Note: Descriptions are shown in the official language in which they were submitted.
DESCRIPTION
AMC)RPHOUS AMTIPILFERAGE MARKER
BACKGROUND OF THE INVENTION
1. Field of the Inventlon
This invention relates to antipilferage
systems and markers for use therein. More particularly,
the invention provides ductile, amorphous metal markers
that enchance the sensitivity and reliability of the
antipilferage system. The markers contain lower pro-
portions of costly and stategic metals.
2. Description of the Prior Art
Theft of articles such as books, wearing
apparel, appliances and the like from retail stores and
state-funded institutions is a serious problem. The
cost of replacing stolen articles and the impairment of
services rendered by institutions such as libraries
exceeds $6 billion annually and is increasing.
Systems employed to prevent ~heft of articles
generally comprise a marker element secured to an object
to ~e detec~ed and instruments adapted to sense a signal
produced by the marker upon passage thereof through an
interrogation ~one~
One of the major problems with such theft
detection systems is the low signal level produced by
the marker. This limits the sensitivity and reliability
of the theft detection system~ Ancther problem is the
dificulty of preventing degradation of the maker signal.
If the marker is broken or bent, the signal can be lost
or altered in a manner that impairs its identifying
6~6
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characteristics. Such bending or breaking of the marker
can occur inadvertently during manufacture of the marker
and subsequent handling of merchandise by employees and
~ustomers, or purposely in connection with attempted
theft of goods. The present invention is directed to
overcoming the foregoing problems.
SUMMARY OF THE INVENTION
.
BrieEly stated, the invention provides an
amorphous ferromagnetic metal marker capable of produc-
ing identifying signal characteristics in the presenceof an applied magnetic field. The marker comprises an
elongated, ductile strip of amorphous ferromagnetic
material having a composition consisting essentially of
the formula FeaCrbccPdMoecufB9sih where "a" ranges from
about 63-81 a~om %, "b" ranges from about 0-10 atom ~,
~c" ranges from about 11-16 atom %, "d" ranges from
about 4-10 atom %, "e~ ranges from about 0-2 atom ~,
"f " ranges from about 0-1 atom ~, 119~ ranges from about
0-4 atom % and "i" ranges from about 0-2 atom %, with
the proviso that the sum (c~d+g~h) ranges from 19-24
atom % and the fraction [c/(c~d-~g+h)] is less than
about 0.84.
The marker is capable of producing magnetic
fields at fre~uencies which are harmonics of the
frequency of an incident field. Such frequencies have
selected ~ones that provide the marker with signal
identity. A de~ecting means is arranged to detect
magnetic field variations at selected tones of the
harmonics produced in the vicinity of the interrogation
zone by the presence of the marker therewithin. The
marker retains its signal identity after being flexed
or bent. ~s a result, the theft detection system is
more reliable in operation than system wherein signal
degradation is effected by bending or flexing of the
marker. Further, ~he marker contains no costly and
strategic metals such as nickel or cobalt.
BRIE~ DESCRIPTION OF THE DRAWINGS
The invention will be more fully understood
and further advantages will become apparent when
reference is made to the following detailed description
of the preferred embodiment of the invention and the
accompanying drawings in which:
FIG~ 1 is a block diagram of a magnetic theft
detection system incorporating the present invention;
FIG. 2 i~ a diagrammatic illustration of a
typical 6tores installation of the system of Fig. l;
: 3 FIG. 3 is an isomeric view of a marker adapted
for use in the system of Fig. l;
FIG. 4 is an isomeric view of a desensitizable
marker adapted for use in the system of Fig. l; and
FIG. 5 is a schematic electrical diagram of a
harmonic signal amplitude ~est apparatus used to measure
the signal retention capability of the amorphous ferro-
magnetic metal marker of this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to Figures 1 and 2 of the drawings,
there is shown a magnetic theft detection system 10
responsive to the presence of an article within an
interrogation zone. The system 10 has means for de-
fining an interrogation zone 12. A field generating
means 14 is provided for generating a magnetic field
within the interrogation zone 12. A marker 16 is
secured to an article 19 appointed for passage through
the interrogation zone 12. The marker comprises an
elongated, ductile strip 18 of amorphous, ferromagnetic
metal having a composition consisting essentially of
ula FeacrbccpdMoecufBgsih where ~a~ ranges from
30 about 63-81 atom %, "b" ranges from about 0-10 atom %,
"c" ranges from about 11-16 atom %, "d" ranges from
about 4-10 atom ~, "e" ranges from abou~ 0--2 atom %,
"f" ranges from about 0~1 atom %, llgll ranges from about
0-4 atom % and "i" ranges from about 0-2 atom ~, with
the proviso that the sum (c+d+g+h) ranges from 19-24
atom % and the fraction [c/lc~d~g+h)] is less than
about 0~84.
