Xilian Wang

Novel modification of Nafion®117 for a MEMS-based micro direct methanol fuel cell (μDMFC)

Nowadays the micro direct methanol fuel cell (μDMFC) has received much attention as a leading candidate for portable power of the future. This paper presents a novel modification method of the commercial proton exchange membrane Nafion®117 to produce an improved polymer electrolyte membrane for the μDMFC. The method involves using γ-ray radiation and electroless palladium deposition on a Nafion®117 membrane. Specific scopes of the γ-ray radiation dose may cause membrane crosslinking, thus reduce the membrane swelling ratio and decrease methanol crossover. The electroless palladium deposition on the γ-ray radiation modified Nafion®117 further decreases methanol crossover. The modified membrane was characterized using a scanning electron microscope (SEM), an energy dispersive x-ray spectrometer (EDX) and x-ray diffraction (XRD). Water uptake, methanol permeability and membrane conductivity tests were also carried out. By reducing the membrane swelling ratio and methanol permeation, the single μDMFC with the modified Nafion®117 membrane produced reasonable power density performance as high as 4.9 mW cm−2 under 2 M methanol solution at room temperature.

A model for estimating the performance of synchronous parallel network simulation

Abstract This paper describes a model for estimating the performance of synchronous network simulation. The model is developed based on the BSP model, and includes various factors that may affect the performance of synchronous network simulation, such as load balancing, communication overhead, lookahead, and hardware plat-forms for running simulation. The model can not only predict but also help to improve the performance of synchronous network simulation. Experiments show that the model can estimate performance exactly. Treating the model as an objective function when the net-work topology is partitioned for synchronous simulation efficiently improves the performance of synchronous network simulation.

Design of Readout Circuits Used for Micro-machined Capacitive Accelerometer

This paper describes a closed-loop micro-machined accelerometer implemented in a bulk-micromachining technology with integrated CMOS circuit. The operational principle of accelerometer is detailed. We establish a mathematical model of closed-loop system to compare the performance with the open accelerometer. Electrostatic force is served as a negative feedback in closed-loop operating mode to improve the bandwidth, linearity and dynamic range of micro-machined capacitive accelerometer. The noise source affected readout circuit is discussed to optimize circuit structure. The circuit is simulated using Hspice. The result of the circuit simulation shows good sensitivity and low power consumption. The sensor is designed to measure plusmn5g acceleration. Device sensitivity is larger than 15mV/g.

The study of the improved wavelet thresholding with translation invariant de-noising on capillary electrophoresis signal

According to the characters of CE signal, improved wavelet thresholding with translation invariant was described to denoise for microchip capillary electrophoresis in this paper. The improved thresholding function has muti-derivative compared with the soft thresholding. The denoising method can not only remain the geometrical characteristics and keep the amplitudes of the original electrophoresis signal waveforms efficiently, but also suppress impulsive noise to some extent. In order to suppress Pseudo-Gibbs phenomena combining the translation-invariant de-noising was proposed. The experimental results indicated that the proposed methods in the paper have good signal-to-noise ratio through testing the actual electrophoresis signal. The baseline of the denoised signal is smooth and the peak shape has not distortion.

The influence of doping concentration on piezoresistive temperature characteristics of polysilicon nanofilms

Compared with ordinary polysilicon films and monocrystalline silicon, heavy doped polysilicon nanofilms have better piezoresistive properties and better temperature characteristics. Therefore, pressure sensors made of polysilicon nanofilms will have many corresponding advantages, including high sensitivity and complete self-compensation of temperature coefficients. In this paper, the influence of doping concentration on temperature coefficient of resistance (TCR) and temperature coefficient of gauge factor (TCGF) is deeply studied to optimize doping concentration in order to make temperature coefficients lowest. TCR and TCGF of samples with doping concentration of 4.1×1019cm-3, 1.0×1020cm-3, 2.0×1020cm-3, 4.1×1020cm-3, 7.1×1020cm-3 are tested at temperature range 23°C to 270°C, respectively, and the microstructures of the samples are also observed by the method of scanning electron microscopy (SEM) and transmission electron microscope (TEM). The experimental results have been explained reasonably based on the tunneling piezoresistive theory proposed before. Based on both experimental results and theoretical analyses, to obtain a zero value of TCR and a low value -0.1%/°C of TCGF, the optimal doping concentration of the films of 80nm thickness should be about 3×1020cm-3.

Field-portable Capillary Electrophoresis Instrument with Conductivity Detection

In this paper a novel capillary electrophoresis chip (CEC) is presented with integrated platinum electrodes and simplified conductivity detector. CEC is fabricated by the method of mechanical modification with probe on organic glass. Capillary electrophoresis chip can rapidly completed ion separation by simulation of concentration distribution and zone-broadening. Detection circuit is simple which can detect pA order current. This system has those advantages such as small volume, low power consumption and linearity, and well suit for field analysis.

Investigation of electrostatic bonding time model with point cathode

This paper discusses a novel method of modeling and simulation of anodic bonding technique, which is widely used in fabrication of MEMS device and micro system. The emphasis are the bond expansion model and extended time formula of silicon-glass anodic bonding, and based on which, visual simulation of the process is achieved. In practical experiments, by utilizing the math model, simulation result matches well with the real process, perfectly displaying the electricity characteristics. This novel approach of simulation possesses high practicality, and additionally, will be important and valuable in the development of MEMS technology and microelectronics.

Effect of the detector parameters on the sensitivity of contactless conductivity detector for microchip electrophoresis

The contactless conductivity has attained great attention in the last decade. But the application of contactless conductivity is restricted by its sensitivity, how to improve the sensitivity has become the key of contactless conductivity. Some simple equivalent circuits have been used to explain the basic functioning of a capacitively coupled contactless conductivity detector, it can not explain some experiment phenomena. A new equivalent circuit of the cell is given in this paper according the physical structure of cell, which takes into account the effects of the spatial component of the solution conductivity as the electrophoretic zones pass inside the detector. The effect of the detector geometry on the sensitivity of contactless conductivity is studied. By simulation, the optimal parameters were found. This paper has guidance to improve the sensitivity of contactless conductivity.

The Effects of Different Flow Channels on Silicon-based Micro Direct Methanol Fuel Cells

Based on CFD (computational fluid dynamics), modeling and numerical simulation of the muDMFC (micro direct methanol fuel cell) are carried out ,meanwhile the influence of the muDMFC with various flow channels design is studied using the CFDRC commercial code. The simulation results show that the performance of the muDMFC with the parallel flow field excelled the one with the dot flow field. The experimental results show the same performance compared with the simulated data, and the muDMFC with parallel flow field has a maximum power density of 5.92mW/cm2 at the voltage of 192.9mV while the one with dot flow field has a maximum power density of 4.37mW/cm2 at the voltage of 180.7mV.

Self-testable Pressure Sensors Based on Phase Change

Novel self-testable pressure sensors based on phase change have been fabricated. The sensors were built in a glass-silicon-glass sandwich structure. Water acted as the phase change material (PCM) was injected into the cavity of the pressure sensor. Applying voltage to the heating resistor, the PCM boiled. The vapor produced by phase change can produce high enough self-testable output. Therefore, the method had been used for large-scale pressure sensors. The design and simulation of the new structure, the main fabrication process, and the experimental results on the self-testable function were presented. The self-testable output is up to 3.0% of the full-scale output