WO2006068525A1

WO2006068525A1 - Improvements in or relating to identification reader systems

Info

Publication number: WO2006068525A1
Application number: PCT/NZ2005/000347
Authority: WO
Inventors: Gordon Irving; Christopher Lewis Anderson; Murray Greenman
Original assignee: Edit Id Limited
Priority date: 2004-12-24
Filing date: 2005-12-23
Publication date: 2006-06-29

Abstract

An electromagnetic identification tag reader which provides an electromagnetic interrogation field to elicit a response from an identification tag. The reader includes an electromagnetic interrogation field controller which modifies the shape of the interrogation field. The shape may be varied over time and a series of shapes may be provided within a predefined timeframe.

Description

IMPROVEMENTS IN OR RELATING TO IDENTIFICATION READER SYSTEMS

TECHNICAL FIELD

This invention relates to improvements in or associated with identification reader systems. In particular the present invention may provide improvements with respect to radio frequency identification devices or tags (RFID tags), and preferably may improve the reliability of such readers systems in their capacity to read a valid return signal from an RFID tag. Reference through out this specification will also be made to the present invention being used in this application, but those skilled in the art should appreciate that other embodiments may not necessarily revolve around the reading of RFID tags, and reference to the above only should in no way be seen as limiting.

BACKGROUND ART

Radio frequency identification devices (referred to herein after as RFID tags) have been used in a wide variety and number of applications. Comparatively small tags may be applied to stock items, injected subcutaneously into animals or used in security applications as pass key or authorisation identifiers. RFID tags can also be used in livestock management applications through being integrated within an ear tag or other form of external piercing or attachment to an animal. In such applications the radio frequency range employed is generally between 100-15OkHz to ensure penetration of the radio frequency signals through water or body tissues.

The tags involved are capable of being interrogated by a reader component or device which can extract a unique identification code from each tag interrogated.

Passive RFID tags have been developed which are relatively small and which do not require their own power source. Passive tags are excited by the energy present in an initial reader/transmitter signal and are used to modify a return echo from the tag back to the reader where the return echo has the identification information of the tag encoded into it. Such passive tags, repeatedly convey a fixed frame of data (known as a "telegram"), the commencement of which may or may not be synchronised with the commencement or cessation of the interrogation or excitation field.

Reference to passive RFID tags which modify a return echo from the tag back to the reader should be understood by those skilled in the art to encompass both HDX and FDX tag types. In the case of FDX tags reference to the provision of a return echo from the tag should be taken as the effect of the tag on the magnetic field of a reader's antenna assembly.

Those skilled in the art would also recognise that these passive RFID tags have an optimum axis of orientation with respect to any incident interrogating field flux lines. Existing RFID readers generally employ a static or fixed shape magnetic field to excite an RFID tag. The tags involved will extract the greatest amount of power or energy from the initial excitation field of the reader if the tag is placed or moved with its optimum axis of orientation parallel to the incident magnetic flux lines. This optimum orientation of a tag will in turn generate the highest possible power return echo signal, thereby potentially resulting in the reader obtaining a valid identification signal.

Conversely if the tag is presented or moved with its optimum axis of orientation perpendicular to the incident magnetic flux lines then minimal energy will be received by the tag. This in turn may result in the tag generating a return echo of insufficient power to be detected by the reader or could result in the generation of a corrupted echo signal, or a signal with a low signal to noise ratio, or no signal at all if the interrogation or excitation field is not sufficient to excite the tag.

This aspect of RFID tag return signal generation can result in specific regions in an interrogation field where a tag with a likely orientation or trajectory through the field is unlikely to be read effectively. These regions may be described as non-readable zones.

It is often not possible to predict the orientation which an RFID tag will have when presented or moved within the region of the reader's excitation field. This in turn can limit the read rate that may be achieved by a reader or alternatively can reduce the reader's read rate over increased read ranges.

The reliability of an RFID tag reader and its ability to provide a high read rate is a significant factor in many applications. For example, in livestock management applications such as the management of dairy cows coming into a milking shed, it is important to identify sick or medicated animals, or any other animals which should not have their milk collected. The reliability of the identification system and its ability to identify such animals is of significant importance.

In this application it is not necessarily practical to use a manual hand held reader to be placed in proximity to an RFID tag incorporated into an animal ear tag or similar attachment. The use of such hand held readers is comparatively slow, ergonomically difficult, and will also cause a stressful disturbance to the animals. In other situations where large excitable animals are involved the use of a hand held reader can heighten the risk of operator injury.

