Experimental and theoretical investigations of Lamb wave excitation and sensing using piezo patch transducers and the laser vibrometer technique have been performed, aiming at the development of adequate mathematical and computer models for the interpretation of sensing data and for the choice of optimal parameters for structural health monitoring. The proposed models are validated by experimental results. Furthermore, a methodology is presented which allows for the determination of central frequencies at which maximal values of the structural response spectrum can be expected in the case of wave propagation monitoring with laser vibrometry.

Scanning laser vibrometry is a widely used tool to observe Lamb wave fields for structural health monitoring (SHM) purposes. Lamb waves propagate over long distances in thin-walled structures and interact with structural inhomogeneities, for example, damages, in spite of wavelengths several times of the damage size. In SHM of sheets and glass-or carbon-fibre-reinforced plastic plates, this effect is used for determining the position as well as the size of structural faults. With the often employed one-dimensional vibrometry, a geometrically induced, systematic error occurs when measuring oblique-angled motion. This error can be, in the specific case of Lamb waves, of a non-negligible quantity. The nature of this geometrical measurement error in general and concerning Lamb waves in special is discussed analytically for both amplitude and phase data. It is shown that this matter should be taken into account in some applications.

Development of a low frequency shear horizontal piezoelectric transducer for the generation of plane SH waves AIP Conference Proceedings 1706, 030019 (2016) Abstract: Lamb wave propagation in fiber-reinforced composite plates is featured by a pronounced directivity of wave energy transfer along the fibers from a point surface source. In the case of non-point (sized) source, the main lobe of radiation diagram may turn with frequency up to the orthogonal to the fibers direction. This effect has been theoretically studied and physically explained in the context of semi-analytical integral-equation based mathematical model. The present paper gives its experimental verification.

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