For the past five years, cantilevered beams with piezoceramic layer(s) have been frequently used as piezoelectric energy harvesters for vibration-to-electric energy conversion. Typically, the energy harvester beam is located on a vibrating host structure and the dynamic strain induced in the piezoceramic layer(s) results in an alternating voltage output across the electrodes. Vibration modes of a cantilevered piezoelectric energy harvester other than the fundamental mode have certain strain nodes where the dynamic strain distribution changes sign in the direction of beam length. It is theoretically explained and experimentally demonstrated in this paper that covering the strain nodes of vibration modes with continuous electrodes results in strong cancellations of the electrical outputs. A detailed dimensionless analysis is given for predicting the locations of the strain nodes of a cantilevered beam in the absence and presence of a tip mass. Since the cancellation issue is not peculiar to clamped-free boundary conditions, dimensionless data of modal strain nodes are tabulated for some other practical boundary condition pairs and these data can be useful in modal actuation problems as well. How to avoid the cancellation problem in energy harvesting by using segmented electrode pairs is described for single-mode and multimode vibrations of a cantilevered piezoelectric energy harvester. An electrode configuration-based side effect of using a large tip mass on the electrical response at higher vibration modes is discussed theoretically and demonstrated experimentally.

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The long composite blades on large wind turbines experience tremendous stresses while in operation. There is an interest in implementing structural health monitoring (SHM) systems inside wind turbine blades to alert maintenance teams of damage before serious component failure occurs. This paper proposes using an energy harvesting device inside the blade of a horizontal axis wind turbine to power a SHM system. The harvester is a linear induction energy harvester placed radially along the length of the blade. The rotation of the blade causes a magnet to slide along a tube as the blade axis changes relative to the direction of gravity. The magnet induces a voltage in a coil around the tube, and this voltage powers the SHM system. This paper begins by discussing motivation for this project. Next, a harvester model is developed, which encompasses the mechanics of the magnet, the interaction between the magnet and the coil, and the current in the electrical circuit. A free fall test verifies the electromechanical coupling model, and a rotating test examines the power output of a prototype harvester. Copyright © 2013 John Wiley & Sons, Ltd.

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