Sasi, B., B. Rao, and T. Jayakumar. “Dual-Frequency Eddy Current Non-Destructive Detection of Fatigue Cracks in Compressor Discs of Aero Engines”. Defence Science Journal, Vol. 54, no. 4, Oct. 2004, pp. 563-70, doi:10.14429/dsj.54.2069.