A method of in situ chemical analysis by use of small, simple, robust sensors has been proposed. The basis for the proposal is the discovery that chemical reactions emit acoustic waves, and that characteristic frequency spectra are associated with specific reactions. The acoustic frequencies of interest range from about 0.1 to several megahertz. If a newly recorded acoustic spectrum were to match a previously recorded spectrum of a known chemical reaction, then the newly recorded spectrum would be deemed to indicate the presence of that reaction. The amplitude of a spectrum would be taken as an indication of the rate of the corresponding reaction.
A chemical-analysis instrument based on this concept would include an array of miniature piezoelectric acoustic sensors, each with a typical area of no more than a fraction of a square millimeter. The sensors would be able to withstand accelerations up to about 105 times that of normal Earth gravitation (about 106 m/s2).
The instrument would include circuitry for flash analog-to-digital conversion of the sensor outputs, plus a moderately powerful digital data processor that would Fourier-analyze the digitized sensor outputs to obtain acoustic spectra. The instrument would also include electronic circuitry for (1) matching the newly acquired spectra with previously recorded spectra of known reactions and/or (2) recording and/or transmitting the newly acquired spectra for further processing by a computer to find matches to known spectra. The durations of typical chemical reactions of interest range from tens of seconds to hours; on this time scale, there would be no difficulty in time-multiplexing readouts from multiple sensors.
In the original proposed application, such an instrument would be used to find the chemical compositions of gases and dust in the Martian atmosphere, soil, and/or rocks. A similar terrestrial use would be monitoring gaseous, liquid, and solid pollutants in the field. For this purpose, the piezoelectric transducers would be coated with materials that engage in known chemical reactions with the pollutants or other substances of interest. Coatings could include adhesives to assist in collection of dust (and/or magnets to assist in collection of magnetic dust). Alternatively or in addition, reactive liquids could be injected into reaction sites at analysis time. Because the sensors would have low thermal masses, heating the sensors to reaction temperatures (if necessary) would consume little power -- no more than milliwatts at the highest temperatures likely to be needed.
This work was done by Frank Hartley of Caltech forNASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com under the category.
NPO-20222
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In Situ Chemical Analysis via Acoustic-Emission Spectra
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Overview
The document outlines a novel method for in situ chemical analysis developed by NASA's Jet Propulsion Laboratory, focusing on the use of miniature piezoelectric sensors to detect chemical reactions through acoustic-emission spectra. The core principle is based on the discovery that chemical reactions emit acoustic waves, which produce characteristic frequency spectra associated with specific reactions. By matching newly recorded acoustic spectra with previously documented ones, the presence of particular chemical reactions can be identified, and the amplitude of the spectra indicates the reaction rate.
The proposed chemical-analysis instrument consists of an array of small piezoelectric sensors, each measuring a fraction of a square millimeter, capable of withstanding extreme accelerations (up to 105 g). The sensors are designed to be robust, power-efficient, and have low thermal mass, allowing for minimal power consumption even when heating is required to initiate reactions. The instrument includes circuitry for flash analog-to-digital conversion and a digital data processor that performs Fourier analysis on the sensor outputs to derive the acoustic spectra.
The application of this technology is twofold: it aims to analyze the chemical compositions of gases and dust in the Martian atmosphere, soil, and rocks, as well as monitor pollutants in terrestrial environments. The sensors can be coated with materials that react with specific pollutants, and additional methods such as injecting reactive liquids or using adhesives to collect dust can enhance the analysis. The expected duration of chemical reactions of interest ranges from tens of seconds to several hours, allowing for effective time-multiplexing of multiple sensors.
The document emphasizes the advantages of this approach over traditional in situ chemical analysis equipment, which tends to be complex, large, and power-intensive. By utilizing simple, robust sensors and advanced data processing techniques, this method offers a versatile and efficient solution for real-time monitoring of chemical reactions in various environments.
Overall, this innovative technology represents a significant advancement in chemical analysis, with potential applications in planetary exploration and environmental monitoring, showcasing the capabilities of small, efficient sensors in capturing complex chemical data.
