A Radio Frequency Sensor For Measurement Of Small Dielectric Property Changes

Abstract

We propose a sensitive radio frequency (RF) sensor for the measurement of small dielectric property changes. Interference is used to cancel parasitic background signals to improve sensitivity. The device consists of two Wilkinson power dividers, a 180 degree reversephase and an in-phase CPW (coplanar waveguide)-slotline back-toback balun. The small dielectric property changes between de-ionize water and two sets of primary alcohol-water mixtures with different concentrations in terms of molar fractions are measured with clear sensing and identification. The sensor offers almost thirteen times greater sensitivity than conventional transmission lines. Experimental results also show that the lowest detection limit for the molarity of primary alcohol is about 0.25% across the sensitive sensor. Compared with microwave soil moisture sensors the proposed RF device is more sensitive.