Method, system and apparatus for use in article surveillance

An electronic surveillance system marker comprises an active component responsive to incident magnetic energy for causing an associated article surveillance system to render an output alarm and deactivatable, through change in the molecular organization of the active component, without requirement for disruption of the unitary character of the component or change in its chemical composition. The marker component is selected to be of molecularly unorganized, e.g., amorphous, matter and the deactivation step involves molecularly organizing such matter, e.g., by rendering crystalline at least a portion of the component. The amorphous matter is preferably selected to be a metal composition. The deactivation step is desirably practiced by maintaining such portion of the marker component at a temperature above the crystallization temperature of the component and thereby to crystallize a coercive force in the portion different from the coercive force in the remainder of the component. Alternatively, the marker component is selected to have retained stress which is mechanically constrained therein, the deactivation step involving the relieving of such retained mechanical stress.

FIELD OF THE INVENTION 
The present invention relates broadly to article surveillance and more 
particularly to article surveillance systems generally referred to as of 
the magnetic type and to methods and apparatus therefor. 
BACKGROUND AND SUMMARY OF THE INVENTION 
Common to prior art magnetic type article surveillance systems is the 
detection of perturbations induced in an incident magnetic field by an 
article marker in the course of reversal of magnetic polarity of the 
field. Typically, such prior art systems include a magnetic field 
generator, operative to establish an alternating magnetic field in an area 
of interest, i.e., a surveillance control zone, and a receiver operative 
to detect perturbations in the magnetic field which may be induced, 
specifically those of such markers. 
When the marker magnetic material is driven around its hysteresis loop, 
from one polarity to the opposite, as occurs upon its exposure to the 
alternating magnetic field, a signal pulse is produced by the receiver. 
The shape of this pulse is a function of the time it takes to reverse 
polarity, i.e., proceed from one saturation point to the other, or from a 
residual induction point to the reverse saturation point. This time 
element, in prior art systems, is a function of the time rate of change of 
the incident field between levels sufficient to effect such polarity 
reversal. 
The primary prior art effort has been directed to the finding of marker 
magnetic materials with higher and higher permeability and lower and lower 
coercivity, thereby to give rise to increased slope of the transition from 
one polarity to the other, otherwise stated, lesser time for the 
transition. Since the generation of higher order harmonics of sufficient 
amplitude to be readily detectable attends such increased slope, enchanced 
discrimination as against perturbations induced in the magnetic field by 
commonplace objects in the surveillance control zone is thereby 
attainable. With the same purpose in view, prior art systems have looked 
to operation at relatively high frequencies and/or with strong incident 
fields, and the latter is generally sought by establishing narrow 
surveillance control zones to limit the distance from marker to antenna. 
In applicant's view, these efforts have not yielded magnetic markers which 
produce article tags which, in response to a surveillance field 
interrogation, provide a signal sufficiently unique that the marker is 
free from being mimicked by at least some commonplace article. For 
example, certains samples of nickel plating have been observed to produce 
signals, responsively to such magnetic fields, that cause false alarms in 
systems intended to selectively respond to markers containing Permalloy as 
their magnetic matter. 
In the above-referenced related patent application of applicant, 
incorporated herein by this reference thereto, applicant reports the 
inclusion, in magnetic tag markers, of a magnetic material exhibiting a 
reversal of magnetic polarity that occurs in a regenerative fashion, such 
as with a large Barkhausen discontinuity in its hysteresis loop. 
In a specific embodiment, the marker of the referenced related application 
comprises a body of magnetic material having a magnetic hysteresis loop 
with a large Barkhausen discontinuity such that exposure of the body to an 
external magnetic field, whose field strength in the direction opposing 
the instantaneous magnetic polarization of the body exceeds a 
predetermined threshold value, results in a regenerative reversal of the 
magnetic polarization. Quite high harmonics of readily detectable 
amplitude are provided by the marker, as shown and discussed in the 
related application. 
