Passive Microwave Sensors

Abstract

This thesis presents novel passive microwave-based sensors measuring the levels of sodium chloride in human sweat for non-invasive dehydration and cystic fibrosis monitoring. First, a new interface technique using cellulose filter papers as a superstrate for sampling Liquid under test (LUT)/Sweat was proposed and tested. Using filter paper had enhanced the sensitivity of the sensors compared to other traditional liquid sampling mechanisms such as capillary and container techniques reported in the literature. Second, a set of 4 designs using coupled slots (CPW) to coupled microstrip transitions as well as their developed circuit models were used in designing a family of resonator-based sensors. Those models managed to accurately model the behavior of the sensor under various stimuli. Consequently, the parameters of sensors can be optimized using circuit simulations instead of time-consuming EM simulations. The prototypes were fabricated and verified experimentally using prepared sodium chloride solutions with concentrations in the range of 0.01-2 mol/L. Finally, a novel low-cost wi-fi-based system had been proposed to complement the proposed sensors in transmission measurements. Preliminary measurements with the proposed system show the potential to bring microwave sensors to an affordable price point for the public consumer market. The proposed sensors have simpler structures, a simpler sampling mechanism for liquids, excelling performance, enhanced sensitivity as well as lower operating costs. The proposed sensors are not limited to sweat monitoring but could also fit in