Use of microwave dielectric spectroscopy measurements for moisture prediction in Vidalia onions

Abstract

Microwave Sensing offers an opportunity to nondestructively determine the amount of moisture in materials by sensing the dielectric properties of the material. In this study, dielectric properties of Vidalia onions were analyzed for moisture dependence between 6% and 92% moisture content, temperature dependence between 0 °C and 45 °C, and frequency dependence, between 200 MHz and 20 GHz. Dielectric constant at higher measured frequencies was linearly correlated with moisture content over the entire moisture range. Dielectric constant and loss factor were both directly and inversely related to temperature depending on frequency and moisture content. Use of a density-independent function that incorporates both the dielectric constant and loss factor enabled prediction of moisture content with extremely high accuracy up to 40% moisture content. The same function was utilized in development of temperature-compensated moisture prediction equations between 6% and 18% moisture content.