GB2449650A

GB2449650A - RFID marker

Info

Publication number: GB2449650A
Application number: GB0710202A
Authority: GB
Inventors: David Milnes; Simon Stringer
Original assignee: RITAG
Current assignee: RITAG
Priority date: 2007-05-30
Filing date: 2007-05-30
Publication date: 2008-12-03
Also published as: GB0710202D0

Abstract

An identification arrangement comprises a marker 41 having a marker receiver coil 44 and a marker transmitter coil 45, the marker receiver coil 44 is arranged to be electrically inducible by a power magnetic field to provide electrical power to stimulate an identification signal in the marker, the marker transmitter coil 45 is arranged to receive the identification signal to modulate an identifier magnetic field which is transmitted from the marker. The marker receiver coil and the marker transmitter coils are operated separately from each other rather than being a single transceiver coil. A reader 42 includes a transmitter coil 43 for inducing power to the marker 41 and a receiver coil 46 for receiving the identifier signal from the marker. The marker may be used on underground pipes or cables to locate and identify them for excavation work.

Description

An Identification Arrangement The present invention relates to

identification arrangements and more particularly identification arrangements utilised in conjunction with a reader device as a system for providing identification with regard to works such as street excavations or any underground apparatus.

The nature of modern urban life requires repeated excavation and renovation work with respect to paved and tarrnaced areas such as highways.

Excavators and restorers may include Street authorities as well as utilities and other contractors. It is important that the quality and condition of these works are controlled and regulated to ensure reinstatement after excavation is up to an acceptable standard. It will also be understood that monitoring and control of access to inventory such as underground electrical cables and water conducts may desirable.

In order to regulate excavation and reinstatement works it is known to provide registers maintained by local street authorities. Unfortunately, simple registers dependent upon the accuracy with which geographical details are maintained and particularly with regard to excavations approximate definitions of location would be unacceptable. It will be appreciated that several excavations may be performed within a relatively small area and differentiating between one particular excavation and reinstatement and another and between contractors maybe difficult leading to disputes when what is required is immediate remedial work. In such circumstances, recently reinstatement tagging and identification has been provided through markers buried during the reinstatement process. These markers comprise typically a radio frequency identifier device (RFIO) and a reader which stimulates electric current within the device (RFID) such that an identification signal is returned to the reader for identification purposes. Advantages with RFID tags and markers include that a marker does not need to incorporate a long term electrical battery or other storage device reducing costs and providing long operational time periods for identification of excavation and reinstatement works. Furthermore RFID tags are relatively cheap, reliable and easy to operate as identification markers.

Unfortunately, as indicated the RFID tags must be buried and so are typically encapsulated or located within a robust housing to withstand harsh usage and environments. Such packaging for the RFID tag as well as location within soil and building materials such as tarmac, concrete and aggregate which may be wet, can lead to difficulties with respect to producing the necessary electrical power charging for operation and acceptable transmission ranges for the identification signal It is to be understood that typically the marker device will include a transponder having a single wire coil for transmitting and receiving. This wire coil has electrical current induced into it by a power magnetic field and generated typically by a coil in the reader device. An electrical current is passed through a power coil in the reader to generate the power magnetic field which as indicated induces electrical current in the receiver coil within the identification marker (RFID). This receiver coil then acts as a transmitter coil for return of identification signals indicative of the marker. It is understood that use of a single coil leads to comprises in terms of a maximum read/write range for the identification coupling between the reader device and the marker. For example, adjusting certain coil attributes in order to maximise reception range such as a high number of turns or thinner wiring for coil size, can have a detrimental affect on the transmission range as a high number of turns will increase the direct current (DC) resistance of the coils as will the use of thinner wire.

In accordance with aspects of the present invention there is provided an identification arrangement comprising a marker having a marker receiver coil and a marker transmitter coil, the marker receiver coil arranged to be electrical inducible by a power magnetic field to provide electrical power to stimulate an identification signal in the marker, the marker transmitter coil arranged to receive the identification signal to modulate an identifier magnetic field, the marker receiver coil and the marker transmitter coils are operated separately from each other.

Typically, the power magnetic field is modulated for interrogation of the marker as a trigger signal.

Generally, the marker receiver coil is optimised for induction of electrical power.

Typically, the marker transmitter coil is optimised for producing the identifier magnetic field modulated by the identification signal.

