Underwater backscattering experiments were conducted in a laboratory tank on plane layers of granular material at a frequency of 222 kHz. Measurements were made to determine the backscattering coefficient, defined as the backscattering cross-section, as a function of grazing angle, with alterations in mean diameter and the type of granular material; the layer depth, the layer support material and lateral displacement. The experimental data were converted to values of the backscattering coefficient by use of a method presented by Nolle and were compared with results presented by Nolle and Mifsud. Backscattering was found to be a function of the particle size, increasing with increasing particle diameter. For layer depths less than ten centimetres deep an interference mechanism operative on the energy backscattered from the upper and lower interfaces of the layer was found to occur. Some practical aspects of the design and construction of high frequency transducers based on polarized ceramic active elements were also investigated.
|Date of Award||1975|