GB2429878A

GB2429878A - Electromagnetic radiation decoupler for an RF tag

Info

Publication number: GB2429878A
Application number: GB0603542A
Authority: GB
Inventors: Christopher Robert Lawrence; Paul Richard Clarke; James Robert Brown; William Norman Damerell
Original assignee: Qinetiq Ltd
Current assignee: Qinetiq Ltd
Priority date: 2005-06-25
Filing date: 2006-02-23
Publication date: 2007-03-07
Anticipated expiration: 2026-02-23
Also published as: GB0603542D0; GB2429878B

Abstract

An electromagnetic radiation decoupler for decoupling radiation in the wavelength range g min to g max. The decoupler has a first conductor layer 1 in contact with a dielectric layer 5 which comprises at least one area of absence 9 and the thickness of the decoupler is less than g min/4n, where n is the refractive index of the dielectric. The dielectric layer may be sandwiched between two conductor layers, one of which has the structure described above. The conductive layer may comprise two or more islands separared by an aperture of sub-wavelength dimension. Various configurations are described. An RF tag is positioned over the area of absence or aperture, and is decoupled from the detrimental effects of mental surfaces to which the tag is attached. Also disclosed is a method of manufacture using an ink composition, a reducible silver salt and autocatalytic deposition solution.

Description

Electromagnetic Radiation Decoupler This invention relates to the field of

electromagnetic radiation absorbing or attenuating devices and more specifically relates to the field of decoupling RF (radio frequency) tags from metallic surfaces. The invention relates to any RF tag, particularly those that rely upon propagating wave interactions (as opposed to the inductive coupling exhibited by magnetic tags), Hence our preferred embodiment involves application to long-range system tags (e.g. UHF-range and microwave-range tags).

RF tags are widely used for the identification and tracking of items, particularly for articles in a shop or warehouse environment. One commonly experienced disadvantage with such tags is that if directly placed on a metal surface their read range is decreased to unacceptable levels and more typically the tag cannot be read or interrogated. This is is because a propagating-wave RF tag uses an integral antenna to receive the incident radiation: the antenna's dimensions and geometry dictate the frequency at which it resonates, and hence the frequency of operation of the tag (typically 866MHz,or 91 5MHz for a UHF (ultra-high frequency) range tag and 2.4-2.5 GHz or 5.8GHz for a microwave- range tag). When the tag is placed near or in direct contact with a metallic surface, the tag's conductive antenna interacts with that surface, and hence its resonant properties are degraded or- more typically - negated. Therefore the tracking of metal articles such as cages or containers is very difficult to achieve with UHF RF tags and so other more expensive location systems have to be employed, such as GPS.

UHF RFID tags also experience similar problems when applied to any surfaces which interact with RF waves such as, certain types of glass and surfaces which possess significant water content, such as, for example, certain types of wood with a high water or sap content. Problems will also be encountered when tagging materials which contain/house water such as, for example, water bottles, drinks cans or human bodies etc. One way around this problem is to place a foam spacer between the RF tag and the surface, preventing interaction of the antenna and the surface. With currently-available systems the foam spacer needs to be at least 10-15mm thick in order to physically distance the RF tag from the surface by a sufficient amount. Clearly, a spacer of this thickness is impractical for many applications and is prone to being accidentally knocked and damaged.

Summary of the Invention

It is therefore an object of the invention to provide an electromagnetic radiation decoupler material that substantially overcomes or mitigates the problems associated with prior art systems, namely those of thickness, size and flexibility.

According to a first aspect of the invention there is provided a radiation decoupler for an electronic device, for decoupling said device from a surface comprising at least one dielectric layer sandwiched between at least one first conductor layer and at least one second conductor layer, wherein the at least one first conductor layer has at least one area of absence where the first conductor layer does not overlie the dielectric layer and the decoupler is adapted such that, in use, an electromagnetic field is enhanced in the vicinity of the area of absence of the first conductor layer.

is According to a further aspect of this present invention there is provided a radiation decoupler for RF tags, for decoupling radiation from a surface in a wavelength range Amin to Amax, comprising a dielectric layer sandwiched between first and second conductor layers wherein the first conductor layer comprises two or more islands separated by at least one aperture of sub-wavelength dimension, wherein the resonant frequency of the decoupler is selected to substantially match the resonant frequency of the RF tag and/or RF reader.

Preferably the device or RF tag is located substantially over the area of absence or aperture.

By the term at least one aperture of sub-wavelength dimension it is meant that the aperture is less than Amjn in at least one dimension.

RE tags may be designed to operate at any frequencies, such as for example in the range of from 100MHz up to 600GHz. In a preferred embodiment the RF tag is a UHF tag, such as, for example, tags which have a chip and antenna and operate at 866MHz or 915MHz, or a microwave-range tag that operates at 2.4-2.5 GHz or 5.8GHz.

Preferably the wavelength of the enhanced electromagnetic field will lay in the range of Amin to 1max.

It should be noted that that references to wavelength in this document refer to the in vacuo wavelength unless otherwise specified.

The invention provides for a multi-layer structure that acts as a radiation decoupling device. First and second conductor layers sandwich a dielectric core. One of the conductor layers contains one or more subwavelength apertures (i.e. less than Amin in at least one dimension) which expose the dielectric core to the atmosphere.

The apertures could be small, discrete crosses or L-shapes but more conveniently are slits wherein the width of the slit is less than Amin.

It should be noted that the conductor layers do not have to be in direct contact with the dielectric core. For example, there may be a thin adhesive or other material layer separating them.

Any material that has a metallic response at the electromagnetic wavelengths of interest can be used as a conductor material in the respective conductor layers. Conveniently the conductor may be electrically conducting. Preferably such materials are metals metal alloys or carbon. The thickness of such a conductor material must be such that it is at least partially opaque to the target wavelengths (this is determined by both impedance mis-match and skin depth calculations which will be known to the skilled man). The thickness of the conductor material will hence generally be greater than 0.10 microns, and preferably the thickness is in the range of from 0.25 to 5 microns, more preferably in the range of from 1 to 2 microns. The thickness may be increased beyond 5 microns if desired, particularly if this is required in order to ensure that the chosen conductive material provides at least a partially opaque barrier to the target wavelengths. However any significant increase in thickness may affect flexibility and increase production costs.

Clearly, there is no maximum thickness requirement for the second conductor layer.

Conveniently, the second conductor layer thickness may be selected from the same range as the first conducting layer. This may be desirable to retain flexibility.

The multi-layer structure is less than a quarter-wavelength in its total thickness and is therefore thinner and lighter compared to prior art systems. It can also be designed in such a manner as to be flexible, enabling it to be applied to curved surfaces.

The above aspect of the invention provides for two conductor layers to form the decoupler. However, in cases where the material is to be applied to a metallic surface (e.g. a car, container, vessel or roll cage) then only the first conductor layer and the core layer are required since the metal structure itself will act as the second conductor layer as soon as the material is applied to the structure.

Accordingly a further aspect of the invention provides a radiation decoupler for an electronic device, for decoupling radiation from a conducting surface comprising at least one conductor layer in contact with at least one dielectric layer, wherein the at least one first conductor layer has at least one area of absence where the first conductor layer does not overlie the dielectric layer and the decou pier is adapted such that, in use, an electromagnetic field is enhanced in the vicinity of the area of absence of the first conductor layer. Preferably the electronic device is an RF tag.

Accordingly a further aspect of the invention there is provided a radiation decoupler for RF tags, for decoupling radiation from a metallic surface in a wavelength range Amin to Amax, comprising a conductor layer in contact with a dielectric layer, wherein the conductor layer comprises two or more islands separated by at least one aperture of sub-wavelength dimension, wherein the resonant frequency of the decoupler is selected to substantially match the resonant frequency of the RF tag and/or RF reader system In certain applications the size of the decoupler is not important, such as for example on a logistics container, however increasingly a large number of consumer items as hereinafter defined are required to be tracked by an RF tag means. Therefore a decoupler with a smaller footprint is highly desirable, accordingly there is provided a single island decoupler for RF tags for decoupling radiation from a surface in a wavelength range Amjn to Amax, comprising a dielectric layer sandwiched between a first and second conductor layers wherein the first conductor layer conductor layer comprises at least one aperture located substantially at a point on the decoupler which corresponds to an increased electromagnetic field, wherein the electronic transceiver is located substantially on the aperture, and further wherein the resonant frequency of the decoupler is selected to substantially match the resonant frequency of the RF tag and/or a RE interrogating source.

The length G of the first conducting layer may be determined by A 2nG, where n is the refractive index of the dielectric, and A is the intended wavelength of operation of the decoupler.Clearly this is for the first harmonic frequency, other resonant frequencies may be employed As above the apertures may take the form of discrete crosses, L-shapes or more conveniently slits. The slit may be a linear aperture which may extend part, all or substantially all across the width and or length of the decoupler. When the slit extends fully across the decoupler it may produce two or more electrically isolated islands.

However, if the slit does not extend fully i.e. it extends either part or substantially all across the surface of the decoupler the islands may be electrically joined at the ends of the slits. Complete electrical isolation between the two or more islands is not an essential feature of the invention.

In one embodiment there may be a broad band decoupler, which is a decoupler which may operate at more than one resonant frequency, such that there may be provided a decoupler further comprising a third conducting layer adjacent a second dielectric layer wherein third conducting layer has at least one area of absence where the third conducting layer does not overlie the second dielectric layer and wherein the second dielectric layer is located between the third conducting layer and the second conducting layer. To achieve a broad band decoupler preferably the first conducting layer is different to the length of the third conducting layer.

In an alternative arrangement there may be provided at least one first conducting layer and at least one dielectric located on two surfaces of the second conducting layer. The different length first conducting layers are mounted on opposing sides of the second conductor layer.

In an alternative arrangement the at least one aperture or slit may be substantially non parallel to at least on of the edges of the decoupler. This will provide a decoupler which has a first conductor layer with a plurality of different period lengths, such that it may function at a plurality of wavelengths, as hereinbefore described. Thus the use of nonlinear aperture or non-linear slit or alternatively an aperture or slit which is linear but is lies non-parallel with respect to one or more of the edges of the decoupler will allow an increased range of wavelength to be decoupled. This may be used in combination with the multiple layer broad band decoupler embodiment as hereinbefore defined.

The surface that is to be decoupled from, may be considered as a surface which, due to the presence of charges within or on the surface of the material, would otherwise have a detrimental effect on the operation if the tags antenna.

The decoupler will work on surfaces which are both non reflective and reflective to incident RF radiation. The advantage of the invention may be seen more clearly on surfaces which are reflective or have a detrimental effect to incident radiation. The surface may be formed from a conductive material, a material which comprises a high liquid content or a surface which forms part of a containment means for a fluid. It has been found that certain types of glass also interact with RF tags and so the decoupler may also find use on glass or silicas ceramics which have a detrimental effect on the operation if the tags antenna. The containment means may be any barrier, membrane or part of a container which separates a liquid on one side of the surface with a further environment on the opposing side of the surface. The opposing side of the surface may preferably be an external surface on which the decoupler is located, preferably the containment means is part of a container and may be a food, drink, or chemical container.

