A passive wireless hydrogen surface acoustic wave sensor based on Pt-coated ZnO nanorods

Using a passive wireless sensor to detect hydrogen can reach the goals of reducing cost and increasing the lifetime since the sensor can work without batteries. In this paper, a passive wireless hydrogen SAW sensor operating at room temperature has been achieved by combining a SAW tag and a resistive hydrogen sensor. The SAW tag is fabricated on a 128 degrees YX-LiNbO(3) substrate and its central frequency is 433 MHz. The resistive hydrogen sensor with the Pt-coated ZnO nanorods as the sensing film has the advantages of high stability, good repeatability and simple fabrication. The ZnO nanorods are synthesized by using the aqueous solution method and the Pt coating is employed as a catalyst for the hydrogen detection. The property of the resistive hydrogen sensor is examined before combining with the SAW tag. Results show that the resistance changes caused by the variations of relative humidity and temperature are negligible. Finally, the hydrogen SAW sensor is configured and measured wirelessly for various hydrogen concentrations at room temperature. The difference of the relative return loss caused by the hydrogen concentration variation is obvious and recognizable. All responses show that the proposed hydrogen sensor not only has good repeatability and high sensitivity but is capable of passive wireless detection.