Information
-
Patent Grant
-
6271756
-
Patent Number
6,271,756
-
Date Filed
Monday, December 27, 199924 years ago
-
Date Issued
Tuesday, August 7, 200123 years ago
-
Inventors
-
Original Assignees
-
Examiners
Agents
- Akin, Gump, Strauss, Hauer & Feld, L.L.P.
-
CPC
-
US Classifications
Field of Search
US
- 340 5721
- 340 5724
- 340 5727
- 340 5681
- 340 571
- 340 928
- 340 82531
- 340 82535
- 343 867
- 343 761
- 343 762
-
International Classifications
-
Abstract
A security tag detection and localization system for detecting a resonant security tag in a security zone comprising a Plurality of detection zones, and generating an alarm signal localizing the resonant security tag to a detection zone. The system includes an antenna array for radiating interrogation signals and receiving response signals. The antenna array forms the upper boundary, the lower boundary or both the upper and lower boundaries of a security zone and extends horizontally across the width and length of the security zone. The antenna array comprises at least two antennas. The antennas forming the upper and lower boundaries are disposed side-by-side in a single horizontal plane with each antenna being electromagnetically coupled to one of the detection zones. The security tag detection and localization system also includes one or more electronic article security (EAS) sensors for transmitting interrogation signals to the antenna array, receiving response signals from the antenna array, and generating an alarm signal. The security tag detection and localization system also includes an annunciator connected to each EAS sensor, for receiving the alarm signal and indicating a detection zone corresponding to the alarm signal.
Description
BACKGROUND OF THE INVENTION
The present invention relates generally to electronic article security (EAS) systems for detecting the presence of a security tag within a security zone and more particularly to an improved electronic article security system having the capability for localizing a resonant security tag within a portion of the security zone.
The use of electronic article security systems for detecting and preventing theft or unauthorized removal of articles or goods from retail establishments and/or other facilities such as libraries has become widespread. In general, such EAS systems employ a security tag, which is detectable by the EAS system and which is secured to the article to be protected. Such EAS systems are generally located at or around points of exit irom such facilities to detect the security tag, and thus the article, as it transits through the exit point.
Due to environmental and regulatory considerations, individual EAS systems are generally effective over only a limited area in which a security tag attached to a protected article may be reliably detected. Such area, typically referred to as a security zone, is generally limited to about six feet in width for a single EAS system. While many stores and libraries have only a single exit doorway of a size commensurate with such a six foot wide security zone, many other retail establishments have eight or ten exit doorways arranged side by side. Furthermore, large mall stores frequently have a generally wide open area or aisle of ten feet or more in width serving as a connection with the mall. Thus, in many such situations, a plurality of EAS systems are required to fully protect exit/entrance points having a width greater than that which can be reliably protected by a single EAS system.
In a large mall entryway that needs to be protected, it is likely that the store owner will not want to employ a traditional EAS system installation which would include multiple, large, side-side “pedestal” antenna structures, due to aesthetic visual or marketing reasons. Such store owners would prefer an “invisible” EAS system in which the EAS antenna structure is mounted in the floor beneath the entryway, hung over the entryway or both. Such EAS systems usually provide adequate detection of tagged merchandise transiting through the security zone but fail to provide a localization of a detection to a specific portion of the security zone. Thus, when many customers are in proximity of the entryway when an alarm is activated, store personnel generally have no way, other than trial and error, to determine which customer has set off an alarm with the tagged merchandise. This leads to either a lack of use of the EAS system as an effective security aid, or the owner having disgruntled customers who take their business elsewhere.
The present invention overcomes the problem of an “invisible” EAS system not being able to localize a tag detection to a specific portion of the security zone in a large entryway by utilizing a plurality of EAS sensors of the pulse-listen type, in combination with a plurality of antennas placed either above or below the entryway. The resulting EAS system determines the relative proximity of a detected security tag transiting through the security zone to each of the plurality of antennas in the array. The resulting EAS system achieves localization of a security tag to within a small portion of the security zone.
