Relative humidity sensing by PVA-coated dual resonator SAW oscillator

A highly sensitive Surface Acoustic Wave (SAW) sensor system for relative humidity (RH) detection using chemically interactive polyvinyl-alcohol (PVA) film with implemented electronic module is described. The system configured as a dual resonator SAW oscillator consists of two SAW resonators, two RF amplifiers, and a mixer. The mixed frequency has been considered as output of the SAW sensor. The SAW response toward 60% RH has been measured as a frequency change of about −11.5 MHz, at room temperature. A cross-sensitivity of the PVA film toward organic vapours with bonded OH groups has been also detected. The RH sensing characteristics, at room temperature, of the PVA-based dual SAW sensor have been analyzed in terms of sensitivity, calibration curve, detection limit, noise, water-resistance, short–medium term repeatability, aging, and sensing performances comparison.