Differential, LED-excited, resonant NO2 photoacoustic system

We introduce the application of a differential microphone in an LED-excited photoacoustic system devoted to NO2 measurement. The microphone ports pick up out-of-phase signals generated in two resonators, thus achieving a larger electrical signal and good common mode noise rejection. The reduced noise floor and LEDs with higher optical power, made it possible to measure NO2 down to 60 ppbV, a figure that enables quantifying the amount of such a gas produced by gasoline engines equipped with catalytic converter.