Sensitive Metamaterial-Inspired Microwave Sensor for Investigation of Storage Container and Temperature Effects in Extra Virgin Olive Oil

The type of container and environmental conditions, as the two critical factors in which olive oil is stored, significantly affect its naturalness and may even cause adverse effects that can threaten human health. In this regard, various sensors such as electronic nose, UV-VIS spectrophotometer, and gas chromatography have been developed to examine these factors. Although each of them has unique advantages, they have some drawbacks (lower sensitivity, laborious setup initialization, and expense), limiting their application. In this study, we propose a high-quality and sensitive metamaterial (MM)-based microwave (MW) sensor for the first time in the literature to monitor and quantify the effect of different storage containers (green poly(ethylene) terephthalate (PET), dark glass, and tinplate) and environmental conditions (temperature variations: $23~^{\circ } $ C and $60~^{\circ } $ C) on electromagnetic properties of extra virgin olive oil (EVOO) over 90 days time period. Built on a relatively inexpensive FR-4 dielectric substrate, the proposed sensor has a reflection response $|S_{11}| \cong -49.11$ dB at the resonance frequency $f_{r} \cong 4.97$ GHz. Considering the performance of the sensor for different container types and temperatures over the entire time period, it has a superior quality factor and sensitivity reaching, respectively, up to 242 (158 on average) and 5.61% (4.98% on average), which together bring the sensor to the forefront against similar MM-based MW sensors in the literature. From our study, the resonance frequency of the proposed sensor is noted to be changing with time for oil samples stored in any container type at a given environmental condition. Besides, oil samples stored in green PETs produce a larger resonance frequency shift due to their high dielectric constant. In addition, it is observed that the resonance frequency of the sensor redshifts for a sample stored in any container type with an increase in temperature, which is closely associated with the augmented reaction of the oil sample with its container. Finally, a fitting function (power function) is established to quantify resonance frequency shift for different storage containers and environmental conditions.