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WO2000026989A1 - Systeme servant a detecter et eventuellement communiquer avec des transpondeurs tels que des transpondeurs antivol ou d'identification - Google Patents

Systeme servant a detecter et eventuellement communiquer avec des transpondeurs tels que des transpondeurs antivol ou d'identification Download PDF

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Publication number
WO2000026989A1
WO2000026989A1 PCT/NL1999/000675 NL9900675W WO0026989A1 WO 2000026989 A1 WO2000026989 A1 WO 2000026989A1 NL 9900675 W NL9900675 W NL 9900675W WO 0026989 A1 WO0026989 A1 WO 0026989A1
Authority
WO
WIPO (PCT)
Prior art keywords
loop
antenna
capacitors
transponders
loop antenna
Prior art date
Legal status (The legal status 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 status listed.)
Ceased
Application number
PCT/NL1999/000675
Other languages
English (en)
Inventor
Tallienco Wieand Harm Fockens
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Nederlandsche Apparatenfabriek NEDAP NV
Original Assignee
Nederlandsche Apparatenfabriek NEDAP NV
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 Nederlandsche Apparatenfabriek NEDAP NV filed Critical Nederlandsche Apparatenfabriek NEDAP NV
Priority to AU11895/00A priority Critical patent/AU1189500A/en
Publication of WO2000026989A1 publication Critical patent/WO2000026989A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G06—COMPUTING OR CALCULATING; COUNTING
    • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
    • G06K7/00—Methods or arrangements for sensing record carriers, e.g. for reading patterns
    • G06K7/10—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation
    • G06K7/10009—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves
    • G06K7/10316—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves using at least one antenna particularly designed for interrogating the wireless record carriers
    • G06K7/10336—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves using at least one antenna particularly designed for interrogating the wireless record carriers the antenna being of the near field type, inductive coil
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q7/00—Loop antennas with a substantially uniform current distribution around the loop and having a directional radiation pattern in a plane perpendicular to the plane of the loop
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q7/00—Loop antennas with a substantially uniform current distribution around the loop and having a directional radiation pattern in a plane perpendicular to the plane of the loop
    • H01Q7/005—Loop antennas with a substantially uniform current distribution around the loop and having a directional radiation pattern in a plane perpendicular to the plane of the loop with variable reactance for tuning the antenna
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q9/00—Electrically-short antennas having dimensions not more than twice the operating wavelength and consisting of conductive active radiating elements
    • H01Q9/04—Resonant antennas
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B5/00—Near-field transmission systems, e.g. inductive or capacitive transmission systems
    • H04B5/20—Near-field transmission systems, e.g. inductive or capacitive transmission systems characterised by the transmission technique; characterised by the transmission medium
    • H04B5/24—Inductive coupling
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B5/00—Near-field transmission systems, e.g. inductive or capacitive transmission systems
    • H04B5/40—Near-field transmission systems, e.g. inductive or capacitive transmission systems characterised by components specially adapted for near-field transmission
    • H04B5/45—Transponders
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B5/00—Near-field transmission systems, e.g. inductive or capacitive transmission systems
    • H04B5/20—Near-field transmission systems, e.g. inductive or capacitive transmission systems characterised by the transmission technique; characterised by the transmission medium
    • H04B5/22—Capacitive coupling
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B5/00—Near-field transmission systems, e.g. inductive or capacitive transmission systems
    • H04B5/70—Near-field transmission systems, e.g. inductive or capacitive transmission systems specially adapted for specific purposes
    • H04B5/77—Near-field transmission systems, e.g. inductive or capacitive transmission systems specially adapted for specific purposes for interrogation