Typically, the identifier magnetic field is provided by the electrical power induced in the marker receiver coil Possibly, the marker includes an electrical power storage device. Possibly, the electrical power storage device is charged by electrical power induced in the marker receiver coil by the power magnetic field Possibly, the electrical power storage device is a battery or electrical capacitor within the marker.

Possibly, the marker is utilised to identify inventory such as electrical cable work or pipes and positions of that inventory to facilitate couplings.

Also in accordance with aspects of the present invention there is provided an identification system comprising an identification arrangement as described above and a reader device, the reader device including a reciprocal transmitter coil for the marker receiver coil and a reciprocal receiver coil for the marker transmitter coil, the reciprocal transmitter coil and the marker receiver coil couple configured wttfl at least an objective of inducing electrical power in the marker receiver coil and the reciprocal receiver coil and the marker transmitter coil couple configured with at least an objective of inducing a reader electrical signal in the reciprocal receiver coil corresponding to the identification signal.

Typically, the reader device includes an electrical power source for the reciprocal transmitter coil to provide the power magnetic field. Generally, the electrical power source comprises a battery.

Generally, the marker is encapsulated and/or otherwise environmentally sealed.

Generally, the marker receiver coil is arranged to be inducible by different strengths of the power magnetic field to stimulate a respective identification signal in the marker for each power magnetic field Possibly, the coils are optimised by configuration in terms of number of wire turns and For thickness of wire. Possibly, the coils are optimised by switching or providing electrical components such as electrical resistance and/or capacitance and/or inductance.

Further in accordance with aspects of the present invention there is provided a method of identification within an identification system provided by a identification arrangement and a reader, the identification arrangement configured to have a marker receiver cod and a marker transmitter coil, the reader configured to have a reciprocal transmitter coil marker to the receiver marker, and a reciprocal receiver coil to the marker transmitter coil, the method comprising providing a power magnetic field from the reciprocal transmitter coil to the marker receiver coil to induce electrical power within the marker stimulating an identification signal in the marker when electrical power is induced in the marker receiver coil, presenting the identification signal to IL...

....I. & ....:I ...._..i. .I_&_. L.....DTD: iV LI1 fIIdI UdI II IJIIL( LUII (0 tJI0UU1d( IUI UYYI III I(IL. IIIU provided by the marker transmitter coil and configuring the reciprocal receiver coil to receive the modulated identification power magnetic field to identify a marker of the identification arrangement.

Aspects of the present invention will now be described by way of example only with reference to the accompanying drawings in which; Figure 1 is a schematic illustration of an identification system in accordance with aspects of the present invention; Figure 2 is a schematic illustration of a marker used in an identification arrangement as part of an identification system in accordance with aspects of the present invention, Figure 3 is a graphic representation illustrating a transmit coil and receive coil couple in accordance with aspects of the present invention; and, Figure 4 illustrates schematically coil couples in accordance with aspects of the present invention in a reader device and a marker of an identification system in accordance with aspects of the present invention.

As indicated above identification systems are utilised in a wide range of environments. Utilisation of radio frequency identifier devices (REID) is known with respect to location of a number of articles such as garments within a retail environment, books within a library or other situations where tracking of location or movement of an item is required. RFID have a place and forest usage facility of particular interest with regard to aspects of the present invention is the utilisation of such identification systems to act as an on site interrogateable identifier for excavation reinstatement in highway and other paved areas. However, the device could also be used in less stabilised --i-. ,,_,,1.-.....k i....1.&L , itui1e,, rubble to act as an identifier for correct disposal. As indicated above it is known to utilise REID devices for such identification systems and arrangements but there are limitations with respect transmit and receiving ranges particularly in view of the potential attenuation effects of damp ground and other materials such as tarmac and especially reinforced concrete. These materials may diminish transmission and receive ranges and as indicated there are compromises with coil design.

Figure 1 provides a schematic illustration of a typical excavation reinstatement cross section. Thus, a paved area 1 has a paved or tarmaced surface 2 with an underlying ground foundation 3. The ground foundations 3 will normally incorporate aggregate in order to appropriately support and present the surface 2 or alternatively may simply comprise compacted earth.

As illustrated a trench or excavation 4 has previously had some of the earth removed along with part of the foundation 3 and a proportion of the surface 2 typically to allow access to a pipe or other conduit 5 buried within the earth or IS foundation works 3. Upon reinstatement the trench or excavation 4 is refilled with appropriate materials 3a then compacted and resurfaced with a surface portion 2a.

