U.S. patent number 3,631,442 [Application Number 04/747,050] was granted by the patent office on 1971-12-28 for anti-shoplifting system.
Invention is credited to Robert E. Fearon.
United States Patent |
3,631,442 |
Fearon |
December 28, 1971 |
ANTI-SHOPLIFTING SYSTEM
Abstract
Article theft detection system wherein a passive nonlinear radio
transponder is attached to each article to be protected, and an
exit way is monitored by a loop antenna which is energized by
currents of two different frequencies. The transponders radiate the
difference frequency when subjected to a field of the two
energizing frequencies. Receiving means connected to the loop
antenna detects signals having a frequency equal to the difference
between the two energizing frequencies, and actuates an alarm.
Inventors: |
Fearon; Robert E. (Tulsa,
OK) |
Family
ID: |
25003460 |
Appl.
No.: |
04/747,050 |
Filed: |
March 22, 1968 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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680666 |
Nov 6, 1967 |
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Current U.S.
Class: |
340/572.2;
343/787; 340/572.3; 340/572.6; 342/42 |
Current CPC
Class: |
G08B
13/2474 (20130101); G01S 13/753 (20130101); G08B
13/2408 (20130101); G08B 13/2431 (20130101); G08B
13/2442 (20130101); G08B 13/2437 (20130101); G06K
7/10009 (20130101) |
Current International
Class: |
G08B
13/24 (20060101); G06K 7/10 (20060101); G01S
13/00 (20060101); G01S 13/75 (20060101); G08b
013/24 () |
Field of
Search: |
;340/258D,258,252TR
;333/3M ;343/787X ;179/82 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Caldwell; John W.
Assistant Examiner: Trafton; David L.
Parent Case Text
This application is a continuation-in-part of U.S. application for
Pat. Ser. No. 680,666, filed Nov. 6, 1967 and now abandoned.
Claims
What is claimed is:
1. A system for sensing passage of objects through a surveillance
area and useful for detecting theft of an object from an area,
comprising:
means proximate the area for concurrently producing at least two
oscillating electromagnetic energy components of different
frequency in the area;
an electromagnetically nonlinear marker associated with each object
for reradiating electromagnetic energy at frequencies equal to sums
and differences of the frequencies of said components when said
components are coupled to the marker; and
means for sensing electromagnetic energy in said area and for
producing a signal in response to sensing energy reradiated by a
marker.
2. A system according to claim 1 wherein said energy component
producing means comprises at least two emitting means each of which
produces a said energy component and each of which comprises a
combination of a coil winding and a capacitor, which combination is
resonant at the frequency at which the emitting means produces its
said energy component and wherein each emitting means receives no
energy from any other emitting means concurrently producing an
energy component.
3. A system according to claim 2 wherein said emitting means which
produce energy components concurrently have no mutual
inductance.
4. A system according to claim 2 wherein each said emitting means
further comprises a filter coupled in electrical series with said
combination, which filter has a narrow passband centered about the
resonant frequency of said combination to prevent energy from any
other concurrently producing emitting means from being received by
the emitting means of said combination.
5. A system according to claim 2 further comprising a deactivating
device for producing a recognizable change in a merchandise marker
to permit deactivation of the marker of a good the removal of which
from the designated area has been authorized.
Description
There are in existence several systems for detecting or preventing
the theft of articles of value. One of these corresponding with
U.S. Pat. No. 3,292,080, granted to E. M. Trikilis, Dec. 13, 1966,
makes use of a magnetometer and utilizes a magnetized object which
identifies the article unless checkout procedure has removed the
magnetism from the object. The magnetized object is attached to or
becomes a part of the merchandise or article of value, and by
energizing the magnetometer system as it passes through the
doorway, is detected. If the magnetized object has been
demagnetized it causes no magnetic signal as it passes through the
doorway and is not detected. Demagnetizing is done in the process
of checking out the merchandise. Thus by the checkout procedure an
individual has free passage with the merchandise that has been paid
for or recorded by the clerk. Any additional merchandise not paid
for and however concealed radiates a magnetic influence, and
energizes the magnetometer at the doorway, creating an awareness of
security department personnel that something is being stolen.
Another system involves radioactive material which emits nuclear
radiation. When the label containing the magnetic material is
removed from the merchandise, the radiation is no longer emitted,
and therefore radiation detectors situated in the doorway are not
energized. On the other hand, if the radiation emitters remain on
the merchandise, doorway sensors of nuclear radiation react, and
security personnel are in a position to prevent the theft.
In another system currently being employed in a men's wear
department in Macy's in New York City, the operator uses a radio
frequency generating device embedded in a rubber pad. The radio
frequency emitting device is fastened to the men's clothing, and if
not removed, will energize radio frequency detecting antennae at
the doorway. In the normal course of events, when the merchandise
is sold, a special fastener is unlocked and the radio frequency
emitter is removed from the clothing at the time it is sold,
permitting the buyer to pass through the doorway without attracting
the attention of the store detective.
All of the foregoing systems have severe difficulties of one kind
or another. The Trikilis system unfortunately requires a rather
large piece of ferromagnetic material for the marking of the
merchandise. If too small a piece of ferromagnetic material is
used, ambient variations in the magnetic field are greater than the
changes caused by the Trikilis merchandise marker. In the case of
the radioactive dot, there is a severe health problem involving
danger to people from the nuclear radiation, and involving danger
to those who remove the markers and store them. The system in use
in Macy's Store unfortunately is limited by the extreme costliness
of the radio frequency transmitter, and the limited period of time
during which its emission can be maintained by the little batteries
with which it is provided. True, larger radio frequency emitting
pads could be made, but these tear or injure the clothing, and are
impractically bulky.
I have discovered a practical solution to the problems presented
but not solved by the workers in the prior art as described above.
As a matter of convenience, I choose to employ electromagnetic
radiation. However, because of the inconvenience of supplying
energy in a contraband marking, the energy to be radiated from the
contraband marked device is delivered, instead, from structural
members of my sensing doorway.
I have found it extremely difficult to reradiate or reflect energy
in a distinctive manner from any merchandise marker for the reason
that all solid bodies and all electrically conductive masses
(including the human body which is largely composed of salt water)
also reflect or disperse electromagnetic radiation and therefore
must be considered in the recognition of any merchandise marking. A
human being reflects more electromagnetic energy than any practical
size of merchandise marker.
I have solved the problems just described by my discovery of an
extremely simple device which can receive energy and reemit it,
receiving the energy in a frequency spectrum entirely distinct from
the frequency spectrum which is reemitted. I do this by making use
of the properties of electrically and electromagnetically nonlinear
systems. In general, it is the property of a nonlinear system that
if a frequency F is imposed at an energy level at which the
nonlinearity of the system becomes important, the system will
generate frequencies 2F, 3F, 4F, etc. Similarly, if I impose on a
nonlinear system signal sources which deliver approximately equal
energy in each of two frequencies, the nonlinear system will
generate other frequencies, not originally present. If the
frequencies which I impose are F.sub.1 and F.sub.2, the nonlinear
system will generate signals having frequencies F.sub.1 +F.sub.2,
F.sub.1 -F.sub.2, F.sub.1 +2F.sub.2, 2F.sub.1 +2F.sub.2, and
various other combinations of sums and differences of multiples of
the frequencies which I impose.
