Patent Application
20080314984
This invention is generally in the field of security techniques, and relates to a security system and method for reading a magnetic tag, as well as a magnetic tag configuration.
Documents or other valuable items are usually 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 optical tags (barcodes) and magnetic markers. Such encoded security means may be either visible or hidden from view.
Conventional optical barcodes suffer from the fact that dust or dirt incidentally appearing on either a data recording medium or a data reader device may cause read errors. As for magnetic markers utilizing magnetic strips, they suffer from that recorded data may be damaged by the influence of an ambient magnetic field or an elevated temperature.
U.S. Pat. No. 6,622,913, assigned to the assignee of the present application, discloses a method and system for reading a code pattern formed by a plurality of spaced-apart magnetic elements, when the code pattern is displaced in a reading direction with respect to a reading head. The reading head comprises a magnetic material producing a high-gradient static magnetic field, and a sensing element of a kind responsive to signals produced by the magnetic elements. The magnetic material is designed such that it defines an extended narrow region where the static magnetic field vector is substantially equal to zero. The sensing element is located substantially within the zero-field region, and is thereby responsive to signals generated by each of the magnetic elements, when the magnetic element is located in the zero-field region.
U.S. Pat. No. 6,556,139 discloses a magnetic microwire for use in a magnetic tag attachable to a product to enable authentication of the product, and a detector device and system for product authentication. The magnetic microwire is a glass-coated amorphous magnetic microwire characterized by a large Barkhausen discontinuity and substantially zero or positive magnetostriction. The microwire is responsive to an external alternating magnetic field generated by the detector device to produce short pulses of magnetic field perturbations.
There is a need in the art to facilitate encoding of various items by providing a novel method and system for reading a code formed by one or more elongated magnetic elements.
The main idea of the present invention consists of reading a multiple-element tag by simultaneous interrogation of all the elements in the tag, without the need for scanning, i.e., without the need for a relative displacement between the reading system and the tag. This is achieved by subjecting the tag to an interrogating magnetic field having an AC traveling magnetic field component, which has a space phase shift distribution along an axis perpendicular to a direction of force lines of the AC traveling magnetic field. By this, a time shift is provided between waveforms of the magnetic field component which is proportional to distances between the magnetic elements, and accordingly a pattern formed by response signals of all the magnetic elements to this magnetic field component repeats the pattern of the magnetic elements and allows for retrieving the information in the tag.
There is thus provided according to one broad aspect of the invention, a method of reading a magnetic tag, which is formed by an array of elongated magnetic elements arranged in a spaced-apart parallel relationship in accordance with a pattern of coded information, the method comprising applying to the tag an interrogating field, which has an alternating traveling magnetic field component with a space phase shift distribution along an axis perpendicular to a direction of force lines of the alternating traveling magnetic field component.
The AC traveling magnetic field is preferably applied to the tag such that the force lines of this field are directed substantially along the longitudinal axis of the elongated magnetic element.
Preferably, the interrogating magnetic field includes a low-frequency (e.g., DC) gradient magnetic field component. The field gradient is directed along the force lines of the AC traveling field component.
A value of the magnetic field gradient is preferably selected to satisfy a certain condition to compensate for an angular orientation of the longitudinal axes of the magnetic elements with respect to the force lines of said AC traveling magnetic field component. The value of the magnetic field gradient satisfying the compensation condition is such that, for each point of the magnetic element, the biasing gradient field component effects a shift of the response of said magnetic element to the AC traveling field component which is equal and opposite in direction to a shift of the magnetic element response caused by the phase distribution of the AC traveling magnetic field component. Generally, the value of a biasing gradient is proportional to the angle of tag inclination.
The above may be achieved by sweeping the magnetic field gradient within a certain range of values to thereby obtain the value satisfying the compensation condition.
The AC traveling magnetic field component may be produced by at least two coils operable to provide a phase shift between electric currents trough the coils.
The AC traveling magnetic field component and the biasing gradient magnetic field component may be produced by appropriately operating electric currents through at least two coil pairs. In this case, the electric current through each coil has an AC component that creates the space phase shifted distribution of the magnetic field created by this coil, and a biasing component that creates the magnetic field gradient.
According to another broad aspect of the present invention, there is provided a system for use in reading a magnetic tag formed by at least one elongated magnetic element, the system comprising:
According to yet another aspect of the present invention, there is provided a magnetic tag carrying coded information, the tag comprising an array of magnetic elements arranged in a spaced-apart parallel relationship being substantially equally spaced from one another, one or more of said magnetic elements, selected in accordance with the coded information, being defected so as to be undetectable by a tag reading system, the defected magnetic element being thereby recognizable by the tag reading system as a free space between non-defected magnetic elements.
