WIN & Systems Design Engineering Joint Seminar - Professor Muhammad R. Hajj "Identification of Nonlinear Piezoelectric Coefficients"

In this joint WIN-System Design Engineering Seminar, Dr. Muhammad R. Hajj will discuss his work on identification of nonlinear piezoelectric coefficients.

Abstract

Attention to piezoelectric materials has increased dramatically in recent years. This interest rises from the potential for their use in many applications for various objectives. They have been suggested for developing self-powered micro systems and sensors, active-passive vibration control and damping systems, energy harvesters, and impedance based structural health monitoring devices. In more recent studies, piezoelectric/ceramic materials have been proposed in biomedical applications such as wearable sensors for knee joints and harvesters to oxygenate tumors and charge pacemakers. Extending the realm of applications of piezoelectric materials comes with a price, as large strains can cause the material to behave in a nonlinear manner and exhibit amplitude-dependent resonant frequencies, sub- and super-harmonics in the response, saturation phenomena, and hysteretic behavior. As such, identification of the nonlinear electromechanical constitutive relation must be performed to design, analyze, optimize and/or exploit such behaviors.

We discuss a parameter identification scheme that exploits the vibration response of an energy harvester to estimate parameters representing nonlinear piezoelectric coefficients. We develop the governing equations of a beam with tip mass and piezoelectric layer using generalized Hamilton's principle and accounting for mechanical energy, virtual work and electric enthalpy. We then use the method of multiple scales to determine the approximate solution of the response to a direct resonant excitation. We show that the nonlinear behavior captured by the method of multiple scales in the form of an approximate solution and amplitude and phase modulation equations can be used to identify parameters of the nonlinear piezoelectric constitutive relations.

Biography

Muhammad R. Hajj is the J. Byron Maupin Professor of Engineering at Virginia Tech. He is a faculty member in the Department of Biomedical Engineering and Mechanics and the Associate Dean of the Graduate School. He is also the Director of the NSF I/UCRC Center for Energy Harvesting Materials and Systems (CEHMS). His research has been funded by many government agencies and industry. He has spent summer fellowships at NASA Langley Research center and the AFRL at Wright-Patterson Air Force Base. He has advised 24 PhD students to completion. He has given keynote and invited lectures at several international workshops and conferences. Dr. Hajj is a Fellow of the Engineering Mechanics Institute. He received a B. Eng. degree (with distinction) from the American University of Beirut and M.S. and Ph.D. degrees in Civil Engineering from the University of Texas at Austin. He joined Virginia Tech in 1992 after spending two years as a Research Scientist in the Department of Aerospace Engineering and Engineering Mechanics at the University of Texas at Austin. In July 2018, he will join Stevens Institute of Technology as Chair of the Department of Civil, Environmental, and Ocean Engineering and as Director of the Davidson Laboratory.