Papers by Author: Chia Yen Lee

Abstract: The purpose of this study is to propose and apply a MEMS-based gas chromatography (GC) device comprising a miniature serpentine column. A 2 m long, 200 μm wide and 250 μm deep column was fabricated using a wet etching process and bonded to a Pyrex cover plate. After the GC column was coated with Carbowax 20M as the stationary phase, the concentrations of benzene, toluene, Ethylbenzene and m-Xylene were successfully detected in the mixed sample. The leakage test and mixed gas separation test achieved a useful separation result for Ethylbenzene-Xylene and Benzene-Toluen mixture at a 17.1 cm/s linear flow rate in a GC chip column.

Abstract: The purpose of this paper is to apply MEMS techniques to manufacture a gas flow sensor that consists with an airflow rate and airflow direction sensing units for detection of airflow states. This study uses a silicon wafer as a substrate which is deposited silicon nitride layers. To form the airflow rate sensing unit, a micro heater and a sensing resistor are manufactured over a membrane that released by a back-etching process. The airflow direction sensing unit is made of four cantilever beams that perpendicular to each other and integrated with piezoresistive structure on each micro-cantilever, respectively. As the cantilever beams are formed after etching the silicon wafer, it bends up a little due to the released residual stress induced in the previous fabrication process. As air flows through the airflow rate sensor, the temperature of the sensing resistor decreases and the evaluation of the local temperature changes determines the airflow rate. On the proposed sensor, the airflow direction can be determined through comparing the resistance variation caused by different deformation of cantilever beams at different directions.

Abstract: This paper studies the residual stress distributions and tip deflections of microfabricated bilayer cantilevers of varying beam thickness and platinum electrode length. The bilayer cantilevers discussed here are composed of low-stress silicon nitride films deposited on silicon beams. Platinum electrodes are deposited and patterned on the low-stress silicon nitride layers. A thermal elastic-plastic finite element model is utilized to calculate the residual stress distribution across the cantilever cross-section and to determine the cantilever tip deflection following heat treatment. A contact model is introduced to simulate the influence of contact on the residual stress distribution. The influences of the beam thickness and the platinum electrode length on the residual stress distribution and tip deflections are thoroughly investigated. The numerical results indicate that a smaller beam thickness leads to a larger compressive residual stress within the platinum electrode and delivers a larger tip deflection. The results also indicate that a larger platinum electrode length delivers a smaller tip deflection.

Abstract: This paper proposes a numerical and experimental investigation of mixing behaviors of two liquid samples in microchannels that are shaped into different geometric barriers. The micro-mixers utilized in this study are fabricated on low-cost glass slides using a simple and reliable fabrication process. Samples are driven by a hydrodynamic pump to lead them into the mixing section of the microchannels. The effects of mixing performance of various kinds of barrier shape are discussed in this study. The numerical and experimental results show that a better mixing efficiency can be obtained in the microchannels while using the elliptic-shape barriers in compare with the leaking side-channels. In this study, the simulated and experimental results are in good agreement. The investigation of mixing efficiency in microchannels with different geometric barriers could be crucial for microfluidic systems.

Abstract: Initiation and propagation of interfacial crack along bimaterial interface are considered in this study. A series of interfacial crack initiation and propagation experiments are conducted using the biaxial loading device for various mixed modes. Normal crack opening displacement (NCOD) is measured near crack front by a crack opening interferometry and used for extracting fracture parameters. From mixed mode interfacial crack initiation experiments, large increase in toughness with shear components is observed. Initial velocity of crack propagation is very dependent upon the mode-mixes. It increased with positive mode-mix due to the increase of stress singularities ahead of crack front and decreased with negative mode-mix resulting from the increase of the degree of compressive stress behind the crack front. Crack propagation was less accelerated with positive mode-mix than the negative mode-mix.