Plate elements are common engineering structures and it is important to monitor damage evolution in these plates to ensure the integrity of the structure. Due to stress concentration in the vicinity of existing defects such as voids, inhomogeneities and surface cracks, microfracture events may occur locally in a plate highly stressed before final failure takes place. As a result, the stored strain energy radiates out in the form of elastic waves which carry information regarding the nature of the source. Due to the highly dispersive character of Lamb waves, their forms change as the disturbance propagates away from the source, and understanding the characteristics of these waves is a prerequisite to extracting source information from measured waveform.