WO2007125319A1

WO2007125319A1 - Rfid receiver with distributed intelligence

Info

Publication number: WO2007125319A1
Application number: PCT/GB2007/001516
Authority: WO
Inventors: Christopher Bullock; Damian Mark Mallinson; Peter Whaites
Original assignee: Active Tagging Limited
Priority date: 2006-04-26
Filing date: 2007-04-26
Publication date: 2007-11-08
Also published as: GB0608224D0

Abstract

The present invention relates to security systems. In particular, the invention relates to security systems comprising a plurality of RFID tags to be attached to persons including babies, patients and other objects whose movements are to be monitored An RFID receiver is provided comprising: means for registering with the receiver an identification code of at least one RFID tag; means for determining whether an identification code of a tag detected by the receiver corresponds to an identification code of a registered tag, wherein a registered tag is a tag registered with the receiver; alert means, said alert means being adapted to issue a receiver alert signal when a signal received from a registered tag comprises a tag alert signal.

Description

RFID RECEIVER WITH DISTRIBUTED INTELLIGENCE

The present invention relates to security systems. In particular, the invention relates to security systems comprising a plurality of RFID tags to be attached to persons including babies, patients and other objects whose movements are to be monitored.

BACKGROUND

Security tags are used in a multiplicity of environments to facilitate monitoring of the movement of objects including persons. For example, security tags may be attached to items of merchandise in a retail outlet, to persons vulnerable to aoαuction such as babies and young children, or other objects or persons whose movements are to be confined to a particular area. Detectors located at strategic positions such as exit paths may be employed to detect the tags, and provide an alert in the event that an attempt is made to remove a tagged object from that area.

RFID tags communicate by transmitting a radio frequency identification (RFID) signal. Two main categories of tags are known; active tags have their own onboard power supply, usually in the form of a miniature battery. Passive tags have no onboard power supply, and are powered by the RF energy transmitted by a tag reader. When interrogated by a tag reader, an active tag may be designed to transmit a unique identification code. Active tags have the advantage that communication between the active tag and a tag reader may be maintained over larger distances than in the case of a passive tag.

Active tags may fall into one of two categories. The first category comprises tags that transmit a signal in response to an electromagnetic signal received from a tag reader. The onboard power supply is typically relatively small and enables the tag to transit more complex signals, and to transmit over a longer range. The second category comprises tags that transmit an electromagnetic signal independently of a signal from a tag reader. The signal may be transmitted to a passive reader, i.e. to a reader that does not transmit a signal, but rather waits to receive a signal from a tag. For example, the tag may wake itself periodically from a 'sleep mode' and transmit a signal for reception by a reader independently of whether the tag is in range of a reader. The present invention relates particularly, but not exclusively, to this second category of active tags.

A variety of methods of implementing RFID security tag systems are known. For example, the tag system may be required to raise an alert in the event that the presence of a tag is detected by a tag reader. In retail environments, tag readers are typically located at exit points from the retail outlet. In the event that an attempt is made to pass a tagged object through the exit point, an alert will be triggered.

Alternatively, each of a plurality of tags may have a unique identity, or be associated with a particular 'class' of object, such as a class of objects that are permitted to pass through an exit, or a class of objects that are not permitted to pass through an exit. In this situation the tag reader is required to determine the identity of a tag before deciding whether or not to raise an alert.

For certain applications, it is desirable to obtain positive confirmation of the presence of a tag within an environment. For example, in the case of a baby in a maternity unit it is desirable to positively confirm that the baby is still present in the maternity unit, and that the baby has not been abducted. Type 2' active RFID tags are the preferred choice in applications such as this one, since the larger communication range of a type 2 active tag compared with a passive tag reduces the number of tag readers required to provide continuous coverage in a given area.

Clearly, in applications where it is critical to know at all times that a tag is within a predetermined area, 'blind transmissions' by an active tag are sufficient. One or more tag readers within the area may be programmed to listen for transmissions from the tags irTorder to confirm that each tag^" is^~ within ^"the predetermined areaT In the event that a signal from a tag is not detected, when it is determined that a signal from the tag should be detected, the system may provide an alert so that action may be taken to recover the tagged object.

