Carbon nanotubes humidity sensor based on high testing frequencies

A multiwall carbon nanotubes (MWCNTs) humidity sensor based on alternating current (AC) testing is made, and its frequency characteristic is studied. When the testing frequency (f) increases, both the sensor conductance and the sensitivity (S) to relative humidity (RH) ascend accordingly. Under the testing frequency (f) of 1 MHz the sensitivity is about −95 times of that at f = 50 Hz. The mechanism of the sensor response to RH under alternating current testing can be interpreted by the theory of capillary condensation and dielectric physics, and the electrical model of the sensor is explored by both experimental and theoretical analysis. The stability, repeatability and response time of the sensor are investigated in details. Experiment results show that the sensor under AC testing demonstrates higher sensitivity and better reversibility. The response time and recovery time are 16 s and 8 s, respectively.