WO2001008085A1

WO2001008085A1 - Multi-bit magnetically encoded tag

Info

Publication number: WO2001008085A1
Application number: PCT/US2000/019935
Authority: WO
Inventors: David Edwards; Karl Josephy; Richard K. Childers; Peter J. Kuzma; Arthur B. Moore
Original assignee: Avery Dennison Corporation
Priority date: 1999-07-21
Filing date: 2000-07-21
Publication date: 2001-02-01
Also published as: AU6116600A; EP1203347A1

Abstract

A label for storing information includes a substrate having a pressure sensitive adhesive applied to one surface and a plurality of magnetic elements secured to the pressure sensitive adhesive which exhibit a detectable response upon the application of a magnetic field of a certain field strength with at least one of the magnetic elements providing a reference response. Also disclosed is a method of selectively encoding the magnetic elements.

Description

TITLE: MULTI-BIT MAGNETICALLY ENCODED TAG

FIELD OF THE INVENTION

This invention relates generally to a device for encoding information, particularly, to a device that encodes information magnetically and that may be read remotely, and, more particularly to a tag or label that is encoded with information and 5 that may be read remotely when placed in a magnetic field.

BACKGROUND OF THE INVENTION

It is well known to employ various labels or tags (collectively, labels) to track, identify or sort items bearing such a label. Typically, the label is applied to a product

10 and may include a bar code or similar optical code that can be encoded with a limited amount of information. This information is specific to the application and for, say, delivery services may include a pointer to a data base of information containing the source of the product and its destination. Using an optical scanner, the information encoded in the bar code can be retrieved and used to aid in delivering the package and ι tracking its location in the delivery process. Identification and tracking labels, such as bar codes, are also used as airline baggage tags to track baggage through an airport and to a plane as well as in retail applications to indicate product identification and price information.

One disadvantage to optically encoded labels is that a direct line of sight

20 between the optical code and the optical scanner is required for the scanner to read the information encoded in the optical code. Consequently, the product bearing the label or the scanner must often be re-oriented to ensure that the optical code can be read when necessary.

One system that does not require a direct line of sight between the encoded

2_ label and the reader employs a magnetic material contained in the label that allows the label to be remotely sensed. Such a label conventionally incorporates one or more strips or wires of a suitable magnetic material, such as an amorphous magnetic material, that when passed through an alternating magnetic field experiences a reversal in the polarity of its magnetic properties. This reversal produces a change in the

30 magnetic flux of the magnetic material that can be externally detected. By using magnetic strips of different coercivities, each strip produces a response at a time which is a function of the strength of the applied magnetic field. In other words, for a label having five strips of increasing coercivity, the strips will individually exhibit a polarity inversion at five different times as the strength of the applied magnetic field is increased. Unfortunately, the functionality and response of such systems is built into the label during manufacture and cannot be changed. Examples of these systems are disclosed in U.S. Patent Nos. 5,175,419 and 5,204,526 assigned to Fuji Electric Co., Ltd.

Since the product to which a label is applied may often include materials which create an uneven distribution across the magnetic field, such as items including ferrous metals, the response of a magnetic label may be inconsistent unless the variance of the magnetic field can be compensated for. Consequently, the device disclosed in the Fuji patents generates two alternating magnetic fields. One, of a known maximum value, is used to produce a reference response. A second alternating magnetic field is used to read the label and the response is corrected based on the reference response. The use of plural magnetic fields adds complexity to the system, increases its cost, and does not fully correct for anomalies in the magnetic field induced by the product to which it is applied.

It would be desirable to produce a label which could be encoded or "written to" when desired to produce the desired response and which facilitated making compensation for variances in the magnetic field in its vicinity.

SUMMARY OF THE INVENTION

The present invention provides a system for encoding and retrieving information in an inexpensive manner that does not require line of sight reading of a label or tag. The system preferably includes a label or tag having a number of magnetic strips or wires that selectively and individually produce a discernible response in the presence of a magnetic field. The label may include one or more reference strips or wires that also individually produce a discernible response in the presence of a magnetic field and that can be used to calibrate the system and compensate for variance in the magnetic field. The system also preferably includes a generator for generating a magnetic field to induce a response in the magnetic wires or strips, a sensor for sensing the response of the magnetic wires or strips and an apparatus for writing to the magnetic wires or strips to selectively null certain wires or strips so that they do not produce a response in the presence of the applied magnetic field. In accordance with one aspect of the invention a device for storing information includes a substrate and a plurality of magnetic elements which exhibit a detectable response upon the application of a magnetic field of a certain field strength, at least one of the magnetic elements representing a reference element.

