Key Engineering Materials Vols. 645-646

Abstract: The stable range of MEMS electrostatically actuated beam during the pull-in process is crucial to the device performance. Different devices have specific requirements for stable pull-in region based on their applications. In this paper, Rayleigh-Ritz energy method is used to establish dynamic pull-in model of electrostatic cantilever actuated by a step voltage. Modified trial function is derived according to different position of bottom electrode. The model takes into account the effects of fringe capacitance and variable cross-sectional beam. Published numerical methods and experimental data are used to verify the model . The impact of bottom electrode position on pull-in parameters is analyzed in present model. With fitting empirical equations, pull-in parameters can be easily satisfied through the distribution of bottom electrode, which provide an effective reference for the design of MEMS electrostatically actuated beam under given pull-in parameters .

Abstract: In this paper, the quartz crystal microbalance (QCM) sensors coated with polyvinyl pyrrolidone (PVP)-multiwalled carbon nanotubes (MCWNTs) nanocomposite thin films were developed by the spray process, which were used for the detection of low concentration formaldehyde at room temperature. The surface morphology and structure of films was analyzed by scanning electron microscope (SEM), UV-Vis absorption spectrometry, respectively, and the formaldehyde-sensing properties of sensors were investigated. The results showed that the prepared QCM gas sensor exhibited the linear characteristic, fast response, good reproducibility to low concentration formaldehyde within 6 ppm, and the poisoning of films was observed when the formaldehyde concentration exceeded 6ppm. Moreover, the sensitivity of the sensor could achieve up to 1Hz/ppm and had the good stability of response values.

Abstract: Micro direct formic acid fuel cell (DFAFC) is currently one of the promising technologies to power micro/nano devices and systems. Compared with micro direct methanol fuel cell (DMFC), micro (DFAFC) can have higher proton conductivity and energy density, and crossover of formic acid through Nafion membrane is significantly less than methanol. In this paper, a micro DFAFC has been developed. Polydimethylsiloxane (PDMS) is chosen as the material for fluid flow plates in both cathode and anode of the micro DFAFC in order to simplify its structure and improve its packaging performance. The developed micro DFAFC has been tested and results show that its input concentration of formic acid solution can reach up to 10mol/L with its peak power output of 13.6mW/cm² and maximum output current of 97.66mA/cm².

Abstract: Microfluidic time gates are applied to control accurate flow time of liquids in the autonomous capillary systems, which are critical structures for point-of-care diagnostic and analytical applications. The time gate employs several abruptly changing geometry of the flow path to change the wettability of micro-channels to meet the requirement of delaying flow. However, obtaining desirable flow of liquids in microfluidics is still a limiting factor in the practical implementation. The work demonstrates a novel 2D serial cross-channel time gate and 3D serial cross-channel time gate. They are fabricated in PDMS-based autonomous capillary system. 2D serial cross-channel time gate is comprised of multiple paralleled channels of changeable width with dimensions from 300-800μm. The number of the channels and the width variation of the cross intersections are crucial factors to influence the flow velocity of liquids. Compared with the 2D serial cross-channel time gate, the 3-D structures can eliminate the problem of entrapping air and improve the flow velocity of liquids in the time gate. The controlling time of the flow in 3D serial cross-channel time gate and 2D serial cross-channel time gate are 9~13s and 5s~51s, respectively.

Abstract: In this paper, we presented a novel method for fabricating the integrated electrochemical sensor based on a microfluidic device. The device included: printed circuit board (PCB) substrate with vertical embedded electrodes; polymethyl methacrylate (PMMA) with micro structures; PMMA cover with amperometric detection sensor (ADS). The ADS employed three-electrode sensor system which was composed by two Au electrodes and an Ag/AgCl reference electrode. The polyvinyl chloride (PVC) membrane was used as ion-exchange medium of reference electrode and installed between Au electrodes. Then, the potential changes and the standardization oxidation-reduction experiments were executed to characterize the integrated reference electrode performance. Finally, the ADS system was tested by cyclic voltammetry (CV).

