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Structural Health Monitoring
with Piezoelectric Wafer Active Sensors


                Current research activities

Exact modeling of power and energy transduction for optimum design of structurally integrated thin-film active sensors

The project is to develop fundamental understanding and predictive modeling of power and energy transduction in structurally integrated thin-film active sensors. This transformative interdisciplinary research will cross the boundaries of engineering disciplines and will create the foundation for the mechatronics design for the development of energy-efficient SHM active sensors and systems. A coordinated approach is proposed to understand the fundamental aspects of ultrasonic power and energy transduction inside a hybrid system consisting of active material sensors on a load-bearing structure in the presence of multi-modal guided Lamb waves.

Self powered wireless sensor network for structural bridge health prognosis This project is focused on the use of fused sensor data with multiple sensor types to provide information related to the degradation state of the bridge structure and its correlation to a global performance index. The acoustic emission detection method will be combined with additional active sensor (piezoelectric wafer active sensor) to strengthen the damage detection process on the steel bridges. Though PWAS has been developed for thin wall aircraft structures, its application and development for thick steel bridge structures is novel. The structures will be scanned efficiently and cracks can be imaged remotely.
Modeling, simulation and sensing of progressive damage at multiple scales for performance prognosis in metallic and composite aero structures An integrated modeling-simulation-sensing research program for prognosis of composite and metallic components in aero-structures is being developed. The research efforts combine (a) recent advances in structural level modeling and simulation of load bearing capacity with cohesive zone modeling for flaw initiation and propagation, (b) a new physics-based material level modeling and predictive method for distributed damage accumulation in composites, and (c) multi-level sensing for characterization of in-situ damage detection in materials and structures.

                Past research projects

Lamb-wave interaction between piezoelectric wafer active sensor and host structure during structure health monitoring Structural health monitoring (SHM) addresses problems of aging structures, a major concern of the engineering community. Recently, damage detection through Lamb waves has proven to be an attractive option for SHM because it allows condition-based maintenance inspection instead of schedule driven inspections. Through Lamb wave detection, fewer numbers of sensor can be used to monitor a structure and to actively investigate the health of a structure system. One of the major limits to Lamb wave testing has been the use of bulky permanent transducers integrated in the structure. The introduction of piezoelectric wafer active sensors (PWAS) had helped to overcome this issue. PWAS can be bonded on the surface of the structure or embedded in it. The modeling and characterization of Lamb waves generation and sensing using surface-bonded/embedded piezoelectric wafer transducers for SHM has received little attention, and often the various parameters involved are chosen without mathematical foundation. Lamb wave detection techniques using structurally integrated PWAS for SHM is still in its formative years and little mathematical basis is provided for the choice of the various testing parameters involved such as transducer geometry, dimensions, location and materials, excitation frequency, and bandwidth among others. Few efforts have been made towards modeling Lamb-wave excitation and sensing using surface-bonded/embedded transducers. The objective of this work is to develop the concepts of the load transferred between actuator and structure, trough the bonding layer at frequencies were the wave modes have no more a linear displacement distribution across the thickness and more then two modes are present. The load derived will be uses to determine the PWAS tuning frequencies for an isotropic or composite plate. The research will also investigate Lamb waves scattering from flaws such as cracks through the boundary element method, in order to understand the mode conversion from complicated defect geometries.
Ferroelectric Thin-Film Active Sensor Arrays for Structural Health Monitoring The research objective is to develop the fabrication and optimum design of thin-film active sensor arrays for structural health monitoring applications. This interdisciplinary research will cross the engineering and science boundaries and will address the problem in a coordinated approach focused on understanding the fundamentals aspects of fabricating and using thin-film active sensors on typical structural materials.

In-situ Damage Detection using Piezoelectric Wafer Active Sensor Guided Waves Phased Array

This research is focused on using piezoelectric wafer active sensors (PWAS) to construct guided Lamb-wave phased arrays for in-situ structural health monitoring. A unique feature of this method, which makes it essentially different from the traditional piezoelectric phased arrays, is that the PWAS phased array performs virtual scanning by steering the beam through a signal post processing procedure. Generic beamforming formulas for using PWAS phased array are developed, followed with design, beamforming simulation, and practical implementations of PWAS phased arrays in 1-D and 2-D patterns. Advanced signal processing techniques are introduced to improve the phased array performance and detection capability. Proof-of-concept laboratory experiments have successfully verified the potential of using PWAS phased arrays for damage detection and structural health monitoring of plate and shell-type thin-wall structures.