Low-Cost CSRR Based Sensor for Determination of Dielectric Constant of Liquid Samples

Abstract

In this work, we have designed and fabricated low-cost microwave sensor for the determination of the dielectric constant of liquid samples with high accuracy. The biggest challenge with the microwave planar sensor is its low sensitivity and limited sensing range. A triple Complementary Split Ring Resonator (CSRR) with highly optimized dimensions has been proposed. Two sets of sensors are designed to operate at two different frequencies, viz. 1.2 GHz and 2.4 GHz. Since the resonant frequency of the microwave sensors changes with the variation of the dielectric constant of the liquid in contact, eight different liquids are used to record the shift in the resonant frequency of the sensors. For this, we have measured the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{S}_{{21}}$ </tex-math></inline-formula> parameter of the sensors using Vector Network Analyzer (VNA). Sensitivity as high as 0.87% has been achieved, which is much higher than most of the reported sensors. Fit equations have been developed for both the real and imaginary part of the permittivity from which the complex permittivity of unknown samples are obtained with less than 4% of error. Due to low-cost materials and ease of fabrication, the sensor may be a good alternative to expensive commercial sensors for dielectric characterization and impurity measurement of liquids.