In accordance with another aspect of the invention, a device for storing information includes a substrate, a plurality of magnetic elements which exhibit a detectable response upon the application of a magnetic field of a certain field strength, each of the magnetic elements having a different coercivity; and means for altering the coercivity of at least one of the magnetic elements.

In accordance with another aspect of the invention, a device for storing information includes a substrate including a pressure-sensitive adhesive applied to at least one face, a plurality of magnetic elements which exhibit a detectable response upon the application of a magnetic field of a certain field strength; each of the magnetic elements having a different coercivity, and means for altering the ability of at least one of the magnetic elements to exhibit a reversal in polarity. In accordance with another aspect of the invention, a device for storing information includes a substrate including a pressure-sensitive adhesive applied to at least one face and a plurality of magnetic elements of differing coercivities; two of the magnetic elements representing reference elements with one of the reference elements having the highest coercivity of any of the magnetic elements. In accordance with a further aspect of the invention, a method of reading information encoded in a device including a plurality of magnetic elements having differing coercivities includes the steps of subjecting the magnetic elements to a ramping magnetic field, detecting the responses of the magnetic elements to the magnetic field, and using the magnitudes of the responses of the magnetic elements with the highest and lowest coercivities to correct the responses detected from others of the magnetic elements. In accordance with a still further aspect of the invention, a method of encoding information in a device including a plurality of magnetic elements having differing coercivities includes the steps of altering the response of certain magnetic elements to a magnetic field. In accordance with another aspect of the invention, a device for storing information includes a substrate and a plurality of magnetic elements coupled to the substrate. The magnetic elements are operatively configured to exhibit a detectable response upon the application of a magnetic field of a certain field strength. The magnetic elements are also individually, selectively negatable so as to no longer exhibit the detectable response.

In accordance with still another aspect of the invention, a device for storing information includes a substrate and a plurality of magnetic elements coupled to the substrate. The magnetic elements are operatively configured to exhibit a detectable response upon the application of a magnetic field of a certain field strength. At least one of the magnetic elements has a different coercivity than other of the magnetic elements. The magnetic elements have nonuniform orientations.

To the accomplishment of the foregoing and related ends, the invention comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the annexed drawings:

Figure 1 is a cutaway illustration of a magnetic multi-bit label in accordance with one embodiment of the invention embodying a number of magnetic elements; Figure 2 is an illustration of the method of reading the label of Figure 1 ; Figure 3 is an illustration of an alternate embodiment magnetic multi-bit label, having a number of magnetic elements, each with different regions for storage of a bit of information;

Figure 4 is a representation of the label of Figure 3 showing selected areas of magnetic elements having had their respective coercivities adjusted; and

Figure 5 is an illustration of another alternate embodiment magnetic multi-bit label, having a number of magnetic elements which encode information by orientation.

DETAILED DESCRIPTION OF THE INVENTION With reference to the figures and initially to Figure 1 there is shown a multi-bit magnetic label or tag 10 (herein collectively, "label") including a substrate layer 12, a number of magnetically bistable elements 14 secured to the substrate layer in a parallel array, such as through a pressure sensitive adhesive, and a backing layer 16. The magnetic elements 14 preferably include a pair of reference elements 18 and 20 and several bit storage elements 22a through 221.

It will be appreciated that many suitable substrate materials and pressure- sensitive adhesives are well-known in the art. Examples of suitable substrate materials are PVC (polyvinyl chloride) films, polypropylene films, PET (polyethylene teraphthalate) films, and various kinds of paper, such as 42 pound super-calendered kraft paper. Examples of suitable adhesives are Ashland Chemical #1860Z45 solvent acrylic adhesive, and BASF AC resin #258 or #203 acrylic hot melt adhesive.

