Less is more in piezoelectric energy harvesting

Engineerblogger
March 12, 2012

Piezoelectric materials can harvest energy from vibrations,
such as the slight movement of a footbridge as pedestrians
walk across it (image courtesy of iStockphoto)

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.

Markys Cain, one of NPL's leading scientists, who is working on the project said:

"The energy harvesting market was worth $605 million in 2010 but is predicted to reach $4.4 billion by 2020. For the market to reach its true potential we need to develop the products that can guarantee a greater energy yield and drive industrial adoption of energy harvesting products. The work undertaken by the Functional Materials Group at NPL will do exactly that, providing a model for more efficient piezoelectric energy harvesting methods."

Read the paper, Charge redistribution in piezoelectric energy harvesters, published in Applied Physics Letters 100, 073901 (2012).

Source: National Physics Laboratory (NPL)