HK1133125B - Merchandise surveillance system antenna and method - Google Patents

Description

Merchandise surveillance system antenna and method

Technical Field

The present invention relates to merchandise surveillance systems, and more particularly to antennas for detecting merchandise markers.

Background

In a surveillance system, an antenna, such as a magneto-acoustic EAS (electronic article surveillance) antenna or an RF (radio frequency) antenna, transmits interrogation signals, which in the case of radio frequency id (rfid) are received by RF tags; in the case of EAS, these interrogation signals are received by magneto-acoustic markers, where the RF tags and magneto-acoustic markers are located on items within the enterprise. The tags send corresponding signals back to the antenna. Thus, the interaction between the antenna and the tag establishes an interrogation zone that can provide an enterprise, such as a retail store, with a security system for the merchandise.

Conventional EAS monitoring systems, such as operating at 58kHz, include EAS antennas located in pedestals, floors, ceilings or walls or any combination, whereby the EAS antennas are capable of monitoring large spaces with a minimum number of antennas. Although these types of systems are well suited for large department stores and supermarkets, small retailers have different concerns because their security budgets can be low and floor space can be at a premium. In addition, since small retailers ' facilities are typically smaller than large retailers ' facilities, the small retailers ' stored goods may need to be placed in close proximity to the detection system, thereby increasing the likelihood of false alarms. If a large base is utilized, the space required for the cargo may have to be reduced.

Accordingly, there is a need to address the problems of the prior art, and more particularly, a need for a smaller and more efficient marker detector for use in merchandise surveillance systems.

Disclosure of Invention

Embodiments of the present invention address deficiencies of the art in respect to detecting merchandise surveillance markers and provide a novel and non-obvious method, system and apparatus for detecting merchandise surveillance markers.

According to one aspect, the present invention provides a transceiver for detecting merchandise markers, wherein a first antenna includes a first circuit having a first loop defining a first area and a second loop defining a second area, the second area being substantially coplanar with the first area. The second antenna is substantially coplanar and orthogonally disposed with the first antenna. The second antenna includes a second circuit having a third loop defining a third area and a fourth loop defining a fourth area, the fourth area being substantially coplanar with the third area.

According to another aspect, the invention provides a method for detecting a magneto-acoustic marker, wherein a first magnetic field is generated by sending a current in a first direction via a first transceiver antenna. The first transceiver antenna has a first loop defining a first area and a second loop defining a second area that is substantially coplanar with the first area. A second magnetic field is generated by transmitting a current in a second direction through a second transceiver antenna having a third loop defining a third region and a fourth loop defining a fourth region, the fourth region being substantially coplanar with the third region. The second transceiver antenna is substantially coplanar and orthogonally disposed with the first transceiver antenna. The magnetoacoustic marker is detected by receiving a signal from the first or second antenna.

In another embodiment of the present invention, a method of detecting a magnetoacoustic marker is disclosed. The method includes generating a first magnetic field by transmitting a current in a first direction via a first transceiver antenna, the first transceiver antenna including circuitry having a first loop defining a first area in which the current flows in the first direction and a second loop defining a second area coplanar with the first area, wherein the current flows in the second direction in the second loop. The method may also include generating a second magnetic field by transmitting a current in a second direction via a second transceiver antenna, the second transceiver antenna including circuitry having a first loop defining a third region and a second loop defining a fourth region coplanar with the third region, wherein the current flows in the first loop in the first direction and the current flows in the second loop in the second direction, and wherein the first antenna is coplanar with the second antenna. The method may further comprise detecting the magneto-acoustic marker by receiving a signal from the first or second antenna.

According to another aspect of the invention, there is provided a system for detecting merchandise markers, wherein a first antenna includes a first circuit in the form of a figure 8. The second antenna comprises a second circuit in the form of a figure 8. The first antenna is substantially coplanar and orthogonally disposed with the second antenna. The controller sends the current via the first antenna and the second antenna. The detector detects the merchandise marker via the first or second antenna.

According to another aspect, the present invention provides a system for detecting a radio frequency tag in which a first antenna having a first conductive planar member is substantially coplanar with a second conductive planar member. The second antenna is substantially coplanar and orthogonally disposed with the first antenna. The second antenna has a first conductive planar member substantially coplanar with a second conductive planar member.

Additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The aspects of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description, serve to explain the principles of the invention. The embodiments illustrated herein are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown, wherein:

FIG. 1 illustrates a system for detecting merchandise surveillance markers according to one embodiment of the present invention;

FIG. 2 illustrates a coordinate system for identifying directions;

FIG. 3 illustrates a first antenna in a system for detecting merchandise surveillance markers according to one embodiment of the present invention;

FIG. 4 illustrates a second antenna in a system for detecting merchandise surveillance markers according to one embodiment of the present invention;

FIG. 5 illustrates the first antenna of FIG. 3 and the second antenna of FIG. 4 integrated into a single transceiver of a system for detecting merchandise surveillance markers according to one embodiment of the invention;

FIG. 6 shows another view of the single transceiver of FIG. 5;

FIG. 7 illustrates a first antenna in a system for detecting merchandise surveillance markers according to one embodiment of the present invention;

FIG. 8 illustrates a second antenna in a system for detecting merchandise surveillance markers according to one embodiment of the present invention;

FIG. 9 illustrates the antenna of FIG. 7 and the antenna of FIG. 8 integrated into a single hybrid transceiver of a system for detecting merchandise surveillance markers;

FIG. 10 is a graph showing magnetic field strength for a single antenna in a vertical direction;

FIG. 11 is a graph showing magnetic field strength for a single antenna in the horizontal direction;

FIG. 12 is a graph showing magnetic field strength for a single antenna in a transverse direction;

FIG. 13 is a graph showing magnetic field strength for a hybrid transceiver antenna in a vertical direction;

FIG. 14 is a graph showing magnetic field strength for a hybrid transceiver antenna in a horizontal direction; and

fig. 15 is a graph showing magnetic field strength of a hybrid transceiver antenna in a transverse direction.

Detailed Description

Referring now to the drawings in which like reference designators refer to like elements, there is shown in FIG. 1 a system for detecting merchandise surveillance markers constructed in accordance with the principles of the present invention and designated as "100". The system 100 includes an outer window pane 102 of a door 104, the door 104 including an inner window portion 106. The outer pane 102 may be formed from a conventional building material for doors, such as wood or aluminum. The door 104 also includes a horizontal push bar 108 for pulling or pushing the door 104 to open it. The door 104 is positioned within a door sill or door frame 110 and is hingedly coupled to the door sill or door frame 110 via a pair of hinges 112 such that the door 104 can rotate about the hinges 112.

Fig. 1 also shows a transceiver antenna 120, which is located on the bottom pane of the door 104. The transceiver antenna 120 and its function are described in more detail below. The transceiver antenna 120 is connected to the transceiver controller 118 via a conductive member 115, the conductive member 115 comprising a wire, cable or other conductive trace. Transceiver controller 118 includes a current generator for sending a current or currents through transceiver antenna 120, a detector for detecting signals received from transceiver antenna 120 (due to the presence of an article surveillance tag, such as an EAS tag or an RFID tag), and a processor for making alarm decisions. In one embodiment of the invention, the transceiver antenna 120 includes a resonant or tuned RLC circuit. It is also contemplated that a tuned RLC circuit can be provided as part of transceiver controller 118. The loop 114 in the conductive member 115 allows the conductive member 115 to hang loosely around the portion of the door 104 that rotates when the door 104 is opened or closed. In addition, an alarm 116 is also shown, wherein when activated by the transceiver controller 118, it may generate an audio or visual indicator of the presence of the merchandise surveillance marker.

In embodiments of the present invention, the door 104 may be a side-hung swing door that is hung on the left or right side. In addition, the antenna 120 can be mounted on either surface of the door 104, embedded within the door 104, mounted to one side of the inspection corridor, or mounted adjacent to or under the conveyor belt to detect the passage of merchandise surveillance markers. In the case of a double door, the antenna 120 can be mounted on each side of the double door. In another embodiment of the invention, the transceiver antenna 120 can have separate transmitter and receiver coils.