The problem exists that attempts may be made to remove the tag from the object by an unauthorised person, allowing the object to be removed from its location undetected. It is therefore desirable to ensure that any attempt to remove a tag from an object will be detected. It is known to provide a security device for monitoring personnel movement comprising an RFID tag and a non-stretchable strap, the strap comprising an electrical conductor that may be looped around a limb of the wearer. In order to remove the security device from the person the strap must be severed. The act of severing the strap breaks the electrical continuity of the strap, thereby triggering an alert.

In some cases, the strap comprises a pair of flexible members connected to opposing ends of the tag. Each of the flexible members has an electrical conductor running through it, which is connected to a terminal of an electronic circuit. The free ends of the flexible members may be releasably connected to each other by a metal press-stud fastener, which also completes an electrical circuit through the strap, between terminals of the electronic circuit. If the strap is cut, the electrical characteristics of the strap will change. The change may be detected by the circuit and an alert triggered.

In some alternative designs, the tag contains a switch sensitive to the presence of a magnetic field, such as a reed switch. The tag is fixed to the object to be monitored using double sided adhesive tape. Within the tape, a permanent magnetic material is concealed. If the tag is removed from the object, the tag is separated from the magnet resulting in a change of state of the switch. The tag reports a tamper event in response to the change of state of the switch.

Known RFID systems comprise a plurality of RFID readers connected to a control system that monitors the signals detected by the RFID readers. The problem exists that a plurality of systems may be required to operate in close proximity to one another such that readers monitoring one area are able to read tags within a neighbouring area. If a tag in one area emits a tamper alert, a reader monitoring the neighbouring area may

^"detect the tamper ^"alert and trigger a tamper alert in the neighbouring ^"area ^"also.^"

Similarly, a portal RFID reader, monitoring an exit area, may detect a tag on a different floor of the building and secure that exit. Additionally, the portal RFID reader may detect a tag in a room bordering the corridor. The wearer of the tag may be safely confined within the room, however the portal RFID reader is not able to determine this without further information.

BRIEF SUMMARY OF THE DISCLOSURE

In a first aspect of the present invention there is provided an RFID receiver comprising: means for registering with the receiver an identification code of at least one RFID tag; means for determining whether an identification code of a tag detected by the receiver corresponds to an identification code of a registered tag, wherein a registered tag is a tag registered with the receiver; alert means, said alert means being adapted to issue a receiver alert signal when a signal received from a registered tag comprises a tag alert signal

The invention has the advantage that an alert may be issued directly by a receiver in the event of a tag alert signal being received from a tag registered with the receiver. Thus, if a control system to which a plurality of receivers are connected becomes unavailable, for example due to a malfunction or due to a power outage, RFID receivers may continue to monitor tag transmissions for tag alert signals.

Preferably the receiver is provided with communication means, the receiver being adapted to communicate to a controller an identity of a tag via said communication means when a tag is detected by the receiver.

Preferably the receiver is adapted to communicate to the controller that a tag alert signal has been received by the receiver when a tag alert signal is received by the receiver.

This has the advantage that the controller can provide information to a user of the system. The information may include an indication of the last known location of the tag, and an identity of the object to which the tag has been attached.

Preferably said alert means comprises means for providing at least one selected from amongst an audible alert and a visual alert.

This feature has the advantage that the receiver may provide an audible and/or a visual alert to personnel independently of any external control system. Thus, in the event that an external controller with which the receiver communicates is inoperative, alerts may still be provided by a receiver.

The tag alert signal may comprise a tamper alert signal. This feature has the advantage that an attempt to remove a tag from a tagged object may be detected and attention drawn to such an event.

Preferably the tag alert signal comprises a battery level alert signal.

This feature has the advantage that a level of charge remaining in a battery may be detected and attention drawn to the need to replace the battery or discard the tag before failure of the tag due to a low battery level occurs.

Preferably the means for registering a tag with a receiver comprises a communication signal transmitted from the controller to a receiver.

