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 expensive) limiting their application. In this study, we propose a high-quality and sensitive metamaterial (MM)-based microwave sensor for the first time in the literature to monitor and quantify the effect of different storage containers (green pet, dark glass, and tinplate) and environmental conditions (temperature variations: 23°C and 60°C) on electromagnetic properties of extra virgin olive oil over 90 days time period. Built on a relatively inexpensive FR-4 dielectric substrate, the proposed sensor has a reflection response (|<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub>| ≅ −49.11 dB at the resonance frequency <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f_r</i> ≅ 4.97 GHz. Considering the performance of the sensor for different container types and temperatures over entire the time-period, it has superior quality factor and sensitivity reaching, respectively, up to 242 (158 on the average) and 5.61% (4.98% on the average), which together bring the sensor to the forefront against similar MM-based microwave 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.