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A Method for Designing Low-Pass FIR Digital Filters

Time-domain filters are first constructed in the frequency domain, using special window functions. A class of finite-impulse-response (FIR) digital filters has been developed to perform certain frequency-limiting, decimation, and differentiation (with respect to time) functions on a time series of data samples. The method is implemented by use of design equations that contain parameters that can be adjusted to obtain the desired functionality while limiting such undesired effects as aliasing and gain ripple. The original application is processing of a time series of raw range data from the proposed Gravity Recovery and Climate Experiment (GRACE), in which microwave phase tracking between two small spacecraft orbiting the Earth would yield the time-tagged raw range data, which would be processed to extract information on the structure of the gravitational field of the Earth. The method is general enough to be applicable in other situations that involve similar signal-processing requirements.

Posted in: Information Sciences, Briefs

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High-Temperature Switched-Reluctance Electric Motor

Motors like this one would be incorporated into gas turbines as starter/generators. An eight-pole radial magnetic bearing has been modified into a switched-reluctance electric motor capable of operating at a speed as high as 8,000 rpm at a temperature as high as 1,000 °F (Å540 °C). The motor (see figure) is an experimental prototype of starter-motor/ generator units that have been proposed to be incorporated into advanced gas turbine engines and that could operate without need for lubrication or active cooling.

Posted in: Mechanics, Mechanical Components, Briefs

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Thermocouple Rakes for Measuring Boundary-Layer Flows

Flows can be measured extremely close to surfaces. Thin-film devices that comprise heaters in combination with thermocouples have been developed for measuring flow velocities extremely close to solid surfaces, at several distances from the surface of interest. Devices that perform this function are denoted generally as “boundary-layer rakes.” The measurement data acquired by boundary-layer rakes are needed for calculating viscous shear forces, for developing mathematical models of turbulence to be used in computational fluid dynamics, and as feedback in some flow-control systems.

Posted in: Physical Sciences, Briefs

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Electrical Monitoring of Thicknesses of Semiconductor Wafers

Electrical fuses would be implanted at depths corresponding to desired thicknesses. A technique based on electrical-continuity measurements has been proposed as a means of monitoring and controlling the thicknesses of semiconductor wafers during lapping, polishing, and etching. The technique is expected to contribute to the development of microelectromechanical systems by making it possible to lap and polish wafers with precision greater than has been achieved previously, thereby further making it possible to fabricate wafers of unprecedented thinness (thicknesses of 5 µm or possibly even less). Unlike some prior techniques for measuring the thicknesses of semiconductor wafers, this technique does not entail the timeconsuming intermittent stopping of processing to take measurements. Also, in comparison with most prior techniques, this technique offers the potential for greater precision at lower cost.

Posted in: Manufacturing & Prototyping, Briefs

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