Conversely remote reader systems which generate an interrogation field do not necessarily work well with the physical dimensions of milking parlour bails within which dairy animals are to stand during milking. The interrogation fields generated by standard RFID readers are generally symmetrical, and the range of the reader can spill over into adjacent bails when extended large enough to cover the area in the bail which an animal's tag could be located. This can result in a single reader picking up signals from tags on animals in adjacent bails, and therefore having difficulty in distinguishing which animal is currently located within a bail associated with the reader.

Standard field shaping techniques (such as modifying the form or shape of a particular antenna coil) can result in an interrogation field covering only a single bail of interest. However, these field shaping techniques will generally increase the size or extent of zones within the interrogation field where limited flux will be intercepted by a tag passing through in a likely orientation. These "non-readable" zones will reduce the read rate of the reader and compromise its reliability and usefulness in such applications.

It would be preferable to have an improved identification reader system which addresses the above issues. In particular a reader which in practice could provide a high read rate at usable or practical ranges would be of advantage. It would be of advantage to have a reader which improved the usability and reliability of the identification system involved and also increase the speed at which tags can be interrogated and identified. Furthermore an improved identification reader system which could present a comparatively compact interrogation field within preferably only a region of interest and which did not necessarily increase potential non- readable zones within the field would also be of advantage.

All references, including any patents or patent applications cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinency of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents form part of the common general knowledge in the art, in New Zealand or in any other country. It is acknowledged that the term 'comprise' may, under varying jurisdictions, be attributed with either an exclusive or an inclusive meaning. For the purpose of this specification, and unless otherwise noted, the term 'comprise' shall have an inclusive meaning - i.e. that it will be taken to mean an inclusion of not only the listed components it directly references, but also other non-specified components or elements. This rationale will also be used when the term 'comprised¹ or 'comprising' is used in relation to one or more steps in a method or process.

It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.

Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.

DISCLOSURE OF INVENTION

According to one aspect of the present invention there is provided an electromagnetic identification tag reader which includes:

at least one transmitter assembly adapted to provide at least one interrogation signal for an identification tag;

at least two antenna assemblies adapted to radiate said at least one interrogation signal to provide an electromagnetic interrogation field of a given shape to elicit at least one response signal from an identification tag;

at least one receiver assembly adapted to detect said at least one response signal;

an interrogation field controller adapted to modify the shape of the interrogation field generated by at least one of said antenna assemblies. Preferably, the interrogation field controller is adapted to modify the shape of the at least one interrogation field over time.

Preferably, the interrogation field controller is adapted to modify the shape of the interrogation field generated collectively by the at least two antenna assemblies.

Preferably, the interrogation field controller is adapted to modify the shape of the interrogation field by modifying the power level of the interrogation signal provided for at least one of said antenna assemblies.

Preferably, the interrogation field controller is adapted to modify the phase of the interrogation signal provided for at least one of said antenna assemblies by switching between 0 degrees and 180 degrees phase shifts.

Preferably, the at least two antenna assemblies include two or more conductive coils.

Preferably, the two or move electrically conductive coils include two similar coils separated spacially.

Preferably, the interrogation field controller is adapted to operate in a time dependant manner to provide a predefined set of field shapes within a given time frame.

Preferably, the time frame is selected to correspond to an identification tag being expected to be substantially static within the interrogation field.

Preferably, the antenna assemblies and interrogation signal controller are adapted to provide at least two predefined shapes of the interrogation field.

Preferably, at least two antenna assemblies are provided an interrogation signal by the same transmitter assembly. Preferably, the electromagnetic identification tag reader includes a processor assembly adapted to receive signals from the one or more receiver assemblies.

Preferably, each said assembly is adapted to provide a unique identifier to the processor assembly.

Preferably, the interrogation field controller is adapted to control an actuator which is adapted to mechanically actuate the at least one antenna assemblies.

Preferably, the electromagnetic identification tag reader includes at least one phase switch adapted to the control by the interrogation field controller.

According to a further aspect of the present invention there is provided an identification tag reader substantially as described above wherein the interrogation field controller is configured to modify the shape of the interrogation field to generate a set of field shapes in the vicinity of the identification tag reader over time.

The present invention relates to improvements in and modifications made to identification reader systems. Preferably the present invention may be implemented as a radio frequency identification tag reading system which can interrogate RFID tags in the vicinity of such a reader system.

