National Physical Laboratory

Efficiency measurement in piezoelectric vibration energy harvesters

Further Information

Published: 22 August 2013

Authors: P.M. Weaver, Maciej Rokosz, P. Woolliams, M.G. Cain

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Vibrational energy harvesters convert energy from vibrations and movement in the environment into electrical energy which can be used to power a device such as a wireless sensor node. The energy source is often considered as waste energy and energy harvesting performance is typically characterised by power output under specified conditions of vibration amplitude and frequency.

This takes no account of the energy extracted from or available from the source. This is important where account needs to be taken of the loading of the source by the harvester. This includes parasitic harvesting where the energy derived from the source is not free or wasted, and use of the energy harvester increases the power consumed by the source.

Examples include human or vehicle powered applications where it is the availability of the energy source rather than energy saving that is the main motivation. It is also important in situations where the power from the source is limited. In the! se cases, the ratio of power out to power in, or the efficiency needs to be known. Measuring efficiency is more complex than measuring power out under well-defined vibration conditions, because of the requirement to measure the power transferred from the source to the energy harvester.

Often the harvested power is a small fraction of the total power delivered by the system. We are not aware of any published reports of measurement of efficiency, although it is discussed in some mathematical models of energy harvesters. In this paper we describe an experimental method of measuring efficiency for resonant piezoelectric cantilever energy harvesters based on a damped oscillator response to an impulse input. Experimental results for typical energy harvesting devices are presented.

Last Updated: 6 Mar 2017
Created: 29 Apr 2013

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