Electrospun CeO2 nanoparticles/PVP nanofibers based high-frequency surface acoustic wave humidity sensor

Nowadays the working frequencies of surface acoustic wave (SAW) sensors are usually not higher than 500 MHz, typically in the range of a few dozen to hundred megahertz, while an increase of working frequency should be beneficial to the sensor performance. Thus, a high frequency SAW resonator operating at 1.56 GHz was fabricated for relative humidity (RH) detection. The CeO2 nanoparticles (NPs)/polyvinylpyrrolidone (PVP) nanofibers were prepared by electrospinning of PVP solution with CeO2 NPs working as the sensitive layer. The inorganic CeO2 NPs were synthesized previously using a hydrothermal method. In contrast with SAW sensor working at lower resonant frequency (879 MHz), the resonant frequency shift of the sensor based on 1.56 GHz was about 2.5 MHz in the RH range of 11% to 95%, which was approximately 8 times of the former one. Further analysis demonstrated that the additional acoustoelectric loading effect arising from increased electrical conductivity of CeO2/PVP nanofibers in high RH improved the frequency response compared with pure PVP nanofibers based SAW sensor. Moreover, the SAW sensor based on inorganic/organic nanohybrid also showed high stability under humid environment and negligible cross-sensitivity effects ensuring further wireless humidity detection. (C) 2015 Published by Elsevier B.V.