Larry Langebrake

A micro-fluidic galvanic cell as an on-chip power source

We present a micro-fluidics actuated galvanic cell for on demand power generation. The galvanic cell is an aluminum anode/alkaline electrolyte/air cathode cell. The concept is based upon an actuation mechanism that pushes an electrolyte into a micro-channel containing electrodes. When the electrolyte reaches the electrodes of a galvanic cell, it produces energy through an electrochemical reaction. The proof of concept is presented herein by fabricating and characterizing a single cell using micro-fabrication techniques. The actuation mechanism is based on the thermal expansion of a working fluid. A brief discussion on the optimization of this actuation is also presented. The open voltage of this micro-cell was experimentally measured to be around 1.9 V. The Al/air galvanic cell chemistry has been compared with commercial Zn/air battery and has been found to perform better. The present micro-cell design (with an area of 0.75 cm 2 ), is capable of providing an energy of 5 J after 6.0 min when subjected to a load of 20 � . The actuation mechanism takes less than a minute and consumes about 3.5 J.

Spectrometric Determination of the Refractive Index of Optical Wave Guiding Materials Used in Lab-on-a-Chip Applications

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.

A finite element method modeling approach for the development of metal/silicon nitride MEMS single-use valve arrays

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.

Small form factor microsensor system using optical MEMS for passive optical digital communications (PODC)

A small form factor microsensor system with optical MEMS devices is discussed in this paper. The key components in the microsensor system include a temperature and humidity sensor for environmental monitoring, a microprocessor for signal processing, and an optical MEMS device (active corner cube retroreflector or CCR) for remote free space optical communication. A flexible circuit design and a folded packaging scheme have been utilized to minimize the overall form factor. Flat, flexible polymer batteries are incorporated to minimize the vertical profile to a few millimeters. The entire fully packaged sensor system is about 30mmx30mmx6 mm. MEMS design of the CCR, fabrication, hermetic packaging of CCR, flexible circuit design and fabrication, flip chip bonding of die form microprocessor, and a battery replacement scheme for extended operation lifetime are crucial elements for the development of a real product for the microsensor system. Optical MEMS CCR is a torsion mirror design and was fabricated using surface micromachining with Si3N4 as a structural layer. A finite element analysis (FEA) model was developed to optimize design and performance of the MEMS structures. The sensor system has a miniature mechanical switch for local actuation and an optical switch for remote actuation. The applications of such a microsensor system include both tracking, tagging, locating (TTL) and remote sensing.

Rapid Design, Fabrication and Optimization of a Single Event Thermo-Pneumatic Microactuation for the Delivery of Minute Amounts of Liquids

The need for efficient metering control of liquids in small devices has led to a boom in the advent of different micro-fluidic actuation mechanisms. Here we present a brief study on a thermal-pneumatic actuation mechanism for an on-demand delivery of minute amounts of liquids. A closely coupled, iterative design-fabrication strategy is used for optimization of a system in which no freely moving membranes are included. Special consideration was given to the heating device, minimizing the energy consumed. The fabrication method and performance of two types of fabricated resistors are compared herein. The first, a conventional Nickel-Chromium resistor using, lift-off micro-fabrication techniques, was initially tested. The second, a Copper cladded liquid crystal polymer in conjunction with a novel mask-less patterning system was used to produce nonconventional heating micro-ohmic heaters. The heating efficiency was proven to be superior using the latter approach. Various micro-fabricated fluidic devices have been designed as case studies and have been fabricated and integrated using a variety of materials to illustrate the functionality of the approach. The combination of design and fabrication steps, the simplicity of the resistive device, and the materials selected combined, yield a direct path to making fluidic transport devices for micro-analytical and power systems.Copyright

Novel, MEMS-Fabricated, Reserve, Galvanic Cells for Deployable Underwater Sensors: Depth-Sensitive Activation & In-Situ Generation of Electron-Acceptors Species

With the aim of benefiting miniaturized sensing systems in environmental applications a discussion on the preliminary development of portable galvanic batteries of the reserve type, i.e. activated on-demand via specific-depth immersion, is presented. Two major aspects in the design of the presented batteries are discussed. First, two possible novel chemistries are presented herein that allow for the batteries to be activated using water. Electrochemical characterization, in the form of polarographic curves obtained from tests of the fabricated cells, is presented. Using aluminum as an anode, the cells have open voltage circuits of 1.6 and 1.8 volts, respectively, and are capable of providing power densities up to 3 and 15 mAmps/cm . The fabrication routes of batteries with thin-form factors are detailed. Second, a micro fabricated pressure sensitive membrane is described, realized and tested as an automated way to activate the cells, via the immersion depth. So far the fabricated silicon nitride membranes (2times2 mm2 times 2 mum) can withstand up to 30 meters of depth underwater. Additional benefits of the proposed novel cells such as simplicity in their fabrication and use, safety, and their potential for powering underwater environmental sensors are also outlined.

Novel Microfabricated Batteries for Marine Sensors: In-situ Catholyte Generation via Water Addition

Flat micro fabricated galvanic cells have been reported in the recent literature. In this work we present an aluminum-anode cell, which has been loaded with an oxyhalogenated organic compound (sodium dichloro-s-triazinetrione) that releases hypochlorite ions via a hydrolysis reaction when water is added. A catalytic metal is used as the current collector. This novel concept in micro cells and the electrochemical characterization of the fabricated cells are presented herein. The results show that the fresh in-situ formation of hypochlorite ions, using the mentioned hydrolysis reaction, constitute a packaging strategy for the oxidizer that leads to advantageous features, especially for battery systems to be used in marine applications. Cells with improved operational life and capacities (about six to ten times larger than in a cell activated with the 10% sodium hypochlorite solution, recently reported in literature) are described herein.