BRIEF SUMMARY OF THE INVENTION
Briefly stated the present invention provides a security tag detection and localization system for detecting a resonant security tag in a security zone comprising a plurality of detection zones, and generating an alarm signal localizing the resonant security tag to a detection zone. The system comprises: an antenna array for radiating interrogation signals and receiving response signals, the antenna array forming at least one of an upper and a lower boundary of the security zone and being arranged horizontally across a width and a length of the security zone, wherein the antenna array comprises at least two antennas, the antennas forming one of the upper and lower boundaries being disposed side-by-side in a single horizontal plane, each antenna being electromagnetically coupled to one of the detection zones; at least one electronic article security (EAS) sensor for transmitting interrogation signals to the antenna array, receiving response signals from the antenna array and generating an alarm signal; and an annunciator connected to each EAS sensor, for receiving the alarm signal and indicating a detection zone corresponding to the alarm.
In accordance with another aspect of the present invention there is an EAS sensor of the pulse-listen type for detecting and localizing a resonant security tag to a specific portion of a security zone comprising: a transmitter for generating an interrogation signal; a receiver for receiving a response signal from the security tag; a plurality of transmitting antennas for receiving the interrogation signal from the transmitter and radiating the interrogation signal into the security zone; a plurality of receiving antennas for receiving the response signal from the security tag and providing the response signal to the receiver, the response signal being a result of the interrogation signal interacting with the security tag and being re-radiated from the security tag; and an antenna switch connecting the transmitter to the transmitting antennas and the receiver to the receiving antennas, the antenna switch sequentially selecting pair-wise permutations, with replacement, of the antennas once over a predetermined time interval, such that each selected pair consists of one transmitting antenna and one receiving antenna, wherein an amplitude of an output from the receiver resulting from each permutation of the antennas is compared, thereby determining the location of the security tag to correspond with the portion of the security zone being in closest proximity to the antenna pair having the receiver output signal with the largest amplitude.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
The foregoing summary, as well as the following detailed description of preferred embodiments of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. In the drawings:
FIG. 1
is a functional block diagram of a security tag detection and localization system/according to a preferred embodiment of the present invention;
FIG. 2
is a more detailed functional block diagram of the preferred embodiment of the present invention;
FIG. 3
is a functional block diagram of an electronic article security (EAS) sensor;
FIGS. 4
a-c
are diagrams illustrative of the various timing signals utilized by the preferred embodiment of the present invention; and
FIG. 5
is a flow diagram describing the process for generating an alarm.
DETAILED DESCRIPTION OF THE INVENTION
Referring to the drawings, where like numerals are used to indicate like elements throughout, there is shown in
FIG. 1
a functional block diagram of a security tag detection and localization system
10
for detecting a resonant security tag
13
in a security zone
11
comprising a plurality of detection zones
18
(not shown) one of which is shown as
18
-
1
,
1
and localizing the resonant security tag
13
to one or more of the detection zones
18
. The tag detection and localization system
10
comprises from one to N EAS sensors
12
, shown individually as
12
-
1
through
12
-N; an antenna array
17
comprising from one to n individual antennas connected to each EAS sensor
12
, shown individually as
17
-
1
,
1
through
17
-N, n; and an annunciator
14
.
The security tag
13
is of a type which is well known in the art of EAS systems having a resonant frequency vithin the frequency range of the EAS detection and localization system
10
with which the tag
13
is employed. Preferably, the tag
13
has a circuit Q of between 50 and 100 and resonates at or near a frequency of 8.2 MHz., which is a resonant frequency commonly employed by EAS systems from a number of manufacturers. Typically, the resonant frequency of a security tag
13
has a tolerance of +/−10%, thus requiring each EAS sensor
12
to operate over a range of about 7.6 to 8.7 MHz. However, a security tag
13
having a resonant frequency of about 8.2 MHz. is not to be considered a limitation of the present invention. As will be appreciated by those skilled in the art, the security tag detection and localization system
10
is suitable for operating at any frequency for which the security tag detection and localization system
10
is capable of establishing a suitable electromagnetic interaction between the antenna array
17
and the security tag
13
.
