Wave transmission through structural inserts

The transmission of waves through two discontinuities in a one-dimensional waveguide system is considered. Attention is focused on transmission throug h a structural insert, which is defined here to be a waveguide segment whic h is inserted into an otherwise continuous structural member with different properties. A general expression for the net transmission through the inse rt is found. It has bandpass/stop characteristics and its frequency average is somewhat greater than that normally assumed due to the coherent interac tion of the waves in the insert. The particular case is then considered whe re the insert comprises a three-layer composite beam inserted in a thin bea m which vibrates in bending. The composite beam comprises two elastic facep lates and a core filled with a tunable electro- or magneto-rheological flui d. 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 characterist ics of the insert. (C) 2001 Acoustical Society of America.