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Ultrasonics, that is mechanical waves with a frequency greater that 18 kHz. are employed in a number of diverse and distinctive industries. One important niche occupied by ultrasound, and the focus of this thesis, is its application in ultrasonic cleaning systems whereby the rapid pulsing of mechanical waves at ultrasonic frequencies forms thousands of microscopic voids (or cavities) in the liquid. It is the implosions of these voids during the positive pressure phase of the wave that assists th removal of contaminants from the surface of an immersed load and is known as cavitation. A thorough literature review conducted as the foundation of this work uncovered a significant deficit in knowledge regarding the positions of cavitating fields within ultrasonic vessels. Further to this, the effects on the cavitating field of a number of industrially relevant parameters, such as transducer placement. the introduction of baskets and cleaning loads to the liquid and variations in the level of the cavitating medium, were found to be deficient within both academic and industrial knowledge base. The outcomes of the literature review clearly indicated that it was evident that the development of a "toolset" capable of modelling the bulk cavitating fields within ultrasonic vessels would not only sustain the strong industrial relevance of the programme of work, but would also add significantly to extant knowledge concerning the design and production of commercial ultrasonic vessels. This work describes the development of such a toolset, detailing the mathematical modelling behind the simulation system and the logical progression of the work, from basic 2D models used for rapid prototyping to full 3D models used to simulate a wide variety of complex systems with parameters hitherto un-described within the literature. A variety of methods of quantifying the simulation outputs are reviewed and discussed during the thesis, leading to the logical selection of one qualitative and one quantitative indicator of cavitating fields. A comparison of the simulation outputs to the respective empirical data showed an excellent degree of con-elation, leading to a high level of confidence in the simulation toolset. Use of the verified model together with the developed design methodology was used to address the industrially relevant issues detailed in the literature review and this further promoted the contribution to knowledge presented in this work. As in any industrial design. pragmatic approximations were used in the production environment and this occasionally appeared to show discrepancies between the simulation outputs and the practical data obtained. Specific causes behind these differences are critically analysed. and along with further questions arising from such analysis. The outcomes formed the backbone of a future work proposal presented along with a comprehensive review and summary of the results and improved synthesis techniques.

Thesis (MTech (Radiography))--Peninsula Technikon, Cape Town, 2000 / Ultrasound has, until recently, been regarded as a sophisticated diagnostic modality, reserved for tertiary health care. In reality, it is a cost-effective, reliable and safe modality that is highly suited to primary health care. Secondary level centres provide the only access to ultrasound for many of the obstetric primary health care patients, as primary health care has limited ultrasound resources. The increasing monthly statistics, at one secondary centre, bares witness to the need for ultrasound in primary health care. At the time of this study ultrasound scans were not routine for every obstetric patient. Experience indicates that only the patients who clinically suggest a possible risk are referred for ultrasound to confirm, or rule out problems. However, there are a number of complications, which have little or no early clinical indications. [Palmer, 1995:285] This means that many of the problems encountered are often in late gestation and they have a marked bearing on the obstetric management of the patient. This was a retrospective study, of approximately 1000 patients attending an ultrasound department at a secondary centre. Most of the obstetric patients that were sent for an ultrasound examination came from the primary health care centres in the region.

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An ultrasonic method to determine bladder volumes could help eliminate some of the risk and discomfort resulting from catheterizations. A system using "A" mode ultra-sound correctly estimates bladder volumes to within 50 cc's. Near and far walls of bladder sections found at various positions define the bladder, and volumes calculated from these sections are added together for a bladder volume estimate. Accurate volume estimates (mean error of -1.9 cc.'s with standard deviation of 28 cc.'s) were obtained when bladder section characteristics such as: depth of the near wall of the bladder, thickness of the far wall echo, distance between near and far bladder walls, and amplitude of the far bladder wall echo, were considered. Most bladders were completely scanned with the transducer placed at the bodies midline, approximately 5 to 7.5 cm. above the pubic bone.

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Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2007. / Includes bibliographical references (leaves 79-82). Also available in electronic version.