Registers – Coded record sensors – Particular sensor structure
Reexamination Certificate
2000-10-20
2003-09-23
Lee, Michael G. (Department: 2876)
Registers
Coded record sensors
Particular sensor structure
C235S450000, C235S451000, C235S375000, C235S493000
Reexamination Certificate
active
06622913
ABSTRACT:
FIELD OF THE INVENTION
This invention is generally in the field of security techniques, and relates to a security system for encoding documents and other valuable items with code patterns, and a method for reading these code patterns.
BACKGROUND OF THE INVENTION
It is often the case that documents or other valuable items need to be protected from tampering, falsification and unauthorized use. The accepted way of protection consists of introducing one or more security means into, or attaching these means to, a document or an item. The documents and items to be protected include ID cards, passports, licenses, security passes, currency, checks, travel tickets, keys and key cards, and the like. The most widely used encoded security means are so-called “optical bar codes” and magnetic strips. Such encoded security means may be either visible or hidden from view.
Conventional optical bar codes suffer from the drawback associated with the fact that dust or dirt incidentally appearing on either a data recording medium or a data reader device may cause read errors. Additionally, in magnetic strips, the recorded data may be damaged by the influence of an ambient magnetic field or an elevated temperature.
U.S. Pat. No. 4,883,949 discloses a system with increased code reliability. In this system, data recording means are defined by intermittent patterns of different materials that can affect the high frequency impedance of the magnetic coil of a reading head. The pattern materials may differ in electric conductivity and/or magnetic permeability.
Another common drawback of the optical bar codes and magnetic strips, is that they can be easily read out and duplicated by conventional means. To increase the security of important documents and valuable items from unauthorized use or falsification, it was proposed to incorporate a magnetic bar code strip or other pattern hidden within the document or item substrate or concealed under other “dummy” security elements such as optical bar codes or holograms.
In the known devices of the kind specified, magnetic materials were used mostly in the form of magnetic inks containing powders of high magnetic coercivity, e.g., Fe
2O
3
, BaFe
12
O
19
and the like. However, it is recognized that the strong persisting magnetic field of such materials allows for reading out and duplicating the encoded pattern.
In U.S. Pat. No. 5,616,911, it is proposed that the hidden magnetic bar code pattern be formed using the low concentration magnetic ink exhibiting very low, approximately zero, remanance. Such magnetic inks may be formed from soft magnetic materials including Fe-powder, ferrites, Sendust alloy powder, amorphous alloys in a powder form and the like. The concentration of these materials in an ink or binider medium of less than 10% by volume is preferred. A reading head utilizing an in-field magneto-resistive sensing element is employed to magnetize the bar code pattern bands and detect their width or the space between them, whilst they move with respect to the head. After being read, the code pattern exhibits practically no residual magnetic field and is not readable by a magnetic viewer. One of the disadvantages of the proposed security system is in that the applied soft magnetic powders are easily available and their magnetic signature is not specific, and therefore the document counterfeiting is still possible. Another disadvantage is in that the sensitive area of the reading head with a magneto-resistor sensing element is large. The size of the code pattern elements and the distance between them cannot be smaller than the reading head sensitive area, otherwise these elements would not be unambiguous. Therefore, the information density of such a coding system is intrinsically low. Moreover, the reading head resolution deteriorates strongly with the increase in the distance between the magneto-resistive sensing element reading head and the code pattern. The same is relevant for the bar code system disclosed in the above-indicated U.S. Pat. No. 4,883,949.
U.S. Pat. No. 5,801,630 discloses a method for preparing a magnetic material with a highly specific magnetic signature, namely with a magnetic hysteresis loop having large Barkhausen discontinuity at low coercivity values. This material is prepared from a negative-magnetostrictive metal alloy by casting an amorphous metal wire, processing the wire to form longitudinal compressive stress in the wire, and annealing the processed wire to relieve some of the longitudinal compressive stress. One disadvantage of such material in security pattern applications is the relatively large wire diameter, which is approximately 50 &mgr;m. Another disadvantage is the complicated multi-stage process of the wire preparation. Yet another disadvantage of the material is the amorphous wire brittleness which appears due to wire annealing Such brittleness will prevent using the material in security patterns formed in paper documents like currency, checks, passports, etc.
According to another known technique, a glass-coated magnetic microwire is used as a magnetic material having unique magnetic properties. This microwire is cast directly from the melt by a modified Taylor method, which is well known in the art, and is disclosed, for example, in the article of I. W. Donald and B. L. Metcalf “
The Preparation Properties and Applications of Some Glass-Coated Metal Filaments Prepared by the Taylor
-
Wire Process
”, Journal of Materials Science, Vol. 31, pp 1139-1149, 1996. It is an important feature of the Taylor process that it enables pure metals and alloys to be produced in the form of a microwire in a single operation, thus offering an intrinsically inexpensive method for the manufacture of microwire. The glass-coated microwires can be produced with very small diameters (ranging from 1 &mgr;m to several tens micrometers), from a variety of magnetic and non-magnetic alloys and pure metals. Magnetic glass-coated microwires may be prepared also with amorphous metal structures, as disclosed in the article of H. Wiesner and J. Schneider “
Magnetic properties of Amorphous Fe
-
P Alloys Containing Ga, Ge and As
”, Physica Status Solidi, Vol. 26, pp 71-75, 1974, and other publications cited as references in the above-indicated review of Donald and Metcalf. These amorphous magnetic glass-coated microwires have good mechanical strength, flexibility and corrosion resistance, so that they can be easily incorporated in paper, plastic and other document substrate materials, Amorphous magnetic glass-coated microwires are characterized by their unique response which may resemble, inter alia, that of die-drawn amorphous wires of the above cited US '630.
SUMMARY OF THE INVENTION
There is accordingly a need in the art to improve security systems by providing a novel security system utilizing a code pattern formed by magnetic elements with extremely low coercivity and high permeability, and a novel reading head and method for reading the code pattern.
It is a major feature of the present invention to provide such a system that has a high density magnetic read-only code pattern, which is not visible to the Individual's eyes, and a reading head capable of reading this code pattern
It is another feature of the present invention to provide such a reading head that is designed to match the unique response characteristic of the code pattern material.
The main idea of the present invention is based on the following. A read-only code pattern, to be attached to a document that is to be protected, is formed by magnetic elements having extremely low coercivity (substantially less than 10 &mgr;m) and high permeability (substantially higher than 20000). A reading head, in addition to the conventionally used magnetic sensing element (e.g., coils), is provided with a magnetic means (e.g., at least two permanent magnets) creating a static magnetic field of a specific configuration. This static magnetic field, on the one hand, affects the magnetic elements so as to provide their magnetic response to this static filed, and, on the other hand, has such a
Antonenco Alexandru
Brook-Levinson Edward
Manov Vladimir
Sorkine Evgeni
Advanced Coding Systems Ltd.
Browdy and Neimark , P.L.L.C.
Lee Michael G.
Paik Steven S.
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