Papers by Author: Wei Hua Li

Abstract: In this study, the MRE was manufactured, and the sandwich beam was also fabricated by treating with MRE between two thin aluminum layers. The experiment test rig was set up to investigate the vibration response of the MRE sandwich beam under non-homogeneous magnetic field. The experimental results show that the MRE sandwich beam had the capabilities of left shifting first natural frequency when the magnetic field was increased in the activated regions. It is also obvious that the first natural frequency of the MRE sandwich beam decreased as the magnetic field that applied on the beam was moved from the clamped end of the beam to the free end of the beam.

Abstract: As an important member of smart materials, magnetorheological elastomers (MREs) exhibit characteristics that their modulus can be controlled by an external magnetic field. Based on these experimental results, a viscoelastic solid model with four parameters was proposed to predict the performance of MRE. A building model, three stories high, was constructed using MATLAB SIMULINK to evaluate the performance of an MRE device in structural control. In addition, the performance of an MRF damper and an MRE device in structural control, where the resultant peak force was selected as a criterion in the evaluation process, was compared and discussed. Two controllers, passive on and passive off control strategy were used to compare the response of structure. The effectiveness of an MRE bearing in structural control was well justified.

Abstract: This paper presents the development of a variable stiffness and damping isolator using magnetorheological (MR) fluid technology. The MR fluid isolator is composed of two variable volume rubber bladder filled with MR fluid, a pipe and a MR valve connecting them. One of the bladders supports disturbance force and the MR fluid flows between two bladders because of the variation of bladder volume due to deformation. The shear stress of the MR fluid in MR valve is varied by an applied magnetic field, which thereby varies the characteristics of the isolator, such as its stiffness and damping. A mathematical model of the isolator was derived, and a prototype of the MR fluid bladder spring was fabricated and its dynamic behavior was measured in vibration force for a wide range of frequencies under various applied magnetic fields. The parameters of the model under various magnetic fields were calculated and the bladder dynamic performances were evaluated. A non-resonant control was employed to minimize the vibration amplitude of the system. Numerical simulation results indicated that the semiactive control system produced much better isolation performance than a passive system.

Abstract: This paper presents both theoretical and experimental study of particle motion in a typical interdigitated electrode array. Both finite element method and numerical simulation were performed to predict the movement of particles. The simulation results indicated that the particle motion and separation behaviors strongly depend on the combined contributions of a number of parameters, such as the frequency of the electric field, applied voltage, dielectric properties of the particles and the surrounding medium.

Abstract: This paper presents the study of rheological and mechanical properties of MR elastomers fabricated using small and large particle. Analysis indicated that MR elastomers fabricated with bimodal particles at a specific particle ratio ingredient show enhanced MR effect compared with those fabricated with monoparticles. MR elastomer samples were fabricated by using small and large particles with sizes of 5m and 50m respectively. Their rheological and mechanical properties were characterized with a MR rheometer. Experimental results agree well with the analysis.

Abstract: This paper presents fabrication and characterizing of a new functional material, magnetorheological shear thickening fluid (MRSTF), by mixing micron-sized magnetizable particles with nano-sized silica particle based shear thickening fluid. Dynamic properties of the MRSTF were characterized by using a parallel-plate rheometer. The effects of steady-state shear rate and magnetic field on MRSTF rheological properties were addressed. The suspension shows an abrupt increase in complex viscosity beyond a critical dynamic shear rate and a magnetic field controllable characteristic, as well as reversible.

Abstract: A dielectrophoretic barrier is generated with two layers of microelectrode structures so called paired electrode array (PEA) constructing face to face on the top and bottom sides of a microchannel. The barrier is designed to control the movement of particles in combination with a fluid flow. Depending on the relative strength of the DEP force and hydrodynamic force, microparticles or cells carrying by a laminar flow can either penetrate the barrier or be deflected from there. The threshold velocity at which the barrier firstly fails to hold back the particles is a significant parameter to validate the performance of the device. This paper presents an experimental study on the performance of the microfabricated paired electrode array. The electrodes were fabricated with conventional microfabrication techniques. Micron-sized latex beads were used in the investigation. The holding capacity was defined by measuring the threshold velocity of the system. The results provide crucial information for the design of the dielectrophoretic barrier for microparticle manipulation and separation.

Abstract: In this paper, the behavior of microparticles subjected to the AC electric fields generated by planar microelectrode systems is studied. Microelectrodes including interdigitated array, castellated array, and jagged array are constructed using microfabrication techniques. Micron-sized latex beads are used to study their movements. Positive and negative dielectrophoresis (DEP) are studied. In the interdigitated electrodes, particles experiencing n-DEP are levitated stably to certain heights where the vertical DEP force is balanced by the gravitational force. The levitation heights of the particles are measured using the consecutively focusing method. The results provide significant instructions for the dielectrophoretic manipulation and separation of bioparticles.