Definitions

  • This invention relates to a system for detecting and optionally communicating with transponders comprising a resonant circuit, such as antitheft transponders and identification transponders, comprising a transmitter and receiver device, an antenna configuration coupled with the transmitter and receiver device, comprising at least one loop antenna for radiating an electromagnetic interrogation field, and at least one transponder of which the resonant circuit is caused to resonate when the at least one transponder is introduced into the interrogation field, the transmitter and receiver device further being arranged for detecting when the resonant circuit resonates.
  • a resonant circuit such as antitheft transponders and identification transponders
  • the invention also relates to a transmitter and receiver device coupled with an antenna configuration of that system.
  • Such systems are known per se .
  • identification and detection systems use is made of loop antennas for generating the electromagnetic interrogation field.
  • This electromagnetic interrogation field is necessary to interrogate a transponder and often also to feed it energetically.
  • This transponder transmits a reply signal, which can be received by means of the same loop antenna or by means of a second loop antenna.
  • the interrogation fields in question can have different frequencies. Examples of known operating frequencies are 120 kHz, 3.25 MHz, 6.78 MHz, 8.2 MHz, 13.56 MHz and 27.12 MHz. Higher operating frequencies are often desired in view of an attendant rise m msensitivity to interference. Examples of inductive systems utilizing these loop antennas are described m patent applications NL 9202158 and EP 0, 608, 961.
  • the dimensions and the number of turns are limited by the total length of the loop of the loop antenna. Further, it is well known that on an axis of the loop antenna the field strength decreases very strongly with the distance to the plane of the loop antenna as soon as this distance exceeds half the diameter of the loop antenna. If it is to be possible for a transponder to be read out m a predetermined detection area, a magnetic field strength will have to be sufficiently high at all points in that detection area to enable the transponder to function. In combination with the limited dimensions of the loop antenna, this means that the magnetic field strength closer to the loop antenna must be very much greater than at positions m the detection area located at a greater distance from the loop antenna. Strength ratios of a factor of 10 or more are quite common.
  • the system according to the invention is characterized in that the loop antenna is interrupted at a plurality of points by capacitors included m the loop antenna at these points, so that the loop antenna is made up of electrically conductive loop parts, with the loop parts and capacitors connected in series.
  • the invention is based on the insight that the reactance of a self -inductance, X L , is opposite to the reactance of a capacitance X c . That means that if a self -inductance element and a capacitance element are connected in series, the reactances of the two elements partly compensate each other. At one frequency this compensation is even complete.
  • this principle is utilized by interrupting the loop at a number of points and connecting it through a series capacitor.
  • the capacitors must then have that value at which the reactances thereof wholly or partly compensate the reactances of the self -inductance of the intervening loop parts.
  • the electromagnetic interrogation field comprises a frequency f, while a loop part located between two capacitors has a dimension smaller than c/2*p ⁇ *f, where c is equal to the speed of light.
  • each of the loop parts located between two capacitors has dimensions smaller than c/2*p ⁇ *f.
  • the electromagnetic interrogation field comprises a frequency f, while the capacitors have such capacitive values that at the frequency f the reactance of the capacitors and the reactance of self -inductances of the loop parts located between the capacitors compensate each other.
  • the antenna configuration can function as transmitting and reception antenna, and m particular a single antenna loop functions as transmitting and reception antenna. It is also possible, however, that the antenna configuration comprises at least one first loop antenna which, in use, functions as a transmitting antenna and at least one second loop antenna which, m use, functions as reception antenna.
  • the loop antenna consists of a cable provided with a plurality of conductive loop parts and capacitors, with the conductive loop parts and the capacitors connected m series, such that two adjacent conductive loop parts are connected with each other through one of the capacitors.
  • the cable is provided with a sheath in which the conductive loop parts and the capacitors are included.
  • Fig. 1 shows a system for detecting transponders fitted with a loop antenna according to the prior art
  • Fig. 2 shows a schematic representation of spread self -inductances and capacitances m the loop antenna according to Fig. 1;
  • Fig. 3 shows the current and voltage distribution according to an extreme example of the loop antenna according to Fig. 1 in the form of an electric half wave dipole;
  • Fig. 4 shows a top plan view of a passageway for persons, having on opposite sides loop antennas with associated magnetic field lines of the system according to Fig. 1;
  • Fig. 5 shows a system for detecting transponders according to the invention
  • Fig. 6 shows a top plan view of a passageway for persons, fitted with a loop antenna of the system according
  • Fig. 7 shows a cable from which a loop antenna according to Figs. 5 and 6 can be constructed.
