WO2008078089A1 - Accroissement et decouplage de rayonnement - Google Patents

Accroissement et decouplage de rayonnement Download PDF

Info

Publication number
WO2008078089A1
WO2008078089A1 PCT/GB2007/004932 GB2007004932W WO2008078089A1 WO 2008078089 A1 WO2008078089 A1 WO 2008078089A1 GB 2007004932 W GB2007004932 W GB 2007004932W WO 2008078089 A1 WO2008078089 A1 WO 2008078089A1
Authority
WO
WIPO (PCT)
Prior art keywords
edge
layer
decoupler
tag
conducting
Prior art date
Application number
PCT/GB2007/004932
Other languages
English (en)
Inventor
Christopher Robert Lawrence
James Robert Brown
Original Assignee
Omni-Id Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Omni-Id Limited filed Critical Omni-Id Limited
Publication of WO2008078089A1 publication Critical patent/WO2008078089A1/fr

Links

Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q1/00—Details of, or arrangements associated with, antennas
    • H01Q1/12—Supports; Mounting means
    • H01Q1/22—Supports; Mounting means by structural association with other equipment or articles
    • H01Q1/2208—Supports; Mounting means by structural association with other equipment or articles associated with components used in interrogation type services, i.e. in systems for information exchange between an interrogator/reader and a tag/transponder, e.g. in Radio Frequency Identification [RFID] systems
    • H01Q1/2225—Supports; Mounting means by structural association with other equipment or articles associated with components used in interrogation type services, i.e. in systems for information exchange between an interrogator/reader and a tag/transponder, e.g. in Radio Frequency Identification [RFID] systems used in active tags, i.e. provided with its own power source or in passive tags, i.e. deriving power from RF signal

