Key Engineering Materials Vols. 609-610

Abstract: In this paper, a novel bonding method for microfluidic devices was presented. The organic solvent fumigation bonding method can be used to produce multi-layer PMMA microfluidic devices under the condition of room temperature and low pressure. During the bonding, we choose chloroform as bonding solvents, the polyimide tape was used to protect no-need-bonding side of the cover sheet and the sealant silicone adhesive was used to protect the microstructure in the bonding side. The substrate was fumigated for 5minutes in the saturated steam conditions, then remove the polyimide tape as well as the sealant silicone adhesive. Assemble the fumigation cover sheet to the substrate with microchannel by using fixtures, soon after put the fixture and the substrates into the oven, dried at 50 °C for 10 minutes. Finally, remove the fixture, the bonding complete. Because of the bonding was accomplished under conditions of low temperature and pressure, the deformation of microchannel is very small. When the method was used for multilayer chip bonding, it also achieved good results.

Abstract: Orientation adjustment is an important issue in the micromanipulation of cells. A non-contact method based on a swirl for cell orientation control was introduced in this paper. The swirl is produced by a pair of opposite micro-fluids squirting from two parallel tubes. Cell orientation adjustment is realized by cells rotation due to swirl viscous drag, which drives cells to desired configurations. The appropriate distances between the end face of the two tubes and the distance between the axes of them are 1-3 times tube diameter for the cells rotating in the swirl central zone. Especially when the distances are kept double the cell diameter, cells rotate steadily round the swirl central point. By pulsating jetting, fluctuant micro-fluid are generated which make cell rotating a certain angle. Adjusting the pulse duration, pressure and jetting velocity, the cell rotation angle can be controlled which make orientation control more precisely. The method is valid for cells of different shapes and sizes. The effectiveness of the proposed non-contact method for cell configuration control was verified by experiments.

Abstract: Novel chiral temperature-sensitive microgels based on N-isopropylacrylamide are reported in this paper. Such particles, poly (N-isopropylacrylamide-co-acrylic acid-L-phenylalanine ethyl ester)[ poly (NIPAM-co-ALPhe)], were prepared by free radical polymerization of NIPAM, chiral monomer ALPhe and crosslinker N,N,-methylene-bis (acrylamide). The microgels exhibit spherical shape and favorable monodispersity. Increasing the content of ALPhe units incorporated into the microgel network will increase the average diameter, but decrease the swelling ratios and the transition temperature of particles.

Abstract: Digital microfluidic Biochips are widely used on safety-critical biomedical applications, and dependability is an essential attribute for them. To reduce dispensing time, a new test droplets dispensing solution for digital microfluidic biochip parallel testing is proposed in the paper, where multiple test droplets are allotted to the limited test dispensing sources to transmit them to the corresponding test target. The goal is minimizing the dispensing time, and then reduces the system testing time. Even thought the problem is shown to be NP-complete, it can be solved exactly for practical instances using integer linear programming (ILP). The experimental results demonstrate that optimal solutions to the test droplets dispensing problem in microfluidic biochip parallel testing are indeed feasible.

Abstract: In order to broaden the application range of liquid crystals, a new microfluidic drive and control method is proposed. Through a simulation model construction that links the plate motion and the liquid crystal backflow, we can study the coupling of the internal alignment and velocity fields of the liquid crystal in the model. On applying a continuous square wave electric field, the upper plate of the cell can be driven to move continuously, and the moving state can be related to the structure of the cell. When the gap between the two plates was 50 μm, the range of the change of tilt angle at the center of the cell was 6090°, and the induced backflow velocity profile was an S-shape. When the gap was 110 μm, because of the influence of the kickback effect, the range changed to 90100°, and the velocity profile was a double S-shape.

Abstract: In order to broaden the application range of LCP, the simulation of the LCP Hele-Shaw flow in the square cavity was conducted. The temperature of the cavity was constant 300°C. In the simulation the Leslie-Ericksen and TIF theories were used. With this simulation results, we can predict the position of the flow front at any time during the whole injection process and grasp the change of the pressure field and the velocity field. The change of the pressure and the velocity fields were very slow, there was no distortion point in the whole flow field. In the layer near the wall, the directors arranged evenly according to the direction of the flow and in the center layer it was decided by the shear rate in the X-Y plane.

Abstract: Aiming at such defects as the widely distributed threshold and poor universal performance in traditional inertial switch, a MEMS universal inertial switch was designed. The switch consisted of two annular lectrodes, each electrode was suspended by four serpentine flexures and could move freely. There was a gap between the two electrodes and the gap kept the swtich open during non-working state . When the absolute value of acceleration along a particular direction in the x-y plane exceeded a certain threshold value, one of the electrode (the sensing mass) contacted with the other electrode, the ON-state was held and the duration of the ON-state extended because of the flexible distortion of serpentine flexures . The finite element dynamic model was established and simulated in LS-DYNA and the simulation results showed that under the effect of 800g acceleration, the response time and the contact time of the switch were approximately 0.135ms and 20respectively. Compared with other inertial switch, the designed switch exhibited the higher trigger sensitivity and contact reliability. The micro inertial switch was fabricated using the MEMS bulk micromachining process, including the crucial technology of KOH etching, ICP etching spray coating method and so on. The testing system was designed and the shock testing was selected to test the performance of the switch. The test results showed that when the acceleration reached 800g, about 83% switches could work normally.

Abstract: In this paper, based on the design theory of CPW equalizer with low VSWR, microwave reconfigurable equalizers with various equalization curves have been designed. The combined structures of the reconfigurable equalizer with low VSWR and small sizes via MEMS switches have been optimized by ADS and HFSS software. The equalizer can be used in the frequency range from 20GHz to 24GHz. With the control of switches, the reconfigurable equalizer can realize the variation of the equalization curves and achieve the minimal insertion losses of around-1dB, respectively. In order to improve the minimal insertion losses, a matched structure has been presented. The matched structure reduces the minimal insertion losses compared with the former structure significantly.

Abstract: Micro-perforated panel (MPP) is known for its remarkable noise absorption capability and has been studied and developed for decades. Although the panel and cavity walls of traditional MPP are rigid, some previous works have shown that the absorption bandwidth of flexible MPP can be improved by the vibration of the panel. But this result is only tested at low frequencies. In this paper, the flexible MPP aiming at high frequency range is studied under a control experiment. But the perforations of high frequency MPP are in the range of micron and difficult to be fabricated in traditional mechanical methods. A new process, based on MEMS silicon mold technology and PDMS casting method, is developed to meet this challenge. Experimental results show that the noise absorption bandwidth of flexible MPP does get widened conspicuously only at a little sacrifice of absorption peak.

Abstract: This is mainly due to the high chemical reactivity and spontaneous etching nature of the fluorine radicals towards silicon, and the high volatility of the silicon fluorides as reaction products. Anisotropy can only be achieved by the inclusion of sidewall passivation schemes to the process. The existing approaches to deep reactive ion etching (DRIE) of silicon are distinguished by the way sidewall passivation is achieved, the key to anisotropy and overall performance of the etch process. Cryogenic etching and the so-called Bosch process with alternating etch and passivation cycles are the two most well-known high-aspect-ratio silicon etch processes and are discussed in this paper.