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Published online 22 January 2008 | Nature | doi:10.1038/news.2008.518
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The sound of a bad penny
Acoustic method could quickly catch counterfeit coins.
You might assume that counterfeiters only bother with high-value bank notes, but there is a chance that some of the coins jangling around in your pocket right now are fake. If Mototsugu Suzuki gets his way, it may be that jangling that gives them away.
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Did I not hear of Mars having developed vending machines that detected counterfeit coins by analysing the sound spectrum from their dropping onto an anvil at least 20 years ago?
I have noticed this different acoustical effect for US coins made of Silver produced pre-1964. I can reliably tell the difference between Silver and non-silver coins just by the sound they make when dropped on a table. Although, the new Presidential Quarters trip me up a bit.
I meant the new State Quarters. The Presidents are on the dollar coins.
In my own house in India, in earlier times when Silver coins were still in use and the collections were so much that they needed to be wieghed in hundreds of kilograms At that time my grand mother tells me our family used to employ specialized people who had a keen sense of hearing, who would make these sliver coins flow out from thier hands onto a marble slab. As they feel down the countefiet ones made a very different sound from the real ones, and these speacialized people simply kept rejecting the fake coins based on the acoustics. It was a foolproof method. Pallava Bagla pbagla@vsnl.com +91 11 2271 2896
The term bankruptcy (from the Italian banco rotto - broken bank), at least in some interpretations stems from the breaking of the marble slab money was thrown onto. The resulting sound allowing to distinguish genuine precious metal coins from fake (e.g. lead containing) ones. Breaking it rendered it useless and destruction of this vital piece of equipment would mean the end of business activities.
It's amazing how an old knowledge took so long to be studied and approached in a technological manner. I wonder how many other human experiences and knowledge are around, that could be used with advantage to the human race.