Thermopile Sensors for the Detection of Airborne Pollutants

We have developed sensors for airborne pollutants using 36-junction thermopiles as the sensing platform. The thermopiles detect heat released when airborne pollutants react with chemical coatings applied to the sensing junctions. Our thermopiles consist of microfabricated thin film bismuth-antimony junctions on thin polyimide or polyethylene terephthalate drumhead membranes that are supported by aluminum substrates. The sensitivity of our thermopiles (> 5 V-s/J) was measured using solvent evaporation and acid-base reactions. A copper oxalate coating on the sensing junctions enables the detection of ammonia vapor. The integrated sensor output is proportional to the logarithm of the ammonia concentration in the air injected into the test chamber. Sub-ppm concentrations of ammonia in air can be detected Detection of acid vapors (e.g., HC1) is also described.