An integrated passive impedance-loaded SAW sensor

An integrated passive impedance-loaded SAW H2S sensor working at room temperature has been presented in this paper. The sensor consists of a SAW transponder with delay line structure and a resistive H2S sensor as an impedance-loaded sensor. The SAW delay line was fabricated on a 128° LiNbO3 substrate and its center frequency is 233 MHz. The resistive sensor composed of the nano-crystalline SnO2 film and aluminum electrodes was also fabricated on the same substrate. The gas sensing properties of the resistive H2S sensor have been tested separately. In order to maximize the sensitivity of the whole sensor, the resistance of the impedance-loaded sensor was adjusted to match the output impedance of the SAW interdigital transducer (IDT) by changing the resistivity of the Sb-doped SnO2 nano-crystalline films and optimizing the electrode structure. The variation in the return loss magnitude was increased to 2.51 dB. Finally, the impedance-loaded SAW sensor was configured and measured wirelessly for various H2S concentrations at room temperature. The measurement results show that the proposed H2S sensor not only has good repeatability and high sensitivity but also is capable of passive wireless detection at room temperature.