Preferably, each magnetic element 14 has a different coercivity and is capable of undergoing a detectable reversal in polarity when subjected to a magnetic field of sufficient field strength. By selectively turning one or more individual bit storage elements 22 "off so that they do not experience a detectable polarity inversion upon being subjected to the appropriate magnetic field or by leaving one or more bit storage elements "on" so that they do experience a polarity inversion, the bit storage elements can be used to store a desired binary number or code. In other words, the first bit storage element 22a of lowest coercivity represents the number 0 or 1 , the second bit storage element 22b has a higher coercivity and represents 0 or 2 and the third bit storage element 22c has an even higher coercivity and represents 0 or 4 and so on in a conventional binary scale. The number of bit storage elements 22 needed for a particular application is therefore chosen to represent in binary form at least the number of bits of information to be stored. In addition, two of the magnetic elements 14 would be used as reference elements 18 and 20. For example, if the application depended on storing a number from 0 to 1 ,000,000 (2²⁰), then the label would require at least twenty bit storage elements 22 and preferably have two reference elements 18 and 20 for a total of twenty-two magnetic elements 14. In the exemplary label 10 of Figure 1, there are two reference elements 18 and 20 and twelve bit storage elements 22a-221, capable of encoding and storing a number up to 2¹² (0 to 4095), for a total of fourteen magnetic elements 14.

A bit storage element 22 may be selectively negated (turned "off) by one or more of several methods: 1) by severing the element so that its length is less than a certain critical length necessary for magnetic bistability, so that the element has either a) no response to a magnetic field, or b) a reduced response which may be below a threshold level detectable by a reader; 2) by applying a localized high strength magnetic field so that the bit storage element does not exhibit a polarity reversal when subjected to a magnetic field, or so that the element has its ability to exhibit a reversal in polarity is otherwise altered; 3) by placing a piece of ferrous material or ferromagnetic material (or a material having ferromagnetic properties, for example containing particles of ferrous or ferromagnetic materials) in close proximity to the element so that the bit storage element does not exhibit a polarity reversal when subjected to a magnetic field, or so that the element has its ability to exhibit a reversal in polarity is otherwise altered, diminished, or rendered undetectable; 4) by shifting the coercivity of a bit storage element sufficiently that a) it does not undergo a polarity inversion within the range of strengths of the applied magnetic field, or b) it does not undergo a polarity inversion within the range of magnetic field for which a reader is scanning, such as by heating a portion or the entire bit storage element; 5) by heating, annealing and/or thermally shocking the element so that the element has either a) no response to a magnetic field, or b) a reduced response which may be below a threshold level detectable by a reader; and/or 6) by breaking, fracturing, or removing all or a portion of a coating on the element, such as a glass coating, so that the element has either a) no response to a magnetic field, or b) a reduced response which may be below a threshold level detectable by a reader. The heating described above may be carried out, for example, by heating with laser pulses (for example using laser diodes, or by induction heating of a wire using a high frequency coil to induce a current in the wire which heats it via Joule heating. In effect, the bit storage element 22 may be "written to" by one or more of the above methods in order to change the bit storage element from "on" to "off."

Putting aside for a time compensation that may be desirable for the magnetic field to which the label is exposed for the sake of simplicity, the process of reading a multi-bit magnetically bistable device 10, which has twelve bit-storage elements 22 that are encoded with the numerical value "674," is illustrated in Figure 2. The binary equivalent of the value "674" is "001010100010." Accordingly, the bit storage elements 22c, 22e, 22g and 22k remain "on" or able to undergo a polarity inversion, while bit storage elements 22a, 22b, 22d, 22f, 22h-j and 221 are written to in order to disable their polarity inversion capabilities. When the label 10 encoded as such is subjected to a ramping, alternating magnetic field as designated by the ramp 24, at field strengths corresponding to the coercivities of the bit storage elements 22c, 22e, 22g and 22k, the bit storage elements will individually undergo a polarity reversal. The polarity reversal influences a simultaneously applied electric field which is detected through a sensor, such as a pick-up coil. The influence on the electric field is shown as pulses 26c, 26e, 26g and 26k. The pulses are identified as being emitted from the polarity inversion of specific bit storage elements by correlating the time of the pulse (caused by the inversion) with the field strength of the magnetic field at that time. The label is preferably subjected to the magnetic field several times and at several different magnetic field orientations, and the responses appearing most accurate, such as those that generate the highest response, are used for analysis. In practice, however, the strength of the magnetic field actually felt by the individual bit storage elements 26 can be expected to often differ from the strength of the generated magnetic field because of local anomalies or distortions in the magnetic field attributable to nearby metallic objects, such as in a package or luggage to which the label is applied, or because of the orientation of the bit storage elements relative to the magnetic field. Consequently, during the process of reading the label 10 it is desirable to compensate for anomalies in the magnetic field in the vicinity of the label so that it is known that a detected pulse relates to a certain bit storage element 26. This accomplished through the reference elements 18, 20.

