In light of the insurmountable sedimentation of magnetorheological (MR) fluid, it is of great significance to ensure the performability of an MR damper by introducing a sensing method for MR fluid settling, and a key indicator to identify the health status of the MR damper is critical. However, the settling monitoring system for MR fluid can nowadays only function in a laboratory with transparent and non-magnetic tubes, which is not qualified for the in-situ sensing in a steel-made cylinder. Under the analysis of an open plate capacitor (OPC) configuration, the relationship between the concentration of magnetorheological fluid and the capacitance is investigated by simulation and experiments, and based on OPC, an in-situ sensing method for the settlement monitoring of magnetorheological fluid is designed. Long-time settling monitoring is carried out with home-made MR fluids, and the test results show that the sensing method can effectively reflect the status of settled MR fluids, and has the potential to be utilized in the identification of MR fluid compression points, which provides the strategic signal for the probable active or operational re-dispersing of MR fluid.

Magnetorheological (MR) fluid-based applications have accelerated new approaches for vibration and shock control in many scenarios such as the automotive suspension, earthquake mitigation, recoil system and landing gears. However, one of the most serious problems to resolve for successful applications is to mitigate the sedimentation of MR fluids. The sedimentation of MR fluid is inevitable due to the density mismatch between the particles and base liquid. So, several efforts have been made to prevent MR fluid from the settling through additives to match between dispersed phase and dispersing medium, failed because of the difficulty for balancing the density mismatch between the carbonyl iron particles and carrier liquids such as silicone oil. In this work, an active method to resolve the settling problem is proposed and its effectiveness is validated through an experimental test. This work presents an active dispersing mechanism (ADM) with the features of twin tubes structure and full circulation generated by rotary blades driven by an electric motor. A new measurement method based on inductive sensing is provided to characterize the permeability of MR fluid continuously and instantaneously, which is directly pertinent to the dynamic volume concentration of MR fluid in the phase of settling and dispersing. Based on the simply prepared MR fluid, the sedimentation is traced for 24 h and active dispersing is operated after a relatively short time settling of 3 h. The measured results show that the proposed ADM is very effective to recover settled MR fluid after starting the rotary blades less than 1 min.

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