Engineering topics

Wu, W. H.

Publications and source records attributed to Wu, W. H..

7 records

NASA NTRS2002

Development of Microfabricated Chemical Gas Sensors and Sensor Arrays for Aerospace Applications

Aerospace applications require the development of chemical sensors with capabilities beyond those of commercially available sensors. In particular, factors such as minimal sensor size, weight, and power consumption are particularly important. Development areas which have potential aerospace applications include launch vehicle leak detection, engine health monitoring, fire detection, and environmental monitoring. Sensor development for these applications is based on progress in three types of technology: 1) Micromachining and microfabrication (Microsystem) technology to fabricate miniaturized sensors. 2) The use of nanocrystalline materials to develop sensors with improved stability combined with higher sensitivity. 3) The development of high temperature semiconductors, especially silicon carbide. However, due to issues of selectivity and cross-sensitivity, individual sensors are limited in the amount of information that they can provide in environments that contain multiple chemical species. Thus, sensor arrays are being developed to address detection needs in such multi-species environments. This paper discusses the needs of space applications as well as the point-contact sensor technology and sensor arrays being developed to address these needs. Sensors to measure hydrogen, hydrocarbons, hydrazine, nitrogen oxides (NO,), carbon monoxide, oxygen, and carbon dioxide are being developed as well as arrays for leak, fire, and emissions detection. Demonstrations of the technology will also be discussed. It is concluded that microfabricated sensor technology has significant potential for use in a range of aerospace applications.

Hunter, G. W.↗

NASA NTRS1991

Fiber Optic Tactical Local Network (FOTLAN)

A 100 Mbit/s FDDI (fiber distributed data interface) network interface unit is described that supports real-time data, voice and video. Its high-speed interrupt-driven hardware architecture efficiently manages stream and packet data transfer to the FDDI network. Other enhancements include modular single-mode laser-diode fiber optic links to maximize node spacing, optic bypass switches for increased fault tolerance, and a hardware performance monitor to gather real-time network diagnostics.

Bergman, L. A.↗

NASA NTRS1988

A fiber optic tactical voice/data network based on FDDI

An asynchronous high-speed fiber optic local area network is described that supports ordinary data packet traffic simultaneously with synchronous Tl voice traffic over a common FDDI token ring channel. A voice interface module was developed that parses, buffers, and resynchronizes the voice data to the packet network. The technique is general, however, and can be applied to any deterministic class of networks, including multi-tier backbones. A conventional single token access protocol was employed at the lowest layer, with fixed packet sizes for voice and variable for data. In addition, the higher layer packet data protocols are allowed to operate independently of those for the voice thereby permitting great flexibility in reconfiguring the network. Voice call setup and switching functions were performed external to the network with PABX equipment.

Bergman, L. A.↗

NASA NTRS1988

Optical addressing technique for a CMOS RAM

Progress on optically addressing a CMOS RAM for a feasibility demonstration of free space optical interconnection is reported in this paper. The optical RAM chip has been fabricated and functional testing is in progress. Initial results seem promising. New design and SPICE simulation of optical gate cell (OGC) circuits have been carried out to correct the slow fall time of the 'weak pull down' OGC, which has been characterized experimentally. Methods of reducing the response times of the photodiodes and the associated circuits are discussed. Even with the current photodiode, it appears that an OGC can be designed with a performance that is compatible with a CMOS circuit such as the RAM.

Wu, W. H.↗

NASA NTRS1988

Optical interconnection techniques for Hypercube

Direct free-space optical interconnection techniques are described for the Hypercube concurrent processor machine using a holographic optical element. Computational requirements and optical constraints on implementation are briefly summarized with regard to topology, power consumption, and available technologies. A hybrid lens/HOE approach is described that can support an eight-dimensional cube of 256 nodes.

Johnston, A. R.↗

NASA NTRS1987

CMOS detector cells for holographic optical interconnects in microcircuits

This paper reports on the characterization of CMOS detectors for holographic optical interconnects in micro circuits. A VLSI temporal response system has been built, which has high-magnification viewing capabilities to facilitate the identification of the sample area under investigation. An isolated photodiode and load circuit has been characterized to determine responsivity, response time, and light spot positioning effects. The threshold of optical gate cells incorporating the above detectors and a transistor inverter stage to couple to other circuitry has been determined. The rise time and fall time of the optical gate cells have also been determined experimentally. The results were compared with the results of SPICE simulation, and show satisfactory agreement. The time delay of optical gate cell output was thus determined to be 70 ns at 10 microW light input. Threshold power was 0.5 microW light input.

Wu, W. H.↗

NASA NTRS1986

Holographic optical interconnects for VLSI

This paper introduces new applications and design trade-offs anticipated for free-space optical interconnections of VLSI chips. New implementation s of VLSI functions are described that use the capability of making optical inputs at any point on a chip and take advantage of greater flexibility in on-chip signal routing. These include n-port addressable memories, CPU clock phase distribution, hardware multipliers, and dynamic memory refresh, as well as enhanced testability. Fault tolerance and production yields may be improved by reprogramming the optical imaging system to circumvent defective elements. These attributes, as well as those related to performance alone, will affect the design methodology of future VLSI ICs. This paper focuses on identifying the design issues, their possible solutions, and their impact on VLSI design techniques and, finally, presents some preliminary measurements on various system components.

Bergman, L. A.↗