Definitions

  • This invention relates to the local manipulation of electromagnetic fields, and more particularly, but not exclusively, to the use of radiation manipulating devices to allow RF (radio frequency) tags to be mounted on surfaces which would otherwise degrade their performance.
  • 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.
  • 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 915MHz for a UHF (ultra-high frequency) range tag and 2.4-2.5 GHz or 5.8GHz for a microwave-range tag).
  • 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.
  • the present invention provides apparatus comprising a resonant dielectric cavity defined between first and second conducting layers, adapted to enhance an electric field in a region adjacent to said first layer, wherein the edge of said first layer adjacent to said region is profiled to produce a desired variation in enhancement along said edge.
  • Such apparatus provides a mounting or enabling component for an EM tag or device which is responsive to the enhanced field at a mounting site adjacent to the first conducting layer, at an open edge of the cavity
  • the resonant dielectric cavity defined between the first and second conducting layers advantageously decouples or isolates the electronic device from the power source. This property is well documented in applicant's co-pending applications
  • enhancement factors of 200 or even 300 or more can be produced.
  • lower enhancement factors of 20,30 or 40 times may still result in a readable system which would not be possible without such enhancement.
  • the field pattern is such that the electric field is strongest (has an anti-node) at the open ends of the cavity. Due to the cavity having a small thickness the field strength falls off very quickly with increasing distance away from the open end outside the cavity. This results in a region of near- zero electric field a short distance - typically 5mm - beyond the open end in juxtaposition to the highly enhanced field region. An electronic device or EM tag placed in this area therefore will be exposed to a high field gradient and high electrical potential gradient, irrespective of the surface on which the tag and decoupler are mounted.
  • An EM tag placed in the region of high potential gradient will undergo differential capacitive coupling: the part of the tag exposed to a high potential from the cavity will itself be charged to a high potential as is the nature of capacitive coupling. The part of the tag exposed to a low potential will similarly be charged to a low potential. If the sections of the EM tag to either side of the chip are in regions of different electrical potential this creates a potential difference across the chip which in embodiments of the present invention is sufficient to drive it into operation. The magnitude of the potential difference will depend on the dimensions and materials of the decoupler and on the position and orientation of the EM tag.
  • Typical EPC Gen 2 RFID chips have a threshold voltage of 0.5V, below which they cannot be read. If the entirety of the voltage across the open end of the cavity were to appear across the chip then based on a 1mm thick core and simple integration of the electric field across the open end, the electric field would need to have a magnitude of approximately 250V/m. If a typical incident wave amplitude at the device is 2.5V/m - consistent with a standard RFID reader system operating at a distance of approximately 5m - then an enhancement factor of approximately 100 would be required. Embodiments in which the field enhancement is greater will afford greater read-range before the enhancement of the incident amplitude becomes insufficient to power the chip
  • the level or distribution of electric field enhancement, or electric field strength can be controlled along the edge of the first layer, and can be tailored to a particular electronic device at a particular position or in a particular orientation at the mounting site.
  • the edge is profiled to produce a peaked distribution, and this can result in greater field enhancement at the peak than would be possible with a constant distribution along the edge.
  • the field intensification can be considered to be concentrated at the peak, and preferably the peak is located at a point intermediate the length of the edge, typically at the centre of the edge.
  • the electronic device is an RFID tag
  • greater field intensification can result in longer read ranges.
  • the profile of the edge is tapered. This can be a straight taper, or a curved taper, resulting in a point or discrete region where maximum field intensification, and hence field strength occurs.
  • the profile is stepped, providing either a notched profile, or a profile having a 'tab' or inverted notch.
  • An identification device comprising an RFID tag mounted on a component as described above may be provided as a further aspect of the invention.
  • the first layer does not overlie the second layer in at least one area of absence, with the profiled edge bordering this area of absence.
  • the open-ended cavity length is substantially half the wavelength of incident radiation, a standing wave situation is produced, ie the mounting acts as a ⁇ A wave decoupler as defined in the aforementioned PCT/GB2006/002327.
  • the length of the second conductor layer is at least the same length as the first conductor layer. More preferably the second conductor layer is longer than the first conductor layer.
  • a mounting site is located substantially over the area of absence.
