Gas detection method and apparatus using chemisorption and/or physisorption

摘要

Gas species are detected with a capacitor having a solid, ionic dielectric excited by an AC voltage in the range from 0.01-30 Hz, with an amplitude of 1-100 millivolts to allow physisorption processes and/or with an AC voltage in the same frequency range and amplitudes from 0.01-3 volts to achieve chemisorption reactions. The AC impedancae of the capacitor is detected for both physisorption and chemisorption excitation to determine gas species and concentration. In chemisorption, diode like action occurs, and is detected by AC harmonic detection processes. The surface of the dielectric on which the gas is incident is overlaid with a grid or porous electrode, fabricated of inert metal or a catalyst which causes the capacitor to enable preferential adsorption by the dielectric of certain materials, to indicate the presence of certain gases. Plural capacitors, having different adsorption characteristics in response to different gases facilitates detection of plural gases. The dielectric is a rare earth fluoride, preferably lanthanum fluoride. The AC impedance of the capacitor provides the specie and concentration indications.