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Proceedings of the 1999 Application of Lidar to current Atmospheric Topics iii

作者： Blackwell, Timothy S. Li, Ye Peters, Bruce R. Amzajerdian, Farzin Klingmann, Jeff Carlisle, Keith Demiris, Anthony Hamliton, James H. Univ of Alabama in Huntsville Huntsville United States

The measurement of winds from a space borne platform is of significant scientific importance to both weather prediction and climate research. One of the key technologies embodied in coherent detection of winds from space is the use of large aperture, compact, lightweight, high-quality wavefront, photon-efficient optics. This paper discusses the optical design, the mechanical design, material preference, diamond turning issues, polishing requirements, and coating selections for the primary mirror of a 25X afocal beam expander intended for use in space-based coherent lidar systems. Performance requirements levied on a lidar optical system are primarily driven by operational signal to noise budgets, but other factors such as the thermal and launch load environments also factor into the optics design. Therefore, the sensitivity of any coherent lidar is generally limited by the quality of its optical system. Aberrations generated by the optics from manufacturing errors, optical misalignment, or operational thermal activity will substantially affect measurement accuracy's especially when used at the ranges expected from space platforms. The stringent optical performance requirements coupled with demanding physical and environmental constraints have created the need for a design with unique optical and robust mechanical design characteristics. This paper will survey various manufacturing considerations when producing a 25 cm diameter f/0.9;150 mm off axis parabola which is associated with the 2-micron SPAce Readiness Coherent Lidar Experiment (SPARCLE). This mirror has a final figure of better than 1/4 wave p-v at HeNe and surface roughness of better than 15 angstroms RMS.

关键词： optical radar

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Recent advances in remote field eddy current NDE techniques and their applications in detection, characterization, and monitoring of deeply hidden corrosion in aircraft structures

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Proceedings of SPIE - The International Society for optical engineering 1999年 3586卷 200-210页

作者： Sun, Yushi Ouyang, Tianhe Udpa, Satish Iowa State Univ Ames United States

The remote field eddy current (RFEC) technique is based on the RFEC phenomenon which is characterized by differences in the energy flow patterns in the near and remote field regions. The energy released by the probe excitation coil traverses the pipe wall twice before reaching the pickup coil. The RFEC technique, currently used in metallic tube inspection, is therefore characterized by its equal sensitivity to a flaw irrespective to its location in the tube wall. It can be used for detecting defects located several skin-depths away from the excitation source, since its inspection capacity is not limited by the skin-depth of the specimen, but by the signal-to-noise ratio for a particular measurement condition. The paper presents two new developments of the RFEC technique. The first one is to extend the technique to the inspection of flat geometry objects. Experimental measurements have shown that anomalies located in the second and third layers in multi-layered aluminum structures up to total thickness of 25.4 mm can be detected. The second development is related to the extension of the technique to pulsed excitation. Finite element modeling results show that the pulsed RFEC signals contain additional information about the object under inspection. A proper analysis of the pulsed RFEC signals can yield information about the surface, subsurface and the rear wall condition of a conducting object when an appropriate probe is used. A demonstration of the potential applications of both techniques in detecting deeply hidden cracks in aircraft structure samples is presented.

关键词： Nondestructive examination

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Passive millimeter wave camera images, current and future

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Proceedings of SPIE - The International Society for optical engineering 1999年 3703卷 68-75页

作者： Mirth, Lee Pergande, Al Eden, Dayton Chu, Lawrence Lockheed Martin Electronics & Missiles

Rapidly improving technology is transitioning current laboratory images into reality with fielded systems expected within two years. W-band radiometers have been shown to be effective in detecting metallic and non-metallic weapons concealed under heavy garments in both outdoor and indoor situations. Systems that are in development will provide real-time display and weapon detection in controlled situations. The incorporation of technology improvements that have already been demonstrated will double the sensitivity and provide affordable systems with rapid scanning for general use. Lockheed Martin and Intelligent Machine Technology are working to build a demonstration system for the Department of Justice and the Air Force Research Laboratory that can be extended to take advantage of rapidly moving semiconductor improvements. Our current radiometer modules use a PIN switch for the Dicke calibration function followed by multiple low noise amplifier stages, a Schottky detector and a video amplifier. Sensitivity of such modules is primarily a function of the insertion loss and noise figure of the front end MMIC circuits. Processing improvements at Lockheed Martin and refined chip design will result in a 3 dB improvement in the effective noise figure within the next year. Imaging is also greatly improved by achieving greater effective bandwidth and higher operating frequency. Whereas present modules operate from 80 to 90 GHz, MMIC improvements will provide for operation up to 140 GHz with a doubling of the bandwidth in the near term. Receiver operation up to 540 GHz has also been demonstrated at other labs.

