Piezoelectric materials convert electrical energy into strain, or vice versa.
These materials are used to harvest energy from everyday mechanical vibrations -- such as an air conditioning unit rattling, or a footbridge vibrating as pedestrians walk across it.
Generally power levels are low, but the environmental benefit of the technology is to replace batteries, and the associated costs of replacement, rather than saving energy per se. For example, researchers are looking to use the technology to power implanted medical devices, where the cost of the operation far outweighs the battery costs.
Piezoelectric energy harvesters are usually vibrating cantilevers covered with a layer of piezoelectric material. The piezoelectric material converts the mechanical strain (e.g. vibrations) into a charge that can power an electrical device. Typically the entire length of the cantilever is covered with piezoelectric material as you would imagine that this would harvest the most energy.
However, NPL scientists have found that, surprisingly, reducing the amount of piezoelectric material covering the cantilever increases the power output. To get the most energy out you only need to cover the cantilever for two thirds of its length.
NPL is working on this European Metrology Research Programme project with seven other national measurement institutes.
- Mark Stewart, Paul M. Weaver, Markys Cain. Charge redistribution in piezoelectric energy harvesters. Applied Physics Letters, 2012; 100 (7): 073901 DOI: 10.1063/1.3685701
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