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Accoustic Imaging of Defects in Shelf-stable Food Packages


The objective of the project was to determine the conditions under which a leak or seal defect can result in bacterial contamination or package integrity failure in a flexible plastic pouch. These results, combined with nondestructive defect detection techniques, will eventually be used to establish general guidelines for a real time, nondestructive, on-line system that will accurately evaluate package integrity.

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Newer food processing and packaging techniques include retortable pouches, "plastic cans" and aseptically packaged foods. Newer inspection techniques must be developed to address fundamental changes in food processing and packaging which compromise food safety by producing defects in the heat-seal portion of packages. In this study,channel defects were fabricated and then characterized and imaged using scanning laser acoustic microscopy (SLAM). SLAM uses sound waves to produce images. It has the ability to detect, classify and accurately reproduce the internal structure of opaque materials, and the defects contained therein. Ultrasound can be used to image flaws in opaque packaging materials. The results obtained here significantly exceeded expected results. A 10?m channel was detected using a SLAM (100MHz) with a 20 ?m resolution. The resolution of the SLAM is inversely proportional to its frequency.Therefore, when the frequency is doubled, the resolution is halved. Thus,a 200 MHz SLAM should detect channels smaller than 10m.

Meerbaum, H
National Center for Food Safety & Technology
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