In this thesis, surface vibration amplitudes and modes of piezoelectric
transducers are studied. A system is developed to measure these
amplitudes and observe the modes in different media.
Piezoelectric transducers are used for underwater sound transmission.
They are energized individually or in array form by continuous or pulsed
electrical power and the acoustic energy is transmitted from the radiating
front surface. This acoustic transmission and its beam pattern
correspond to the vibration amplitudes and modes of transducer radiating
surface when the electrical energy is applied. Optical techniques are
the most common methods used to determine the small vibration amplitudes
of objects and the Electronic Speckle Pattern Interferometry Technique
(ESPI) has been used to detect the small movements of objects down to 10-20A in real time. Hogmoen and Lokberg have described a method for real time detection and have carried out measurements of small vibrations
at frequencies up to 30 KHz . They claimed detection limits of 20A by
visual observation and O.lA by photoelectric measurements using a lock in technique. In the thesis, the reference beam modulation is performed by an
e1ectro-optic modulator in the path of the reference beam. This allowed
ESPI to be used to measure high frequency vibration amplitudes into the
MHz region semi-automatically. A video integrator gated by a digital
scanner is used to sample the video information directly from a television screen. Various vibration modes of a PZT-4 transduter radiating surface
were studied at its resonant frequencies in 3 different media. By using an automatic calibration procedure and a phase-sensitive detection
technique, absolute vibration amplitude measurements were successfully
Various experimental surface vibration modes are related to
the theoretical values by using simple plate vibration theory which
suggests that a PZT-4 transducer behaves like a simply-supported thin
plate at low power levels.
The relationship between transducer radiation beam patterns and
the surface vibration amplitudes under water is presented in Chapter 8.
An optical study of the Michelson Interferometer has been given
alongside the speckle interferometer and the results of early experiments
with the Miche1sori is presented. The reasons for abandoning
the Miche1son Interferometer and using the speckle interferometer are
given extensively in Chapter 1.
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.