J.M. McCarthy

The Effect of the Configuration of the Amplification Device on the Power Output of a Piezoelectric Strip

We investigated the behaviour of a polyvinylidene-fluoride piezoelectric strip (‘stalk’) clamped at the leading edge, and hinged to an amplification device (‘leaf’) at the trailing edge. Flutter of this cantilevered system was induced within smooth, parallel flow, and an AC voltage was generated from the PVDF strip. A polypropylene, triangle comprised the leaf. Two leaf parameters were varied so as to quantify their effect on the power output of the system: 1) the area, and 2) the aspect ratio. It was found that the highest power output was realised with the 2nd-largest leaf across a range of wind speeds, but the variation in power measurements was large. Thus, the 3rd-largest leaf was found to give the highest power output with the lowest power variation. This leaf area was then fixed and the aspect ratio varied. It was found that the largest aspect ratio-leaf rendered the highest power output, but had a relatively high start-up wind speed.Copyright

Dual field finite element simulations of piezo-patches on fabrics: a parametric study

There is an increasing demand for powering on-person-devices (for communications, health-care purposes, and soldier protection) without the burden of the parasitic weight and toxicity of conventional batteries. This demand calls for an alternative power source from fibre-sized piezoelectric generators that can be integrated into garments. These piezopatches convert human movement induced mechanical strain on the fabric into electrical energy. In this paper, a dualfield computational analysis, combining harmonic and piezoelectric models, has been undertaken using the ANSYS Finite Element package. A Polyvinylidene Fluoride (PVDF) patch bonded to a material representative of a flexible fabric has been modeled in ANSYS. The electrodes are connected to a resistor that is matched to the piezo properties and loading conditions. The parametric variables used in this study include: surface area of the piezo-patches, aspect ratio, input force amplitude and the operational frequency. The complex interaction of these variables to the power output is explored and discussed in the context of the intended application. It is observed that the maximum output occurs at 5Hz for an optimal dimension of 400mm2 which makes it feasible as an energy harvesting system for low energy selfpowered electronics such as portable and wearable medical and communication devices.

Investigation of Asymmetrical Configurations for Piezoelectric Energy Harvesting From Fluid Flow

Energy harvesting from wind-induced flutter using piezoelectric Polyvinyledene Fluoride (PVDF) was investigated. Previous studies suggested that coupled bending-torsion mechanical vibrations were capable of producing about 30% more power output compared to a pure bending case. In this work, asymmetrical configurations, with amplification devices hinged to the PVDF, capable of bending-torsion vibrations were investigated for energy harvesting from fluid flow. Results indicated that asymmetrical configurations, when excited by fluid flow, were more prone to chaotic flapping and hence provided lower power output compared to a symmetrical harvester. Also, asymmetrical configurations were more prone to fatigue due to excessive non-linear strains. A detailed study of the power output, flutter behavior, piezoelectric operating modes and their limitations are provided in this work.Copyright

Energy Harvesting from Flows Using Piezoelectric Patches

The highly nonlinear phenomenon of fluid–structure interaction is discussed, including examples drawn from nature and early work on aircraft flutter. Recent work on extracting the energy in a fluid stream by piezoelectric elements is reviewed, including some of the underlying physics. Whilst the energy extracted from fluttering elements is low, it is a subject of interest for powering Ultra-Low Power (ULP) devices and systems since this method of energy extraction is thought to offer a quiet alternative to conventional wind turbines. Researchers have investigated the use of thin piezoelectric patches coupled to a geometrically shaped, polymeric membrane (via a revolute hinge) which can amplify the bending, strain and hence power. Such systems respond via flutter induced by resonant bending instability of the system, or by the utilisation of time-varying external pressure gradients formed around the system. Key factors that influence performance are examined, such as critical flutter speed, mass ratio, position of revolute hinge, aspect ratio and type of piezoelectric material. The chapter concludes with a discussion of the practical implications of such systems in the future.