Thus, the receivers may be provided with a list of tags registered to that receiver by a central control system. Programming the receivers from a central location with a list of tags registered to that receiver is typically easier than programming individual receivers manually at the location of the receiver.

Alternatively, or in addition, the means for registering a tag with a receiver may comprise means for manually registering a tag with a receiver, said means being provided at each receiver.

Preferably the alert means is further adapted to issue an alert when an identification code of a tag registered with the receiver is detected by the receiver.

Alternatively the alert means may be further adapted to issue an alert when an identification code of a tag not registered with the receiver is detected by the receiver.

This feature has the advantage that tags entering an unauthorised area may be detected and attention drawn to such an event.

The receiver may be adapted to provide a signal to seal a portal when an unauthorised tag is detected.

Preferably an unauthorised tag is a tag having an identification code that corresponds to an identification code of a registered tag. An unauthorised tag may be a tag having an identification code that does not correspond to an identification code of a registered tag.

Alternatively an unauthorised tag may be a tag having an identification code that corresponds to an identification code of a registered tag when a further condition is met.

The further condition may be that a current time corresponds to a time registered with the system for which a tag is considered to be an unauthorised tag.

The receiver may be provided with a portal antenna.

Preferably the portal antenna is adapted to receive RFID transmissions from tags located in a portal area, said portal antenna oeing adapted to not receive transmissions from tags located in a blind area, said blind area being an area laterally adjacent to said portal area.

This feature has the advantage that RF signals transmitted by tags worn by persons located in said areas will not be received by the receiver associated with the exit.

Said portal area may comprise a portion of a corridor, and a portion of a periphery of a blind area is defined by a wall of the corridor.

The portal antenna may comprise a Yagi antenna.

The portal antenna may be provided in the form of a substantially flat panel.

Alternatively or in addition, a receiver may be provided with a patch antenna, the patch antenna being adapted to be mounted remotely from the receiver.

This feature has the advantage that an antenna may be positioned in a location that is unsuitable for mounting a receiver, such as a ceiling location in the centre of a lift lobby area.

Preferably the patch antenna is adapted for connection to the receiver by a cable. Preferably, when a tag is detected having an identification code that corresponds to an identification code of a registered tag, and a portal associated with the receiver is in a closed condition, the receiver is adapted to maintain the portal in a closed condition.

The receiver may be further adapted to communicate to a controller that the portal is being maintained in a closed condition.

Preferably, when a tag is detected having an identification code that corresponds to an identification code of a registered tag, and a portal associated with the receiver is in an open condition, the receiver is adapted to provide an alert.

This feature has the advantage that one or more taαs mav be reαistered with a rprpivpr that are not permitted to pass beyond the receiver. If a registered tag is detected by the receiver and a portal associated with the receiver is closed, the portal may be locked. If the portal is in an open condition, an alert may be generated.

A receiver may be associated with a portal having means for automatically opening the portal.

Preferably, in the event that the portal is in an open condition and a tag is detected having an identification code that corresponds to an identification code of a registered tag, the receiver is adapted to close the portal.

This feature has the advantage that a tagged individual walking past a closed door only overrides the lock on the door for the period during which they are present in the vicinity of the door. No alarm is generated, therefore reducing a stress level of staff working in the vicinity.

The signal to seal a portal may be provided only if the receiver determines that the time at which the tag is detected corresponds to a time during which the tag is not permitted to pass through the portal.

This feature allows tags to be permitted to pass through a portal between certain times, such as during office hours or daylight hours. Alternatively the receiver may be adapted to provide a signal to seal a portal when a tag is detected not having an identification code that corresponds to an identification code of a registered tag.

This feature may be used in situations where only registered tags are to be permitted to pass through a portal.

In a second aspect of the invention there is provided a security system comprising a plurality of RFID receivers as claimed in any preceding claim.

Preferably the system further comprises a controller, wherein the controller is adapted to communicate with the receivers.

This feature has the advantage that central control of the RFID receivers is possible.

Preferably the controller comprises means for registering a tag with the system.

Preferably the controller further comprises means for registering a tag with a receiver.

