Modelling of piezoelectric ultrasonic transducers with application to high speed gas flow measurement

Abstract

The design and testing of an ultrasonic time of ight Mach number probe for use in the bypass duct of an aircraft gas turbine is presented. Analysis of the time and frequency domain behaviour of the type of thickness mode transducers selected for use in the probe, and the effects of beam profile and attenuation on the transmitted ultrasonic wave in a owing medium are also covered and extended. The results of this analysis are implemented in a computer model which is used to aid in the design of various parts of the probe. Experimental assessment of the transducers designed for the probe is presented together with the results of tests on the performance of the selected probe configuration. A digital signal processing system to control the probe and compensate for the poor signal to noise ratio of the received signal is developed together with analogue circuitry to interface this system to the transducers. A novel method of compensating for the beam sweep encountered at the Mach numbers to b measured using 'ski-ramps' is then developed and implemented. Results from the final configuration including the ski-ramps is then presented.