Consumption-related development in microelectroforming

 High-aspect ratio microelectroforming is one of the most challenging techniques in MEMS microfabrication. This is particularly true with plating metal into the very tall micropatterned polymer molds made by X-ray lithography for primary or secondary metal structures or metal mold inserts within the framework of the LIGA process. Among various problems are: (1) the time consumption in plating very tall parts or using microelectroplating as a replication technique; (2) the cost of material, in particular in the formation of very high-aspect-ratio absorber structures for X-ray masks in the deep and ultra-deep X-ray lithography step. Received: 7 July 2000/Accepted: 23 August 2000     

Fabrication of collimating grids for an x-ray solar telescope using LIGA methods

 We are fabricating sub-collimating X-ray grids that are to be used in an orbiting solar X-ray telescope. The telescope optics consist of twelve rotating pairs of high aspect ratio grids. The pitch for the grids ranges from 34 μm to 317 μm. The grid thickness-to-grid-slit ratio must be approximately 50:1, resulting in grid thicknesses of 1 to 10 millimeters. We are implementing a design in which a 34 μm pitch, free-standing PMMA grid is fabricated with 20 μm wide slits through a 800 μm thickness. After exposure and developing, metal is electrodeposited into the slits in the PMMA grid and the PMMA is left in place to hold the individual metal pieces. For optimum imaging performance, the root-mean-square pitch of the two grids of each pair must match to within 1 part in 10000 and simultaneous exposures of stacked sheets of PMMA have insured that this requirement is met. Received: 30 October 1995 / Accepted: 25 January 1996     

SLIGA Based underwater weapon safety and arming system

 The Naval Surface Warfare Center, Indian Head Division (NSWCIHD) is applying microelectromechanical system (MEMS) technology to underwater weapon Safety and Arming (S&A) system development. MEMS technology provides an opportunity to develop a miniaturized S&A system that is more sophisticated with improved safety and reliability at a lower cost compared to current systems. An S&A system prevents premature initiation of the weapon while reliably ensuring initiation at the appropriate time. An S&A system uses multiple sensors and devices. In comparison with other weapon S&A systems, a critical aspect of underwater weapon S&A systems is the mechanical interlock system utilizing actuators and mechanical sensors. This paper describes the design, development and fabrication of S&A SLIGA device prototypes and of a SLIGA based S&A system. NSWCIHD worked with members of the HI-MEMS Alliance during design, development and fabrication. Advancements achieved by the HI-MEMS Alliance and SLIGA S&A design issues are discussed. Received: 25 August 1997/Accepted: 10 September 1997     

Tapered microvalves fabricated by off-axis X-ray exposures

 A method for creating angled structures for use in microvalve devices applicable to control of liquid flow is presented. This technique utilizes a modified LIGA process with successive angled and rotated exposures into free standing acrylic sheets to form a tapered valve seat structure. These valve seats are integrated with bulk micromachined silicon diaphragms and tapered PMMA valve bosses to complete the microvalve. The long term goal of this research effort is to develop a normally-closed, low power, microfabricated valve for use in an implantable drug delivery system. This paper reports on the design and fabrication of microvalves using off-axis LIGA exposures. Flow testing and fluid handling characterization results are also presented. Received: 25 August 1997 Accepted: 22 October 1997     

Chimie douce hydrogen production from Hg contaminated water,with desirable throughput,and simultaneous Hg-removal

Hydrogen's widespread use is fraught with many difficulties. The challenges currently are to do with safety concerns in gas storage and transportation, and low rate of production leading to non-viability of technologies at the point-of-use. Another global concern of immediate relevance involves heavy-metal ion pollution. Viable processes which can simultaneously remove and result in beneficiation of the contaminants are hitherto rarely reported. In this context we report a single-step, in situ co-reduction approach which has the dual advantage of (i) Hg contaminant removal, and (ii) room temperature hydrogen production. Hydrogen is produced via galvanic corrosion of in situ synthesized nanoaluminium amalgam. The production rate (720 mL/min for 0.5 g-Al salt) is far superior to what would be expected from the use of pure hydrides, and/or using bulk amalgams at room temperature. The method is simple, chimie douce (i.e soft chemical), hence potentially affordable, and capable of providing a means of beneficiating Hg contaminated water present in effluents from certain industries (for example, industries which uses chlor-alkali process). The in situ co-reduction approach helps in bypassing the usual rate limiting step which involves formation of an alumina passivation layer on hydrolytic material surface. Given the potential that exists in scale down and up, this approach offers a method to address the long standing challenge of point-of-use hydrogen availability.     

A translinear principle based low-power high-precision RMS-to-DC converter in CMOS technology

Analog Integrated Circuits and Signal Processing - In the present study, a low-power high-precision current-mode CMOS true root mean square (RMS)-to-DC converter is presented based on the...     

Distributed composition of complex event services in IoT network

The Journal of Supercomputing - In this paper, a distributed solution is presented for the composition of complex event services in the Internet of Things (IoT) environments. The composition of...     

Novel composite membrane based on zirconium phosphate-ionic liquids for high temperature PEM fuel cells

Composite membranes composed of zirconium phosphate (ZrP) and imidazolium-based ionic liquids (IL), supported on polytetrafluoroethylene (PTFE) were prepared and evaluated for their application in proton exchange membrane fuel cells (PEM) operating at 200 °C. The experimental results reported here demonstrate that the synthesized membrane has a high proton conductivity of 0.07 S cm^?1, i.e, 70% of that reported for Nafion. Furthermore, the composite membranes possess a very high proton conductivity of 0.06 S cm^?1 when processed at 200 °C under completely anhydrous conditions. Scanning electron microscopy (SEM) images indicate the formation of very small particles, with diameters in the range of 100–300 nm, within the confined pores of PTFE. Thermogravimetric analysis (TGA) reveals a maximum of 20% weight loss up to 500 °C for the synthesized membrane. The increase in proton conductivity is attributed to the creation of multiple proton conducting paths within the membrane matrix. The IL component is acting as a proton bridge. Therefore, these membranes have potential for use in PEM fuel cells operating at temperatures around 200 °C.