关键词： Millimeter wave devices

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Recent developments in hybrid mirror technology for the Next Generation Space Telescope

Recent developments in hybrid mirror technology for the Next...

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Proceedings of the 1999 18th Congress of the International Commission for Optics (ICO XViii): Optics for the Next Millennium

作者： Dodson, Kelly J. Mehle, Greg V. Kasl, Eldon P. Composite Optics Inc San Diego CA United States

The objective of this paper is to report the recent developments in lightweight mirror technology at Composite Optics, Incorporated (COI). The developments are a result of the activities being conducted in support of the Next Generation Space Telescope (NGST) Program. The sponsors of these efforts are the NASA Marshall and Goddard Space Flight Centers. The requirements, design approach, performance, and the technology status for the program are summarized. The emergence of composite materials provides exciting potential for nontraditional, accurate, lightweight, stable, stiff, and high strength mirrors. This evolving technology promises significant improvement in reducing weight, cost and cycle time for future infrared, visible, and x-ray systems. Customers currently embracing composite mirror technology for radiometric use are already reaping substantial system performance benefits. Other customers interested in LIDAR, IR, visible, and grazing incidence x-ray applications are eagerly awaiting successful completion of current technology development and demonstration efforts.

关键词： Mirrors

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Qualitative modeling of complex systems for cognitive engineering

Qualitative modeling of complex systems for cognitive engine...

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Proceedings of the 1999 Enabling Technology for Simulation Science iii

作者： Perusich, Karl McNeese, Mike Rentsch, Joan R. Purdue Univ South Bend IN United States

ISBN: (纸本)0819431702

In this paper, the techniques of using fuzzy cognitive maps will be outlined, and demonstrated with an example. Fuzzy cognitive maps will be used as a way to model the causal process in a cognitive system. With such a model interventions to change the dynamics of the system can be developed. In the particular example, the information on a display needed to be improved to support group situation awareness within an AWACS team. A fuzzy cognitive map was developed of the chain of causality that led from the current information structure of the AWACS display to the loss of situation awareness. The map could then be examined to identify ways in which the linkages could be altered to improve situation awareness, and points at which technology could be applied. From this a set of design changes could be recommended.

关键词： Cognitive systems

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Control design which respects characteristic length scales in smart systems and smart structures

Control design which respects characteristic length scales i...

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Proceedings of the 1999 Smart Structures and Materials - Mathematics and Control in Smart Structures

作者： Baillieul, J. Boston Univ Boston MA United States

Although there is a mature and continually growing body of knowledge concerning the ways in which the dynamics of fluids and solids depend on characteristic length scales, current theories governing control design do not take explicit account of length scales. Recent research has demonstrated the need to take such considerations into account in designing control systems for smart materials and smart structures in which the goal is to employ small-scale actuators and sensors with characteristic length scales in the micron to millimeter range. For many applications, sensors and actuators will need to be separated by considerable distances (in terms of characteristic length scales). Closed loop feedback designs in this setting may involve communications delays, and both the communications channels and the sensors themselves will typically be relatively noisy. Hence traditional approaches to the design of feedback control laws need to be rethought and modified to work effectively in the noisy, nonlinear, bandlimited world of microelectromechanical systems (MEMS). This paper discusses one approach to a robust, length-scale respecting theory of control based on oscillatory actuation. It includes a brief outline of recent developments in the control of mechanical systems using oscillatory actuation, emphasizing the dependence on characteristic length scales. The principal applications with which we are working are micro-pendulum designs, micro-piston actuators for deformable mirrors as well as micro-valves for the control of fluid-structure boundary layer control.

关键词： Intelligent structures

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Anomalous drain current-voltage characteristics in AlGaN/GaN MODFETs at low temperatures

Anomalous drain current-voltage characteristics in AlGaN/GaN...

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Proceedings of the 1999 design, Characterization, and Packaging for MEMS and Microelectronics

作者： Umana-Membreno, Gilberto A. Dell, John M. Faraone, Lorenzo Wu, Yi-Feng Parish, Giacinta Mishra, Umesh K. Univ of Western Australia Nedlands

This paper reports the observation of defect-related anomalous low temperature drain current-voltage characteristics in AlGaN/GaN MODFETs. We have performed our study on devices with a relatively large number of lattice defects, generally referred to as nanopipes or nanotubes, in their active area. The observed low temperature anomalies appear as `kinks' in the Ids-Vds characteristics and are observable at temperatures <210 K. In a device with a large density of defects, we observe current collapse and large threshold voltage shifts at 80 K, which depend on bias history. We attribute the observed behaviour to impact ionization of charge accumulated in the AlGaN layer by high-energy electrons injected from the 2DEG via real space transfer (RST). The existence of these mechanisms indicates that device self-heating is not the solely responsible for the negative differential resistance at high electric fields in AlGaN/GaN MODFETs. These mechanisms may have significant influence on the high frequency performance of power transistors and on our current understanding of high electric field parallel transport phenomena in iii-nitride heterojunctions.

