Asymmetric coplanar strip based stepped monopole sensor for liquid permittivity measurements

Abstract

Investigation of dielectric properties of materials has significant applications in the current scenario. A high sensitive microwave submersible sensor for measuring complex permittivity of liquids over a broad range is presented in this paper. An asymmetric coplanar strip (ACS) fed stepped monopole is employed as the sensing element, and the impedance contrast in the stepped monopole maximizes the sensor’s sensitivity. The sensor is immersed in the liquid sample, and its resonant frequency is exploited to determine the real part of permittivity, and the reflection phase or the radiation efficiency is utilized for the imaginary part of permittivity. Analysis of the sensor, loaded with liquid samples of various dielectric constants and loss tangents, is presented in this paper. The proposed sensor operating at 5.3 GHz under unloaded condition has a maximum numerical sensitivity of 13.7%. The sensor is fabricated and experimentally validated with liquids with dielectric constant ranging from 2–78. The proposed sensor is utilized to measure the glucose concentration in an aqueous glucose solution and the concentration of ethanol blending in petrol.

Keywords

• Asymmetric coplanar strip (ACS)
• Complex permittivity
• Radiation efficiency
• Reflection coefficient
• Reflection phase difference
• Stepped monopole