Fig. 9 showsa typical breathing record. As seen, the transmitted SAW ampli-tude varies considerably due to breathing.
The abrupt decrease inthe SAW amplitude corresponds to the breath out, and the moregradual increase takes place during the breath in. The amplitudelevel after each breathing cycle remains constant, indicating thatthe sensor is fully recovered within the breathing cycle. An impor-tant advantage of the BSA-Au NCs on LiNbO3structure is that theresponse and recovery times (when the humidity changes in bothdirections) are very similar, in contrast to some sensors, which haveshort sorption but comparatively long desorption times [33,34].