UBC Theses and Dissertations

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UBC Theses and Dissertations

Studies of some acoustic resonant systems Greaves, Thomas


The resonant frequency shift, δf, of an acoustic resonator by a small spheroidal obstacle is calculated. For a spheroid whose dimensions are small compared to the wavelength of the sound waves it is shown that δf can be expressed in terms of the spheroid geometry and the structure of the acoustic modes in the immediate vicinity of the spheroid, whereas in the usual method of calculating δf one needs to know the detailed structure of the normal modes of the resonator. Interest in the topic is motivated by current studies of the acoustical levitation of materials in microgravity environements. The significance of the results for the study of the acoustical levitation of liquid droplets in neutral buoyancy environments is discussed. With a view to applying these results, the mechanical properties of an electro-acoustic transducer with an impedance well matched to liquids are measured. The transducer consists of neoprene sandwiched between two conducting plates. The displacement of the transducer under different driving conditions has been measured usng an interferometric technique with angstrom sensitivity. An unusual feature of the interferometer is the degree of sensitivity achievable without vibration isolation mountings or temperature control of the environment. Using these measurements a qualitative model is developed to explain the unexpected aspects of the dynamical behavior of the transducer. The thesis concludes with-suggestions for further development of the transducer system.

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