During the reinstatement an identification marker 6 in accordance with aspects of the present invention is located within the trench 4. The marker 6 acts as an identifier for the excavation and reinstatement. The marker 6 will provide a simple registration reference in terms of an alphanumeric number code or otherwise registered within an appropriate authority. A reader device 7 as outlined below is used to identify the marker and possibly through a data base down loaded to the reader device or otherwise addressable by that device allows details about that the reinstatement to be obtained. The marker will emit a characteristic identifying signal which then references the alphanumenc-communication code and information.

The purpose of the marker 6 is to enable association of the subject excavation and reinstatement with a particular contractor responsible for the works. In such circumstances should the works not meet appropriate standards then that contractor can be contacted and recalled to make good

reinstatement to satisfactory standards.

The marker 6 can be interrogated without excavation 2 through to an RFID device coupling between the marker 6 and the reader 7. The reader 7 generally incorporates a head 8 in which electrical coils in accordance with aspects of the present invention are located. These electrical coils stimulate electric current within the RFID device located within the marker 6 as well as receive a modulated radio frequency magnetic field response corresponding to the identifier for the marker 6 The reader 7 also includes a display and/or a logging arrangement 9 to record the received identification signal from the marker.

As indicated above a particular problem relates to the couplings IS between the coils in the marker 6 associated with the RFID device and the transmission and receive functions of the head 8. With a prior single coil arrangement there is a compromise between maximum reception range and maximum transmission range. These problems are further exasperated by the attenuation effects of the surface 2 and typically damp nature of the surface 2 and ground 3 limiting induction ranges.

Figure 2 provides a schematic illustration of a marker 21 utilised in accordance with aspects of the present invention. The marker 21 must be robust and therefore takes the form of a housing 22 which encapsulates and environmentally seals an RFID device 23. The RFID device 23 comprises electrical circuitry in which circuits including wire coils or possible printed circuit rails are located to act as antenna. A power magnetic field 24 (schematically shown by arrowheads) induces an electrical current within the circuitry of the device 23 such that an identification signal is stimulated. This identification signal effectively modulates or produces an identifier magnetic field response 25. The identifier magnetic field may comprise a base magnetic field acting as a carrier modulated by fluctuations as the identifier signal or the marker transmitter coil can resonate as an antenna with a characteristic, possibly unique, identifying radio frequency when appropriately powered by the induced electrical current. With a single coil system there are conflicting objectives of electrical current induction for the empowering electrical current S within the RFID device 23 and electrical resistance limiting emitted identifier

magnetic field strength/range.

Aspects of the present invention comprise providing two transmitter/receiver coil couples in an identification system. A first transmitter/receiver coil couple is optimised for electrical power induction and therefore on a like for like basis will give enhanced electrical power induction within the RFID device compared to a single coil system. A second transmit/receiver coil couple is optimised with respect to transmitting the identifier magnetic field and so on a like for like basis in comparison with a single coil system will achieve a better identifying response from the marker.

A transmitter/receiver coil coupled for maximum reception will generally have a higher number of wire turns with thinner wire to allow an increased number of wire turns on a like for like size basis. Conversely, for increased transmission range greater electrical current flow through the transmitter coil is desirable and therefore a higher number of wire turns will increase direct electrical current resistance and oppose identifier signal strength. It will also be understood that thinner wire on a like for like basis will generally tend to increase direct electrical current resistance and so again reduce identifier

magnetic field strength.

As indicated above two coil couples are provided in accordance with aspects of the present invention so that the marker 6: 21 in accordance with aspects of the present invention will include two wire coils and the reader 7 will atso include two wire coils. One coil in the marker device Will act as a marker receiver coil and the other coil in the marker with act as a marker transmit coil. In the reader device or combination one coil will act as a reciprocal transmitter coil to the marker receiver coil in the marker whilst a reciprocal receiver coil will couple with the marker transmitter coil to create the respective two coil couples as described above. The coil couples will be respectively optimised for inductive receiving to provide electrical power within the marker and to transmit the identifier signal to the reader device.

By aspects of the present approach it will be appreciated that the identifier system can be optimised for best performance. The operating range, whether that is for transmitting identifier signals or creating electrical induction within the marker, can be enhanced. Figure 3 provides a schematic illustration of the relationship between a transmit coil and a receiver coil.

It is possible to calculate the expected maximum operating range, d, if we know the following: Transmit coil input voltage, V,.,.

Transmit coil wire thickness, Xt.

Transmit coil number of turns, N. Transmit coil radius, rr.

Receive coil number of turns, Nr.