The marker is capable of producing magnetic
fields at f~equencies which are harmonics of the
frequency of an incident field. Such frequencies
have selected tones that provide the marker with signal
identity. A detecting means 20 is arranged to detect
magnetic field variations at selected ~ones of the
harmonics produced in the vicinity of the interrogation
zone 12 by the presence of marker 16 therewithin.
Typically, the system 10 includes a pair of
coil units 22, 24 disposed on opposing sides of a path
! 10 leading to the exit 26 of a store. Detection circuitry,
including an alarm 28, is housed within a cabinet 30
located near the exit 26. Articles of merchandise 19
such as wearing apparel, appliances, books and the like
are di~played within the store. Each of the artlcles
19 has secured thereto a marker 16 constructed in
accordance with the present invention. The marker 16
includes an elongated, ductile amorphous ferromagnetic
strip 18 that is normally in an activated mode. When
marker 16 is in the activated mode, placement of an
article 19 between coil units 22 and 24 of interrogation
zone 12 will cause an alarm to be emitted from cabinet
30. In this manner, the system 10 prevents unauthorized
- removal of articles of merchandise 19 from the store.
Disposed on a checkout counter near cash reg-
ister 36 is a deactivator system 38. The latter is
electrically connected to cash register 36 by wire 40.
Articles 19 that have been properly paid for are placed
within an aperture 42 of deactivation system 38, where~
upon a magnetic field similar ~o that produced by coil
units 22 and 24 of interrogation zone 12 is applied to
marker 16. The deactivation system 38 has detection
circuitry adapted to activate a gaussing circuit in
response to harmonic signals generated by marker 16.
The gaussing circuit applies to marker 16 a high mag-
netic field that places the marker 16 in a deactivated
mode. The article 19 carrying the deactivated marker 16
may then be carried through interrogation zone 12
without triggering the alarm 2B in cabinet 30O
- s -
The theft detection system circuitry with
which the marker 16 is associated can be any system
capable of (1) generating within an interrogation zone
an incident magnetic field, and (2) detecting magnetic
field variations at 6elected harmonic frequencies pro-
duced in the vicinity of the interrogation zone by the
presence of the marker therewithin. 5uch systems
typically include means for transmitting a varying
¦, electrical current from an oscillator and amplifier
through conductive coils that form a frame antenna
capable of developing a varying magnetic field. An
example of such antenna arrangement is disclosed in
French Patent 763,681, published May 4, 1934, which
description is incorporated herein by reference thereto.
lS In accordance with a preferred embodiment of
the invention, an amorphous ferromagnetic metal marker
is provided. The marker is in the form of an elongated/
ductile s~rip having a composition consisting essential-
ly of the formula FeaCrbCcPdMoeCufBgSih where "a" ranges
from about 63~81 atom ~, "b" ranges from about 0-10 atom
%,"c" ranges from about 11-16 atom ~, "d" range~ from
about 4-10 atom %, "e" ranges from about 0-2 atom %,
"f" ranges from about 0-1 atom ~, "g" ranges Erom about
0-4 atom % and "i" ranges from about 0-2 atom ~, with
the proviso that the sum (c+d+g+h) ranges from 19-24
atom ~ and the fraction [c/(c+d+g+h)] is less than
about 0.84.