It is an essential part of my invention that I have discovered a
merchandise marker which constitutes a nonlinear system and which
therefore can generate phenomena such as those which have just been
discussed. In making my discovery I have overcome certain basic
difficulties relating to the concurrent delivery of energy at
different frequencies. One of these difficulties lies in the fact
that the output members of oscillators and the like always are at
least a little bit nonlinear. Therefore two frequencies,
concurrently delivered from any emitter, will usually generate
summation and difference tones as above related, generating these
to an appreciable extent and tending to conceal the summation and
difference tones produced by my merchandise markers. I have
discovered a way to avoid this problem by emitting the two
frequencies of electromagnetic energy from two different sources
such as, for example, two large and separate coils in the vicinity
of my doorway structure. The large coils in the doorway vicinity
are arranged so that they have no mutual inductance. Accordingly
therefore energy from one coil does not flow into the system
connected to the other coil and vice versa. In such a system as the
one I have discovered, summation and difference tones are not
produced by any nonlinearities in my signal source oscillators. On
the other hand, even though the two emitter coils have no mutual
inductance to each other, there is available (in the space where
both their magnetic fields exist concurrently) energy at both
frequencies. Energy at both the frequencies can be concurrently
absorbed by a suitably placed small magnetic object or receiver. If
the small object or receiver is in some way adapted to have what
would commonly be called an overload characteristic, it exhibits
nonlinearity, and therefore radiates summation and difference
tones.
I now summarize the elements of my invention. I have discovered a
theft detection and prevention system which comprises a
surveillance doorway containing among other things emitters of two
frequencies of electromagnetic energy adapted to emit an
electromagnetic energy into the same region of space, and so
arranged that the two emitters do not radiate energy to each other.
My system also includes an electromagnetic signal detection means
situated at or near the surveillance doorway designed and adapted
to receive energy at a summation or difference tone resulting from
the concurrent action of the energy of both the frequencies imposed
on a merchandise marker device. My system comprises, among other
things, a plurality of merchandise marking devices capable of
receiving energy at more than one frequency, and reradiating it at
other frequencies resulting from the concurrent action of those
frequencies which are incident upon it. The system which I have
discovered includes means and arrangements to prevent the
generation of any effects due to the concurrent action of several
frequencies from occurring anywhere except in my merchandise marker
itself. My invention also includes a means of altering the
electrical or electromagnetic characteristics of my merchandise
markers during checkout procedure so that the alteration is
recognizable as an indication that the merchandise has been
properly sold.
I now turn to FIG. 1 which is a general view of the manner in which
my system operates in a store to prevent theft of merchandise.
Merchandise 1 is provided with contraband marker elements 2. The
checkout stand area 3 contains a deactivating device 4 which is
capable of changing the electromagnetic properties of the
contraband marker elements 2. An energizing and detecting system 5A
situated in the 5B and 5C vicinity of the outgoing doorway 6
detects the contraband marker elements 2, and identifies those
which have not been subjected to change at the checkout stand area
3 by the deactivating device 4. In the use of my system, one way
traffic, enforced by perhaps a turnstile 7, takes care of persons
entering the store, prohibiting the carrying of merchandise from
the store to areas outside the store except through my outgoing
doorway 6. The turnstile 7 is provided at the entry portal 8.
I turn now to FIG. 2 which illustrates a form of contraband marking
element suitable for use in my system. An easily saturable high
permeability filament or narrow ribbon of specialized magnetic
material such as the one known by the trade name Superpermalloy, is
shown at 9. The filament extends parallel to, and is so situated as
to collect the magnetic flux from two pole piece coupons 10 which
are also composed of high quality magnetic material of the type
having a very low coercive force and a very high maximum magnetic
permeability The coupons 10 are preferably composed of materials
having a maximum permeability in the vicinity of 50,000 or
thereabouts. Attached to the coupons 10 I provide masses or rigid
plastic substance such as polymerized methyl methacrylate 11. In
use, the device is assembled between layers of paper 12 (or
plastic) illustrated in exploded view (removed from the vicinity of
the filament 9 and coupons 10). The filament 9 and coupons 10 are
not shown in exploded form, but are illustrated realistically. In
use, the filament 9 is spaced from the coupons 10 by a few
thousandths of an inch, the space being occupied by a lubricating
particle suspension such as silicone oil with magnesium oxide
particles in it. Any other suitable lubricant may be employed,
together with particles of suitable size. For example, petroleum
lubricant and carbon particles are satisfactory. Fluorocarbon oil
with bentonite clay suspended in it is suitable. In use of the FIG.
2 device, the space between the filament 9 and the adjacent layer
of paper 12 is also filled with a suitable particle suspension
lubricant, to space the filament 9 apart from the paper 12 by an
appropriate distance.
In use, the contraband assembly described in FIG. 2 encounters, at
the outgoing doorway 6 of FIG. 1, a combination of electromagnetic
fields producing an oscillating component of magnetic field
parallel with the axis of the filament 9. The oscillating component
of magnetic field, as provided in the outgoing doorway 6, includes
contributions of two separate frequencies. The magnetic fields thus
provided have a component parallel to the axis of the filament 9 as
shown in the FIG. 2 device, and are of sufficient magnitude to
bring about a substantial degree of magnetic saturation of the
filament 9 parallel to its axis. Because of the nonlinearity of the
magnetic phenomena occurring in the filament 9, summation and
difference tones are produced and radiated in the form of
electromagnetic radiation from the device shown in FIG. 2. The
above-described phenomena occur when merchandise 1 (FIG. 1)
carrying a contraband marker element 2 shown in detail in FIG. 2 is
taken through the outgoing doorway 6 (FIG. 1 ) without paying for
it. When, on the other hand, the customer pays for the merchandise
1 (FIG. 1) the merchandise 1 (FIG. 1) is presented in the vicinity
of the deactivating device 4 (FIG. 1) in the checkout stand area 3
(FIG. 1). The deactivating device 4 (FIG. 1) delivers an extremely
strong magnetic field, a field so strong that it is sufficient to
induce a very large magnetic flux not only through the filament 9,
but also in the coupons 10 of the device of FIG. 2. The large
magnetic flux induced in the coupons 10 (FIG. 2) by the
deactivating device 4 (FIG. 1) would normally bring about an
elongation (or in some instances possibly a shortening) of the
material composing the coupons 10 (FIG. 2) in the direction in
which the magnetic flux is induced. However the plastic substance
11 attached to each coupon 10 is rigid and nonmagnetic. The plastic
substance 11 being firmly attached to the coupons 10 resists the
dimensional change which would otherwise occur due to a strong
magnetic flux in the coupons. The clamping effect which the plastic
substance 11 thus exerts corresponds with a mechanical strain
imposed on the magnetic material of the coupons 10. The mechanical
strain being beyond the elastic limit of the said magnetic
material, it undergoes cold-work which destroys its superior
magnetic properties, degrading its maximum permeability from the
vicinity of 50,000 to the general vicinity of one or two
thousand.
A FIG. 2 device assembled as described in the foregoing paragraph
and deactivated as described, still has demonstrable nonlinear
magnetic properties. However the doorway field intensity required
to induce nonlinear behavior of the filament 9 is substantially
altered, for the reason that the maximum permeability of the
coupons 10 being lowered, they do not collect magnetic flux from
the outgoing doorway 6 environment and feed it into the filament 9
as efficiently as they did before their magnetic properties were
degraded. Thus it is possible for an energizing and detecting
system 5 existing in the vicinity of the outgoing doorway 6 to
determine the presence of unsold merchandise 1, and at the same
time be sensitive to the fact that the same individual, or one
nearby, is also carrying merchandise which has been properly paid
for and carries deactivated contraband marker elements 2 (FIG. 1).