The conductive material may be carbon, metal or metal alloys, typically most containers are metal. The surface material may comprise a high liquid content such as a cellulose material, for example, certain woods, or any other naturally occurring materials which may possess a high moisture content.

Therefore the decoupler may be applied to surfaces which are in environments or areas of high humidity, damp or even to surfaces which are part or completely submerged beneath the surface of a fluid, such as for example a liquid such as water. Therefore the decoupler and RF tag may be located either on the outside or inside of a drinks or food container.

In an alternative arrangement the surface may form part of a containment means for a fluid. It is known that liquids such as water interfere with RE radiation and hence detrimentally influence the performance of RF tags in their vicinity. Therefore the surface may be that of a food, drink or chemical container.

Therefore the decoupler may be applied to materials which contain/house water such as water bottles, drinks cans, food containers or human bodies etc. The tagging system may be applied to persons or animals to track their whereabouts or movement through a particular area, a particular example may be people especially children or babies in a hospital environment.

The exact mechanism by which the decou pIer of the invention shields and thus decouples an RF tag from a metallic surface or from a surface which either contains or forms part of a containment means for a fluid is not completely understood, but may be explained by different models. One possible explanation, which does not limit the scope of the invention, is that when radiation of a certain wavelength, such as for example the resonant frequency of the RF tag, is incident upon the first conductor layer it is channelled through the sub-wavelength apertures and into the dielectric core that separates the two conductive layers. The core acts as highly resonant cavity which on condition that the core is not sufficiently lossy to attenuate the channelled radiation, re- emits the radiation through the aperture to form regions of highly intense electric field.

The RF tag is positioned in the high-intensity field, and interacts with this (i.e. it is not solely dependent upon the less intense fields that arrive direct from the interrogating device, as per the situation in the absence of the decoupler). The channelled radiation may be both that which was made incident upon the RF tag in order to interrogate it, and the signal re-emitted by the RF tag itself (i.e. the response which is sought by the interrogator).

It is the sub-wavelength apertures which allow the energy to emerge from the core, creating regions of high intensity electric field. Regions of high electric field intensity are formed where the standing waves generated in the dielectric create anti-nodes. The tags may be located at any point on the decoupler where there are areas of high electric field.

Other means of focusing or directing energy to create regions of high energy may also be envisaged.

The decoupler may be applied to surfaces which are linear or substantially flat, or surfaces which are singly- or doubly-curved, such as for example cylinders or spherical surfaces, respectively. Thus the invention facilitates the production of food and or drinks containers with RF tags rather than barcodes. The decoupler may be applied to cylindrical containers (e.g. food and drinks cans) such that their whereabouts within a controlled environment may be located by the use of RF ID tracking technology.

Description of the Invention

The following discussion applies to both aspects of the invention namely whether the decoupler is provided with a discrete second conducting layer or the surface of the article to which the RF tag is applied acts as the second conducting layer of the decoupler.

Conveniently, the decoupler will interact with radiation when its thickness is far less than a quarter-wavelength of the incident radiation. For example, radiation will undergo interaction with the decoupler in the instances where the thickness is equivalent to a less than 1110th, preferably less than 11100th more preferably less than 11300th or even a few 111000th, it may also be desirable to use less than 113000th of the wavelength of the incident radiation.

The arrangement of slits on the first conductor layer affects the wavelength or wavelengths of radiation that can interact with the structure. Preferably the slit arrangement is periodic.

In one embodiment the slit arrangement comprises parallel slits. It has been determined by the inventors that a parallel slit arrangement radiation of wavelength A may undergo decoupling according to the following relationship: AN2nG/N where A is the wavelength in the range AmintO Amax where maximum decoupling occurs, n is the refractive index of the core, G is the length of the at least one first conductor layer, or for two or more island decouplers G is the slit spacing and N is an integer ( =1). Note: for two or more island decouplers the slits may be narrow in comparison to the wavelength. It is further presumed that the radiation is linearly polarised such that the electric field vector is orientated perpendicular to the axis of the slit (i.e. its length): by definition typical to this field of research, if the plane of incidence is parallel to the slit then the radiation must be TE- (s-) -polarised (electric vector perpendicular to the plane of incidence); if the plane of incidence is perpendicular to the slit then the radiation must be TM- (p-) -polarised (electric vector within the plane of incidence).

It can be seen from the above relationship that the wavelength of radiation that is decoupled is linearly related to the slit spacing G and also the refractive index of the core. Varying either of these parameters will enable a specific wavelength to be decoupled by the structure.

It can also be seen that radiation will also be decoupled at a number of wavelengths corresponding to different values of N. Each of the frequencies comprises a resonant frequency of the decoupler as the term is used herein. However, preferably the resonant frequency of the tag preferably matches the first resonant frequency of the decoupler that is the resonant frequency at N=1. Clearly, the other harmonic frequencies may also be used to provide decoupling.

This equation is an approximation that is most accurate when the width of the core is equal to the width of the slit. If the slit width is decreased then there is a gradual shift of the resonance to longer wavelengths (the exact shift being related to the ratio of slit width and core thickness).

It should also be noted that only odd values of N give rise to resonances if the radiation is made incident upon the structure at normal incidence.

Power is dissipated by both the core and - to a certain degree - the metal claddings, and hence the permittivities and permeabilities of these materials are important parameters in the design process.

In order to remove any dependency on the azimuthal orientation of the sample relative to the incident radiation, the first metallic layer preferably comprises at least one orthogonal set of slits (a "bi-grating" arrangement). This also has the advantage of reducing polarisation effects exhibited by a single slit array (a "mono-grating" arrangement) for which only one linear polarisation may be decoupled for any orientation (namely the polarisation state with the electric field component perpendicular to the slit direction). The bi-grating arrangement, however, decouples both polarisations.

There may be three sets of slit arrangements at 60 degree azimuthal separation (i.e. forming a triangular pattern). Higher order patterns may be envisaged.

For "wide" slits (i.e. slit width comparable to the wavelength of the incident radiation) the decoupling wavelength varies according to the angle at which the radiation is incident to the surface of the first metallic layer. As the slit width decreases then the angular dependency becomes less pronounced. Therefore preferably the slits are thin compared to the wavelength of radiation to be decoupled.

For wavelengths A corresponding to and in close proximity to the microwave region of the electromagnetic spectrum (e.g. A's generally in the range millimetres to metres) then typically slit widths or apertures are less than l000microns and preferably less than 500 microns and more preferably less than 150 microns and may be less than or equal to 50 microns. It is therefore desirable for other wavelength regions that the apertures may be less than 1/1 00th or more preferably less than 1 150th of the wavelength of incident radiation.

The dielectric core material (or core materials) may be any suitable or commonly used dielectric material, but preferably the dielectric core will not be lossy(i.e. the imaginary components of the complex permittivity and permeability may be optimally zero. The dielectric core may be a void between the first and second conductor, such as for example a partial vacuum or an inert gas or more preferably in part or substantially an air gap between the first and second conductor. Conveniently, non electrically conducting materials such as corrugated cardboard, honeycomb structures or foams which possess a high void content may be used.

Dielectric core materials may be selected any suitable dielectric such as, for example, polymers such as, for example, PET, polystyrene, BOPP, polycarbonate and any similar low-loss RF laminates. Commonly used container materials which may form part of the dielectric layer may be cellulose materials such as paper, card, corrugated cardboard, or wood. Alternatively ceramics, glass, plastics may be used.

In one embodiment the material chosen to be used in the dielectric core is capable of altering its refractive index in order to control the wavelengths of radiation that are to be decoupled. For example, a polymer dispersed liquid crystalline material can be used as the core. If the decoupler structure is arranged such that a voltage can be applied across the core material then its refractive index can be altered and the decoupled wavelengths will shift in a tailored manner. This may be particularly advantageous as one decoupler may then be used for any range of RF tag wavelengths, or controlled such that the decoupling action may be switched on and off.

Further, if the metallic surface, such as, for example, a container, required different RF tags for different locations (e.g. different countries) then a core material with a tuneable refractive index would allow the same decoupler to be used for RF tags which operate at different wavelengths. Alternatively the decoupler may be prepared such that it has different regions which contain different pitch lengths or periods, which may decouple commonly used RF tag frequencies/wavelengths, such as for example 866 MHz, 915 MHz, 2.4 to 2.5 GHz and 5.8 GHz. The decoupler may be have one or more regions comprising different periods suitable for different resonant frequency RF tags.

The decoupler may comprise at least two metallic islands separated by one aperture.

Preferably the RF tag may span the aperture such that the tag is substantially centrally located over the aperture and the antenna is located over the at least two metallic islands. The islands may be any geometric shape, preferably the islands are square or rectangular in shape.

The length of one metallic island (such as, for example, G in the previously stated equation) may be selected depending on the operational wavelength of the RF tag employed. The length of the island multiplied by the refractive index of the core material is selected as being approximately half of the operational wavelength of the RF tag.

Some commercially available RF tags, such as, for example, a tag manufactured by Alien Technology has its wavelength of operation the same length as its dipole antenna.

Hence in this example the length of one island may be approximately the length of one RF tag. Hence the overall length of the decoupler which comprises at least two islands may be at least the length of two tags. Further some commercially available RF tags are able to operate at more than one frequency.

Low -Q antennas may also be used in the application, although the range is likely to be reduced when compared with that of an optimised UHF RF tag on a decoupler. It has been found that UHF RF tags which have low-Q antennas and possess only a few cms or even mms read range in open space may be mounted on a decoupler according to the invention as hereinbefore or hereinafter described. It has been found that low 0 antennas used in combination with a decoupler of the invention may still exhibit useful read ranges approaching that of an optimised RF tag operating in free space without a decoupler. The advantage is that low-Q antennae may be cheaper to manufacture, and may occupy less surface area (i.e. the antenna length of such a tag may be shorter than is usually possible). In a particularly preferred arrangement an RF tag with a substantially reduced antenna area may be mounted onto a single island decoupler as hereinbefore defined, to provide a reduced area decoupler and tag system, which may have a first conductor layer length of substantially A -2nGIN, where A is the wavelength in the range Amin to Amax where maximum absorption occurs, n is the refractive index of the dielectric, G is the period of the at least one first conductor layer and N is an integer greater than or equal to 1.

The width of a metallic island may be determined by the dimensions of the selected RF tag. As an example only, for commonly used UHF RF tags the width of the island has been used at 4 to 5 times the width of the tags.

Preferably the width of the aperture, and both the permittivity and thickness of the dielectric core material will be selected to provide a decou pier which has a resonant frequency substantially the same as that of the RF tag.

The RF tag may be placed directly in contact with the surface of the decoupler.

Preferably there may be a further dielectric material, such as a spacer, placed between the RF tag and the decoupler material. When a spacer is present the length and width dimensions of the spacer must be at least the same as that of the metal area (for example, antennae) of the RF tag. Most RF tags are supplied already mounted on their own substrate, which vary in thickness depending on the manufacturer.

Preferably the (total) gap between the metal part of the RF tag and the decoupler (i.e. spacer thickness + RF tag substrate thickness) is in the range of from 100 to 1000 microns, preferably of from 175 to 800microns, more preferably of from 300 to 800 microns, even more preferably of from 300 to 600 microns. These values may differ if a spacer or tag substrateexhibiting lossiness or an unusually high or low refractive index is used (i.e. if something other than a standard polymer substrate such as a PET is used).

