Transmission of guided sound waves through a layer of fluid or solid.
thesisposted on 19.11.2015, 08:55 by N. Romilly
The thesis considers the transmission of sound waves through a layer of fluid or solid contained in a wave-guide of a simple form. The main aim is to find the transmission coefficient for a lowest order incident mode and to fine the lengths of the layer for which the transmission is a maximum or minimum. The first part of the thesis gives the exact solution for transmission through a layer of inviscid fluid, and for transmission through a layer of viscous fluid when the boundaries of the guide are rigid and lubricated. It also gives approximate solutions for transmission through a layer of viscous fluid when the boundaries of the guide are pressure-free and when they are rigid but not lubricated. The second part of the thesis considers transmission through a layer of solid. It gives the exact solution, in infinite series form, to the problem of the transmission of any incident waveguide mode through a stretched membrane contained in a rigid circular guide. It is shown that above a certain frequency an incident plane wave can never be completely transmitted or completely reflected. Below this frequency complete transmission or reflection can occur, but the frequencies at which it does occur depend on the medium surrounding the membrane. The solution is discussed and results are given for a particular case and compared with approximate solutions obtained by other authors. The same analysis is applied to transmission through a thin plate. The second part of the thesis also contains work on transmission through a thick layer of elastic solid. An exact solution is found using an approximate equation of motion for the solid which should be valid at low frequencies. An attempt is made to find a solution based on the exact equations for the solid, but it is necessary to use an approximation.