(I note that the contraband marker elements 2, as actually
illustrated in FIG. 1, are not deactivated, being shown inside the
store area.)
FIG. 3 illustrates a modified form for the coupons 10 (FIG. 2). In
this modified form the coupons 10 are not attached to any plastic
clamping substance 11 over their entire surface, but material of a
different nature, either more or less magnetic than the material of
the coupons, or not magnetic at all, is deposited in a periodically
spaced pattern in a plurality of closely spaced stripes 13
equidistant from each other on the specially arranged coupon 14,
which has properties generally similar to the properties of the
coupons 10 of FIG. 2. Because of the mass of such periodically
spaced stripes 13, and because of their other properties by which
they are differentiated from the magnetic material composing the
specially arranged coupon 14, the specially arranged coupon 14 in
combination with the stripes 13, exhibits a mechanical resonance
tending to vibrate in such a manner that the material situated at
the stripes 13 undergoes a minimum of movement and/or dilatation.
If mass is the predominant characteristic of the material at the
stripes 13, the stripes 13 will correspond with a minimum of
movement. If mechanical stiffness predominates, the stripes 13 will
correspond with very little change of dimension at the frequency of
the resonance, and with the specially arranged coupon 14 vibrating
in the resonant mode. Because of the influence of the periodically
spaced stripes 13, the specially arranged coupon 14 will always
exhibit a sharply determined mechanical resonance in the manner
just described.
When using contraband marker elements 2 manufactured generally in
accord with FIG. 1, but provided with specially arranged coupons
14, I choose to energize the deactivating device 4 (FIG. 1) at the
frequency corresponding with the resonance, or I make the
deactivating device 4 resonance seeking with respect to the desired
mode of mechanical motion. Inducing the resonant motion, the
deactivating device 4 (FIG. 1) causes mechanical energy to build up
in the specially arranged coupon 14 until the amplitude of movement
and the amplitude of stress and strain involved in the resonant
oscillations approaches the elastic limit of the magnetic material
composing the specially arranged coupon 14. As I have described
before in connection with the deactivation of coupons such as the
coupons 10 (FIG. 2), the cold-work result form the movement causes
the magnetic properties of the specially arranged coupons 14 to be
degraded from the general vicinity of a maximum permeability of
50,000 to a maximum permeability in the vicinity of one to two
thousand. As before, the contraband marker elements 2 (FIG. 1) in
which coupons of whatever type have been degraded, are
recognizable, and may be differentiated from other contraband
marker elements 2 (FIG. 1) which have not passed through the
deactivating process, and not had their coupons degraded.
Although the provision of periodically deposited stripes 13 on the
specially arranged coupon 14 helps to define and select a
particular resonance at which the spacially arranged coupon 14 will
oscillate, it is nevertheless true that the coupon without stripes
13 and without the plastic substance 11 (FIG. 2) can also be
induced to oscillate in a resonance mode. In fact resonant
oscillations can be induced at a wide variety of modes comprising
an extensive plurality of possible choices of resonant frequencies.
This, in fact, is the chief difference between an ordinary
unclamped coupon such as the coupon 10 of FIG. 2 (but without
plastic substance 11 and without stripes 13 as provided in FIG. 3)
and the specially arranged striped coupon 14 of FIG. 3. Because of
the stripes, the specially arranged coupon 14 of FIG. 3 prefers a
particular mode of resonant oscillation and the striped structure
13 tends to suppress the other modes which are a feature of an
unclamped and unstriped coupon. In fact the convenience of the
stripes lies in this, that the otherwise extremely large diversity
of possible oscillatory frequencies is reduced by the stripes 13 to
one chosen and preferred mode and frequency. Through the provision
of this feature, a specially arranged coupon 14, because of its
thickness, mechanical characteristics, and because of the
periodicity of the stripes 13, is distinctly recognizable and can
be differentiated at the outgoing doorway 6 (FIG. 1).
Thus it is possible, using my system, and using the provisions of
my FIG. 3 to distinctly characterize the contraband marker elements
2 (FIG. 1) being employed by Woolworth's, or for example by Sears
Roebuck. In fact, using the recognition capabilities intrinsic in
contraband markers thus manufactured, the outgoing doorway 6
energizing and detecting system 5 (FIG. 1) can report at the Sears
Roebuck store when it detects merchandise 1 that was stolen at
Woolworth's, and determine that it is Woolworth merchandise that is
being observed.
I turn now to FIG. 4 in which there is illustrated an
electromagnetically functionable nonlinear device of another type.
The ring-shaped conductor 15 may be made, if desired, of a flat
piece of metal, or if desired, may be composed of a wire. In any
event the ends of the ring-shaped conductor 15 do not join, but (as
shown in inset A) are separated by a space filled with substance
such as barium titanate 16. The barium titanate filled space 16 is
preferably of appreciable area and thin. As is well known, the
electrical polarization of the barium titanate 16 is a nonlinear
function of the electric field acting on it. Accordingly therefore,
the assembly shown in FIG. 4 radiates energy at frequencies other
than those imposed on it when it is energized by a magnetic vector
17 corresponding with a cyclical variation of magnetic intensity in
the direction indicated. If a single frequency F is imposed as a
result of induction from the electromagnetic induction in the
ring-shaped electrical conductor 15, the frequencies which are
generated as a result, and which may therefore be radiated, are 2F,
3F, 4F, and so on. If the magnetic vector 17 comprises
electromagnetic energy at two frequencies F.sub.1 and F.sub.2, and,
particularly, if these are of approximately equal intensity, the
nonlinear behavior of the barium titanate layer 16 results in the
generation of frequencies such as F.sub.1 +F.sub.2, F.sub.1
-F.sub.2, 2F.sub.1 +F.sub.2, F.sub.1 +2F.sub.2, and various other
combinations of sums and differences of multiples of the
frequencies F.sub.1 and F.sub.2.
In the same manner that the contraband marker elements 2 shown in
FIG. 1 may be composed of an assembly such as I have previously
presented and described in FIG. 2, the contraband marker element 2
(FIG. 1) may be composed of the structure such as I have described
in my FIG. 4. The same uses and results are obtained by employing a
FIG. 4 device, which is in many ways an equivalent to the FIG. 2
device in respect to its function as a contraband marker element.
Additional features in connection with the use of my FIG. 4 device
become evident in the immediately following description.
In the previous description of FIG. 4, I have recited only the
essential components, those which pertain to its electrical and
signal inducing behavior, by which it serves to identify
merchandise 1 (FIG. 1) that is stolen. As in the case of the FIG. 2
device, a checkout stand deactivating arrangement can be employed
in the general manner shown at reference numeral 4 in FIG. 1. In
the use of the contraband marker element 2 of the type set out in
FIG. 4, the deactivating device 4 (FIG. 1) comprises an
electromagnetic energy source which radiates, at least sometimes,
electromagnetic energy corresponding with the frequency of
mechanical resonance of the barium titanate mass 16 and the nearby
portions of the attached metal ring-shaped conductor 15. In this
form of deactivation, the energy of mechanical vibration induced by
the deactivating device 4 (FIG. 1) fractures the barium titanate
mass 16, thus destroying or noticeably changing the behavior of
this type of electromagnetic marker. By this change I can recognize
that the contraband marker element 2 (FIG. 1) was deactivated, and
therefore determine that the attached merchandise 1 FIG. 1) was
sold.