Thus, a tag registered with a particular 'safe area' of a building such as a ward of a hospital may be registered by the system to each of the receivers monitoring that particular area. The user of the system therefore does not need to register the tag with each receiver separately.

A 'safe area' is an area within which it is considered safe for an object to which a tag has been attached to move.

In the case of patient monitoring in a hospital environment, for example, a safe area for a new-born baby may be defined as a post-natal ward. A safe area for a geriatric patient may be defined as a geriatric ward and an enclosed garden area accessed via a corridor and a garden door.

Preferably the controller comprises means for generating a system warning signal when an alert signal is received from a receiver. This feature has the advantage that a warning signal may be provided to a user of the system at a central location. The fact that the generation of a system warning signal has occurred may be logged by the controller for statistical analysis and the identification of problem areas or individuals. Furthermore, the system may provide an indication of a location of a tag that has generated an alert signal. Determination of the location of a tag that has generated an alert signal may be made by reference to the location of the receiver or receivers receiving the alert signal.

In the event that a plurality of warning signals are generated simultaneously, the controller may provide an indication of the nature of each event that has generated a warning signal, and locations of the tags transmitting the alert signals. If this feature were not present, a user may be required to make a check of the entire safe area before an identity of a tag that has generated a warning signal may be determined.

Preferably the system warning signal comprises at least one selected from amongst an audible warning signal and a visual warning signal.

Preferably the alert signal comprises at least one selected from amongst a tamper alert signal, a battery alert signal and an unauthorised presence signal.

This feature has the advantage that the system may be provided with an alert signal when it is determined that a tag has been tampered with, and when a battery is nearing the end of its life. In the event of a tamper alert signal, a user of the system may be directed by the controller to the location of the tag generating the tamper alert signal.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, and to show how it may be carried into effect, reference shall now be made by way of example to the accompanying drawings, in which:

FIGURE 1 is a schematic diagram of an RFID system according to an embodiment of the invention;

FIGURE 2 is a schematic diagram of an RFID receiver installation in a building; FIGURE 3 is a schematic diagram of a portal RFID receiver installation.

FIGURE 4 is a schematic diagram showing a relative reception level of a RFID receiver as a function of distance between a tag and the receiver; and

FIGURE 5 is a schematic diagram of a flat panel YAGI antenna in an orientation suitable for mounting above a door.

DETAILED DESCRIPTION

According to a preferred embodiment of the present invention a security system 10 (FIG. 1) comprises a control module 100 and a plurality of RFID receivers 200 with distributed intelligence. The control module 100 comprises a computer system 10 connected to the RFID receivers 200 via a network 300. In embodiments of the system the network 300 comprises a wired network; alternatively or in addition the network 300 may comprise a wireless network.

RFID receivers are positioned in an area to be monitored such as a hospital building 500 such that the receivers are able to receive RF transmissions from RFID tags 400 located within one or more 'safe areas' of the building.

According to the present embodiment, a patient to be monitored is assigned an RFID tag 400 having a unique identification code. The tag 400 is adapted to transmit a signal comprising the unique identification code at intervals of time.

The identification code of a tag 400 is entered into the computer system 100 together with details of the patient to whom the tag 400 has been assigned. Information is also provided to the computer system defining a safe area for that tag. The safe area may be a predefined area for all patients to be monitored bv that computer system. For example, a computer system monitoring a post-natal ward may define a safe area for all tags registered with that system as the boundaries of the post-natal ward itself. Alternatively, a safe area may include a corridor leading from the post -natal ward to a retail outlet, and the retail outlet itself. The retail outlet mav for example be a restaurant The identification code of each tag 400 registered with the computer system 100 is communicated to the RFID receivers 200 monitoring the safe area within which the tag 400 is permitted to move.

The tag 400 is also adapted to issue a tamper alert in the event that an attempt is made to remove the tag 400 from an object such as a patient. In addition, the tag 400 is adapted to provide a battery level alert when a level of charge remaining in a battery of the tag reaches predetermined levels. In embodiments of the invention, a signal transmitted by the tag 400 comprises the identification code and a charge level signal, the charge level signal indicating a charge level of a battery of the tag 400. The charge level signal provides an indication that the level of charge remaining in the battery is either above substantially 50%; between substantially 50% and substantially 20%; or below substantially 20%.