The related application notes, at page 18 thereof, that amorphous metal 
wire, obtained directly from the rapid quench of molten metal, evidences 
the hysteresis loop desired and above discussed. The referenced text notes 
further that the annealing of such wire gives rise to the loss in such 
metal wire of its magnetic discontinuities. 
In one prior art magnetic type system, deactivation of a magnetic marker is 
effected by the inclusion in a marker of first and second separate and 
distinct components of diverse magnetic material, the first serving to 
generate the detectable signal, and the second serving, upon the 
occurrence of certain marker deactivating events, to mask and render 
inoperative the first component. Such masking takes place at a 
deactivation station and is effected by subjecting the composite marker to 
a magnetic field of such strength as to activate the second component. 
Typically, the marker is subject to a magnetic field adapted to provide 
output indication of an alarm condition upon presence of the marker in the 
surveillance zone on the basis of magnetic polarity reversal of the first 
marker component. On the other hand, upon the presence of the article with 
marker in an authorized checkout area preceding the surveillance zone, one 
can deactivate the marker by disposing the same in a magnetic field of 
character activating the second component that in turn changes the 
magnetic response of the first marker component. 
Another prior approach to makrer deactivation involves the formation, in a 
resonant frequency marker printed circuit, of a fusible link, i.e., a 
portion of lessened cross-section than the remaining marker printed 
circuitry, and the disrupting of the link by exposing the marker to 
increased field energy sufficient to disrupt the integrity of the link. 
Whereas the marker was of reasonant frequency for alarm activation prior 
to the link disruption, it becomes otherwise upon that event, and passes 
freely through the surveillance control zone. 
The deactivation schemes of the referenced prior art have evident 
disadvantage, the former in its requirement for plural separate 
components, respectively for activation and deactivation of the marker, 
and the latter in its requirement for fusible link formation in the marker 
printed circuit. 
The present invention has as its primary object the provision of improved 
system, method and apparatus for the detection of unauthorized marker 
presence in a surveillance control zone and deactivation thereof at 
locations preceding entry into such control zone. 
A more particular object of the invention is to provide for improved 
deactivation method and apparatus for magnetic markers in article 
surveillance systems. 
In attaining the foregoing and other objects, the invention provides, in 
its product aspect, an electronic surveillance system marker which may 
comprise a unitary active component responsive to incident magnetic energy 
for causing an associated article surveillance system to render an output 
alarm, the marker being adapted to be deactivated through change in the 
molecular organization of the active component, without requiring 
disruption of the component or change in its chemical composition. 
In its method aspect, the invention provides for deactivating an article 
surveillance marker such as of type having an active component responsive 
to incident magnetic energy for causing an associated article surveillance 
system to render an output alarm, the method including a step of modifying 
the molecular organization of the active component. 
In a further aspect, the invention provides an electronic article 
surveillance system operative with an article marker such as of type 
comprising a component responsive to incident magnetic energy for causing 
an associated article surveillance system to render an output alarm, the 
marker being adapted to be deactivated through change in the molecular 
organization of its active component, such system comprising transmitting 
means for establishing an alternating magnetic field in a control zone of 
interest, receiving means for detection in said control zone of the 
presence of such marker if same is not deactivated, and means for 
deactivating such marker through such molecular organizational change. 
Turning more particularly to the preferred products, methods and systems of 
the invention, the marker active component is selected to be of 
molecularly unorganized, e.g., amorphous matter, provided such as by metal 
wire obtained directly from the rapid quench of molten metal and having 
dimensions below discussed. In one product aspect, the marker is used in 
such unannealed state as a surveillance device. The deactivation step 
involvles molecularly organizing such matter, e.g., by rendering 
crystalline at least a portion of the component. Such deactivation step is 
desirably practiced by maintaining such portion of the marker component at 
a temperature above the crystallization temperature of the component and 
thereby to crystallize a coercive force in that portion different from its 
previous coercive force. 
