Registers – Coded record sensors – Particular sensor structure
Reexamination Certificate
1999-06-30
2003-07-29
Lee, Diane I. (Department: 2876)
Registers
Coded record sensors
Particular sensor structure
C235S450000
Reexamination Certificate
active
06598793
ABSTRACT:
FIELD OF THE INVENTION
This invention concerns methods and apparatus for identifying articles to allow verification and authentication, particularly articles formed predominantly from non-magnetic material and incorporating magnetic fibres having recognisable magnetic properties. The invention is of particular application in the field of high value documents such as original Agreements, bank notes, value coupons, bonds, passports and the like. However the invention is not limited to such documents and is equally applicable to the recognition and authentication of any nonmagnetic article in which identifiable magnetic particles have been embedded.
RELATED APPLICATION
It has been proposed in EP 96203529.1 filed Dec. 12, 1996 to incorporate magnetic particles of particular shape and magnetic properties as a security feature in articles which need to be recognised. Hitherto the proposal has been linked to the inhibition of photocopying of high value documents such as bank notes by colour copiers and the proposal has been to incorporate a suitable sensor in a colour copier which automatically detects the presence of the magnetic particles or fibres in a document placed on the copying platen. Upon detection of such a document, the sensor is arranged to generate a signal which is utilised within the copier to defeat the copying of the article either by inhibiting the copying function of the machine or degrading the copy so that the article is not reproduced accurately by the copying process.
The detection system on the colour copiers has been achieved with a multi-sensor head mounted on a scanning carriage. The gap between the sensor and the documents is defined from a combination of the glass or platen thickness, a tolerable gap between the scan head and the glass and the depth of focus of the optical system above the glass. This means that the multi-sensor has to work at a distance of a few cm. With the combination of distance and an air core for the magnetic scanning head it was originally noted that with an acceptable coil mass, size and power consumption this would result in a maximum magnetic field, which would mean that the magnetic particles would ideally need to saturate below 1000 A/m, i.e. have a magnetic saturation field H
s
below 1000 A/m.
The terms “magnetic saturation field H
s
” are herein defined as the applied magnetic field at the onset of saturation of the flux density in the ferro-magnetic particles, above which point the variation of the flux density in the particles with the applied field becomes substantially non-linear. In addition it was noted that saturation at the levels of practicable fields could not be achieved unless the demagnetisation factor N was smaller than {fraction (1/250)}, preferably smaller than {fraction (1/1000)} in order to allow for the typical levels of permeability which result from hard drawing materials such as Permalloy. This meant that long thin particles were needed and that round ones would not be suitable.
The demagnetisation factor N is defined in the following well known formula:
H
in
=H
app
−N×M
where M is the magnetisation of the material, H
app
is the applied magnetic field, H
in
is the magnetic field inside the material and N is the demagnetisation factor.
Summarizing other magnetic propties, the magnetic particles had:
i) a magnetic saturation field H
s
being greater than 100 A/m, preferably greater than 200 A/m and most preferably greater than 300 A/m; this lower value is chosen not to trigger off EAS (electronic article surveillance) alarms
ii) a magnetic saturation flux density B
s
being greater than 0.1 Tesla;
iii) a magnetic dynamic permeability &mgr;
d
ranging from 10 to 10000. The term magnetic dynamic permeablity &mgr;
d
is defined here as the ratio of the flux density, to the magnetic field times the permeability of free space, at the onset of saturation.
BACKGROUND OF THE INVENTION
U.S. Pat. No. 5,749,946 discloses a method for checking the authenticity of a security article by detecting the magnetic resonance of an authenticating substance at a resonance frequency.
SUMMARY OF THE INVENTION
The sensor proposed for this application is a magnetic field emitting and detection device adapted for “point of transaction” verification, e.g. where security articles are exchanged for the purpose of goods, services or money. “Point of transaction” locations may be shop tills, Banks and Building Society counters, Ticket issuing offices at railway stations, Bureau de Change, and the like.
An object of the present invention is to provide a compact apparatus which includes a sensing head adapted to be brought into close proximity or actual contact with an article which is to be recognised so that an electrical signal can be generated in response thereto for authenticating the article which is to be presented to the sensing head.
It is also an object of the invention to provide hand held, finger, or thumb mounted devices, for use at point of transaction locations typically in combination with a housing containing a power supply, signal processing and alarm means, for the same purpose.
It is another object of the invention to provide a method of applying a sensor to articles which may or may not contain magnetic fibres or particles to allow an electrical signal to be generated to indicate whether or not the particles are present in the article concerned.
According to one aspect of the invention, there is provided a method for checking the authenticity of a security article containing at least one magnetic element such as magnetic particles having a magnetic saturation field H
s
being greater than 100 A/m. The method comprises the following steps:
(a) generating an alternating field of one or more fundamental frequencies with an amplitude being greater than the saturation field of the magnetic element;
(b) subjecting an article to be detected to the field;
(c) detecting a detection signal emanating from the article to be detected;
(d) examining the detection signal for the presence of any particular harmonics of the fundamental frequencies or of any linear combination of the fundamental frequencies and of the harmonics, the particular harmonics or the linear combination being indicative of the presence of the magnetic element as magnetic particles.
Or, viewed from still another angle, there is provided a method of making a verifiable article which is to be detected by subjecting it to an alternating magnetic field to determine whether there is at least one specific harmonic response generated by interaction between the article and the field due to the non linear response of the flux density with the applied field from particles of magnetic material associated with the article. The method is characterised by selecting the magnetic material properties and the shape of the particles so that they have a magnetic saturation field greater than 100 A/m (preferably greater than 300 A/m) so as to prevent triggering off electronic article surveillance (EAS) systems which also include magnetic fields, and incorporating said particles into the said article.
According to another aspect of the present invention, there is provided a system by which security articles can be verified, wherein authentic articles have incorporated therein particles of a selected magnetic material and selected shape, the particles being saturable by an alternating magnetic field thereby to generate at least one harmonic of the fundamental frequency of the alternating field, and wherein a sensor is provided, a first part of which generates a local alternating magnetic field to which articles as aforesaid are to be subjected for verification, and a second part of which generates by induction electric signals indicative of the response of the material making up the article to the said alternating field. Signal analysing means is provided, adapted to determine if a particular frequency, or a spectrum of frequencies, is present in the generated signals. The system is characterised in that the selection of the magnetic material and the selection
Burrell Jon
Cross David
Fisher John
Robertson Paul
Lee Diane I.
N.V. Bekaert S.A.
Shlesinger & Arkwright & Garvey LLP
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