According to yet another aspect of the present invention, there is provided a method for manufacturing a magnetic tag carrying coded information, the method comprising: (i) arranging multiple magnetic elements in a spaced-apart parallel relationship with substantially equal spaces between them, and (i) defecting one or more of said magnetic elements, selected in accordance with the coded information, so as to make the selected magnetic elements undetectable by a tag reading system, the defected magnetic element being thereby presenting, for a tag reading process, a free space between non-defected magnetic elements.
In order to understand the invention and to see how it may be carried out in practice, preferred embodiments will now be described, by way of non-limiting examples only, with reference to the accompanying drawings, in which:
The present invention provides for a system and method for reading a magnetic tag (marker) including one or more elongated magnetic elements.
In the present example, the tag 10 includes an array of magnetic elements (wires) W, arranged in a spaced-apart parallel relationship on a substrate 12. It should be understood that the substrate 12 may constitute a label attachable to an item with which the tag is associated, or may constitute the item itself, i.e., the magnetic elements being carried directly by the item. Thus, the term “tag” used herein signifies a pattern formed by elongated magnetic elements W. The magnetic elements (wires) W are arranged in the spaced-apart parallel relationship along an axis A, being typically unequally spaced from one another forming together a predetermined pattern (coded information). The pattern formed by the arrangement of wires presents an identification code (secured information) embedded in the tag.
The magnetic element is configured to be responsive to an external interrogating magnetic field. Typically, the response of such an element is detected as its effect on a magnetic field created by a reading coil arrangement.
The magnetic element may be an amorphous ferromagnetic element, designed like as a strip or wire. Preferably, the magnetic element is a glass-coated amorphous microwire, for example such as disclosed in the above-indicated U.S. Pat. No. 6,622,913, as well as U.S. Pat. Nos. 6,441,737; 6,556,139; and 6,747,559, all assigned to the assignee of the present application. Such a glass-coated microwire is composed of a metal core and a glass coat. Generally, such a glass-coated microwire can be produced with a very small diameter ranging from 1-2 micrometers to tens of micrometers, from a variety of magnetic and non-magnetic alloys and pure metals. Preferably, the magnetic core of the microwire is prepared with an amorphous metal structure, and thus the glass-coated microwire has good mechanical strength, flexibility, and corrosion resistance, so that it can be easily incorporated in paper, plastic, fabrics and other substrate materials. An amorphous magnetic glass-coated microwire is characterized by a unique response to an interrogating magnetic field, and significantly faster re-magnetization as compared to the conventional magnetic elements (e.g., magnetic strips). The glass-coated microwire properties can be controlled by varying the alloy composition and the glass-to-metal diameter ratio. Preferably, microwires that are cast from alloys with zero or positive magnetostriction and characterized by a large Barkhausen discontinuity (Co-based or Fe-based alloys) are used in the tag.
As shown in
The entire pattern formed by response signals of the wires (obtained with a receiving system which will be described further below) will repeat the pattern of wires of the tag, and may thus be used to retrieve the secured information. A typical signal (tag response pattern) received from the magnetic tag with the method of the invention is shown in
The present invention thus allows for reading a magnetic tag without a need for mechanical scanning, i.e., without a need for a relative displacement between a magnetic field source and the tag being read. This is implemented by subjecting the tag to the AC traveling magnetic field such that the field has a phase variable along the axis perpendicular to the direction of the force lines B1 of the magnetic field. When the force lines B1 of the magnetic field are directed substantially along the longitudinal axes of the wires W, and is thus phase shifted along the axis A of the magnetic wires arrangement, the wires response pattern can be easily identified and the secured information can be retrieved.
Referring now to
The provision of the gradient biasing magnetic field component is associated with the following. Using only the interrogating AC traveling field component actually requires the magnetic elements of the tag to be strictly aligned with the force lines B1 of this field, since the angle variation of the tag (e.g., about 1-2 degree tilt between the wire's axis and the force lines B1 of the AC traveling magnetic field) deteriorates the response signal, which is thus blurred. This problem can be overcome by applying to the tag both the interrogating AC traveling magnetic field component and the gradient bias magnetic field component. Generally, a value of the magnetic field gradient that affects the wire response depends on an angle between the wire and the force lines of the AC traveling magnetic field. In the case when the angular orientation of the tag is unknown, which is practically the case, a value of the biasing field gradient is swept within a certain range of values. Generally, a ratio between the amplitudes of traveling and biasing fields depends on many factors. For example, the amplitude of traveling field is about three times higher than the amplitude of biasing field.
