Coupled RF inductive sensors for monitoring the conductivity of electrolyte solutions

The use of closely coupled inductors, operating in the region of 10 MHz to 1 GHz, for detection of change in the concentration of ionic species present in a liquid sample, is reported here. The S-parameters were measured for the coupled inductors with liquid samples under varying pH conditions on one inductor only. S12 parameters were used as an indicator for the coupling between the two inductors. The results from this study show that coupled coil systems can be employed in simple sensing systems to monitor electrolyte solutions without the need for direct physical contact to the sensor itself. This design has the potential of being used for applications such as monitoring DNA hybridization or monitoring the conductance of electrolyte solutions with high conductivity while simplifying packaging steps required.