Optimal shape design of three‐dimensional MEMS with applications to electrostatic comb drives

A comb drive is one of the most important microactuators in Microelectromechanical (MEM) systems. In a standard comb drive, the capacitance varies linearly with displacement, resulting in an electrostatic driving force which is independent of the position of the moving fingers (relative to the fixed ones) except at the ends of the range of travel. It is of interest in some applications to have force profiles such as linear, quadratic or cubic. Such shaped comb drives could be useful, for example, for electrostatic tuning or to get actuators with longer ranges of travel than those of standard comb drives. This paper presents a methodology for solving three‐dimensional design (inverse) problems in MEM systems. Design of variable shape comb drives (shape motors) is presented as an application of the general methodology. It addresses issues of simulation, sensitivity analysis and then design of three‐dimensional comb drives. Direct simulation is carried out by the exterior, indirect boundary element method and shape sensitivities are obtained by the direct differentiation approach. The inverse problem determines the height profile of the moving fingers of a comb drive such that the driving force is a desired function of its travel distance. An available optimization code (‘E04UCF’ from the NAG package) is used to solve the inverse problem. Numerical results are presented for shape motors that produce linear or cubic force profiles as functions of travel of the moving fingers. Copyright © 1999 John Wiley & Sons, Ltd.     

SST-1 Refurbishment Progress: an Update

Refurbishment of steady state tokamak (SST-1) primarily focused at addressing the issues and bottle-necks involving various subsystems of SST-1 as observed during earlier commis- sioning attempts, have progressed significantly. Under the refurbishment spectrum, all joints in the superconducting magnet system have been re-fabricated as low DC leak tight joint resistances, all toroidal field (TF) magnets have been equipped with 5 K radiation shields on the inner side and successfully tested for their rated parameters in cold under nominal currents, all vessel sectors and modules have been baked and tested under representative conditions, supporting helium and ni- trogen cryogenic facilities have been made > 99% reliable in various envisaged operating scenarios of SST-1. The reassemblies of the critical subsystems of the SST-1 machine shell have progressed aggressively and are nearing completion. Auxiliaries such as the baking facility for the vacuum vessel and first wall components, current leads assembly distributions, synchronized timing sys- tem, reliable data acquisition and plasma control systems as well as essential diagnostics have also been readied towards the first plasma. A detailed engineering validation of the assembled SST-1 machine shell including field error measurements has been planned prior to first plasma attempts.     

On the Development of Thermo-Kinetic Eh-pH Diagrams

It is shown that thermo-kinetic Eh-pH diagrams can be generated through electrochemical measurements. These diagrams offer an accurate method of determining stability regions for leaching without relying on thermodynamic calculations, which may be inaccurate or for which data may be difficult to obtain. The Fe-NH₃-CO₃-H₂O system is studied here. Potentiodynamic polarization experiments were performed on an iron sample in ammoniacal solution in de-aerated condition at different temperature and pH. Polarization plots show that both active anodic dissolution and passive regions are present for pure iron in ammoniacal solution depending on the potential. The electrochemically obtained potential-pH data were used to generate the thermo-kinetic Eh-pH diagrams for the Fe-NH₃-CO₃-H₂O system.     

Efficient Recovery of Combustibles From Coking Coal Fines

The processing of three Indian coking coal fines with feed ash values of 25.12% (S1), 22.97% (S2), and 30.38% (S3) was studied. Substantial improvement in the overall recovery of combustible could be obtained by splitting sample S1, exhibiting good washability but poor release behavior, into a coarser and a finer fraction and treating them by gravity and Jameson cell flotation, respectively. Sample S2 had over 70% of the material below 100 µm and had excellent release characteristics. The Jameson cell flotation indeed resulted in very high recovery of combustibles at the desired target ash values and split processing was not required for this sample. The floatability and washability characteristics of sample S3 indicated that gravity-based methods might improve combustible recovery in terms of theoretical yield at the desired product ash values. A combination of spiral concentration of the coarser fraction and froth flotation of the finer fraction using a Jameson cell showed some improvement in the combustible recovery of this sample. It was established in this study that if the floatability is poor or moderate, then split processing improves coal cleaning performance. Flotation alone may be recommended only when samples exhibit excellent floatability.     