Receive coil radius, rr.

Receive coil required output voltage, V. Receive coil Q factor, Qr.

Operating frequency, f.

To calculate the maximum operating range, we need to determine the magnetic flux, B0, generated by the transmit coil at a point, d metres from the perpendicular from the centre of the coil, (at the receive coil). We then need to determine the magnetic flux, B0, required in order to induce the desired voltage on the receiver coil. These two equations can be equated and then solved for distance, d.

The magnetic flux, B, generated by the transmit coil at a distance of, d, metres from the perpendicular to the centre of the coil can be calculated with the following equation: B0 = poltN,r2 I 2(d2 + r,2) 3/2 where Po is the permeability of free space.

The magnetic flux, B0, required to generate a specific output voltage, V, on the receiver coil can be calculated as: B0 = V0/ 2it2rr2fNrQr.

By equating the two equations, we can now solve for an operating range, d.

lJolNr2 / 2(d2 + rt2) 3/2 = v I 2ir2rr2fNrQr.

IS

We know the input voltage, Vrn, therefore, if the coil impedance, R, can be calculated, we can then calculate the transmit coil current, I,, and substitute this into the above equation.

R11 = R + RAG.

R = 2rN / ax12 where the skin depth of copper wire at the operating frequency 125 KHz and a is the conductivity of the wire.

RAc=R(xt/28).

= 2r1N1 / aA + 1 I 2wtö.

R = 2rN1 I YX12(1 + Xt / 28).

Therefore the coil current, I, is: It = V,. I Substituting into the onginal equation now gives: p0v1N,d2 I 2R11 (d2 + r12) = V / 2it2rr2fNrQr.

Therefore; 0 = ((poV,nNtNrm2rr2rt2fQr / V0R11) -to it can be seen from the above equation that the maximum operating range is proportional to the cube root of the product of the number of turns of the transmit coil, N, and receive coil Nr.

So d is proportional to 3/( NN) It is important that the coil product, NN,, is maximised whilst keeping the transmit coil impedance, R1, low and receive coils Q factor, Qr, at a reasonable level. Too low a Q factor may result in a poor operating range and too high a Q factor will result in a low data transfer rate since the voltage induced wilt take a considerable amount of time to decay.

Standard "off the shelf" REID systems are designed such that only the coils and their respective resonant capacitors need to be designed by the user.

The coils interface circuitry has already been designed. This means that with a dual coil identification system in accordance with aspects of the present invention can only really be applied to custom designed RFID systems as standard systems only allow for single coils to be connected.

As indicated above by separating the induction functions from the transmit functions optimisation can be achieved for both functions enhancing performance. Figure 4 provides a schematic illustration of an identification system in accordance with aspects of the present invention. Schematically, a marker 41 incorporates an RHO device in a form of a transponder in which induced electrical power stimulates an identification signal transmitted to a reader device 42. In such circumstances as indicated above respective coil couples are provided optimised for the respective functions of electrical power induction and identification signal transmission.

Advantageously the marker 41 includes an electronic or similar storage device which stores a number of descriptors such as locations, owner, date of installation etc. To access each descriptor the power magnetic field may be modulated to give a district trigger signal for each descriptor or a group of descriptors. Thus, upon receipt of the trigger signal the RFID device will be stimulated to output the identification signal transmission for the descriptor or group of descriptors as required.

IS The reader device includes a reciprocal transmit coil 43 which is coupled with a marker receive coil 44 such that electrical power is induced within the coil 44 to stimulate an identification signal in a marker transmit coil which in turn is coupled to a reciprocal receiver coil 46 of the reader device.

The respective coil couples 43, 44; 45; 46 are operationally separate from each other and as indicated are optimised for the respective functions of electrical power induction and identification signal transmission. By such optimisation greater distances on a like for like basis are achievable by the identification system in accordance with aspects of the present invention.

Operation of the reader device other than with regard to the electrical power induction and transmission functions is similar of a conventional device in terms of RFID function. in

Implementing a dual coil couple identification system in accordance with aspects of the present invention means, it is possible to use a larger number of turns in the receive coil. This Will result in a large induced voltage and probably greater sensitivity to trigger signal modulation. Nevertheless if the receive coil is not able to supply sufficient current to power transmission against the DC resistance it may be necessary to use an active transponder solution. This means that the transponder only needs to detect a small voltage induced in the receiver coil rather than also be dependant on the coil output as a source of power. This means much lower induced voltage levels can be differentiated and thus larger operating ranges are achievable.

