Design and Testing of Low Cost Piezoelectric Film Ultrasonic Transducers

Abstract

Flow measurement using the differential phase technique has shown some promise. However, there are. certain problems that must be overcome in order for it to prove viable. These are the inherent ambiguity in phase and the temperature dependence. In theory, these problems can be overcome by using multiple frequencies. This inevitably leads to the necessary use of broadband ultrasonic transducers over the conventional narrowband ones. A relatively new material that can provide a broadband response, is the piezoelectric film, polyvinylidene fluoride. The focus of this thesis is to look at the design, construction, and testing of wetted transducers, using this piezoelectric film. The design stage looks at the theoretical response of a transducer pair, using a general three port network model. The model provides a means of choosing suitable transducer design parameters. Construction of the transducers is then performed to confirm the validity of the design. Several sets of transducers were constructed with different backing materials having different acoustic properties. The measured responses of each of the sets were compared to each other and to their models. From this, the final transducer design was selected, resulting in a broadband wetted ultrasonic transducer, of relatively low cost. Finally, the transducers were tested in the differential phase flow measurement system. The results showed some improvement over the previously used narrowband transducers. Unfortunately, temperature compensation and the elimination of phase ambiguity were not attempted, due to certain problems with the flow measurement system.