Wang Liding

Investigation of a Microcalorimeter for Thin-Film Heat Capacity Measurement

A microcalorimeter is studied for testing heat capacity of thin films. The microcalorimeter is a suspended membrane supported by six microbridges, which is fabricated by the front-side surface micromachining. Compared to the bulk micro-machined one, the microcalorimeter has excellent mechanical strength and precisely controlled pattern size as well as good thermal characteristics that are essential to a microcalorimeter. The heating rate of the microcalorimeter is up to 2×105 K/s with 4.5 mW heating power in vacuum, and the heat capacity of the corresponding empty microcalorimeter is about 23.4 nJ/K at 300 K. By a pulse calorimetry, the heat capacity of Al thin films with thickness of 40–1150 nm are measured in the temperature range from 300 K to 420 K in vacuum. The mass of each sample is evaluated and the specific heat capacity is calculated. The results show that specific heat capacity of the 1150-nm Al film agrees well with the data of bulk Al reported in the literature. For the thinner films, enhanced heat capacity is observed.

A Microfluidic Pump/Valve Inspired by Xylem Embolism and Transpiration in Plants

In plants, transpiration draws the water upward from the roots to the leaves. However, this flow can be blocked by air bubbles in the xylem conduits, which is called xylem embolism. In this research, we present the design of a biomimetic microfluidic pump/valve based on water transpiration and xylem embolism. This micropump/valve is mainly composed of three parts: the first is a silicon sheet with an array of slit-like micropores to mimic the stomata in a plant leaf; the second is a piece of agarose gel to mimic the mesophyll cells in the sub-cavities of a stoma; the third is a micro-heater which is used to mimic the xylem embolism and its self-repairing. The solution in the microchannels of a microfluidic chip can be driven by the biomimetic “leaf” composed of the silicon sheet and the agarose gel. The halting and flowing of the solution is controlled by the micro-heater. Results have shown that a steady flow rate of 1.12 µl/min can be obtained by using this micropump/valve. The time interval between the turning on/off of the micro-heater and the halt (or flow) of the fluid is only 2∼3 s. This micropump/valve can be used as a “plug and play” fluid-driven unit. It has the potential to be used in many application fields.

Dynamic Characteristic of Microstructure in High g Acceleration Environment

To study the dynamic characteristics of micro electro-mechanical systems(MEMS) microstructures in high-g acceleration environment,the dynamic testing technology in high-g acceleration environment is systematically studied and the dynamic testing equipment is developed.The base excitation device which uses piezoelectric ceramic as the driving source is established.The typical beam─mass block microstructure which integrates the piezoresistive element is prepared.The dynamic characteristic and its change law of the typical MEMS microstructure in 0g to 10 000g acceleration environment are studied through experiments.The experimental results show that under the action of high-g acceleration,when the microstructure has large deformation,thus being in the nonlinear state,the natural frequency of the microstructure gets higher with the increase of acceleration;when the microstructure only has small deformation and is in linear state,its natural frequency does not change with the action of external acceleration.Whether in large or small deformation state,the external high-g acceleration has no effects on the damping ratios of the microstructure.The experimental result is in good agreement with the analysis result of nonlinear finite element modal with stress stiffening effect.

Automatic Micro-bonding Technology of Capillaries with Adhesives

The application of plastic microfluidic chips can be extended with quartz capillaries connected at the end of their microchannels, e.g. UV absorption detection method can be carried out, which responds to almost 80% chemical compounds in detection. Experiment system for automatic microassembly was developed to carry out the task of joining capillaries to plastic microfluidic chips. Experiments were done with different viscosity of UV curing adhesives, dispensing time, dispensing pressure and curing time. Suitable process parameters were determined. Visual feedback is employed in the microassembly system. The automatic positioning of capillary with visual information is described. The problems met during assembly are discussed and solved

Automatic fabrication system for plastic microfluidic chips

An automatic fabrication system for batch production of plastic microfluidic chips was developed. The fabricated chips can be used for capillary electrophoresis analysis. The processing technique of chip fabrication mainly includes three steps: microchannel fabrication using hot-embossing technique, precise alignment of the chips substrate and cover, thermal bonding of the substrate and the cover. Hot-embossing machine, automatic aligning equipment for transparent substrates and thermal bonding machine were developed according to the processing technique. The automatic fabrication system and its constitutional equipments, the embedded processing techniques and auxiliary functions are described and explained in the paper. The auxiliary functions, such as automatic de-embossing and pre-joining of the plastic substrate and cover, are realized for fully automatic fabrication.

