Planar Complementary Spiral Sensor for Permittivity Characterization of Oil Samples

A planar complementary spiral sensor (PCSS) for the characterization of the permittivity (ε<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</inf>) of oil samples is proposed in this paper. A monopole antenna coupled with a complementary spiral resonator is utilized to test the oil samples. The resonant frequency of the proposed sensor is 2.4 GHz in ISM frequency band. The sensor is fabricated on FR4 substrate with dielectric constant (ε<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</inf>) of 4.4, loss tangent (tanδ) of 0.02 and thickness (h) of 1.6mm. The overall dimensions of the PCSS are 13 mm x 10 mm x 1.6 mm. An empirical formula is derived for the extraction of the ε<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</inf> of oil samples. Additionally, the paper presents a method for adulteration detection of coconut oil. High sensitivity and compact size are highlighted as the key features of PCSS.