Another technique of deactivation which may be employed in
connection with the FIG. 4 device makes use of the constriction of
the ring-shaped conductor 15 at the point 18 as shown in the inset
B. In deactivating, I may, if I choose, make use of this
constriction 18 by inducing on the ring-shaped conductor 15 enough
current to melt or destroy the electrically conducting material
present at the constriction 18. If it is desired to make the
constriction 18 sensitive and easily destroyed, the material
present in the constriction 18 may, in fact, be composed of a
substance or substances less well adapted to conduct electricity
than is the main portion of the ring-shaped conductor 15. By such a
choice, heat or other alteration will occur readily at the
constriction 18 causing the circuit involving the ring-shaped
conductor 15 and the barium titanate mass 16 to open up with the
result that the contraband marker element 2 (FIG. 1) will no longer
function to produce summation and difference frequencies, and
therefore is not detected by the energizing and detecting system 5
(FIG. 1) of the outgoing doorway 6 of FIG. 1.
I turn now to FIG. 5, in which I illustrate a further variation of
contraband marker element 2 (FIG. 1). In inset A of FIG. 5 I show a
conductor 19 and a mass of barium titanate 20 at a separation
between the ends of the conductor 19, as shown in inset B. In
addition, a quantity of ferromagnetic material 21 (shown in an
inset B) is disposed in such a manner that it closes a magnetic
circuit surrounding the current flowing in the conductor 19 in a
manner to substantially increase the inductance exhibited by the
one turn loop of the conductor 19. As a result of the use of
ferromagnetic material 21 and because of the relatively large
electrical capacity of the gap containing the barium titanate 20
(as compared with a gap containing ordinary dielectric) the system
illustrated in this figure is, in fact, an inductance and
capacitance loop which, because of the ordinary considerations of
communications engineering, has a resonance frequency of
where L is inductance in microhenries, C is capacitance in
microfarads
In view of the presence of the ferromagnetic material, the
above-described resonance is not as sharp as resonances of air core
coils containing large amounts of electrically conductive material
but containing no ferromagnetic material. For the reason that the
resonance of the system described in FIG. 5 has an appreciable
width, I can, if I choose, energize it with more than one
frequency, the said frequencies differing appreciably, and yet
expect that both frequencies will lie substantially within the
resonance. The operation of my system as set out in FIG. 1,
employing contraband marker elements 2 (FIG. 1) but of the special
type provided in FIG. 5 works in a manner generally similar to the
description I have given in my discussion of the operation of my
system with the contraband marker element of FIG. 4, but will
require that the energy sources at the energizing and detecting
system 5 (FIG. 1) of the outgoing doorway 6 (FIG. 1) supply
frequencies falling within the capacity and inductance resonance of
the system for the greatest efficiency of energy delivery to the
marker. The vector arrow 17 through the center of the loop formed
by the conductor 19 has exactly the same significance as the vector
arrow 17 in FIG. 4.
In FIG. 6 I illustrate a contraband marker comprising a flat coil
of one or more turns short circuited on itself. An equivalent to
the illustrated flat coil 22 would be, for instance, a copper
washer occupying the same region of space, and having in it an
amount of copper equal to the total amount contained in the wire of
the illustrated coil 22. Ferromagnetic elements 23 and 24 (shown in
the inset) are disposed to link the magnetic flux developed by the
coil 22, and are chosen of material of extremely low magnetic
coercive force. Additionally the ferromagnetic elements 23 and 24
are deliberately taken in a form having an insufficient amount of
ferromagnetic material, creating a strong likelihood that magnetic
saturation will occur. By the occurrence of magnetic saturation,
which is a nonlinear process, the flux changes associated with the
nonlinearity cause radiation from the electrically conducting loop
25. The frequencies so radiated correspond with modulation
products, serving the same purposes as the modulation products
developed in connection with the uses of my other contraband marker
elements 2 (FIG. 1).
The ferromagnetic elements 23 and 24 are shown in a form adapted to
serve the purpose of linking the magnetic flux induced in the
presence of my short-circuited coil 22, but do not have to be bent
sharply to go around the flat coil 22. Instead I lay a piece 24
flatwise immediately below the flat coil 22 and another piece 23
similarly above it. The two pieces 23 and 24 approach each other
very closely at their extremities, permitting the easy transfer of
magnetic flux from one piece into the other, thus allowing the
circulation of magnetic flux around the conductor. The marker
element illustrated in FIG. 6 is not provided with any deactivation
capabilities. Instead the user has to remove this type of marker
label from the merchandise at the time of sale. This marker element
of FIG. 6 is described for the purpose of illustrating how a system
not involving deactivation can be combined in my invention. In use,
the energizing and detecting system 5 (FIG. 1) in the vicinity of
the outgoing doorway 6 (FIG. 1) produces and detects from this
contraband element (FIG. 6) a signal showing that the merchandise 1
(FIG. 1) being taken out still has the contraband marker element 2
(FIG. 1) on it. Merchandise from which the clerk has removed the
contraband marker element of FIG. 6, of course, does not give this
effect at the doorway.
In FIG. 7A I show another type of contraband marker element
corresponding with a longitudinally extending strip or rod of
ferromagnetic material 26 capable of responding at the frequencies
F.sub.1 and F.sub.2 delivered at my energizing and detecting system
5 (FIG. 1) in the vicinity of the outgoing doorway 6 (FIG. 8 1).
Linking the equatorial region of the longitudinally extending
ferromagnetic material 26 I provide an electrical conductor 27
which makes one or more turns around the equatorial region of the
said ferromagnetic material 26. The terminations of the electrical
conductor 27 are connected together through a nonlinear electric
element 28 comprising a germanium rectifier junction, a copper
oxide rectifier junction, a silicon rectifier junction, or suitable
other more or less unilaterally electrically conducting
arrangement. In use, the knee of the voltage versus current
characteristic for the nonlinear elements represents a nonlinearity
which imposes its effect on any current induced in or flowing
through the electrical conductor 27. THe nonlinear effect thus
imposed reacts on the magnetic field in the ferromagnetic element
26 causing summation and difference frequencies to be magnetically
radiated, as is the case with the contraband marker elements 2
(FIG. 1) previously described. The utilization of summation and
difference frequencies is, in fact, the same. Deactivation is
produced at the deactivating device 4 (FIG. 1) by inducing through
the diode element 28 a large enough electrical current to destroy
it. In the destroyed form, the nonlinear element either loses its
directional characteristic, which removes the nonlinear behavior,
or on the other hand, it may break up and become an open circuit,
resulting in the passage of no current at all in the electrical
conductor 27 thereby removing the nonlinear effect originally
present due to the nonlinear electrical element 28.
Referring further to FIG. 7A, I may, if I choose, employ a
nonlinear element sufficiently durable that it can resist the work
of my deactivating device 4 (FIG. 1) which I provide in the
checkout stand area 3 (FIG. 1). In this case, the utilization of my
system proceeds through the removal of the contraband marker
element of FIG. 7A by the clerk at the checkout stand area 3 (FIG.