I 0 In circumstances where a small voltage is induced in the receive circuit then that small voltage may stimulate an identification signal in the transponder functions of the marker. This identification signal may simply comprise powering the marker transmit coil in order to emit a radio frequency output to be picked up by the reader device for identification. Alternatively, IS the trigger for stimulation of the identification signal may act to modulate a carrier magnetic identification field such that fluctuations in that field are picked up by the reader device for identification purposes.

As indicated above RFID devices are known to provide radio frequencies which can be uniquely associated with a source and therefore this source identified in accordance with aspects of the present invention. The markers act as identification tags which can be interrogated through a reader device when necessary. As aspects of the present invention allow both transmit and receive ranges to be increased over previous systems such enhanced performance will facilitate use of such REID devices as identification tags with respect to reinstatement issues with regard to highway and other excavation works.

It will be appreciated that the reader device in accordance with aspects of the present invention may incorporate both the reciprocal transmit and receive coils for respective coil coupling with marker transmit and receiver coils. However, these coils may also be separated in different devices such that a reader combination is provided in which one element comprises a stimulator element having an induction coil powered by a battery to stimulate electrical current in the transponder of the marker whilst a scanner or detector device incorporates the reciprocal receiver coil for the identification signal indicative of the marker. Generally the scanner device maybe a PDA or similar device which can then upload or download information from a central processor 10 (figure 1) to a network through wireless connections. In such circumstance the network will be able to identify the contractor who placed the marker in the reinstated excavation etc. It will be appreciated that each I 0 contractor will have their own markers and therefore be able to be identified even after a considerable period of time. Correct location of the marker can be checked on acceptance of the works at hand-over.

Markers in accordance with aspects of the present invention as IS indicated will provide at least one identification signal indicative of the marker.

However, it may be desirable in some instances to provide several identification signals from the marker. This may be achieved through arranging for the marker to be stimulated by the reader device to provide different identification signals in different circumstances. These different circumstances may be different levels of electrical current induction or otherwise although such an approach may lead to errors in view of inherent variability of induction strength/power over distance. Thus, as indicated above trigger signal modulation may be provided as a form of code to access and cause transmission of the identifier signals required. Nevertheless, the identification signals could relate to a unique identifier for the marker as well as more generic information such as the type of excavation reinstated. In such circumstances with the unique identification signals the contactor can be identified as well as the date of work whilst more general information may be given by standard identifier signals for different types of work performed such as initial installation of a UtilIty such as a water pipe or a cable or gas pipe or repair/inspection of a previous installation. By such an approach immediate on site information can be provided with respect to a reinstatement by readers without reference to a register which may require payment of access fees.

it will also be understood that markers and identification systems in accordance with aspects of the present invention may be used for inventory and access control. Thus, a marker in accordance with aspects of the present invention may be buried with new trunk cabling and that marker retrieved when branch cabling is attached to a house with the mark up dated with the new information or replaced with a new marker and/or the old mark taken as a "token" that works have been completed etc. Such inventory control will also allow identification of position and coupling types for access. Thus, on a new housing estate trunk cabling or mains water pipes may be identified with suitable locations for coupling branch cabling or pipes to that trunk cabling or mains with pipes identified by the markers in accordance with aspects of the present invention.

As indicated above a coil couple is utilised in relation to inducing electrical power within the transponder RFID of the marker. Such powering of the transponder will be ongoing but additionally or alternatively a power storage device such as a battery or capacitor may be charged to provide a temporary, source of electrical power to the RFID for transmission of the identification signals in accordance with aspects of the present invention.

The identification arrangement and system in accordance with aspects of the present invention as indicated operates through a method of providing separate coil couples for powering induction and identification signal transmission. Thus, the respective coil couples are chosen and configured for a particular installation and expected operational requirements and such that in use the electrical power generated will adequately stimulate identification signals Alternatively, it may be possible to provide long life batteries which only become operational in order to power the marker transmitter coils when stimulated by appropriate trigger levels induced in the marker receive coil.

Clearly, such batteries will eventually fail but nevertheless will be operational for a considerable period of time in view of the low powerconsumption requirement. Furthermore, it may be possible to effectively charge these batteries periodically during inspections.

As indicated above generally markers in accordance with aspects of the present invention will be rendered sufficiently robust to withstand the operational environments when embedded in a road surface or otherwise. In such circumstances the tags will be relatively large and therefore it may be tO possible to provide more than two transmitireceive coil couplings optimised as indicated for different electrical power induction and transmission performance levels or to give different identifying radio frequency responses.

