Date of Award
Doctor of Engineering Science in Electrical Engineering
Raj Pratap Misra
W. H. Warren Ball
Werner J. Wenisch
Holographic techniques are also applied to the measurement of acoustic parameters and several ways of implementing this application are proposed and investigated. In a number of experiments, the advantages of the holographic method in the field of sonics and ultrasonics are demonstrated, and a theoretical relation comparing this method to the Schlieren method is developed and experimentally confirmed.
A theoretical and experimental study of some possible "couplers", each capable of augmenting the displacement amplitude of an acoustical diffraction pattern as it is transferred from a surface bounded by water to one bounded by air, is also conducted. The "couplers" investigated range from a simple, acoustic impedance transformer to a mosaic of velocity amplifiers.
A detailed study is conducted on the development and testing of a mechanical velocity transformer consisting of two lossy, nearly quarter-wave plates. The theoretical relations describing the behavior of such plates are developed and experimentally verified. An advantage of 9.5 (19.6 dB) at 916 KHz has been obtained across the water/air interface - primarily due to the construction of tuned aluminum-epoxy plates.
A useful method for "tuning" quarter-wave metal-epoxy plates is introduced and demonstrated. Other methods suitable for the measurement of the speed of sound and the attenuation coefficient of epoxy are also discussed.
"Shifted reference holographic interferometry" and the partial impedance matching of water to air, afforded by the tuned velocity transformer, result in a high sensitivity of this optical detector of acoustic vibrations. It is shown that, by these methods, a "holographic sound image converter" having a threshold intensity of 2.8 mw/cm2 at 1 MHz appears feasible. Higher sensitivities (1.6 x 10-11 w/cm2) and full realization of all of the advantages of the "holographic converter" are expected with the use of an "active coupler", ie. one which makes use of electronic amplification.
Fischer, Wolfgang, "Methods for acoustic holography and acoustic measurements" (1972). Dissertations. 1282.