A Sensitive Inexpensive SAW Sensor for Wide Range Humidity Measurement

The conventional relative humidity sensor suffers from low dynamic range, particularly below 20%RH and the sensor is also relatively costlier. This paper presents fabrication of inexpensive humidity sensor over wide dynamic range using surface acoustic wave resonators of 433.92 MHz frequency. Three sets, each are having three sensors have been fabricated by varying coating thickness of poly vinyl alcohol (PVA) sensing film. Experiments have been conducted to observe the resonant frequency shift with the variation of humidity in the range of 0 to 99%RH using HP 8753C VNA. All the sensors show significant frequency shift for the full span. The maximum sensitivity of the 5% PVA coated sensor for 0-30%RH is 3.72 kHz/%RH. Performance parameters of the sensors are compared with other polymer SAW sensors. The fabricated sensors compare well with the sensors reported in the literature. Important features of the sensors are wide dynamic range, inexpensive fabrication and high sensitivity.