1) at the time merchandise is purchased. Otherwise the system
functions generally in the same manner as it does in connection
with my other contraband marker devices.
In a further modification of my FIG. 7A marker element which I have
illustrated as FIG. 7B, I provide the same longitudinally extending
ferromagnetic element 26, the same electrical conductor 27,
extending one or more turns around the girth of the longitudinally
extending ferromagnetic element 26 in the vicinity of its equator,
but the diode or nonlinear electrical conductor 28 which I afforded
in my FIG. 7A is modified (in FIG. 7B) to comprise, instead, two
diodes 29 and 30 connected in parallel, and aiding. The two diodes
29 and 30 are disposed differently, the diode 29 having a much
larger electric current carrying capacity than the other diode 30.
The much larger current capacity of the diode 29 is so chosen that
the deactivating device 4 (FIG. 1) operating in the checkout stand
area 3 (FIG. 1) cannot cause enough electric current to flow in the
conductor 27 to damage the diode 29. On the other hand, the diode
30 which has less current carrying capacity is destroyed. In
addition, to cause the electric current delivered by the conductor
27 to be shared in a predetermined manner between diodes 29 and 30,
I also provide resistors R.sub.1 and R.sub.2, each in series with
the corresponding diodes 30 and 70 29.
In use, the effect 137 the modified form 7B marker device is that
deactivation between deactivating device 4 (FIG. 1) employed in the
checkout stand area 3 (FIG. 1) results in a predetermined and
predictable change in the properties of the contraband marker
element corresponding with this figure, but leaves it still able to
deliver a radiation effect corresponding with modulation products,
at the doorway area. Like my other contraband marker corresponding
with FIG. 2 this contraband marker element as shown in FIG. 7B
affords recognition of stolen merchandise and at the same time
affords, at the outgoing doorway, recognition of the fact that
contraband marking, in deactivated form, is present on the
merchandise being carried by the customer through the outgoing
doorway 6 (FIG. 1).
I turn my attention to the energizing and detecting system 5 (FIG.
1) situated in the outgoing doorway 6 (FIG. 1). Because there are
three perpendicular coordinates available in space of three
dimensions, I can arrange for the two energizing systems and
detecting devices to work in a noninteracting manner. In fact, it
is a characteristic of my plan that within the limits of accuracy
of adjustment of the position and orientation of my electromagnetic
radiating and receiving components, the two radiating components
radiate independently, neither one being capable of transmitting
energy into the other one, and further, the detecting or receiving
pickup does not receive energy directly from either of the
radiating devices. These arrangements of course are valid only when
the space in the doorway is ample, there being no contraband marker
elements 2 (FIG. 1) in it. The manner in which I achieve the type
of arrangement which has been generally recited above is depicted
in more detail in FIG. 8.
In FIG. 8 I have pictured two pedestals 31, each containing near
its center a pair of sending coils 32. All the sending coils 32 are
connected in parallel (or they could have been connected in
series). For illustration only, I will suppose that the frequency
by which these sending coils 32 are energized in 21 kilohertz. Each
such sending coil 32 is separately tuned to exhibit the highest
possible at 21 kilohertz. For illustration only, the coils may be
composed of 99 turns of No. 20 copper wire wound on a 1-inch
diameter coil form in a single layer to produce 99 turns in a total
length of 311/2 inches. Such a coil may be resonated to 21
kilohertz by the use of an electrical capacity of not less than 1
microfarad and not more than 1.1 microfarad. The combination of one
of these coils 33 with it resonating capacitor 34 (as shown in the
inset), when energized at the resonant frequency, represents an
entirely resistive impedance and in the illustrative case exhibits
a resistance between 100 and 150 ohms. A parallel combination of
four such resistive loads has a combined effect adapted to
efficiently load the voice coil outputs of some available audio
amplifiers.
Similarly, there are situated at the bottom and at the top of each
of the pedestals 31, coils 35 intended for transmitting another
chosen frequency such as (for illustration only) 24.5 kilohertz.
The four coils 35 which are intended for 24.5 kilohertz radiation
may be constructed similarly and resonated similarly, but, of
course, resonate with a correspondingly smaller electrical capacity
for each coil. The combination of the first group of four coils 32
is connected to a source of electrical energy 36 at 21 The
combination of the second group of four coils 35 is connected to a
separate, entirely independent, source of electrical energy 37 at
24.5 kilohertz. Because of the arrangement which I have chosen for
the first group of coils 32 and for the second group of coils 35,
there is no appreciable mutual inductance acting to deliver 21
kilohertz energy into the 24.5 kilohertz, or vice versa.
At four other locations I present four more coils 38 with their
axes perpendicular to the plane of the paper. Because all the
contributions of the first group of four coils 32 and the second
group of four coils 35 lie in the plane of the paper, the four
coils 38 with their axes perpendicular to the plane of the paper do
not receive energy neither at 24.5 kilohertz, not at 21 kilohertz.
The four coils 38 with their axes perpendicular to the paper are
resonated at 3.5 kilohertz by choosing an appropriate electrical
capacitance. In order to achieve good sensitivity in these coils,
and in order that they may be resonated efficiently at the
frequency of 3.5 kilohertz, more copper is required in the winding,
preferably four layers of No. 20 wire, each layer containing 99
turns more or less. The capacity required to resonate such a coil
is in the general vicinity of 2 microfarads for 3.5 kilohertz.
I call attention to the fact that the cores of these windings have
not been specified thus far. It is a preferred choice to wind them
on nonmagnetic, electrically nonconducting material, for the reason
that ferromagnetic material (because of its nonlinear properties)
imparts to my system interactions between the energy sources,
interactions which I desire to avoid. Electrically conducting
material, on the other hand, destroys the quality of the inductive
performance of all the coils. As a matter of fact an air core coil
of 99 turns, made in the manner that I have described, has a Q in
the vicinity of 500 at 21 kilohertz when wound on a wooden core.
The resonance cannot be found, nor the inductance measured well
enough to determine the Q if it is wound on an electrical conductor
as a core.
The combination of the four coils, as described, with their axes
perpendicular to the paper (each coil resonated at 3.5 kilohertz by
appropriate electrical capacitance) delivers its output to the
ingoing end of a high gain tuned amplifier 39 adapted to
selectively receive and amplify electrical signals at 3.5
kilohertz. The amplifier 39 delivers its output to an alarm
mechanism 40, or to a carrier frequency module, which I discuss
further on. To achieve a closer impedance match with respect to the
commonly prevailing input resistance of the amplifiers that are the
most convenient, I may choose to vary from the connections shown in
FIG. 8, and connect the four receiving coils 38 (the ones with
their axes perpendicular to the paper) in series. The resistive
component of these coils (with their resonators connected) comes
out for each such resonated system in the vicinity of 100 ohms,
with the result that the series of four of them are a close match
to the communications impedance figure of 500 ohms, a common choice
for amplifiers, filters, etc.
I turn now to FIG. 9 presented for the purpose of diagrammatically
assisting in the explanation of the manner of functioning of the
energizing and detecting system 5 (FIG. 1) which I have
particularly detailed and described in connection with FIG. 8. In
FIG. 9 the axis X may be taken to represent the action of the 21
kilohertz radiator, the perpendicular axis Y illustrates the action
of the 24.5 kilohertz radiator, and the axis Z represents the
receiving sensitivity or direction of the 3.5 kilohertz receiving
coils 38 of FIG. 8. The vector .theta. is illustrated in a
direction not parallel to nor perpendicular to any of the three
axes. The vector .theta. represents the direction in which a
contraband marker element 2 (FIG. 1) is capable of receiving and
reradiating energy. Because the vector .theta. has an appreciable
component in all three axes, the contraband marker element 2 (FIG.
