Radome Inspection Based on Ultrasonic Frequency Tomography and Ultrasonic Energy Propagation Imaging

A focusing-free ultrasonic imaging system for in-situ ground structural health monitoring (SHM) was developed using a Q-switched laser and a 2D laser mirror scanner. Two imaging methods, i.e. a frequency-selectable Ultrasonic Energy Propagation Imaging (UEPI) and Ultrasonic Frequency Tomography (UFT) methods were included. The UEPI result movie could be seen as ultrasonic energy wavefront emerging from the sensing location with concentrated energy at structural damages. The UFT generates tomograms that show different frequency components of the ultrasonic waves. Structural damages could be seen in the tomograms as high ultrasonic energy concentrated at the locations of damages. Synthesizing the UEPI and UFT could generate results with optimized frequency and dramatically improve the damage evaluation capability of the system. As demonstration, a fighter jet pod quartz/epoxy radome with honeycomb core was inspected. A 5.42J impact damage of 25mm diameter was successfully evaluated using UEPI and UFT. Improved UEPI result using synthesized UFT and UEPI shows exclusive high energy concentration at an area of which size and location agreed well with the impact damage. In conclusion, this imaging system is a robust in-situ ground SHM system suitable for complex and demanding structures.