Engraved Microwave Metasurfaces for Potential Application in Honey Quality Control.

In this study, millimeter-scale metasurfaces are examined concerning their capability as potential honey quality control sensors. In particular, complementary split-ring resonator metasurfaces were developed through the Computer Numerical Control engraving method. Under unloaded conditions, the metasurfaces exhibited fundamental resonance frequencies in the range of 3-6 GHz, depending on their size as well as the measurement orientation. Moreover, their electromagnetic response was studied in the presence of different honey types, such as chestnut, pine, and orange blossom honey. A corresponding resonance frequency shift was observed, suggesting the distinct electromagnetic response of the fabricated structures with respect to the honey type. Furthermore, the hereby studied resonators were tested against various types of honey adulteration, such as sweeteners (sugar and maple syrup), as well as microplastic contamination. The metasurfaces exhibit a discrete resonance frequency shift along with modulation of the resonance intensity in honey adulteration, enabling them to act as efficient honey quality detectors. In addition, their electromagnetic performance was compared to other state-of-the-art spectroscopic techniques dedicated to honey contamination, in particular, Raman and FTIR. It was found that spectroscopic evidence is consistent with the metasurface electromagnetic response, giving credence to their performance. All in all, it is evident that the hereby studied metasurfaces exhibit significant performance in honey adulteration sensing, allowing their potential application as sensors for honey quality control.