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Aluminum-anode micro fabricated electrochemical cells activated on demand are a power-MEMS alternative. Cells of this type activated with alkaline electrolyte aqueous solution (20 µl) that contains hydrogen peroxide continue to be studied herein. Hydroxide concentration in this liquid and the cell configuration are the two issues investigated. Both affect the mechanistic kinetics of the chemical reactions involved in the production of energy and can be used to improve the energetic gravimetric density of these cells. Of the four electrolyte recipes, the highest energetic densities per activation are found in cells with a 3 M hydroxide concentration. The cell fabrication involved depositing aluminum lines on a patterned dielectric structure on top of a platinum cathode. The mesh-shaped electrode structure on the masks is designed so cells with three dissimilar cathode:anode surface areas are fabricated, each with a different number and width of aluminum lines, allowing us to deconvolute the electrode area ratio effect from the cells' dimensional characteristics. The electrode area ratio can in fact be used to obtain energetic output up to 14 KJ g−1 of aluminum and is capable of providing a power output of 3.5 mW cm−2 (at a potential of approximately 0.6 V) for about 5 min.

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The design and optimization of light-based analytical devices often require optical characterization of materials involved in their construction. With the aim of benefiting lab-on-a-chip applications, a transmission spectrometric method for determining refractive indices, n, of transparent solids is presented here. Angular dependence of the reflection coefficient between material-air interfaces constitutes the basis of the procedure. Firstly, the method is studied via simulation, using a theoretical algorithm that describes the light propagation through the sample slide, to assess the potentially attainable accuracy. Simulations also serve to specify the angles at which measurements should be taken. Secondly, a visible light source and an optical fiber spectrometer are used to perform measurements on three commonly used materials in optical lab-on-a-chip devices. A nonlinear regression subroutine fits experimental data to the proposed theoretical model and is used to obtain n. Because the attainable precision using this method of refractive index determination is dictated by the uncertainty in the transmission measurements, the precision (with 95% confidence) for mechanically rigid samples, namely glass and poly(methyl methacrylate) (PMMA), is higher than those estimated for the elastomer sample (in-house-molded poly(dimethylsiloxane) (PDMS)). At wavelengths with the highest signal-to-noise ratio for the spectrometer setup, the estimated refractive indices were 1.43+/-0.05 (580 nm) for PDMS, 1.54+/-0.02 (546 nm) for glass, and 1.485+/-0.005 (656 nm) for PMMA. Accurate refractive index estimations with an average precision equal to 0.01 refractive index units (RIU) were obtained for PMMA and glass samples, and an average precision of 0.09 RIU for the PDMS molded slide between 550 and 750 nm was obtained.

The problem of controlled liquid delivery to a microelectromechanical system (MEMS) device is one that is being continuously investigated. There are many types of valves being fabricated for different applications. For single-use systems, burst valves are an ideal choice. These types of valves ensure that there is no leaking of the fluid to the rest of the system. Models have been developed using COMSOL multiphysics incorporated in an optimization routine to study and predict the behavior of valves made with metallic resistors over silicon nitride membranes, with the goal of developing a tool that can be used to design low-power valves. Power and temperature data for valves made in our MEMS facility have been used to obtain an average overall heat transfer coefficient, which in turn is used to predict the voltage, temperature and stress of the breaking point of the valves. The simulation results were found to be adequate to represent the behavior of valves for two ohmic heater designs fabricated with gold and platinum. The models can be used to compare different valve designs to minimize the energy required for actuation. Experimental data showed that the valves could be broken with between 15 and 50 mJ.