Similarly, a shift to higher or lower frequencies of operation may affect spacer thickness.

The decou pIer must at least have the same width and length dimensions as the RF tag and the optional spacer to in order to decouple an RF tag from an RE reflective surface.

The read range of the tag will not be optimal when the decoupler is at least the same width and length dimensions as the tag; however the decoupling effect may still be used.

The metal antennas of RF tags may be easily deformed or scratched by normal handling.

Advantageously the RF tag and decoupler may be in part or enveloped by a protective housing. The housing may be a non-conducting material deposited on the surface of the RF tag and the decoupler. The non- conducting material may simply be further dielectric material applied as a spin coating, such as for example PET, PETG UPVC, ABS or any suitable potting compound, such as, for example, an epoxy etc. It has been found that such housing coatings in the range of from 250 -2000 microns and even up to 5000microns do not affect the read range of RF tags. Clearly the thickness of the housing will be selected depending on the environment and the flexibility required from the tag.

The conductor surface, such as for example the islands which form the decoupler, may be manufactured by any known process, such as: etching of a metal-coated dielectric surface, photolithography, use of conductive inks such as carbon or high-loaded silver inks, deposition of block foils (such as by hot stamping), vapour deposition (optionally etching afterwards), or the use of catalytic inks in combination with a pattern transfer mechanism for additive electroless deposition and optionally electrodeposition.

Accordingly, in a further aspect of the invention there is provided a method of making a decoupler according to the invention comprising the steps of coating a dielectric material with an ink composition in a pattern according to the invention, wherein said ink composition comprises an ink formulation suitable for printing the substrate to be coated, silver as a reducible silver salt and filler particles, wherein said reducible silver salt is selected such that when reduced is capable, once the coated substrate is introduced into an autocatalytic deposition solution, of catalysing the deposition of a metal from the autocatalytic deposition solution, onto the coated areas of the substrate, and wherein the proportion of the reducible silver salt is such that the ink composition contains less than 10% by weight of silver, optionally subjecting said coated area to electrodeposition.

Conveniently an ink and or method may be used such as that disclosed in co-pending Patent Application number GB0422386.3.

The ink formulation may be deposited by any known pattern transfer mechanism, such as, for example ink jet, gravure, flexo or screen printing techniques. The deposited ink may then be subjected to standard electroless deposition techniques for autocatalytic deposition. It may be desirable to increase further the thickness of the electrolessly deposited metal by using electrodeposition, which may be achieved by a reel to reel process (such as that described in co-pending Patent Application number GB0512191.8.) As an example a metal food container may act as the second conducting layer, to this may be applied a thin coat of dielectric material. The first conducting layer may then be deposited by any known means into the desired decoupler pattern on the dielectric material. There may optionally be a further dielectric applied to create a spacer material.

The RF tag may be located over the aperture and a protective housing printed or applied over the tag and or decoupler. The protective housing may comprise the finished coloured design for the item being sold.

A decoupler according to this invention can be constructed such that it is flexible. If it is backed with an adhesive material then it can be applied to any surface of interest in the form of a tape or appliqué film. The ability to construct a very thin decoupler (relative to the wavelength of radiation to be decoupled) means that it can effectively be moulded to any surface contour.

Accordingly there is also provided the use of an electromagnetic (elm) radiation absorber as a decoupler for shielding RF tags from surfaces in a wavelength range Amin to Amax comprising a dielectric layer sandwiched between first and second conductor layers wherein the first conductor layer carries a plurality of apertures of sub-wavelength dimension and wherein the thickness of the absorber is less than,lmjn/4n, where n is the refractive index of the dielectric.

A further aspect provides the use of an electromagnetic radiation absorber as a decoupler for shielding RF tags from metal surfaces in a wavelength range 4min to Amax comprising a conductor layer in contact with a dielectric layer wherein the conductor layer carries a plurality of apertures of sub-wavelength dimension and wherein the thickness of the absorber is less than,4mjn/4n, where n is the refractive index of the dielectric.

Preferably the wavelength thicknesses are less than Amn/3U, more preferably less than 4min'10 even more preferably less than Amn/300 and may even be less than Amjn/500.

A further aspect of the invention provides an RF tag mounted on the surface of a decoupler as hereinbefore described.

There is further provided a tagging system comprising at least one decoupler as hereinbefore defined, at least one RF tag, optionally a spacer between the at least one decoupler and at least one RF tag and optionally a protective housing covering part, all or substantially all of the at least one decoupler.

In a yet further aspect of the invention there is provided a surface wherein a proportion of the surface is partially, substantially or completely covered in a decoupler or a tagging system as hereinbefore defined.

There is further provided a body or container which comprises at least one surface as hereinbefore defined. In one embodiment the at least one surface may be curved. In a further preferred embodiment said body or container may be a logistics container such as for example a rollcage, stillage, or food or drinks container, particular examples may be drinks cans or canned food.

As a yet further aspect of the invention there is provided a metallic container wherein a proportion of the surface of the container is covered in a decoupler or tagging system as hereinbefore defined.

The type of logistics container i.e. rollcages stillages, etc are just generic names for wheeled caged containers used for the transport of goods in the logistics chain. These are found in all types of logistics, typically supermarkets, post office, courier, airlines or dairies etc. It will be apparent that any logistics container or item to be tracked may be fitted with a tagging system as herein defined, such as, for example, pallets, shipping containers, supermarket trolleys or baskets, hospital beds and/or equipment, items of clothing, animals, humans, food and drink containers.

As an example, logistic containers such as rollcages typically carry an identification plate, which usually displays barcode or visual indications i.e. written/typed identification means. As mentioned above, previous decouplers for REID which have used thick foam spacers have also been mounted on the identification plates, but these devices protrude from the surface of the plate and are prone to being knocked and accidentally removed from the plate.

A further aspect of the invention provides a logistics container, for example a roUcage comprising a decoupler or a tagging system according to the invention. There is further provided an identification plate comprising a recessed portion said portion comprising a tagging system as hereinbefore defined, and a protective layer to produce a substantially flush identification plate. The protective layer may be selected from the same range of material as the protective housing as hereinbefore defined. In this embodiment the protective layer may replace the requirement for the protective housing. It has been found that such protective layer coatings in the range of from 250 -2000 microns even up to 5000microns do not affect the read range of RF tags. The protective layer may be applied as a liquid, such as, for example, a potting compound which may be cured to "pot's the components or alternatively the protective layer may be applied as a film or sheet which is inlayed into the identification plate.

The advantage is that the tagging system (i.e. the decoupler and RF tag) is located beneath the surface of the identification plate to provide further protection to the components. For example from environmental hazards such as for example adverse weather and also from collision hazards and scratches. The identification plate comprising the tagging system may then be welded or riveted directly to the container or roll cage. This provides a useful solution in that it the decoupler becomes an intrinsic part of the logistics container or roll cage.

The identification plate may be manufactured from any suitable material, such as metal or their alloys therein, laminates, plastics, rubbers, silicones, or ceramics. If the plate is manufactured from a conducting material, the tagging system must be electrically isolated from the plate. However if the plate is metallic and also provides the second conductor layer, then the first conductor layer must be electrically isolated from the metallic plate.

A yet further advantage is that the identification plate comprising the tagging system may have a further identification means applied, such as the traditionally-used identification means, such as, for example, a barcode or visual indications (i.e. written/typed identification means). This allows the gradual integration of the RF tracking system into a working environment or allows different companies to monitor the logistics containers by different tracking methods.

In a further aspect of the invention there may be provided a decoupler according to any one of the preceding claims wherein the dielectric layer may be formed from in part or substantially all of a non conducting containment means. Particularly preferred material for the non conducting containment means may be natural or man made fibres, plastic, cellulose, glass or ceramic. In this arrangement a container such as bottle or carton made from a non conducting material, such as plastic or card may form the dielectric layer. Therefore a first conductor and second conductor layer may be formed by any means hereinbefore defined on either side of said container, such that the conductor layers are co-located to form a decoupler according to the invention. It may be convenient to use a further dielectric material on one or both sides of the non conducting containment means, such as to improve the dielectric nature of the dielectric core.

The dielectric core of the decoupler may also be formed using in part or all of a non conducting label or covering for an article to be tagged.

There is also provided a method of tracking a body or a container comprising the steps of applying to a proportion of the surface of said body or container a decoupler or a tagging system as hereinbefore defined, interrogating the at least one RF tag with RF radiation, and detecting the response from the at least one RF tag. The body or container may be manufactured from a conducting material, such as for example metals or their alloys therein, or the body may be a surface which either contains or houses a fluid, such as, for example water, as herein before defined.

A highly inefficient decoupler may be made by using a commercially available double sided PCB blanks, that is one with conducting layers on both sides of the board, the board may then be cut to a length which is approximately half the wavelength of the incident radiation. In this set up the aperture may be considered to be the exposed dielectric core. An RF tag may then be placed on the edge of the side of the board, such that the RF tag is orthogonal to the board. Therefore for a low Q antenna this may provide a minimal amount of decoupling from a metal surface.

Decouplers which possess one or more slits and when used with RF tags which posses directional antennae may only achieve large enhanced field effects when the reader and tag mounted on the decoupler are substantially parallel. This may be overcome by using transmitter/receivers which operate in a plurality of orientations. Alternatively, in a further aspect of the invention, there is provided a polarisation independent decou pIer, such that the position and subsequent activation of the RF tag on the decoupler becomes independent of the polarisation or orientation of the incident radiation. Accordingly, the area of absence of the first conducting layer comprises at least one non linear aperture, preferably a substantially curved or more preferably circular patterned aperture or yet further preferably a circular slit may be formed in the first conducting layer.

Commercially available tags which can be read in free space may have antennae in the order of 10cm, and may not be suitable for identifying many of the small samples commonly found in laboratories, whether medical, chemical or otherwise. The active chip from a UHF tag is of the order of one or two millimetres and therefore may be easily deployed onto a small containers or articles. Alternatively, it may be desirable to place RF tags in discrete or confined areas of a surface or article to be tagged. The UHF chip without the antennae will not function, even if the interrogating system is placed next to the chip. However when the chip and optional spacer is located on a decoupler as herein defined, the chip may be read. Further, it may not be convenient to place directly a decoupler onto the small container or article. In a further aspect of the invention there is provided a method of detection or identification of a surface or article comprising the steps of bringing together a surface comprising an RF tag or low Q RF tag, with an optional spacer, with a decoupler as herein defined, interrogating said RF tag, wherein the RF tag may only be read when in close proximity to said decoupler.

This is particularly useful where an optimally sized decoupler may not be readily incorporated on to a small body or article. In a further aspect there is provided a kit of parts comprising an RF tag with an optional spacer and a decoupler according to the invention. It may be desirable that the RF transmitter/reader system comprises an integral decoupler. Therefore an advantage is that small bodies which may only have sufficient room on their surface for an RF tag with a low 0 antenna, may be successfully interrogated by using a decoupler according to the invention.

