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One class of Surface Acoustic Wave (SAW) devices employs reflecting arrays to determine device characteristics. Dots of metal film and grooves have been used as reflectors; reflection is caused by the mechanical discontinuity. This research project is a study of an alternative reflector, the thin metal dot, which reflects by interacting with the electric field that accompanies the SAW on a piezo-electric material. Experimental work is done on Y-cut LiNbO₃, a common SAW material, the aim being to characterise the reflection mechanism sufficiently to design devices, particularly on this material. Reflectivities of a large range of dot sizes is reported. Velocity change due to dots, another parameter required in device design, is also measured. In addition, holes in a metal film, physically the opposite of dots, are also studied. A theorectical model is developed to predict the behaviour of dots in devices. For a <strong>Z</strong>-propagating wave in LiNbO₃, the SAW velocity for completely free and completely metallised surfaces were used to specify the properties of the material. For propagation in other directions on the surface, particularly near the <strong>X</strong> direction, a different acoustic mode, the Leaky Surface Wave (LSW), has an influence on SAW reflections, and the model also requires the LSW velocities under the same two conditions. The model uses these parameters, together with dot geometry, to determine reflectivity in any direction and velocity change due to the dots. The results agree well with experiments. A device (a RAC) is designed using this model, to bring out any unforseen difficulties in the use of dot arrays. The device performed as expected except for some unanticipated attenuation in the arrays, which can almost certainly be predictably allowed for in future designs, being broadband and not very severe.

Typescript (Photocopy) / viii, 138 leaves : ill ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Depts. of Applied Mathematics and Mechanical Engineering, 1990

The work presented in this thesis consists of two parts: development and application of a novel passive acoustical approach for field measurement of breaking surface waves, and interpretation of the resulting observations in terms of wave field information so as to improve the understanding of wave breaking. The development of the acoustical approach has been motivated by the difficulties inherent in measurement of breaking waves. This approach makes use of an array of four broadband hydrophones which is able to track individual breaking waves by passive detection of the naturally generated sound of wave breaking. The Generalized Cross Correlation method is used to determine time differences of acoustic signals from breaking waves arriving at the array, allowing the breaking waves to be located with the given array geometry. Observations of breaking waves were made by means of this technique during the Surface Wave Processes Program (SWAPP). The spatial and temporal statistics of breaking waves, including breaking wave density, travel velocity, lifetime of breaking and spacing, are obtained from the observations. Statistical models are developed to assess, and where appropriate, correct for any bias resulting from limitations of the measurement approach. The breaking wave statistics provide important information about the physical process of wave breaking and its distribution in different wave fields. It is found that wave breaking in the open ocean occurs at a scale substantially smaller than the scale associated with the dominant wind wave component in the wave spectrum. Numerical simulation of breaking wave statistics and comparison with the observations demonstrates that the scale of breaking can be predicted from the directional wave spectrum by a linear model with a single breaking threshold. These results will provide input to comprehensive models of wave dissipation. Acoustical radiation properties of individual breaking waves are a further aspect of wave breaking that has been observed with the aforementioned technique. Investigation of the sound radiated from breaking waves reveals information both on the nature of the sound generation mechanism by breaking and the dimension of breaking waves. Statistical analysis of the acoustic source intensity associated with wave breaking suggests that the source intensity can be related to the breaking scale and wave energy dissipation, thus implying that surface wave dissipation could be remotely measured by using ambient sound. / Graduate

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Surface Acoustic Wave (SAW) devices are manufactured using standard metallization and photolithographic techniques that have been established by the semiconductor industry. The facilities in the newly developed Microelectronics laboratory at the University of Central Florida will be utilized in the fabrication of a SAW device. This thesis will outline the complete procedure beginning with the initial design from given specifications, up to mask generation, fabricating and testing of the device. This will serve to calibrate the fabrication process for future work in SAW device and semiconductor fabrication. The models that are used in the SAWCAD design software will be verified by comparing the theoretical and experimental results.

The propagation of acoustic plate-mode waves in composite membranes is studied. A computer program has been developed and used to calculate the wave velocity and electromechanical coupling factor in these structures which may consist of any combination of piezoelectric layers with arbitrary orientation and surface metallization. In particular, shear modes (SH) in zinc-oxide and selenium membranes, as well as stiffened-Lamb modes in ZnO membranes and ZnO/Si, ZnO/GaAs composite membranes are studied. / The surface-acoustic-wave propagation in selenium and in selenium layers on tellurium has been extensively studied using an improved computer program. The study shows that surface-wave coupling factors in the range of 0.5 to 1.5% are possible with these structures. The calculated sensitivity of the velocity and coupling factor to errors in material constants shows that an accurate value of the e(,11) constant for selenium is necessary for an accurate estimate of the coupling factor. / A technology for fabricating selenium-tellurium layered structures for SAW propagation has been successfully developed. Measurements on fabricated SAW delay lines were carried out and estimates of the coupling factor and the acoustic attenuation obtained. These measurements, taken together with previously published results, confirm that the published value of e(,11) = 0.32 C/m('2) is too small.