GB2476050A

GB2476050A - Electronic tag detector and deactivation system

Info

Publication number: GB2476050A
Application number: GB0921496A
Authority: GB
Inventors: Paul Cox; Mervyn Lear
Original assignee: Redcliffe Magtronics Ltd
Current assignee: Redcliffe Magtronics Ltd
Priority date: 2009-12-08
Filing date: 2009-12-08
Publication date: 2011-06-15
Anticipated expiration: 2029-12-08
Also published as: GB2500134A; GB2476050B; GB0921496D0; GB2500134B; GB201309642D0

Abstract

An electronic article surveillance (EAS) tag detector comprises a signal generating circuit for generating a tag detection signal and an antenna arrangement for transmitting the tag detection signal. The tag detection signal comprises a group of at least three bursts, where the first and second bursts are separated by a first time interval and the second and third bursts are separated by a second time interval which is different from the first time interval. The detector may additionally comprise a detector circuit for receiving a reradiated signal from the tag, and comparing it to a reference. The system may further generate a tag deactivation signal for de-energizing a tag within the detection area. The format of the detection signal reduces interference between the tag detector and mains operated EAS equipment.

Description

Tag Detector

Technical Field

This invention relates to a detector for detecting electronic article surveillance (EAS) security tags.

Background Art

EAS is a well -known technology used for preventing theft from retail stores.

Typically, EAS tags are fixed to items of merchandise for sale in a store and a store sales clerk removes the tag from an item or deactivates the tag when a customer properly purchases the item at a point of sale (POS). Detection systems are located at exits of the store which generate electromagnetic fields for sensing the presence of active tags as customers leave the store. In response to an active tag being sensed, typically, an alann is sounded.

It is not un-common for a sales clerk to fail to correctly dc-activate the tag on a purchased item. When the customer attempts to leave the store, the detection system senses the tag and an alarm sounds. Until recently, in order for the tag to be correctly de-activated, the customer would have to have returned to the point of sale where a fixed location non-portable tag deactivator was kept. Nowadays, portable hand held deactivators are known, which can be kept or easily taken to the exit to deactivate a tag in such circumstances.

The present inventors have appreciated that a problem with known portable tag deactivators is that in the presence of other EAS equipment, for example, a detection system at a store exit, the portable deactivator may detect signals generated by the equipment causing the deactivator to falsely sense that an active tag is present.

Furthermore, signals generated by known portable deactivators my cause the detection system to falsely sense that an active tag is present and hence activate an alarm.

Some embodiments of the invention aim to overcome these problems.

I

Summary of the Invention

According to the invention there is provided an electronic article surveillance tag detector, comprising: a signal generating circuit for generating a tag detection signal; an antenna arrangement for transmitting the tag detection signal; wherein, the tag detection signal comprises a group of at least three bursts, the group comprising a first pair of consecutive bursts separated by a first time interval and a second pair of consecutive bursts separated by a second time interval different from the first time interval.

According to the invention there is also provided a method of operating an electronic article surveillance tag detector, the method comprising: generating a tag detection signal comprising a group of at least three bursts, the group comprising a first pair of consecutive bursts separated by a first time interval and a second pair of consecutive bursts separated by a second time interval different from the first time interval; transmitting the tag detection signal; and detecting a return signal generated by a tag in response to the tag detection signal.

Brief Description of the Drawings

Figure 1 illustrates an electronic circuit of a tag deactivator; Figure 2 illustrates a signals timing diagram; Figure 3 illustrates a tag deactivator.

Detailed Description of the Invention

Referring to Figure 1, there is illustrated a circuit for a hand held portable Acoustic -Magnetic (AM) tag deactivator embodying the present invention. Although this described embodiment is for detecting and deactivating AM tags, it will be appreciated by those skilled in the art that alternative embodiments can readily be adapted for use with other types of EAS tags, for example, magnetic, radio -frequency or microwave tags.

Acoustic magnetic tags comprise a magnetostrictive, ferromagnetic strip and a magnetic metallic strip both of which are free to oscillate mechanically. The ferromagnetic strip typically has a resonance frequency of 58 Kl-Iz (or alternatively 66kHz).