  • the electromagnetic field may also be enhanced at certain edges of the dielectric core layer, and therefore the mounting site may conveniently also be located on at least one of the edges of the dielectric core layer which exhibits increased electric field.
  • RF tags may be designed to operate at any frequencies, such as for example in the range of from 100MHz up to 600GHz.
  • the RF tag is a UHF (Ultra-High Frequency) tag, such as, for example, tags which have a chip and antenna and operate at 866MHz, 915MHz or 954MHz, or a microwave-range tag that operates at 2.4-2.5 GHz or 5.8GHz.
  • the area of absence will typically be defined by the profile of the edge or edges of the adjacent conducting layer, which may be rectilinear or curvilinear for example.
  • the area of absence may optionally be filled with a non conducting material or further dielectric core layer material.
  • the invention can therefore provide for a multi-layer structure that acts as a radiation decoupling device.
  • First and second conductor layers sandwich a dielectric core.
  • the first conductor layer contains at least two islands i.e. separated by an area of absence or a slit, preferably the one or more areas of absence is a sub- wavelength area of absence (i.e. less than ⁇ in at least one dimension) or more preferably a sub wavelength width slit, which exposes the dielectric core to the atmosphere.
  • the area of absence occurs at the perimeter of the decoupler to form a single island or where at least one edge of the dielectric core forms the area of absence then said area of absence does not need to be sub wavelength in its width.
  • the sum thickness of the dielectric core and first conductor layer of the decoupler structure may be considerably less than a quarter-wavelength in its total thickness, and is therefore thinner and lighter compared to prior art systems.
  • Selection of the dielectric layer can allow the decoupler to be flexible, enabling it to be applied to non- planar or curved surfaces.
  • the decoupler may not be planar and may take the form of a non-planar or curved geometry.
  • n the refractive index of the dielectric
  • ⁇ the intended wavelength of operation of the decoupler .
  • the physical length G will vary along the width of the decoupler according to the profile of the edge, but as explained below, an effective length can be used as an approximation.
  • harmonic operation may offer advantages in terms of smaller footprint, lower profile and enhanced battery life even though it is not idealised in performance terms.
  • first layer and the second layer are electrically connected at one edge, forming a substantially "C" shaped section.
  • the cavity length is substantially a quarter the wavelength of incident radiation, a standing wave situation is produced, ie the mounting acts as a 1/4 wave decoupler as defined in the aforementioned GB0611983.8
  • the two conductor layers can be considered to form a cavity structure which comprises a conducting base portion connected to a first conducting side wall, to form a tuned conductor layer, and a second conducting side wall, the first conducting side wall and second conducting side wall being spaced apart and substantially parallel.
  • the conducting base portion forces the electric field to be a minimum (or a node) adjacent to the base portion and therefore at the opposite end of the cavity structure to the conducting base portion the electric field is at a maximum (antinode).
  • An electronic device or EM tag placed in this area therefore will be located in an area of strong field, irrespective of the surface on which the tag and decoupler are mounted.
  • the first conducting side wall has a continuous length of approximately ⁇ d /4 measured from the conducting base portion, where ⁇ d is the wavelength, in the dielectric material, of EM radiation at the frequency of operation v.
  • ⁇ d is the wavelength, in the dielectric material, of EM radiation at the frequency of operation v.
  • an effective length can be used as an approximation, where the physical length varies along the width of the decoupler.
  • Both the Vz and % wave embodiments described above comprise a tuning conductor layer and a further conductor layer; preferably this further conductor layer is at least the same length as the tuning conductor layer, more preferably longer than the tuning conductor layer. According to the present invention the edge of the tuning conductor layer is profiled to achieve a desired enhancement distribution.
  • the two conductor layers are separated by a dielectric layer, they may be electrically connected at one end to create a closed cavity VA wave decoupler as hereinbefore defined, or contain conducting vias between the two conductor layers in regions of low electric field strength. However, there should be substantially no electrical connections between the two conductor layers in regions of high electric field strength or at the perimeter of the decoupler for open ended Vz wave embodiment, or at more than one end or perimeter for VA wave (closed end) embodiment.
  • a metallic body which is to be tracked by RFID that at least one of the conductor layers is part of said metallic body. Preferably, it will not be the tuned conductor layer.
  • RF tags generally consist of a chip electrically connected to an integral antenna of a length that is generally comparable with (e.g. 1/3 rd of) their operational wavelength.
  • tags having much smaller and untuned antennas i.e. which would not normally be expected to operate efficiently at UHF wavelengths
  • tags with such 'stunted' antennas possess only a few centimetres or even millimetres read range in open space.
