Sedimentation of magnetorheological fluids measured using an automated vertical axis inductance monitoring system

Stable magnetorheological fluids (MRFs) are inevitably required to develop reliable MRF-based applications. Suspension stability of MRFs can be studied using an automated vertical axis inductance monitoring system (AVAIMS), where an inductance sensor is translated vertically along a column of MRF to measure particle concentration as a function of column height and time. The AVAIMS allows for tracking the particle concentration discontinuities due to the sedimentation of MRFs including the mud-line, the gel-line, and the cake-line. The sedimentation progress of MRFs can be evaluated by analyzing these boundaries. In this study, the AVAIMS design was improved to better identify the sedimentation zone boundaries by using an optimized inductance sensor that measures the concentration gradient as a function of time. The inductance sensor design, material selection, and geometry were optimized to improve the sensor sensitivity. The calibration curve of the sensor was obtained by measuring samples with different particle volume fractions. The sensor design was validated by examining an MRF sample with a particle concentration of 20% volume fraction for seven consecutive days. These tests show the effectiveness of the AVAIMS optimized to better localize the sedimentation zone boundaries using the concentration gradient profile method.