When an RFID receiver 200 receives a signal from a tag 400 that is registered with that receiver, the receiver 200 communicates to the computer system that the tag 400 having that particular identification code has been detected by the receiver 200. The computer system 100 monitors the reception by receivers 200 of the identification codes of tags 400 registered with the system. In the event that a time lapse between successive communications to the system that a particular tag has been detected exceeds a critical value (ie a tag has 'timed out'), the system generates a warning signal.

The warning signal comprises a visual and an audible alert. In embodiments of the invention the identity of the patient to whom the tag has been assigned is displayed by the computer system, together with an indication of a location where the tag was last detected. The location where the tag was last detected corresponds to the location of the last receiver from which a communication signal was received indicating that the presence of the tag had been detected.

In addition to receivers 200 detecting and reporting the 'presence' of a tag, portal RFID receivers 250 are also provided. Portal receivers 250 are provided at locations beyond which it is not permitted for a tag 400 to pass. For example, a portal RFID receiver 250 may be located at an exit door 260. In the event that a tag 400 is detected by a portal RFID receiver 200 with which the tag 400 has been registered, the system is adapted to issue an alert. In embodiments of the invention the system may be adapted to lock a door 260. For example, if the portal receiver 250 is located at an exit door 260, the system may lock the door 260 when a registered tag 400 is detected by the portal receiver 250. In some embodiments, if the door is in an open condition the system generates a signal to close the door. In further embodiments, where the system is not able to close the door, an audible and/or visual alert is generated.

The advantage of this feature is that an alarm is only generated if a registered tag generates an alert when it is not possible to lock the door. This feature reduces the chance of an alert being generated, thus reducing a level of stress experienced by hospital staff and other persons in the area of the door.

Alternatively, the system may be adapted to lock the door 260 and/or issue an alert when a tag 400 that is not registered with the portal receiver 250 is detected by the portal receiver 250.

In some embodiments of the invention, certain tags are only allowed to pass through a door between certain hours. For example, a geriatric patient may only be allowed to pass through a door to a garden area between 9am and 6pm. Outside these hours, if a portal receiver 250 detects the presence of the tag, the door may be locked and/or the system may issue an alert.

A system having distributed intelligence as described is able to continue monitoring tags 400 registered with the receivers 200, 250 even in the event that the computer system 100 becomes inoperable. Thus, in the case of a portal receiver 250, an alert will still be generated in the event that a tag 400 not authorised to be in the vicinitv of the exit 2RO is detected. In the case of a tag 400 issuing a tamper alert or a battery level alert, an alert wilhbe generated if a receiver 200, 250 with which the tag is registered receives the alert signal.

In alternative embodiments of the system, all tag receivers within an environment such as a hospital send a signal to a computer system when a tag is detected. The computer system then determines whether the location of the RFID receiver that has detected the tag corresponds to an RFID receiver located in the safe area defined for that particular tag. If the tag is determined to be outside the safe area, an alert is generated. Thus, if a tag is detected in a geriatric ward corresponding to a tag for which movement has been limited to a post -natal ward, an alert is generated. Similarly, if a tag 400 is detected by a portal receiver 250 at an exit 260 of a post -natal ward corresponding to a tag 400 attached to a baby that is not permitted to be removed from the post -natal ward, an exit alert is generated. A door 270 located at the exit 260 is then locked. A person attempting to open the door would be unable to do so unless authorised. For example, an unauthorised person would be unable to open the door, e.g. by turning a handle, pressing a release button, or swiping a smart card.

In embodiments of the invention, only a person authorised to open a door 260 with a smart card authorised to override an exit alert, such as a senior hospital staff member, would be permitted to open the door 260. The person opening the door 260 would be provided with an indication that a tag 400 that was not permitted to exit through the door 260 had been detected in the vicinity of the door 260. The indication may be in the form of an audible alert. Alternatively or in addition the indication may be in the form of a visual alert.

