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The article presents an asymmetric single split resonator (ASSR) unit cell, its resonant properties, and an electrically small microwave sensor employing the complementary asymmetric single split resonator (CASSR) structure with high quality factor (Q) on the FR4 substrate. The structure is compared with the conventional symmetric split ring resonator. The CASSR sensor designed and fabricated on a substrate of dielectric constant 4.4 and a thickness 1.6 mm has an electrically small size of 0.127λ 0 × 0.127λ 0 × 0.007λ 0 at 1.27 GHz, which yields ka = 0.56 < 1 with low radiation efficiency. The properties and performance of the proposed CASSR for extracting the permittivity of both solid and liquid samples using amplitude and phase sensing in a simple lab-in-touch approach are validated with full-wave simulations and experimental results.

Adulteration detection of liquids is an emerging field in the present scenario. Purity detection of engine oils and fuels is essential for the smooth functioning of automobiles. An asymmetric coplanar strip fed stepped impedance resonator (SIR) coupled single split ring resonator (SSRR) sensor is used for purity and adulteration detection of engine oil and fuels in automobiles. The sensor operating at 5.95 GHz in free space on a low-cost substrate with a compact size of 10 Â 11.5 Â 1.6 mm 3 is demonstrated in this article. The impedance contrast between the two lines of SIR and the coupled SSRR improves the electric field distribution and thus the sensitivity. The resonant frequency of the proposed sensor changes with the aging of the oil or the adulteration level. The sensor performance is analyzed with simulations and validated with measurements.

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