GB2315352A

GB2315352A - Bank-note validator

Info

Publication number: GB2315352A
Application number: GB9614715A
Authority: GB
Inventors: Ronald Clifford Davies
Original assignee: Individual
Current assignee: Individual
Priority date: 1996-07-12
Filing date: 1996-07-12
Publication date: 1998-01-28
Anticipated expiration: 2016-07-12
Also published as: GB2315352B; GB9614715D0

Abstract

A device for authenticating a bank-note (12) which includes a metallic element (10), comprises a first coil (L2) and a second coil (L3) arranged such that the mutual inductance between the first and the second coils varies in accordance with the proximity of the coils to the metallic element. The device also comprises means for detecting the variation in mutual inductance to provide a signal indicative of the authenticity of the bank-note. Preferably the coils overlap and ar

Description

Bank-Note Tester The present invention relates to a device for authenticating a bank-note, and more particularly to a device for detecting a metallic anti-counterfeiting element of a banknote.

It is well known to form bank-notes with an embedded metallic element as an anti-counterfeiting feature. Such an element typically comprises a strip extending laterally across the width of the bank-note, which strip is intended to provide a visible indication of the authenticity of the bank-note.

Recently, however, it has become possible to reproduce such features, at least to such an extent that visual inspection alone is insufficient to distinguish between a genuine and a forged bank-note.

I have now devised an electronic device for authenticating a bank-note by generating a signal indicative of the presence, within or upon that note, of a valid metallic anti-counterfeiting element.

In accordance with the present invention, there is provided a device for authenticating a bank-note which includes a metallic element, said device comprising a first coil and a second coil arranged such that the mutual inductance between said first and said second coils varies in accordance with the proximity of said coils to said metallic element, and means for detecting that variation to provide a signal indicative of the authenticity of said bank-note.

Preferably an alternating signal in said first coil induces a corresponding alternating signal in said second coil.

Preferably said device comprises an oscillator for exciting said first coil. Preferably said oscillator comprises a Colpitts oscillator which preferably generates a 25MHz excitation signal.

Preferably said detecting means comprises means for comparing the signal induced in said second coil with one or more reference values. Preferably the or each reference value is adjustable.

Most preferably said comparing means generates an output signal if the magnitude of the induced signal exceeds that of a single reference value, thus indicating the presence of a metallic element. However, by providing one or more adjustable reference levels, then, in addition to differentiating between metallic and non-metallic elements, the device may also be configured to distinguish between valid and invalid metallic elements whose respective induced signals vary in magnitude according to such distinguishing factors as dimension and/or metallic composition.

Preferably said detecting means comprises means for rectifying said induced signal, and applying the rectified signal to said comparing means, which rectifying means preferably comprises a diode.

Preferably said detecting means comprises means for filtering said rectified signal, before applying that signal to said comparing means.

Preferably said detecting means comprises a monostable circuit, triggered by said comparing means, to provide a fixed duration signal indicative of the authenticity of said banknote, which signal may comprise an audible and/or visible signal.

In a first preferred embodiment of the present invention, said first and second coils are arranged such that, in use, their respective windings lie in the same or parallel planes perpendicular to the surface and to two opposite edges of said bank-note. In this case, preferably the longitudinal axes of said first and second coils lie in a plane parallel to the surface of said bank-note and extend perpendicularly of said same or parallel planes.

In a second preferred embodiment of the present invention, said first and second coils are arranged such that, in use, their respective windings lie in the same or parallel planes parallel to the surface of said bank-note. In this case, preferably the longitudinal axes of said first and second coils lie in a plane perpendicular to the surface and to two opposite edges of said bank-note, and extend perpendicularly of the surface of said bank-note.

Preferably where said metallic element comprises a strip extending across the bank-note, said two opposite edges comprise those edges parallel to said strip.

Said coils may be of any shape, e.g. ellipsoid or rectangular, and may have differing respective dimensions.

Preferably the axial dimension of said first and/or said second coil parallel to the surface of said bank-note is greater than its axial dimension perpendicular to the surface of said bank-note. Preferably the axial dimension of said second coil parallel to the surface of said bank-note exceeds that of said first coil.