For example, the tag and optional spacer may be placed on any small container, vessel, surface or piece of kit to be identified. Such as, for example, a medical sample, surgical instrument, a microscope slide, vial or bottle, such that when the surface bearing the RF tag and optional spacer is placed in close proximity to the decoupler that it would be capable of being read by an interrogating device.

In yet a further aspect of the invention there is provided a low Q RF tag wherein the antenna has a major dimension substantially less than 2cm, more preferably the antenna has a major dimension substantially less than 1 cm.

There is further provided a low Q RF tag suitable for use with a decou pier as herein before defined,wherein said low Q RF tag is optionally mounted on a spacer, preferably the thickness of the spacer and the low Q RF tag together is in the range of from 175 to 800microns. A further advantage is that the smaller dimensioned single island decoupler may be conveniently used a low 0 RF tag, to provide a smaller footprint tagging system.

In a further embodiment it may be desirable to provide increased protection to the RF tag. Accordingly there is further provided a decoupler as hereinbefore defined wherein a low 0 RF tag is located within or forms an integral part of the dielectric layer, optionally, the RF tag may comprise substantially no antenna. Where an antenna is present, it may extend outside of the dielectric core, but must be electrically isolated from the first conductor This has the advantage that the overall thickness of the RF tag and the decoupler or RF tagging system is substantially just the thickness of the decoupler.

In a yet further embodiment it may be desirable to form a decoupier effectively in-situ, such that the decoupler functions when the component parts of the decoupler are brought into alignment. Accordingly there is provided a method of forming a decoupler suitable for the detection or identification of a surface comprising the steps of i) providing a surface comprising an RF tag or low Q RF tag with an optional spacer, and at least one conductor layer in contact with part or substantially all of at least one dielectric layer, wherein the at least one first conductor layer has at least one area of absence where the first conductor layer does not overlie the dielectric layer, ii) bringing together the surface of step I) with a second conductor layer or conducting surface to form a decoupler as herein defined.

The advantage is that the decoupler may be formed by the act of bring the component parts into alignment. For example a folded document or article may be configured such there is a first conductor layer on one side of a fold with a Low 0 RF tag and in the second side of the fold a second conductor layer, such that in an open state the book cannot be read, but when closed the pages of a book or contents of the article form the dielectric layer and the first and second conductor layers are brought into alignment such that a decoupler according to the invention is formed and the low Q RF tag may be interrogated and read.

The advantage of using the Low 0 RF tags is that they are significantly smaller than commercially available RF tags which typically have large antennae. Therefore low Q RF tags with minimal antenna in combination with a decoupler as herein defined may be placed more discreetly into documents, and/or credit card sized information documents such as, for example, passports, identification cards, security cards, driving documents, **toll cards etc, Wherein the plastic f the card or pages of the document form in part the dielectric layer. Therefore the movement of people or goods within controlled zones or through controlled entry points may be facilitated, without requiring direct contact or visible scanning of documents.

Embodiments of the invention are described below by way of example only and in reference to the accompanying drawings in which: Figure 1 shows a basic representation of an electromagnetic radiation decoupler according to the present invention.

Figure 2 shows a further decoupler according to the present invention.

Figure 3a and 3b shows a side view and plan view respectively of a two island decoupler.

Figure 4a-c shows a) a UHF tag located on a four island decoupler in plan and side views respectively.

Figure 5a-c shows a plan view of alternative positions of a UHF tag on a 4 island decoupler as described in the examples.

Figure 6 Plot of the electric field vector along the slit parallel to the incident electric field.

Figure 7 Plot of the electric field vector along the slit perpendicular to the incident electric

field.

Figure 8 Plot of the electric field vector along a line perpendicular to the surface of the decou pier.

Figure 9 Magnitude of the electric field in the y-direction along line 1: parallel to the z-axis through the decoupler dielectric core and the air space above.

Figure 1 Oa and b show a plot of the magnitude of the electric field in the y-direction along 3 different lines all parallel to the z-axis.

Figure 11 shows a plot of the magnitude of the electric field in the ydirection along line 4 (as generated in Figure lOa and b) Figure 12 shows a cross section of a recessed identification plate.

Figure 13 shows a top view of a recessed identification plate.

Figure 14: shows the relationship of read-range upon spacer thickness.

Figure 15: Plot of the magnitude of the electric field in the dielectric core of the decoupler at the fundamental resonant frequency.

Figure 16 shows a cross section of broad band decoupler with two or more islands.

Figure 17 shows a graph of the performance of an 866MHz tag and a Sensormatic reader, without a decoupler.

Figure 18 shows a modelled graph of the decoupler curve and the same reader curve as in Figure 17.

Figure 19 shows a single island tag with a low Q antenna (small area, non optimised antenna).

Figure 20 a and b show example configurations for broadband single island decouplers.

The first conductor layer 1 has a number of apertures (slits) of pitch (separation) 7 and width 9.

Figure 21a-e show a top view of a variety of geometric designs for the first conductor layer.

Figure 22a, b and shows examples of a low Q tags mounted on a single island decoupler.

Figure 23 shows a graph of three different core materials at a variety of thicknesses Figure 24a and b shows a two island and one island decoupler respectively, with at least one slit 125, which does not have a uniform distance from at least one edge of the decoupler, to create a broad band decoupler.

Figure 25 shows a cross section of an RF tag located within the dielectric layer.

Figure 26a, b and c shows three configurations for a decoupler where the first and second conductor layer are separated by an air gap.

Turning to Figure 1, a multi-layer electromagnetic radiation decoupling material comprises a first conductor layer 1 and a second conductor layer 3. Conductors I and 3 sandwich a dielectric core 5.

In an example of a decoupler constructed for use with an 866 MHz UHF RF tag the thickness of each of the copper conductor layers 1 and 3 was 2.5 microns and the thickness of the dielectric was approximately 360 microns. Slit width was 0.490 mm. Slit pitch was 95mm. Such a construction led to resonance at around a wavelength of 95mm due to a core refractive index of approximately 1.8. It should be noted that the total thickness of the material (approx. 400 microns) is around 11100th the wavelength of the incident radiation.

Figure 2 shows a further example of a radiation decoupler according to the present invention. In this case copper layers 11 and 13 sandwich a polyester layer 15. The upper copper layer 11 contains a slit arrangement 12.

The structure of Figure 2 was constructed by autocatalytically depositing the copper layer 11 onto the polyester layer 15. A sensitising material 17 was used to promote the deposition reaction. A layer of adhesive 19 bonds the polyester layer 15 to the bottom copper layer 13.

In the example constructed and tested, the copper layer 11 was of thickness 1.5-2 microns, the sensitiser layer 17 was of thickness approx. 3-4 microns, the polyester layer 15 was of thickness approx. 130 microns, the adhesive layer 19 was of thickness approx.

microns and bottom copper layer was of thickness 18 microns.

Figure 3a -b shows a two island decoupler according to the invention with copper layers 21 and 23 sandwiching a dielectric layer 25 bonded to the lower copper layer 23 by an adhesive layer 29. The upper copper layer 21 has been deposited by electroless followed by electrolytic deposition on a sensitising material 27 and is configured to contain a slit arrangement 22. An RF tag 24 is mounted on a spacer 26 to provide a stand off from the surface of the decoupler. The tag plus spacer is mounted on top of the first conductor layer 21, such that the chip at the centre of the tag (not shown) is located directly above the centre point between the two islands.

Figure 4a shows a plan view of a commercially available standard UHF tag (in this example an 866MHz Alien technologies UHF Tag), comprising a chip 37, with antenna 40. The width of the tag 41 is 8mm and the length of the tag 42 is 95mm.

Figure 4b and 4 c show a four island 31, decoupler. The four islands 31 are arranged on the surface of a dielectric core material 35. The islands 31 are separated by apertures 32. The apertures are substantially orthogonal to each other. They are located such that the point of intersection of the two apertures 32 crosses through the centre of the decoupler. Fiducial marks 46 show the absolute centre of the length dimension and fiducial mark 45 shows the absolute centre of the width dimension. The tag 34 is placed directly over the point of intersection, such that chip 37 sits directly on the point of intersection of the lines drawn from point 46 and 45.

The island 31 has a length 44 which is calculated using the approximate formula of island length -A/(2n), in which n is the refractive index of the core, providing an island length 44 of approximately 95mm (PETG as core material). The width of the island 43 depends on the physical size of the RF tag and the wavelength of the interrogating radiation that is being used. In this particular example the width of the island 43 was taken as 4 times the width of the tag, approximately 35mm.

Figure 5a-c shows a plan view of various configurations for the location of the RF tag.

Figure 5a presents a sixteen-island decoupler to illustrate the orientations of interest on one schematic: figures 5b and 5c illustrate the four-island decoupler that was previously discussed. The effect of the configurations is discussed in specific examples 6, 7 and 8.

Although the above examples relate to the absorption of millimetric to centimetric wavelengths the skilled person will appreciate that the above principles can be applied with different slit structures and layer thicknesses in order to produce an electromagnetic decoupling material that can interact with radiation in other parts of the e/m spectrum, e.g. infra-red, visible, radiowaves etc. Figure 6 shows a plot generated by High Frequency structure simulator (HFSS) provided by Ansoft , which was used to model a four island decoupler also referred to as a bi- grating designed to operate at 866MHz. the full decoupler 71 was not modelled and only the centre portion 70 was modelled.

The dielectric core is 1mm PET, the overall period of the structure is 95. 12mm, with a width of 190mm with 0.49mm wide slits. The aim was to identify the regions of enhanced electric field and determine how field strength varied with distance above the surface and along slits either parallel or perpendicular to the incident electric field vector. In all cases the incident electric field had an amplitude of 1V/m and is polarised parallel to the y-axis.

The direction of the incident electric field vector is shown by the arrow labelled E. The half-wavelength resonance can be seen clearly: the nodes are present at the boundaries of the model (midway between the slits), and there is an anti-node at the slit.

It can be seen from the plot that the region of enhanced electric field occurs at the antinode. Conveniently it is advantageous to locate RE tags at the regions of enhanced

electric field.

Figure 7 shows a plot of the electric field vector along the slit perpendicular to the incident electric field. Note the change of scale: the field has been enhanced to over 1 20V/m compared to 75V/m for the original slit. The strength of the electric field decays as the perpendicular distance from the surface of the decoupler increases. Again the plot is not of the full decoupler and only for the centre portion as for Figure 6.

Figure 8 shows a further plot of the electric field vector along a line perpendicular to the surface of the decoupler, again with a Max 1 20V/m scale. The strength of the electric field decays as the perpendiculardistance from the surface of the decoupler increases Figure 9 shows the magnitude of the electric field in the y-direction (this may be seen in Figure lOa along line 1): parallel to the z-axis through the decoupler dielectric core and the air space above. Figure 9 shows data from Figures 7 & 8 which have been resolved into x- y- and z-components. The ycomponent are plotted with the position of the decoupler superimposed on the graph to demonstrate where the high field regions occur.

The top surface 31 with slit, is formed on a dielectric core 35 and comprises a second metallic surface 33. The graph shows the expected trend: the field is low adjacent to the lower metal surface within the core and increases to a maximum of 220V/m within the slit. In the air above the decoupler itself the field strength is high but falls rapidly as distance from the decoupler surface increases. Above 10mm the enhanced field is no longer apparent and the field behaviour returns to sinusoidal.

