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Submitted to: IEEE Sensors Letters
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 10/25/2017 Publication Date: 11/2/2017 Citation: Trabelsi, S. 2017. New calibration algorithms for dielectric-based microwave moisture sensors. IEEE Sensors Letters. 1(6):1-4. Interpretive Summary: Moisture content of many food materials, such as grain and seed crops, is an important characteristic that determines suitability for harvest, processing, and storage. Grain with moisture content that is too high will suffer quality deterioration in storage and may spoil completely as food material for animals and humans. Thus, techniques for moisture sensing and instruments for rapid moisture content measurement are essential in the grain and seed trade and processing industries. Instruments that sense high-frequency dielectric properties (electrical characteristics) of grain and seed, which are highly correlated with moisture content, have been used as moisture meters for many years. Research on moisture sensing at microwave frequencies by using the dielectric properties of such materials has shown advantages for the higher frequencies, and the ability to sense moisture content independent of bulk density of grain and seed has been proven. This paper describes research on new techniques for microwave sensing of moisture content in granular materials. Data on the dielectric properties of several kinds of grain and seed, wheat, soybeans, oats, grain sorghum, and barley, were collected from measurements at a microwave frequency of 10 GHz at 24 degrees C along with bulk densities of the materials when their dielectric properties were measured over a range of moisture contents. Working with these data, relationships with the partial densities of water and dry material were studied, and three new algorithms were developed for determining moisture content of these grain and seed materials from measured microwave dielectric properties. The new algorithms performed well, and they can be can be implemented in microwave sensors regardless of the measurement technique used. Moreover, they can be applied to any moist granular or particulate material, and their use would provide moisture information useful in improving product quality and processing efficiencies, which would benefit producers, processors and consumuers as well. Technical Abstract: New calibration algorithms for determining moisture content in granular and particulate materials from measurement of the dielectric properties at a single microwave frequency are proposed. The algorithms are based on identifying empirically correlations between the dielectric properties and the partial densities of water and dry matter of a given material. Both situations where the bulk density is known or unknown were considered. Validations of the performance of the new algorithms are presented for grain and seed samples for which the dielectric properties were measured by free-space transmission at 10 GHz and 24 oC. |