  • a tag with a low-Q antenna mounted on a decoupler of the present invention may be operable and exhibit useful read ranges approaching (or even exceeding) that of an optimised commercially-available EM tag operating in free space without a decoupler.
  • Low-Q antennas 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) than a conventional tuned antenna. Therefore the EM tag may be a low Q-tag, i.e. an EM tag having a small, untuned antenna.
  • the device will incorporate a low Q antenna, such that upon deactivation of the decoupler the read range of the low Q tag is caused to be that of a few centimetres or even millimetres.
  • Figure 1 is a perspective view of a component according to the present invention.
  • Figures 2a - 2d show possible edge profiles.
  • Figure 3 is a perspective view of a quarter wave embodiment of the present invention.
  • Figures 4 illustrates electric field vectors.
  • Figure ⁇ shows modelled electric field values for different taper angles.
  • Figure 6 illustrates reference features on the abscissa of Figure 5.
  • FIG 7 illustrates a parameter for a device having a tapered upper layer.
  • a mounting component has an aluminium lower conducting layer 102, a PETG dielectric layer 104, and an aluminium upper layer consisting of two portions or islands 106a and 106b.
  • the upper islands do not meet at the centre, and result in an area of absence 108 of the upper conducting layer, where the dielectric is exposed.
  • the edge 110a and 110b of each island adjacent to the area of absence is tapered, having straight sides meeting at a point. The separation of the points is less than 0.5mm.
  • edges 110a and 110b results in enhancement of an electric field which is greater at the points than it is at either edge. It is hypothesised, although the applicant is not limited to such a hypothesis, that high electric field strengths along the edges 110a and 110b results in a build up of opposite charges thereby creating a potential difference across the area of absence, or mounting site, which can be exploited by an electronic device located there. By tapering these edges, the charge is focussed or concentrated at the points, thereby increasing the potential.
  • Figure 2 shows various different possible geometries for the upper conducting plane.
  • Figure 2a shows the tapered arrangement of Figure 1 , with a symmetrical taper.
  • the position of an RFID tag is shown at 202 in dashed line.
  • Such a tag would typically be electrically isolated from the upper conducting layer by a thin insulating mount.
  • Figure 2c shows a geometry having tapered edges formed of curves.
  • the curves may desirably be parabolic.
  • Figure 2d shows a stepped profile, with each edge having a 'tab' 206.
  • the edge may be profiled only locally. In Figures 2c and 2d, only the central third or tenth of the edge may be affected for example. The inverse of these geometries, having a notch in each edge may also be desirable in certain applications. Furthermore, combinations of different geometries are possible. For example the edge could include two locally tapered portions. These could be arranged symmetrically either side of a centre line, as per Figure 2b for example.
  • Figure 3 shows a 'single island' component or decoupler, having a similar tapered edge profile to the decoupler of Figure 1.
  • Figure 3 is arranged as a quarter wave device, with upper conducting layer 306 and lower conducting layer 302 electrically connected by end portion 310.
  • Dielectric layer 304 is sandwiched between layers 302 and 306, and together with lower layer 302 extends beyond the profiled edge 308 of the upper layer, to define an area of absence or mounting site 312. It will be understood that the profiling of edges referred to herein is equally applicable to 'single island' embodiments having a single upper conducting layer.
  • the direction of the electric field vector is that in which a free positive charge would move.
  • the free charges in the metal are electrons and carry a negative charge they move in the opposite direction to that of the electric field.
  • E sin ⁇ there is a component of the electric field parallel to the edge: E sin ⁇ .
  • the peak field strength increases: for 60° the peak field is around 3000 V/m compared to only 500 V/m for the case where there is no taper.
  • the taper angle increases the component of the electric field from the incident wave that lies along the edge increases thus driving more charges towards the vertex. This clearly demonstrates that the tapering of the upper conducting layer increases the peak electric field strength as expected.
  • the optimum frequency of operation, or resonant frequency of a decoupler is directly dependent on the length of the decoupler.
  • determination of the length is straightforward. With a profiled edge, determination of the length becomes more difficult.
  • the effective length can be determined quite simply by experiment, by progressively reducing the length of a decoupler having a particular edge profile and determining the read range of an RFID tag mounted over the area of absence, using a reader of a particular frequency. The results will tend to produce a distribution having a maximum read range value, and the length at that vale can be taken as the effective length.
  • the effective length is the length from the base of the taper to the opposite edge of the device. This length G is illustrated in Figure 7. In other embodiments, the effective length may extend to a point mid way up the taper. It will be understood that the present invention has been described above purely by way of example, and modification of detail can be made within the scope of the invention.