Modifications and alterations to the embodiments in the invention IS described above will be understood by those skilled in the technology Thus, as indicated aspects of the present invention provide respectively transmitjreceive col couplings optimised for power induction and identification signal optimisation. Generally, wound copper wire will be utilised to provide the coils but alternatively it may be possible to provide printed circuit elements as the coils for transmit and receive functions.

Whilst endeavoring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

Claims 1. An identification arrangement comprising a marker having a

marker receiver coil and a marker transmitter coil, the marker receiver coil arranged to be electrical inducible by a power magnetic field to provide electrical power to stimulate an identification signal in the marker, the marker transmitter coil arranged to receive the identification signal to modulate an identifier magnetic field, the marker receiver coil and the marker transmitter coils are operated separately from each other.
2. An arrangement as claimed in claim I wherein the power magnetic field is modulated for interrogation of the marker as a trigger signal.
3. An arrangement as claimed in claim I or claim 2 wherein the marker receiver coil is optimised for induction of electrical power.
4. An arrangement as claimed in any of claims 1, 2 or 3 wherein the marker transmitter coil is optimised for producing the identified * *, magnetic field modulated by the identification signal. S. 20 S...
5. An arrangement as claimed in any preceding claim wherein the identifier magnetic field is provided by the electrical power induced in :. the marker receiver coil. S..

: 25
6. An arrangement as claimed in any preceding claim wherein the marker includes an electrical power storage device.
7. An arrangement as claimed in any preceding claim wherein the electrical power storage device is charged by electrical power induced in the marker receiver coil by the power magnetic field.
8. An arrangement as claimed in any preceding claims wherein the electrical power storage device is a battery or electrical capacitor within the marker.
9. An arrangement as claimed in any preceding claim wherein the marker is utilised to identify inventory such as electrical cable work or pipes and positions of that inventory to facilitate couplings.
10. An identification arrangement substantially as hereinbefore described with reference to the accompanying drawings.
11. An identification system comprising an identification arrangement as claimed in any preceding claim and a reader device, the reader device including a reciprocal transmitter coil for the marker receiver coil and a reciprocal receiver coil for the marker transmitter coil, the reciprocal transmitter coil and the marker receiver coil couple configured with at least an objective of inducing electrical power in the marker receiver coil and the reciprocal receiver coil and the marker transmitter coil * *. couple configured with at least an objective of inducing a reader electrical signal in the reciprocal receiver coil corresponding to the identification signal. * S. * * S S.. *
12. A system as claimed in claim 11 wherein the reader device includes an electrical power source for the reciprocal transmitter coil to provide the S...

power magnetic field.
13. A system as claimed in claim 12 wherein the electrical power Source comprises a battery.
14. A system as claimed in any of claims 11 or claim 13 wherein the marker is encapsulated and/or otherwise environmentally sealed.
15. A system as claimed in any of claims 11 to 14 wherein the marker receiver coil is arranged to be inducible by different strengths of the power magnetic field to stimulate a respective identification signal in

the marker for each power magnetic field.

S
16. A system as claimed in any of claims 11 to 15 wherein the coils are optimised by configuration in terms of number of wire turns and br thickness of wire.
17. A system as claimed in claim 16 wherein the coils are optimised by switching or providing electrical components such as electrical resistance and/or capacitance and/or inductance.
18. An identification system substantially as hereinbefore described with reference to the accompanying drawings.
19. A method of identification within an identification system provided by a identification arrangement and a reader, the identification arrangement * ** configured to have a marker receiver coil and a marker transmitter coil, the reader configured to have a reciprocal transmitter coil marker to the receiver marker, and a reciprocal receiver coil to the marker transmitter coil, the method comprising providing a power magnetic field from the ** reciprocal transmitter coil to the marker receivçr coil to induce electrical power within the marker stimulating an identification signal in the **** *..* : 25 marker when electrical power is induced in the marker receiver coil, presenting the identification signal to the marker transmitter coil to modulate an identifier power magnetic field provided by the marker transmitter coil and configuring the reciprocal receiver coil to receive the modulated identification power magnetic field to identify a marker of the identification arrangement.
20. A method of identification within an identification system substantially as hereinbefore described with reference to the accompanying drawings. * S *0 * * ** * * ** ** * * * S S *** $

S S..

S S.. * . S ** . S. S

S SS I **