To facilitate the explanation, let us assume a DC magnetic field gradient. As indicated above, the value of the biasing field gradient that affects the wire response depends on the angle between the wires and the force lines of the interrogating magnetic field B1. In a real system, a sweeping magnetic gradient is applied such as to cover a range of possible angles between the magnetic element and the force lines of the interrogating field. When the tag is inclined with respect to the force lines of the AC traveling field B1, two parts W′ and W″ of the magnetic element W are oriented at opposite angles with respect to the force lines B1. As a result, these two parts W′ and W″ of the magnetic element W are differently affected by the biasing field.
H
W′
=H
m·Sin(wt)+Hb
H
W″
=H
m·Sin(wt)−Hb
wherein Hm is the amplitude of the AC traveling field, w is the frequency of this field, t is the time, and Hb is the amplitude of the biasing field.
The application of the biasing field provides for compensating for the possible wires inclination with respect to the force lines of the interrogating traveling field. The general principle of this aspect of the invention may be easily understood from the following consideration for the wire response of positive polarity. While a magnetic wire is strictly aligned with the force lines B1 of the interrogating traveling magnetic field, all points of the wire simultaneously undergo a magnetization process, and the wire response represents a single sharp pulse. When a magnetic wire is inclined relative to the force lines B1 of the interrogating field, the situation changes: different points of the wire undergo the magnetization process at different moments of time. As a result, the wire response pulse has a larger width and smaller amplitude, as compared to those of the strict alignment between the wire and force lines B1. This results in an overlap between the responses produced by locally adjacent wires. If the biasing field gradient (e.g., DC magnetic field gradient), which has a constant value along the wire axis, is applied to the wire, all points of the wire are subjected to this biasing, which will produce a time shift of the wire response to the interrogating field. Accordingly, the points of the wire, which later respond to the interrogating AC traveling field (wire part W′) due to the wire inclination, will be subjected to the positive biasing field (+Hb) and their response will pass ahead. Similarly, the points of wire, which respond earlier (wire part W″), will be subjected to the negative biasing field (−Hb), and their response will be delayed. The preferred value of the magnetic gradient (i.e., the optimal compensation for the wire inclination) should be such that for each point of the wire a shift of the wire response to the interrogating traveling field due to the biasing field is equal and opposite in direction to the shift of the wire response caused by the phase distribution of the interrogating traveling field.
As indicated above, the value of the magnetic field gradient that affects the wire response depends on the angle between the wire and the force lines of the interrogating traveling magnetic field. So, in the case when the angular orientation of the tag is known, the magnetic field gradient is selected such that for each point of the wire a shift of wire response to interrogating field component due to the biasing field is equal and opposite in direction to the shift of response caused by the phase distribution of the interrogating field component. In the case when the angular orientation of the tag is unknown, the value of the magnetic gradient is slowly swept to satisfy the compensation condition.
Reference is made to
The magnetic field source assembly 102 is configured to generate an interrogating AC traveling magnetic field component, with or without a biasing gradient field component compensating for a possible tag tilting. The AC traveling magnetic field component can be generated by at least two coils appropriately operated by electronic device 104 to provide a desired relation between electric current through the coils, as described further below. To implement the compensating component, either the same AC traveling magnetic field source (coils) may be used or an additional magnetic field source generating a sweeping gradient magnetic field component.
Generally, the interrogating AC traveling magnetic field component is created by at least two coils with a certain phase shift between electric currents in the coils. The electronic device 104 is configured and operable to provide the desired shift between the electric currents through the coils. The same electronic device or another suitable electronic utility is used to affect amplification and filtration of the output signal of the receiving unit, which is to be processed and analyzed. The control unit controls the interrogating means (magnetic field source) and the receiving unit, analysis the tag response signal and retrieves information secured in the tag.
H1(x)˜Hm·F(x−x1)·Sin(wt)
H2(x)˜Hm·F(x−x2)·Cos(wt)
wherein Hm is the amplitude of the magnetic field, F(x) is a function describing a drop of the magnetic field with an increase of a distance between point x and a source of the magnetic field (i.e., respective one of the coils); x1 and x2 are positions of coils L1 and L2, respectively; and w is the magnetic field frequency.