关键词： Microelectronics

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Advanced Solar Coronal Explorer mission (ASCE)

Advanced Solar Coronal Explorer mission (ASCE)

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Proceedings of the 1999 Ultraviolet and X-Ray Detection, Spectroscopy, and Polarimetry iii

作者： Gardner, L. Kohl, J. Cranmer, S. Fineschi, S. Golub, L. Raymond, J. Smith, P.L. Strachan, L. Howard, R. Moses, D. Socker, D. Wang, D. Fisher, R.R. Davila, J. Cyr, C.St. Harvard-Smithsonian Cent for Astrophysics Cambridge United States

The Advanced Solar Coronal Explorer (ASCE) is one of five missions selected for a Phase A Concept Study in the current round of proposed MIDEX missions. ASCE's instrument complement is supported by a SPARTAN 400 reusable carrier. The spacecraft is carried into orbit and deployed by the Space Shuttle;at mission's end, nominally 2 years later, it is retrieved and returned to earth for post-flight calibration. ASCE comprises two instrument modules, the Spectroscopic and Polarimetric Coronagraph (SPC) and the Extreme Ultraviolet Imager (EUVI). The external occulter for the coronagraph is supported on a boom, which is extended 10 meters beyond the instrument apertures once the spacecraft is on station. Large aperture optics can therefore be used, and this, in combination with improvements in optical and photon detection efficiencies, will provide spectroscopy of the extended solar corona with unprecedented sensitivity and spatial resolution, routine measurements of the electron temperature, and polarimetry of the H I Lyman lines. SPC also extends the short wavelength limit to 28 nm. As a consequence, SPC will be able to perform the first He II 30.4 nm and He I 58.4 nm spectroscopy of the extended corona. In the visible part of the spectrum (450-600 nm), SPC's Large Aperture Spectroscopic Coronagraph (LASCO) channel will provide polarimetric images with 1.8 arc second resolution elements, which will allow the determination of polarized brightness of the coronal plasma. In a separate parallel channel LASCO will also provide images at single minor ion line wavelengths from which can be determined the shapes and Doppler shifts of those lines. The distant external occulter provides for major improvement in stray light suppression. The EUVI instrument will take high cadence images of the full disk and low corona at four selectable wavelengths with 0.9 arc second resolution elements. A description of the instrument design and performance capabilities is presented.

关键词： optical instruments

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Advanced optical sensor performance in transmission and distribution applications

Proceedings of the IEEE Power Engineering Society Transmissi...

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Proceedings of the IEEE Power engineering Society Transmission and Distribution Conference 1999年 1卷 259-265页

作者： Cruden, A. Michie, W.C. Niewczas, P. Madden, W.I. McDonald, J.R. Andonovic, I. Univ of Strathclyde Glasgow United Kingdom

This paper reports on recent developments within research into optical fibre based voltage and current measurement equipment for metering and protection applications. Several parameters (thermal variations, intensity fluctuations due to mechanical disturbance, electronic noise) are known to influence the performance of these sensors and this paper summarises an analysis of the effect of such disturbances providing design criteria for the realisation of protection and metering class OCTs. Laboratory trials have shown that the compensation schemes devised reduce vibration errors by 20 to 30 dB and compensate for temperature induced drift to better than 0.1%. Extended engineering evaluation field trials of both OCT and OVT devices within a three phase 132 kV installation have been undertaken over the past two years. Details of these trials are presented to provide an appreciation of the potential difficulties which may be encountered and the benefits which may be derived.

关键词： optical sensors

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Recent advances in remote field eddy current NDE techniques and their applications in detection, characterization, and monitoring of deeply hidden corrosion in aircraft structures

Recent advances in remote field eddy current NDE techniques ...

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Proceedings of 1999 Nondestructive Evaluation of Aging Aircraft, Airports, and Aerospace Hardware iii

作者： Sun, Yushi Ouyang, Tianhe Udpa, Satish Iowa State Univ Ames IA United States

关键词： Nondestructive examination

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