A device for sensing the presence of and measuring the concentration of a specific non-aqueous particle or gas material in an environment, the device comprising an interdigitated capacitor having at least a pair of selected covering layers thereupon, said pair of layers comprising a first passive electrically...http://www.google.co.uk/patents/US4571543?utm_source=gb-gplus-sharePatent US4571543 - Specific material detection and measuring device
