Guided waves for structural health monitoring - Theory, system development, and applications

Traditional vibration-based monitoring techniques provide global information about the structure under investigation by identifying and analyzing specific resonance modes. Due to the low frequencies only large defects can be identified and moreover, cannot be precisely localized in general. For crucial parts of a structure, vibration monitoring can be efficiently supplemented by using elastic waves in the kHz frequency regime. These ultrasonic waves have a shorter range but are more sensitive to smaller defects and thus, can serve as an early-warning system raising an alarm long before critical damage occurs. If the wavelengths are comparable with or larger than typical dimensions of the structure, geometrical dispersion cannot be neglected. In this case, the waves are called "guided waves". In the present paper the theoretical foundations of guided wave propagation in various structures and their interaction with potential defects are reviewed and displayed by wave front pictures and animations. Moreover, the methodical concepts of active and passive monitoring systems based on acoustic signature analysis and acoustic emission techniques, respectively, are discussed and various examples of application are given. Finally, the integration of the monitoring system into a modular development platform based on Match-X micro-systems technology is presented by a technical demonstration parallel to the paper presentation.