Although the present invention is primarily described herein with reference to EAS magnetoacoustic markers whose system operates, for example, at 58kHz, it is contemplated that the present invention can be used to detect Radio Frequency Identification (RFID) markers. In an embodiment of the present invention directed to RFID tags, system 100 provides a method for detecting goods to which RFID tags are attached. RFID is an automatic identification method that relies on storing and remotely retrieving data using devices called RFID tags or transponders. RFID tags are small objects that can be affixed to or incorporated into products, animals or humans. RFID tags contain a silicon chip and an antenna so that they can receive and respond to radio frequency interrogations from an RFID transceiver. Passive tags require no internal power source, while active tags require a power source. The RFID tag can operate at low frequencies such as 125-134.2kHz and 140-148.5kHz, and high frequencies such as 13.56MHz and ultra high frequencies such as 868MHz-928 MHz.

In an alternative embodiment of the present invention, the system 100 includes a multi-directional or microstrip antenna 120 attached to the door 104. A directional or microstrip antenna can comprise a conductive linear element such as a coil, or a conductive planar element such as a metal sheet or shield. Phase cancellation techniques can be used to generate appropriate magnetic fields for detecting corresponding merchandise surveillance markers. The controller 118 includes a current generator for sending a current or currents through the antenna 120, a detector for detecting signals received from the antenna 120, and a processor for performing alarm decisions. The alarm 116, when activated by the controller 118, may generate an audio or visual indicator that marks the presence. In another embodiment of the present invention, various other types of antennas can be used for the antenna 120.

Fig. 2 illustrates a coordinate system 200 for identifying directions of an exemplary embodiment. As used herein, directions refer to those directions defined in fig. 2. The horizontal direction 202 refers to a direction parallel to the plane of the door 104 and the plane of the floor 210. The outward or lateral direction 206 refers to a direction parallel to the plane of the floor 210 and perpendicular to the plane of the door 104. The vertical direction 204 refers to a direction parallel to the plane of the door 104 and perpendicular to the plane of the floor 210.

Fig. 3 illustrates a first antenna 300 in a system for detecting merchandise surveillance markers according to one embodiment of the invention. The antenna 300 comprises one half of the exemplary transceiver antenna 120 of fig. 1. A complete circuit is formed in one plane by antenna 300 through which current is sent from transceiver controller 118. The antenna 300 includes a conductive member comprised of a wire, cable or other conductive path, whereby when a current flows through the conductive member, a corresponding magnetic field is generated.

Also shown is an antenna 300 in the form of substantially the numeral 8. In general, the number 8 version includes two separate regions 320 and 322 surrounded by two separate circuit loops of the antenna 300. In one embodiment of the present invention, the two separate areas 320 and 322 encompassed by the circuitry of the antenna 300 are substantially the same size. In another embodiment, the two separate areas 320 and 322 encompassed by the circuitry of the antenna 300 are not the same size. Additionally, although FIG. 3 shows a rectangular ring, the invention supports other shapes such as oval, circular, pear, kidney, etc. In another embodiment of the present invention, the two separation regions 320 and 322 are substantially different in size. In this embodiment, the smaller area would be surrounded by one or more additional coils of the conductive member 115, thereby increasing the magnetic field strength produced by the smaller area such that the magnetic field strength produced by the areas 320 and 322 is substantially the same. In another embodiment of the present invention, the magnetic field generated by the smaller or reduced regions 320, 322 is comparable to the magnetic field generated by the larger regions 320, 322 at a low frequency setting when operating at ultra high frequencies, such as 868MHz-928 MHz. In this way, the size of the regions 320, 322 can be changed to a larger or smaller magnitude, but still generate similar magnetic field strengths, with corresponding modifications to the operating frequency of the antenna 300.

Fig. 3 also shows a series of arrows showing the current flow within the antenna 300. These arrows show: current flows upward through circuit portion 302, then leftward through circuit portion 304, then downward through circuit portion 306, then rightward through circuit portion 308, then downward through circuit portion 310, and then leftward through circuit portion 312 to complete the circuit. Note that: the conductive feature-forming portion 302 is positioned around the conductive feature-forming portion 308 to avoid forming a short circuit. This arrangement of current flow causes the magnetic flux exiting region 320 to be in the opposite direction to the magnetic flux exiting region 322.

