Prasad et al [2004] have looked into the possibility of constructing tomograms from a network of sensors generating and sensing Lamb waves in thin, multi-layered, anisotropic composite plates. Lamb wave tomography offers a new dimension to the challenging field of in situ health monitoring of structures. The improved tomogram results when the anisotropic and attenuative characteristics of composite plates are accounted for by using the newly identified energy of the earliest Lamb wave signals as the reconstruction parameter. Normalizing the Lamb wave energy data of the defective sample with respect to that of the defect-free sample, they have concluded that the energy of the early part of the Lamb waveform is an effective parameter for tomographic reconstruction and narrow bandwidth transducers such as PZT crystals excited by tone burst signals are found to be more suitable than commercial transducers which have larger bandwidths.

Wang et al [2005] have investigated the interaction between a crack of a cantilevered composite panel and aerodynamic characteristics by employing Galerkins method in coupled bending and torsion modes. Iwasaki et al [2004] have implemented unsupervised statistical damage detection method for delaminated composite beams. Takeda [2001] has presented an overview of structural health monitoring project for smart composite structure systems as a university-industry collaboration program. The range of studies has indicated that there is a strong correlation between the extent of damage and reduction in natural frequencies, particularly in the low frequency range for laminated composites. It has also revealed that frequency response method is more suitable for such analysis and recommended a combined analysis based on finite element upgradation and experimental modal analysis. Studies related to the use of different sensors and information fusion based on the reliability of each sensor is still a gray area of research.