Influence of peanut orientation on microwave sensing of moisture content in cleaned unshelled peanuts

Authors: JULRAT, SAKOL - Oak Ridge Institute For Science And Education (ORISE); Trabelsi, Samir

Submitted to: IEEE Sensors Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/14/2022
Publication Date: 6/1/2022
Citation: Julrat, S., Trabelsi, S. 2022. Influence of peanut orientation on microwave sensing of moisture content in cleaned unshelled peanuts. IEEE Sensors Journal. https://doi.org/10.1109/JSEN.2022.3168664.
DOI: https://doi.org/10.1109/JSEN.2022.3168664

Interpretive Summary: Determining moisture content in unshelled peanuts and in peanut kernels is possible from measurement of the dielectric properties of unshelled peanuts at a single microwave frequency. The measurement are rapid, nondestructive, and do not require any sample preparation. The unshelled peanuts are loaded in a sample holder and moisture readings are provided in real time. However, orientation of the peanut pods may influence the accuracy of the moisture readings. In this paper, an inexpensive microwave moisture meter with a cubical sample holder was built and tested for the influence of the unshelled peanuts orientation on moisture determination accuracy. The peanut pods were loaded in the cubical sample holder either arbitrary orientation or horizontally aligned and dielectric measurements were performed in 6 different directions by rotating the sample holder. Because of the total number of kernels interacting with the incident electric field is different for each direction, the measured dielectric properties were found to be orientation dependent. By averaging the measurements over 6 different directions, the dielectric properties were found to be more representative of the bulk sample and thus provided a better standard error of calibration for moisture predictions. In field testing showed that moisture content in unshelled peanuts can be predicted with a standard error of performance of 0.8%.

Technical 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 low-cost printed Yagi-Uda antennas for cleaned unshelled peanut measurement. The peanut sample was placed between the transmitting and receiving antennas in a cubical polyester sample container (76 mm x 76 mm x 76 mm). Two orientations of the peanut pods, arbitrary and horizontally aligned, were studied with 2, 3, 4 and 6-direction measurements which were obtained by rotation of the cubical sample container. The dielectric properties were determined through attenuation and phase-shift measurements. 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 compensation function for the dielectric properties and subsequent moisture content determination was established for in-field testing. Results of the in-field microwave moisture measurements are compared with values obtained by the official moisture determination method.