Development of a Wireless, Battery-Free SAW Volatile Organic Compounds Sensor Integrated with Temperature Sensor

摘要

A 440 MHz wireless and passive surface acoustic wave (SAW) based micro-sensor was developed for the simultaneous measurement of temperature and volatile organic compound (VOC). The developed sensor is composed of a SAW reflective delay line structured by an IDT (Inter-Digital Transducer) and four shorted grating reflectors, and a VOC-sensitive film (multi-walled carbon nano tubes (MWCNTs). The MWCNTs were functionalized by dipping them in an ethanol-based organic solvent to obtain a high selectivity for ethanol vapor. In wireless testing, using a network analyzer, sharp reflection peaks with a high S/N ratio, small signal attenuation, and only a few spurious peaks, were observed in the time domain. A high sensitivity and a good selectivity were observed in each VOC concentration. The measured sensitivities were 13.45°/ppm for ethanol and 4.07°/ppm for xylene.