In a preferred embodiment, the marker deactivating means of systems of the 
invention modifies the molecular organization of the marker component by 
including an electric current supply for selective electrical connection 
to at least a portion of the marker component and providing such current 
level therein as to maintain the portion of the marker component at a 
temperature above the crystallization temperature of the component, 
thereby to crystallize such coercive force in the portion different from 
its previous coercive force. Radiant energy may also be employed in this 
deactivating practice. 
Alternatively, the marker active component has stress mechanically induced 
therein, as by annealing wire in twisted state and constraining same in 
untwisted form following cooling. Stress-relieving deactivation here 
involves the relieving of such retained mechanical stress, as by releasing 
the constraint on the active component. In this instance, the deactivating 
means may impart mechanical force or radiant energy to the marker 
component. 
The foregoing and other objects and features of the invention will be 
further understood from the following detailed discussion of preferred 
embodiments and practices thereof and from the drawings wherein like 
reference numerals identify like parts throughout.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS AND PRACTICES 
Referring now to FIG. 1, a typical prior art marker designated generally by 
the reference numeral 10, is shown as consisting of a substrate 11 and an 
overlayer 12 between which is sandwiched and concealed a length of ribbon 
13 of high permeability magnetic material. The undersurface of substrate 
11 can be coated with a suitable pressure sensitive adhesive for securing 
the marker to an article to be maintained under surveillance. 
Alternatively, any other known arrangement can be employed to secure the 
marker to the article. By way of example, ribbon 13 may be formed from 
4-79 Molybdenum Permalloy 0.100 inches wide, 0.001 inches thick, and 3.0 
inches long. Material coercivity, H.sub.c, may be 0.05 oersteds, and 
permeability at one hundred hertz may be from 45,000 to 55,000. 
The hysteresis loop or curve of ribbon 13 is shown in rather general terms 
in FIG. 2. No attempt has been made to draw the loop to any type of scale 
or in scale proportions for such curve would appear very tall along the B 
axis and very narrow along the H axis. What is significant is that the 
curve between the knee at 14 and positive saturation at 15, as well as 
from the knee 16 down to the negative saturation point at 17, has a finite 
slope less than infinite. In order to reverse the magnetic polarity of 
ribbon 13, it is necessary to subject it to an external field of at least 
Hm to bring the material to at least its maximum induction point 18. The 
speed with which this can be accomplished is a direct function of the rate 
of change of the incident magnetic field, and the rate of change is 
proportional to both the frequency and the peak amplitude of such incident 
field. 
Another composition for the prior art marker under discussion is "Metglas" 
ribbon, 0.070 inches wide and 3.0 inches long, particularly "Metglas" 
strip/2826MB2, having a maximum permeability of 180,000, a coercivity of 
0.035 oersteds, and a saturation magnetization of 9,000 Gauss. 
Referring to FIG. 3, there is shown a marker 20 in accordance with the 
invention and having substrate 21 and overlayer 22 that can be the same as 
the components 11 and 12 above discussed in FIG. 1, and can be attached to 
an article in similar fashion. However, instead of ribbon 13, the active 
element in the embodiment of FIG. 3 is a length of unannealed amorphous 
metal wire 23. By way of example, marker 20 may be approxiamtely 7.6 cm. 
(three inches) in length, with a diameter of 0.125 mm., and its 
composition essentially satisfying the formula Fe.sub.81 Si.sub.4 B.sub.14 
C.sub.1, where the percentages are in atomic percent. These parameters 
should be considered only as representing one example for purposes of 
explanation since, as will appear from the ensuing discussion, the 
diameter can range between 0.09 and 0.15 mm. while the length can range 
between about 2.5 and 10 cm. for use as a surveillance marker. The 
demagnetizing factor for the length of wire 23, preferably does not exceed 
0.000125. At present, however, the dimensions of the above sample are 
preferred for the wire 23. 
