Abstract
A capacitive humidity-sensing device was created by thermal evaporation of 99.999% aluminum. The substrate used for the coating was etched double-sided printed circuit board. The etched printed circuit board serves as the dielectric of the capacitor while the aluminum thin films deposited on either side serve as the plates of the capacitor. The capacitance was measured before and after exposure to humidity. The device was then calibrated by comparing the readings of capacitance with that of the relative humidity sensor of the Vernier LabQuest2. It was found that there is a linear relationship between the capacitance and relative humidity given by the equation C=1.418RH+29.139 where C is the capacitance and RH is the relative humidity. The surface of the aluminum films is porous and it is through these pores that water is adsorbed and capillary condensation occurs, thereby causing the capacitance to change upon exposure to humidity.
Highlights
The other methods for fabricating these sensors are quite complex and involve complicated processes to create the porous surface needed
The aluminum thin films serve as the plates of the capacitor while the etched printed circuit board serves as the dielectric between the plates
The pores of the film are filled by the water molecules through capillary condensation as shown previously in figure 1
Summary
The other methods for fabricating these sensors are quite complex and involve complicated processes to create the porous surface needed. The novelty of the method presented in this paper is that it makes use of a simpler method of creating the porous structures It is a one step process where the film has to be deposited at a normal incidence to the substrate. The use of the already porous surface of etched printed circuit board, as the substrate for the coatings, produces a porous film and allows an easier method for constructing the capacitive humidity sensor. The aluminum thin films serve as the plates of the capacitor while the etched printed circuit board serves as the dielectric between the plates. This capacitor was used as a relative humidity sensor and its response to humidity was studied and compared to a commercially available sensor
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