A novel serial high frequency surface acoustic wave humidity sensor

A novel topology of surface acoustic wave (SAW) humidity sensor was proposed. An interdigital electrode (IDE) was added in serial with a SAW resonator (SAWR) as the sensitive component. Silicon-containing polyelectrolyte humidity sensitive film was deposited on the surface of IDE instead of SAWR. By this way, the stringent technical requirements for film coating on SAW surface could be avoided, which was helpful to bring down the processing cost of the sensor. At the same time, vacuum packaged SAWR could provide a more stable and high operating frequency (433 MHz) for the sensor, which was profitable for both stability and sensitivity of the sensor. Sensitivity, stability, response-time, temperature coefficient of the novel sensor were tested and compared with the traditional SAWR sensor in our previous work. The results showed that both sensitivity (0.4 kHz/%RH at low humidity level; >1 kHz at high humidity level) and stability (noise level <10 Hz) of the sensor have got remarkable improvement for the new design.