Reference throughout this specification will be made of the present invention being implemented as a RFID tag reader which may also include its own RFID tags, or alternatively may be interfaced with third party tags if required. Reference throughout this specification will also be made to the RIFD tags in question being passive tags. However, those skilled in the art should appreciate that other implementations of identification systems are also within the scope of the present invention and reference to the above only throughout this specification should in no way be seen as limiting. Reference throughout this specification will also be made to the present invention implementing a tag reader system designed to operate in the 100-15OkHz frequency range. Again however, those skilled in the art should also appreciate other types of tags which may also operate in differing frequency ranges may also be used in conjunction with the present invention if required.

In a preferred embodiment an identification reader system provided in accordance with the present invention may include at least one transmitter assembly, at least two antenna assemblies and at least one receiver assembly. A transmitter assembly may be adapted to generate at least one interrogation signal which, when transmitted via the antenna assemblies, results in the generation of a magnetic interrogation field in the vicinity of the reader system. Those skilled in the art should appreciate that the generation of such magnetic interrogation fields are well known with respect to RFID tag technology.

Furthermore those skilled in the art should also appreciate the reader provided in accordance with the present invention can employ at least one receiver assembly to detect at least one response signal elicited from an RFID tag within the reader's interrogation field. Such a response signal can be detected by one or more receiver assemblies and interpreted or decoded to provide an intelligible identification code using techniques and practises again well known in the art.

In a preferred embodiment a receiver assembly may be implemented through any form of appropriate radio frequency signal detection circuitry known in the art. Preferably the circuitry employed to implement the receiver assembly may function effectively for the appropriate frequency ranges and power levels employed in the operation of the present invention.

In a preferred embodiment the identification reader provided includes two or more antenna assemblies. These antenna assemblies may be powered or operated at the same time to transmit interrogation signals which in turn result in the generation of an interrogation field in the vicinity of the reader. Those skilled in the art should appreciate that the concurrent operation of a plurality of antenna assemblies will result in a single interrogation field being generated. The shape and extent of this field will be dictated by the coupling or interaction between each of the antenna assembly's transmissions. The resulting shape and extent of the interrogation field can therefore be modified depending on how each antenna assembly is driven, powered, configured or otherwise controlled.

In a preferred embodiment an identification reader provided in accordance with the present invention may include two antenna assemblies only. Two antenna assemblies can function effectively to generate an interrogation field in the vicinity of the reader and preferably one or both of the antenna assembly's transmissions may be modified to in turn modify the shape and extent of the field generated over time.

However in an alternative embodiment three or more antenna assemblies may be provided for an identification reader. Three or more antenna assemblies can give significant flexibility with respect to the shapes of field which can be generated, at the cost of additional components or hardware being required to implement the reader involved.

Reference through out this specification will also be made to the identification reader provided including two antenna assemblies only which are spatially displaced from one another. However those skilled in the art should appreciate that other configurations of an identification reader are also envisioned and reference to the above only throughout this specification should in no way be seen as limiting.

In a preferred embodiment the pair of antenna assemblies provided may be formed from a pair of coiled electrical conductors. Preferably each antenna assembly may be substantially identical to the other provided, and may be spatially displaced and arranged with respect to one another to facilitate the generation of two or more different shapes of interrogation fields.

In a preferred embodiment a transmitter assembly may be provided for each antenna assembly integrated into the identification reader. However, in alternative embodiments a single transmitter assembly may be used to generate a single interrogation signal which in turn may be modified or changed and subsequently supplied to each antenna assembly. Reference to the provision of a pair of transmitter assemblies with the pair of antenna assemblies discussed above should in no way be seen as limiting, as should be appreciated by those skilled in the art.

In a preferred embodiment a receiver assembly may be provided for each antenna assembly integrated into the identification reader. Each reader assembly may in turn be linked to a single processor component, such as, for example a microprocessor. Unique identification data signals may preferably be supplied to such a processor component by each receiver, where the processor is used to provide a single output identifier selected from the outputs of the receiver assemblies.

Reference throughout this specification shall also be made to the present invention including a receiver assembly for each antenna assembly employed. However those skilled in the art should appreciate that in alternative embodiments each antenna assembly may not necessarily be associated with a receiver, and reference to the above only throughout this specification should in no way be seen as limiting.

In a preferred embodiment an identification reader may include an interrogation field controller adapted to modify the shape and extent of the interrogation field generated by one or both of the antenna assemblies. Preferably this controller may operate in a time dependent sequential manner to cycle through a set of field shapes within a set period of time. In such embodiments the controller may be employed to expose an RFID tag within the vicinity of the reader to a plurality of varying or differing field shapes to in turn promote the generation of a response signal from the tag.

