APRIL 27, 2009--Systems using terahertz (THz) radiation have recently been demonstrated as quick and reliable mail-inspection devices. Like radio waves, THz radiation is not significantly scattered by soft materials such as paper, wood, and plastics, and creates clear images of hidden objects. In addition, many materials exhibit unique THz-absorption spectra—fingerprint spectra—which can be used to identify the contents of suspicious packages.
At the Terahertz Sensing and Imaging Laboratory at RIKEN (Aramaki, Japan), a prototype apparatus has been built to inspect all mail handled in Japanese international post offices (around 100,000 items per day). However, the THz spectrometer takes too long to examine every package.
Therefore, to achieve complete inspection, the process has been divided into two stages. The first involves rapid screening using x-rays and THz waves, and the second identifies the suspicious substances selected in the first stage.
The initial screening stage uses x-rays to exclude envelopes containing only paper. Images revealing shadows are then scanned and measured at 0.54THz. For more information, go to: http://spie.org/x33690.xml?ArticleID=x33690
-- Posted by Conard Holton, Vision Systems Design, www.vision-systems.com
