Wednesday, October 7, 2015

Better detection of counterfeit banknotes through new terahertz wave light source technology

Researchers at Tohoku University's School of Engineering have developed a new terahertz wave light source - featuring both light and radio-wave characteristics - that can lead to faster and more efficient detection of counterfeit and damaged banknotes.
Terahertz waves are radio waves with frequencies tens to thousands of times higher than those used by cell phones. They were previously known as "unattainable wavebands" because they were extremely difficult to generate and detect. (Fig 1)
Figure 1
(Figure 1)
Ultrathin resin tape is attached to the banknotes of many currencies for the purpose of detecting forgeries and damage. The tape is approximately half to a quarter width of a human hair, and the most common method currently available for detecting this tape is with stylus profiling. Because physical contact is required with stylus profiling, the speed with which the tape can be detected is limited. And the physical contact also comes with the risk of damage.
To get around those limitations, the research team, led by Professor Yutaka Oyama, created a database of terahertz permeability characteristics for banknotes and resin tapes, and then successfully attained visibility of the extremely thin tape without physical contact. (Fig 2)
Figure 2
(Figure 2)
Unlike irradiation methods using X-rays and gamma rays which are conventionally used for transmission inspections, this new terahertz wave method is also believed to be safe even when exposed to the human body.
The research team expects this new method to improve inspection speeds and prevent paper damage, thus drastically improving the efficiency of banknote inspections carried out every day throughout the world.
The research was a joint project between Tohoku University and Laurel Bank Machines Co. Ltd. Part of the results were announced at the CLEO (Conference on Lasers and Electro-Optics) Pacific Rim Conference held in Busan, South Korea, in August 2015.


Yutaka Oyama
Department of Materials Science
Tohoku University, Graduate School of Engineering
Tel: +81-22-795-7327

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