Where said rectifying means comprises a diode, preferably a portion of said first and said second coils overlap. Thus, a residual level of mutual inductance exists between said first and second coils, which acts to overcome the effects of diode forward-voltage drop by biasing said diode into conduction.

In order to authenticate a bank-note, using a device in accordance with the present invention, the coils of the device are held adjacent the surface of the bank-note, whilst the device is swept from one end of the bill to the other. As the device passes over a metallic anti-counterfeiting feature, such as a strip embedded in the bank-note, the momentary variation in mutual inductance between the coils causes the induced signal in the second coil to exceed a preset threshold level.

The variation in mutual inductance may be caused by increased flux linkage through a strip of magnetically permeable material, but more likely by eddy current effects in a strip of non-magnetically permeable material, e.g. aluminium. The resulting output from the comparing means indicates the authenticity of the bank-note.

Preferably said device comprises a portable hand-held unit, but may alternatively comprise a fixed detector under which notes are sequentially passed.

Embodiments of the present invention will now be described by way of examples only and with reference to the accompanying drawings, in which: FIGURE 1 is a circuit diagram of a device in accordance with the present invention; FIGURE 2 is a perspective view of a first preferred coil arrangement; and FIGURE 3 is a perspective view of a second preferred coil arrangement.

Referring to Figure 1 of the drawings, a circuit is shown comprising four principal sections, 2,4,6 and 8. The first section 2 comprises a Colpitts oscillator, whose passive components are chosen such that a 25 MHz excitation signal is supplied to al primary coil L2.

The primary coil L2 is arranged to induce a alternating signal in a secondary coil L3, the mutual inductance between the two coils being determined both by their physical relationship to one another, and by their proximity to a metallic element of a bank-note.

In the second section 4, the signal induced in the secondary coil L3 is rectified and smoothed by means of a diode D1 an RC filter arrangement R4,C5 respectively.

The third section 6 comprises a comparator CPl arranged to provide an output when the rectified and smoothed signal from the second circuit section 4 exceeds a threshold level set by a voltage divider formed by resistors VR1 and R5. The resistance of resistor VR1 may be varied to adjust the sensitivity of the device according to the type of note to be authenticated. Thermistor TH1 provides temperature compensation for the comparator CP1.

The output of the comparator CPl is passed to the fourth circuit section 8 which comprises a light-emitting diode LED1 and a speaker SPKR1, each device having respective driver circuitry (not shown).

In order to authenticate a bank-note using the device thus disclosed, the coils L2 and L3 of the device are held adjacent the surface of a bank-note, whilst the device is swept from one end of the bill to the other. As the device passes over a metallic anti-counterfeiting feature, such as a strip embedded in the bank-note, the momentary variation in the level of mutual inductance between the coils L2 and L3 causes the signal induced in the secondary coil L3 to exceed the preset threshold level of the comparator CP1. The resulting output from the comparator CPl causes audible and visible signals to be emitted from the speaker SPKR1 and light-emitting diode LED1, thereby indicating the authenticity of the bank-note.

However, according to such a swiping action, the duration of the output signal from the comparator CPl will be very short. It would therefore remain in accordance with the present invention for the fourth circuit section 8 to comprise a monostable or other pulse-stretching means for increasing the duration of the output signal.

Figures 2 and 3 illustrate preferred alignments of the two coils L2 and L3 when used to detect an anti-counterfeiting metallic element 10 of a bank-note 12. In the arrangement of Figure 2, the two coils L2 and L3 are arranged so that their respective windings lie in adjacent parallel planes, generally perpendicular to the surface of the bank-note 12, whereas in the arrangement of Figure 2, the two coils L2 and L3 are arranged so that their respective windings lie in adjacent parallel planes, generally parallel with the surface of the bank-note 12.

In each of Figures 2 and 3, the coils L2 and L3 partially overlap to provide a small degree of mutual inductance between them, such that even in the absence of the metallic element 10, the excitation signal supplied to the primary coil L2 induces a sufficient level of signal in the secondary coil L3 to overcome the forward-voltage drop of the diode D1.