1) oriented in accord with this vector is able to receive energy
concurrently at 21 kilohertz, and likewise at 24.5 kilohertz. For
similar reasons, if the contraband marker element 2 (FIG. 1)
reradiates at 3.5 kilohertz (not being deactivated) then detection
axis Z is so directed with respect to the vector .theta. that the
said detection system is not insensitive to radiation emitted by
the contraband marker element 2 (FIG. 1).
The user, considering the information presented in connection with
FIG. 8, the information just presented in connection with FIG. 9,
will realize that the reception of a 3.5 kilohertz in my system is
a distinctive and an exclusive evidence of the presence of
contraband marker elements 2 (FIG. 1). One or more such elements
must be in the domain of energy radiation sensitivity provided by
the arrangements shown in my FIG. 8 to deliver a 3.5-kilohertz
signal. Other entities than contraband marker elements are not
entirely without effect, but they do not present the same
effects.
To aid the understanding of another modification of my system which
I have described, I turn again to FIG. 9. In FIG. 9 I have
represented the directions of action of the energy source
frequencies X and Y (21 and 24.5 kilohertz sources) and the
direction of sensitivity of the system that detects the difference
tone Z in the form of three perpendicular axis. To the worker
skilled in the art, it is evident that if contraband vector .theta.
is exactly perpendicular to either of the signal source axes X or
Y, I eliminate the energy corresponding with the vector to which
the vector .theta. is perpendicular. Furthermore if the vector
.theta. lies in the X-Y plane, it is perpendicular at all times to
the axes Z which therefore prohibits the reception of any energy in
my signal receiving system 38, FIG. 8. It is, in fact, true that
the vector .theta. must have appreciable and comparable components
or direction cosines aligned with all three of the vectors X, Y,
and Z. For those directions .theta. which do not fulfill these
conditions, either the difference tone signals are not produced or
they are not observed (if produced) by the contraband marker
element 2 (FIG. 1) The fact that there are so many blind spots and
so many requirements on the direction of contraband, causes my
system, conceived as in the foregoing, to sometimes fail to
recognize contraband markers passing through the outgoing doorway 6
(FIG. 1). It still remains a fact that nothing other than a
contraband marker will ring the alarm. However, I have discovered a
way to reduce the inconvenience resulting from the above-noted
limitations (which now and then permit a contraband marked piece of
stolen merchandise to get through).
The user will note in FIG. 8 that in the foregoing I have excluded
the energy from the 21 kilohertz source from getting into the 24.5
kilohertz source by arranging for separate radiators, and arranging
that these be noninteracting because of their perpendicularity
arrangement. Another approach to excluding wrong pathways of signal
energy is quite applicable in the frequency range which I have
chosen, an approach not dependent on geometry. My modification
permits advantages in the simplification of the doorway
structure.
The system which I contemplate for the reduction of the number of
blind spots in respect to the direction of the vector .theta. (FIG.
9) substitutes rigorously designed wave filters, containing passive
elements only. These perform the function performed by the
geometric isolation in the system of FIG. 8. Such wave filters can
be designed for the range of frequency in the vicinity of 20 to 50
kilohertz without the use of ferromagnetic material or anything
else which would impose a nonlinearity. The wave filters thus used,
if provided in a sufficient number of sections, propagate the
desired energy substantially without loss and are able to reject
the unwanted signal frequencies to whatever extent is desired,
through the use of a sufficient number of networks. A properly
designed M or pi derived filter network will exclude unwanted
frequencies by over 100 decibels in just a few networks.
Lattice-type filters may be employed for single frequency rejection
and are extremely effective. In fact, the only serious limitation
of the rejection brought about by a lattice-type filter is imposed
by variation in frequency of the signal which it is desired to
reject. A lattice-type filter, for example, may comprise two
electrical capacitances and two inductive elements as the four
components of a bridge. The input to the bridge and the output to
the bridge have a ratio which theoretically is infinite at the
frequency at which it balances. Thus it is theoretically possible
to exclude a single frequency to any extent, by a single network of
such a filter. At the same time a single network lattice filter can
transmit very efficiently energy corresponding with signal
frequencies that are substantially different from the signal
frequency at which the bridge balances.
For 20 kilohertz or more, substantially perfect inductances
(inductances with a Q in the realm of thousands) can be delivered
in the space of a few cubic inches, and need not contain more than
an ounce or two of copper wire. Again, in the frequency spectrum
involving a metal box comprised of iron or copper, and with a coil
spaced from the walls, inside the box, the coil neither radiates
nor absorbs electromagnetic energy appreciably in this kilohertz
range. Capacitances constructed of aluminum foil and wound with
such a dielectric as wax paper (or mylar or polystyrene) form a
substantially perfect electrical performance in my preferred
frequency range. It is, accordingly, entirely feasible to
contemplate the substitution of rigorous filtering in place of my
previous geometric means of arranging radiator coils so that energy
is not transferred from one system to another. Moreover, the use of
well designed filters has a further advantage, that the presence of
conducting bodies of any description in the doorway 6 (FIG. 1) does
not cause energy to flow from one system to the other, since the
wave filters function independently of whatever bodies are situated
in the doorway 6 (FIG. 1). On the contrary my geometric arrangement
of coils is sensitive to the presence of electrically conducting
bodies in the doorway 6 and the favorable results which I achieve
by making these coils 32, 35, and 38 (FIG. 8) perpendicular are
partly destroyed whenever a large electrically conducting body
passes through the outgoing doorway 6 (FIG. 1).
I turn now to FIG. 10 which illustrates the plan comprised in a
general way in the foregoing discussion. In FIG. 10, for simplicity
I illustrate one common radiating and receiving means 41, and one
only, since this shows the flexibility of my modified plan most
clearly. In the block diagram, the user will note that there are
provided three distinct wave filters, each connected at its input
to a separate electrical entity. The electrical entity to which the
first two wave filters are connected is in each instance an
oscillator. For convenience, the filters 42 and 43 are also
designed by the symbol F.sub.1 and F.sub.2 to indicate the center
of a pass band which each of the said filters 42 and 43 selectively
transmits. The third filter 44 is designated by the symbol F.sub.1
-F.sub.2 to indicate the fact that the center of its pass band is
chosen at the difference frequencies corresponding with the
difference between the two frequencies F.sub.1 and F.sub.2. The
filters in question are deliberately taken from designs which
permit extremely strong selectivity and extremely high exclusion of
the unwanted frequencies.
As an example of a frequency corresponding with a capability of
extremely strong filtering, F.sub.1 may be 31 kilohertz, F.sub.2
may be 21 kilohertz, and F.sub.1 -F.sub.2, in fact, 10 kilohertz.
