Influence of Dry Layers in Solute Concentration Measurement with Planar Microwave Sensors

This work presents an experimental study on the influence that dry layers (i.e. solid layers between the sensor and a liquid sample) have in the measurement of solute concentration in liquids with planar microwave resonant sensors. The study involves four sensors with different capacitive regions, as well as a measurement setup aimed at removing any possible influence other than that from the dry layers, including air removal by vacuum suction. The capabilities of the sensors for glucose concentration detection in aqueous solutions are tested with polytetrafluoroethylene dry layers of different thicknesses. The results show a clear decrement of the sensibilities as the thickness of the dry layers increase. The findings reported here suggest the need for comprehensive study of dry layers in these sensors, and the development of design strategies to minimize their influence.