A Magnetorheological Damper with Embedded Piezoelectric Force Sensor: Experiment and Modeling

Semiactive control systems that offer the reliability of passive control systems as well as the versatility and adaptability of active control systems have received significant attention for structural vibration control (Jung et al., 2004). Magnetorheological (MR) fluid dampers have emerged as such a class of semiactive damping devices. By activating the MR fluid contained in the device through magnetic field, it can reversibly change from liquid to semisolid in milliseconds, which results in a continuously controllable device with high bandwidth. Moreover, MR dampers require minute power for the field activation and are insensitive to impurity penetration such as are commonly encountered during manufacture and usage (Carlson et al., 1996). More importantly, they are inherently fail-safe devices in that they can still operate as passive dampers once the control hardware fails. Recognizing the attractive characteristics and promising potential of the MR-based damping technique, numerous researchers and engineers have investigated the feasibility and application of the MR dampers in a wide variety of areas, such as seismic protection of building and bridge structures (Dyke et al., 1996; Gordaninejad et al., 2002; Loh et al., 2007), vibration control of bridge cables (Johnson et al., 2000; Ko et al., 2002; Ni et al., 2002; Duan et al., 2005; Weber et al., 2005b; Li et al., 2007), vibration damping of suspension systems of trains and vehicles (Liao and Wang, 2003; Song et al., 2005; Choi et al., 2009), and stability augmentation of helicopters (Gandhi et al., 2001; Hu & Wereley, 2008). While possessing controllable damping capability, the existing MR dampers are incapable of monitoring structural vibrations or excitations exerted on structures, and require extra sensors for implementing closed-loop semiactive control. As a consequence, the MR dampers are usually used as adjustable passive dampers in an open-loop mode in the current practices of civil structural control, like in vibration control of bridge cables (Chen et al., 2004; Weber et al., 2005a), which hinders full utilization of their controllable damping capability. Recently, a self-sensing MR damper embedded with a piezoelectric force sensor has been developed to possess dual functionality of force sensing and controllable damping; thus it has the potential to facilitate real-time closed-loop control in a relatively simple and cost-effective manner (Or et al., 2008). One of the important tasks to fully exploit the potential of an MR damper in control implementation is to establish an accurate model that can characterize its intrinsic highly