The marker is capable of producing ma~netic
fields at frequencies which are harmonics of the
frequency of an incident field
Examples of amorphous ferromagnetic marker
compositions within the scope of the inve~tion are
set forth in Table I below:
~ Ei9~
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TABLE X
COMPOSITION PERCENT
Fe Cr Mc~ C~ C P B Si
1 Atom % 73025 6 0.25 0 13 7 0.5 0
Weight % 85.14 6.49 0.50 0 3.25 4.51 0.11 0
2 Atam % 73.25 6 0.25 0 15 5 0.5 0
Weight ~ 85.81 6.55 0.50 O 3.78 3.25 0.11 O
3 ~tom % 71.25 ~ 0.25 O 13 7 0.5 O
Weight % 82.94 8.67 OD50 O 3.25 4.52 0.11 O
4 Atc~n % 71.25 8 0~25 0 15 5 0.5 0
~eight % 83.60 8.74 0.50 O 3.78 3.25 0.11 O
Atcm % 73.5 6 1.0 0 13 7 0.5 0
W~ight % 83.92 6.38 1.96 0 3.19 4.43 0.11 0
6 Atom % 73.5 6 1.0 0 15 5 0.5 0
W~ight % 84.58 6.43 1.98 0 3.71 3.19 0.11 0
7 Atom % 70.5 8 1.0 0 13 7 0.5 0
Weight % 81.56 8.62 1.99 0 3.23 4.49 0.11 0
8 ~tom % 70.5 8 1.0 O 15 5 0.5 O
We.ight % 82.20 8.69 2.00 O 3.76 3.23 0.11 O
9 Atan % 79 0 0 0 13 4 2 2
Wei~ht ~ 92.5 O O O 3.27 2.60 0.45 1.8
- 10 Atom % 73.15 6 0.25 0.1 15 5 005 0
Weight % 85.68 6.54 0.50 0.13 3.78 3.25 0.11 O
11 Atcm % 71.0 10 0 0 14 4.5 0.5 0
Weight % 82.64 .10.84 0 0 3.50 2.90 0~11 O
12 Atar % 71.5 6 2 0 15 5 0.5 0
Weight % 82055 6.45 3.97 O 3.72 3.20 0.11 0
l 30
Examples of amorphous metallic alloys that
have been found suitable for use as a magnetic theft
detection system marker but which are outside the
scope of this invention and are set Eorth in Table
II below:
TABLE II
COMPOSIT _N PERCENT
Fe Co Ni Mo _ P Si
Fe-Ni-Mo-B Atom % 40 - 40 2 18 - -
We.ight% 45 - 47 4 4
Fe-Ni-P-B Atom % 39.2 - 40.2 - 6.2 14.4 -
Weight % 43.23 - 46.62 - 1.32 8.83 -
Fe-Ni-B Atom % 40 - 40 - 20
Weight % 46.6 - 48.9 - 4.5 -
Fe-B Atom % 79.7 - - - 20.3 - -
Weight % 95.38 - - - 4.62 -
Fe-Mo-B Atom % 77.5 - - 2.520
Weight % 90.47 - - 5.01 4.52 -
Co-FeiMo- Aton % 5.5 67.5 - 2 12 - 13
B-Si Weight % 6.19 80 - 3.86 2.61 - 7.34
Examples of amorphou.s me*al alloys that have
been found unsuitable for use as a magnetic theft detec-
tion system are set forth in Table III below:
'l~i'
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TABLE III
Composition Percent
Example 1 Example 2
Ni Atom % 71.67 Ni Atom % 65.63
Weight % 84.40 Weight % 76.97
Cr Atom % 5.75 Cr Atom % 11~55
Weight % 6 Weight % 12.0
B Atom ~ 12.68 B Atom % 11.58
Weight % 2.75 Weight % 2.5
Si Atom ~ 7.10 Si Atom % 7.13
, 10Weight % 4 Weight % 4
Fe Atom ~ 2.23 Fe Atom % 3.14
Weight ~ 2.5 Weight % 3.5
C Atom % .25 C Atom ~ .12
Weight % .06 Weight % .03
P Atom % .032 P Atom %
Weight ~ .02 Weight %
S Atom % .031 S Atom %
Weight % .02 Weight ~ -
Al Atom % .093 Al Atom %
Weight % .05 Weight %
- Ti Atom ~ .052 Ti Atom %
Weight % .05 Weight %
Zr Atom ~ .027 Zr Atom %
Weight % .05 Weight ~ -
Co Atom % .085 Co Atom % .85
Weight ~ .1 Weight % 1.0
The amorphous ferromagnetic metal marker of
the invention is prepared by cooling a melt of the
desired composition at a rate of at least about 105C/
sec, employing metal alloy quenching techniques well-
known to the glassy metal alloy art; see, e.g., U.S.