  • reference numeral 1 designates a system for detecting transponders 2 and optionally communicating with transponders 2 such as antitheft transponders and identification transponders. These transponders are known per se and comprise a resonant circuit known per se .
  • the system comprises a transmitter and receiver device 4 and an antenna configuration 6 coupled with the transmitter and receiver device, which antenna configuration 6 comprises at least one loop antenna for radiating an electromagnetic interrogation field.
  • the antenna configuration consists of a loop antenna with a loop comprising a single turn.
  • the system further comprises at least one transponder
  • the transmitter and receiver device 4 is further arranged for detecting when the resonant circuit resonates. For relatively low operating frequencies, such as
  • the loop antenna mostly consists of many turns and the dimensions can be more than two by two meters.
  • the loop antenna For the medium frequencies, such as 8.2 MHz, the loop antenna consists of one turn (as shown m Fig. 1) having smaller dimensions, for instance about 0 5 by 1 4 meters
  • the loop antenna likewise consists of one turn (as shown m Fig. 1) having dimensions of, for instance, about 0.5 by 1.0 m.
  • the dimensions and the number of turns are limited by the total length of the loop.
  • the loop antenna 6, as said, contains one turn and is connected at the top to a capacitor 8, which causes the loop antenna to resonate at the operating frequency f when a transmitted signal is fed to the loop antenna 6 by means of the transmitter and receiver device 4.
  • the loop antenna 6 is connected to the transmitter and receiver device 4, with the loop antenna 6 functioning both as transmitting antenna and as reception antenna.
  • the antenna configuration includes two loop antennas, the first loop antenna being connected with the transmitter and receiver device 4 and functioning as transmitting antenna, while the second loop antenna is connected with the transmitter and receiver device 4 and functions as reception antenna.
  • the connecting points 10 of the loop antenna 6 to the capacitor 8 can also be the points with which the loop antenna is connected to the transmitter and receiver device 4, as shown in this example, but this may also be designed m many other ways.
  • the manner of connection to the transmitter and receiver device is not relevant to the invention and is therefore not further considered here.
  • the transmitter and receiver device can be designed m various ways known per se, for instance including separate transmission and reception units. This is not relevant to the invention either and will not be further explained here.
  • the loop antenna 6 together with the tuning capacitor 8 forms a resonant circuit consisting of a concentrated self -inductance which is formed by the self -inductance of the conductive loop 12, and of the capacitance of the tuning capacitor.
  • the loop antenna starts to exhibit transmission line behavior, which is the result of the fact that the loop antenna consists of a spread self -inductance and a spread capacitance.
  • Fig. 2 this is depicted schematically.
  • the consequence of the spread self -inductance and capacitance is that the current through the loop 12 is not of equal magnitude everywhere.
  • the alternating voltage is zero and the current is maximal.
  • the voltage increases towards the top.
  • a capacitive current will start to flow through lateral space capacitances 14 and through mutual capacitances 15. This current reduces the current through the parts of the loop located above these capacitances. Eventually, the current is minimal at the position of the tuning capacitor 8.
  • the current is not constant along the circumference. This means that the resulting magnetic field is not uniform but is deformed in that the upper part of the loop contributes less to the field.
  • the tuning capacity 8 will have a low value; the space capacitances 14 and 15 contribute relatively much to the total resonance capacitance. This renders tuning highly sensitive to ambient influences. Nor is it possible anymore to incorporate the loop 12 m materials having a relative permeability >1, unless the dimensions are limited still further. Also, the great influence of the space capacitances renders the loop 11 sensitive to damping through dielectric losses in the material of incorporation. In particular moisture in these materials can have a highly adverse influence on the operation. 3.
  • the relatively small resonance capacitance together with the datum that the loop antenna consists of a single turn through which flows a high current to be able to achieve the required magnetic field strength, causes great high-frequency voltages to arise across the tuning capacitor, and hence on those parts of the loop antenna adjacent the tuning capacitor.
  • Fig. 4 shows such a passageway in which arrow 22 indicates the direction of passage.
  • a detection area 24 of the passageway in which it must be possible for a transponder to be detected is hatched.
  • the antenna configuration here comprises two loop antennas 6, 6', which are placed on either side of the passageway and here function as transmitting and reception antennas.
  • the magnetic field lines are designated by 26, and also indicated is the common axis 28 of the loop antennas 6, 6'. It is well known that on the axis of the loop antenna 6, 6', the field strength decreases very strongly with the distance to the plane of the loop antenna as soon as this distance exceeds half the diameter of the loop antenna.
  • the magnetic field strength m the middle of that passageway will have to be sufficiently high to enable the label to function.
  • the magnetic field strengths m the middle of that passageway must be sufficiently high to enable the label to function.