Fig. 4 illustrates a second antenna 400 in a system for detecting merchandise surveillance markers. The antenna 400 includes the other half of the exemplary transceiver antenna 120 shown in fig. 1. As with antenna 300, a complete circuit is formed in one plane in accordance with antenna 400 through which current from transceiver controller 118 is transmitted. The antenna 400 includes a conductive member.

In addition, a substantially figure 8 shaped antenna 400 similar to antenna 300 is also shown. In one embodiment of the invention, the two separate areas 420, 422 encompassed by the circuitry of the antenna 400 are substantially the same size. In another embodiment, the two separate areas 420, 422 encompassed by the circuitry of the antenna 400 are different sizes. In another embodiment, the two separate areas 420, 422 encompassed by the circuitry of the antenna 400 are the same size as the areas 320, 322 of fig. 3. In another embodiment of the present invention, the two separation regions 420, 422 are substantially different in size. In this embodiment, the smaller area would be surrounded by one or more additional coils or loops of the conductive member 115, thereby increasing the magnetic field strength generated by the smaller area, thereby causing the magnetic field strength generated by the areas 420, 422 to be substantially the same.

Fig. 4 also shows a series of arrows showing the current flow within the antenna 400. These arrows show: current flows up circuit portion 402, then to the right through circuit portion 404, then down circuit portion 406, then to the left through circuit portion 408, then down circuit portion 410, and then to the right through circuit portion 412 to complete the circuit. Note that: the conductive member forming portion 402 is positioned around portion 408 to avoid forming a short circuit. This arrangement of current flow causes the magnetic flux exiting region 420 to be in the opposite direction to the magnetic flux exiting region 422.

Fig. 5 illustrates the first antenna 300 of fig. 3 and the second antenna 400 of fig. 4 integrated into a single transceiver 500 of a system for detecting merchandise surveillance markers according to one embodiment of the invention. Briefly, fig. 5 illustrates antennas 300, 400 overlapping each other in a substantially coplanar fashion such that they occupy the same overall area. Fig. 5 shows the two antennas 300, 400 slightly offset to better show the current flow arrows. However, the two antennas 300 and 400 are actually positioned orthogonally to each other (rotated approximately 90 degrees). In one embodiment of the invention, antenna 300 is positioned above antenna 400 or overlapping antenna 400, while in another embodiment, antenna 400 is positioned above antenna 300.

Fig. 5 shows: the current flow direction of circuit portions 302 and 402 is the same, thereby amplifying the magnetic flux emanating from the area surrounding circuit portions 302 and 402. On the other hand, fig. 5 shows: the current flow of circuit portions 308 and 408 is in opposite directions, thereby eliminating or clearing the magnetic flux emanating from the area surrounding circuit portions 308 and 408. As shown, the two antennas are oriented orthogonally (rotated approximately 90 degrees) to each other. All other magnetic fields remain as described above with reference to fig. 3 and 4. Thus, the end result of stacking antennas 300 and 400 together is that the overall magnetic flux is consistent with the magnetic flux emitted by each antenna individually, except for a) the reduction or elimination of magnetic flux in the area surrounding circuit portions 308 and 408, and b) the amplification of magnetic flux in the area surrounding circuit portions 302 and 402.

Fig. 6 shows another view of the single transceiver 500 of fig. 5. Fig. 6 shows two antennas 300 and 400 stacked and aligned with each other, with a slight offset from that of fig. 5. The arrows in fig. 6 show the current flow within each circuit section. As described above, the resulting magnetic field generated by the single transceiver 500 is the overall magnetic flux described for each antenna, for example, except for a reduction in the magnetic flux in the area surrounding circuit portions 308 and 408 and an amplification of the magnetic flux in the area surrounding circuit portions 302 and 402.