The reference elements 18 , 20 have coercivities, ref_min and ref_max , respectively, at either end of the range of coercivities for the bit storage elements 22. Thus, if the bit storage elements 22a-221 have coercivities of, say, 2 through 13, respectively, the reference element 18, ref_min, might have a coercivity of 1 and the reference element 20, ref_max, might have a coercivity of 14. Generally, the reference element 18, ref_min, allows the local field strength to be inferred at the location of the label 10, while the reference element 20, ref_max, is used to verify that all of the bit storage elements of the label 10 have been read, although both reference elements 18, 20 can be used to interpolate a magnetic field distribution across the label as explained more fully below.

Consider the process of reading the label 10 as depicted in Figure 2, again, in which variations or distortions in the magnetic field have been accounted for using the reference elements 18 and 20. Initially, the magnetic field is ramped from zero until a first pulse (not shown in Figure 2) is detected - this pulse will represent ref_min - which will occur at a field strength "y." This field strength is generally higher than the absolute or theoretical field strength "x" at which the reference element 18 would be expected to reverse its polarity and generate a pulse in the absence of any anomalies or distortions in magnetic field. The magnetic field then continues to rise until the next pulse is achieved - this will represent the first non-nulled bit storage element 26; in the example, bit storage element 26c. The field strength at which this bit storage element 26 experiences a polarity inversion is "z." The position of this bit storage element 26 in the overall binary scale is then determined by the following equation (which assumes that the ref_min has a value x, and the incremental increase from one magnetic element 14 to a subsequent element is x):

((z-y-x)/x)-l. Thus, for example, suppose that upon interrogating the label 10 with a swept and increasing magnetic field the first pulse - which is attributable to the reference element 18, ref_min - occurs at an emitted field strength of 2 oersted, instead of at the theoretical 1 oersted. Then it is inferred that in the vicinity of the label that when a magnetic field of 2 oersted is generated, the actual field strength felt by a magnetic element 14 in the label is at 1 oersted (i.e., the field is undergoing mitigation). Upon further increasing the magnetic field the next pulse occurs at, say, 5 oersted. It is then inferred that the this pulse is attributable to the third bit storage element 26c and that the first and second bit storage elements 26a, 26b were nulled or negated (i.e., their codes were 0). The above process is repeated, with each pulse event being referenced to ref_mιn until ref_max is encountered. In this scenario reading a pulse attributable to ref_max confirms that the local field strength was sufficient to ensure that all of the bit storage elements 26a-261 on the label have been read.

The pulses may each be associated with a reference value, ref_mιn , for reference element 18 that is determined after the detection of each previous pulse. In other words, the strength of the magnetic field is dropped back to zero after each pulse detection and then increased again to cause polarity inversion of reference element 18, ref_mιn, and then next lowest unread and non-nulled bit storage element is referenced. Alternatively, the same reference value, ref_mιn , for reference element 18 may be used for all pulses detected during a reading operation. A further alternative method would be to find the lowest and highest magnetic field strengths at which a pulse is detected, ref_mιn and ref_max, which are necessarily attributable to reference elements, 18 and 20, respectively. The magnetic field strength gradient across the label is then interpolated based on the values for ref_mιn and ref_max. Consequently, all of the remaining non-nulled bit storage elements could be then looked for and detected in the next sweep of the label.

Once a number has been read from the label 10, the number can be coupled with information in a database, such as the source of the item to which the label is affixed, the destination, etc. Alternatively, information could be encoded into the label directly. The magnetic elements may be any of a number of materials, alloys or compositions that exhibit a pronounced response at a known magnetic field strength. For example, amorphous magnetic materials or nanocrystalline magnetic materials in the form of fine wires or strips having glass sheaths may be used that exhibit a polarity inversion and emit a pulse upon the inversion. It is desired that the label is read or interrogated by the magnetic field in a number of planes or orientations so that during reading a near-to-normal orientation of the label to the field can be achieved. This would ensure that the maximum signal response from the magnetic elements of the label are read. During sweeping of the label with the magnetic field many samples may be taken, and preferably those with the strongest signal responses would be used to decode the label. Any number of known techniques for generating a magnetic field or fields or orienting the field or fields in different directions to maximize the responses of the magnetic elements, and sensing a response by the magnetic elements can be employed, such as are described in U.S. Patent Nos. 5,175,419 and 5,204,526 assigned to Fuji Electric Co., the entire disclosures of which are incorporated herein by this reference.