  • the magnetic field strength closer to the loop antennas 6, 6' must be very much greater; strength ratios of a factor of 10 or more are quite common. Since at the points adjacent the tuning capacitor 8 (see Fig. 1) high voltages arise on the antenna loop, high electric field strengths will also be present m situ.
  • an object of the invention is to make possible an antenna configuration such that a passageway for persons can be largely covered for reading a label without excessive magnetic and/or electric field strengths occurring there, which field strengths could be disadvantageous to the carriers of medical implants, or which field strengths enter into such interaction with the tissue of the human body as to involve an adverse influence.
  • this principle can be utilized by interrupting the loop at a number of points and connecting it through a series capacitor 30. The capacitor must then have that value at which its reactance compensates, at least partly, the reactance of the self -inductance of the intervening loop parts.
  • the capacitance of the series capacitors 30 is rendered large and hence the influence of the space capacitances 14, 15 small.
  • FIG. 5 schematically shows a loop antenna according to the invention.
  • the loop antenna 6 is therefore interrupted at a plurality of points 34, while capacitors 30 included m the loop antenna at the points referred to are connected m series with the capacitors m the loop antenna.
  • the loop antenna is interrupted at a plurality of points by capacitors included m the loop antenna at the points referred to, so that the loop antenna is made up of electrically conductive loop parts and the capacitors, with the loop parts and capacitors connected m series.
  • the electromagnetic interrogation field i.e. the resonant frequency of the loop antenna 6 with the capacitor 8
  • a loop part 32 located between two capacitors has a dimension 1 which is smaller than c/2*p ⁇ *f, where c is equal to the speed of light.
  • each of the loop parts located between two capacitors has dimensions smaller than c/2*p ⁇ *f.
  • the table below gives an indication of the relation between the length 1 of the loop parts 32, each forming a self -inductance L which is indicated in the drawing by the symbol of the coil, and the capacitance of the series capacitors at an operating frequency of 13.56 MHz:
  • Length 1 1.0 0.75 0.5 0.25 0.1 m
  • Capacitance C 138 184 276 551 1378 pF .
  • An additional advantage m the use of a high capacitance value, and hence short loop parts 32, is that at equal current the high-frequency voltage developed across the series capacitors 30, and hence on the whole loop antenna 6, relative to the surroundings, is low.
  • antenna shapes are enabled where a loop antenna 6 is formed by a single turn laid around a passageway, so-called walk- through antennas.
  • Fig. 6 shows such a walk-through antenna arrangement.
  • Arrow 22 indicates the direction of passage, which intersects the loop antenna 6. It will be immediately clear that the physical dimensions of the loop antenna must be so large as to allow persons to walk through the turn, and that m the use of high operating frequencies a solution such as indicated m this invention is necessary.
  • the transponders to be detected or read out pass the plane of the turn, in which the magnetic field strength of the loop antenna is maximal .
  • This maximum field strength can now be much lower than in the case of loop antennas on the side of a passageway, as has been discussed with reference to Fig. 4. Risks of medical implants being influenced are thereby minimized, as are disadvantageous influences on the human body.
  • the loop parts can be integrated with the interposed capacitors, yielding a cable which is reactance-free for one frequency.
  • loop antennas of unlimited dimensions can be constructed.
  • the cable 40 comprises a multiplicity of conductive loop parts 32 and capacitors 34, with the conductive loop parts and the capacitors connected in series, such that two adjacent conductive loop parts are connected with each other through one of the capacitors.
  • a cable is provided with a sheath 42 of, for instance, plastic material in which the conductive loop parts and the capacitors are included.
  • the interrogation field has a frequency f greater than or equal to 8.2 MHz. More particularly, this frequency is greater than or equal to 13.56 MHz. However, other frequencies are also possible.
  • the system can be designed as a transmission system, known per se . It is also possible, however, that a system is designed as an absorption system for detecting the transponders .
  • the system comprises an antenna configuration which functions both as transmitting antenna and as reception antenna.
  • the antenna configuration in this example comprises a loop antenna 6, which comprises a single turn.
  • Other variants, however, are also possible.
  • the antenna configuration comprises a transmitting antenna, with a loop antenna as has been discussed with reference to Figs. 5 and 6.
  • the reception antenna can then consist of a separate, different type of loop antenna.
  • the loop antenna, as shown in Fig. 5 comprises more than one turn. These turns can then be part of more extended antenna shapes.
  • transponders can also be made of programmable design. Such variants are all understood to fall within the scope of the invention.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Health & Medical Sciences (AREA)
  • Toxicology (AREA)
  • Physics & Mathematics (AREA)
  • General Health & Medical Sciences (AREA)
  • Artificial Intelligence (AREA)
  • Computer Vision & Pattern Recognition (AREA)
  • General Physics & Mathematics (AREA)
  • Theoretical Computer Science (AREA)
  • Electromagnetism (AREA)
  • Details Of Aerials (AREA)
  • Radar Systems Or Details Thereof (AREA)
  • Near-Field Transmission Systems (AREA)

