HUMIDITY SENSING USING SOFT FERRITES

The electrical properties of polycrystalline soft ferrites, namely Cu- Zn system are considerably changed by doping controlled amounts of Lit hium and Calcium salts. The room temperature resistivity is found to e xceed 1000 M Omega cm at 45% relative humidity. Variation of resistivi ty with percentage relative humidity is found to be linear in the rang e above 60% RH and is of the type (rho) = (rho)0 - MRH. M being a slop e of the curve which is humidity sensitivity. In the range 45 to 60% R H, log rho Vs % RH exhibits linear relation and is governed by the nat ure (rho) = (rho)0e-krh. K being humidity sensitivity. The statistical tools are employed for the analysis of the curves and all the paramet ers are tested giving best results. The response time in the disc form , for both negative and positive step is of the order of 6 to 7 second s for 5% change while it is of the order of 7 to 8 minutes for -ve ste p and one minute fbr +ve step for 45% to 85% change in RH. The materia l does not exhibit any aging effect. In the entire range of humidity, the pellets do not become watery. Basically, ferrites are temperature sensitive and therefore, humidity and temperature sensing both can be done ill a single device, because there is no any effect of humidity o n the magnetic properties of these materials.