National prosperity and quality-of-life depend upon the massive infrastructure systems that service society.  For example, transportation networks move people and supply chain goods, pipelines deliver energy from source to consumer, while levees and dams protect urban environments from flooding.  Unfortunately, recent catastrophic events in the United States have revealed serious issues associated with the safety of infrastructure systems.  For example, the levees in New Orleans dramatically failed during Hurricane Katrina culminating in the loss of human life and the destruction of the built environment. Similarly, surveys of the national network of dams reveal 1,819 major dams with functional deficiencies which place the public at risk.  Aging and deterioration of infrastructure systems represents another major challenge for the engineering community.  Perhaps the best example of the challenges associated with aging infrastructure is the case of highway bridges.  Of the nearly 600,000 bridges in the United States, almost a quarter of them are consistently rated as structurally deficient or functionally obsolete.  While the number of “distressed” bridges is high, the economic resources available to address these safety concerns continues to decline.  For example, the Highway Trust Fund which finances upkeep of the transportation network will run a multi-billion dollar deficient by the end of 2009.  In addition to consuming economic resources, the endless cycles of build-rebuild commonly associated with infrastructure systems also comes with high environmental costs.  For example, concrete is one of the most popular materials used in the construction of infrastructure systems with over 12 billion tons produced every year; this represents 5% of greenhouse gases produced annually.  
 
The safety and sustainability of civil infrastructure systems can be dramatically enhanced through the adoption of structural health monitoring (SHM) systems.  SHM systems are envisioned to continuously monitor a structure and its environment using sensors, automatically interrogate sensor data to detect structural damage and degradation, and to offer tools for prognosis.  Unfortunately, SHM systems currently do not exist even though significant advances have been made in sensors and data acquisition technology over the past decade.  Undoubtedly, structural monitoring systems have existed for more than four decades with their use generally limited to seismic monitoring applications (i.e., record the behavior of critical structures to strong ground motion).  However, these monitoring systems simply record sensor data and make no efforts to automate the processing of sensor data.  In addition, these monitoring systems suffer from technological drawbacks that limit their extension to SHM applications.  For example, monitoring systems are designed using extensive lengths of coaxial wiring to transfer sensor data to a centralized data repository.  These wires are expensive and require significant manpower to install.  Another constraint is that centralization hinders the scaling of the traditional monitoring system to high sensor counts.  As such, new and radical approaches to the design of SHM systems are direly needed.