The sound absorption characteristic of a clean, open-cell con guration, typical polyurethane exible foam is shown against that of an auxetic foam made from it, and this same foam after it has been seeded with a magnetorheological uid (then dried), having 2-5 mm carbonyl iron particles and subjected to zero, weak and concentrated magnetic elds in an acoustic impedance tube facility. The resultant foam indicates the capability of shifting the peak acoustic absorption coef cient within a given frequency bandwidth when constant intensity magnetic elds are applied.

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It is now well known that smart fluids (electrorheological (ER) and magnetorheological) can form the basis of controllable vibration damping devices. With both types of fluid, however, the force/velocity characteristic of the resulting damper is significantly nonlinear, possessing the general form associated with a Bingham plastic. In a previous paper the authors suggested that by using a linear feedback control strategy it should be possible to produce the equivalent of a viscous damper with a continuously variable damping coefficient. In the present paper the authors describe a comprehensive investigation into the implementation of this linearization strategy on an industrial scale ER long-stroke vibration damper. Using mechanical excitation frequencies up to 5 Hz it is shown that linear behaviour can be obtained between well defined limits and that the slope of the linearized force/velocity characteristic can be specified through the choice of a controller gain term.

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In this paper, the authors describe the development of a mathematical model of a controllable vibration damper intended for eventual application to ground-vehicle suspension systems. The damper under investigation employs electro-rheological (ER) fluid as the working medium which enables a continuously variable damping force to be provided in response to an electrical control signal. There are some difficulties inherent in characterizing the ER damper's behaviour which the present study attempts to overcome.The paper begins by describing a novel form of non-dimensionalization which drastically reduces the number of variables required to characterize the quasi-steady behaviour of the ER fluid. The construction of the ER damper is described and, on the basis of physical reasoning, it is shown how a dynamic model can be derived by taking account of ER fluid inertia and compressibility. A recently developed iterative scheme is introduced in order to solve the resulting non-linear equations of motion. The paper concludes with a case study involving the application of the ER damper to controlling the lateral vibrations of a rail vehicle.

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