Special Coverage

Supercomputer Cooling System Uses Refrigerant to Replace Water
Computer Chips Calculate and Store in an Integrated Unit
Electron-to-Photon Communication for Quantum Computing
Mechanoresponsive Healing Polymers
Variable Permeability Magnetometer Systems and Methods for Aerospace Applications
Evaluation Standard for Robotic Research
Small Robot Has Outstanding Vertical Agility
Smart Optical Material Characterization System and Method
Lightweight, Flexible Thermal Protection System for Fire Protection

Metal/Dielectric Color Filters for Flat Panel Displays

A report expands on the proposal described in “Low-Absorption Color Filters for Flat Panel Display Devices” (NPO-20435) NASA Tech Briefs, Vol. 23, No. 12 (December 1999), page 34. To recapitulate: The dye pixel color filters in a conventional liquid-crystal or other display device would be replaced with interference filters, which are less absorptive, and optics would be configured so that light reflected from the filters would be reused as illumination. The overall effect would be to increase brightness and efficiency. The present report adds specificity by proposing that the interference filters be of the type described in “Metal/Dielectric-Film Interference Color Filters” (NPO-20217), NASA Tech Briefs, Vol. 23, No. 2 (February 1999), page 70: Each filter would be made of three thin metal films interspersed with two thin dielectric films. In comparison with conventional multilayer all-dielectric filters, the proposed filters would contain fewer layers, and therefore could be fabricated more easily and at lower cost.

Posted in: Briefs, TSP, Physical Sciences, Displays, Product development, Fabrication, Metals


Multiphase-Flow Model of Fluidized-Bed Pyrolysis of Biomass

A report presents additional information about the subject matter of “Model of Pyrolysis of Biomass in a Fluidized- Bed Reactor” (NPO-20708) NASA Tech Briefs, Vol. 25, No. 6 (June 2001), page 59. The model is built on equations for the dynamics of three components — gas, sand, and biomass — partly by taking suitable ensemble averages of the coupled conservation equations for the gas, and for the biomass and sand particles. Equations for exchanges of mass, momentum, and energy between phases are included. Equations for transport of the solid phase are closed by use of separate distribution functions for sand and biomass particles. Interparticle collisions are described in the framework of the kinetic theory of dense gases, using inelastic- rigid-sphere models.

Posted in: Briefs, TSP, Physical Sciences, Mathematical models, Soils, Biomaterials, Gases


Tiger Fibers for Enhanced Optical Sensing of Volatiles

Striped polymer coats on optical fibers would induce gratings upon exposure to analytes. Improved fiber-optic transducers, denoted tiger fibers, have been proposed for sensing volatile compounds. Tiger fibers are so named because, as described below, their sensitive portions would be coated with periodically alternating stripes of different polymers, reminiscent of a tiger’s stripes.

Posted in: Briefs, TSP, Physical Sciences, Fiber optics, Sensors and actuators, Performance upgrades, Coatings, colorants, and finishes


Using Laser Diodes to Characterize Force and Pressure Sensors

A proposed method of characterizing microphones and other pressure and force sensors would exploit the temporally varying forces of impingement of amplitude-modulated light beams from inexpensive laser diodes. What makes the method likely to be practical is the surprising fact that these forces, albeit small, are nevertheless large enough to enable quantification of the noise floors, sensitivities, and frequency responses of many modern pressure sensors. The time-averaged force of impingement of a pulsed beam of light on a surface is given by F = SDP/c, where S ranges from 1 for a totally absorptive (black) to 2 for a perfectly reflective surface, D is the pulse duty cycle, P is the peak power of the beam, and c is the speed of light. Hence, if one knows S, D, and P, it may be possible to determine the absolute sensitivity of the sensor. Even if one does not know one or more of these parameters, it should be possible to determine the relative sensitivities of different sensors by measuring their responses to the same modulated beam, or to determine the relative frequency response of a given sensor by measuring its output while sweeping the modulation frequency.

Posted in: Briefs, TSP, Physical Sciences, Measurements, Lasers, Sensors and actuators


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: Briefs, TSP, Physical Sciences, Computational fluid dynamics, Mathematical models, Semiconductor devices, Test equipment and instrumentation, Turbulence


Boundary Conditions for Computing Flows of Real Gas Mixtures

It is possible to suppress errors that arise in a simplistic formulation. An improved formulation of equations of flow of a general gas mixture includes consistent boundary conditions that are applicable to real gases. An analysis of prior formulations, with focus on boundary conditions, led to the conclusion that boundary conditions based on ideal mixtures and/or perfect gases can lead to errors in computed flows of real gases. The improved formulation makes it possible to achieve greater accuracy in computation of flows of real (including chemically reactive) gas mixtures, and is expected to be especially beneficial in computing flows of supercritical fluids like those in diesel engines, gas turbine engines, rocket engines, supercritical-fluid extraction processes, and crude oil under high pressure.

Posted in: Briefs, TSP, Physical Sciences, Computational fluid dynamics, Mathematical analysis, Gases


Seed-Wing Flyers for Exploration

Scientific instruments would be dispersed from aloft by use of miniature autogyros. Small instrumented, free-flying (unpowered) rotary aircraft have been proposed for use in gathering scientific data from hazardous or inaccessible terrain on remote planets as well as on Earth. These aircraft are called “seed-wing flyers” because they would resemble winged seeds (e.g., maple seeds) in both appearance and aerodynamic behavior.

Posted in: Briefs, TSP, Physical Sciences, Test equipment and instrumentation, Fixed-wing aircraft, Spacecraft, Unmanned aerial vehicles


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