The general purpose ice detector/accumulator proposed in this document employs two ultrasonic sensing modes. Rayleigh waves (surface waves) are used to detect the onset of icing, and time-offlight measurements in a normal incident reflection of ultrasonic pulses from the ice layers are used for measuring apprecialbe buildup thickness of the ice (>0.5mm). The basic principles underlying a time-of-flight thickness gauge require a pulser/receiver for generating and receiving electrical voltage pulses and an ultrasonic transducer. When the propagating ultrasonic pulse encounters an acousitc discontinuity, some of the energy is reflected. The time required for the ultrasonic pulse to transverse the ice layer twice is (t(2) -t(1)). The thickness of the ice is given by the speed of sound in ice=v as the following equation: l=v/2) (t(2)-t(1)) l=thickness of ice. Icing onset detection - rayleigh waves (surface waves) propagates on the surface of a solid. As build up occurs on the surface, they will scatter/dampen the wave. This decrease in amplitude of the reflected wave from an acoustic discontinuity can be used to detect the amount of icing.
