Location: Quality & Safety Assessment ResearchTitle: Attenuation-only method for moisture sensing in granular materials
Submitted to: Internation Society for Electromagnetic Aquametry Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 3/25/2021
Publication Date: N/A
Interpretive Summary: Microwave moisture sensing has been applied successfully in agriculture, food and other industries. However, the limited use of this promising technology is related to the cost, which remains relatively high and the complexity of calibration of devices using this technology. In this paper, a simplification was introduced to lower the cost and simplify the calibration process. The measurement principle is based on measurement of the attenuation at a single microwave frequency. Measurement of attenuation is simple and straightforward and consists of comparing the power levels of the incident wave with and without sample. Components of a microwave circuit for attenuation measurement are inexpensive and once a calibration is established for a given material it can be easily programmed in a measuring device for moisture determination from attenuation measurement. To validate this concept of measurement, measurements were performed on wheat, corn, and soybeans at 23 oC and microwave frequencies ranging from 7 Gigahertz to 12 Gigahertz. Results show that moisture content in wheat, corn , and soybeans can be predicted with standard errors of calibration between 0.65% and 0.78% for wheat, 0.34% and 0.59% for soybeans, and 1.01% and 1.45% for corn.
Technical Abstract: A method for nondestructive moisture content determination in granular materials from measurement of attenuation only at microwave frequencies is proposed. In this instance, the measurements were carried out on wheat, corn, and soybeans at room temperature (23 oC) for frequencies ranging from 7 GHz to 12 GHz with a free-space transmission technique. Linear correlations between attenuation and moisture content provided moisture content were identified. For each material and each frequency moisture content calibration equations were established. At each frequency, performance of these equations in moisture prediction from attenuation measurement were evaluated by calculating the standard error of calibration (SEC). Values of the SEC ranged from 0.34% to 1.45%.