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Sound Determines if Coins are Sound
By Richard Giedroyc

It has been pointed out in the "Around the World" column in the past that with coins increasingly replacing low denomination bank notes in circulation there has been a renewed interest in counterfeiting circulating coinage worldwide. The call to arms now includes recruiting Mototsugu Suzuki, a Japanese scientist with a doctorate in applied physics from Osaka University, who has recently developed a new counterfeit coin detection method for the Yomiuri Metropolitan Police Department.

Suzuki's method sounds relatively simple, no pun intended. Slide a coin down a brass-plated chute. A computer analyzes the sound the coin makes as it slides, determining if the coin is genuine or not from the noise the coin generates. This relatively quick method is increasingly replacing labor intensive methods the Japanese police had to use, either using a microscope or subjecting coins to fluorescent X-rays, which could take up to three to five minutes per coin.

Can you imagine if coin collectors could use Suzuki's method on collector coins? Well, you'd better hurry if you want to develop such technology yourself, since the Japanese police have already applied for a patent on Suzuki's invention!

There are practical applications for this new concept far beyond police or the U.S. Secret Service detecting counterfeit coins. (Yes, I am aware this won't detect date or mintmark alterations on collector coins.) There is already talk about applying this technology to vending machines, where according to the Feb. 26 Daily Yomiuri or Yomiuri Shimbun newspaper in Japan, a 30 millimeter brass composition chute allowing for oscillation provided by an accompanying high-performance microphone would allow computer analysis of each coin vended.

Suzuki told the Japanese newspaper he is aware of different frequencies between each coin denomination and of the difference in frequencies between genuine and fake coins. He was particularly focused on the hardness and density of each coin.

Suzuki is quoted in the newspaper article as saying, "I hit upon the idea of making the device from my image of a coin clinking when it is put into a piggy bank."

That's some piggy bank. It took the inventor about two years to build his first successful genuine coin detecting device. The best part about the device is that it can examine large numbers of coins at a time, making the device handy for use in coin counting machines as well as vending machines.

Software can be developed to examine virtually any coinage. The Japanese MPD has already stated it is interested in developing the project further in collaboration with private sector companies.

There are good reasons why such a technology is important. As higher value coins are increasingly used in place of low denomination bank notes, counterfeiters are increasing their technical skills almost as quickly as mints are developing new anti-counterfeiting devices for coins. As an example, a number of countries (notably Spain, Taiwan, and Japan) are now using a latent image on some circulation coins that changes when the coin is viewed at different angles.

According to the MPD, counterfeiters have already mastered this latent image technology and are using it on fake 500-yen coins, although the number of fake coins of this denomination detected so far was not revealed.


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