Our research group works in the general area of structural health monitoring (SHM), which is continuous or autonomous monitoring of the structural integrity of systems, structures, and materials and any subsequent intervention. SHM is a vital technology for reliability critical systems. There are four intended outcomes of SHM: maintain safety, improve asset readiness for service, decrease overall life cycle costs, and spur a paradigm shift in design. Our group focuses on using ultrasonic guided waves to detect, locate, and classify damage as well as estimate the extent of damage. This information can be used to shift from schedule based maintenance to condition based maintenance and to predict remaining useful life. SHM is extremely multidisciplinary, requiring us to innovatively synthesize solutions based on knowledge of: material behavior, degradation, and failure; propagation of ultrasonic waves in waveguides; finite element analysis; sensory materials like piezoelectrics, transducers, and arrays of transducers; signal processing and data analysis; damage visualization and pattern recognition. In addition, we research and develop solutions for the allied field of nondestructive evaluation and testing. Applications for our research are abundant and diverse, including for example aircraft, power generation equipment (turbines, pumps, gear boxes), energy distribution systems, pressure vessels, bridges, pavement, buildings, ships, and rail. Some of our recent research projects focus on delaminations in composite materials, degradation of adhesively bonded joints, characterization of fatigue cracks near fastener holes, development of optimal transducers, real-time phased arrays for ultrasonic beam steering, and tomographic imaging. A current thrust is nonlinear ultrasonic guided waves for microstructure characterization.