The invention can also be practiced using magnetic elements 14 of the same coercivity but each of different length to diameter ratios (and/or of different compositions), and using the peak amplitude of the polarity inversion as the characteristic. In this method the magnetic elements are of different length to diameter ratios (and or compositions) and consequently emit pulses upon polarity inversion that are proportional to this ratio. Again, two reference wires could be used to reference all the observed pulses and to verify that the entire label has been swept.

A number of other techniques can also be employed to encode a multibit magnetic label in accordance with the present invention. For example, a label could be encoded during the manufacturing process by incorporating a large number of magnetic elements of random coercivities into the label. The customer would then read a label before placing it on an item and if that number had not previously been used then it would be attached to the item, and information about the item would be provided to a host computer and coupled to the number of the label. If the number revealed by reading the label was still in use, the label would be returned to the bottom of the stack for later use. This implementation would have greatest utility where labels are used frequently and for a very short duration, such as in package delivery systems or luggage tracking.

Another technique would be to encode the labels at the point of use by incorporating magnetic elements into the label corresponding to the desired code. In this application, a labeling device including a magnetic element dispenser capable of dispensing a number of magnetic elements of different coercivities is employed and then only magnetic elements corresponding to a bit used in a number to be encoded would be embedded into a label. If, for example, the number 91006 were to be encoded into a label, it would only be necessary to dispense and embed eleven magnetic elements of the desired coercivities into the label. The label would then be read as discussed above.

A further embodiment of a magnetically encoded label is shown in Figures 3 and 4. A label 30 includes a number of magnetic elements, for example, six elements, 32a - 32f, of different coercivities. In this example each magnetic element functions as a bit storage element, although it would be desirable to include reference elements as discussed above. Before being encoded, the first magnetic element 32a has a coercivity of, say, 1 oersted; the second magnetic element 32b has a coercivity of 4 oersted; and the third magnetic element 32c has a coercivity of 7 oersted and so on with a separation of three oersted per magnetic element. Further, each magnetic element 32 can be subdivided and encoded as three distinct regions, each having the ability to independently experience a polarity inversion. Consequently, each magnetic element 32 can encode three bits of information. A label therefore would need only six magnetic elements to encode eighteen bits of information in this example, it being recognized that the label could include any number of magnetic elements subdivided into as many separate regions as could be accommodated while still functioning with magnetically bistable characteristics.

The magnetic elements 32 are divided into different regions by assigning them different coercivities within the range of coercivities between the subject magnetic element and the next magnetic element in the binary scale. For example, for the magnetic element 32a, the leftmost region would be assigned a coercivity of 1 oersted, the center region a coercivity of 2 oersted and the rightmost region a coercivity of 3 oersted. To encode the magnetic element 32a to function to produce the binary code "010" as shown in Figure 4, the leftmost and rightmost regions are heated, such as by a modified printer, to a coercivity outside the range of the magnetic field to be applied and the center region is heated to adjust its coercivity to two oersted. Consequently, during reading only the center region will experience a polarity inversion and produce a detectable pulse as discussed above. For the magnetic element 32b to produce the binary code "110," the leftmost region is left untreated at 4 oersted, the coercivity of the center region is heated to 5 oersted and the rightmost region is heated to a coercivity outside the range of the magnetic field to which the label will be subjected. The remaining magnetic elements 32c - 32f would be encoded in a similar manner. The encoded label 30 would then be read as discussed above.

In the foregoing discussion the elements or their portions have been referred to as having definite coercivities (e.g., a portion at 4 oersted). However, it will be appreciated that the elements or portions thereof may have coercivities within a range of coercivities (e.g., between 3.7 and 4.3 oersted). The coercivity ranges of different elements or portions will in general be non-overlapping, and may be of any suitable, practical size.