In an embodiment of the present invention, the controller 118 periodically changes the direction of current flow through one antenna relative to the other, thereby periodically changing the area having reduced and amplified magnetic flux. For example, if the controller 118 shown in fig. 5 switches the current flowing through the antenna 300 to the opposite direction, the resulting magnetic field generated by the single transceiver 500 will be the overall magnetic flux described above for fig. 5, except for the amplification of the magnetic flux in the area surrounding the current portions 308 and 408 (since current will flow in the same direction in both portions) and the reduction or elimination of the magnetic flux in the area surrounding the circuit portions 302 and 402 (since current will flow in opposite directions in both portions). Thus, when current flowing through antenna 300 alternates, portions 302 and 402 periodically alternate between reduced magnetic flux and amplified magnetic flux, and portions 308 and 408 periodically alternate between reduced magnetic flux and amplified magnetic flux. Note that the description of the direction of current flow here is simplified to aid understanding and can be easily explained. It is assumed that one of ordinary skill in the art will understand that the current flowing in antenna portions such as portions 302 and 402 is Alternating Current (AC) and that the directional current arrows shown in the figures illustrate the direction of current flow over 1/2 cycles of the AC waveform.

Thus, in this embodiment, the weak portion of the magnetic field (i.e., that portion of the single transceiver 500 that is the collinear current portion through which current flows in opposite directions) is mitigated by alternately launching a weak (or non-existent) and amplifying magnetic field. In this manner, the magnetic field generated by the system 100 can minimize the exposure of weak magnetic fields and optimize its ability to detect merchandise surveillance markers.

Fig. 7 illustrates a first antenna 700 in a system for detecting merchandise surveillance markers according to the principles of the present invention. The antenna 700 may comprise one half of the exemplary transceiver antenna 120 of fig. 1. A complete circuit is formed in one plane by the antenna 700 through which current from the transceiver controller 118 is sent. The antenna 700 includes a conductive member.

Also shown is a substantially figure 8 shaped antenna 700. In one embodiment of the present invention, the two separate areas 720 and 722 encompassed by the circuitry of the antenna 700 are substantially the same size. In another embodiment, the two separate areas 720 and 722 encompassed by the circuitry of the antenna 700 are of different sizes. Additionally, although FIG. 3 shows a rectangular ring, the invention supports other shapes such as oval, circular, pear, kidney, etc. Note that: the angle 726 between the two regions 720 and 722 is greatly exaggerated in order to show the current flow arrows. The actual angle 726 between the two regions 720 and 722 may be substantially zero so that it appears that the two rectangles are adjacent to each other.

Fig. 7 also shows a series of arrows showing the current flow within the antenna 700. These arrows show: current flows upward through circuit portion 702, then leftward through circuit portion 704, then downward through circuit portion 706, then rightward through circuit portion 708, then downward through circuit portion 710, then leftward through circuit portion 712, then upward through circuit portion 714, and then rightward through circuit portion 716 to complete the circuit. Note that: the conductive member forming portion 716 is positioned around the conductive member forming portion 708 to avoid short circuits. This arrangement of current flow causes the magnetic flux exiting region 720 to be in the opposite direction to the magnetic flux exiting region 722.

Fig. 8 illustrates a second antenna 800 in a system for detecting merchandise surveillance markers, in accordance with one embodiment of the present invention. The antenna 800 includes the other half of the exemplary transceiver antenna 120 of fig. 1. As with antenna 700, a complete circuit is formed in one plane by antenna 800 through which current from transceiver controller 118 is transmitted. The antenna 800 includes a conductive member.

Also shown is a substantially figure 8 shaped antenna 800 similar to antenna 700. In one embodiment of the invention, the two separate areas 820, 822 encompassed by the circuitry of the antenna 800 are substantially the same size. In another embodiment, the two separate areas 820, 822 encompassed by the circuitry of the antenna 800 are different sizes. In another embodiment, the two separate areas 820, 822 encompassed by the circuitry of the antenna 800 are the same size as the areas 720, 722 of fig. 7.

Fig. 8 also shows a series of arrows showing the current flow within the antenna 800. These arrows show: current flows upward through circuit portion 802, leftward through circuit portion 804, downward through circuit portion 806, rightward through circuit portion 808, upward through circuit portion 810, rightward through circuit portion 812, downward through circuit portion 814, and leftward through circuit portion 816 to complete the circuit. Note that: the conductive element forming portion 802 is positioned around the conductive element forming portion 810. This arrangement of current flow causes the magnetic flux exiting region 820 to be in the opposite direction of the magnetic flux exiting region 822.

