Name of Guide :Dr. Balaji Srinivasan
Year of Joining: 2016
Research Topic: Structural Health Monitoring of Composites using Fiber Bragg Gratings
Position: PhD

• Pursued B.Tech in Electronics and Instrumentation at Sree Vidyanikethan Engg College, Tirupathi, AP in 2013.
• Pursued M.Tech in Instrumentation at National Institute of Technology Kurukshetra, Haryana in 2016.

Structure health monitoring (SHM) plays a vital role in the Aerospace industry. Defect identification is an integral part of such structural health monitoring. The usage of composites in aircraft is increasing rapidly due to their favourable properties like light weight and stifness. However, unlike metals, these composites may give little or no warning before failing. These material failures like delamination will cause severe damage. Using guided waves and embedding Fiber Optic Sensors (FOS) in laminates will help to detect the material defects at an earlier stage thereby avoiding severe damage. Structural health monitoring of composites has been demonstrated through several techniques including monitoring of curing, the presence of delamination, measuring stiness of composite plates and other mechanical properties. For these techniques, interrogation with ultrasonic guided waves are attractive as it provides the facility for defect identification and localization. However, the exact position and length of delamination is dicult to estimate as guided waves generated in composites are attenuated much before they reach the sensor. Among FOS, Fiber Bragg Grating (FBG) based sensors are widely adopted in SHM due to their rugged wavelength-encoded transduction mechanism, immunity to EM waves, multi-parameter sensing including temperature and strain, small size and less cost compared to conventional sensors. A novel technique for detecting the defects such as dis-bonding and delamination in the composites would be to excite ultrasonic modes in the embedded optical ber containing the FBG sensor.

As a regular research scholar, there was a time in my life nothing was turning up properly. One fine day I decided to visit my granny’s house. We had good food and talked a lot. And then she started asking me about my research. In my mind I thought, again we are going to have a problem,
I told her ” I am working on nondestructive testing of complex structures using ultrasonic guided waves and fiber Bragg gratings.”

She looked at me for few extra seconds and said:” wow, brilliant and perfect I never previously heard such a clear explanation”

I understood that. This was not the correct way to explain my research. So I gave another shot, this time I used an analogy.

I said ”I am a doctor for structures like aeroplanes, ships, tank floor, bridges etc. Generally, these structures are non-living and they don't have heartbeats. So I create artificial heartbeats in these structures and use a special stethoscope made of glass to listen to them. Based on their heartbeats, I can tell whether the structure is defective.”

This time granny was interested, that I could see from her face, she asked me with curious ” but why this is so important ?”

I explained to her ” Generally In aeroplanes, a small defect may lead to catastrophic failure of the structure and subsequent loss of life. These techniques will avoid such incidents”

After listening to my explanation, she brought some of her crockeries and asked me to check if they are good ones.

1. Tabjula, JL, Kanakambaran, S, Kalyani, S, Rajagopal, P, Srinivasan, B. Outlier analysis for defect detection using sparse sampling in guided wave structural health monitoring. Struct Control Health Monit. 2021;e2690.
2. T. L. Jagadeeshwar, B. Srinivasan and P. Rajagopal, “Visualisation of wave propagation using Reduced Number of Samples” In Proceedings of the National Conference on NDE, Bengaluru, 2019.
3. Abhinav Agarwal, Tabjula Jagadeeswar, Srijith Kanakambaran, Mohit Shrivastava and Balaji Srinivasan, “Acoustic Emission-Based Leakage Detection System using Coherent Optical Time Domain Reflectometry (COTDR)”,ICOL-2019, Dehradun, 2019
4. T. L. Jagadeeshwar, P. Rajagopal and B. Srinivasan, "Detection of Guided Waves in a Composite Plate Using Surface Bonded Fiber Bragg Gratings Sensor," 2018 IEEE SENSORS, New Delhi, 2018, pp. 1-4
5. T. L. Jagadeeshwar, B. Srinivasan and P. Rajagopal, “Generation of Ultrasonic Guided Waves in Optical Fiber and Reception using Fiber Bragg Gratings Sensor,” In Proceedings of the National Conference on NDE, Mumbai, 2018.
6. T. L. Jagadeeshwar, B. Srinivasan and P. Rajagopal, “In-Situ Cure Monitoring of GFRP Composite using Fiber Bragg Gratings,” In Proceedings of the National Conference on NDE, Chennai, 2017.