Physical Sciences

Fiber-Optic Transducers for Distributed Sensing of Volatiles: An Optical Nose

Volatiles would swell polymers on optical fibers, inducing changes in indices of refraction. The term "optical nose" refers to a fiber-optic chemical sensor of a type that has been proposed to enable distributed measurement of the concentrations of volatile compounds. Optical noses should not be confused with electronic noses, which are single-point sensors based on chemical-induced variations of the electrical resistances of carbon-black/polymer composite films. Optical noses could enable rapid measurement of gas mixtures (e.g., volatile compounds in air) at multiple sensing locations along their lengths, which could be of the order of kilometers. Optical noses could function well in locations where audio- and radio-frequency electromagnetic interference renders electronic noses ineffective. Moreover, it may be easier to fabricate optical noses than to fabricate electronic noses because it would not be necessary to handle carbon black.

Posted in: Briefs, TSP, Physical Sciences, Fiber optics, Sensors and actuators, Chemicals, Composite materials, Polymers


Rare-Earth Optical Temperature Sensors

These sensors exploit the narrow-band emission peculiar to rare earths. A recently developed type of fiber-optic temperature sensor utilizes narrow-band near-infrared radiation emitted by rare-earth ions. These sensors are suitable for use in harsh environments at temperatures above the maximum (1,700 °C) that Pt/Rh thermocouples can withstand. The maximum operating temperature for these optical temperature sensors can equal or exceed 2,000 °C, the exact values depending on the choice of fiber-optic and rare-earth-containing radiative materials. The minimum temperature measurable by use of a sensor of this type, related to the minimum detectable radiation, has been found to be ≈700 K (≈427 °C).

Posted in: Briefs, TSP, Physical Sciences, Measurements, Fiber optics, Sensors and actuators, Radiation


Capacitive Sensor for Measuring Level of Liquid Nitrogen

The liquid is used as a dielectric layer in a parallel-plate capacitor. The feasibility of a capacitive sensor for measuring the level of liquid nitrogen in a container has been demonstrated. The basic sensor design could also readily be adapted to measurement of the levels of cryogenic liquids other than nitrogen.

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


Microelectromechanical Sensors Based on Magnetoresistance

These would offer advantages over similar sensors based on quantum-mechanical tunneling of electrons. Microelectromechanical sensors based on magnetoresistance have been proposed. Like other microelectromechanical sensors, these would be used to measure physical quantities that can be made to manifest themselves in small mechanical displacements. Potential applications for microelectromechanical sensors include accelerometers, magnetometers, bolometers, pressure sensors, seismometers, Golay cells, and microphones. Potential markets include the aerospace, biomedical, semiconductor, automotive, and defense industries.

Posted in: Briefs, TSP, Physical Sciences, Microelectromechanical devices, Sensors and actuators


Model of Pyrolysis of Biomass in a Fluidized-Bed Reactor

Complex dynamics and heat transfer are represented more realistically than in prior models. A mathematical model has been formulated to describe the pyrolysis of biomass in a bubbling fluidized-bed reactor. The reactor is a vertical cylinder that contains a mixture of biomass particles and sand. Superheated steam enters the reactor through holes in the bottom and flows out freely at the top. The sand is a high heat capacity medium used for heating the biomass. The biomass particles, initially at room temperature, are introduced into the already hot reactor and become heated primarily through contact with the sand. Upon reaching a threshold temperature, the biomass particles undergo chemical reactions, the gaseous products of which are carried away by the flow of steam. The "bubbles" are regions of the fluidized bed that are mostly devoid of particles; these regions occur as a result of the interaction of the turbulent gaseous flow with the particles.

Posted in: Briefs, TSP, Physical Sciences, Thermodynamics, Biomaterials, Chemicals, Gases, Test equipment and instrumentation


System for Delivering Gas Samples to Multiple Instruments

A system that samples gases at multiple remote locations and delivers the gases to two or possibly more gas-monitoring instruments (e.g., mass spectrometers) has been developed. The system includes a transport (suction) pump that draws the gases from the sampling locations, through transport tubes, into a plenum, which is large enough to act as a buffer against changes in pressure in the transport tubes. Connected to each transport tube at a location near the plenum are two or more sample tubes that are, in turn, connected to manifolds of sample-selector valves through which gases are drawn into the instruments. Each instrument is equipped with a sampling (suction) pump that draws gas from one of the transport tubes that has been selected by opening the corresponding sample-selector valve. Each sampling pump is operated under feedback flow and pressure control to maintain a steady instrument-inlet pressure needed to ensure stable instrument readings. The sample flow thus diverted from the transport tube is kept to one-fifth or less of the transport flow in order to minimize the perturbation of the transport flow and thus, further, minimize any effect of one instrument on the other.

Posted in: Briefs, TSP, Physical Sciences, Gases, Test equipment and instrumentation, Spacecraft


Atmospheric Source of Atomic Oxygen for Cleaning Paintings

A vacuum chamber is no longer necessary. A portable apparatus that operates at atmospheric pressure generates a beam of monatomic oxygen. The apparatus is designed to be used in a dry, noncontact process for removing organic contaminants from the surfaces of paintings. Organic contaminants that can be wholly or partly removed by use of this apparatus include some deposited in acts of defacement (e.g., lipstick and marks left by felt-tip and ball-point pens) and some deposited from fire (e.g., soot and charred binder). In some cases, this apparatus may make it possible to restore works of art that were previously counted as lost.

Posted in: Briefs, TSP, Physical Sciences, Maintenance, repair, and service operations, Oxygen


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