Use of dielectric mixture equations for the characterization of uncleaned peanuts

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

Submitted to: Measurement: Food
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/4/2022
Publication Date: 1/19/2022
Citation: Julrat, S., Trabelsi, S. 2022. Use of dielectric mixture equations for the characterization of uncleaned peanuts. Measurement: Food. 5. https://doi.org/10.1016/j.meafoo.2022.100022.
DOI: https://doi.org/10.1016/j.meafoo.2022.100022

Interpretive Summary: The presence of foreign materials in unshelled peanuts delivered by farmers to peanut buying points is of major concern. If quantities of foreign material are too high, the peanut loads must be cleaned before they can be regraded and sold by the farmers. Therefore, a rapid means for measuring the foreign material content would be of real value in saving time and expense associated with grading and cleaning of peanuts. Dielectric properties sensing, based on a non-destructive microwave free-space transmission measurement has the potential for detecting and providing foreign material determination in unshelled peanuts. This is mainly because the effective dielectric properties of unshelled peanuts are influenced by the presence of foreign materials such as sticks, peanut shells, peanut raisins (shrivelled and immature peanuts) and stones. Most foreign material in uncleaned peanuts consists of peanut shells because peanut pods are broken during the harvesting process. Other physical parameters that influence the effective dielectric properties include moisture content, air gaps, geometrical shape, size, orientation and position of foreign materials in unshelled peanuts. Therefore, it would be advantageous to have a dielectric mixture model that can be used to characterize the effective dielectric properties of the foreign materials mixed with unshelled peanuts. A dielectric mixtures study of foreign materials such as peanut shells, sticks, peanut raisins and stones mixed with cleaned unshelled peanuts was conducted. The dielectric properties of the foreign materials mixed with cleaned unshelled peanuts were measured with a microwave free-space transmission technique at 10 GHz. Dielectric mixture equations, such as linear, quadratic, cubic and logarithmic models, were used to describe the mixtures of foreign materials and cleaned unshelled peanuts. Volume fractions of foreign materials and cleaned unshelled peanuts, and the dielectric constants of foreign materials and cleaned unshelled peanuts were used with the models. Physically, the volume fractions of foreign materials are related to the mass and the density of foreign materials, as well as the volume fraction of cleaned unshelled peanuts. Several dielectric mixture models were developed based on the assumption that the cleaned unshelled peanuts sample is a homogenous host medium and the foreign materials are randomly distributed inclusions. The effective dielectric properties of mixtures of single and multiple types of foreign materials with cleaned unshelled peanuts were determined with the modes and compared to measured data for the same mixtures. The logarithmic dielectric mixture equation showed the best estimate of dielectric constants compared to linear, quadratic and cubic dielectric mixture formulas for all types of foreign material mixtures. The proposed dielectric mixture models provide a basic knowledge of dielectric mixture of foreign materials and cleaned unshelled peanuts. The proposed dielectric mixture models for uncleaned peanut samples will be helpful; in the development of microwave techniques for reliably sensing the foreign material content in uncleaned unshelled peanuts at the buying points, saving time and expense in the grading and sale of farmers peanuts.

Technical Abstract: A dielectric mixtures study of foreign materials such as peanut shells, sticks, peanut raisins and stones mixed with cleaned unshelled peanut is presented for the first time. The dielectric properties of the foreign materials mixed with cleaned unshelled peanuts were measured by microwave free-space transmission technique at 10 GHz. Dielectric mixtures equations such as linear, quadratic, cubic and logarithmic were used to describe the mixtures between the foreign materials and cleaned unshelled peanuts. Volume fractions of foreign materials and cleaned unshelled peanuts, and the dielectric constants of foreign materials and cleaned unshelled peanuts were supplied to the models. Physically, the volume fractions of foreign materials are related to the mass and the density of foreign materials, as well as the volume fraction of cleaned unshelled peanuts. The effective dielectric mixtures of a single and multiple types of foreign materials were determined and compared to the measured data. Results of the logarithmic dielectric mixture model showed the best estimate of dielectric constant for all types of foreign materials compared to the linear, quadratic, cubic dielectric mixture equations, respectively.