A versatile gas transmission device with precise humidity control for QCM humidity sensor characterizations

Previously, several high-sensitivity and inexpensive humidity sensors with rapid response times have been reported. However, obtaining reliable humidity characteristics of highly sensitive devices, such as quartz crystal microbalance (QCM) sensors, requires the development of new, affordable gas transmission setups. With that in mind, we developed a novel, comprehensive gas transmission system that combined elements from two commonly used systems (saturated salts and gas mixing), which facilitated automatic gas humidity changes, reliable gas flows in closed measurement chambers, and limited the influence of the external atmosphere/pollutants. The gas transmission device performance was tested using a commercial digital hygrometer and highly sensitive QCM coated with graphene oxide for six different humidity sets in range 5.3–82.6% RH. The dynamic repeatability tests proved the superb stability of the system, as QCM frequency deviation did not exceed 2% of frequency shifts among ten switching cycles (one hour each). Therefore, this system allowed a thorough investigation of humidity sensors properties in a controlled environment with a high precision.