The antenna array
17
forms either the upper boundary of the security zone
11
, the lower boundary of the security zone
11
, or the antenna array
17
may be apportioned to both the upper and lower boundaries of the security zone
11
. In the preferred embodiment, the full horizontal extent of the combined upper and lower portions of the antenna array defines the approximate width and the approximate length of the security zone
11
. When forming the lower boundary of the security zone
11
, the antenna array
17
is generally made integral with the floor. As will be appreciated by one skilled in the art, the antenna array
17
could also be mounted beneath the floor or mounted above the surface of the floor. When the array of antennas
17
is located above the security zone
11
, it may be concealed in a ceiling or suspended beneath the ceiling, within the spirit and scope of the invention.
The antenna array
17
comprises at least two antennas, the antennas
17
comprising each of the upper and the lower boundaries being disposed side-by side in a single horizontal plane. In the antenna array
17
each individual antenna
17
-
1
,
1
,
17
-N, n, is electromagnetically coupled to one of the detection zones
18
. Thus, because of the side-by-side configuration of the individual antennas
17
-
1
,
1
,
17
-N, n, the beams of the individual antennas
17
-
1
,
1
,
17
-N, n, illuminate adjoining detection zones
18
, which may also overlap, depending on the specific shape of the beams of the individual antennas
17
.
In the preferred embodiment the antennas
17
are combined transmitting and receiving loop-type antennas of a kind which do not create a null in the far field of the major beam of the antenna and are of a conventional design well known to those skilled in the art. As will be appreciated by those skilled in the art, it is not required to use the same antenna
17
for transmitting and receiving. Separate transmitting and receiving antennas
17
could be used, within the spirit and scope of the invention. Further, the type of antenna
17
is not limited to a non-nulling loop-type antenna. Any type of antenna
17
having a beam shape commensurate with the desired size and shape of the detection zones
18
is within the spirit and scope of the invention.
The security tag detection and localization system
10
also includes one or more electronic article security (EAS) sensors
12
for transmitting interrogation signals to the antenna array
17
, receiving response signals from the antenna array
17
and generating an alarm signal localizing the security tag
13
to a detection zone
18
.
Referring now to
FIG. 2
there is shown a preferred embodiment having three EAS sensors
12
-
1
,
12
-
2
and
12
-
3
, each of which is connected to two antennas
17
-
1
,
1
,
17
-
1
,
2
;
17
-
2
,
1
,
17
-
2
,
2
; and
17
-
3
,
1
,
17
-
3
,
2
. Also shown are the detection zones
18
-
1
,
1
,
18
-
1
,
2
;
18
-
2
,
1
,
18
-
2
,
2
; and
18
-
3
,
1
,
18
-
3
,
2
, corresponding to the antennas
17
-
1
,
1
,
17
-
1
,
2
;
17
-
2
,
1
,
17
-
2
,
2
; and
17
-
3
,
1
,
17
-
3
,
2
. In the preferred embodiment, the detection zones
18
of adjoining antennas
17
overlap, giving rise to an alarm signal on signal lines
32
which may correspond to a single detection zone
18
or to adjoining detection zones
18
. In the latter case, the annunciator
14
localizes a security tag
13
to more than one detection zone
18
. Also shown in
FIG. 2
is a slave signal line
30
for synchronizing the separate EAS sensors
12
, as discussed in more detail below. As will be appreciated by those skilled in the art, the number of EAS sensors
12
that could be included in a single security tag detection and localization system
10
is not limited to three and may be greater or less than three. Also, the number of antennas
17
which could be connected to each EAS sensor
12
is not limited to two and could be greater or less than two, and still be within the spirit and scope of the invention.