Figure lOa and b shows a plot of the magnitude of the electric field in the y-direction along three different lines (1-3) all parallel to the to z-axis. The lines all pass through the slit that runs perpendicular to the incident electric field vector.

Figure lOb shows that the trend is the same for all three curves: there is a high electric field in the slit region, which decreases quickly with increasing distance along the z-axis, i.e. as the field moves away from the surface of the decoupler. The maximum field strength is approximately 40V/m greater for lines 2 and 3 than for line 1. This may be due to curvature of the field lines at the point where the slits cross i.e. the line through which line 1 passes. This can be seen more clearly in figure 11 where the field strength along line 4 has been plotted, which is in agreement with the plot in figure 8.

Figure 11 shows a plot of the magnitude of the electric field in the ydirection along line 4, as shown in figures lOa and b. Line 4 runs through the slit that is parallel to the x-axis.

The slit is 0.49mm wide and has its centre at 47.6mm.The main feature on the graph is approximately 0.5mm wide and is centred on the slit thus confirming that the electric field in the y-direction is slightly weaker where the slits cross.. However, it is advantageous to place the tag on this crossing point since its antenna then lies along the y-axis slit, maximising its exposure to regions of high electric field.

Symmetry dictates that the field strengths along lines 2 and 3 should be identical. The variance between them gives an indication of the accuracy of the solution. As an approximate measure: the peak field strength along line 2 is in the region of 10% greater than that along line 3, hence it can be said that all field values are subject to an error of +1-10%.

Figure 12 shows a cross section of the recessed identification plate. The identification plate 58 is not shown to scale and the wall thickness may not be in true perspective with regards to the other components. A decoupter 50, has four islands in the surface layer 51 which are arranged on the surface of a dielectric core material 55. The islands 51 are separated by apertures 52. The apertures are substantially orthogonal to each other.

They are located such that the point of intersection of the two apertures 52 crosses through the centre of the decoupler. The tag 54 is placed directly over the point of intersection, such that chip 57 sits directly on the point of intersection. The tag 54 is separated from the decoupler 50 by way of a spacer material 56.

The lower metallic surface 53 of the decoupler may be a discrete layer or it may form part of the plate 58 if the base of this plate is made from a conducting material. The void areas in the plate are then filled with a protective layer material 59 to substantially envelope the tagging system and prevent damage to the chip 57 and the decoupler 50.

Figure 13 shows a top view of a recessed identification plate 58. The top of the plate may optionally have a lipped edge 60, the decoupler 50 with aperture 52 has an RF tag 54(shown in outline only) placed over the intersection of two slits. The decoupler or tagging system may be reversibly attached to the plate 58, and a protective layer 59 may be applied as a sheet material to cover the decoupler. The decoupler 50 (or tagging system) and protective layer 59 may be removed from the identification plate. The protective layer may be suitable compound such as for example Polyurethane, Epoxy PVC or ABS. The plate 58 may be manufactured out of any sheet metal or cast metal.

The plate 58 may be made from any suitable material such as 1mm thick mild steel, formed using a punch, more lightweight materials such as alloys or Aluminium are also cheap and easy to manufacture.

Figure 14: shows the dependence of read-range upon spacer thickness, see example 8 Figure 15: shows a plot of the magnitude of the electric field in both the dielectric core of the decoupler and the vicinity of the slit, at the fundamental resonant frequency. The paler the shading, the more intense the electric field, with the white region above the slit indicating approximately a 150- to 200-fold field enhancement.

Figure 16 shows a cross section of broad band decoupler with two or more islands, i.e. a decoupler which may decouple radiation at more than one frequency. There is shown in both 16a and 16b two example configurations. In 16a there is provided a second conducting layer 73 and on a first surface there is a first conductor layer 71 and a dielectric layer 72 sandwiched in between the conductor layers 71 and 73. The first conductor layer has been designed to decouple radiation at a frequency 2B (and may have a period of ?BI2). An RF tag 76 may be placed over the aperture. Similarly there is on a second surface of the second conducting layer 73 a dielectric layer 74 sandwiched in between the first conductor layer 75 and second conductor 73. The first conductor layer has been designed to decouple radiation at a frequency XA (and may have a period of 2A/2). An RF tag 76 may be placed over the aperture. This is useful where RF tags with different resonant frequencies are required.

Figure 16b shows a different arrangement of the broad band decoupler. In this arrangement the different frequency first conducting layers 75 and 71, are separated respectively by dielectric layers 74 and 72, and are both mounted on the same first surface of the second conductor layer 73. Layer 75 corresponds to frequency A.A and layer 71 corresponds to a frequency XB. there may be one or more RF tags 76 mounted on the surface of layer 71 which are activated at frequencies XA and XB. It would be possible to have this arrangement of two or more decouplers on both sides of second conducting layer 73 to give 4 or more different frequencies.

Figure 17 shows a graph of the performance of an 866MHz tag and a Sensormatic reader, without a decoupler. The deeper the reader curve the more power the reader antenna is emitting. The deeper the tag curve the more power the tag is taking up from the wave emitted by the reader antenna. The more power gets into the tag the greater is the read-range, hence it is best to have the two curves centred on the same frequency: the tag is picking up power optimally at the frequency at which the reader is emitting the most power. Whilst aligning the two curves produces the best performance, the tag will operate, with a lesser read- range, if its curve overlaps any part of the reader curve.

Figure 18 shows a modelled graph of the decoupler curve and the same reader curve as in Figure 17. The de-coupler intercepts power emitted from the reader antenna. This power is channelled through an aperture at a point of high electromagnetic energy into the dielectric core between the first conductor layer and the second conductor layer.

There is a very high concentration of power through the aperture. Placing an RFID tag over the aperture exposes it to this region of high power and is sufficient to couple energy into the tag and hence power the chip whereupon the EPC is transmitted.

The de-coupler, much like the reader and the tag, intercepts power over a range of frequencies and performs optimally at one particular frequency. As in Figure 17, the maximum read-range for the tag on the decoupler will be achieved by getting the maximum amount of power into the de-coupler and hence into the tag. This may be achieved by getting the centre of the two performance curves to line up - that of the de- coupler, tag and the reader.

It has been observed that the de-coupler, originally designed for 866MHz, can also de- couple tags that operate at 915MHz in free-space. The Alien 915MHz tag is very similar to the Alien 866MHz tag - the only difference is in the main bulk of the antenna, the impedance loop is largely identical. It has been shown that the de-coupler renders the main bulk of the antenna redundant. Hence when the antenna is on the de-coupler it is only the impedance loop that matters.

The de-coupler is still intercepting power optimally at 866MHz and incepting virtually no power at 915MHz, as can be seen in the graph. Therefore the tag, despite being designed to operate at 915MHz, is being driven into operation at 866MHz. This is possible because the chip will operate almost as well at 866MHz as it will at 915MHz.

Therefore the decoupler absorbs over a frequency range, but the maximum performance will be achieved when the decoupler, tag and reader are operated at the same frequency.

Figure 19 shows a single island tag with a low Q antenna (small area antenna) 86. The decoupler has a similar structure to the 2 island decoupler except that there is only one island on the first conductor layer 81 and the aperture 87 is located at the end of the first conductor layer 81. The first conductor layer 81 and second conductor layer 83 sandwich the dielectric layer 82. The period of the first conductor layer will determine the frequency of the decoupler, (for a specific dielectric layer).

Figure 20 a and b show two example configurations for broadband single island decouplers (based on figure 16a and b). Figure 20a shows a cross section of broad band decoupler there is provided a second conducting layer 93 and on a first surface there is a first conductor layer 91 and a dielectric layer 92 sandwiched in between the conductor layers 91 and 93. The first conductor layer has been designed to decouple radiation at a frequency 2B (and may have a period of XBI2). An RF tag 96 may be placed over the aperture. Similarly there is on a second surface of the second conducting layer 93 a dielectric layer 94 sandwiched in between the first conductor layer 95 and second conductor 93. The first conductor layer has been designed to decouple radiation at a frequency 2A (and may have a period of 2AJ2). An RF tag 96 may be placed over the aperture 97. This is useful where RF tags with different resonant frequencies are required.

Figure 20b shows a different arrangement of the broad band decoupler. In this arrangement the different frequency first conducting layers 95 and 91, are separated respectively by dielectric layers 94 and 92, and are both mounted on the same first surface of the second conductor layer 93. Layer 95 corresponds to frequency 2A and layer 91 corresponds to a frequency 22. there may be one or more RF tags 96 mounted on the surface of layer. 91 which are activated at frequencies AA and 2.B. It would be possible to have this arrangementof two.or more decouplers on both sides of second conducting layer 93 to give 4 or more different frequencies.

Figure 21a-f show a top view of a variety of geometric designs for the first conductor layer 101, with an aperture 102, with an RF tag 106 placed over the aperture. Figures a- d are single island decouplers and the shape or geometry may be selected depending on the item or surface to which the decou pIer may be provided. Preferably the first conductor layer may have a period A 2nGIN, where A is the wavelength in the range 1mirl to Amax where maximum absorption occurs, n is the refractive index of the dielectric, G is the period of the at least one first conductor layer and N is an integer greater than or equal to 1. There may be one or more tags placed on the apertures or slits, ideally at a distance which satisfies the above relationship. For example in figure b, there may be an aperture at one, two, three or four sides of the first conductor layer. The decoupler may be formed in any polygonal shape with a number of sides (n) containing a range of from 1 to n respective apertures. This would tend towards providing a substantially circular arrangement such as in figure d. In an alternative arrangement it may be desirable to use a polarisation dependent decoupler with a plurality of RF tags, such that the orientation of an article with respect to a polarised radiation source may be deduced by the subsequent activation of RF tags as they come into alignment with the interrogating field.

Figures c, d, e and f show substantially circular decouplers which are substantially polarisation independent, such that the tag may be interrogated irrespective of the direction/polarisation of the incoming RE field. A particular preferred arrangement for a polarisation independent tag is shown in figure f, where the first conductor layer 101 has a circular aperture or slit 102 present. The RF tag 106, and in particular lowQ tags with nominal sized antenna, may be placed at any location on this slit. It has been shown that in this particular arrangement that the shape of the remainder of the first conductor layer that is the shape of the overall decoupler outside of the circular slit need not be circular, in fact a non circular outer shape appears to be advantageous, further advantage lies in a substantially non uniform outer shape. it was shown that the most advantageous results were obtained when the diameter of the slit approached /4, as opposed to ?J2 is for the other decoup!er designs. The side view of figure f shows the first conductor layer 101 and second conducting layer lOla sandwiching the dielectric layer 102a, with aperture 102 present in said first conductor layer.

Figure 22a shows an example of a low Q tag 116, which has a small inductance loop 118 which drives a chip 117. The low Q tag 116 does not function in free space, unless the reader is located within 1 or 2 mm of the chip, this is because the antenna 118 is very poor. The low 0 tag which may be only slightly larger than the chip itself may be placed on any decoupler according to the invention. In Figure 22b the tag 116 is placed on the aperture 112 (part of the dielectric layer, see figure 19) of a single island decoupler which has a first conductor layer 111 (other layers not shown) which is preferably matched to the frequency of the RE tag. The read range is not as good as an optimised RF tag, however the small compromise in read range is compensated for by the very small area of the decoupler and RE tag. The decoupler and tag may have an area which is only just larger than X 2nG/N. This is an idea size for small articles such as clothing tags, small consumables or for more covert tagging systems. Figure 22c shows a number of designs for low Q RE tags, that is RF tags where the antenna design (as shown in figure 4a) has been substantially removed to leave just the small loop section as shown in figure 22a.

