Guided waves for SHM applications

Substitution of metal constructions by fiber composite materials is gaining tremendous reductions in weight of technical structures. The advantages for e.g. aircrafts are obviously in the reduction of fuel consumption. On the other hand new maintenance techniques are required. That leads to development of structural health monitoring systems worldwide. In this paper a monitoring system based on acoustic detection methods containing distributed sensor nodes is presented. Passive and active acoustic monitoring concepts are explained for guided wave detection of delamination and impacts. Applied and integrated PZT bulk and fiber ultrasonic transducers and corresponding electronics are presented. The electronics consist of a 3D package of printed circuit boards containing amplifier, digitalization signal processing and transmission units. Finally applications for distributed sensor systems are given. Several work performed at the Fraunhofer Institute IZFP Dresden on photo and particle acoustic methods is presented. It includes both, modeling activities by an explicit numerical method (CEFIT) and experimental work. The given examples of applied excitations are photons (Laser acoustics) and electrons (Scanning Electron Acoustic Microscopy, SEAM). Both, time resolved measurements by pulse excitation as well as monofrequent measurements by periodic excitation together with signal recovery (lock-in technique) are discussed.