The particular wire used for the element 23 is identified by a 
discontinuous hysteresis characteristic, preferably by a large Barkhausen 
discontinuity, such that when the magnitude of an incident field of 
appropriate direction relative to the magnetic polarity of the wire 
exceeds a low threshold value, in this case substantially less than 1.0 
oersted, the magnetic polarity of the wire will reverse regeneratively, 
independent of any further increase in the incident field, up to its 
maximum induction point. The threshold for the above sample is actually 
less than 0.6 oersted. 
The nature of the hysteresis loop is shown in FIG. 4. Again, the scale and 
proportions in FIG. 4 are grossly distorted from reality for the sake of 
convenience in explanation. Thus, the magnetizing field from the negative 
residual induction point 24 to the threshold point 25 is less than 1.0 
oersted. Once the magnetizing field exceeds the threshold value for the 
sample, there occurs an abrupt regenerative reversal of the polarity, 
represented by the broken line segment 26 of the hysteresis loop, until 
the maximum induction point 27 is reached. If the magnetizing field 
continues to increase above the threshold point, the flux density will 
increase toward the positive saturation point 28. Otherwise, the element 
23 will head toward its positive residual induction point 29 as the 
magnitude of the magnetizing field approaches zero, and will remain there 
until the magnetizing field departs from zero. If the magnetizing field 
now increases in the negative direction, the flux density will follow the 
stable portion of the loop to the negative threshold point 30 from which 
it shifts regeneratively and substantially instantaneously along the 
broken line segment 31 to the negative maximum induction point 32 and then 
to a point between saturation at 33 and threshold 25 as a function of the 
magnetizing field. 
Change in the magnetic polarity of wire 23 between either points 25 and 27 
or 30 and 32 occurs independently of the rate of change of the magnetizing 
field. All that is required for such change is that the magnetizing field 
exceed the threshold level of the particular wire element 23. 
The above-mentioned sample of wire 23 was 7.6 cm. long. It has been found 
that varying the length over the mentioned range will influence the 
hysteresis loop by changing the slope of the portions 28-30 and 33-25, 
shown in solid lines. As the wire is made shorter, the aforementioned 
slope will increase, while as the wire is made longer, the slope in 
question will decrease. Changing the aforesaid slope will alter the 
sharpness of a receiver output pulse. Generally, it is the sensitivty and 
selectivity of the surveillance system in which the marker is to operate 
that determines what pulse wave shapes can be tolerated, and, therefore, 
the wire length can be shortened subject to the constraints of the 
detection system. That is, wire 23 must be long enough to produce a pulse 
of sufficient amplitude that it can be detected by the detecting system. 
The material of wire 23 may be used to produce a ribbon of amorphous metal 
such as is shown in FIG. 5. The ribbon designated 35 in FIG. 5, can be 
produced by any known method for rapidly quenching molten metal to avoid 
crystallization. Starting with a ribbon about 2 mm. wide and about 0.025 
mm. thick and between 3.0 and 10.0 cm. long, it should be twisted up to 
four turns per ten centimeters and annealed while so twisted, the 
annealing being performed at about 380 degrees Centigrade for about 
twenty-five minutes, i.e., at a temperature less than the crystallization 
temperature. When cool, the ribbon should be untwisted and laminated in 
mechanically constrained manner within substrate and overlayer in a flat 
condition similar to that shown in FIG. 1. The flattened ribbon will have 
locked in stresses providing a helical easy axis of magnetization and 
giving rise to the subject discontinuities. In other words, the ribbon or 
strip should have stress induced magnetic discontinuity when restrained in 
flattened condition. 
The dependency of prior art markers on time rate of change of the incident 
field has led prior workers in the article surveillance field toward the 
use of higher and higher frequencies. However, because of the unique 
qualities of markers according with the invention, there is an advantage 
to be obtained from resorting to lower rather higher excitation 
frequencies. This follows from the fact that since the subject markers are 
relatively insensitive to the rate of change of the incident field, the 
suject markers respond well to very low frequency excitation. However, the 
low frequency, coupled with the same low field strengths as used 
heretofore, gives rise to smaller rather than larger rates of change of 
field, and this causes responses from Permalloy or other similar magnetic 
marker materials to become less rather more readily detectable. In this 
connection, it has been found that the wire marker described above with 
reference to FIG. 3 will produce a signal pulse of less than four hundred 
microseconds duration when excited by a 1.2 oersted field at twenty hertz. 
