Investigating the influence of grain and seed variety on calibrating microwave moisture sensors

Authors: Trabelsi, Samir; Lewis, Micah; Nelson, Stuart

Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/27/2023
Publication Date: N/A
Citation: N/A

Interpretive Summary: One of the most critical phases in developing microwave moisture sensors is their calibration against the standard method. For grain, seed, and nuts, there is a concern whether there is a need for calibrating these sensors for individual varieties as it is the case for the electronic moisture meters operating in the megahertz range. To tackle this concern dielectric properties of samples of wheat, corn, and soybeans of different varieties were measured at 10 gigahertz and 25 oC. By plotting the dielectric properties as a function of oven moisture content, it was observed that for each material data corresponding to different varieties were superimposed. To further investigate the influence of variety on calibration, performance of moisture calibration equations established for each variety was compared to a single moisture calibration equation established for all varieties combined through computation of the standard error of calibration (SEC). The SECs corresponding to individual varieties were nearly the same as the one corresponding to all varieties combined. Therefore, it was concluded that at microwave frequencies there is no need for individual calibration corresponding to each variety of a given material. This simplifies considerably the calibration process and represents an advantage over existing electronic moisture meters.

Technical Abstract: Microwave moisture sensors represent a sound solution for real-time, nondestructive determination of moisture content in grain, seed, nut and other agricultural products. One of the most critical phases in developing these sensors is their calibration against the standard method, in this instance the oven-drying technique. For grain and seed, a question of concern during the calibration process of sensors operating in the GHz frequency range: Is there a need for individual calibration for each variety for a given material as encountered in electronic moisture meters operating in the MHz frequency range (around 10 to 20 MHz)? In this study, dielectric properties of different varieties of wheat, corn and soybeans were measured a 10 GHz and 25 oC to investigate the influence of variety. Dielectric properties measured for all varieties for a given material were nearly superimposed and the same was observed when plotting density-independent calibration function, , Psi , as a function of moisture content. Performance of individual moisture calibration equations in predicting moisture content was compared to that from a single moisture calibration equation established for all combined varieties through computation of the standard error of calibration (SEC). In most instances, the SEC corresponding to individual varieties was equal to that corresponding to all verities combined.