Generation of electrical energy for portable devices Comparative study of an electromagnetic and a piezoelectric system

This paper presents the comparative study of two different electromechanical systems, in order to conceive autonomous portable generators capable of harvesting human mechanical energy. The first one is an electromagnetic system, made of a magnet in translation within a coil. The second one is a piezoelectric system, which is a PZT ceramic bar, polarised longitudinally, embedded at one end and constrained at the other end. The analytical models described in this paper present a high similarity and a duality in signal levels, adapted load and optimal working frequency, the two latters corresponding to the maximal electrical power generated. (C) 2004 Elsevier B.V. All rights reserved.