Sensitive Microwave Sensor for Detection and Quantification of Water in Adulterated Honey

Honey is a rich source of sugar and is one of the indispensable ingredients in infant foods. Thus, it can be subjected to adulteration due to its cost. Measurement techniques such as liquid chromatography and near-infrared spectroscopy, used for detecting any adulteration, are expensive and need to be conducted by highly trained personnel for off-line analysis. Microwave measurements, as a fast, simple, and relatively inexpensive analysis, have recently shown great potential in detecting adulteration within honey samples. Nonetheless, sensor types used in such measurements are conventional. In this study, a reflection-type sensitive microwave sensor terminated by a metal back is proposed for the first time in the literature for the detection and quantification of water percentage (δ) level (mass-to-mass basis) within water-adulterated honey samples. When compared with other resonance-based microwave cavity sensors, thanks to its eight strips located at the centers of two closed circular loops, it demonstrates superior frequency selectivity and sensitivity (S =5.13%) validated by full-wave 3-D simulations performed by the CST Microwave Studio and equivalent circuit analysis carried out by the Advanced Design System (ADS) software. For example, for ethanol, the proposed sensor gives a frequency shift of more than 1 GHz in the X band. Resonance frequency shift and variation of the reflection coefficient amplitude (|S11|) are measured at X band to detect honey samples with up to 8% adulteration level. Three different honey samples (flower honey, highland honey, and thyme honey) were examined to test the performance and applicability of the proposed sensor.