Alternatively, the small loop section may not form a continuous loop and may extend outwards or partially wrap around the spacer. In Figure 22d there is shown a low 0 RE tag, where the loop section lies along the axis of two intersecting slits, thereby increasing the polarisation independence of the RE tag.

Figure 23 shows a graph of three different core materials at a variety of thicknesses as described in Example 10.

Figure 24a shows a two island decoupler with at least one slit 125, which does not have a uniform distance from at least one edge of the decoupler. This provides a decoupler capable of working over a range of wavelengths. Therefore, the wavelength that the decoupler may function across may be increased or decreased by "x", in increments of "6" depending on the angle of the slit with respect to the edge of the decoupler. This concept may be used on decouplers with four or more islands.

The same concept may also be provided on a single island decoupler as shown in figure 24b, where the edge of the area of absence on the first conductor layer forms a line which is not parallel to the edge of the decoupler. This concept may decouple radiation over an increased wavelength range. The wavelength range is only limited by the initial dimensions of the decoupler and the angle of the slit with respect to the edge of the decoupler.

This concept may also be used in conjunction with the broadband decouplers used in figures 16a and b and figure 20.

Figure 25 shows a cross section of a decoupler 126, has two or more islands in the first conducting layer 127 which are arranged on the surface of a dielectric core material 128.

The islands 127 are separated by apertures. The tag 129 is located over the aperture.

The antenna 130 (if present) of the tag are separated from the first conducting layer 127 by way of a spacer material 131. The lower metallic surface 132 of the decou pier may be a discrete conducting layer or it may form part of a conducting surface to which the decoupler may be applied. The tag 129 and its antenna 130 if present need to be electrically isolated from the first 127 or second 132 conductor layers. The RF tag is then protected by the decoupler structure and the material of the dielectric layer.

Figure 26a shows a decoupler which possess a void 138 as the dielectric layer. The decoupler may be prepared on a supported layer or may use part of a box for a support.

A container possessing a upper side 143, may have a first conducting layer 137 deposited on the internal surface of 143 in a pattern as hereinbefore defined, either of the single island or two or more island design. At the aperture an RF tag,139a which may be either low 0 or a normal tag, may be located over the aperture, with an optional spacer 141. Alternatively an RF tag 139 may be located on the upper surface of 143, such that the upper surface 143 acts as an optional spacer.

The sides of the container 144 provide a means of support to create a void 138 between the upper surface of the container 143 and the lower surface of the container 145. A second conductor layer 142 may be deposited according to any method herein defined on either the first or second surface of the lower surface of the container 145. It may be particularly convenient to place the first 137 and second 142 conductor layers and the RE tag 139 within the void 138, to provide protection. The void may be filled with a dielectric fluid such as, for example, an air gap, a partial vacuum, or filled with an inert gas or inert liquid. It may also be filled with a non conducting high void content foam or non conducting dielectric filler material. Alto 2mm air gap approximately l/l7O of the wavelength of the incident RF wavelength has provided useful read ranges when used with RF tags.

Figure 26b, the same features are present as in Fig 26a except that the sides of the container may not be present and may be replaced by non conducting vias or non conducting support means 144a to provide the correct thickness of dielectric layer 138.

Figure 26c, the same features are present as in Figures 26a or 26b, except that the first conductor layer 137 forms a single island decoupler. The RF tag 139 or I 39a may then be located either side of the upper surface 143. Conveniently, the non conducting support means 144a, may alternatively be sides of a container 144 as shown in Figure 26a.

Conveniently, the decouplers shown in Figures 26a to c respectively may incorporate any of the features defined herein, such as for example the use of one or more first conductor layers to create broadband decoupler or the use of patterns to create substantially polarisation independent decouplers.

Example 1

Using a non-conducting QMP catalytic ink (as disclosed in Application GB0422386.3.

supplied by Sun Chemical under product names QS1, QS2 or DP1607), the decoupling units are screen printed (double sided) onto a polymer, (which forms the dielectric core) of known electrical properties. The dimensions of the UHF decoupler are subject to the electrical properties and thickness of the polymer. For example using Quinn plastics, Spectar grade PETG sheet at a thickness of 1mm, the relative dielectric constant is 3.2, resulting in a decoupler period of 95mm and a minimum decoupler length of 190mm (using the approximate formula island length A/(2dielectric constant)). The front side of the polymer is printed with the decoupler pattern,- four substantially equally sized islands which are separated by two orthogonal lines which intersect at the centre of the decoupler. The reverse side of the decoupler is printed as a solid area.

The ink is cured by heating the sample to approximately 8000 for 10 minutes (for QSI and QS2 systems) or by a process of UV curing (for DP1607), in both cases causing the ink to solidify and adhere to the substrate. The printed samples are then placed in a commercially available electroless plating solution (e.g. Enthone 21 30 at 46 C or Rohm and Haas 4750 at 52 C) and copper metal is deposited only over the areas which are covered with the catalytic ink, at a thickness of 0.1-3 microns. The rate of electroless deposition is well defined and hence the thickness of the deposition may be monitored as a function of exposure time. The electrolessly deposited material may optionally be subjected to electrodeposition, if so required.

The resultant product is then laminated with a spacer being placed between the front side of the decoupler and the UHF tag (in this example a 866MHz, 1 5micron UHF tag made by Alien technologies). Typical spacer materials are polymer films for example Hifi films PMX 946 250micron PET film. The UHF tag and spacer are located centrally over the aperture, which is the intersection point of the orthogonal lines.

Example 2

Using a conducting ink, for example Acheson Electrodag PR4O1 B Carbon ink or Acheson Electrodag 503 silver ink, the decoupling units are screen printed (double sided) onto a polymer of known electrical properties. The dimensions of the UHF decoupler are subject to the electrical properties and thickness of the polymer. For example using Quinn plastics, Spectar grade PETG sheet at a thickness of 1 mm, the relative dielectric constant is 3.2, resulting in a decoupler period of 95mm and a minimum decoupler length of 1 gOmm*. The front side of the polymer is printed with the decoupler pattern and the reverse side is printed as a solid area.

The ink is cured by heating the sample (for Acheson Electrodag PR4O1 B Carbon ink and Acheson Electrodag 503 silver ink) causing the ink to solidify and adhere to the substrate.

The resultant product is then laminated with a functional spacer and mounted on the decoupler in the same manner as defined in example 1.

Example 3

Using a metal covered polymer film (e.g. DuPont Mylar PET film), an etch resist ( e.g. Sun chemical XV750) is screen printed over the metal surface. Once dried the etch resist is adhered to the surface of the metal in the pattern of the decoupler. The film is then placed in a corrosive solution (e.g. in MAX ETCHTM 20R from Old Bridge Chemicals mc). This process removes the un-coated area of metal leaving non conductive substrate only. The metalised patterned film can then be laminated onto a core material and sandwiched with a further metalised un-patterned film, for use as the back plate.

is This would then require spacer lamination and tagging as defined in examples 1 and 2.

Example 4

Decoupler testing method A 866MHz UHF tag reader system (e.g. Sensomatic agile 2 reader unit) is setup with a computer interface as a detector unit for 866MHz UHF tags. The reader antenna is placed on a stand facing along a fixed vector, and a tape measure is placed along this path in order to assess read range. All metallic objects are removed from the reader field area to minimise reflective reads. An 866 MHz UHF tag (e.g. an Alien Technologies tag) is taken and placed on a cardboard substrate. This is moved from a distance of approximately 5m directly towards the reader antenna whilst observing the reader display, the read range is taken to be the maximum displacement at which the tag gives a constant read over a period of 1 minute. This value is taken to be the standard read range for the specific UHF tag used.

The tag is then mounted on the decoupler unit and the decoupler is adhered to a metallic substrate (in this example an identification plate from the side of a roll cage). The tag, decoupler and metallic substrate are placed in the EM field, to the point at which the system reliably reads the tag over 1 minute. This value is taken as the read range of the decoupled tag system.

Example 5

The method outlined in example 4 was used to identify the optimal 2D position of a UHF tag on a decoupler, when the decoupler was mounted on the metallic substrate. Figure 5, a, b, c show the relative positions of a tag and decoupler systems.

Figure 5a Figure 5a schematically represents the possible positions of a tag placed over an aperture or apertures. When applied to a four-island decoupler, the following data is obtained: Experiment ref Positional ref Read range (m) As shown in Figure 5a 1 2.1 2 3.5 3 2.4 Table 1 - relative position of a tag with respect to a decoupler.

From the test with a 866MHz UHF tag, it was found that the read range was significantly improved when the chip of the tag was located over the aperture. The read range was improved further when the chip (and hence antenna) was centrally located at the point of intersection of two orthogonal apertures or slits.

Example 6

Figure 5b shows the effect of precise location at the point of intersection of the slits on the read range of a UHF tag. This has the effect of showing how manufacturing tolerances in locating the tag on the decoupler may influence the effectiveness of the decoupler and hence the tag's read range.

Experiment ref Positional ref Read range (m) As shown in Figure 5 (b) 5mm,Omm 1.2 - -2.5mm,Omm 1.2 -lmm,Omm 2.5 Omm,Omm 4-4.5 lmm,Omm 4-4.5 2.Smm,Omm 3.5 5mm,Omm 2.0 Omm,-5mm 0.5 Omm,-2.5mm 1.2 Omm,-lmm 3.0 Omm,Omm 4 - 4.5 Omm, lmm 3.0 Omm,2.5mm 1.5 Omm,5mm 0.5 Table 2 precise position of atag with respect to a decoupler The location 0,0, as referred to in Table 2, denotes the absolute centre of the decoupler unit. The centre of the tag was considered to be the location of the chip (even though the chip in this instance was not in the centre of the RF tag). It was found that the read range was significantly improved when the chip of the tag was centrally located at the point of intersection of two orthogonal apertures or slits, at a point 0,0mm. Minor deviations of a few mm along either the x or y axis still provide a useful read range, compared to the nil reading of an RF tag placed directly onto a metal surface.

Example 7

Figure 5c shows the effect of the azimuthal location at the point of intersection on the read range of a UHF tag.

Experiment ref Positional ref a Read range (m) I As shown in Figure 5(c) -4 4.0 00 445 2 4.0 6 2.0 14 1.2 Table 3 absolute rotational position of a tag with respect to the slit on the decoupler The positional reference a as referred to in Table 3, denotes the angle of rotation from the slit of the decoupler unit. The reading of 0 was taken to be the tag was aligned parallel to the slit (even though the chip in this instant was not in the centre of the RF tag). It was found that the read range was significantly improved when the chip of the tag was centrally located at the point of intersection of two orthogonal apertures or slits, at a point 00. Minor deviations from a parallel relationship with the slit, such asrotations of less than 6 provide a useful read range, compared to the nil reading of an RF tag placed directly onto a metal surface. More significant deviations in excess of 10 provided a tag which could be read, however the read range was significantly reduced.

