Piezoelectric Energy Harvesting PZT products can be deformed


repeatedly to generate energy and power devices, with typical applications being sensors and industrial equipment. The piezoelectric effect was discovered by Jacques and Pierre Curie in 1880. The French brothers learned that by subjecting certain crystals to mechanical strain, they became electrically polarised, with the degree of polarisation proportional to the applied strain. The Curies also realised that these same materials deformed when exposed to an electrical field, which is now known as the inverse piezoelectric effect.


subjected to a heavy pressure must be exposed to a fast ‘impulse’ to ensure the charge does not dissipate quickly. Furthermore, the choice and design of the electronic recovery circuit is of equal importance. It is essential to carefully consider components to minimise leakage currents and increase energy transfer efficiency.


The advantages to piezoelectric energy harvesters are numerous. The process offers some of the highest efficiencies and power outputs by size and cost, and is therefore extremely appealing to those in search of


Pressure based energy harvesting


But how do piezoelectric ceramic materials generate power through the conversion of mechanical energy into electrical? The smallest of deformations can produce a measurable charge. As a result, a PZT cylinder can generate voltages that are high enough to draw a spark across an electrode gap. The energy created can then be stored in a capacitor and used to power a circuit or another application. However, there are a range of factors which govern the performance of any power generated in this way, including the shape of the PZT transducer, the style in which the transducer has been installed and the nature of the electrical load. For instance, a PZT disc that is


compressed between two metal surfaces will never be able to expand as readily as a long, narrow PZT cylinder, which is only constrained at its flat top and bottom ends, resulting in greater potential for the straight parallel sides to expand. Essentially, it is important to allow the material some freedom to expand radially, since energy generation is directly proportional to deformation. If the force that can be applied is limited, then the energy converted can be optimised by ensuring it is applied to a particular area where the material has the freedom to expand outwardly.


Another important consideration is the impedance – the measure of opposition to the flow of an alternating current – of the load. When the current is created, it is important to match the electrical impedance of the piezoelectric component to the electronic recovery system, in order to maximise the energy transfer to the reservoir capacitor. The charge must be allowed to flow away quickly, otherwise the electrical field generated will tend to dissipate through the electronic components. As a result, applications


www.cieonline.co.uk


an effective, high-performance solution. The environmental benefit is to substitute batteries and other means of charging, and their associated replacement costs, rather than solely focusing on saving energy. In terms of market opportunities in the


future, independent research from IDTechEx found that the energy harvesting market is expected to grow from £450m in 2012 to more than £950m by 2017. Tests are already being carried out for piezoelectric energy harvesters to be used in an extensive variety of applications. For instance, modules can be installed on roads or rail networks that react to heavy vehicles passing overhead, to generate energy that can be used to power LED lighting in signs or traffic lights. Industrial applications undoubtedly


represent the biggest opportunity for piezoelectric energy harvesters, with electrical charge harnessed from vibrations in an engine shaft being just one key example. Industrial environments, such as oil and gas and manufacturing, will find energy harvesting a cost-effective alternative to wired infrastructure, which can be expensive. One of the greatest future challenges for piezoelectric energy harvesting is the ability to convert energy from broadband frequencies, harnessing a number of different sources of vibrations at various frequencies to produce a consistent supply of electric charge. Nevertheless, the opportunities for piezoelectric energy harvesting going forward are considerable – an exciting prospect for those seeking efficient new ways of generating power.


Morgan Technical Ceramics | www.morgantechnicalceramics.com


Fred Pimparel, Technical Manager at Morgan Technical Ceramics


Components in Electronics May 2013 21


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