The E-Sylum:  Volume 11, Number 4, January 27, 2008, Article 25

DIAGNOSTIC COIN 'RING TEST' STUDIED IN JAPAN

Dick Johnson writes: "A scientist in Japan, Mototsugu Suzuki,
a researcher at the Tokyo Metropolitan Police Department’s
Criminal Investigation Laboratory, has developed a way of
examining coins based on the sound they make. In effect, he
is studying the veracity of the age-old 'ring test' employed
by regular citizens and numismatists alike to test genuineness
of coins.

He published his method of testing in 'Forensic Science
International' -- reported in the January British publication
'Nature.'  In Suzuki’s method, coins slide down a slope and
then fall onto a brass block. The sound they make on impact
is relayed via a microphone to a computer.

His study of this acoustic test of coins was brought on by
a large number of counterfeit 500-yen coins (worth just under
US$5 each) in circulation. So many were found in cash dispensers
in 2005 that the coin was temporarily removed from use.

Suzuki stated: although the human ear cannot usually tell the
difference between real and fake, a computer can. Genuine
500-yen coins showed four distinctive peaks of natural resonance
frequencies in the 5-20 kilohertz range. This was not the case
for fakes; some fakes produced only three peaks, while others
showed four but at different frequencies to genuine coins.

For my own comments on ring test for coins I would offer:
Any small metal object will ring due to its internal structure.
Thus its alloy, thickness and any gas pockets will affect its
tone. Both cast and struck coins will ring, but with notes of
different pitch. A ring test can detect different metal
compositions, but not minute differences of alloy.

The use of computer analysis of ring tone resonance for one
coin may be useful but it would not be the same for coins of
other size, composition or thickness. An extensive database
of these tone profiles would be required for such full scale
testing.

To read the report in Nature magazine by Daniel Cressey, click on:
Full Story

[Thanks also to George Fuld for forwarding a copy of this
article.  -Editor]

  Wayne Homren, Editor

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