Example 8

Improvements to the maximum read-range (compared to an isolated tag in free space) may be achieved by optimising the spacer thickness. As presented in Figure 14, the dielectric spacer between the decoupler and the tag may improve the read range of the tag, compared to a tag being read in free space. As PET spacers of increasing thickness are introduced the tag starts to increase its read range, until - at a spacer thickness of approximately 300microns - the response is identical to that of an isolated tag.

Interestingly, at 400 microns a read-range of 4.5m is attained, adding 0. 5m to the expected maximum. Further increases in the thickness of the spacer slightly degrade the value, although it remains essentially equivalent to that of the isolated tag. After 1000 microns the read range is not as useful in this example, although the tag may still function on a RF reflective surface. Clearly these values show that the decoupler may increase the read range of a RF tag. Advantageously the tag when mounted on a metal surface or a surface where a fluid is present, may possess a normal read range (again comparable to a tag in free space).

It appears that the decoupler performs the function of trapping the incident 866MHz radiation from the antenna. In the absence of the tag it would normally absorb the power, but the REID element provides an alternative channel: the electric field strength both in and just above the slit is intense this is shown in Figure 15, (generally enhanced 150 to 200-fold) and this may interact with the tag if it is placed at a suitable height above the metal surface.

Whilst a PET core device (complex permittivity (3.20, 0.0096)) has been demonstrated successfully, a lossier core material such as FR4 (permittivity (4.17, 0.0700)) may not function as efficiently as PET. This is because the power that is initially trapped by the decoupler is simply absorbed into the core if it is sufficiently lossy, and interaction with the tag may not occur to the same extent. The best decouplers exhibit low core attenuation, although a structure exhibiting a lossless core may instead be designed to dissipate incident power into its metallic elements if so desired.

The read range in the above experiments 5 to 8 are standardised read range measurements as defined in example 5 (a stable 1 minute reading). Deviations from a substantially centrally located tags (both angular and/or linear displacement) still provide a tag which can be interrogated on a metallic surface. Conveniently exact centrality of the tag on the slits of the decoupler is not a prerequisite for the decoupler to function, however it does provide improved performance. However, in a real life situation only a fraction of the standardised (1 minute read time) is required to achieve interrogation and response from the tag, hence the actual read range of the tag may be higher than that stated in the above experiments.

Example 9

A four island decou pier was made by the method in Example 1. The decoupler was prepared for an 866Mhz tag and was manufactured with a l000micron polyester core.

An Alien Technologies 866Mhz tag was located centrally over the aperture to provide for optimum response. An RF tag without a decoupler and the RF tag on a decoupier were mounted on a variety of surfaces and articles to assess the affect of the surface on a normal RF tag and the effectiveness of the decoupler.

Surface Read-range Read-range with .Jo De-coupler (cm) De-coupler (cm) Free Space 320 320 Corrugated cardboard only (dry) 310 320 cardboard + backed by plastic 125 310 mineral water bottles _____________________ ________________________ cardboard + backed by cartons of 110 310 Orange Juice - __________________ cardboard + backed by Metallic baked 120 310 beans cans _______________________ __________________________ cardboard + backed by glass lager 125 310 bottle _______________________ __________________________ On damp cardboard 180 320 (12.5% moisture content) _____________________ ________________________ On wet cardboard 50 310 (19.5% moisture content) ____________________ _______________________ With 1/2 tag obscured by human hand 70 250 Table 4 read range of RE tags without decoupler and with 1000pm polyester decoupler.

--

As expected the read-range of the de-coupler in free-space matches that of the tag in free-space at 320cm. It can be seen that the presence of consumables inside the cardboard box reduces the read-range of the tag without a de-coupler to between one- third and one-half of that of the read range value obtained in free-space. The advantage of using the decoupler is that the read range is effectively the same as that in free space and is independent of the surface on to which it is mounted.

Dampening the cardboard or even saturating it makes almost no difference to the read- range afforded by the de-coupler whereas it severely reduces the read- range when no de-coupler is used. Only the obscuration of 50% of the de- coupler surface slightly reduces the read-range. Clearly his would overcome the attempts of a person attempting to conceal an item.

Example 10.

Three different core materials were tested polyester, polypropylene and polycarbonate at a variety of different core thicknesses. The first and second conductor layer patterns were all the same geometry and thickness and optimised for an 866MHz RF tag and reader. The decou pier was placed on a metallic surface such that an RF tag without a decoupler would give substantially zero read range. From the graph in Figure 23 as the core thickness increases the read range increases. Modelling which has been validated as shown in Example 11, has shown that there is only a few cms increase in read range when you increase the core thickness from l000microns to 2000microns.

The wavelength at 866MHz in free-space is 346mm. If the core material is polyester then the wavelength in the material is 193mm at 866MHz. Hence if the core is lmm(l000microns) thick then the material is 1/346 of a free-space wavelength thick or 1/1 93 of a material wavelength thick. Hence wavelength in the material is the free-space wavelength divided by the refractive index which for polyester is c.1.8 Material thickness (mm) Fraction of the wavelength in the material 1 1/193 0.5 1/387 0.25 1/774 Table 5 shows the fraction of wavelengths tested in figure 23

Example 11

A series of decouplers were manufactured to the dimensions that would give the greatest field enhancement at 866MHz as determined by using HFSS. To ensure optimum performance and validate the model HFSS, a series of tests were performed. These entailed starting with a de-coupler that had metal islands in the upper layer that were longer than the requisite value obtained from HFSS. The read-range was measured as the length of the metal islands was progressively reduced: starting at the ends of the de- coupler and working inwards towards the centre. Results for the prototype polycarbonate de-couplers are shown in below. The optimum metal island lengths determined by these tests are in very close agreement with those determined from HFSS modelling Dielectric core material Optimum island length Optimum island length - HFSS (cm) -read-range (cm) Polyester 9.65 9.5-9.9 Polycarbonate 10.0 9. 7 - 10 Polypropylene 11.2 11.1 -11.3 Table 6 Optimised island lengths for an 866Mhz tag.

Example 12

A series of single island decouplers with different core thicknesses and widths were evaluated. The decoupler was prepared according to that of example 1 using copper as the conductor layer and a PETG core. The pattern of the decoupler is that as shown in figure 22b. The tag employed was a low 0 antenna (ie not optimised for use at 866MHz), of the type shown in figure 22a. The read range of the tag in free space is negligible as it does not have an optimised antenna. Similarly, when the low-Q tag was placed directly on a metal surface there was no read range. The table below shows results of the RF tag on a decou pIer, where the decoupler is placed on a metal surface.

Decoupler Length(mm) Nidth(mm) Ehickness ag type Read range on metal l-F200 110 20 0.25mm CIassi Gen 1 0.2m l-F-750 110 20 0.5mm Classi Gen 1 0. 75m l-R-1 500 110 20 1.0mm Classi Gen 1 1.5m l-R-2500 110 48 1.0mm Classi Gen 1 2.5m Table 7 single island decouplers It can be clearly seen that the decoupler allows low-Q tags to be decoupled from metal surfaces. As the thickness of the core increases so does the read range of the RF tag.

Similarly as the width of the tag increases for a fixed core thickness the read range increases. Certain applications such as tracking logistics containers will benefit from larger area and thicker core tags as read range may be important. However, consumer items may only require read ranges of a few cms at a point of sale or checkout and so may benefit from smaller area and thinner tags.

Further materials which may be used as the dielectric core are foamed materials, such as for example PVC, polystyrene etc. The real part of the permittivity of this material is very low as is the imaginary part. This lends itself to making a de-coupler that is very thin as the lower permittivity will give good read-range at small thicknesses. in order to metallise the foam it may be necessary to create a laminate structure in which the metal is deposited on very thin (e.g. 10 micron) polymer film which is then stuck onto the foam core. Alternatively high-spec. Radio Frequency laminates may be used. There exists a variety of PCB laminate materials specifically designed for the production of highly efficient radio frequency circuits. These consist of a metal-dielectric-metal sandwich of which the upper metal layer could be selectively etched to produce a de-coupler.

Examples include; Rogers RO 4003 or TR I Duroid 5880, Arlon DiClad 880, Neltec NY9220 or Taconic TLY. Yet further alternatives include Ceramic materials; these will have high real permittivities and may therefore result in thinner and less flexible de- couplers, examples include Alumina, silica, glass etc. It may even be desirable to use elastomers e.g. silicone rubber due to their flexible nature. Furthermore, mixing a filler into an elastomer matrix could allow the material properties to be tailored.

Example 13

A polarisation independent decoupler of the type shown in figure 21f was prepared by scoring a circular slit (x) into the copper layer of a first conducing layer on a circular copper-PETG-copper laminate of radius 4. 65cm. The tag was mounted onto a spacer.

The inductance loop was located on the slit (x) and the read range measured as detailed previously using the reader system. It was found that the read range improved when the loop antenna was substantially at a position at a tangent to the curve, position a, compared to when the antenna was orthogonal to the slit.

The diameter of the inner circle was increased from 30-50mm diameter. 15_

Position A Inner circle Read Range Rotation Diameter (mm) (cm) (degrees) 20 360 34 120 360 36 40 45 90 360 42 20 10 43 40 360 25 40 8 20 Table 8 the effect of the diameter of circular slit on read range As the diameter of the inner circle increases, the read range in general decreases, so to do the degree of rotation achievable for that read range.

Variation of the overall decoupler shape, i.e. circular, square rectangular quadrangle etc, i.e. the area outside of the circular slit, does have some effect on the performance, such that the read-range is not simply proportional to the overall area. Preferably the shape of the overall decoupler, when used with a circular slit, is a quadrangle with non uniform sides. One possible explanation, which does not limit the scope of the invention, is that with regular shapes a series there may be an increased chance of RF radiation combining to cause destructive interference.

The experiments above correlate well with the modelled data shown in figures 6 to 11 inclusive.

Claims

1. A radiation decoupler for an electronic device, for decoupling said device from a surface comprising at least one dielectric layer sandwiched between at least one first conductor layer and at least one second conductor layer, wherein the at least one first conductor layer has at least one area of absence where the first conductor layer does not overlie the dielectric layer and the decoupter is adapted such that, in use, an electromagnetic field is enhanced in the vicinity of the area of absence of the first conductor layer.

2. A radiation decoupler for an electronic device, for decoupling radiation from a conducting surface comprising at least one conductor layer in contact with at least one dielectric layer, wherein the at least one first conductor layer has at least one area of absence where the first conductor layer does not overlie the dielectric layer and the decoupler is adapted such that, in use, an electromagnetic field is enhanced in the vicinity of the area of absence of the first conductor layer.

3. A decoupler according to claim 1 or claim 2 wherein the electronic device is an RF tag.

4. A decoupler according to any one of the preceding claims intended for operation in a range of target wavelengths Amin to Amax wherein the thickness of the decoupler is less than AmnI4n, where n is the refractive index of the dielectric.

