Tech Briefs

Silicon Carbide Junction Field-Effect Transistor Devices for Scalable Solid-State Circuit Breakers

Power electronic converters functioning as components in high-power systems, such as those of hybrid military ground vehicles, require fast fault isolation, and in most cases, benefit additionally from bidirectional fault isolation. To prevent converter damage or failure, fault current interrupt speeds in the hundreds of microseconds to few millisecond range are necessary. Presently used mechanical contactors do not provide adequate actuation speeds, and suffer severe degradation during repeated fault isolation. Instead, it is desired to use a large array of semiconductor devices having a collectively low conduction loss to provide large current-handling capability and fast transition speed for current interruption.

Posted in: Briefs, Electronics & Computers, Power electronics, Transistors, Semiconductors
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Indoor Navigation for Unmanned Aerial Vehicles

This research proposed the use of inexpensive, lightweight range sensors for indoor unmanned aerial vehicle (UAV) navigation. Two potential range sensors were tested for suitability and error characteristics. The SHARP infrared range sensors provide a narrow beam and a higher resolution distance measurement, at the expense of de creased range (approximately 150–180 cm maximum). The MaxBotix® EX1™ ultrasonic range sensors had a longer range (up to 6.45 m) and a wider beam.

Posted in: Briefs, Physical Sciences, Navigation and guidance systems, Sensors and actuators, Flight tests, Unmanned aerial vehicles
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Modular, Portable, and Reconfigurable Wireless Sensing System

A modular, portable, reconfigurable wireless sensor system monitors and records environmental conditions in an aircraft cabin. By designing a sensor system that can be easily configured for different needs (with the ability and flexibility to accommodate different/ extra sensors), the system can be used to measure parameters that meet multiple research requirements. Through design considerations such as generalized signal interface, and hierarchical code structure that can be easily reworked for new sensors, this system can be used to measure parameters that meet multiple research requirements. This sensor system, the ASCENT 1000, is configured with temperature, humidity, sound level, carbon di-oxide, and pressure sensors. The system has been calibrated in the laboratory without the use of a pressure chamber.

Posted in: Briefs, Physical Sciences, Sensors and actuators, Wireless communication systems, Passenger compartments
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Performance Evaluation of Commercial Carbon Monofluoride Materials in Lithium Batteries

The performance of six different commercially available carbon monofluoride (CFx) materials was evaluated at four different discharge rates. The physical and chemical properties of the CFx materials were correlated to cell performance in lithium coin cells. This study was undertaken to determine how the physical and chemical properties of commercial CFx materials affect discharge capacity, discharge voltage, rate capability, and voltage delay in Li-CFx cells.

Posted in: Briefs, Materials, Lithium-ion batteries, Performance tests, Test procedures
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Nanodomain Model of Polymer-Derived Ceramics

Areport discusses a model developed to explain the unusual properties of polymer- derived ceramics (PDCs), which are so named because they are made by controlled pyrolysis of cross-linked polymers. PDCs are metastable ceramics that have potential to be further developed into high-temperature materials that can be tailored to have properties needed to perform specific functions. The PDCs studied thus far have comprised silicon, carbon, nitrogen, and oxygen. The unusual properties of PDCs are the following: They bear similarity to both polymers and metallic glasses, even though the pyrolysis temperatures used in producing them are with experimental data.

Posted in: Briefs, Materials, Simulation and modeling, Ceramics, Heat resistant materials, Materials properties, Polymers
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Lightcraft Propulsion for Launching a Small Satellite

A study of lightcraft propulsion systems in general has led to the conception and analysis of such a system for launching a small (having a mass no more than a few kilograms) satellite into a low orbit around the Earth. This study built on theoretical and experimental investigations of the feasibility of lightcraft, performed by a number of researchers during the past two decades. The word “lightcraft” signifies an aircraft or spacecraft that derives its propulsive energy from a laser beam aimed toward it from an external platform that, for the purpose of the present study, would be a ground station.

Posted in: Briefs, Mechanical Components, Mirrors, Lasers, Propellants, Satellites
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Eccentric Mounting and Adjustment System for Belt-Driven Devices

This design relates to an eccentric mounting and adjustment (EMA) system for belt driving, or for belt-driven devices, that is installed and operated within the restricted confines of an engine compartment, typically a motor vehicle. It satisfies two essential requirements for automotive devices driven by an endless flexible belt, including a reliable mounting to the engine block assembly, and a continuous provision of a proper amount of tension to the belt for either driving or driven devices. As a result, there is minimal wear and tear on device bearings and the belt, which reduces operational failures and assures maximum efficiency for these devices.

Posted in: Briefs, Mechanical Components, Mountings, Engine components
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