Fig. 9 illustrates the first antenna 700 of fig. 7 and the second antenna 800 of fig. 8 integrated into a single transceiver 900 of a system for detecting merchandise surveillance markers, in accordance with one embodiment of the present invention. Briefly, fig. 9 illustrates antennas 700, 800 overlapping each other in a substantially coplanar manner such that antennas 700 and 800 occupy the same overall area. Fig. 9 shows the two antennas 700 and 800 slightly offset to better show the current flow arrows. As shown, the two antennas 700 and 800 are placed orthogonally (rotated approximately 90 degrees) to each other. In one embodiment of the present invention, the antenna 700 is located on the antenna 700 or overlaps the antenna 700, while in another embodiment the antenna 800 is located on the antenna 700. In another embodiment of the present invention, the antenna 700 is positioned above and aligned with the antenna 800, while in another embodiment the antenna 800 is positioned above and aligned with the antenna 700 (see FIG. 9 for a more detailed description of the present embodiment below).

The arrows of fig. 9 show the current flow within each circuit portion. Fig. 9 shows: the current flow direction is the same for circuit portions 804 and 704 and circuit portions 706 and 806, which amplifies the magnetic flux emanating from the area surrounding these circuit portions. On the other hand, fig. 9 also shows: the current flow of circuit portions 806 and 714 and 808 and 712 is in opposite directions, which eliminates or clears the magnetic flux emanating from the area surrounding these circuit portions. Note that although fig. 7-9 illustrate antennas 700 and 800 having shapes with portions 708, 716, 802, and 810 forming obtuse angles with respect to their corresponding outer walls (e.g., 702 and 706), with radii of curvature of the wires forming the circuit, it is contemplated that portions 708, 716, 802, and 810 can also be disposed substantially at right angles to the outer wall portions. Therefore, it is noted that the shapes of the antenna 700 and the antenna 800 as shown in fig. 7 to 9 are merely illustrative.

In addition, the direction of current flow of circuit portions 812 and 704 and 814 and 702 is reversed, thereby canceling the magnetic flux in these areas, and the direction of current flow of circuit portions 814 and 710 and circuit portions 712 and 816 is the same, thereby amplifying the magnetic flux in these areas. In addition, since circuit portions 708 and 716 and 810 and 802 are substantially collinear, the magnetic flux in these areas is amplified. Thus, the resulting magnetic field generated by a single transceiver 900 includes: a) an amplified magnetic flux around the inner portion of all quadrants of a single transceiver 900, b) a zero or reduced magnetic field in the outer portion of the upper right and lower left quadrants, c) a magnetic field generated by one antenna in all other regions of a single transceiver 900.

In an embodiment of the present invention, the controller 118 periodically changes the direction of current flowing through one antenna, thereby periodically alternating those areas having reduced and amplified magnetic flux. For example, if the controller 118 switches the current flowing through the antenna 700 to the opposite direction shown in fig. 7, the resulting magnetic field generated by the single transceiver 900 will include: a) an amplified magnetic flux around the inner portion of all quadrants of a single transceiver 900, b) a zero or reduced magnetic field in the outer portion of the upper left and lower right quadrants, c) a magnetic field generated by one antenna in all other regions of a single transceiver 900. Therefore, when the current flowing through the antenna 700 is alternately changed, the outer portions of the upper right and lower left quadrants are periodically alternately changed between the reduced magnetic flux and the amplified magnetic flux, and likewise, the outer portions of the upper left and lower right quadrants are periodically alternately changed between the reduced magnetic flux and the amplified magnetic flux.

With respect to small retail stores where floor space is significantly reduced, embodiments of the present invention, as described with respect to the single transceivers 500 and 900, are capable of generating a "focused" magnetic field that is strong enough to detect merchandise surveillance markers but low enough in amplitude to avoid detecting merchandise surveillance markers that may be placed in close proximity to the detector. In addition, embodiments of the present invention can advantageously generate sufficient magnetic fields with reduced power and small antenna footprint.