Patent 3,856,513 to Chen et al. The purity of all
compositions is that found in normal commercial
practice.
A variety of techniques are available for
fabricating continuous ribbon, wire, sheet, etc. Typi-
cally, a particular composition is selected, powders or
granules of the requisite elements in the desired por-
tions are melted and homogeni~ed, and the molten alloy
is xapidly quenched on a chill surface, such as a
rapidly rotating metal cylinder, a rapidly moving metal
- 9 -
belt or the like.
Under these quenching conditions, a meta-
stable, homogeneous, ductile material is obtained. I'he
metastable material may be glassy, in which case there
is no long-range order. X-ray diffraction patterns of
glassy metal alloys show only a diffuse halo, similar
to that observed for inorganic oxide glasses. Such
glassy alloys must be at least 50~ glassy to be suffi-
ciently ductile to permit subsequent handling, such as
stamping complex marker shapes from ribbons of the
alloys without degradation of the marker's signal iden-
tity. Preferably, the glassy metal marker must be at
least 80% glassy to attain superior ductility.
The metastable phase may also be a solid solu-
tion of the constituent elements. In the case of themarker of the invention, such metastable, solid solution
phases are not ordinarily produced under conventional
processing techniques employed in the art of fabricating
crystalline alloysO X-ray diffraction patterns of the
solid solution alloys show the sharp diffraction peaks
characteristic of crystalline alloys, with some broaden-
ing of the peaks due to desired fine-grained size of
crystallites. Such metastable materials are also duc-
tile when produced under the conditions described above.
The marker of the invention is advantageously
produced in foil (or ribbon) form, and may be used in
theft detection applications as cast, whether the
material is glassy or a solid solution. Alternatively,
foils of glassy metal alloys may be heat treated to
obtain a crystallilne phase, preferably fine-grained, in
order to promote longer die life when stamping of com-
plex marker shapes is contemplated. Markers having par-
tially crystalline, partially glassy phases are parti-
cularly s~ited to be desensitized by a deactivation
system 38 of the type shown in Fig. 2~ Totally amor-
phous ferromagnetic marker strips can be provided with
one or more small magnetiæable elements 44. Such ele-
ments 44 are made of crystalline regions of ferromagne-
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tic material having a higher coercivity than thatpossessed by the strip 18. Moreover, totally amorpho~s
marker strip can be spot welded, heat treated with
coherent or incoherent radiation, charged particle
beams, directed flames, heated wires or the like to
provide the strip with magnetizable elements 44 that are
integral therewith. Further, such elements 44 can be
integrated with strip 18 during casting thereof by
selectively altering the cooling rate of the strip 18.
Cooling rate alteration can be effected by quenching
the alloy on a chill surface that is slotted or contains
hea~ed portions adapted to allow partial crystallazation
during quenching. Alternatively, alloys can be selected
that partially crystallize during casting. The ribbon
thickness can be varied during casting to produce
crystalline regions over a portion of strip 18.
