A Promising Surface Acoustic Wave Humidity Sensor Based on Multi-Walled Carbon Nanotubes/Nafion Composite Film for Low Humidity Detection

The requirement for a humidity sensor with excellent performance for low humidity detection is becoming more and more urgent. Surface acoustic wave resonator (SAWR) with high resonance frequency was fabricated as basic sensitive component. Multi-walled carbon nanotubes and Nafion (MWCNTs/Nation) composite material was prepared as humidity sensitive films, deposited on surface of SAWR by dropping method. In the composite film, Nafion with high water absorbing efficiency was mainly for detecting the little change of moisture content. MWCNTs were profitable for improving the sensor's sensitivity and dynamic characteristic due to its large specific area and special ionic conductivity. Characteristic of the composite material could make a full use of the multiple sensing mechanisms of the SAW device. Experiment results showed that the present sensor had both a high RH sensitivity and excellent dynamic characteristic in the whole RH range. For low humidity detection, the present sensor showed quite a high sensitivity up to 260 kHz/%RH and good linearity with R-2 > 0.99. Detection precision of the sensor could reach 0.3%RH at low humidity level below 10%RH.