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Magnetorheological (MR) dampers are one of the most advantageous control devices for civil engineering applications to
natural hazard mitigation due to many good features such as small power requirement, reliability, and low price to
manufacture. To reduce the responses of a structural system by using MR dampers, a control system including a power
supply, control algorithm, and sensors is needed. The control system becomes complex, however, when a lot of MR
dampers are applied to large-scale civil structures, such as cable-stayed bridges and high-rise buildings. Thus, it is
difficult to install and/or maintain the MR damper-based control system. To overcome the above difficulties, a smart
passive system was proposed, which is based on an MR damper system. The smart passive system consists of an MR
damper and an electromagnetic induction (EMI) system that uses a permanent magnet and a coil. According to the
Faraday law of induction, the EMI system that is attached to the MR damper can produce electric energy and the
produced energy is applied to the MR damper to vary the damping characteristics of the damper. Thus, the smart passive
system does not require any power at all. Besides the output of electric energy is proportional to input loads such as
earthquakes, which means the smart passive system has adaptability by itself without any controller or sensors.
In this paper, the integrated design method of a large-scale MR damper and Electromagnetic Induction (EMI) system is
presented. Since the force of an MR damper is controllable by altering the input current generated from an EMI part, it is
necessary to design an MR damper and an EMI part simultaneously. To do this, design parameters of an EMI part
consisting of permanent magnet and coil as well as those of an MR damper consisting of a hydraulic-type cylinder and a
magnetic circuit that controls the magnetic flux density in a fluid-flow path are considered in the integrated design
procedure. As an example, a smart passive control system for reducing stay cable responses is considered in this
investigation and it will be fabricated and tested through experiment in the future.
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