Piezoelectric Energy Harvesting Devices (PEHDs) for the Development of Selfpowered Structural Health Monitoring Systems

Abstract

The underlying idea that guides the work presented in this dissertation is the vibration-based energy harvesting as an enabler for the successful development of self-powered sensors applied to long-term monitoring of civil structures. The energy requirement of the monitoring system has typically been solved by the installation of grid-connected sensors, which is a solution with a fixed additional economic and environmental cost difficult to maintain in the long term. In addition, the remote location of many structures makes mains power supply unfeasible. The novelty of this proposal is the self-supply of the sensors applying a totally clean energy collection system that uses the vibrations of the structures to generate energy. This vibration-based energy harvesting system makes use of devices in which the piezoelectric energy conversion mechanism takes place. The performance of piezoelectric energy harvesters is strongly dependent on the excitation source, represented by the vibration of the host structure. Numerous variants of these devices have been proposed in the literature but the most widely tested consists of a small cantilever beam with one/two layers of piezoelectric material (unimorph/bimorph configurations) and optionally a mass attached to the free end to move the resonance frequency towards some desired point (tuning) and/or amplify the conversion effect. The study of piezoelectric energy harvesting devices has been approached in this thesis with a twofold focus. On the one hand, the numerical modelling of composite beams such as those that constitute piezoelectric energy harvesting devices is addressed. A new formulation based on the Proper Generalized Decomposition method to solve the forced vibration problem in bi-dimensional laminated beams with piezoelectric layers is developed and validated. A harmonic space-frequency description of the dynamic problem is considered and a variable separation in the spatial domain is introduced. The result is a 2D solution in frequency domain with 1D computational complexity. On the other hand, more geared to practice, the feasibility of a piezoelectric vibration-based energy harvesting system for a real highway bridge is studied. A new semi-analytic formulation based on the measured traffic-induced vibration has been used to evaluate the available power from real vibrations of a bowstring highway bridge located in Palma del R´ıo, C´ordoba (Spain). Two different situations have been considered from which conclusions on the assessment of harvested power are drawn: i) operational vibration records with the bridge open to regular traffic, ii) ambient vibrations with the bridge closed to traffic.