Segregation and Process Features in a Teeter Bed Separator as Revealed by High-Speed Videography and Image Processing

Gravity concentration in a liquid fluidized bed floatex density separator (FDS) was investigated through high-speed videography and image analysis. Process performance in terms of yield and grade of the product for fine coal beneficiation in the FDS was established experimentally. The feed coal (?1.18 mm) with 36% ash was enriched to 24% ash at a mass yield of 65%. Coarsest underflow with a d₅₀ of 700 μm was obtained at 5.8 kPa bed pressure, 120 kg/h feed rate, and 12 lpm teeter water flow. The lowest SG₅₀ of 1.62 was obtained at 5.4 kPa, 15 lpm, and 80 kg/h. At 9 lpm water flow, steady state was achieved in 400 sec when the voidage and suspension density distributions became constant. From the suspension density distribution, the SG₅₀, 1.69 under this set of conditions, was estimated with reasonable accuracy. Increase in teeter water was shown to increase the time required for attaining steady state. It was established that particle size distribution at the bottom of the bed in the column offers a good indication of the separation performance. The influences of the operating variables on the axial steady state profile of the suspension density and voidage were also established. Image analysis is shown to be quite useful in collecting quantitative transient and steady state data that may be difficult to obtain otherwise. The process performances were adequately described using such transient and steady state observations.     

Numerical studies of a tube-in-tube helically coiled heat exchanger

In the present study a tube-in-tube helically coiled (TTHC) heat exchanger has been numerically modeled for fluid flow and heat transfer characteristics for different fluid flow rates in the inner as well as outer tube. The three-dimensional governing equations for mass, momentum and heat transfer have been solved using a control volume finite difference method (CVFDM). The renormalization group (RNG) k– model is used to model the turbulent flow and heat transfer in the TTHC heat exchanger. The fluid considered in the inner tube is compressed air at higher pressure and cooling water in the outer tube at ambient conditions. The inner tube pressure is varied from 10 to 30 bars. The Reynolds numbers for the inner tube ranged from 20,000 to 70,000. The mass flow rate in the outer tube is varied from 200 to 600 kg/h. The outer tube is fitted with semicircular plates to support the inner tube and also to provide high turbulence in the annulus region. The overall heat transfer coefficients are calculated for both parallel and counter flow configurations. The Nusselt number and friction factor values in the inner and outer tubes are compared with the experimental data reported in the literature. New empirical correlations are developed for hydrodynamic and heat-transfer predictions in the outer tube of the TTHC.     

Analysis of free and bound aroma compounds of pomegranate (Punica granatum L.)

Volatile aroma compounds were isolated from pomegranate arils by high vacuum distillation (HVD) and solvent extraction with diethyl ether. The HVD distillate exhibited a fresh-fruity and characteristic pomegranate aroma while the total ether extract was devoid of this note in its concentrate. Gas chromatography–mass spectroscopy (GC–MS) analysis revealed the presence of 3-octen-1-yl acetate, trans-3-hexen-1-ol, hexanol and 2-methyl pentanol only in the high vacuum distillate. Ether extract was dominated by 2-heptanol, 2-nonanol and 3-methyl-2-butanol. Based on olfactometric analysis of the HVD isolate, 3-octen-1-yl acetate was identified as the key odorant of pomegranate. Chemical synthesis of this compound, further confirmed its structure. Among the bound aroma compounds, 2-phenylethanol (40%), alpha-terpineol (4.53%) and 2-heptanol (6.35%) were identified as the major compounds existing as glycoconjugates. Identification of the character impact compound and the occurrence of glycosidic precursors in pomegranate are being reported here for the first time.     

Immobilization of horseradish peroxidase onto a gold-nanoparticle-adsorbed poly(thionine) film for the construction of a hydrogen peroxide biosensor

An amperometric hydrogen peroxide (H2O2) biosensor was developed based on the immobilization of horseradish peroxidase (HRP) onto a gold-nanoparticle (GNP)-adsorbed conducting poly(thionine) (PTH) film. The modification process was characterized by scanning electron microscope (SEM), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The effects of experimental parameters such as the concentration of the mediator (hydroquinone, HQ), the pH of the solution, and the working potential were investigated for optimum analytical performance. In the presence of the mediator, the immobilized HRP showed excellent electrocatalytic activity towards the reduction of H2O2. The linear dynamic range of 5-150 microM with the regression coefficient of 0.999 was obtained. The detection limit was calculated to be 1.5 microM based on a signal-to-noise ratio of 3. The reproducibility, repeatability, and stability of the biosensor were studied, with satisfactory results. The biosensor performance was evaluated with respect to the possible interferences and the application of the biosensor to real-sample analysis.