The magnetic field created by source 102 in every point along the line A may be expressed as a superposition of the magnetic fields H1(x) and H2(x), and thus the magnetic field H(x,t) in point x at time t is determined as follows:
H(x,t)=Hm·F(x−x1)·Sin(2·π·w·t)+Hm·F(x−x2)·Cos(2·π·w·t) (1)
Evaluation of this equation provides the phase of the interrogating magnetic field as a function of coordinate x:
wherein the phase shift as a function of coordinate x is defined by the member of equation arctn((F(x−x1)/F(x−x2)).
As indicated above, in order to compensate for a possible inclination of the tag with respect to the force lines of the AC traveling magnetic field, the same magnetic field source generating this field may be used to produce the field-compensating component (biasing field). This is implemented by appropriately operating (by electronic device denoted 104 in
I
1
=I
m·Sin(wt)+Ib
I
2
=I
m·Cos(wt)+Ib
I
3
=I
m·Sin(wt)−Ib
I
4
=I
m·Sin(wt)−Ib (2)
wherein Im is the amplitude of the AC component of the electric current through the coil, and Ib is the biasing component of the electric current.
According to the above equations (2), a part of the electric current comprising AC components, Im, creates a space phase shifted distribution of the interrogating field, while the biasing components, Ib, create a magnetic field gradient necessary to compensate for the tag inclination with respect to the force lines of the magnetic field.
The magnetic field source assembly 102 is configured for generating, in the interrogating zone IZ, an AC traveling magnetic field components (AC field with a space phase shift distribution along an axis perpendicular to the force lines of this field component) and a sweeping biasing magnetic field component having a gradient directed along the force lines of the traveling field component. To this end, the magnetic field source 102 includes interrogating coils—eight such coils L1-L8 in the present example, wound on ferrite C-cores—four cores C1-C4 in the present example, and the electronic device operates to provide an appropriate phase shift between electric currents through the coils L1-L8, as described above.
The receiving unit 106 includes two pairs of receiving (pickup) coils S1 and S2 (i.e., four pick-up coils forming two coil pairs S1 and S2). A tag 10, when located in the interrogating zone IZ, responds to the interrogating field, and this response is received by the coil pairs S1 and S2 (i.e., affects the magnetic field generated by these coils). The coils of the pairs of coils S1 and S2 are connected such as to compensate a low frequency signal induced by the interrogating magnetic field (AC traveling field component). The position of the pairs of receiving coils S1 and S2 relative to the C-cores C1-C4 is chosen such as to minimize a spurious low frequency signal.
The phase shift between the electric currents I1-I8 flowing through the coils L1-L8, respectively, is set such as to create a nearly linear space phase distribution of the magnetic field, generated by these coils, along the X-axis (the magnetic force lines being directed along the Y-axis). This is achieved by providing the electric currents I1-I8 through the coils I1-I8 satisfying the following equations.
I
1
=I
m·Sin(wt)+Ib
I
2
=I
m·Cos(wt)+Ib
I
3
=−I
m·Sin(wt)+−Ib
I
4
=−I
m·Sin(wt)+Ib
I
5
=I
m·Sin(wt)−Ib
I
6
=I
m·Cos(wt)−Ib
I
7
=−I
m·Sin(wt)−Ib
I
8
=−I
m·Sin(wt)−Ib (3)
As seen from equations (3), AC current components through the adjacent coils are shifted at 90 degrees with respect to one another. In addition, electric currents passing through the coils I1-I8 have low frequency components (Ib) to create a sweeping bias gradient inside the interrogating zone IZ. As mentioned above, this gradient allows for compensating for the tag's angular orientation (inclination) relative to the force lines of the interrogating magnetic field.
For example, the amplitude of the electric current flowing through each coil is 35 mA. This current generates the interrogating AC traveling magnetic field component of 200 A/m amplitude at a distance of 10 mm above the receiving coils. The frequency of the interrogating field is 300 Hz. The compensation component of the electric current in each coil is about 10 mA. The frequency of compensation current is 40 Hz.
V
1(t)=V10·Sin(2·π·f1·t)
wherein V10 is the amplitude of the first signal.
A second generator 42 creates a voltage signal, V2, oscillating harmonically with a frequency f2=40 Hz, and determined as:
V
2(t)=V20·Sin(2·π·f2·t)
wherein V20 is the amplitude of the second signal.
