RESUMO
The transmission of waves through two discontinuities in a one-dimensional waveguide system is considered. Attention is focused on transmission through a structural insert, which is defined here to be a waveguide segment which is inserted into an otherwise continuous structural member with different properties. A general expression for the net transmission through the insert is found. It has bandpass/stop characteristics and its frequency average is somewhat greater than that normally assumed due to the coherent interaction of the waves in the insert. The particular case is then considered where the insert comprises a three-layer composite beam inserted in a thin beam which vibrates in bending. The composite beam comprises two elastic faceplates and a core filled with a tunable electro- or magneto-rheological fluid. The net transmission and the stop bands depend on the properties of the insert. Since these properties are tunable by adjusting the field to which the tunable fluid is exposed, then so too are the transmission characteristics of the insert.