The device thus described provides a relatively simple yet highly effective means for authenticating bank-notes which include a metallic anti-counterfeiting feature, the device being suited for use as part of either a hand-held or automatic-feed apparatus.

Claims

1) A device for authenticating a bank-note which includes a metallic element, said device comprising a first coil and a second coil arranged such that the mutual inductance between said first and said second coils varies in accordance with the proximity of said coils to said metallic element, and means for detecting that variation to provide a signal indicative of the authenticity of said bank-note.

2) A device as claimed in Claim 1, comprising an oscillator for exciting said first coil.

3) A device as claimed in Claim 2, wherein said oscillator comprises a Colpitts oscillator.

4) A device as claimed in Claim 3, wherein said Colpitts oscillator generates a 25MHz excitation signal.

5) A device as claimed in any preceding claim, wherein said detecting means comprises means for comparing the signal induced in said second coil with one or more reference values.

6) A device as claimed in Claim 5, wherein the or each reference value is adjustable.

7) A device as claimed in Claim 5 or Claim 6, wherein said detecting means comprises means for rectifying said induced signal, and applying the rectified signal to said comparing means.

8) A device as claimed in Claim 7, wherein said rectifying means comprises a diode.

9) A device as claimed in Claim 8, wherein a portion of said first and said second coils overlap.

10) A device as claimed in any of Claims 7 to 9, wherein said detecting means comprises means for filtering said rectified signal, before applying that-signal to;said comparing means.

11) A device as claimed in any of Claims 5 to 9, wherein said detecting means comprises a monostable circuit, triggered by said comparing means, to provide a fixed duration signal indicative of the authenticity of said bank-note.

12) A device as claimed in Claim 11, wherein said fixed duration signal comprises an audible signal.

13) A device as claimed in Claim 11 or Claim 12, wherein said fixed duration signal comprises a visible signal.

14) A device as claimed in any preceding claim, wherein said first and second coils are arranged such that, in use, their respective windings lie in the same or parallel planes perpendicular to the surface and to two opposite edges of said bank-note.

15) A device as claimed in Claim 14, wherein the longitudinal axes of said first and second coils lie in a plane parallel to the surface of said bank-note.

16) A device as claimed in Claim 15, wherein the axial dimension of said first coil parallel to the surface of said bank-note is greater than its axial dimension perpendicular to the surface of said bank-note.

17) A device as claimed in Claim 15 or Claim 16, wherein the axial dimension of said second coil parallel to the surface of said bank-note is greater than its axial dimension perpendicular to the surface of said bank-note.

18) A device as claimed in any of Claims 15 to 17, wherein the axial dimension of said second coil parallel to the surface of said bank-note exceeds that of said first coil.

19) A device as claimed in any of Claims 1 to 13, wherein said first and second coils are arranged such that, in use, their respective windings lie in the same or'parallel planes parallel to the surface of said bank-note.

20) A device as claimed in Claim 19, wherein the longitudinal axes of said first and second coils lie in a plane perpendicular to the surface and to two opposite edges of said bank-note.

21) A device as claimed in Claim 20, wherein the axial dimension of said first coil parallel to the surface of said bank-note and perpendicular to said two opposite edges is greater than its axial dimension parallel to the surface of said bank-note and to said two opposite edges.

22) A device as claimed in Claim 20 or Claim 21, wherein the axial dimension of said second coil parallel to the surface of said bank-note and perpendicular to said two opposite edges is greater than its axial dimension parallel to the surface of said bank-note and to said two opposite edges.

23) A device as claimed in any of Claims 20 to 22, wherein the axial dimension of said second coil parallel to the surface of said bank-note and perpendicular to said two opposite edges exceeds that of said first coil.

24) A device as claimed in any preceding claim, comprising a portable hand-held unit.

25) A device as claimed in any of claims 1 to 23, comprising a fixed detector under which notes are sequentially passed.

26) A device for authenticating a bank note, the device being substantially as herein described with reference to the accompanying drawings.