Novel Microwave Moisture Sensor for In-shell Nuts and Grains

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

Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 2/24/2023
Publication Date: N/A
Citation: N/A

Interpretive Summary: During the peanut grading process kernels moisture content, which is the main parameter to declare the trailer load "sale" or "no sale" is determined towards the end of the process after cleaning, sorting, sizing , and shelling about 500-grams of the original the peanut pods sample of 1500 -grams. Out of the original sample only 250-grams of peanut kernels are tested for moisture with an official electronic moisture meter. A cost-effective microwave moisture meter equipped with a multiple antennas system was assembled, calibrated, and tested for kernel moisture determination from measurement of the dielectric properties of peanut pods. With this meter, the entire sample of peanut pods (1500 -grams) is scanned and kernel moisture content is determined while the kernels are still in the pods. This allows to move moisture determination to the front end of the grading process which results in significant savings in time and labor. With this original design, a better averaging of moisture content throughout the entire sample is achieved resulting in a more accurate reading of kernel moisture content.

Technical Abstract: Moisture content is the one single most important parameter in assessing the value, quality, and safe conditions for storage of grains and nuts. During the peanut grading process a 1500-1700 grams of unshelled peanuts are taken from a trailer load and moisture content is determined after removing foreign materials, visually inspecting the unshelled peanuts, and sizing. Only 500 grams of the original sample are shelled to determine moisture content with an official electronic moisture meter. The latter is a capacitance-type meter operating at a frequency in the MHz range. It is well established that at these frequencies, the measured dielectric properties are prone to the influence of interfacial polarization phenomenon and ionic conduction which affect the instrument calibration and consequently the moisture determination accuracy. In contrast, at microwave frequencies, above 3 GHz, only orientational (dipolar) polarization related to the polar nature of the water molecules is at play making microwave sensors operating at these frequencies highly effective in moisture sensing. In this paper, a novel microwave sensor design consisting of four pairs of antennas is presented. The sensor operates in transmission mode at 9.6 GHz and allows the scanning of the entire sample volume. In addition, peanuts kernels moisture content can be determined from measurement of the dielectric constant and the dielectric loss factor of unshelled peanuts. This simplifies considerably the grading process and provides a moisture content that is more representative of the entire sample. Results of laboratory calibration of a sensor prototype for moisture determination of peanut kernels while still in the pods are presented.