CHANNEL DEFECT DETECTION IN FOOD PACKAGES USING INTEGRATED BACKSCATTER ULTRASOUND IMAGING

Hermetically-sealed flexible food packages require very effective seal integrity testing to extend the shelf stability of thermally processe d food. The initial goal of this study was to estimate the detection l imits of laboratory-generated channels which simulate defects in food packages using pulse-echo ultrasonic imaging techniques. Packages with well characterized (via transmission optical microscopy) laboratory-g enerated channels that simulate defects with diameters between 9 and 3 25 mu m in the seal plane traversing the major axis of the heat seal w ere generated in heat-sealed microwavable retort-pouch plastic film (t rilaminate). Pulse-echo techniques in the 13-17 MHz center frequency r ange were investigated. The samples were examined with a conventional B-mode imaging technique, which was found to be inadequate for subwave length imaging of the types of typical channel defects found in shelf- stable food packages. Based on conventional B-mode image features, a n ew goal of this study was established to develop and evaluate an imagi ng technique which would exhibit subwavelength imaging capabilities. T he new imaging technique called backscattered amplitude integral (BAI) is introduced here. It was observed that BAI-mode imaging has the abi lity for subwavelength detection of channel defects, e.g., detection o f a 10-mu m diameter channel defect ata center frequency of 13.1 MHz ( lambda = 182 mu m).