Abstract

L'invention concerne un système servant à détecter et éventuellement communiquer avec des transpondeurs comprenant un circuit résonant, tels que des transpondeurs antivol et des transpondeurs d'identification, composés d'un émetteur et d'un récepteur, d'une configuration d'antenne couplée avec l'émetteur et le récepteur, consistant au moins en une antenne à boucle servant à irradier un champ d'interrogation électromagnétique, ainsi qu'au moins un transpondeur dont on provoque la résonance du circuit résonant quand le transpondeur est introduit dans le champ d'interrogation, l'émetteur et le récepteur étant, de plus conçu pour détecter quand le circuit résonant résonne. Selon l'invention, l'antenne à boucle est interrompue au niveau d'une pluralité de points par des condensateurs compris dans cette antenne au niveau de ces points, de sorte que l'antenne à boucle est constituée par des pièces de boucle électriquement conductrices et branchées en série avec les condensateurs.
PCT/NL1999/000675 1998-11-03 1999-11-03 Systeme servant a detecter et eventuellement communiquer avec des transpondeurs tels que des transpondeurs antivol ou d'identification Ceased WO2000026989A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU11895/00A AU1189500A (en) 1998-11-03 1999-11-03 System for detecting and optionally communicating with transponders such as antitheft transponders and identification transponders

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
NL1010457A NL1010457C2 (nl) 1998-11-03 1998-11-03 Grote lusantennes.
NL1010457 1998-11-03

Publications (1)

Publication Number Publication Date
WO2000026989A1 true WO2000026989A1 (fr) 2000-05-11

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PCT/NL1999/000675 Ceased WO2000026989A1 (fr) 1998-11-03 1999-11-03 Systeme servant a detecter et eventuellement communiquer avec des transpondeurs tels que des transpondeurs antivol ou d'identification

Country Status (3)

Country Link
AU (1) AU1189500A (fr)
NL (1) NL1010457C2 (fr)
WO (1) WO2000026989A1 (fr)

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2001041253A1 (fr) * 1999-12-01 2001-06-07 Logitech Europe S.A. Technique de reduction des parasites sur une antenne-cadre
WO2003041295A1 (fr) * 2001-11-09 2003-05-15 Commissariat A L'energie Atomique Dispositif passif d'accroissement de l'efficacite de transmission de systemes radiofrequence
US6570541B2 (en) 1998-05-18 2003-05-27 Db Tag, Inc. Systems and methods for wirelessly projecting power using multiple in-phase current loops
EP1494311A1 (fr) * 2003-07-02 2005-01-05 Sensormatic Electronics Corporation Antenne à boucles decallées à compensation de phase et annulant le champ lointain
US6960984B1 (en) 1999-12-08 2005-11-01 University Of North Carolina Methods and systems for reactively compensating magnetic current loops
EP1538558A3 (fr) * 2003-12-03 2006-05-03 Hitachi, Ltd. RFID à circuit résonnant
CN108417972A (zh) * 2018-04-02 2018-08-17 广东电网有限责任公司 一种用于输电线路异常放电检测的波浪式谐振天线

