Ice detection by ultrasonic guided waves

Abstract

This paper describes a method for inflight ice detection using ultrasonic guided waves that is little studied until now. Unlike existing systems, the proposed method can immediately detect icing at the place of formation. The detection area can also include whole structural segments and the proposed sensor can be integrated into a wing structure without any effect on the flow around the aerofoil or increase in drag. The proposed detection method is based on excitation with a burst signal and a sine sweep. The system was tested on a plate made from carbon fibre-reinforced plastic (CFRP) and two leading edges of a NACA 0012 profile. Ice was applied to the CFRP-plate in a cooling chamber using regular water and built up onto the leading edges in an ice wind tunnel using super cooled water droplets. Piezo ceramic patches and discs were affixed to the testing model structures for use as transceivers and receivers, respectively, to initiate the guided waves and convert them back into electric signals. The influence of variation in ice layer thickness and temperature on the sensor output signal was then investigated using the average and maximum absolute sensor output and runtime to calculate the group velocity, which was then compared to calculated group velocity values. Based on the test results, the proposed method was determined to be sensitive to the build-up of ice and, thus, effective in principle.