Acoustic gas sensors using airborne sound properties

Known acoustic gas sensors use SAW-elements or mechanical resonators, covered with a sensitive layer, as primary transducers. Some of these indirect-working acoustic gas sensors are selective. But they show instabilities relating to contamination and high temperatures. These disadvantages can be eliminated by using as sensing effect the direct variability of properties of airborne sound in gas mixtures, e.g. the variable isentropic and anisentropic speed of sound and the resonance absorption. Potentialities in design of different types of electric-acoustic and fluidic-acoustic gas sensors are described. As an example, a fluidic-acoustic humidity sensor is presented.