Axisymmetric propagation modes in a liquid‐filled elastic waveguide

Using Del Grosso’s theoretical treatment [V. A. Del Grosso, ‘‘Errors in Ultrasonic Propagation Parameter Measurements. Part 4—Effect of Finite Thickness Solid Tubes Enclosing the Liquid Cylinder of Interest,’’ NRL Report 6852, Naval Research Laboratory, Washington, DC (1968)] as a foundation, axisymmetric modes of progressive wave propagation in a liquid‐filled elastic waveguide are studied. The waveguide system consists of a liquid cylinder surrounded by a hollow cylinder of elastic solid of arbitrary thickness. Dispersion curves and particle displacement profiles for propagating modes are calculated for several liquid/solid combinations. Modal characteristics are compared to those in the extreme cases of the rigidly bound cylinder and the empty hollow elastic cylinder. It is also shown that certain liquid/solid combinations can produce a near‐plane‐wave mode propagating at the intrinsic sound speed of the liquid over a range of frequencies. Experimental measurements demonstrating modal properties are presented. [Work supported by ONR.]