The electronic article security sensor
12
further includes an annunciator
14
connected to each EAS sensor
12
, for receiving the alarm signal over alarm signal lines
32
and for indicating the detection zone
18
corresponding to the alarm signal. In the preferred embodiment, the annunciator
14
is a series of lamps (not shown), each lamp uniquely associated with a single detection zone
18
and emitting visible light when a security tag
13
is detected and localized to a detection zone
18
corresponding to the lamp. As will be appreciated by those skilled in the art, the method of annunciation provided by annunciator
14
is not limited to visual annunciation. Other methods for annunciation could be used including, but not limited to, a combined audio and visual display, or a TV type display, within the spirit and scope of the invention.
Referring now to
FIG. 3
, the preferred embodiment of the EAS sensor
12
-
1
, representative of the EAS sensors
12
, comprises a transmitter
20
for generating an interrogation signal and providing the interrogation signal to an antenna switch
26
, and a receiver
24
, synchronized with the transmitter
20
, for receiving a response signal from the antenna switch
26
and generating an output signal. The EAS sensor
12
-
1
further includes antennas
17
-
1
,
1
and
17
-
1
,
2
for receiving the interrogation signal from the antenna switch
26
and radiating the interrogation signal into the security zone
11
, and receiving the response signal re-radiated from a security tag
13
located in one of the detection zones
18
and providing the response signal to the receiver
24
. The EAS sensor
12
-
1
also includes the antenna switch
26
, connecting each EAS sensor
12
to the antennas
17
-
1
,
1
and
17
-
1
,
2
and a digitally controlled frequency synthesizer (DCFS)
22
for providing a carrier output signal which tunes the transmitter
20
to a transmitting frequencv and tunes the receiver
22
to a receiving frequency. The transmitter
20
, the DCFS
22
, the receiver
24
and the antenna switch
26
are conventional in design and well known to those skilled in the art, and therefore need not be described in detail for a complete understanding of the present invention.
The preferred embodiment also includes a controller
40
for setting the frequency of the carrier output signals generated by the DCFS
22
and for providing timing signals to the DCFS
22
, the transmitter
20
, the receiver
24
and the antenna switch
26
for determining the time for transmission and reception of the interrogation and response signals respectively. As further shown in
FIG. 3
, the controller
40
includes a digital signal processor (DSP)
52
for executing the principal control and computational tasks of the controller
40
. The controller
40
also includes a programmable read only memory (PROM)
50
for storing a computer program and table data, a random access memory (RAM)
54
for storing temporary data and a programmable logic device (PLD)
56
for interfacing the controller
40
to the DCFS
22
, the transmitter
20
, the receiver
24
and the antenna switch
26
. The controller
40
further includes an analog-to-digital converter
58
for accepting the (analog) output signal from the receiver
24
, converting the output signal from the receiver
24
into a digital representation and inputting the digital representation of the output signal from the receiver
24
into the controller
40
. Additionally, the controller
40
includes an input/output device
60
for interfacing the controller
40
to the annunciator
14
over the alarm signal lines
32
and to other EAS sensors
12
over timing signal lines
42
,
44
and blocking signal lines
46
,
48
.
The DSP
52
executes a program stored in the PROM
50
to generate command signals responsive to parameters also stored in the PROM
50
. The PLD
56
generates control signals for tuning the DCFS
22
to the correct transmitting and receiving frequencies based upon the command signals received from the DSP
52
and activates the transmitter
20
and the receiver
24
during the transmission and reception time periods. As will be appreciated by those skilled in the art, the structure of the controller
40
is not limited to that disclosed in FIG.
3
. For example, microprocessor chips or a single microchip, including software for implementing the function of some or all of the separate components shown in
FIG. 3
, would be suitable for use in the controller
40
. Likewise, different storage devices and interface devices could be used, and still be within the spirit and scope of the invention.