A person issued with a smart card that is not authorised to override an exit alert would be unable to open the door 260. Persons not having smart cards authorised to override exit alerts may include members of non-medical staff such as cleaning staff.

In a preferred embodiment of the invention, a portal receiver 250 comprises an antenna adapted to receive signals from an area of a floor of a building limited substantially to the vicinity of the exit 260.

In order to achieve this, a flat panel antenna 290 is provided. The principles of operation of the flat panel antenna 290 are based on those of a YAGI antenna. The antenna 290 is implemented in a flat panel PCB design on a substantially flat substrate 292 in order to reduce the dimensions of the antenna. Furthermore, the system is configured such that the YAGI antenna detection pattern is rotated through 90 degrees. This allows an

^"antenna 290 to be located above an exit door with the plane of the antennal panel oriented is a substantially vertical plane. In such an orientation, the antenna has a primary pickup area in a direction vertically downwards, with a secondary pickup area defined as an oval (in plan view) which may extend along a corridor. The oval detection pattern is important in preventing detection of RFID tags present in rooms located laterally either side of a corridor leading to the door. To achieve the detection pattern as desired the reflector section of a conventional YAGI antenna design has been rotated through an angle of 90 degrees, so that the reflector section 295 lies in the plane of the flat panel antenna 290. A pair of substantially parallel linear elements are located either side of the reflector section 295; a first element 293 is slightly shorter than a second element 297.

The antenna 290 is located at the doorway to be monitored, and is preferably placed in a location directly above the doorway. The antenna is oriented with the substrate 292 in a vertical plane, substantially orthogonal to a direction along which it is desirable to detect the presence of a tag. The first and second elements are oriented in a substantially horizontal plane, with the second element positioned substantially above the first element.

The antenna has the characteristic that it is capable of receiving transmissions from tags located on floors below and above that on which it is located. In order to prevent the receiver from locking or unlocking the exit in response to signals received from tags on other floors of the building, the feature of distributed intelligence is used.

Thus, according to the first embodiment of the invention the portal receiver 250 is adapted to seal the exit or issue an alert in the event that a tag registered with the receiver as prohibited from passing through the exit is detected. If a tag is detected that is not registered with the portal receiver 250, no action is taken by the portal receiver

250. Thus, signals detected from tags located on floors other than the floor on which the portal receiver 250 is located that are not registered with the system, such as tags registered with an RFID installation in a ward on the level below the level of the portal receiver 250, will be ignored by the portal receiver 250.

Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of the words, for example "comprising" and "comprises", means "including but not limited to", and is not intended to (and does not) exclude other moieties, additives, components, integers or steps.

Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise. Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith.

Claims

CLAIMS:

1. An RFID receiver comprising: means for registering with the receiver an identification code of at least one RFID tag; means for determining whether an identification code of a tag detected by the receiver corresponds to an identification code of a registered tag, wherein a registered tag is a tag registered with the receiver; alert means, said alert means being adapted to issue a receiver alert signal when a signal received from a registered tag comprises a tag alert signal.

2. The receiver as claimed in claim 1 further comDrising communication means, the receiver Deing adapted to communicate to a controller an identity of a tag via said communication means when a tag is detected by the receiver.

3. The receiver as claimed in claim 2 wherein or claim 3 wherein the receiver is adapted to communicate to the controller that a tag alert signal has been received by the receiver when a tag alert signal is received by the receiver.

4. The receiver as claimed in claim 3 wherein said alert means comprises means for providing at least one selected from amongst an audible alert and a visual alert.

5. The receiver as claimed in any one of claims 1 to 4 wherein the tag alert signal comprises a tamper alert signal.

6. The receiver as claimed in any one of claims 1 to 5 wherein the tag alert signal comprises a battery level alert signal.

7. The receiver as claimed in any preceding. claim wherein the means for registering a tag with a receiver comprises a communication signal transmitted from the controller to a receiver.

8. The receiver as claimed in any preceding claim wherein the means for registering a tag with a receiver comprises means for manually registering a tag with a receiver, said means being provided at each receiver.

