Apparatus and method for early detection and identification of dilute chemical vapors

摘要

A detector and method for identifying a chemical vapor and determining its concentration in the ambient atmosphere. The chemical detector apparatus (120) preferably includes a plurality of surface acoustic wave (SAW) devices (10), each including a piezoelectric substrate (20), one-half (32) of which is coated with a selected polymer. The polymer characteristically absorbs one or more of a group of chemical vapors. Diffusion of a chemical vapor into the polymer increases its mass and proportionately changes the resonant frequency of the SAW device. A microcomputer control (186) is operative to determine a predicted time constant (or rate) for diffusion and a predicted equilibrium concentration of the chemical vapor within the polymer coating of the SAW device and to identify the chemical vapor and its relative concentration in the ambient atmosphere using the predicted values for these parameters long before the SAW device has reached equilibrium with the chemical vapor.