Coupled inductive sensors for monitoring the pH of electrolyte solutions

Variations of the coupling between two inductors in the presence of a strong electrolyte with varying pH value is investigated. Inductors were placed at a distance of 15.875 mm apart. S12 parameters were measured and used as an indicator to the strength of coupling between the two inductors. The pH of the electrolyte solution was reduced from 4.2 to 0.2, A shift of 3.5 MHz in the frequency at which maximum coupling occurs was observed for the corresponding pH change. The system was also simulated using a Finite Element package. A discussion on the relevance of the simulated data and experimental values is offered. The design discussed in this paper has the potential of being used in monitoring conductive electrolyte solutions and qualitative monitoring of chemical reactions.