ARS | Publication request: A LOW-COST MICROWAVE MOISTURE SENSOR

Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: June 13, 2006
Publication Date: September 10, 2006
Citation: Trabelsi, S., Nelson, S.O., Ramahi, O. 2006. A low-cost microwave moisture sensor. Proceedings of the 36th European Microwave Conference, Manchester, UK. September 10-15,2006, pp. 447-450.

Interpretive Summary: Moisture content of cereal grains is the most important characteristic that determines their suitability for storage, and it is also important in determining the selling price. Electronic moisture meters are used almost universally in the grain trade for determining the moisture content of samples taken from lots being delivered to grain elevators, transportation facilities, processors, etc. However, reliable moisture sensing equipment for continuously monitoring grain and seed moisture content on harvesting equipment, when loading and unloading grain, and in processing is needed to provide better moisture content information for managing these operations. It has been shown that microwave measurements on grain and seed can provide reliable moisture information independent of packing variation in the grain. A prototype microwave meter for sensing moisture content in grain has been assembled from off-the-shelf components and tested for performance in measuring moisture content in wheat and corn. The purpose in building the prototype microwave moisture meter was to demonstrate the usefulness of a low-cost microwave grain moisture meter operating on principles developed from laboratory research with complex and expensive equipment. Measurements on wheat and corn show that good reliability of moisture measurement can be achieved with the low-cost prototype meter. The new technique provides an incentive for the development of practical microwave moisture sensing instruments that can provide new tools for the maintenance of high quality in such agricultural products, thus benefiting farmers and consumers as well.

Technical Abstract: A low-cost microwave moisture sensor for granular materials operating at a single frequency of 5.8 GHz has been built and tested. The sensor principle is based on measurement of the two components of the relative complex permittivity. From these measurements, a density- and material-independent calibration function is calculated. The linear correlation between the calibration function and moisture provides moisture content in different materials independent of bulk density.