Detection of ppb ozone using a dispersive surface acoustic wave reflective delay line with integrated reference signal

We report the characterization of a dispersive surface acoustic wave (SAW) delay line for the detection of ozone in air at parts-per-billion (ppb) concentrations. Augmenting recent developments in wireless SAW tag technology, we fabricated 435 MHz SAW devices and prepared them with polybutadiene coatings to serve as ozone-specific gas sensors. We measured the frequency dependent one-port electromagnetic scattering parameter, S11(f), at regular time intervals as the gas stream was adjusted using an EPA primary standard ozone calibrator. The temperature and relative humidity were also recorded using an independent commercial sensor. The data allowed us to estimate the sensitivity to ozone and to temperature, and we estimated other parameters useful in personal dosimetry: saturation dose, shelf life, and limit of detection. Finally, the built-in time multiplexed response provided reference data for first order temperature compensation, yielding a chemical limit of detection of 63 ppb-min ozone.