Upon permanent magnetization of the elements
44, their permeability is s~bstantially decreased~ The
magnetic fields associated with such magnetization bias
the strip 18 and thereby alter its response to the mag-
netic field extant in the interrogation zone 12. In the
activated mode, the strip 18 is unbiased with the result
that the high permeability state of strip 1~ has a pro-
nounced effect upon the magnetic field applied thereto
by field generating means 14. The marker 16 is deacti-
vated by magnetizing elements 44 to decrease the effec-
tive permeability of the strip 18. The reduction in
per~neability significantly decreases the effect of the
marker 16 on the magnetic field, whereby the marker 16
loses its signal identity (e.g., marker 16 is less able
to distort or reshape the field). Under these condi-
tions, the protected articles 19 can pass through
interrogation zone 12 without triggering alarm 28.
The amorphous ferr~magnetic mar~er of the
present invention is e~ceedingly ductile. B~ d~ctile is
meant that the strip 18 can be bent to a bend diameter
less than 35 mils. The term ~'bend diameter" is defined
as D=S-2T, where D is the bend diame~er in mils, S is
the minimum spacing between micrometer anvils within
which a ribbon may be looped without breakage and T is
the ribbon thickness. Such bending of the marker pro-
duces little or no degradation in magnetic harmonics
generated by the marker upon application of the inter-
rogating magnetic field thereto. As a result, the
marker retains its signal identity despite being flexed
or bent during (1) manufacture (e7g., cutting, stamping
or otherwise forming the strip 18 into the desired
length and configuration) and, optionally, applying hard
magnetic chips thereto to produce an on/off marker, (2)
application of the marker 16 to the protected articles
19, (3) handling of the articles 19 by employees and
customers and (4) attempts at signal destruction
designed to circumvent the system 10.
Generation of harmonics by marker 16 is caused
by nonlinear magnetization response of the marker 16 to
an incident magnetic field. High permeability - low
coercive force material such as Permalloy, Supermalloy
and the like produce such nonlinear response in an
amplitude region of the incident field wherein the mag-
netic field strength is sufficiently great to saturate
the material. ~morphous ferromagnetic materials have
nonlinear magneti~ation response over a significantly
greater amplitude region ranging from relatively low
magnetic fields to higher magnetic field values
approaching saturation. The additional amplitude region
of nonlinear magnetization response possessed by
amorphous ferromagnetic materials increases the magni-
tude of harmonics generated by, and hence the signalstrength of, marker 16, This feature permits use of
lower magnetic fields, eliminates false alarms and
improves detection reliability of the system 10.
The following examples are presented to pro-
vide a more complete understanding of the in~ention.The specific techniques, conditions, materials and
reported data set forth to illustrate the principles
and practice of the invention are exemplary and should
-12-
not be construed as limiting the scope of the invention.
EXAMPLE I
In order to demonstrate quantitatively the
improved harmonic generation of the amorphous antipil-
ferage marker of the invention, elongated strips corn-
posed of ferromagnetic amorphous and crystalline
materials were prepared. The strips ~7ere evaluated to
determine their signal strength before and after flexure
using a harmonic signal amplitute test apparatus 100.
A schematic electrical diagram of the test apparatus
100 is shown in Fig. 5. The apparatus 100 had an oscil-
lator generator 101 for generating a sinusoidal signal
at a frequency of 2.5 KHz. Oscillator generator 101
drove a power amplifier 102 connected in series with an
applied field coil 104 through a sampling resistor 106.
The current output of amplifier 102 was adjusted to
produce a magnetic field of 1.0 Oersted within applied
field coil 104. The voltage, V, across sampling
resistor 106 was measured by digital voltmeter 100, and
the current, I, in the coil 2 was calculated from Ohms
Law, I = V/R. A dc 0.41 Oersted field was used to bias
the sample and the coil 104 were oriented perpendicular
to the earth's magnetic fieldO Applied field coil 104
was constructed of 121 twins of closely wrapped, #14
AWG. insulated copper wire. Coil 104 had an inside
diameter of 5.1 cm and was 45.7 cm long. Pick up coil
112 was constructed of 540 turns of closely wrapped ~26
AWG. insulated copper wire. The coil 112 had an inside
diameter of 1.9 cm and was 7.6 cm long. A sample marker
110 was placed in pick-up coil 11~, which is coaxially
disposed inside the applied field coil 104. The voltage
generated by the pick-up coil 112 was fed into ~unable
wave analizer 114 comprised of a frequency selectable
band pass filter and a c voltmeter. The band pass
filter was tuned to 15 KHz, an integer multiple of the
drive frequency generated by the oscillator generator
101. The amplitude of harmonic response by the sample
marker 110 was measured with the wave analyzer 114 and
-13-
indicated by an analogue display. A dual channel
oscilloscope 116 was also used to graphically display
the applied and reradiated signal.
