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Publication Title | A micro electromagnetic generator for vibration energy harvesting

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IOP PUBLISHING JOURNAL OF MICROMECHANICS AND MICROENGINEERING

J. Micromech. Microeng. 17 (2007) 1257–1265 doi:10.1088/0960-1317/17/7/007

A micro electromagnetic generator for vibration energy harvesting

S P Beeby1, R N Torah1, M J Tudor1, P Glynne-Jones1, T O’Donnell2, C R Saha2 and S Roy2

1 School of Electronics and Computer Science, University of Southampton, Highfield, Southampton, Hampshire, SO17 1BJ, UK

2 Tyndall National Institute, Prospect Row, Cork, Republic of Ireland

E-mail: spb@ecs.soton.ac.uk

Received 22 March 2007, in final form 6 May 2007 Published 5 June 2007

Online at stacks.iop.org/JMM/17/1257

Abstract

Vibration energy harvesting is receiving a considerable amount of interest as a means for powering wireless sensor nodes. This paper presents a small (component volume 0.1 cm3, practical volume 0.15 cm3) electromagnetic generator utilizing discrete components and optimized for a low ambient vibration level based upon real application data. The generator uses four magnets arranged on an etched cantilever with a wound coil located within the moving magnetic field. Magnet size and coil properties were optimized, with the final device producing 46 μW in a resistive load of 4 k from just 0.59 m s−2 acceleration levels at its resonant frequency of 52 Hz. A voltage of 428 mVrms was obtained from the generator with a 2300 turn coil which has proved sufficient for subsequent rectification and voltage step-up circuitry. The generator delivers 30% of the power supplied from the environment to useful electrical power in the load. This generator compares very favourably with other demonstrated examples in the literature, both in terms of normalized power density and efficiency.

(Some figures in this article are in colour only in the electronic version)

1. Introduction

Wireless sensor systems are receiving increasing interest since they offer flexibility, ease of implementation and the ability to retrofit systems without the cost and inconvenience of cabling. Furthermore, by removing wires there is the potential for embedding sensors in previously inaccessible locations. At present, the majority of wireless sensor nodes are simply battery-powered. Despite measures such as low power techniques for communicating (e.g. IEEE 802.15.4 and Zigbee protocols) and the intelligent management of the sensor node’s power consumption, batteries will still require periodical replacement. Replacing batteries is not compatible with embedded applications nor is it feasible for networks with large numbers of nodes.

The advances made in low power wireless systems present an opportunity for alternative types of power source. Solutions such as micro fuel cells [1] and micro turbine generators [2] are capable of high levels of energy and power density.

However, they involve the use of chemical energy and require refuelling. Energy harvesting approaches that transform light, heat and kinetic energy available in the sensor’s environment into electrical energy offer the potential of renewable power sources which can be used to directly replace or augment the battery. Such renewable sources could increase the lifetime and capability of the network and mitigate the environmental impact caused by the disposal of batteries. In this context, solar power is the most well known.

The subject of this paper is a kinetic energy generator which converts mechanical energy in the form of vibrations present in the application environment into electrical energy. Kinetic energy is typically converted into electrical energy using electromagnetic, piezoelectric or electrostatic transduction mechanisms [3]. Vibrations are an attractive source since the energy present can be harvested by compact inertial devices that benefit from a high Q-factor amplifying the base excitation amplitude. Suitable vibrations can be found in numerous applications including common household goods

0960-1317/07/071257+09$30.00 © 2007 IOP Publishing Ltd Printed in the UK 1257

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