The frequencies can be very stringently filtered against one
another and, in fact, exclusivity can be achieved to whatever
extent is required. I therefore indicate these entities as being
each connected to a single electronic device in the doorway
detecting and energizing system 41. A suitable doorway sensing and
detecting device 41, one adapted for the purpose is a flat wound
coil 41 diagrammatically shown in FIG. 10. Such a flat wound coil
serves effectively because the two input energy sources 46 and 47
cause a concurrent influence on the contraband at the frequencies
F.sub.1 and F.sub.2 whenever a contraband element has a significant
component of its vector .theta. in a direction not in the plane of
the coil. In a completely reciprocal manner, the illustrated
doorway coil 42 is able to receive energy at the difference tone
F.sub.1 -F.sub.2 with good efficiency, and can do so whenever the
contraband marker element 2 (FIG. 1) exhibits and appreciable
component perpendicular to the plane of the doorway (shown in FIG.
10) (at the time the contraband element 2 (FIG. 1) is passing
through the plane of the said doorway).
I refer again to FIG. 10. In this figure it will be noted that I
have provided two frequency sources F.sub.1 and F.sub.2, and two
filter systems. It is obvious that if the frequency sources which
deliver energy at F.sub.1 and F.sub.2 are adjusted so that the
frequency F.sub.1 =F.sub.2, and furthermore, if I impose the
requirement that these two alternating current energy sources be in
phase, then, in this degenerate case, the entire system comprising
the frequency sources delivering energy at the two frequencies
F.sub.1 and F.sub.2 has the same effect as one oscillator and one
filter. Accordingly therefore I achieve the same result if I simply
omit the filter F.sub.1 and the oscillator 46. In a system
comprised by such an omission, since F.sub.1 =F.sub.2, the quantity
F.sub.1 -F.sub.2 has no significance as alternating current for the
reason that F.sub.1 -F.sub.2 equals zero. However in modulation
products, as has been stated, earlier one of the functions that is
generated is F.sub.1 +F.sub.2. For the case in which F.sub.1
=F.sub.2, F.sub.1 +F.sub.2 is of course 2F.
In the modification of my system which I am now describing with the
help of FIG. 10, I envision omitting the oscillator 46 and the
filter 42. I provide the substitution of a filter adapted to pass
the frequency 2F.sub.1 instead of a filter 44 (as illustrated) to
pass the frequency F.sub.1 -F.sub.2. The recognition of contraband
marked merchandise by this modified system is identically the same
as has been described in the other embodiments of my invention.
From an engineering standpoint it is required that the filter 43 of
FIG. 10, be adapted to particularly stringent rejection of the
frequency 2F. In a lattice filter designed for single frequency
rejection elimination of the unwanted frequency 2F.sub.1 from the
output of this filter can be accomplished to more than 100 decibels
in two meshes, providing the stability of the frequency of the
oscillator 47 is sufficiently good. This is easily arranged by
employing crystal control to stabilize the oscillator 47. I
envision the use of a temperature insensitive cut of the quartz
crystal and, if necessary, I employ a temperature controlled
environment to further improve the frequency stability of the
oscillator 47. The stability of oscillators has been controlled
within one part per billion over long periods by the careful use of
these techniques. Since I do not need such extreme frequency
control, the adequacy of the methods which I propose is quit
obvious.
In the use of my antishoplifting systems there is a problem of
communicating the warning signal indicating that merchandise is
being stolen, and bringing the indication to the attention of
security guards who are not, necessarily, at the same place. To
make this procedure convenient in finished buildings where the
wiring is already in place, I propose the use of ordinary carrier
frequency signaling techniques that are well known in the art, and
propose that the carrier frequency signals be inserted on the
electric power system.
Since my warning devices are electrically powered, it is convenient
to insert the carrier warning signal on the cord through which the
power requirements of the system are served, making communications
connections of a separate nature unnecessary. The electronic
equipment necessary to put the carrier frequency warning message
into the power cord will generally be a part of, or will be
situated close to the other parts of the antishoplifting system. In
fact all these things may be on the same panel rack or may be built
up in the same stack of shielded boxes, a proves convenient. I
visualize such carrier frequency systems as a valuable and useful
feature in combination with the other elements of my invention. In
FIG. 10, the carrier frequency module is, as desired, the element
48.
In FIG. 10 the operator will note that there are six electrical
connections, comprising three pairs, going from the systems: (a) 46
and 42, (b) 47 and 43, and (c) 48 and 45. My U.S. Pat. No.
2,520,677 Aug. 29, 1950) makes a similar use of six wires in the
form of three pairs, and provides an especially effective means for
filtering out the noise from the signal frequency F.sub.1
.+-.F.sub.2 (F.sub.1 -F.sub.2, as used in the discussion in this
patent application). I contemplate the use of all the same means
and methods for improving the signal to noise ratio in my
antishoplifting system, and employ the same in combination with the
other features of my antishoplifting system to better reject
unwanted noise and electrical disturbances of all kinds.
I refer once more to FIG. 10, and particularly I employ the device
of FIG. 10 with the omission of elements 43, 44, 45, 47, and 48. I
further describe the filter F.sub.1 (element 42) as a
nonsignificant component comprised in this use of my FIG. 10 device
as simply a pair of wires going straight through from left to
right. In effect I omit the function of this filter. In this use of
my FIG. 10 device I also construe the oscillator 46 as one emitting
relatively very strong electrical oscillations, and one which may
at times be adjusted or at least have its frequency reset to
another value as required. Further the oscillator 46 may be a
"warble" oscillator adapted to cyclically retraverse a small range
of frequency.
In the use which I am now describing for my FIG. 10 device, I
insert the coil identified in FIG. 10 as "doorway" at the point
shown for the device 4 in FIG. 1. The coil 41 is assumed to be
taken to a proper scale so that it will fit in the space provided
at location 4 in FIG. 1. My FIG. 10 device so arranged is, in fact,
suitable to perform the deactivating function. To assure the upward
radiation of a strong electromagnetic effect through the belt 2A of
the checkout stand 3 shown in FIG. 1, I arrange the design of the
checkout stand so that there are no closed metallic loops between
the device 4 and the merchandise 1 with contraband marker 2. I
further designate that the plane of my FIG. 10 coil 41 will be the
same as the plane of the largest side of the box-shaped space
designated at numeral 4 in FIG. 1. For this use, and for all the
other uses of the FIG. 10 device, it is understood that the
mechanical coil support which is illustrated in FIG. 10 is an
electrically nonconducting material, and a nonferromagnetic
material.
In addition to the systems described in the preceding, we have
found an especially useful way to practice this invention. If we
employ an extremely favorable high permeability ferromagnetic
material, as for example, a substance having a maximum permeability
of 400,000 or thereabouts and a coercive force of 0.02, and if we
choose a very slender cross section compared with length, as for
example a cross-sectional area of 0.0004 square centimeters, and a
length of 4 centimeters or more, the same being comprised in a
ribbon not thicker than 0.00125 centimeters thick, and if such a
contraband marker element is presented with its axis approximately
parallel to the oscillating magnetic field in a doorway such as is
illustrated in FIG. 1, the oscillating magnetic field having an
intensity of the order of magnitude of three oersteds (such a
contraband element, being generally similar to element 9 in FIG. 2)
the magnetic element so chosen returns harmonic frequencies of a
very high order, extending up to and including 1.6 megacycles when
excited by a frequency such as 60 cycles per second.
If a contraband element as above described, and generally similar
to element 9 of FIG. 2 and particularly represented by element 49
of FIG. 11 is accompanied by other ferromagnetic elements also of a
very slender nature, such other ferromagnetic elements being
disposed close to and parallel with ferromagnetic elements which
were first described, very valuable and useful results are
obtained. The additional ferromagnetic elements 50 and 51 of FIG.
