Influence of Peanut Orientation on Microwave Sensing of Moisture Content in Cleaned Unshelled Peanuts

Abstract

An investigation of the influence of unshelled peanut orientation on microwave moisture sensing from measurement of dielectric properties is presented for the first time in this article. A free-space dielectric measurement technique was used for measurement on cleaned unshelled peanuts at 9.6 GHz with a pair of low-cost printed Yagi-Uda antennas. The peanut sample was placed between the transmitting and receiving antennas in a cubical polyester sample container (76 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times76$ </tex-math></inline-formula> mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times76$ </tex-math></inline-formula> mm). Influence of orientations of the peanut pods, were studied with 2, 3, 4 and 6-direction measurements of the dielectric properties of the sample. The different measurement directions were obtained by rotation of the cubical sample container. The dielectric properties were determined from measurements of the attenuation and phase-shift caused by the peanut sample when placed between the antennas. The dielectric properties of the peanut sample were found to be dependent on the orientation distribution of pods. The average value of dielectric properties determined from 6-direction measurement was more representative of the dielectric properties of the bulk peanut sample. A temperature-compensated function for the dielectric properties and subsequent moisture content calibration equation were established and used during the in-field testing. Results of the in-field microwave moisture measurements are compared with values obtained by using the official moisture determination method (capacitance-type meter).