The signal V1 from the first generator 41 passes through a phase shifter 43. An output signal, V3, of the shifter 43 is 90 degrees shifted relative to the output signal V1 of the generator 41, namely:
V
3(t)=V10·Cos(2·π·f1·t)
The signal, V1, from the first generator 41 inputs a summation unit 44 and a subtraction unit 45. The signal, V2, from the second generator 42 enters other input ports of units 44 and 45. Hence, an output signal, V11, of the summation unit 44 is equal to:
V
11(t)=V10·Sin(2·π·f1·t)+V20·Sin(2·πf2·t)
Consequently, an output signal, V12, of the subtraction unit 45 is equal to:
V
12(t)=V10·Sin(2·π·f1·t)−V20·Sin(2·πf2·t)
The signal, V3, from the shifter 43 inputs a summation unit 46 and a subtraction unit 47. The signal, V2, from the second generator 42 also inputs these units (via other input ports thereof). An output signal, V21, of the summation unit 46 is equal to:
V
21(t)=V10·Cos(2·π·f1·t)+V20·Sin(2·πf2·t)
An output signal of the subtraction unit 47 is equal to:
V
22(t)=V10·Cos(2·π·f1·t)+V20·Sin(2·πf2·t)
The voltage signals V11, V12, V21, V22 passes current drivers 51-58, which drive currents through the coils L1-L8, respectively. The coils L1-L8 create magnetic fields H1—H8, respectively, determined as follows.
H
1(t)=A·Sin(2·π·f1·t+B·Sin(2·πf2·t)
H
2(t)=A·Cos(2·π·f1·t+B·Sin(2·πf2·t)
H
3(t)=−A·Sin(2·π·f1·t+B·Sin(2·πf2·t)
H
4(t)=−A·Cos(2·π·f1·t+B·Sin(2·πf2·t)
H
5(t)=A·Sin(2·π·f1·t−B·Sin(2·πf2·t)
H
6(t)=A·Cos(2·π·f1·t−B·Sin(2·πf2·t)
H
7(t)=−A·Sin(2·π·f1·t−B·Sin(2·πf2·t)
H
8(t)=−A·Sin(2·π·f1·t−B·Sin(2·πf2·t)
wherein A and B are the coefficients, determined by coils construction.
Superposition of the magnetic fields H1—H8 provides the interrogating magnetic field with a space phase distribution enabling identification of the response pattern and a bias magnetic gradient compensating for the possible tag inclination with respect to the force lines of the AC traveling field component.
A tag placed inside the interrogating zone responds to the interrogating magnetic field by a series of electromagnetic pulses. The time positions of these pulses are in strict correspondence with the space positions of wires of the tag.
The wires' response is detected by the pairs of receiving coils S1 and S2, and then signals from the receiving coils are amplified by an amplifier 63 and converted by an analog-to-digital converter 64 into the digital representation thereof. The so-obtained digitized response of the tag is received by a central processor unit 65 (control unit 108 in
As indicated above, the code pattern carried by the tag is in the form of an array of magnetic elements arranged in accordance with the coded information, i.e., typically defined by spaces between the magnetic elements. Generally, the magnetic elements can be initially unequally spaced from one another in accordance with a predetermined code. However, this complicates the tag manufacturing process.
The present invention solves the above problem by arranging magnetic elements with equal spaces between them, and then “defecting” some (one or more) or the magnetic elements so as to be unreadable. By this, non-defective (readable) magnetic elements become unequally spaced from each other in accordance with predetermined coded information.
The above technique simplifies the process of fabricating a tag carrying coded information. It should be understood that any other means may be used for “defecting” selective magnetic elements.
Thus, the present invention provides a system and method for reading a tag formed by an array of elongated magnetic elements arranged in accordance with certain coded information. The reading is implemented by applying to the tag an interrogating AC traveling magnetic field with the force lines directed substantially long the longitudinal axis of the magnetic element and phase shift distribution along an axis perpendicular to the force lines direction. Preferably, the magnetic field applied to the tag also includes a low-frequency field component with a gradient directed along the force lines of the AC traveling field component. Additionally, the present invention provides a novel magnetic tag configuration and a method for manufacturing such a tag.
Those skilled in the art will readily appreciate that various modifications and changes can be applied to the embodiments of the invention as hereinbefore exemplified without departing from its scope defined in and by the appended claims. For example, the interrogating field, which is an AC traveling magnetic field may and may not include a low-frequency (e.g., DC) gradient field component. The latter may be produced using a separate magnetic field source or by the same magnetic field source generating the AC traveling magnetic field. Interrogating the entire tag by the AC traveling magnetic field provides for producing the tag response pattern indicative of the magnetic elements' arrangement in the tag and thus indicative of the coded information secured in the tag. The provision of the DC gradient magnetic field component provides for compensating a possible inclination of the magnetic elements with respect to the force lines of the AC traveling field component.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0416603.9 | Jul 2004 | GB | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IL2005/000770 | 7/20/2005 | WO | 00 | 1/26/2007 |
