real-time inspection system using a terahertz technique to detect microleak defects in the seal of flexible plastic packages

• Published in: Journal of food protection Vol. 68; no. 4; pp. 833 - 837
• Main Authors: Morita, Y, Dobroiu, A, Otani, C, Kawase, K
• Format: Journal Article
• Language: English
• Published: Des Moines, IA International Association of Milk, Food and Environmental Sanitarians 01.04.2005
• Subjects: Biological and medical sciences; electromagnetic radiation; Food Contamination - prevention & control; Food industries; food inspection; Food Microbiology; food packaging; Food Packaging - methods; Food Packaging - standards; Fundamental and applied biological sciences. Psychology; General aspects; Handling, storage, packaging, transport; Infrared Rays; packaging materials; plastic film; polyethylene; product defects; transducers (equipment); ultrasonography; Carnivora; Vertebrata; Mammalia; Plastic bag packaging; Seals; Inspection; Defect; Seal; Conditioning; Pinnipedia; Real time system
• ISSN: 0362-028X; 1944-9097
• DOI: 10.4315/0362-028x-68.4.833

A method to detect production faults in flexible plastic packages with the use of terahertz radiation is presented. Relying on the large difference between the absorption coefficients of plastic and water (for water-filled channel defects) and on the refraction index difference between plastic and air (for air-filled channel defects), our technique consists of focusing and scanning a terahertz beam on the sealed area of the package, followed by detection of the transmitted signal. Compared with previous methods, such as visual and ultrasound inspection, our technique can be applied to optically opaque packages and does not require immersion in a matching liquid. We tested our system on defects that we fabricated as water-filled and air-filled channels imbedded in polyethylene films, with diameters in the range of 10 to 100 micrometer. The detection limit (the minimum size of a detectable defect) depends on the conveying speed; this relationship was determined and analyzed. The results show that our system has the potential for application in an actual production line for real-time inspection.