Submitted to: Sensors
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/1/2008
Publication Date: 8/1/2008
Citation: Pelletier, M.G., Barnes, E. 2008. Microwave imaging of cotton bales. Sensors. 8(11):7241-7258. Interpretive Summary: Modern moisture restoration systems are increasingly capable of adding water to cotton bales. However, research has shown that some systems create large internal variations in moisture, which are not readily detectable from the outside. This excess water has led to the degradation of large numbers of cotton bales during storage and shipment to international buyers. While modern microwave moisture sensing systems can measure average bale moisture, this can be deceptive where water is unevenly distributed, as high moisture areas within the bale are not specified. As the latter are known to cause significant fiber degradation, a critical need for the industry is to develop a system to detect them. This study describes the development of a tomographic imaging technique to address this issue. Impulse response tests of this technique indicate sensitivity to small-scale variations in moisture. Preliminary testing on a wet commercial universal density (UD) bale demonstrated the ability of this method to accurately image and determine the location of a pre-placed wet layer. Incorporation of this technology into modern microwave sensing systems will ensure effective monitoring of average moisture content and moisture distribution, and allow for detection and avoidance of high moisture bales by cotton gins. It will also allow manufacturers of cotton gin moisture restoration systems to fine-tune new technology to ensure uniform distribution of added water.
Technical Abstract: Modern moisture restoration systems are increasingly capable of adding water to cotton bales. However, research has identified large variations in internal moisture within bales that are not readily monitored by current systems. While microwave moisture sensing systems can measure average bale moisture, this can be deceptive where water is unevenly distributed. In some cases, localized internal moisture levels exceed 7.5%, the upper safe limit for cotton bale storage as determined by the USDA, as above this level, bales degrade and lose value. A high proportion of stored bales containing excess moisture have been discovered throughout the US in increasing numbers over the past several seasons, making the detection and prevention of this occurrence a critical goal. Previous research by the authors resulted in the development of microwave moisture-sensing technology. The current study examines an extension to this technology to allow for detailed cotton bale moisture imaging. The new technique incorporates a pencil-beam imaging antenna coupled to a tomographic imaging algorithm. The imaging technique was able to resolve small (< 1 cm) high-permittivity structures against a low permittivity background. Moreover, the system was able to identify structures of known permittivity with high accuracy (coefficient of determination (r2) > 0.99). In preliminary testing on a wet commercial UD bale, the technique was able to accurately image and resolve the location of the pre-placed internal wet layer.