Characterization of guided microwave spectrometry using water-ethanol mixtures

On-line measurement of food composition plays an important role in ensuring good quality control during processing operations. Microwave based instruments provide on-line measurement of the bulk sample due to the relatively long wavelength. Characterization of Guided Microwave Spectrometry (GMS) was conducted in this study. The GMS spectra and dielectric properties of water-ethanol mixtures with ethanol contents (v/v) of 0, 25 and 50% were measured at 10°C, 23°C and 40°C. The effects of coaxial cables and antenna were examined and the detection limits of the GMS analyzer were determined. The dielectric properties of the material being measured affected the GMS spectrum by shifting the cutoff region and changing the spectral amplitude over the entire operating frequency span. Temperature affected the spectrum by changing the dielectric properties of the material. Coaxial cables did not have a significant effect on the spectrum and the characteristic dip in the passband region was due to antenna resonance. The antenna affected the number of the resonances present in the spectrum, the frequency location and the amplitude of the resonances. GMS system has both a lower and upper amplitude limit beyond which its resolution decreases significantly. This can be resolved by using a signal attenuator and a smaller sensor body.