PERFORMANCES OF MASS-SENSITIVE DEVICES FOR GAS-SENSING - THICKNESS-SHEAR MODE AND SURFACE-ACOUSTIC-WAVE TRANSDUCERS

In this work we investigated different thickness shear mode resonators (TSMRs) with fundamental frequencies of 10 and 30 MHz and surface aco ustic wave devices with fundamental frequencies of 80 and 433 MHz. Fou r aspects were of primary interest in this comparison: noise levels an d signal-to-noise ratios (S/N), influence of the polymer film thicknes s, influence of temperature on the transducer signal before and after coating, and minimum threshold values for monitoring different volatil e organic compounds in the environment. We limited our investigations to a temperature range between 298 and 308 K, with 303 K the routine m easuring temperature. Analyte concentrations (n-octane, tetrachloroeth ene) were chosen from the minimum detection limit up to 5000 mu g/L. T he temperature was found to strongly affect the performance of all the devices. The sorption of the analyte vapors into the polymeric films was demonstrated to be transducer-independent (identical partition coe fficients for all the devices). The 30 MHz TSMRs showed very satisfyin g results in terms of S/N and limits of detection.