The preferred embodiment the EAS sensor
12
employs a technique known to those skilled in the art as the pulse-listen technique, typified by the Strata™ System, manufactured by Checkpoint Systems, Inc. of Thorofare, N.J. for detecting and localizing a resonant security tag
13
to a specific portion of the security zone
11
. In the preferred embodiment of the EAS sensor
12
, the transmitter
20
generates an interrogation signal comprising a repeating sequence of discrete frequency, burst type RF signals over a range of RF frequencies, such that the RF frequency of at least one burst falls near the resonant frequency of the resonant security tag
13
to be detected. During quiescent periods between the RF bursts, the receiver
24
receives a response signal re-radiated from the resonant security tag
13
as a result of a resonant circuit in the security tag
13
interacting with the preceding RF burst.
In the preferred embodiment, the antenna switch
26
sequentially selects pair-wise permutations, with replacement, of the antennas
17
connected to each EAS sensor
12
such that for each selected pair of antennas
17
, one antenna transmits the interrogation signal and one antenna
17
receives the response signal and each permutation of the pair of antennas
17
is selected only once over a predetermined time interval. The amplitude of the output of the receiver
24
resulting from each permutation of the pairs of antennas
17
is compared in the DSP
52
for each frequency generated by the DCFS
22
. The location of the security tag
13
is determined to correspond with the portion of the security zone
11
in the closest proximity to the pair of antennas
17
having the output signal of the receiver
24
with the largest amplitude.
In the preferred embodiment, the number of permutations with replacement, of the antennas
17
, is computed by the formula n
k
, where n is the number of antennas connected to an EAS sensor
12
, and k is the number of antennas to be selected for each permutation. Thus, in the preferred embodiment of the EAS sensor
12
-
1
, for example, comprising two antennas
17
-
1
,
1
and
17
-
1
,
2
connected to the EAS sensor
12
-
1
, there would be four different pair-wise antenna permutatons. However, as previously indicated, more than two antennas can be connected to an EAS sensor
12
. In the case of three antennas connected to eacn EAS sensor
12
there would be nine pair-wise permutations of the antennas
17
, for four antennas connected to each EAS sensor
12
there would be
16
pair-wise permutations of the antennas
17
, etc. However, as will be appreciated by those skilled in the art, the desired localization capability of the security tag detection and localization system
10
is only negligibly degraded if only adjoining antennas
17
are used for antenna pairs. Accordingly, it is within the spirit and scope of the invention to reduce the number of permutations by selecting only adjacent antennas for each of the pairs of antennas
17
.
As shown in
FIGS. 4
a
-
4
c
. each EAS sensor
12
operates in accordance with a frame interval. The frame interval
200
(
FIG. 4
a
) is divided into as many subframe intervals
202
as there are antennas
17
connected to the EAS sensor
12
for receiving. Within each subframe interval
202
there is a period of transmission and reception
204
consisting of further subdivisions called bins
206
(
FIG. 4
b
). Each bin
206
provides for an EAS sensor
12
transmission and reception at a different frequency, the span of frequencies corresponding to the combined frequency uncertainty of the security tag
13
and the EAS sensor
12
. As shown in
FIG. 4
c
, each bin
206
is further divided into as many sub-bins
208
as there are antennas
17
connected to the EAS sensor
12
for transmitting, with each sub-bin
208
having a noise reception period
210
, an interrogation transmission period
212
and a response signal transmission period
214
. In the preferred embodiment there are two subframe intervals
202
per frame interval
200
, each subframe interval
202
having sixteen bins
206
with two sub-bins
208
per bin
206
. In the first subframe interval
202
a
, reception is from antenna
17
-
1
,
1
and transmission is from antenna
17
-
1
,
1
(phase A) and antenna
17
-
1
,
2
(Phase B). In the second subframe interval
202
b
, reception is from antenna
17
-
1
,
2
and transmission is from antennas
17
-
1
,
1
(Phase C) and
17
-
1
,
2
(Phase D).
