Frequency Modulated Thermal Wave Imaging for Non destructive Testing

Ravibabu Mulaveesala1 and Masahiro Takei2

1 Electronics and Communication Engineering Research Group, PDPM­Indian Institute of Information Technology Design and Manufacturing, Jabalpur, Megwan, Dumna, Jabalpur, India­482005 ravibabucareiitd@yahoo.co.in

2 Dept. of Mechanical Engineering, College of Science and Technology, Nihon University, Kanda Surugadai, Chiyoda­ku, Tokyo, 101­8308, Japan

masa@mech.cst.nihon­u.ac.jp

ABSTRACT

Increased demand for greater sub­surface probing in InfraRed Non­Destructive Testing (IRNDT), for subsurface sensing is often thwarted by the requirement of high speed IR cameras and very high peak power heat sources. Present approach highlights subsurface exploration based on pulse compression approach. This offers a means of increasing average power available to illuminate test specimen without any loss of the depth resolution needed for the tactical requirements. This is accomplished by transmitting a long duration pulse, in which the incident heat flux is frequency modulated and then, by adopting correlation based method on the captured temporal data. This leads to a time compression of the received signal to a much narrower pulse of high effective peak power. For the demonstration, a mild steel sample having flat bottom holes at various depths is introduced. And detection capability of the proposed correlation based approach has been studied, by considering the full width at half power points of the compressed pulses, from various defects.

Keywords Thermal waves; Non stationary signals; Correlation; Thermal non­destructive testing