9. The receiver as claimed in any preceding claim wherein the alert means is further adapted to issue an alert when an identification code of a tag registered with the receiver is detected by the receiver.

10. The receiver as claimed in any preceding claim wherein the alert means is further adapted to issue an alert when an identification code of a tag not registered with the receiver is detected by the receiver.

11. The receiver as claimed in any preceding claim wherein the receiver is adapted to provide a signal to seal a portal when an unauthorised tag is detected.

12. The receiver as claimed in claim 11 wherein an unauthorised tag is a tag having an identification code that corresponds to an identification coαe oτ a registered tag.

13. The receiver as claimed in claim 11 wherein an unauthorised tag is a tag having an identification code that does not correspond to an identification code of a registered tag.

14. The receiver as claimed in claim 11 wherein an unauthorised tag is a tag having an identification code that corresponds to an identification code of a registered tag when a further condition is met.

15. The receiver as claimed in claim 14 wherein the further condition is that a current time corresponds to a time registered with the system for which a tag is considered to be an unauthorised tag.

16. The receiver as claimed in any preceding claim wherein the receiver is provided with a portal antenna.

17. The receiver as claimed in claim 16 wherein said portal antenna is adapted to receive RFID transmissions from tags located in a portal area, said portal antenna being adapted to not receive transmissions from tags located in a blind area, said blind area being an area laterally adjacent to said portal area.

18. The receiver as claimed in claim 16 wherein said portal area comprises a portion of a corridor, and a portion of a periphery of a blind area is defined by a wall of the corridor.

19. The receiver as claimed in any one of claims 16 to 18 wherein the portal antenna comprises a Yagi antenna.

20. The receiver as claimed in claim 19 wherein the Yagi antenna is provided in the form of a substantially flat panel.

21. The receiver as claimed in claim 20 wherein the panel comprises a pair of substantially parallel conducting strips having a conducting strip in the form of an onen loop disposed therebetween.

22. The receiver as claimed in any preceding claim wherein the receiver is provided with a patch antenna, the patch antenna being adapted to be mounted remotely from the receiver.

23. The receiver as claimed in claim 22 wherein the patch antenna is adapted for connection to the receiver by a cable.

24. The receiver as claimed in any one of claims 16 to 23 wherein when a tag is detected having an identification code that corresponds to an identification code of a registered tag, and a portal associated with the receiver is in a closed condition, the receiver is adapted to maintain the portal in a closed condition.

25. The receiver as claimed in claim 24 wherein the receiver is further adapted to communicate to a controller that the portal is being maintained in a closed condition when the portal is maintained in a closed condition by the receiver.

26. The receiver as claimed in any one of claims 16 to 25 wherein when a tag is detected having an identification code that corresponds to an identification code of a registered tag, and a portal associated with the receiver is in an open condition, the receiver is adapted to provide an alert.

27. The receiver as claimed in any one of claims 16 to 26 wherein in the event that the portal is in an open condition and a tag is detected having an identification code that corresponds to an identification code of a registered tag, the receiver is adapted to close the portal.

28. A security system comprising a plurality of RFID receivers as claimed in any preceding claim.

29. The system as claimed in claim 28 wherein the system further comprises a controller, wherein the controller is adapted to communicate with the receivers.

30. The system as claimed in claim 29 wherein the controller comprises means for registering a tag with the system.

31. The system as claimed in claim 30 wherein the controller further comprises means for registering a tag with a receiver.

32. The system as claimed in any one of claims 28 to 31 wherein the controller comprises means for generating a system warning signal when an alert signal is received from a receiver.

33. The system as claimed in claim 32 wherein the system warning signal comprises at least one selected from amongst an audible warning signal and a visual warning signal.

34. The system as claimed any one of claim 32 or claim 33 wherein the alert signal comprises at least one selected from amongst a tamper alert signal and a battery alert signal.

35. An RFID receiver substantially as hereinbefore described with reference to the accompanying drawings.

36. A security system substantially as hereinbefore described with reference to the accompanying drawings.