Design of a wireless active sensing unit for localized structural health monitoring

The recent years have witnessed an increasing interest in using wireless structural monitoring as a low-cost alternative to tethered monitoring systems. Previous work considered wireless sensors strictly as passive elements in the monitoring system, responsible only for collection of response measurements. This paper explores expansion of the wireless structural monitoring paradigm by including actuation capabilities in the design of a wireless active sensing unit. To validate the performance of the prototype unit in structural health monitoring applications, an aluminum plate monitored by piezoelectric active sensors is used. Piezoelectric actuators mounted to the surface of the plate are commanded by the wireless active sensing unit to excite and record the element. System identification models are then used to model the linear relationship between the input excitation and the corresponding plate response. A novel damage detection methodology is proposed that uses the characteristic equation roots obtained from an autoregressive with exogenous input time-series model. Complex roots (poles) of the model's characteristic equation are sensitive to structural damage causing a change in their location on the complex plane. Using the mean value of pole clusters, the migration of model poles are shown to be well correlated to the severity of crack damage intentionally introduced in the plate. Copyright (c) 2005 John Wiley & Sons, Ltd.