Localization of scattering sources via active ultrasonic inspection in plate-like structures requires knowledge of the structure's dispersion relation and material properties. Often the dispersion relation and material properties are unknown, uncertain, or difficult to model due to material complexity and variability in material properties, geometry, and/or environment, thereby requiring in situ estimation. Two methods are presented for estimating guided wave dispersion curves (phase and group velocity) in a multimodal, multipath environment using a phased array. Phase and group velocities are estimated in situ on an aluminum and carbon fiber plate and compared to theoretical values. Scattering from plate boundaries is localized using the estimated phase and group velocity curves through beamforming and ranging via time of flight. © 2013 The Author(s).

The detection and localization of damage using an array of closely spaced transducers is investigated theoretically and experimentally using single- and multiple-mode guided wave active sensing models. Detectors are derived using a generalized likelihood ratio approach assuming that amplitude, absolute phase, and source location of a scattered wave are unknown, while frequency, group velocity, and phase velocity are known. Theoretical detection performance for processing with each detector is derived and related to the energy-to-noise ratio of a scattered mode as a metric of determining when processing with multiple modes provides increased performance over processing with a single mode. Experimentally, detectors are implemented to detect scattering from a small mass glued to the surface of an aluminum plate with a 7 × 7 array of transducers. Relative detection and localization performance is compared through receiver operating characteristic curves and histograms of distance from true damage location for 1000 no-damage and damaged measurements. A single-mode, multi-frequency detector is shown to have the best detection and localization performance for the tested damage scenarios. © The Author(s) 2013.