This configuration of the present invention and its use of an interrogation field controller may eliminate problems associated with non-readable zones present in a single field shape, and may also be used to control the volume of space in which the interrogation field generated is present.

In a preferred embodiment the controller may cycle rapidly through the set of field shapes selected within a timeframe in which an identification tag is comparatively static or in which the tag involved is moved through the interrogation field. This approach can improve the read rate of the resulting reader. A tag present in or moving through a non-readable zone of one field shape will subsequently experience an alternative field shape which preferably does not have a non- readable zone at the current position of the tag.

Furthermore, the interaction of the two antenna assembly's transmissions may be employed to modify the overall shape and/or extent of the interrogation fields generated to reside within a localised area of interest only.

In a further preferred embodiment the interrogation field controller may in operation be adapted to generate or cycle through a set of two field shapes only. The two field shapes generated may still contain non-readable zones but these zones preferably do not intersect with one another. However, in alternative embodiments the interrogation field controller provided may be adapted to repeat a set of three or more differing field shapes if required. Those skilled in the art should appreciate that reference to the generation a set of two shapes only in conjunction with the present invention should in no way be seen as limiting.

In a preferred embodiment the interrogation field controller may be implemented as control and signal processing circuitry associated with a transmitter assembly of one of the pair of antenna assemblies. The interrogation field controller in this instance may modify the phase or power level characteristics of the interrogation signal provided to the selected antenna assembly so as to in turn modify the resulting interrogation field generated by the operation of both antenna assemblies.

In a further preferred embodiment an interrogation field controller may modify the field shapes generated through introducing phase or power level differentials between essentially the same interrogation signals to be transmitted by both antenna assemblies. A phase or power level differential may be integrated into the driving interrogation signal of one or more antenna assembly periodically by the controller to in turn periodically modify the resulting interrogation field shape generated.

In a further preferred embodiment an interrogation field controller may be adapted to facilitate the generation of two field shapes through driving the antenna assemblies with identical interrogation signals which are in phase with one another, and identical interrogation signals which are 180° out of phase. This phase differential will then result in two differing shapes of interrogation field being generated in an alternating pattern over time, where each field shape exists for the period of at least one RFID tag interrogation cycle (or "telegram").

However, in alternative embodiments phase differentials between the interrogation signals employed may not necessarily be used to generate varying interrogation field shapes. For example, in one alternative embodiment the interrogation field controller may be associated with the transmitter assembly of one antenna assembly to modify the power of the resulting antenna assembly's transmissions. The current, voltage or combination of both current and voltages of an interrogation signal may therefore be modified to in turn present a modified interrogation field shape.

In yet another alternative embodiment the actual physical characteristics of a particular antenna assembly may be modified by the interrogation field controller. In such instances the interrogation field controller may be implemented to include a motor to move a physical antenna coil assembly, or alternatively may be implemented as one or more switches used to supply varying interrogation signals to an antenna, or alternatively to supply an interrogation signal at varying points or positions along the length of a conductive coil of one antenna assembly. Those skilled in the art should appreciate that reference to the use of phase differentials only within interrogation signals should in no way be seen as limiting.

The present invention may provide many potential advantages over prior art identification reader systems.

The provision of two or more antenna assemblies within such a reader and the use of an interrogation field controller can allow a plurality of interrogation field shapes to be generated rapidly and experienced by an identification tag within the vicinity of the reader. These varying field shapes can eliminate the non-readable zones present in the fields experienced by a tag to in turn more reliably elicit a response signal from the tag to be read. Non-readable zones present in one of these field shapes are preferably not present at the same location in an alternative field shape, thereby effectively eliminating the non-readable zone problem. Furthermore, the interaction of the transmissions made from an array of antenna assemblies can also be employed to implement a field shaping facility. The field generated and its shape can be customised or modified for the particular region of interest of a reader without necessarily spilling over to other regions in which a tag may be present.

BRIEF DESCRIPTION OF DRAWINGS

Further aspects of the present invention will become apparent from the following description which is given by way of example only and with reference to the accompanying drawings in which:

Figure 1 shows a block schematic diagram of electrical circuitry assemblies used to implement an identification tag reader in accordance with a preferred embodiment, and

Figures 2A, 2B, 2C and 2D show a side schematic view of the pair of antenna assemblies discussed with respect to figure 1 , and the various field shapes which can be generated by such assemblies, and

Figure 3 shows a circuit diagram of an interrogation field controller as discussed with respect to figure 1.