Turning now to Figure 5, another embodiment, a magnetically encoded label 40, is shown. The label 40 includes a number of non-parallel magnetic elements 42a- 42g, each of which may encode information by their orientations. For example, each of the elements may be oriented at any of 36 angular orientations, at 5 -degree increments over a range of 180 degrees. Thus the amount of information which is encodable in a label is greatly increased when compared with a label without orientation encoding having the same number of elements.

The orientation of the magnetic elements 42a-42g may be relative to the orientation of one or more reference elements. The reference elements of the label 40 may be similar to the reference elements described previously, in that the reference elements of the label 40 may have the highest and lowest values of coercivity from among the elements 42a-42g.

The orientation of the magnetic elements 42a-42g may alternatively be determined by comparing orientations between the elements, without use of a reference element. For example, the orientation of the elements 42a-42g may be determined by comparing the orientation of each of the elements to a "greatest angle" or "big gap" in which none of the elements are oriented. An example of such a scheme of referencing orientations of elements is described in PCT Publication WO 99/35610, the disclosure of which is herein incorporated by reference in its entirety.

The elements 42a-42g may be in a single layer or may alternatively be in multiple layers, and may either overlap or not overlap. The elements 42a-42g may, as suggested from the above discussion, each have a different coercivity. It will be appreciated that combining encoding by different coercivities and encoding by orientation enables encoding of a large amount of information by a relatively small number of elements. Alternatively, it will be appreciated that some or all of the elements 42a-42g may have substantially the same coercivity.

It will be appreciated that the elements 42a-42g may be configured such that they can be selectively negated or nulled (turned "off), using one or more of the methods described earlier.

The elements 42a-42g may be substantially co-planar, with information encoded by the orientation of the elements 42a-42g within a plane. It will be appreciated that the elements 42a-42g may alternatively be otherwise oriented, with one or more of the elements not being co-planar with other of the elements. For example, the substrate may be other than flat, and/or the substrate may be flexible and may be place on a non-planar surface. It will further be appreciated that it may be possible to encode information by placing elements various three-dimensional (non- co-planar) orientations. Such encoding by orienting elements in three dimensions may greatly increase the amount information that may be encoded by a given number of elements.

The labels described above may be read using a tunnel reader system which has a detection zone therein in which a magnetic field is created. The magnetic field may be spatially uniform or spatially nonuniform. A spatially nonuniform field may advantageously be employed to distinguish between labels when multiple labels are present in the detection zone. Drive coils of the reader may produce the time-varying ramping magnetic field described above. Sense coils in the reader may be used to pick up polarity-reversal signals caused by reversal of polarity of the elements. Electromagnetic signals received by the sense coils may be digitized and sent to a computer, with software in the computer used to decode the signals to determine the element coercivities and/or orientations. The software may include an algorithm that solves the appropriate three-dimensional magnetic field equations. Further details regarding software algorithms for decoding orientation-encoded tags may be found in PCT Publication WO 99/35610. One process for a making a multi-bit magnetic label involves a roll fed printing process in which a pressure sensitive base roll is used. The face stock will be printed with the desired press printed graphics. The stock will then be de-laminated prior to integration of the magnetic elements. The exposed face sheet/adhesive will go through the magnetic element integration process, while the liner will bypass this operation. The magnetic elements are first heated prior to incorporation into the label to establish the coercivity of the elements. The magnetic element integration process feeds multiple spools of magnetic elements onto the face sheet with exposed adhesive. Each magnetic element is then cut at the desired length and adhered to the exposed adhesive on the face sheet.

The liner is then brought through a rotary die station and a window may be cut out so that each label has exposed magnetic elements on the adhesive side that can be individually accessed and cut at a later stage. Adhesive is than applied over the magnetic elements on the face sheet and the liner is re-laminated onto the adhesive side of the face sheet. If the liner has a window cut in it then the adhesive will be zoned so that none exists in the area of the liner window. The construction then passes through rotary die stations where the final label shape is cut and the matrix removed. The finished material is finally finished into rolls.

The encoding of each magnetic element or the process of setting a magnetic element to null can be accomplished by heating the element or by cutting a magnetic wire so that it no longer is capable of operating with bistable magnetic properties (or by the other methods of negating or nulling described above). Where the encoding of the magnetic elements is performed through heating, the label can be fed into a modified thermal transfer imprinter.

