POSSIBILITIES TO USE THE EIGENFREQUENCIES TO IDENTIFY COINS

The acoustic diagnostics is one of the oldest methods for non-destructive control. The present paper, analyzing the recorded sound of a coin, falling on a hard pad or strike with an impulse hammer, defines the first three eigenfrequencies of contemporary coins that are in circulation (1 BGN 2002, 1EUR 2002, 1 TRL). It is noticeable that the dispersion of the frequencies when measuring a series of coins is the lowest (about 1%) in the Turkish coin, which is the newest coin. On the base of the frequencies measured, Labview-based application is created to identify coins. As the coins are bimetal, the properties of the equivalent thin circular plate model are calculated by FEA using optimization procedure.