Referring now to
FIG. 2
, the antenna
17
connections for one frame
200
of transmission and reception for the preferred embodiment of the security tag detection and localization system
10
consisting of three EAS sensors
12
are shown in Table I.
TABLE I
|
|
EAS #1
EAS #2
EAS #3
|
TX Ant.
RX Ant.
TX Ant.
RX Ant.
TX Ant.
RX Ant.
|
|
Phase A
1, 1
1, 1
2, 1
2, 1
3, 1
3, 1
|
Phase B
1, 2
1, 1
2, 2
2, 1
3, 2
3, 1
|
Phase C
1, 1
1, 2
2, 1
2, 2
3, 1
3, 2
|
Phase D
1, 2
1, 2
2, 2
2, 2
3, 2
3, 2
|
|
As indicated above, the number of antennas
17
that may be connected to each EAS sensor
12
may be greater than two. As will be appreciated by those skilled in the art, if more than two antennas
17
are connected to the EAS sensor
12
, the number of subframes and the number of sub-bins are increased according to the number of the receiving and the transmitting antennas respectively. Accordingly, EAS sensors
12
having a greater number of subframes per frame and sub-bins per bin than two are within the spirit and scope of the invention.
As will be appreciated by those skilled in the art, the Security Tag Detection and Localization System
10
is not limited to employing the pulse-listen technique. For example, the well known EAS technique whereby the EAS sensor
10
sweeps the transmission frequency over the RF band of interest, either continuously or in discrete steps, could also be employed, within the spirit and scope of the invention.
Also shown in
FIG. 3
are RF signal input and output lines
34
,
36
, timing signal input and output lines
42
,
44
and blocking signal input and output lines
46
,
48
interconnecting the EAS sensors
12
, corresponding collectively to the slave signal line
30
shown in FIG.
2
. In the preferred embodiment, the method for interconnecting the EAS sensors
12
is by daisy-chaining the RF signal lines
34
,
36
, the timing signal lines
42
,
44
and the blocking signal lines
34
,
36
between the separate EAS sensors
12
. However, as will be appreciated by those skilled in the art, any type of interconnection method, such as bus type methods, is within the spirit and scope of the invention.
In the preferred embodiment, one EAS sensor
12
is arbitrarily selected as a master for distributing the RF carrier output signal from the DCFS
22
to all the other EAS sensors
12
, hereinafter called slave EAS sensors
12
. Accordingly, the RF carrier output signal ofthe DCFS
22
is provided over RF output signal line
34
to the input line
36
of a slave EAS sensor
12
. The slave EAS sensor
12
provides the received RF carrier output signal to the transmitter
20
and receiver
24
and also outputs the received RF carrier signal to another slave EAS sensor
12
. In this manner, the transmitted interrogation signals for every EAS sensor
12
are maintained to be substantially in-phase with each other. Similarly, the master EAS sensor
12
provides timing signals for the frame
200
, subframe
202
, bin
206
, sub-bin
208
and transmitting and receiving periods
210
,
212
,
214
. The aforementioned timing signals originate in PLD
56
, are distributed from the master EAS sensor
12
to the slave EAS sensors
12
such that the frames
200
, subframes
202
, bins
206
, sub-bins
208
and transmitting and receiving periods
210
,
212
,
214
of all the EAS sensors
12
are synchronized.