The process of producing tags is similar to that for producing labels except that two rolls of material are used. The first material is a pressure sensitive roll stock. It is processed substantially the same as the label stock except that the de-laminated liner is discarded. A tag stock is then joined to the pressure sensitive roll stock. It can be printed and a window die cut in it to provide access to the magnetic elements. An imprinting process then puts a laminate over the window after the magnetic elements have been encoded.

A second method for producing a magnetic label involves making rolls of the magnetic label on a press without a liner. In this case an imprinter has full exposure to the entire magnetic element for encoding purposes. The selectively negating or nulling of elements of the label may be performed by an end user of the label (e.g., a purchaser of the label), using one or more of the various methods described above for negating an element (turning the element "off). Although the invention has been shown and described with respect to a certain embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described elements (components, assemblies, devices, compositions, etc.), the terms (including a reference to a "means") used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment or embodiments of the invention. In addition, while a particular feature of the invention may have been described above with respect to only one or more of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application.

Claims

What is claimed is:

1. A device for storing information, comprising: a substrate; and a plurality of magnetic elements coupled to the substrate, the magnetic elements operatively configured to exhibit a detectable response upon the application of a magnetic field of a certain field strength, wherein the magnetic elements are individually, selectively negatable so as to no longer exhibit the detectable response.

2. The device of claim 1, wherein at least one of the magnetic elements has a different coercivity than other of the magnetic elements.

3. The device of claim 1 or claim 2, wherein the magnetic elements have nonuniform orientations.

4. A device for storing information, comprising: a substrate; and a plurality of magnetic elements coupled to the substrate, the magnetic elements operatively configured to exhibit a detectable response upon the application of a magnetic field of a certain field strength; wherein at least one of the magnetic elements has a different coercivity than other of the magnetic elements, and wherein the magnetic elements have nonuniform orientations.

5. The device of claim 4, wherein each of the magnetic elements has a different coercivity.

6. The device of claim 4 or claim 5, wherein the magnetic elements are individually, selectively negatable so as to no longer produce the detectable response.

7. The device of any of claims 1 to 6, wherein one of the magnetic elements is a reference element.

8. The device of claim 7, wherein the reference element has a highest coercivity from among the elements.

9. The device of claim 7 or claim 8, wherein another of the magnetic elements is a further reference element.

10. The device of claim 9, wherein the further reference element has a lowest coercivity from among the elements.

11. The device of any of claims 1 to 10, wherein some of the elements are not co-planar with other of the elements.

12. The device of any of claims 1 to 11, wherein the substrate has a pressure- sensitive adhesive backing thereupon.

13. A method of encoding information on the device of any of claims 1 to 12, the method of encoding comprising selectively negating one or more of the magnetic elements such that the negated elements exhibit a detectable response upon the application of a magnetic field of a certain field strength.

14. The method of claim 13, wherein the negating includes severing one or more of the magnetic elements.

15. The method of claim 13, wherein the negating includes applying a localized high strength magnetic field to one or more of the magnetic elements.

16. The method of claim 13, wherein the negating includes placing material having ferromagnetic properties in close proximity to one or more of the magnetic elements.

17. The method of claim 13, wherein the negating includes shifting the coercivity of one or more of the magnetic elements.

18. The method of claim 17, wherein the shifting includes heating one or more of the magnetic elements.

19. The method of claim 13, wherein the negating includes heating, annealing and/or thermally shocking one or more of the magnetic elements.

20. The method of claim 13, wherein the negating includes breaking, fracturing, and/or removing all or a portion of a coating on each of one or more of the magnetic elements.

21. A method of reading encoded information encoded by the method of any of claims 13 to 20 on a device of any of claims 1 to 12, the method for reading comprising: placing the device in a magnetic field; detecting responses of the magnetic elements of the device to the magnetic field; using the responses to determine the encoded information.

22. The method of claim 21, wherein the magnetic field is a time- varying magnetic field.

23. The method of claim 22, wherein the time-varying magnetic field is a ramped magnetic field.

24. The method of any of claims 21 to 23, wherein the using the responses includes using the responses of one or more of the elements to correct the responses of other of the elements.

25. The method of any of claims 21 to 24, wherein the magnetic field is a spatially nonuniform magnetic field.