In order to first detect an AM tag, an AM tag deactivator embodying the present invention is adapted to emit a signal comprising a pattern of bursts (typically containing 58kHz sinewaves) of E-M radiation, the radiation of each burst having a frequency that matches the resonance frequency of a tag. These bursts cause the ferromagnetic strip of a tag in close enough proximity to the deactivator to vibrate longitudinally. When a tag is active, the magnetic metallic strip is magnetised which makes the ferromagnetic strip respond more strongly to the detection bursts emitted by the deactivator. The vibration of the ferromagnetic strip causes a change in its magnetisation that, in the presence of a magnetised metallic strip, induces at the deactivator a detectable signal that matches in terms of signal frequency and burst repetition, the detection signal emitted by the deactivator. If a detected signal has the correct signal frequency and burst pattern, tag detection is declared, and in response the deactivator is arranged to emit a decaying oscillating magnetic field which de-magnetises the metallic strip of the tag. With the metallic strip de-magnetised the response of ferromagnetic strip to any subsequent detector is too small for it to: be detected by that detector and the tag is thus deactivated.

The electronic circuit 1 comprises a tag detection branch 2, a tag deactivation branch 3, a detection and deactivation coil 4, a control means 5, for example a PlC micro-controller, for controlling the detection branch 2 and deactivation branch 3 and a power source 6, for example a DC battery set, for powering the circuit 1.

The tag detection branch 2 comprises a first amplifier 7, for example a push -pull bipolar transistor for amplifying a signal to be transmitted, a capacitor 8, a first filter/amplifier stage 9 for filtering/amplifying a received signal, a demodulator 10 for demodulating a received signal, a pass filter/amplifier 11 for filtering and amplifying a demodulated received signal, a comparator 12 for comparing a received de-modulated signal to a reference input (not shown) and a blanking switch 13 for isolating the filters/amplifiers 9 and 11 when the detection branch 2 is transmitting a signal.

In operation, in response to a user command input by suitable data input means (not shown) for example a control panel, to implement a tag detection procedure, the PlC micro-controller 5 generates a BURST signal which is amplified by the first amplifier 7, passes the capacitor 8 and is transmitted as E-M radiation by the coil 4.

The coil 4 may for example be a single multi-turn coil antenna of about 7.5 to 10cm diameter.

Figure 2(a) illustrates a preferred format for the detection signal 30 generated and transmitted by the circuit 1. The detection signal 30 comprises a repeating pattern of three bursts 31. Each of the three bursts 31 in the pattern comprises radiation that matches the expected resonance frequency of the tags (for example 58KHz), has a particular burst duration, for example about 2ms, and the time period between bursts differs. In this example, the period between the first burst and the second burst is about 1 0.4ms and the period between the second burst and the third burst is longer at; about. l5ms. This pattern of burst repeats at a given repetition period, for example, about 230ms.

As is illustrated in Figure 2(b), the PlC micro-controller 5 generates a BLANKING signal 40 that is coincident in time with the BURST signal 31 and which controls the blanking switch 13 so that the switch is open and consequently the filter/amplifier 9 and the filter/amplifier 11 are isolated whenever a burst 31 of the detection signal 30 is being transmitted. The blanking switch 13 is closed whenever a burst 31 of the detection signal 31 is not being transmitted to enable detection of a resonance signal from a tag.

As is illustrated in Figure 2(c), the PlC micro-controller 5 further generates a DEMODULATION signal 50 comprising a repeating pattern of three bursts 51 that matches the repeating pattern of the detection signal 31 in that the burst durations, the time periods between bursts and the repetition periods are identical for both. The frequency of the demodulation signal 50 is slightly offset from that of the detection signal and is in this example 56kHz. The timing of the bursts in DEMODULATION signal 50 is also slightly behind the timing of the bursts in the detection signal 31 and matches the expected timing of the bursts in a received signal generated by a tag in response to the detection signal 31.

If the coil 4 receives a valid returned signal generated by tag in response to the detection signal 31, the returned signal passes through the filter/amplifier stage 9 and is input to the demodulator stage 10 which outputs a demodulated received signal that matches the demodulation signal except that the bursts have a difference frequency that is equal to the difference between the frequencies of the received signal and the demodulation signal, 2kHz in this example. The filtered and amplified demodulated signal is input to the comparator 12 which detects the difference frequency.

