GB2029074A - Magnetic recording and playback - Google Patents

Abstract

A system for validating valuable documents, e.g. bank notes, bearing a track 11 of magnetisable material with coded information recorded thereon comprises a transducer device 14, 15 or 16 for detecting the coded information and a further transducer device 13 for detecting the overall resultant signal from the record track 11. The transducer devices may be magneto-resistive transducers. <IMAGE>

Description

SPECIFICATION Marking of valuable documents This invention relates to the marking of valuable documents, such as bank notes, credit and cash cards, share certificates, passports and the like with secure, machine-readable identification details.

It is known, for example from United States Patent No. 3245534, with a mesh pattern of magnetisable ink lines specific to each value.

It had been proposed, for example in British Patent Specifications Nos. 1095286 and 1127043, to write on or mark the security thread in a bank note with optical of magnetically detectable markings to make fraudulent replication more difficult. It has also been proposed, in British Patent Specification No.

1411477, that the security thread should be punched with a machine readable code which includes a serial number individual to each bank note to permit a check both for authenticity and origin or ownership. However, the proposals relating to marked security threads have not described any arrangement for the rapid and easy recovery of the form of the marking, which is essential for any automatic checking system, such as in a vending machine.

It is an object of the invention to provide an improved valuable document marking and marking recovery system.

According to the invention there is provided a secure document system of at least one rectangular banknote or document having a structured magnetic thread across the shorter dimension and a read-out device, of a magnetic transducer to pick-up the structured thread form and an authenticity pick-up transducer to respond to the average characteristic of the thread. The coded structure of the magnetic thread may represent the monetary value of a banknote or document.

Embodiments of the invention will now be described with reference to the accompanying drawings, in which: A structured magnetisable material layer, which structure is permanent unless the layer is damaged and is detectable after unidirectional magnetisation as disclosed in British Patent specification No. 1,331,604. This patent discloses, among other things that acicular gamma iron oxide particles in a binder can be aligned in different directions in different areas while the binder is fluid and are fixed in these alignments by the irreversible setting of the binder. The alignments provide a detectable remanence variation on undirectional magnetisation. The magnetic particles need not necessarily be of acicular form provided their orientation will respond to an aligning magnetic field and may, for example be barium ferrite.

If such a structured layer were to be used as, or as part of, a security thread in a valuable document e.g. a bank note, it may be required to detect the coded information represented by the positions of transitions from high to low remanence in the structure, in a vending machine. In other applications it may be required to validate the banknote or document without detecting the coded structure but by merely sensing the presence of the magnetic security thread in compatible manner to the sensing of an instructured magnetic thread.

Fig. 1 shows one embodiment of the invention. A banknote, 1, has a structured thread 2, shown enlarged and simplified for clarity, placed parallel to the shorter edges of the banknote. The arrows 21, 22 represent particle alignment directions parallel and perpendicular to the long edge direction respectively. If it is required merely to sense the magnetic thread in compatible manner with an unstructured thread, the banknote is transported along the direction indicated by the arrow 3 in the direction of the long edge and the magnetic thread is "developed" with a D.C. magnetizing field which has a strong component in the direction of the arrow 3.A magnetic replay head 4 has its sensing element 5 parallel to the thread and perpendicular to the transitions in remanance, and, if its track width is considerably longer than the lengths of the coded elements of the strip, the head 4 will detect a signal dependent on the average remanence of the thread. The coded structure may be alternatively read so as to derive a sequence of coded pulses using read out head 8, by transporting the note in the direction of the arrow 6 in a direction parallel to the short edge, the thread having previously been "developed" by a DC field which has a strong component in the direction of the arrow 6.

The developing field may be applied, for example, by a permanent magnet or a DC energised recording head. A single developing field may be applied in a skewed direction, shown by arrow 7, during one or other of the modes of feed, to provide read-out in either mode, provided its components in directions 3 and 6 are sufficiently high for each element of the structured layer to have a component of remanence in both directions 3 and 6. The read-out heads may be of conventional inductive form, in which case the sensing elements 5 and 9 will be the head gaps. Alternatively the heads may be thin film magnetoresistive transducers of vertical or horizontal form as described in the article "A Magneto-resistive Readout Transducer" by R. P. Hunt in IEEE Transactions in Magnetics, Vol. MAG-7 No.

