Margaret Ryan

Monitoring Space Shuttle air quality using the Jet Propulsion Laboratory electronic nose

A miniature electronic nose (ENose) has been designed and built at the Jet Propulsion Laboratory (JPL), Pasadena, CA, and was designed to detect, identify, and quantify ten common contaminants and relative humidity changes. The sensing array includes 32 sensing films made from polymer carbon-black composites. Event identification and quantification were done using the Levenberg-Marquart nonlinear least squares method. After successful ground training, this ENose was used in a demonstration experiment aboard STS-95 (October-November, 1998), in which the ENose was operated continuously for six days and recorded the sensors response to the air in the mid-deck. Air samples were collected daily and analyzed independently after the flight. Changes in shuttle-cabin humidity were detected and quantified by the JPL ENose; neither the ENose nor the air samples detected any of the contaminants on the target list. The device is microgravity insensitive.

Monitoring Space Shuttle Air for Selected Contaminants Using an Electronic Nose

A miniaturized electronic nose has been constructed at JPL in collaboration with Caltech. This array of conductometric sensors has been trained to detect and quantify the presence of vapors in the air; the compounds detected have been found as contaminants in shuttle air. This device has potential application as a miniature, distributed device for monitoring and controlling the constituents in air.

Expanding the capabilities of the JPL electronic nose for an International Space Station technology demonstration

An array-based sensing system based on polymer/carbon composite conductometric sensors is under development at JPL for use as an environmental monitor in the International Space Station. Sulfur dioxide has been added to the analyte set for this phase of development. Using molecular modeling techniques, the interaction energy between SO2 and polymer functional groups has been calculated, and polymers selected as potential SO2 sensors. Experiment has validated the model and two selected polymers have been shown to be promising materials for SO2 detection.

Expanding the Analyte Set of the JPL Electronic Nose to Include Inorganic Species

An array-based sensing system based on 32 polymer/carbon composite conductometric sensors is under development at JPL. Until the present phase of development, the analyte set has focused on organic compounds (common solvents) and a few selected inorganic compounds, notably ammonia and hydrazine. The present phase of JPL ENose development has added two inorganics to the analyte set: mercury and sulfur dioxide. Through models of sensor-analyte response developed under this program coupled with a literature survey, approaches to including these analytes in the ENose target set have been determined.

Temperature effects on polymer-carbon composite sensors: Evaluating the role of polymer molecular weight and carbon loading

We report the effect of temperature coupled with varying polymer molecular weight and carbon loadings on the performance of polymer-carbon black composite films, used as sensing media in the JPL Electronic Nose (ENose). While bulk electrical properties of polymer composites have been studied, with mechanisms of conductivity described by connectivity and tunneling, it is not fully understood how environmental conditions and intrinsic polymer and filler properties affect polymer composite sensor characteristics and responses. Composites of polyethylene oxide (PEO)-carbon black (CB) considered here include PEO polymers with molecular weights of 20K, 600 K and 1M. The effects of polymer molecular weight on the percolation threshold of PEO-carbon composite and incremental sensor temperature effects on PEO-carbon sensor response were investigated. Results show a correlation between the polymer molecular weight and percolation threshold. Changes in sensor properties as a function of temperature are also observed at different carbon loadings; these changes may be explained by a change in conduction mechanism.

Using temperature effects on polymer-composite sensor arrays to identify analytes

The sensor response of six different polymer-carbon-black composite sensors to three different analytes has been investigated as a function of temperature where the temperature range is 28-36/spl deg/C (/spl Delta/T is 4-8/spl deg/C). We tested the response of these polymer-carbon-black sensors to water, methanol and methane from 28-36/spl deg/C. All of the sensors showed a decrease in response to an analyte with increasing temperature; however, each sensors response changes differently with temperature. This variation of response to temperature change creates distinct temperature-dependent fingerprints and will be useful in extending the range of data available for analyte identification and quantification.

Sniffing out problems for humans in space

The goal of this study was to determine the rapidity and magnitude of metal oxide sensor response to airborne contaminants on the target analyte list for the third generation ENose. The immediate and sharp response of the metal oxide sensors indicates that they would indeed serve as a reliable event indicator for the ENose. A custom fabrication procedure to deposit metal oxide on the microhotplate array that will be used in the third generation ENose would also need to be established. With the resulting sensors subjected to characterization, testing, and training for the ENose data analysis software.