In the preferred embodiment, the receiver
24
in each EAS sensor
12
generates the received output signal corresponding to the amplitude of the response signal received by the receiver
24
for each permutation of the antennas
17
connected to the EAS sensor
12
and for each frequency generated by the DCFS
22
during each frame interval
200
. The receiver output signal is received by the analog-to-digital converter
58
and provided to the DSP
52
. For each frequency, the DSP
52
generates a detection signal corresponding to the largest receiver output signal, Sm, for each permutation of the antennas
17
for which the receiver output signal, So, exceeds a predetermined detection threshold, Td, for a predetermined number, Nd, of frame intervals
200
, signifying a valid detection of a security tag
13
in at least one detection zone
18
. The DSP
52
includes an arbitrator
53
which arbitrates between the detection signal generated by the EAS sensor
12
, and a blocking signal having a predetermined duration, Tb, generated by another EAS sensor
12
. The arbitrator generates an alarm signal and the blocking signal if the detection signal is received by the arbitrator at a time when the blocking signal is not present. Thus, the arbitrator blocks the alarm of a second occurring detection by another EAS sensor
12
for the duration of the blocking signal. In the preferred embodiment, the duration of the blocking signal is about three seconds. It will be appreciated by those skilled in the art that the duration of the blocking signal is dictated by the particular configuration of the security tag detection and localization system
10
and may be other than about three seconds within the spirit and scope of the invention.
Referring now to
FIG. 5
, the process for arbitration
100
of the preferred embodiment is shown comprising first setting a frame counter, FC, equal to a value of one (step
101
) and receiving the output signal from the receiver
24
into the DSP
52
at step
102
. For each frequency, the largest output signal, Sm, from the receiver
24
is compared against the predetermined detection threshold, Td, step
103
. If the magnitude of the largest receiver output signal, Sm, exceeds the threshold value Td, the frame counter is advanced by one (step
104
) and the value of the frame counter is compared to a predetermined duration, Nd, at step
105
. If the largest receiver output signal, Sm, has remained above the threshold, Td, for Nd frame intervals, the arbitration process
100
determines if a blocking signal has been received (step
106
). If a blocking signal from another EAS sensor
12
has not been received, the alarm signal and the blocking signal of duration, Tb, are generated at step
107
, thereby blocking any alarms from other EAS sensors
12
for the duration of the blocking signal duration. If at step
103
, the output of the receiver
24
fails to satisfy the threshold criteria, Td, the frame counter is reset to a value of one. If at step
106
, the blocking signal is active when the output of the receiver satisfies the criteria at step
104
, thereby preventing a new alarm for the duration of the blocking signal, the frame counter, FC, is reset to a value of one before comparing additional outputs from the receiver
24
with the detection threshold Td.
It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.
Claims
- 1. A security tag detection and localization system for detecting a resonant security tag in a security zone comprising a plurality of detection zones, and generating an alarm signal localizing the resonant security tag to one of the detection zones, the system comprising:an antenna array for radiating interrogation signals and receiving response signals, the antenna array forming at least one of an upper and a lower boundary of the security zone and being arranged horizontally across a width and a length of the security zone, wherein the antenna array comprises at least two antennas, the at least two antennas forming one of the upper and lower boundaries being disposed side-by-side in a single horizontal plane, each antenna being electromagnetically coupled to one of the detection zones; at least one electronic article security (EAS) sensor for transmitting interrogation signals to the antenna array, receiving response signals from the antenna array and generating a detection signal in response to the tag being in the security zone; an arbitrator connected to the at least one EAS sensor for receiving the detection signal from the at least one EAS sensor, the arbitrator generating an alarm signal localizing the tag to the one of the plurality of detection zones based on the first received detection signal; and an annunciator connected to each EAS sensor, for receiving the alarm signal and indicating the detection zone corresponding to the alarm.
- 2. A security tag detection and localization system according to claim 1 wherein each antenna is a combined transmitting and receiving antenna.
- 3. A security tag detection and localization system according to claim 1 wherein the antenna array comprises separate transmitting and receiving antennas.
- 4. A security tag detection and localization system according to claim 1, wherein the antenna array is mounted below the security zone.
- 5. A security tag detection and localization system according to claim 1, wherein the antenna array is mounted above the security zone.