11 are chosen to have distinctive magnetic properties, properties
not the same in the two additional ferromagnetic elements, and
neither of the two additional ferromagnetic elements 50 and 51 are
at all similar to the first ferromagnetic element 49. The
ferromagnetic element 50 may be chosen from among those substances
high in iron content which have a coercive force in the general
vicinity of 15 oersteds.
The ferromagnetic element 51 may be chosen from among ferromagnetic
substances high in iron which have a coercive force of
approximately 100 oersteds. Other elements, not shown, may be
chosen having still higher magnetic coercive force characteristics.
The magnetic element 50 is of such a cross section (as for example
less than 0.0004 square centimeters) that if it is left as strongly
magnetized as possible, the number of lines that it will deliver is
insufficient to saturate the first magnetic element 49. The
cross-sectional area of the ferromagnetic element 51 is so chosen
that if it is left as fully magnetized as possible, and if at the
same time the element 50 is also as fully magnetized as possible,
and in the same direction, the lines carried by both these
ferromagnetic elements are but little more than sufficient to
magnetically saturate the magnetic element 49.
The ferromagnetic elements 49, 50, and 51 are shown in FIG. 11
separately, and we have illustrated nothing else, for the purpose
of simplicity of the discussion. However, it will be understood
that, in the use of the FIG. 11 device consisting of the
combination of ferromagnetic elements shown therein, paper cards
generally similar to elements 12 of FIG. 2 may be employed to
sandwich, support, and conceal the ferromagnetic elements 49, 50,
and 51 in a contraband label or marker.
The spectrum of reradiated frequencies which results from the
combination of ferromagnetic elements 49, 50, and 51 has three
possibilities when the combination of adjacent ferromagnetic
elements 49, 50, and 51 is carried through a doorway such as is
illustrated in FIG. 1. The first possibility represents the type of
reradiation that occurs when the ferromagnetic elements 50 and 51
have been degaussed and when the ambient or zero value of the
magnetic field in the doorway is neutralized to have approximately
no component parallel to the axis of the oscillating field
components.
The second possibility occurs when the condition of the doorway is
generally the same but the contraband element shown in FIG. 11 is
presented in the condition in which element 50 is approximately
fully magnetized but the element 51 is not magnetized. This
condition is achieved by imposing a magnetic field sufficient to
magnetize the element 50 but not adequate to magnetize the element
51.
A third condition of the arrangement shown in FIG. 11 exists when
both the ferromagnetic elements 50 and 51 are magnetized, and are
left as strongly magnetized as possible in the same direction. In
this case also it is understood that the ambient condition of the
doorway in FIG. 1 is the same as was previously described in
connection with the spectrum condition number one referred to.
A fourth magnetic state of the arrangement shown in FIG. 11 can be
obtained by arranging for the ferromagnetic elements 50 and 51 to
exist in magnetized condition, but magnetized with opposite
polarization. This state is achieved by first imposing a very
strong magnetic field which leaves both the elements 50 and 51
magnetized in the same direction, and afterward applying a weaker
field sufficient to reverse the magnetization of the element 50 (in
view of its lower coercive force) but not sufficient to reverse the
magnetization of the ferromagnetic element 51.
Referring now to spectrum condition number one, the expected output
consists entirely of odd harmonics of the power frequency of 60
cycles. This conclusion is particularly rigorous for the case in
which the loop antenna which receives the energy is chosen with a
very insufficient number of turns and produces in an approximately
rigorous manner an electrical voltage proportional to the time
derivative of the surface integral of the magnetic flux threading
through the loop antenna. The loop antenna may be element 5B of
FIG. 1, for example.
Spectrum condition number two deviates from spectrum condition
number one in that even harmonics appear and represent an important
contribution to the energy.
Spectrum condition number three corresponds with "silence" in the
sense that the combination of elements does not radiate. The
voltage wave delivered by the output in the four described spectrum
conditions (in the order above presented) is shown in FIGS. 12A,
12B, 12C, and 12D. In FIG. 12A the operator will note that the
successive alternating cups of voltage are evenly spaced. In FIG.
12B the alternating cusps are no longer evenly spaced but are
closer to one another in pairs. In FIG. 12C the cusps have in fact
disappeared. In FIG. 12D corresponding with spectrum condition four
as previously described, the cusps are unevenly spaced, but the
degree of uneveness is different from the unevenness shown in FIG.
12B. The distinction between the FIG. 12B information and the FIG.
12D information is that the ratio of energy delivered in even
harmonics to that delivered in odd harmonics is significantly
different in the two cases. Actually as the condition approaches
the disappearance of the cusps, they move up until the positive and
negative pulse crowd each other. As the positive pulse moves into
the negative pulse, the two cancel and the information gathered by
these features disappears.
In the use of the contraband elements of the particularly
advantageous type which we have described, we employ again the FIG.
10 arrangement for the electronic energizing and readout at the
doorway. In this use of the FIG. 10 arrangement, we omit elements
42 and 46, energizing the doorway with but a single frequency. The
element 44 which has been hitherto characterized as a wave filter,
we characterize instead as an electronic device for selecting even
and odd harmonics present on the ingoing leads to element 44. The
device 44 in this arrangement delivers a voltage proportional to
the ratio of the selected even and odd harmonics on the wires going
out to amplifier element 45. In such a manner of use, the FIG. 10
device and the doorway coil 41 illustrated in connection with it,
serve to energize the security readout system and communications
system 48 (which relies on the output of the amplifier 45) for the
purpose of energizing alarms, lighting lights, etc.
When so used, the element 44 is further qualified to indicated the
condition when it receives no signal at all. Accordingly, the
device 44 can deliver distinctive signals corresponding with three
conditions in which energy is retransmitted from the contraband
elements and finally the condition of silence when nothing is
retransmitted. This number of possibilities is sufficient for
codified identification of merchandise being stolen.
Another very valuable way of using the arrangement of FIG. 11 is
accomplished by omitting the ferromagnetic element 51 and choosing
ferromagnetic element 50 to have a sufficient cross section that
when it is fully magnetized, it is more than adequate to saturate
the ferromagnetic element 49. A combination so chosen constitutes a
marker that has two conditions that are clearly definable. The
first signal producing condition, the unmagnetized one, corresponds
with the voltage curve shown in FIG. 12A. The condition of sold
merchandise, in which the marker has been commanded to be silent,
is shown in FIG. 12C. This condition is brought about at the
checkout stand by imposing on the marker (consisting of the
elements 49 and 50, as previously set out) a magnetic field
sufficiently strong to leave the element 50 in a fully magnetized
condition. This modification of the marker has particular merit
where it is merely desired to determine whether merchandise has
been sold or not as it is carried out the doorway, and where it is
not necessary to determine in codified detail what kind of
merchandise is involved in a potential theft. For the more
complicated problems, we prefer the previously described
arrangement with at least three ferromagnetic elements, and for
more complicated codes, even as many as four, all being slender and
lying in reasonable close proximity to each other and essentially
parallel, as shown in general in FIG. 11.
In addition to the use of the systems and apparatus disclosed
herein as an antishoplifting means the invention may equally well
be utilized in various arrangements for classification, recognition
on production lines, security, and for identification of objects
such as I.D. cards, canceled tickets, and other such similar
applications.
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