A design of efficient transport layer protocol for wireless sensor network gateway

It is necessary that in the small-or-medium-size wireless sensor networks, the networking information of network and monitoring data of sensors should be sent to the remote computers through the gateway to achieve remote monitoring for the target area. Wireless sensor network data characterize strong bursts, instability of traffic and small amount of data in a single packet. Considering these features as well as the bandwidth of wireless network, the paper proposes a Transport Control Protocol (TCP) with an improved Nagle algorithm. The experiments prove that the improved algorithm obviously enhances the utilization of wireless channel and reduces system energy consumption, while it ensures transmission reliability.

New Developments on Micro-nano Manufacture Technology in China

The current status of micro-nano manufacture technology in China is outlined firstly.The new research developments on micro mechanical properties,micro friction wear and sticking,micro fluidics in typical micro flow device,topological optimum application in micro-nano structural design,micro thermal transforming behavior in micro electro mechanical system(MEMS)are emphasized.The new achievements on design methodology of MEMS,the manufacture techniques including silicon base and no silicon base are introduced,the new developments on such as micro sensors,micro actuators,micro system as well as lab-on-chip device and micro power system are also listed.Finally,some conclusions are given out.

Relationship between coupler curve properties of a 4-bar linkage and its dimensional types

Three types of 4-bar linkages can trace the same coupler curve according to the cognate mechanism law. Based on the investigation of the relationship between dimensions of a linkage and the harmonic component characteristic parameters of the coupler curve of the linkage, it was found that six types of linkages are related to the same coupler curve, and they belong to two groups of cognate mechanisms, in which the coupler curves have the same shape and are symmetric. The relationships among the dimensional types of these six mechanisms are presented. The corresponding examples have also proved these conclusions. This work enriches the cognate mechanism law, and can result in more candidate mechanisms for mechanism dimensional synthesis.

Study on distribution of electrokinetic microfluid in rectangular microchannel

Electroosmotic flow is widely used as a primary method of species transport in microfluidic devices. In this work, the characteristics of electroosmotic flow in rectangular microchannels with the hydraulic diameter of 20 /spl mu/m/spl sim/30 /spl mu/m were investigated. Exact solutions for the velocity distribution and electroosmotic flow field are obtained by solving the complete Poisson-Boltzmann equation, describing the net charge field distribution induced by electric double layer next to a charged solid surface, and the Navier-Stokes equation, describing the hydromechanical momentum, under analytical approximation for rectangular microchannel. The simulation results of flows driven by mixed electroosmotic and pressure gradient are given. A method to extract the velocity profile from time sequence images was presented. The experiments consist of accurate observation and the behavior measurement of flow mean velocity by the digital particle images velocity (DPIV) systems. The experimental images of the electroosmotic flows profile under various value of the pressure gradient are consistent with the normalized velocity distribution. The microfluidic velocity were measured and studied as a function of hydraulic diameter ranging from 20 /spl mu/m to 30 /spl mu/m. The flow rate are linearly dependent on applied electric field strength. The linearity errors with standard deviation are (0.0050-0.0202) cm/s. No significant departures from continuum fluid theory have been observed ignoring the temperature changes. Thus, the behaviors of the microfluidic flow, at least down to 30 /spl mu/m diameter, can be predicted by the traditional fluid theory and EDL theory. At the same time, the Joule heating gradient effect caused by the high electric strength must be considered when the channels dimensional size increase.