In addition, the use of a digital 8-shaped conductive member or coil as a receiver increases the detection performance of the merchandise surveillance system 100. The remote signal source affects both halves of the digital 8 coil equally, thereby creating opposing currents in each half of the coil, which will cancel them out. Thus, the environmental signal sources cancel themselves out, and merchandise surveillance markers that are close to the magnetic field will typically be closer to one loop than the other, thereby inducing a larger current in one coil for detection. Thus, merchandise surveillance markers in close proximity to the magnetic field have an improved signal-to-noise ratio for ambient noise. Using a figure 8 shaped conductive member or coil as a transmitter reduces interference because the field of each half turn of the coil is approximately the same over a distance but out of phase and will thus be self-canceling.

Embodiments of the present invention are still advantageous for mounting the system 100 on a door 104 having a metal frame (de-tuning of the magnetic field is reduced or eliminated). The magnetic flux of one half of the antenna (such as half 320 of antenna 300) generates a current in the door frame 102 in a direction opposite to the direction of the current in that half of the antenna 300. However, the magnetic flux of the other half of the antenna (such as half 322 of antenna 300) creates a current in the opposite direction in the door frame 102, thereby canceling the previous current induced in the door frame 102. Thus, the currents induced in the doorframe 102 by these two half-turns of the figure 8 shaped conductive member oppose and cancel each other out, meaning that there is no loss of magnetic field by coupling to the metal doorframe 102, and likewise, there is no detuning (detuning) antenna for the same reason.

Thus, in this embodiment, the weak portion of the magnetic field, i.e., that portion of the collinear circuit portion of the single transceiver 900 that flows current in opposite directions, is mitigated by alternately launching weak (or non-existent) and amplified magnetic fields. In this manner, the magnetic field generated by the system 100 can minimize the exposure of weak magnetic fields and optimize its performance in detecting merchandise surveillance markers.

Fig. 10 is a graph illustrating magnetic field strength of a single antenna 700 in the vertical direction 204 (see fig. 2). In the graph of fig. 10, the y-axis 1002 represents height and the x-axis 1004 represents magnetic field strength. The arrangement of the antenna 700 is shown at 1006. The graph shows that the field strength of the antenna 700 reaches a peak 1010 halfway across the antenna 300 and gradually decreases at the top 1012 and bottom 1014 edges of the antenna 700.

Fig. 11 is a graph showing the magnetic field strength of a single antenna 700 in the horizontal direction 202. In the graph of fig. 11, the y-axis 1102 represents horizontal distance and the x-axis 1104 represents magnetic field strength. The arrangement of the antenna 700 is shown at 1106. The graph shows that the field strength of the antenna 700 exhibits a peak-valley 1110 midway through the antenna 700 and tapers off at the edges 1112 and 1114 of the antenna 700.

Fig. 12 is a graph showing magnetic field strength of a single antenna 700 in the transverse direction 206. In the graph of fig. 12, the y-axis 1202 represents the lateral distance and the x-axis 1204 represents the magnetic field strength. The arrangement of the antenna 700 is shown at 1206. The graph shows that the field strength of the antenna 700 is high 1210 at the antenna 700, exhibits a peak valley 1212 at a distance from the antenna 700, increases 1214 after the peak valley, and then gradually decreases 1216 as the distance from the antenna 700 continues to increase.

Fig. 13 is a graph illustrating magnetic field strength for a hybrid transceiver antenna 900 (such as the hybrid antenna shown in fig. 6) in the vertical direction 204 (see fig. 2). In the graph of fig. 13, the y-axis 1302 represents height and the x-axis 1304 represents magnetic field strength. The arrangement of the antenna 900 is shown at 1306. The graph shows that the field strength of the antenna 900 peaks 1310 halfway across the antenna 900, falling off at the top 1312 and bottom 1314 edges of the antenna 900 but remaining sufficiently large. Comparing the graph of fig. 13 with the graph of fig. 10 shows that the magnetic field strength increases at the top and bottom edges 1312 and 1314 of the antenna 900.

Fig. 14 is a graph illustrating magnetic field strength of the hybrid transceiver antenna 900 in the horizontal direction 202. In the graph of fig. 14, the y-axis 1402 represents horizontal distance and the x-axis 1404 represents magnetic field strength. The arrangement of the antenna 900 is shown at 1406. The graph shows that the field strength of the antenna 900 is relatively constant throughout the antenna 900 and decreases slightly at the edges 1412 and 1414 of the antenna 900. Comparing the graph of fig. 14 with the graph of fig. 11 shows that the peaks and valleys 1110 (fig. 11) in fig. 14 disappear. The field strength shown in fig. 14 is more uniform than the field strength shown in fig. 11.

