performed through experimental testing on both uniform and non-uniform samples manufactured in-house. For the harvester composition used in this work, the magnitude of material non-linearity exhibited by the piezoelectric layer is 35 times greater than that of the substrate layer. It is also observed that material non-linearity, responsible for reductions in resonant frequency with increases in base acceleration, is dominant over geometric non-linearity for standard piezoelectric harvesting devices. Finally, over the tested range, energy loss due to damping is found to increase in a quasi-linear fashion with base acceleration. During an optimization study on piezoelectric layer coverage, results from the developed model were compared with those from a linear model. Unbiased comparisons between harvesters were realized by using devices with identical natural frequencies—created by adjusting the device substrate thickness. Results from three studies, each with a different assumption on mechanical damping variations, are presented. Findings showed that, depending on damping variation, a non-linear model is essential for such optimization studies with each model predicting vastly differing optimum configurations.

Forced vibration experiments on flexible piezoelectric devices operating in air and water environments

In this paper, forced vibration experiments on flexible piezoelectric devices operating in both air and water environ- ments are discussed. Validation of the theoretical analysis method for such devices, via experimental means, is needed in order to achieve future cost effective design optimisations. In aim of this, numerous devices of differing dimensions are manufactured and tested, in various operating conditions, with comparison and discussion to simulation results provided.

Simply-supported multi-layered beams for energy harvesting:

This paper develops an analytical model for predicting the performance of simply-supported multi-layered piezoelectric vibrating energy harvesters. The model includes the effects of material and geometric non-linearities, as well as axial pre-tension/compression, and is validated against experimental devices for a large range of base accelerations. Numerical and experimental investigations are performed to understand the benefits of using simply-supported devices compared to cantilevered devices. Comparisons are made in an unbiased manner by tuning the resonant frequency to the same value by modifying the geometry, and the results obtained indicate that simply-supported devices are capable of generating higher voltage levels than cantilever devices. The model is also used to investigate the benefits of using multi-layered devices to improve power density. Depending on harvester composition, power-per-unit-volume of piezoelectric material for a device is increased through the stacking of layers.