The harmonic generation test apparatus 100 was
used to test marker samples composed of material identi-
fied in Table IV. Each of the samples, numbered 1-15 in
Table IV was 10.2 cm long. The samples were placed
inside pickup coil 112 and applied field coil 104 and
the amplitude of harmonic response for each sample 110
was obse rve d.
TABLE IV
Sample
No Fe Ni Cr Mo Cu C P B Si
_
Alloys of ~his Invention
1 73O25 0 6 0.25 0 13 7 0.5 0
2 73.25 0 6 ~.25 0 15 5 0.5 0
3 71.25 0 8 0.25 0 13 7 0.5 0
4 71.25 0 8 0.25 0 15 5 0.5 0
73.5 0 6 1.0 0 13 7 0.5 0
6 73.5 0 6 1.0 0 15 5 0.5 0
7 70.5 0 8 1.0 0 13 7 0.5 0
8 70.5 0 8 1.0 0 15 5 0.5 0
Marker
Dimensions
Sample Length Width THK Harmonic Signal
No. Structure cm cm mV NV/m3
r
Alloys of this Invention
1 Amorphous 10.2 0.041 33 46.7 33.8
2 Amorphous 10.2 0.038 25 41.7 43.0
3 Amorphous 10.2 0.036 31 25.0 22.0
4 Amorphous 10.2 0.046 33 43.3 28.0
~morphous 10.2 0.038 28 31.3 28.8
6 Amorphous 10.2 0.036 38 31.7 22.7
7 Amorphous 10.2 0~036 36 28.3 21.4
8 Amorphous 10.2 0O043 36 35.0 22.2
-14-
Sample
No Fe Ni Cr Mo Cu C P B Si
_lloys Not of This Inventio
9 40 40 0 2 0 0 0 18 0
~0 0 2 0 0 0 18 0
11 40 ~0 0 2 0 0 0 18 0
Marker
Dimensions
SampleLength Width THK Harmonic Signal
No. Structure cm cm mV MV/m3 _
Alloys Not of This Invention
109 Amorphous 10.2 0.051 25 28.3 21.8
10 Amorphous 10.2 0.051 31 20.3 12.6
11 Amorphous 10.2 0.178 58 167 15.8
As shown by the data reported in Table IV, the
samples composed of the amorphous ferromagnetic materi-
als of this invention showed equal or improved harmonic
amplitude per unit volume of sample compared to the
control samples. Thus sample No. 2 of Table IV of
composition Fe 73.25, Cr 6, Mo 0.25, C 15, P 5, B 0.5
showed a harmonic signal of 43.0 megavolts per cubic
20 meter ~MV/m3) of sample compound to 12.6 to 21.8 MV/m3
for the control samples. It should be further noted
that the alloys of this invention contained no content
of strategic and costly metals such as nickel or cobalt
other than in concentrations which normally would be
present as impurities.
The samples of Table IV were helically woundaround a 5-mm diameter mandrel to produce a degraded
condition, straightened and placed in pickup coil 112
and applied field coil 104, as before, to observe the
amplitude of harmonic response produced thereby. All
samples retained in excess of 90% of their original har-
monic amplitude after flexing and bendingO
Having thus described the invention in rather
full detail, it will be understood that these details
need not be strictly adhered to but that further changes
and modifications may suggest themselves to one having
ordinary skill in the art, all falling within the scope
of the invention as defined by the subjoined claims.
