The shear modulus and damping loss factor of electro-theological (ER) fluids vary when the fluid is exposed to an electric field. This behaviour can be exploited to engineer smart structures with controllable dynamic properties. This paper describes one example of such a system. The intention is to control the transmission of structure-borne sound through a structural member such as a beam. This is achieved by inserting a composite ER beam, comprising two elastic layers between which is sandwiched a layer of ER fluid, into the otherwise uniform beam. The insert behaves as a filter. The frequency characteristics of the energy transmitted through the insert can be controlled by varying the voltage applied to the ER beam. Expressions for the power transmitted through the beam/ER beam/beam combination are given and numerical results are presented.
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