Compact Nandavarta-shaped metamaterial sensor for microwave detection of edible-oil adulteration

This paper presents a compact dual-band metamaterial absorber sensor based on a Nandavarta-shaped labyrinth resonator for microwave detection of edible-oil adulteration. The device addresses a critical food-safety gap by quantifying mineral-oil adulteration levels (0%, 10%, and 20%) in four commonly consumed edible oils through dielectric perturbation of two K-band resonances. The proposed 9 × 9 mm2 unit cell consists of a patterned copper meta-surface, a 1.6 mm FR-4 substrate, and a continuous copper ground plane. Four identical resonators arranged in a symmetric 2 × 2 configuration provide strong inductive–capacitive loading and enhanced near-field confinement. Full-wave CST simulations show two near-perfect absorption peaks at 18.015 and 20.13 GHz with absorption of 98.82% and 99.58%, respectively, along with polarization-insensitive and angle-stable performance. Metamaterial behavior is confirmed through effective-parameter retrieval and an equivalent RLC circuit model. Sensing is demonstrated using a 1 mm oil superstrate with controlled mineral-oil adulteration, producing distinct and monotonic resonance shifts. Experimental measurements using a vector network analyzer validate the simulated results.