Landscapes

  • Details Of Aerials (AREA)

Abstract

L'invention concerne un dispositif conçu pour accroître un champ électrique incident. Ce dispositif comprend une cavité diélectrique résonnante formée entre deux couches conductrices (102, 106a, 106b). Le champ incident est accru le long du bord de la couche supérieure (10Sa, 106b), ce bord étant profilé de façon appropriée pour obtenir une variation souhaitée d'accroissement le long du bord. Ce bord est généralement effilé jusqu'à un certain point, mais il peut également comprendre une languette, une encoche ou d'autres profils.
PCT/GB2007/004932 2006-12-22 2007-12-21 Accroissement et decouplage de rayonnement WO2008078089A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB0625718A GB0625718D0 (en) 2006-12-22 2006-12-22 Radiation decoupling mounting component
GB0625718.2 2006-12-22

Publications (1)

Publication Number Publication Date
WO2008078089A1 true WO2008078089A1 (fr) 2008-07-03

Family

ID=37758903

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB2007/004932 WO2008078089A1 (fr) 2006-12-22 2007-12-21 Accroissement et decouplage de rayonnement

Country Status (2)

Country Link
GB (1) GB0625718D0 (fr)
WO (1) WO2008078089A1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9104952B2 (en) 2005-06-25 2015-08-11 Omni-Id Cayman Limited Electromagnetic radiation decoupler

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2990547A (en) * 1959-07-28 1961-06-27 Boeing Co Antenna structure
US3065752A (en) * 1959-11-14 1962-11-27 Philips Corp High frequency therapeutic radiator
WO2000021031A1 (fr) * 1998-10-06 2000-04-13 Intermec Ip Corp. Etiquette de systeme d'identification radiofrequence presentant un dipole sur une antenne a plan de sol
US6307520B1 (en) * 2000-07-25 2001-10-23 International Business Machines Corporation Boxed-in slot antenna with space-saving configuration
WO2006006898A1 (fr) * 2004-07-13 2006-01-19 Telefonaktiebolaget Lm Ericsson (Publ) Antenne a profil bas
WO2007144574A1 (fr) * 2006-06-16 2007-12-21 Omni-Id Limited Amélioration et découplage d'un rayonnement electromagnétique

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2990547A (en) * 1959-07-28 1961-06-27 Boeing Co Antenna structure
US3065752A (en) * 1959-11-14 1962-11-27 Philips Corp High frequency therapeutic radiator
WO2000021031A1 (fr) * 1998-10-06 2000-04-13 Intermec Ip Corp. Etiquette de systeme d'identification radiofrequence presentant un dipole sur une antenne a plan de sol
US6307520B1 (en) * 2000-07-25 2001-10-23 International Business Machines Corporation Boxed-in slot antenna with space-saving configuration
WO2006006898A1 (fr) * 2004-07-13 2006-01-19 Telefonaktiebolaget Lm Ericsson (Publ) Antenne a profil bas
WO2007144574A1 (fr) * 2006-06-16 2007-12-21 Omni-Id Limited Amélioration et découplage d'un rayonnement electromagnétique

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9104952B2 (en) 2005-06-25 2015-08-11 Omni-Id Cayman Limited Electromagnetic radiation decoupler
US9646241B2 (en) 2005-06-25 2017-05-09 Omni-Id Cayman Limited Electromagnetic radiation decoupler

Also Published As

Publication number Publication date
GB0625718D0 (en) 2007-02-07

Similar Documents

Publication Publication Date Title
US8684270B2 (en) Radiation enhancement and decoupling
US9590306B2 (en) Electromagnetic enhancement and decoupling
US8289165B2 (en) RFID device with conductive loop shield
US11704985B2 (en) Dual function strap for resonating elements and ultra high frequency antennas
CN101385202A (zh) 射频识别装置用的微带天线
JP2008066808A (ja) キャビティ付き薄型スロットアンテナ及びアンテナ給電方法並びにこれらを用いたｒｆｉｄタグ装置
US20080284666A1 (en) Antenna Configuration for RFID Tags
WO2008078089A1 (fr) Accroissement et decouplage de rayonnement
Zainud-Deen et al. Fractal antenna for passive UHF RFID applications
US20170187118A1 (en) Miniaturized planar inverted folded antenna (pifa) for mountable uhf tags design
Petrov et al. Superdirectivity for coupled dimers of meta-atoms at MHz
EP3005241B1 (fr) Dispositif détectable par radiofréquence

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 07848657

Country of ref document: EP

Kind code of ref document: A1

NENP Non-entry into the national phase

Ref country code: DE

32PN Ep: public notification in the ep bulletin as address of the adressee cannot be established

Free format text: "NOTING OF LOSS OF RIGHTS PURSUANT TO RULE 112(1) EPC" DATED 29.09.2009

122 Ep: pct application non-entry in european phase

Ref document number: 07848657

Country of ref document: EP

Kind code of ref document: A1