Torsional waves in clad cores

Propagation of torsional elastic waves in the clad core is addressed in this paper. The shear velocity of the core is slightly smaller than that in the cladding. Core with cladding of different finite thickness and infinite thickness is investigated. Two types of modes, guided and leaky modes are examined with the discussion of motion in waveguide. Phase, group, and energy velocities, cutoff frequencies are analyzed and the results of first three modes are presented. The change of dispersion curves due to variation of thickness of cladding is discussed and it is found that when the thickness increases the results of finite clad core will approach those of infinite clad core in guided mode, but not in leaky mode. Below cutoff frequencies the wavenumber becomes complex in infinite clad core, while it is pure imaginary in finite clad cores. The group and energy velocity are presented and in leaky mode the group velocity becomes abnormal, while the energy velocity is physically meaningful.