- 6. A security tag detection and localization system according to claim 1, wherein the sensor is a pulse-listen type of EAS sensor.
- 7. A security tag detection and localization system according to claim 6, wherein the EAS sensor further includes an antenna switch for connecting the EAS sensor to a subset of the antennas in the antenna array.
- 8. A security tag detection and localization system according to claim 7 wherein the antenna switch sequentially selects pair-wise permutations, with replacement, of the subset of antennas connected to the EAS sensor such that for each selected pair, one antenna is for transmitting the interrogation signal and one antenna is for receiving the response signal and each permutation of the antennas is selected only once over a predetermined time interval.
- 9. A security tag detection and localization system according to claim 8, wherein the antennas in each pair are selected only from adjacent antennas.
- 10. A security tag detection and localization system according to claim 7, wherein the subset of antennas comprises only two antennas.
- 11. A security tag detection and localization system according to claim 10 wherein the antenna switch sequentially selects pair-wise permutations, with replacement, of the antennas such that for each selected pair, one antenna is for transmitting the interrogation signal and one antenna is for receiving the response signal and each permutation of the antennas is selected only once over a predetermined time interval.
- 12. A security tag detection and localization system according to claim 1, wherein the sensor is a swept frequency type of EAS sensor.
- 13. A security tag detection and localization system according to claim 12, wherein the EAS sensor further includes an antenna switch for connecting the EAS sensor to a subset of the antennas in the antenna array.
- 14. A security tag detection and localization system according to claim 13 wherein the antenna switch sequentially selects pair-wise permutations, with replacement, of the subset of antennas connected to the EAS sensor such that for each selected pair, one antenna is for transmitting the interrogation signal and one antenna is for receiving the response signal and each permutation of the antennas is selected only once over a predetermined time interval.
- 15. A security tag detection anid localization system according to claim 14, wherein the antennas in each pair are selected only from adjacent antennas.
- 16. A security tag detection and localization system according to claim 13, wherein the subset of antennas comprises only two antennas.
- 17. A security tag detection and localization system according to claim 16, wherein the antenna switch sequentially selects pair-wise permutations, with replacement, of the antennas such that for each selected pair, one antenna is for transmitting the interrogation signal and one antenna is for receiving the response signal and each permutation of the antennas is selected only once over a predetermined time interval.
- 18. A security tag detection and localization system according to claim 1, wherein each EAS sensor further includes an arbitrator, the arbitrator receiving a detection signal from the EAS sensor and a blocking signal from another EAS sensor, and generating the alarm signal if the detection signal is received at a time when the blocking signal is not received.
- 19. An EAS sensor of the pulse-listen type for detecting and localizing a resonant security tag to a specific portion of a security zone comprising:a transmitter for generating an interrogation signal; a receiver for receiving a response signal from the security tag; a plurality of transmitting antennas for receiving the interrogation signal from the transmitter and radiating the interrogation signal into the security zone; a plurality of receiving antennas for receiving the response signal from the security tag and providing the response signal to the receiver, the response signal being a result of the interrogation signal interacting with the security tag and being re-radiated from the security tag; and an antenna switch connecting the transmitter to the transmitting antennas and the receiver to the receiving antennas, the antenna switch sequentially selecting pair-wise permutations, with replacement, of the antennas once over a predetermined time interval, such that each selected pair consists of one transmitting antenna and one receiving antenna, wherein an amplitude of an output from the receiver resulting from each permutation of the antennas is compared, thereby determining the location of the security tau to correspond with the portion of the security zone being in closest proximity to the antenna pair having the receiver output signal with the largest amplitude.
- 20. A security tag detection and localization system according to claim 19, wherein the antennas in each pair are selected only from adjacent antennas.
- 21. A security tag detection and localization system according to claim 20, wherein the plurality of antennas connected to the EAS sensor comprises two antennas.
US Referenced Citations (8)