MEMS Electrostatic Actuation in Conducting Biological Media

We present design and experimental implementation of electrostatic comb-drive actuators in solutions of high conductivity relevant for biological cells. The actuators are operated in the frequency range 1-10 MHz in ionic and biological cell culture media, with ionic strengths up to 150 mmol/L. Typical displacement is 3.5 mum at an applied peak-to-peak signal of 5 V. Two different actuation schemes are presented and tested for performance at high frequency. A differential drive design is demonstrated to overcome the attenuation due to losses in parasitic impedances. The frequency dependence of the electrostatic force has been characterized in media of different ionic strengths. Circuit models for the electric double layer phenomena are used to understand and predict the actuator behavior. The actuator is integrated into a planar force sensing system to measure the stiffness of cells cultured on suspended structures.     

Design of XNBR nanocomposites for underwater acoustic sensor applications: Effect of MWNT on dynamic mechanical properties and morphology

In this work, application of rubber‐MWNT nanocomposite for underwater acoustic sensors is explored. The nanocomposite is developed by incorporating multiwalled carbon nanotubes (MWNT) into carboxylated nitrile rubber by mechanical mixing. The addition of MWNT up to 10 phr is found to result in about 330% increase in tensile strength, 140% increase in modulus, and 160% increase in tear strength. Transmission electron microscopy and scanning electron microscopy analyses indicate uniform dispersion of nanotubes in the rubber matrix. Dynamic mechanical analysis shows that damping at ambient temperature gradually increases with increasing filler content. This is attributed to the augmented frictional energy loss at the interface. The damping peak position shifts upward with increase in MWNT concentration, which may be gainfully used to tune to the operational frequency range of underwater acoustic sensors. Payne effect is observed at higher filler concentration due to the breakage of aggregates formed by filler–filler interaction. The nanocomposite may find application for damping structural vibrations and thus to improve the performance of underwater acoustic sensors. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40752.     

Independent testing and validation of prototype hydrogen sensors

In this article, the independent testing and validation of a packaged, electrochemical prototype hydrogen sensor at the National Renewable Energy Laboratory (NREL) is reported. Custom electronics were developed to be compatible with the data acquisition system at NREL. The specialized hydrogen sensor-testing laboratory at NREL used a variety of standardized test protocols to assess sensor performance. The system controlled and monitored humidity, pressure, and hydrogen gas concentration and introduced interference gases such as methane, carbon dioxide, carbon monoxide and ammonia.     

Some computational aspects of discrete orthonormal moments

Discrete orthogonal moments have several computational advantages over continuous moments. However, when the moment order becomes large, discrete orthogonal moments (such as the Tchebichef moments) tend to exhibit numerical instabilities. This paper introduces the orthonormal version of Tchebichef moments, and analyzes some of their computational aspects. The recursive procedure used for polynomial evaluation can be suitably modified to reduce the accumulation of numerical errors. The proposed set of moments can be used for representing image shape features and for reconstructing an image from its moments with a high degree of accuracy.     

Investigation of the selective catalytic reduction of NO by NH3 on Fe-ZSM5 monolith catalysts

Photocatalytic nitric oxide (NO) decomposition and reduction reactions, using carbon monoxide (CO) as a reducing gas, have been investigated over Degussa P25 titanium dioxide photocatalysts, using a continuous flow reactor. The effects of thermal pretreatment temperature and reaction gas composition on the activity and selectivity of the decomposition and reduction reactions have been evaluated. Prepared materials were characterised by X-ray diffraction (XRD), N₂ physisorption, transmission electron microscopy (TEM) and differential scanning calorimetry (DSC) and findings from these techniques were used to explain the observed photocatalytic properties. XRD and TEM results indicated that for the pretreatment temperatures used (70, 120, 200, 450 and 600 °C) there was no appreciable change in the phase composition and the original composition of ca. 77 vol.% anatase and 23 vol.% rutile was maintained even after treatment at 600 °C. It was found that the photocatalytic activity for both the decomposition and reduction reactions decreased with increasing pretreatment temperature. This was attributed to the removal of surface hydroxyl species that act as active sites for reaction. For the decomposition reactions the only products observed were nitrogen and nitrous oxide and the selectivity for nitrogen formation remained constant (ca. 23%) regardless of the pretreatment temperature. The presence of CO in the reaction gas had a dramatic effect on the selectivity of the reactions with nitrogen selectivities as high as 65% being observed. It was found that as the CO/NO ratio increased the selectivity for nitrogen formation increased.