1, March 1971, p. 150, in which case the sensing elements will be current carrying thin film strips of a magnetoresistive metal such as permalloy. There are two disadvantages to the above first embodiment of the invention. First, it is necessary to provide means for transport ing the documents in both the long and short edge direction in order to read both the coded data and the "averaged" signals. Second, when reading the coded data it is necessary to ensure that the read head and the magnetic strip are in register. The position of the magnetic strip may vary from one note to another, so the read head 8 must either be sufficiently wide to cover ali possible positions of the head or, alternatively, means must be provided for laterally moving either the note or the head until the thread and the head are in register at each transaction.

Fig. 2 shows a second embodiment of the invention in which both the "average" and coded signals may be recovered with the note transported in the direction of the long edge, either in the same pass or separate passes of the document 1 0. The structured magnetic thread 11 has transitions of remanence 111, 11 3 which are inclined, their inclination typically being in the order of 45 to the document edges. Adjacent elements of the structured magnetic layers have particle orientations in the directions shown by the arrows 114, 114 which are substantially parallel and perpendicular to the remanence transitions respectively. An example of such a structure is described in U.S. Patent No. 4023204, UK Patent Application No. 44747/74.A DC developing field is applied, having a strong component in the direction 12, perpendicular to the transistors 111, 11 3. A read-out head placed as at 1 3 with its sensing element parallel to the magnetic stripe will sense a signal dependent on the average remanence of the stripe, as in the first embodiment of the invention. A read out head placed as at 14 with its sensing element parallel to the transitions in remanence, 111, 113, detects a pulse sequence which corresponds to reading the magnetic stripe from bottom to top as the stripe is transported from left to right in the direction of the long edge. The read-out heads may again be inductive of magneto-resistive.

When the head 14 is a single magnetoresistive transducer which responds to the whole length of the magnetic stripe, it may be found that the signal-to-noise ratio is low because, for a magnetoresistive element of length AB, only a small portion, equal to distance CD, will be energised by the field from the stripe.

The signal-to-noise ratio may be improved by utilising a number of shorter elements which may be deposited on to a single substrate.

The head 1 5 is an embodiment of the horizontal magneto-resistive head, in which magnetoresistive elements 151, 152, 1 53 and 1 54 are deposited on a substrate which is parallel to the surface of the document and each responds to one quarter of the length of the stripe. Alternatively, replay head 1 6 is an embodiment of the vertical magnetoresistive head having magnetoresistive elements 1 61 and 1 63 deposited on one surface of a substrate perpendicular to the document and interlaced magnetoresistive elements 1 62 and 1 64 deposited on the opposite face, each element again responding to one quarter of the length of the stripe. The replayed signals from each of the elements 151 to 1 54 or 1 61 to 1 64 may be stored and regenerated to create a serial sequence of pulses representing the coding of the whole stripe by using known data handling techniques. An alternative form of vertical multi-track magneto resistive head may have elements 162 and 164 on one substrate and elements 161 and 163 on a second substrate. The two substrates may be assembled together face to face with a thin layer of insulating and non-magnetic material separating their magneto-resistive elements.

Claims (8)

1. A system for validating valuable documents, such as bank notes, bearing a track of magnetisable material with coded information recorded thereon in the form of a physically structured pattern of orientation of the easy axes of magnetisation of said material, the system including a first transducer device capabie of producing electrical signals indicative of said coded information and a second transducer device capable of producing electrical signals indicative of the overall content of the information recorded on said track.

2. A system according to claim 1 wherein the sensing element of said second transducer is aligned along said track and the sensing element of said first transducer is aligned along a different direction substantially coincident with an orientation direction of an easy axis of magnetisation of said material.

3. A system according to Claim 2 wherein the said sensing elements are orthogonally aligned.

4. A system according to Claim 2 wherein the sensing element of the first transducer is aligned at between 30 and 60 to the length of the track.

5. A secure system according Claims 1 to 4 wherein the said transducers are magneto resistive transducers.

6. A secure system according Claim 5 wherein the first transducer comprises a plurality of uniformly spaced magneto resistive elements.

7. A secure system according to Claims 1 to 4 wherein the transducers are gapped inductive replay heads.

8. A secure system as hereinbefore de scribed by reference to and as illustrated in the accompanying drawings.