A STUDY OF LOW-COST SENSORS FOR MEASURING LOW RELATIVE-HUMIDITY

The performance of low-cost commercially available polymeric humidity sensors has been compared to that of prototype thick- and thin-film po lymer-based sensors that will be optimized for improved performance at low relative humidity (RH). The commercially available humidity senso rs examined include polymeric capacitive and resistive types. The prot otype sensors utilize both thick- and thin-film interdigitated electro des, on quartz and ceramic substrates, with polyimide sensing films. B oth capacitive and surface acoustic wave (SAW) sensing mechanisms have been studied for the thin-film structure. The commercial capacitive m icrosensors have a linear response in the range 5-95% RH. The resistiv e sensors are non linear, but the signal-conditioning circuit can be m odified for improved sensitivity in a particular RH range. The prototy pe thick-film sensor has a non-linear response, while the response of the thin-film prototype sensor is comparable to that of the commercial capacitive microsensors. The SAW sensor has the potential for higher sensitivity than the commercial capacitive microsensors, but is less l inear.