US 4,536,709 AGranted

Detecting device having spaced transmitting and receiving coils for detecting a metal strip embedded in paper money

AssigneeTokyo Shibaura Denki Kabushiki Kaisha

InventorTsuyoshi Ishida

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Abstract

The metal detecting device includes first and second coils provided on both sides of a passageway for paper money. This metal detecting device is designed for use in detecting a metal strip embedded in the paper money in order to determine whether the paper money is genuine or counterfeit. The first coil is connected to a high frequency AC source to generate an AC magnetic field. The second coil is connected to a capacitor to form a resonance circuit which resonates at the same frequency as the AC current. The variation of the Q factor of the resonance circuit due to eddy-current losses produced in the metal strip of the paper money is used by a detecting circuit to determine whether the paper money passing through the space between the first and second coils is genuine.

Claims13

Dependent claims

A detecting device for detecting a sheet of genuine paper money having a longer dimension and a shorter dimension, the sheet including an embedded metal strip having a length substantially equal to the shorter dimension of the sheet and a predetermined width, the strip being oriented within the sheet so that its length is substantially parallel to the shorter dimension of the sheet, said detecting device comprising:

transporting means for rapidly transporting the sheet in the direction of its longer dimension along a transportation path;
an electric transmitting coil adjacent one side of the transportation path having a long and narrow shaped plane and having a width larger than the predetermined width of the strip, the long dimension of said long and narrow shaped plane being oriented substantially parallel to the shorter dimension of the sheet as the sheet is transported along the transportation path;
an electric receiving coil adjacent the transportation path directly opposite said transmitting coil having a long and narrow shaped plane and positioned in spaced parallel relationship to said transmitting coil along the transportation path, said receiving coil having a width larger than the predetermined width of the strip, wherein the sheet is transported between said transmitting coil and said receiving coil with the surface of the sheet being parallel to the shaped planes of said coils;
AC current supply means for supplying AC current to said electric transmitting coil to generate a magnetic field;
a capacitor connected to said electric receiving coil in a resonance circuit which generates a resonance signal;
and
detecting means connected to said resonance circuit for detecting variations in the resonance signal of said resonance circuit caused by eddy current losses in said metal strip when said metal strip passes between said transmitting and receiving coils.

4 more elements

transporting means for rapidly transporting the sheet in the direction of its longer dimension along a transportation path;
electric transmitting coil means adjacent one side of the transportation path having a long and narrow shaped plane and having a width larger than the predetermined width of the strip, the long dimension of said long and narrow shaped plane being oriented substantially parallel to the shorter dimension of the sheet as the sheet is transported along the transportation path;
a plurality of electric receiving coil means adjacent the transportation path directly opposite said electric transmitting coil means having long and narrow shaped planes and positioned in spaced parallel relationship with said electric transmitting coil means along the transportation path, said electric receiving coil means having a width larger than the predetermined width of the strip, wherein the sheet is transported between said electric transmitting coil means and said plurality of electric receiving coil means with the surface of the sheet being parallel to the shaped planes of said coil means;
AC current means for supplying AC current to said transmitting coil means to generate a magnetic field;
a resonance element connected to each of said electric receiving coil means to form a resonance circuit which generates a resonance signal;
and detecting means connected to said resonance circuits and responsive to said metal strip for generating a detecting signal, said detecting means detecting a variation in the resonance signal in each of said resonane circuits caused by eddy current losses in said metal strip when said metal strip passes between said electric transmitting coil means and said plurality of electric receiving coil means.

3 more elements

Dependencies are inferred from the claim text.