5. A decoupler according to claim 4 wherein the thickness of the decoupler is less than AminIlO.

6. A decoupler according to claim 5 wherein the thickness of the decoupler is less than AminI300.

7. A decoupler according to claim 6 wherein the thickness of the decoupler is less than Amin/1 000.

8. A decoupler according to anyone of the preceding claims wherein the length G of the first conducting layer is determined by A 2nG where n is the refractive index of the dielectric, and A is the intended wavelength of operation of the decoupler.

9. A decoupler according to any preceding claim further comprising a third conducting layer adjacent a second dielectric layer wherein third conducting layer has at least one area of absence where the third conducting layer does not overlie the second dielectric layer and wherein the second dielectric layer is located between the third conducting layer and the second conducting layer.

10. A decoupler according to claim 9 wherein the length of the first conducting layer is different to the length of the third conducting layer.

11. A decoupler according to any preceding claim wherein the area of absence of the first conducting layer comprises at least one aperture in the first conducting layer.

12. A decoupler according to claim 11 wherein there are a plurality of apertures in the first conducting layer.

13. A decoupler according to claim 12 wherein the apertures are periodic in nature.

14. A decoupler according to any of claims 12- 13 wherein the apertures are slit structures.

15. Decoupler according to any preceding claim wherein the at least one area of absence of the first conducting layer divide the first conducting layer into a plurality of islands separated by orthogonal slits.

16. A decoupler according to claim 15 wherein there are at least 4 islands separated by two intersecting orthogonal slits.

17. A decoupler according to any one of claims 14 to 16 wherein the period of spacing of the slits is determined by A 2nG where n is the refractive index of the dielectric and A is the intended wavelength of operation of the decoupler.

18. A decoupler according to any one of claims 11 to 14 wherein the apertures comprise three sets of slits, the slits in each set being parallel and oriented at 60 degree azimuthal separation from the slits in the other two sets.

19. A decoupler according to any one of claims 11 to 18 wherein the aperture width is less than 500 microns.

20. A decoupler according to claim 19 wherein the aperture width is less than 150 microns.

21. A decoupler according to claim 20 wherein the aperture width is less than 50 microns.

22. A decoupler according to any one of the preceding claims wherein the refractive index of the dielectric layer can be controllably varied.

23. A decoupler according to claim 22 further comprising means for controllably altering the refractive index of the dielectric material.

24. A decoupler according to any one of the preceding claims further comprising an RF tag located in the vicinity of the area of absence of the first conducting layer.

25. A decoupler as claimed, directly or indirectly, in claim 11 further comprising an RF tag located at an aperture in the first conducting layer.

26. A decoupler as claimed, directly or indirectly, in claim 14 further comprising an RF tag located substantially at the point of intersection of the intersecting orthogonal slits.

27. A decoupler according to claim 26 wherein the RF tag is substantially aligned in parallel with at least one of the slits.

28. A decoupler according to any one of claims 24 to 27 comprising a spacer located between said decoupler and said RF tag.

29. A decoupler according to claim 28 wherein the thickness of the spacer and the RF tag together is in the range of from 10 to 1000 microns.

30. A decoupler according to claim 29 wherein the thickness of the spacer and the RF tag together is in the range of from 175 to 800microns.

31. A decoupler according to any one of the preceding claims comprising a protective housing over part, all or substantially all of the decoupler and/or RF tag.

32. A decoupler according to any one of the preceding claims wherein the surface to which the decoupler is applied is a conductive material, a material which comprises a high liquid content or a surface which forms part of a containment means for a fluid.

33. A decoupler according to claim 32, wherein the conductive material is carbon, metal or metal alloys.

34. A decoupler according to claim 32, wherein the material which comprises a high liquid content is cellulose material, wood or naturally occurring material.

35. A decoupler according to claim 33, wherein the containment means is a food, drink, or chemical container.

36. A decoupler for decoupling an RF tag from a surface comprising a dielectric layer sandwiched between a first conducting layer and a second conducting layer wherein the resonant frequency of the decou pIer is selected to substantially match the resonant frequency of the RF tag and/or a RF interrogating source and wherein at least one edge of the first conducting layer does not extend to the edge of the dielectric layer, the gap between the edge of the first conducting layer and the dielectric layer being smaller than the wavelength of EM radiation at the resonant frequency.

37. A decoupler for decoupling an RF tag from a conducting surface comprising at least one conductor layer in contact with at least one dielectric layer surface wherein the resonant frequency of the decoupler is selected to substantially match the resonant frequency of the RF tag and/or a RF interrogating source and wherein at least one edge of the first conducting layer does not extend to the edge of the dielectric layer, the gap between the edge of the first conducting layer and the dielectric layer being smaller than the wavelength of EM radiation at the resonant frequency.

38. A radiation decoupler for RF tags, for decoupling radiation from a surface in a wavelength range Amin to Amax, comprising a dielectric layer sandwiched between first and second conductor layers wherein the first conductor layer comprises two or more islands separated by at least one aperture of sub-wavelength dimension, wherein the resonant frequency of the decoupler is selected to substantially match the resonant frequency of the RF tag and/or a RF interrogating source.

39. A radiation decoupler for RF tags, for decoupling radiation from a metallic surface in a wavelength range Amjn to Amax, comprising a conductor layer in contact with a dielectric layer, wherein the conductor layer comprises two or more islands separated by at least one aperture of sub-wavelength dimension, wherein the resonant frequency of the decoupler is selected to substantially match the resonant frequency of the RF tag and/or a RF interrogating source.

40. A decoupler as claimed, directly or indirectly, in claim 2 or claim 39, further comprising a means of attaching the decou pIer to the surface such that the dielectric layer is adjacent the surface.

41. An adhesive tape comprising at least one decoupler according to any one of the preceding claims..

42. A tagging system comprising at least one decoupler as claimed in any of claims 1 to 23 at least one RF tag, optionally a spacer between the at least one decou pier and at least one RF tag and optionally protective housing covering part, all or substantially all of the at least one decoupler.

43. A surface wherein a proportion of the surface is partially, substantially or completely covered in a decoupler according to any one of claims 1 to 23, an adhesive tape according to claim 41 or a tagging system according to claim 42.

44. A body or container which comprises at least one surface according to claim 43.

45. A body or container according to claim 44 wherein the at least one surface is curved.

46. A body or container according to claim 44 or claim 45, wherein said body or container is logistics container

47. A body or container according to claim 46 wherein the logistics container is a roilcage, stillage, or food or drinks container.

20,

48. A metallic container wherein a proportion of the surface of the container is covered in a decoupler according to any of claims I to 23, an adhesive tape according to claim 41 or a tagging system according to claim 42.

49. A rollcage comprising a decoupler according to anyone of claims 1 to 23, an adhesive tape according to claim 41 or a tagging system according to claim 42.

50. An identification plate comprising recessed portion said recess comprising a tagging system according to claim 42 and a protective layer to envelope said tagging system to produce a substantially flush identification plate.

51. A method of making a decou pIer comprising the steps of coating some or all of a dielectric material with an ink composition in a pattern of a decoupler according to any one of claims 1 to 23, wherein said ink composition comprises an ink formulation suitable for printing the dielectric to be coated, silver as a reducible silver salt and filler particles, wherein said reducible silver salt is selected such that when reduced is capable, once the coated dielectric is introduced into an autocatalytic deposition solution, of catalysing the deposition of a metal from the autocatalytic deposition solution, onto the coated areas of the dielectric, and wherein the proportion of the reducible silver salt is such that the ink composition contains less than 10% by weight of silver, optionally subjecting said coated area to electrodeposition.

52. A method of tracking a body or a container comprising the steps of applying to a proportion of the surface of said body or container a tagging system according to claim 42, interrogating the at least one RF tag with RF radiation, detecting the response from the at least one RF tag.

53. The use of an electromagnetic radiation absorber as a decoupler for shielding RF tags from surfaces in a wavelength range Amin to Amax comprising a dielectric layer sandwiched between first and second conductor layers wherein the first conductor layer carries a plurality of apertures of sub-wavelength dimension and wherein the thickness of the decoupler is less than AmjnI4fl, where n is the refractive index of the dielectric.

54. The use of an electromagnetic radiation absorber as a decoupler for shielding RF tags from metal substrates in a wavelength range Amin to Amax comprising a conductor layer in contact with a dielectric layer wherein the conductor layer carries a plurality of apertures of sub- wavelength dimension and wherein the thickness of the decoupler is less than Amint4n, where n is the refractive index of the dielectric.

55. A decoupler for an RF tag comprising a printed circuit board with first and second conductor layers, wherein the first and second conductor layer and dielectric core substantially the same length, wherein said length G of all three layers is determined by A 2nG, wherein an RF tag is located at edge of the board substantially at orthogonal to the plane of board.

where n is the refractive index of the dielectric, and A is the intended wavelength of operation of the decoupler.

56. A decoupler according to any one of the preceding claims wherein the area of absence is substantially non parallel to at least on of the edges of the decoupler.

57. A decoupler according to claim 56 wherein the area of absence of the first conductor layer comprises at least one circular pattern aperture.

58. A decoupler according to claim 57 wherein the circular apertures are circular slit structures in the first conductor layer.

59. A decoupler according to any one of the preceding claims wherein the dielectric layer may be formed from in part or substantially all of a non conducting containment means or label.

60. A decoupler according to claim 59, wherein the non conducting containment means or label is a natural or man made fibre, plastic, cellulose, glass, cardboard, corrugated cardboard or ceramic.

61. A low Q RF tag wherein the antenna has a major dimension substantially less than 2cm.

62. A low Q RF tag according to claim 61, wherein the antenna has a major dimension substantially less than 1 cm.

63. A low Q RF tag according to claim 61 or 62, suitable for use with a decoupler according to anyone of the preceding claims, wherein said RF low Q tag mounted on a spacer.

64. A low 0 RE tag according to claim 63 wherein the thickness of the spacer and the low 0 RF tag together is in the range of from 175 to 800microns.

65. A decoupler as claimed, directly or indirectly, in any one of claims 1 to 37 or claim 39, wherein a low Q RF tag is located within or forms an integral part of the dielectric layer.

66. A decoupler as claimed, directly or indirectly, in any one of claims 1 to 37 or claim 39, wherein the dielectric layer is formed from a plastic, polymer, ceramic, glass, cardboard, corrugated cardboard, paper, or substantial void.

67. A kit of parts comprising an RE tag or a low 0 RF tag, with an optional spacer and a decoupler according to any one of the preceding claims.

68. A method of detection or identification of a surface comprising the steps of I) bringing together a surface comprising an RF tag or low Q RE tag with an optional spacer, with a decou pier according to any one of the preceding claims, ii) interrogating said RF tag, optional spacer and decoupler, wherein the RE tag may only be read when in close proximity to said decoupler.

69. A method of forming a decoupler suitable for the detection or identification of a surface comprising the steps of i) providing a surface comprising an RF tag or low 0 RE tag with an optional spacer, and at least one conductor layer in contact with part or substantially all of at least one dielectric layer, wherein the at least one first conductor layer has at least one area of absence where the first conductor layer does not overlie the dielectric layer, ii) bringing together the surface of step i) with a second conductor layer or conducting surface to form a decoupler as claimed, directly or indirectly, in any one of claims 1 to 37 or claim 39.

70. Use, method, device as substantially hereinbefore defined in the description or drawings.