BEST MODES FOR CARRYING OUT THE INVENTION

Figure 1 shows a block schematic diagram of electrical circuitry assemblies used to implement an identification tag reader in accordance with a preferred embodiment.

Figure 1 shows an identification tag reader (1). The reader (1) includes a pair of transmitter assemblies (2a, 2b) with each transmitter assembly being linked to one of a pair of antenna assemblies (3a, 3b). Each antenna assembly is in turn also linked to a receiver assembly (4a, 4b). These receiver assemblies (4a, 4b) are configured or adapted to provide an output data signal to a single processor component, shown in this embodiment as a microprocessor (5).

Each of the transmitter assemblies (2a, 2b) is adapted to generate an interrogation signal to be supplied to and transmitted by each of the antenna assemblies (3a, 3b). Transmission of these interrogation signals generates a magnetic interrogation field in the vicinity of the reader, where preferably an RFID tag (6) is located.

This tag (6) will experience the interrogation field generated which will trigger the emission of a response signal from the tag which is picked up or sensed by one or both of the antenna assemblies (3a, 3b). The receiver assemblies (4a, 4b) can then process the signal received from each antenna assembly which is representative of the tag's response signal, and supply to the microprocessor (5) to read the identification tag data. Typically each receiver assembly (4a, 4b) adds a unique identifier to the received signal so the microprocessor (3) can distinguish signals from each receiver assembly.

The reader (1) also incorporates an interrogation field controller (7) which is employed to periodically modify the shape of the interrogation field generated by the reader (1). The field controller (7) is used to facilitate a generation of a set of field shapes in a repeating pattern over time. These different field shapes can increase the read rate of the reader (1) through effectively eliminating non-readable zones within specific field shapes. By generating further field shapes which do not have the same non-readable zones in the same space, a tag will always experience enough of an interrogation field to elicit a response. Therefore the tag (6) will then be exposed to various field shapes to elicit a response signal, irrespective of whether the tag currently resides within a non-readable zone of one of the fields generated.

In the embodiment shown with respect to figure 1 the interrogation field controller (7) is adapted to modify the phase of an interrogation signal generated by the transmitter (2b) and with respect to the phase of an interrogation signal generated by the transmitter (2a). The specific configuration of the interrogation field controller (7) is discussed further with respect to figure 3.

Implementing a phase delay between the two identical interrogation signals supplied to each antenna assembly will result in an alternative or modified field shape being generated in the vicinity of the reader. A change from the transmission of two interrogation signals with no phase differential to the transmission of two signals with phase differential of preferably 180° will modify the existing field shape generated to form a new field shape, preferably without common or intersecting non-readable zones.

Figures 2a - 2d show side schematic views of the pair of antenna assemblies discussed with respect to figure 1 , and the various field shapes which can be generated by such assemblies.

Figure 2a illustrates the condition where two identical interrogation signals with no phase differentials are supplied to each of the antenna assemblies (3a, 3b). As can be seen from Figure 2a, a first field shape illustrated by the field lines is generated in the vicinity of the reader.

Figure 2a shows the field shape illustrated by field lines generated when no phase differential is applied between the two substantially identical interrogation signals used. As can be seen from Figure 2b a significantly different field shape is generated by the effect of a phase differential between these signals, where preferably the two fields generated do not have intercepting non-readable zones. The interrogation field controller may rapidly switch in and out a phase differential into one of the interrogation signals provided to in turn rapidly modify or cycle through the field shapes generated. This will mean that an identification tag will experience multiple field shapes over a short period of time, preferably before the tag is moved through the region occupied by the interrogation field.

Figure 2c and 2d illustrate the interrogation field controller modifying the power of the signal supplied to one of the antenna assemblies involved. In the situation shown with respect to figures 2c and 2d the power of a signal emitted by one of the antenna assemblies is negligible.

In one embodiment (not shown) the antenna assemblies may include two similar or identical electrically conductive coils separated spacially. These may have multiple points at which the interrogation signal can be supplied. The interrogation signal may be switched to various of these points to modify the shape of the interrogation field.

Figure 3 shows a block circuit diagram of components used to implement the interrogation field controller discussed with respect to Figure 1. In the embodiment shown the field controller (7) is used to periodically introduce a phase delay into an interrogation signal supplied by the receiver (2b) discussed with respect to Figure 1.