Fig. 15 is a graph showing magnetic field strength of the hybrid transceiver antenna 900 in the transverse direction 206. In the graph of fig. 15, the y-axis 1502 represents the lateral distance and the x-axis 1504 represents the magnetic field strength. The arrangement of the antenna 900 is shown at 1506. The graph shows that the field strength of the antenna 900 is nearly constant over a range of distances from the antenna 900, except for a narrow valley 1512 at a distance from the antenna 900. Comparing the graph of fig. 15 with the graph of fig. 12 shows that the magnetic field strength increases at all distances from the antenna 900, except for the narrow valleys 1512.

Embodiments of the invention can take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment containing both hardware and software elements. It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Moreover, unless described to the contrary above, it should be noted that all of the accompanying drawings are not to scale. Modifications and variations are possible in light of the above teachings without departing from the scope and spirit of the invention, which is defined by the following claims.

Claims (15)

1. A transceiver for detecting merchandise markers, comprising:

a first antenna comprising a first circuit having a first loop defining a first area and a second loop defining a second area, the second area being substantially coplanar with the first area;

a second antenna disposed substantially coplanar and orthogonal to the first antenna, the second antenna including a second circuit having a third loop defining a third area and a fourth loop defining a fourth area, the fourth area being substantially coplanar with the third area; and

a controller to send current through the first antenna and the second antenna,

wherein the first antenna and the second antenna are configured to receive drive signals from a controller respectively,

wherein the controller sends current through the first circuit in a first direction and sends current through the second circuit in a second direction,

wherein the controller alternates the direction of current flow through one of the first and second circuits.

2. The transceiver of claim 1, wherein the size of the first region is substantially the same as the size of the second region.

3. The transceiver of claim 2, wherein the size of the third region is substantially the same as the size of the fourth region.

4. The transceiver of claim 3, wherein the first region and the second region are substantially the same size as the third region and the fourth region.

5. The transceiver of claim 1, wherein the merchandise tag comprises any one of an EAS tag and an RFID tag.

6. The transceiver of claim 5, wherein the first antenna and the second antenna are directional antennas.

7. The transceiver of claim 1, further comprising a detector that detects merchandise markers by receiving a signal from the first or second antenna.

8. The transceiver of claim 7, further comprising:

an alarm that activates an indicator when the detector detects a merchandise marker.

9. A method for detecting a magneto-acoustic marker, comprising:

generating a first magnetic field by sending a current in a first direction through a first transceiver antenna having a first loop defining a first area and a second loop defining a second area that is substantially coplanar with the first area;

generating a second magnetic field by sending a current in a second direction through a second transceiver antenna having a third loop defining a third region and a fourth loop defining a fourth region, the fourth region being substantially coplanar with the third region, the second transceiver antenna being substantially coplanar with and orthogonally positioned to the first transceiver antenna, wherein the first and second transceiver antennas are configured to receive drive signals from a controller, respectively;

detecting a magneto-acoustic marker by receiving a signal from the first transceiver antenna or a second transceiver antenna; and

alternating a direction of current flowing through one of the first and second transceiver antennas.

10. A system for detecting a magneto-acoustic article marker, comprising:

a first antenna comprising a first circuit having substantially a figure-8 shape;

a second antenna comprising a second circuit having substantially a figure-8 shape, wherein the first antenna is substantially coplanar and orthogonally positioned with the second antenna;

a controller to send current through the first and second antennas, wherein the first and second antennas are configured to receive drive signals from the controller, respectively; and

a detector to detect a magneto-acoustic merchandise marker via the first or second antenna,

wherein the controller alternates the direction of current flow through one of the first and second circuits

11. The system of claim 10, wherein the first and second antennas are transceiver antennas.

12. The system of claim 11, wherein the first and second antennas are directional antennas.

13. The system of claim 10, wherein the merchandise tag comprises one of an EAS tag and an RFID tag.

14. The system of claim 10, further comprising an alarm for activating an indicator when the detector detects the merchandise marker.

15. The system of claim 14, wherein the first antenna and the second antenna are secured to a door.