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.