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A surface acoustic wave (SAW) relative humidity (RH) sensor was prepared by sputtering SiO 2 sensing film on the total surface of an SAW resonator. The prepared humidity sensor exhibits good linear relationship under wide RH range of 10%-80%. Small hysteresis is observed during the adsorption and desorption processes. The sensitivity of the sensor is À1.14 kHz/% for the adsorption process and À1.06 kHz/% for the desorption process. The sensing mechanism of the sensor can be explained from the mass loading effect of the SiO 2 film. The response time is 6.0 s and the recovery time is 21.3 s when the RH switches between 10% and 70%.Moreover, the SAW sensor also shows good repeatability and stability due to the high adhesion of the sputtering SiO 2 film to the substrate.

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