Composites are fast gaining attention as structural materials due to overriding advantages over conventional metallic structures. Owing to their high specific strength and stiffness and very good corrosion and fatigue properties, they are increasingly being used in the design of light weight aerospace, automobile and civil structures. Further, there is an increasing application of advanced composites in varied fields such as marine structures, turbine blades, automobile bodies etc. This increase in usage of composites has raised the necessity for evaluating the in-service performance of such structures.

Due to greater complexity of design, high operational loads and longer lifetime, composite structures are prone to unpredicted failures. Present day non-destructive evaluation (NDE) techniques, such as ultrasonic testing, acoustic emission, eddy current method, radiography and thermography etc., primarily meant for metallic materials are not always very effective for composites because of inherent micro-mechanical complexities. Further, these methods require specialized equipments and skilled manpower. Many times, in-situ evaluation or evaluation on real time basis is not possible. Anisotropy of composites, conducting properties of the fibers, insulative nature of the matrices and unintentional impact damages beneath the surface which are barely visible (BVID) make the damage prediction still more difficult and challenging in composites. These damages may cause a change in strain / stress state of the structure. and hence, its characteristics. By continuously monitoring one or more response quantities causing these changes, it is possible to assess the condition of the structure for its structural integrity. Such a monitoring of the structure is generally known as Structural Health Monitoring. Health monitoring applications have received great deal of attention all over the world due to its significant impact on safety and longevity of the structures.