Development and Evaluation of a Proximal Dielectric Sensor for Nondestructive Measurement of Sugar Concentration in Sugar Beet

Determination of sugar concentration of sugar beet in sugar factories is of great importance and is a basis for valuation of the sugar beet as well as assessment of the sugar production process in the factory. In this study with the aim of development of a non-destructive method for measurement of the sugar concentration of sugar beet in terms of Brix, a proximal dielectric sensor was developed and evaluated. This sensor is an open-end coaxial probe consisting of two metallic concentric ring electrodes which is connected to function generator and spectrum analyzer through coaxial cables. One hundred random samples of sugar beet were selected and measured by the dielectric sensor. Dielectric spectra i.e. amplitude as a function of frequency were obtained in the frequency range of 0-150 MHz. The reference Brix was measured with extracting juice from the points of dielectric measurement using a refractometer. The results showed that in the ranges of 30-50 and 120-140 MHz, the dielectric spectra varied noticeably in relation with variations in sugar beet Brix so that the amplitude decreased with increasing the Brix. The partial least square regression (PLSR) method could model the Brix as a function of the dielectric spectra variables with R2= 0.81 and RMSE of 0.72 Brix. The results of the study indicated that the dielectric sensor and measurement method was a simple and reliable method for non-destructive measuring of sugar beet Brix.