Figure 2(d) illustrates the output signal 60 from the comparator 12 when a valid returned signal from an active tag is received. The output signal 60 comprises three peaks 61, the first and second of which are separated by the same time period as are the first and second bursts of the deteàtion signal 31 (1 0.4ms in this example) and the second and third of which are separated by the same time period as are the second and third bursts of the detection signal 31(1 Sms in this example).

The output of the comparator 12 is connected to a trigger input of the PlC Micro -controller 5. The PlC micro-controller S counts consecutive peaks output form the comparator 12 and on receipt of three consecutive peaks at timings coincident with the timings of three bursts of the demodulation signal and provided no peaks are detected that are not coincident with the timings of three bursts of the demodulation signal, the controller 5 outputs a user alert signal that operates a suitable user alert, for example a sounder and/or light source 14 and outputs a tag DEACTIVATE signal, Figure 2e, which triggers the tag deactivation branch 3 and operates a relay 18 to isolate the detection branch 2 to ground, disconnecting it from the coil 4.

If there is no detection of three consecutive peaks at timings coincident with the timings of three bursts of the demodulation signal and/or a peak is detected that is not coincident with the timings of any of three bursts of the demodulation signal, then the micro controller does not output the user alert signal (or the tag deactivate signal) and repeats the tag detection signal 30.

A tag detection signal 30 of this type comprising three bursts with the time period between the first and second bursts being different from the time period between the second and third bursts is advantageous because it makes it less likely that there will be any interference between the tag deactivator and mains powered EAS security products, for example, the tag detection systems located at store exits. Such mains powered detectors typically transmit a tag detection signal which comprises a plurality of bursts, with successive bursts in the signal all being separated by a time period equal to that of a mains signal (i.e. 2Oms for a 50Hz mains signal, 16.7ms for a 60Hz mains signal). Because the time periods between the first and second bursts and the second and third bursts of the tag detection signal 30 differ from each other, there is a low correlation between the tag detection signal 30 and the detection signals typically transmitted by mains powered EAS security equipment. Consequently, the likelihood is low that a detection signal transmitted by a mains powered EAS security equipment will be received by a deactivator with a timing that coincidently matches that expected from a tag resonating in response to the deactivator. Therefore, it is unlikely that mains operated EAS security equipment can cause the tag deactivator to erroneously sense that an active tag is present. Similarly, it is unlikely that a mains operated tag detection signal receiving the tag detection signal 30 transmitted by the deactivator will erroneously cause the mains tag detection systems to falsely sense an active tag.

Preferably, to minimise the correlation between a tag detection signal 30 from the tag deactivator and a tag detection signal from a mains powered tag detector, at least one or both of the time periods between the first burst and the second burst and the second burst and the third burst of the signal 30 are not equal to the period of the mains signal (or a multiple thereof) used by mains powered EAS equipment in the premises where the deactivator is to be used. Furthermore, preferably, the repeat period of the detection signal 30 is not equal to a multiple of the mains signal period.

Where the relevant mains signal period is 2Oms it is found to be particularly advantageous if the detection signal comprises a group of at least three bursts comprising a first pair of consecutive bursts separated by 10 ±4ms and a second pair of consecutive bursts separated by 15 ±4ms.

The tag deactivation branch 3 comprises a high voltage oscillator 15, a capacitor bank 16 and a triac 17. The high voltage oscillator 15, powered by the battery set 6, is used to maintain the capacitor bank 16 at a peak voltage V. In one embodiment, the oscillator 16 is a 500V oscillator, the capacitor bank 17 comprises four 8J2F capacitors connected in parallel with a peak voltage of 500V dc and the battery set comprises 8 1.2V AA cells connected in series.

The tag DEACTIVATE signal from the PlC micro-controller 5 is received by and triggers the triac 17 enabling the energy stored in the capacitor bank 16 to be transferred into the coil 4 to generate an oscillatory decaying magnetic field which demagnetises the metallic strip of the tag' to deactivate the tag.

When the DEACTIVATE signal goes low, the triac 18 is deactivated and the relay 18 reconnects the detection circuit 2 to the coil 4. The detection signal is repeated but following a successful tag deactivation there is no detectable resonance signal from the tag and the output of the comparator remains low (see Fig 2e).

