Research On Humidity Sensor Based On Surface Acoustic Wave Resonator

Humidity is closely related to our life and social activities.Humidity detection is vital in areas such as medical health,agricultural cultivation,food storage,weather monitoring and maintenance of precision instruments.With the development of technology,higher demands are being placed on humidity sensors in terms of sensitivity,measurement range and device size.Surface Acoustic Wave(SAW)is an acoustic wave that propagates along the substrate surface.It is sensitive to perturbations near the substrate surface and is suitable for a variety of sensors.SAW sensors have attracted great attention due to their high sensitivity,fast response,low cost and ease of integration.In this study,SAW resonators are used as the base device to construct high-performance humidity sensors,with the following main elements.(1)Considering that chitosan(CS)has abundant hydrophilic functional groups,good film formation and adhesion,and nanodiamond(ND)prepared by blasting method has abundant hydrophilic functional groups and large specific surface area,a SAW resonator-based humidity sensor based on nanodiamond-chitosan complex(ND-CS)is constructed in this paper.The humidity sensor exhibits good linearity and high sensitivity(-4.93 kHz/% and-4.83 kHz/% for adsorption and desorption processes,respectively)in the range of 10%-90% relative humidity(RH),with response and recovery times of 17.6 s and 5.2 s.The sensor was used for the detection of human respiration,enabling real-time monitoring of human respiration.(2)Considering the large specific surface area of ZnO nanosheets and the good chemical and thermal stability of AlN,an additional SAW resonator-based humidity sensor based on ZnO nanosheets/AlN films was constructed in this paper.The sensor has a high response(-2.3425 ± 0.02685 MHz)and a very short recovery time(3 s)in the range of 10% to 98% RH,with an average sensitivity of-53.53(ln(kHz)/%)for the adsorption and desorption processes.Good stability and selectivity were also achieved.The sensor was used for non-contact human skin humidity detection,enabling the detection of skin humidity in different areas and verifying the changes in skin humidity before and after exercise,drinking and hand washing,demonstrating the potential application of this humidity sensor for human skin monitoring.