In the preferred reader configuration shown with respect to figure 3 the phase switch (8) associated with the first transmitter assembly (2a) has no effect on the interrogation signal transmitted or radiated by antenna assembly (3a). Conversely the same phase switch operated by field controller (7) may periodically introduce a phase delay into the signal generated and transmitted or radiated by the antenna assembly (3b) bearing from 0-180°. In preferred embodiments an 180° phase shift is cycled into and out of the signal generated by the second transmitter assembly (2b) using the field controller (7).

Also in preferred embodiments the power of interrogation signals provided to antennas (3a) and (3b) by power amplifiers (9a) and (9b) may be varied periodically. Typically the power of each signal will switch from an "off-power" to a

"full power". Various combinations of phase delay and signal power to achieve predefined field shapes. It will be apparent to those skilled in the art which combinations are suitable for achieving desired field shapes or desired sequences of field shapes. Figures 2a to 2d show four examples of achievable with two phases and two power levels.

In some embodiments of the identification tag reader a predefined number of field shapes may be cycled in a predefined time interval to ensure that the occurrence of dead spots is reduced for a defined region in that time frame. If the identification tag is anticipated to move through the defined region at a given rate, the timeframe can be selected to correspond to the identification tag being relatively static in the selected timeframe.

Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof.

Claims

WHAT IS CLAIMED:

1. An electromagnetic identification tag reader which includes:

at least two antenna assemblies adapted to radiate at least one interrogation signal to provide an electromagnetic interrogation field of a given shape to elicit at least one response signal from an identification tag;

an interrogation field controller adapted to modify the shape of the interrogation field generated by at least one of said antenna assemblies.

2. The electromagnetic field controller of claim 1 wherein the interrogation field controller is adapted to modify the shape of the at least one interrogation field over time.

3. The electromagnetic field controller of claim 1 or claim 2 wherein the interrogation field controller is adapted to modify the shape of the interrogation field by modifying the power level of the interrogation signal provided for at least one of said antenna assemblies.

4. The electromagnetic identification reader of any one of the preceding claims wherein the interrogation field controller is adapted to modify the phase of the interrogation signal provided for at least one of the antenna assemblies.

5. The electromagnetic identification tag reader of claim 4 wherein the interrogation field controller is adapted to modify the phase of the interrogation signal.

6. The electromagnetic identification reader of claim 5 wherein the interrogation field controller is adapted to modify the phase for at least one of said antenna assemblies by switching between 0 degrees and 180 degrees phase shift.

7. The electromagnetic identification tag reader of any one of the proceedings claims wherein the at least two antenna assemblies include two or more conductive coils.

8. The electromagnetic identification reader of claim 6 wherein the two or move electrically conductive coils include two substantially identical coils separated specially.

9. The electromagnetic identification tag reader of any one of the preceding claims wherein the interrogation field controller is adapted to operate in a time dependant manner to provide a predefined set of field shapes within a given time frame.

10. The electromagnetic field controller of claim 9 wherein the time frame is selected to correspond to an identification tag being expected to be substantially static within the interrogation field.

11. The electromagnetic identification tag reader of any one of the preceding claims wherein the antenna assemblies and interrogation signal controller are adapted to provide at least two predefined shapes of the interrogation field.

12. The electromagnetic identification tag reader of any one of the preceding claims wherein at least two antenna assemblies are provided an interrogation signal by the same transmitter assembly.

13. The electromagnetic identification tag reader of any one of the preceding claims including a processor assembly adapted to receive signals from the one or more receiver assemblies.

14. The electromagnetic identification tag reader of claim 13 wherein each said assembly is adapted to provide a unique identifier to the processor assembly.

15. The electromagnetic identification tag reader of any one of the preceding claims wherein the interrogation field controller is adapted to control an actuator which is adapted to mechanically actuate the at least one antenna assemblies.

16. The electromagnetic identification tag reader of any one of the preceding claims including at least one phase switch adapted to the control by the interrogation field controller.

17. A method of operating an electromagnetic identification reader including the steps of:

providing at least one transmitter assembly adapted to provide at least one interrogation signal for an identification tag;

providing at least two antenna assemblies adapted to radiate said at least one interrogation signal to provide an electromagnetic field of a given shape to elicit at least one response signal from an identification tag;

providing at least one receiver assembly adapted to detect said at least one response signal; and modifying over time the shape of the interrogation field generated by at least one of said antenna assemblies.

18. An electromagnetic identification tag reader substantially as herein described with reference to the accompanying drawings.