Figure 3 illustrates a plan view of a portable tag deactivator embodying the present invention. The deactivator comprises a plastic housing 60 defining two apertures 61a and 61 b at a handle region 62 by means of which a user can grasp the deactivator.

The figure illustrates regions within the housing 60 where the coil 4, capacitors 16, and batteries 6 are located together with a region 63 where the remaining components of the circuit are located.

The described deactivator has the benefit of being lightweight and portable and is able to detect and deactivate tags at a distance of up to 100mm vertical and 80mm horizontal planes.

The deactivator has a low power usage that provides for long periods of uninterrupted usage. Preferably, the battery set 6 is rechargeable, and the deactivator comprises a connection point (not shown) for a battery charger.

As indicated in Figure 1, an automatic power turn off circuit may be connected to the battery 6 to disconnect the battery from powering the deactivator if the deactivator remains unused for a pre-determined period.

Although the preferred embodiment has been described with respect to a cordless portable handheld tag deactivator, it will be appreciated that the invention is not limited to such a device. Indeed, it will be appreciated that other types of devices that need to detect EAS tags may beneficially embody the present invention, not just tag deactivators.

Modifications of the invention can be made by one skilled in the art without departing from the scope of the invention.

Claims

CLAIMS1. An electronic article surveillance tag detector, comprising: a signal generating circuit for generating a tag detection signal; an antenna arrangement for transmitting the tag detection signal; wherein, the tag detection signal comprises a group of at least three bursts, the group comprising a first pair of consecutive bursts separated by a first time interval and a second pair of consecutive bursts separated by a second time interval different from the first time interval.
2. A detector according to claim 1, wherein, at least one of the first time interval and the second time interval is not equal to an electrical mains signal period or a multiple thereof. 15.
3. A detector according to claim 2, wherein, the first time interval and the second time interval are both less than an electrical mains signal period and the sum of the first interval and the second interval is greater than the electrical mains signal period.
4. A detector according to any of claims I to 3, wherein the first time interval is 10.4 ±4ms and the second time interval is 15 ±4ms.
5. A detector according to any preceding claim further comprising: a signal detector circuit for detecting an expected return signal generated by a tag in response to the tag interacting with the tag detection signal, wherein the return signal comprises a group of at least three pulses, the group comprising a first pair of consecutive pulses separated by the first time interval and a second pair of consecutive pulses separated by the second time interval.
6. A detector according to claim 5, wherein the signal detector comprises a demodulator for applying a demodulating signal to a received signal, the demodulating signal comprising a group of at least three bursts, the group comprising a first pair of consecutive bursts separated by the first time interval and a second pair of consecutive bursts separated by the second time interval.
7. A detector according to claim 6, wherein the signal detector circuit comprises a comparator for comparing a demodulated received signal to a reference and a processor for monitoring the output of the comparator.
8. A detector according to any preceding claim wherein, the signal generating circuit is for generating a tag deactivation signal
9. A detector according to claim 8, wherein the signal generating circuit comprises a capacitor arrangement chargeable by a battery and wherein the capacitor arrangement is discharged through the antenna to generate the tag deactivation signal.
10. A detector according to claim 9 further comprising a battery and a voltage oscillator and wherein the battery charges the capacitor arrangement through the * voltage oscillator.
11. A detector according to claim 9 or 10, wherein the capacitor arrangement * 20 comprises a plurality of capacitors connected together in parallel.
12. A detector according to any of claims 8 to 11, wherein the signal generating circuit automatically generates the tag deactivation signal in response to the deactivator detecting an active tag.
13. A detector according to any preceding claim comprising processing means for controlling the signal generating circuit.
I 4. A detector according to claim 1, wherein, at least one of the first time interval and the second time interval is not equal to 2Oms or a multiple thereof or 16.6ms or a multiple thereof.
15. A method of operating an electronic article surveillance tag detector, the method comprising: generating a tag detection signal comprising a group of at least three bursts, the group comprising a first pair of consecutive bursts separated by a first time interval and a second pair of consecutive bursts separated by a second time interval different from the first time interval; transmitting the tag detection signal; and detecting a return signal generated by a tag in response to the tag detection signal.