Seung-Woo Han

BINGHAM AND RESPONSE CHARACTERISTICS OF ER FLUIDS IN SHEAR AND FLOW MODES

This paper presents field-dependent Bingham and response characteristics of ER fluid under shear and flow modes. Two different types of electroviscometers are designed and manufactured for the shear mode and flow mode, respectively. An ER fluid consisting of soluble chemical starches (particles) and silicon oil is made and its field-dependent yield stress is experimentally distilled at two different temperatures using the electroviscometers. Time responses of the ER fluid to step electric fields are also evaluated under two operating modes. In addition, a cylindrical ER damper, which is operated under the flow mode, is adopted and its measured damping force is compared with predicted one obtained from Bingham model of the shear and flow mode, respectively.

ROBUST SLIDING MODE CONTROL OF AN ELECTRORHEOLOGICAL SUSPENSION SYSTEM WITH PARAMETER PERTURBATIONS.

This paper presents a robust feedback control of an electrorheological (ER) vehicle suspension system with parameter uncertainties. There exist various types of uncertainties in practical vibration control of an ER suspension system, for example, the yield stress of ER fluid that is varied with the operation temperatures, and the sprung mass is to be changed by the number of riding persons and payload. Therefore, it is necessary to design a robust controller, which compensates parameter uncertainties for a vehicle featuring ER suspension system. After identifying the yield stress variation of the employed ER fluid with respect to temperatures, a quarter-vehicle ER suspension system with parameter uncertainties is constructed. A robust sliding mode controller, which has inherent robustness against system uncertainties, is then formulated by treating the sprung mass and the yield stress of the ER fluid as uncertain parameters. For the demonstration of robustness and performance of the proposed sliding mode controller, control responses such as vertical displacement and acceleration are presented in time and frequency domains.

Accurate position tracking control of a moving stage using an electrorheological fluid clutch

Accurate position trajectory control of a moving stage is undertaken by utilizing an electrorheological (ER) fluid clutch. A new type of bi-directional ER clutch is devised and its field-dependent torque transmission is empirically evaluated. A sliding mode controller integrated with a full-order observer is formulated to achieve position tracking of the moving stage. In order to compensate for nonlinear friction components, the sliding mode controller is augmented with a feedback friction compensator. In the synthesis of the controller, the variation of moment of inertia of the moving stage is treated as a parameter variation to guarantee robustness of control. The proposed control system is experimentally realized, and tracking control responses for step and sinusoidal trajectories are evaluated in the time domain.

MECHANICAL BEHAVIOR OF FREESTANDING Mo THIN FILMS FOR RF–MEMS DEVICES

Radio frequency microelectromechanical systems (RF–MEMS) are an attractive solution for wireless telecommunication applications. Freestanding films play an important role in RF–MEMS devices. For the successful commercialization of RF–MEMS devices, however, it is necessary to evaluate the mechanical reliability of freestanding films. The first step in the evaluation is to characterize the mechanical behavior of the films. This study focuses on freestanding Mo thin films. Mo test structures with a thickness of 960 nm were fabricated using sputtering deposition and patterned using a surface and bulk micromachining process. The strip-bending test was used to measure the stress–strain relation of the freestanding Mo thin films. The measured elastic modulus, initial stress, and yield strength of Mo thin films are reported.

Strain rate dependence of mechanical properties for sub 100 nm-thick Au film using Electrostatically Actuated NAno Tensile testing device

We have clarified the strain-rate dependence of mechanical properties of Au thin films with thicknesses less than 100 nm. Stress-strain relations of Au films were examined by tensile tests using the Electrostatically Actuated NAno Tensile testing devices (EANATs). Youngs modulus showed a substantially smaller value of 30 GPa in average compared to bulk material, and it had no strain-rate dependence. However, the yield stress depended on the strain rate. In particular, the yield stresses clearly decreased with decreasing strain rate in the range lower than 0.01 s−1. TEM observation suggests that the differences were caused by the small grain size.