Consequently, the wire of the invention is easily detected while prior art 
markers are essentially invisible to the same interrogation field. 
Amorphous metal has been known for use in surveillance markers. However, to 
the extent that information is available, it has been uniform practice by 
the manufacturers of surveillance marker material to subject the metal to 
a final, stress-relieving, annealing step to improve the mechanical 
parameters of the product. Such stress-relieving annealing would eliminate 
any large Barkhausen discontinuities that might have existed in the 
hysteresis loop of the element and lose herein desired magnetic 
characteristics, if it were of type discussed herein, e.g., amorphous 
metal wire obtained directly from the rapid quench of molten metal and of 
desired dimensions. In accordance with the invention, such wire or the 
annealed mechanically-stressed ribbon of FIG. 5 is used, without having 
its stress relieved, as surveillance tag material and thereafter is 
deactivated by relieving such stress. 
In the course of deactivation of an amorphous material marker in accordance 
with the invention, the unitary character of its active component, wire 23 
or ribbon 35, can be maintained and the chemical composition of the 
component persists unchanged. There occurs, however, a change in the 
molecular organization of the entire active component or a portion 
thereof. Thus, the entire marker active component or the portion thereof 
subjected to temperature elevation through current flow becomes 
molecularly ordered, i. e., is rendered crystalline. The remainder of the 
component remains molecularly unorganized, i. e., amorphous. The magnetic 
perfomance character of the marker is accordingly modified from that 
existing prior to deactivation, in effect, being transformed from a single 
active component into two active subcomponents separated from one another 
by the crystallized portion. The practice preferably is by use of a fast 
pulse of current which flash anneals, locally crystallizing a high 
coercive force band across the active component in contrast to the low 
coercive force prevailing in the remnant amorphous regions of the active 
component. As noted above, the entirety of the active component may be 
crystallized, in which case the coercive force prevailing throughout the 
component differs from its previous coercive force. 
Deactivation in the case of the FIG. 5 type device can be achieved by 
annealing above the crystallization temperature of its material, or by 
mechanical input thereto directly or indirectly. In the latter instance, 
shrinkable jacketing for the material may be heated to impart 
stress-relieving force to the marker material. 
While amorphous metal is presently preferred in practice of the invention, 
the invention contemplates use of any material with which the mentioned 
performance parameters can be obtained. 
Satisfactory results have been obtained with amorphous wire markers having 
the following compositions: 
(a) Fe.sub.81 Si.sub.4 B.sub.14 C.sub.1 ; 
(b) Fe.sub.81 Si.sub.4 B.sub.15 ; and 
(c) Fe.sub.77.5 Si.sub.7.5 B.sub.15 
However, it is believed that a wide range of such materials can be used, 
all falling within the general formula: Fe.sub.85-x Si.sub.x B.sub.15-y 
C.sub.y, where the percentages are in atomic percent, x ranging from about 
three to ten and y ranging from about zero to two. 
The system of the invention is shown in block diagram in FIG. 6. A control 
or surveillance zone, e.g., an exit area of a store, in indicated by 
broken lines at 36 and an article marker 37 of the above-discussed types 
is shown in control zone 36. The transmitter portion of the system 
includes frequency generator 38, the output of which is applied over line 
39 to adjustable attenuator 40. the attenuator output, namely a desired 
level of the output of frequency generator 38, is applied over line 41 to 
field generating coil 42, which accordingly establishes an alternating 
magnetic field in control zone 36. 
The receiving portion of the system of FIG. 6 includes field receiving coil 
43, the output of which is applied over line 44 to receiver 45. When the 
receiver detects harmonic content in signals received from coil 43 in a 
prescribed range, the receiver furnishes a triggering signal over line 46 
to alarm unit 47. 
