1998 - Draper Laboratory

generate typical wave spectra for deep and shallow waters, models forwave kinematics as affected by flat or sloping bottoms, and models forforces and moments on submersibles due to these surface waves. Forcesand moments are computed using two alternative methods. One is a fastmethod based on analytical integration of dynamic pressure forces overthe surface of an elongated ellipsoidal body. It gives first-order forces andmoments limited to horizontal and restrained bodies. The secondmethod, based on the Froude-Krylov approach, uses numericalintegration of dynamic pressures to give forces and moments on anyshape hull in any attitude. Unlike the first method, it can be extended toinclude broaching of the sea surface by the body. Hydrodynamic forcesdue to an unrestrained body’s motion are accounted for with “addedmass” terms. These mathematical models have been implemented in theC language in a real-time computer simulation. They are actively used tostudy the dynamic performance and control of submersibles at periscopedepths.Conley, J. F., Jr.; Lenahan, P. M.; Cole, P.Predictive model of SOI buried oxide charging based onstatistical mechanics and spin resonance data1997 IEEE International SOI Conference Proceedings(Cat. No.97CH36069), pp. 176-177In partially depleted NMOS transistors on SOI, back-channel leakageproblems are caused by radiation-induced hole trapping at point defectprecursors in the Buried Oxide (BOX). Thus, a predictive model of thesehole traps would be quite useful. We show that a model developedrecently for hole trapping in poly-capped thermally-grown oxides alsoeffectively predicts trapped hole densities in Unibond and SIMOX buriedoxides. The model is based on statistical thermodynamics and ElectronSpin Resonance (ESR) measurements of defects known as E’ centers.Connelly, J. H.; Brand, G. N.Advances in micromechanical systems for guidance,navigation, and controlProceedings of the AIAA Guidance, Navigation, and Control Conference,New Orleans, LA, August 1997Draper Laboratory and Boeing North American (formerly the RockwellCorporation) have formed an alliance to develop and manufacturemicromachined inertial sensors and systems. Initial products serve highvolumecommercial markets with target prices below $25 per instrument.Recent performance improvements, however, will enable new systems formany military and space applications. One such application is theaddition of guidance to low-end, previously unguided artillerymunitions. This paper reviews existing and potential new applicationareas and describes micromachined inertial sensor design, operation, andfabrication methods. Development activities for a flexible productionbase to serve DoD/NASA needs are presented. Also included are thelatest test data, projected performance improvements, and new conceptsfor low-cost, miniature, multi-axis systems.Connelly, J. H.; Barbour, N.; Brand, G. N.Manufacturing micromachined inertial sensor systemsProceedings of the Saint Petersburg International Conference onIntegrated Navigation Systems, 4th, St. Petersburg, Russia (A97-3086907-35), pp. 362-370, May 1997A flexible production base is being created to serve DoD system needs atthe low cost enabled by high-volume commercial markets. This paperreviews current micromachined inertial instruments and fabricationmethods, and presents ongoing development activities in low-costmanufacturing for higher-performance applications. The majorchallenges for military systems and improvement plans for cost, size, andperformance are discussed, and concepts for multi-axis systemconfigurations are proposed.Cunningham, B. T.; Bernstein, J. J.Wide-bandwidth silicon nitride membrane microphonesProceedings of the 1997 SPIE Symposium on Micromachining andMicrofabrication, The International Society for Optical Engineering,Issue 3223, pp. 56-63, 1997Small, low-cost microphones with high sensitivity at frequencies greaterthan 20 kHz are desired for applications such as ultrasoniccommunication links. To minimize stray capacitance between themicrophone and its amplifier circuit, process compatibility between themicrophone and on-chip circuitry is also desired to facilitate integration.In this work, we have demonstrated micromachined microphonespackaged with hybrid Junction Field Effect Transistor (JFET) amplifiercircuitry with frequency response extending to 100 kHz, and voltagesensitivity of 1.0 mV/Pa at 40 kHz at a bias voltage of 13.5 V. Themicrophones are fabricated with membranes and fixed backplates madeof low-temperature Plasma-Enhanced Chemical Vapor Deposited(PECVD) silicon nitride. Because the maximum temperature of thefabrication process is 300ºC, microphones may be built on silicon wafersfrom any commercial Complementary Metal-Oxide Semiconductor(CMOS) foundry without affecting transistor characteristics, allowingintegration with sophisticated amplifier circuitry. Low-stress siliconnitride deposition was used to produce membranes up to 2.0-mmdiameter and 0.5-mm thickness with ±0.10-mm flatness as measuredwith a WYCO TM optical interferometer. The excellent planarity of boththe diaphragm and the backplate, combined with a narrow sense gap (~2mm) results in high-output capacitance (up to 7.0 pF). The high-outputcapacitance results in noise spectral density that is approximately 3xlower than silicon diaphragm microphones previously fabricated by theauthors. Diaphragms with corrugations were fabricated to relieve tensilestress, to increase deflection per unit pressure, and to increase deflectionlinearity with pressure. Corrugated and uncorrugated microphonemeasurements are compared.De Fazio, T. L.; Delchambre, A.; De Lit, P.Disassembly for recycling of office electronic equipmentEuropean Journal of Mechanical Engineering, Vol. 42, No. 1,pp. 25-31, Spring 1997Office electronic equipment continues to proliferate and to be discardedfor a variety of reasons. This paper outlines the magnitude of theproblem and why we chose Personal Computers (PCs) as our majorconsideration. The problems associated with discarding PCs are impliedby or embodied in various details of PCs and in the customs of their use.These details and the manner in which they affect the disposal issue arereviewed, and the key issues affecting discarding computers and what isdone in Europe and USA are presented. An attempt is made to captureand predict what the future may bring regarding the goal of reducingelectronic office machinery mass going to the landfill, and policy issuesare reviewed.De Fazio, T. L.; Rhee, S. J.; Whitney, D. E.Design-specific approach to Design-For-Assembly (DFA)for complex mechanical assembliesProceedings of the 1997 IEEE International Symposium on Assembly andTask Planning, ISATP’97DFA issues of complex assemblies are addressed. Complex assemblieshave very high parts counts, offer limited redesign options, and theirassembly is an assembly of subassemblies. Conventional DFA isinadequate for complex assemblies as it omits the combinatorial aspectsof assembly such as assembly sequence choice and partitioningsubassemblies. Here, Assembly Sequence Analysis (ASA) is used as abasis for complex-assembly DFA. Searches for favorable subassemblypartitioning and assembly sequences minimize assembly difficulty as1997 Published Papers4