Phase-sensitive method for background-compensated photoacoustic detection of NO2 using high-power LEDs

Abstract

A photoacoustic (PA) sensor has been developed for the detection of nitrogen dioxide (NO2). Ten amplitude-modulated high-power light emitting diodes (LEDs), emitting a total optical power of 9W at 453 nm, are used to excite the photoacoustic signal in NO2. The LEDs are attached to the circumference of a cylindrical PA cell. The induced longitudinal acoustics waves are detected using two electromechanical film stacks, located at the ends of the cell. Background signal cancelation is achieved by using phase-sensitive detection of the difference signal of the two pressure transducers. The phase-sensitive approach allows for improved dynamic range and sensitivity. A detection limit of 10 parts per billion by volume was achieved for flowing NO2 gas sample in an acquisition time of 2.1 s, corresponding to a minimum detectable absorption coefficient of 1.6 x 10−7 cm−1Hz−1/2. The developed sensor has potential for compact, light-weight, and low-cost measurement of NO2.