415 SOLTANI & ALIMARDANI: INVESTIGATION OF THE RELATIONSHIP BETWEEN MOISTURE AND D C Journal of Scientific & Industrial Research Vol. 72, July 2013, pp. 415-418 *Author for correspondence E-mail: mahsoltani@ut.ac.ir Investigation of the Relationship between Moisture Content and Dielectric Constant of Wheat and Millet Mahmoud Soltani * and Reza Alimardani Department of Agricultural Machinery Engineering, Faculty of Agricultural Engineering & Technology, University of Tehran, Karaj, Iran Received 28 August 2012; revised 27 January 2013; accepted 03 May 2013 Moisture content has significant effects on most properties of agricultural products. One of these properties which are highly affected by moisture content is the dielectric constant of grains and seeds. Capacitive technique is a suitable method for moisture prediction of grains and seeds. In this study, a cylindrical capacitive sensor was used to determine the dielectric constant of Iranian wheat and millet. Results showed that dielectric constant of grains are highly dependent on the moisture content and frequency. Polynomial and hyperbolic regression models were developed between dielectric parameter and moisture content. Results showed that hyperbola model is more suitable and had higher value of R 2 and lower value of SSE and RMSE. The best results were obtained at 500 kHz frequency for wheat and millet with R 2 respectively equal to 0.9999 and 0.9982 in hyperbola regression. Keywords: Dielectric constant, Moisture content, Capacitor, Wheat and millet. Introduction Capacitive technique is a simple, rapid and low cost method to determine the quality of food, fruits and vegetable, seeds and grains. Due to these advantages, this technique is widely used in agriculture. Ragni et al., (2008) predicted the quality indices of eggshell using dielectric technique. They used a parallel plate capacitor as a sensor. In their experiments, samples of eggs were submitted to dielectric measurements in the range of 50– 500MHz after 1, 2, 4, 8, and 15 days of storage at 20 ºC. They reported that models obtained by PLS (partial least square) processing of dielectric spectra showed R 2 values up to 0.996 for the time of storage and 0.876 for the air cell height. Guo et al. (2011) determined chestnut and chestnut weevil as a function of temperature by an open- ended coaxial-line probe and network analyzer. According to their findings, a temperature between 20 and 60 ºC had positive effect on dielectric constant of chestnut and chestnut weevil and loss factor of chestnut over the entire investigated frequency range. The loss factor of chestnut weevil was influenced by temperature positively below 1000 MHz and negatively above 1GHz. Sacilik et al. (2006) determined the dielectric properties of flaxseed in the ranges of 50 KHz to10MHz using a parallel-plate capacitor sample holder. They studied the effects of moisture content, bulk density and frequency on the dielectric properties and concluded that the relative permittivity, loss factor, loss tangent and conductivity were greatly influenced by the moisture content, bulk density and frequency. They also deduced that the moisture content was the most significant factor affecting the dielectric properties of flaxseeds. Bansod and Ritula (2011) designed an instrument and calibrated it for the Indian wheat. They obtained a high degree of correlation between data obtained from the instrument and the oven drying technique (R 2 = 0.995). The dielectric properties include the dielectric constant (ε’) and loss factor (ε’’), real and imaginary parts of relative complex permittivity, ε = ε’–jε’’. The dielectric constant is associated with the ability of a material to store electrical energy in the presence of an external electric field, whereas the loss factor refers to the dissipation of energy in the form of losses (Guo et al., 2008).The permittivity relative to free space, or the absolute permittivity divided by the permittivity of free space, ε 0 = 8.854 × 10 –12 F/m is called dielectric constant (Nelson and Trabelsi 2002).The aim of this paper is to the study the behavior of Iranian wheat and millet as dielectric material at different moisture content and