Abstract: This paper introduce a new polydimethylsiloxan (PDMS) microfluidic chip bonding technology. By studying the influence of prepolymer with different curing agents, curing temperatures and curing time to the PDMS-PDMS chip bonding strength,we get the optimal bonding parameters. The experiment results show that when the cover plate of PDMS with ratio 15:1 bond with the substrate whose ratio is 10:1,the largest strength can be reached. The research which was applied to the packing of microfluidic analysis chip has achieved good results.

Abstract: Experimental research of first inverse, secondary positive piezoelectric effects are performed through the PZT-5 piezoelectric ceramics. Introduce a concept of self-sensing micro-flow injection device based on piezoelectric ceramics. Utilized the characteristic of the first inverse piezoelectric effect which can generate micro-displacement, micro-position and then micro-injection can be realized by the micro-change of piezoelectric ceramic’s volume. Self-sensing displacement in micro-injection process can be obtained by utilizing the secondary direct piezoelectric effect. The experimental data: if the external voltages which were applied to the stack are 20V and 40V, the theoretical displacement generated by the first inverse piezoelectric effect are 4μm and 8μm respectively, the actual measured values are 3.57μm and 8.12μm respectively, self-sensing displacement of secondary direct piezoelectric effect are 1.48μm and 2.53μm respectively. It proves that the theoretical and experimental device could sense the displacement of micro-injection and the integration of sensor and actuator can be achieved.

Abstract: A detection chip is designed and manufactured to study the relationship between iron wear particle content in hydraulic oil and the detected variation of average inductance, which detects content of iron wear particle by means of micro channel - inductive. Through experiments, we obtained inductive values in the cases. The case is that the sizes of iron wear particle are the same, while the content of iron wear particle are different. Thus the curve between content of iron wear particle content and variation of average inductance was drawn. Experimental results show that the inductance value increases with the increase of the iron wear particle content in hydraulic oil. Experiments prove that the way is feasible for the detection of iron wear particle content in hydraulic oil. This study has an important significance for the realization of iron wear particle content detection in hydraulic oil.

Abstract: The dry bias of MEMS humidity sensor induced by solar radiation heating seriously affects the accuracy of the relative humidity (RH) measurement. To solve this problem, this paper presents a novel numerical analysis method for the error correction of RH based on computational fluid dynamics (CFD). Firstly, considering the solar radiation, the distribution of temperature field of MEMS humidity sensor is simulated from the ground to 32km altitude by using CFD soft under the boundary condition of fluid-solid coupled heat transfer. Secondly, the numerical analysis model of RH is put forward for solar radiation dry bias (SRDB) correction based on the working principle of the MEMS capacitive humidity sensor and the definition of RH. The results of numerical analysis show that the error of RH caused by solar radiation is nonlinearly increased with the altitude. Meanwhile the errors decrease with the reflectivity of sensor or of solder point increase. The simulation data also indicate that the SRDB can be reduced by improving the reflectivity of sensor or of solder point, adopting the substrate material with high thermal conductivity or choosing the suitable thickness of sensor. However, the SRDB should be corrected, for it still is more than 20% under the low atmospheric pressure. In this paper, the method based on fluid dynamics simulation provides a new way to correct the error of radiosonde MEMS humidity measurement caused by solar radiation heating.

Abstract: This paper researches the characteristic to the flyer velocity of silicon flyer. The material of flyer is different in comparison to polyimide which is considerde to conditional flyer. It is found that the movement trendency is clearly different of velocity between silicon flyer and polymide flyer, which is resulted by modality change. The silicon flyer velocity decreases gradually with the increase of flyer thickness. The inclusion is also applicable for polyimide flyer. It is clearly that the fatal influence parameter is silicon flyer thickness for slapper detonator based on MEMS fabrication process, which determined the success of explosion.