Marker 48 is shown at a location outside of control zone 36 and accordingly 
not subject to the field established in zone 36. An authorized checkout 
station includes marker deactivation unit 49 of the FIG. 6 system. A 
marker to be deactivated is introduced along path 50 into the deactivation 
unit and issued therefrom as deactivated marker 51, which now may pass 
freely through control zone 36 without acting upon the field therein in 
manner triggering alarm unit 47. 
A first embodiment of deactivation unit is shown in FIG. 7 as including an 
electrical power supply 52 having one output terminal grounded and a 
second output terminal connected through resistor 53 and capacitor 54 to 
ground. The supply, resistor and capacitor are selected to provide the 
desired output current pulse over line 55 when loaded by marker 56, shown 
in section and comprising the above-mentioned layers 21 and 22 and either 
wire 23 or ribbon 35. Insulation-piercing contacts 57 and 58 are provided, 
the former being connected to line 55 and the latter grounded. The 
capacitor will thus discharge into portion P of marker 56, elevating same 
to a temperature above the stress-relief temperature of the material 
comprising the marker active component. 
A variation from the FIG. 7 deactivation unit is shown in FIG. 8. Her, the 
invention looks to preconditioning the marker for localized 
crystallization. Laser 59 has its output directed onto the portion of the 
marker 56 intended to be crystallized. The resultant local heating of the 
marker portion gives rise to an increase in the electrical resistivity of 
the portion. Upon application of electrical current thereafter to the 
marker active component, as long as contacts 57 and 58 straddle the 
preconditioned portion, the current induced heating will be localized at 
the portion of higher resistance and hence crystallization will be 
confined to a narrow range along the component. Where desired, full 
crystallization may be effected through the use of radiant energy, without 
subsequent application of current. 
The deactivator embodiment of FIG. 9 is particularly useful for markers of 
type having locked-in stress. Here, the marker active component 35 is 
confined within heat-shrinkable laminates 60 and 61. Upon application of 
heat to the laminates from heating gun 62, the laminates shrink from their 
illustrated dimensions, thereby relaxing their constraint upon component 
35 and permitting the component to relax and to have its locked-in stress 
released. The resulting marker has vastly different magnetic response 
characteristics since its stress-induced magnetic discontinuity is no 
longer present. It will be understood that the release of locked-in stress 
may be achieved by other mechanical arrangements. 
As noted above, in making markers of type having stress-induced magnetic 
discontinuity, an annealing step is employed at temperature level below 
the material crystallization temperature. Accordingly, the material 
retains its amorphous character to the point of deactivation, and the 
embodiments of FIGS. 7 and 8 also apply for deactivation of this type of 
marker. 
While the practices above discussed for deactivation have involved a change 
in the molecular organization of the marker active component, with the 
separation of the component into subcomponents of a body which remains 
unitary throughout the deactivation, the invention contemplates that one 
can actually cause physical separation of the component into separate 
bodies by use of the capacitor discharge of the FIG. 8 showing. the 
invention thus may be practiced by effecting molecular organization change 
in the course of deactivation involving additional effects, such as 
subsequent unitary body disruption. It is to be appreciated, however, that 
such dispuption is not required for deactivation, but may occur following 
modification of molecular organization, e.g., where the flash deactivation 
current pulse is of level sufficiently high to disrupt the unitary body 
after causing such change in molecular organization. Further, the 
invention contemplates deactivation of surveillance tag markers by 
modification of molecular organization as between surveillance use state 
and deactivation state irrespective of the magnetic character exhibited by 
the marker during surveillance use, e.g., markers subject to deactivation 
by molecular reorganization and not exhibiting large Barkhausen 
descontinuities. 
Various changes in structure and modifications in method may be introduced 
in the foregoing without departing from the invention. Accordingly, it is 
to be appreciated that the particularly depicted and described preferred 
embodiment and practices are intended in an illustrative and not in a 
limiting sense. The true spirit and scope of the invention is set forth in 
the following claims.