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3704180A1 (de) * 1987-02-11 1988-08-25 Licentia Gmbh Antennenanordnung zur abstrahlung von infralaengstwellen
WO1992017866A1 (fr) * 1991-04-03 1992-10-15 Integrated Silicon Design Pty. Ltd. Systeme de tri d'articles
WO1993023909A1 (fr) * 1992-05-10 1993-11-25 Auckland Uniservices Limited Trajet inductif primaire
NL9202158A (nl) * 1992-12-14 1994-07-01 Nedap Nv Identificatiesysteem volgens de transmissiemethode.
WO1997001197A1 (fr) * 1995-06-21 1997-01-09 Motorola Inc. Procede et antenne produisant un diagramme de rayonnement omnidirectionnel

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS63269605A (ja) * 1987-04-27 1988-11-07 Yokogawa Medical Syst Ltd ワンタ−ンル−プ共振回路
DE4218635C2 (de) * 1992-06-05 1996-05-23 Siemens Ag Hochfrequenz-Empfangsantenne einer Einrichtung zur Kernspintomographie mit mindestens einem Kondensator
US5812095A (en) * 1995-10-06 1998-09-22 Ford Motor Company Mounting structure for combined automotive trim accessory and antenna

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3704180A1 (de) * 1987-02-11 1988-08-25 Licentia Gmbh Antennenanordnung zur abstrahlung von infralaengstwellen
WO1992017866A1 (fr) * 1991-04-03 1992-10-15 Integrated Silicon Design Pty. Ltd. Systeme de tri d'articles
WO1993023909A1 (fr) * 1992-05-10 1993-11-25 Auckland Uniservices Limited Trajet inductif primaire
NL9202158A (nl) * 1992-12-14 1994-07-01 Nedap Nv Identificatiesysteem volgens de transmissiemethode.
WO1997001197A1 (fr) * 1995-06-21 1997-01-09 Motorola Inc. Procede et antenne produisant un diagramme de rayonnement omnidirectionnel

Cited By (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6570541B2 (en) 1998-05-18 2003-05-27 Db Tag, Inc. Systems and methods for wirelessly projecting power using multiple in-phase current loops
US6600452B2 (en) 1999-12-01 2003-07-29 Logitech Europe S.A. Loop antenna parasitics reduction technique
US6359594B1 (en) 1999-12-01 2002-03-19 Logitech Europe S.A. Loop antenna parasitics reduction technique
WO2001041253A1 (fr) * 1999-12-01 2001-06-07 Logitech Europe S.A. Technique de reduction des parasites sur une antenne-cadre
US6960984B1 (en) 1999-12-08 2005-11-01 University Of North Carolina Methods and systems for reactively compensating magnetic current loops
US7262743B2 (en) 2001-11-09 2007-08-28 Commissariat A L'energie Atomique Passive device for increasing the transmission efficiency of radio-frequency systems
FR2832272A1 (fr) * 2001-11-09 2003-05-16 Commissariat Energie Atomique Dispositif passif d'accroissement de l'efficacite de transmission de systemes radiofrequence
WO2003041295A1 (fr) * 2001-11-09 2003-05-15 Commissariat A L'energie Atomique Dispositif passif d'accroissement de l'efficacite de transmission de systemes radiofrequence
US7564414B2 (en) 2001-11-09 2009-07-21 Messier-Bugatti Passive device for increasing the transmission efficiency of radio-frequency systems
EP1494311A1 (fr) * 2003-07-02 2005-01-05 Sensormatic Electronics Corporation Antenne à boucles decallées à compensation de phase et annulant le champ lointain
AU2004202918B2 (en) * 2003-07-02 2010-08-05 Sensormatic Electronics, LLC Phase Compensated Field-cancelling Nested Loop Antenna
EP1538558A3 (fr) * 2003-12-03 2006-05-03 Hitachi, Ltd. RFID à circuit résonnant
CN108417972A (zh) * 2018-04-02 2018-08-17 广东电网有限责任公司 一种用于输电线路异常放电检测的波浪式谐振天线

Also Published As

Publication number Publication date
NL1010457C2 (nl) 2000-05-04
AU1189500A (en) 2000-05-22

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