Communications: electrical – Selective – Interrogation response
Reexamination Certificate
1998-03-05
2001-03-27
Horabik, Michael (Department: 2735)
Communications: electrical
Selective
Interrogation response
C340S572300, C340S572500, C340S572700, C340S010200, C340S010300, C607S060000
Reexamination Certificate
active
06208235
ABSTRACT:
BACKGROUND OF THE INVENTION
Tagging of articles for identification and/or theft protection is known. For instance, many articles are identified using a bar code comprising coded information which is read by passing the bar code within view of a scanner. Many articles also include a resonant tag for use in theft detection and prevention. More recently, passive resonant tags which return unique or semi-unique identification codes have been developed. These tags typically include an integrated circuit (IC) which stores the identification code. Such “intelligent” tags provide information about an article or person with which the tag is associated which is detected in the zone of an interrogator or reader. The tags are desirable because they can be interrogated rapidly, and from a distance. U.S. Pat. No. 5,446,447 (Carney et al.), U.S. Pat. No. 5,430,441 (Bickley et al.), and U.S. Pat. No. 5,347,263 (Carroll et al.) disclose three examples of such intelligent tags.
Radio frequency identification (RFID) tags or cards generally include a resonant antenna circuit electrically connected to the IC. The IC is essentially a programmable memory for storing digitally encoded information. The interrogator (transmit antenna) creates an electromagnetic field at the resonant frequency of the RFID tag. When the tag is placed into the field of the interrogator, an AC voltage is induced in the resonant antenna circuit of the tag, which is rectified by the IC to provide the IC with an internal DC voltage. As the tag moves into the field of the interrogator, the induced voltage increases. When the internal DC voltage reaches a level that assures proper operation of the IC, the IC outputs its stored data. To output its data, the IC creates a series of data pulses by switching an extra capacitor across the antenna circuit for the duration of the pulse, which changes the resonant frequency of the tag, detuning the tag from the operational frequency. That is, the tag creates data pulses by detuning itself, which changes the amount of energy consumed by the tag. The interrogator detects the consumption of energy in its field and interprets the changes as data pulses.
Although such RFID tags or cards are known, there are still technical difficulties and limitations associated with the operation of such tags. One problem with attempting to read multiple RFID tags within an interrogation zone of the interrogator is that more than one tag may be activated by the interrogator at about the same time. When such tags are located proximate to each other, the fields generated by one tag can disturb the fields generated by another tag. This problem of mutual inductance is especially significant for RFID tags which transmit their information by detuning, as described above. As a consequence, the effective reading distance drops and the modulation of the tag can become completely ineffective due to the fact that such modulation depends upon the tag being in resonance (or close to it). Thus, such detuning caused by other tags can make the reading of stored information impossible or nearly impossible.
Yet another problem often encountered when reading intelligent tags or cards is a large variation in the received power, for instance, when the tag nears the power transmit antenna of the interrogator. As the tag approaches the transmit antenna, the received power increases, which can cause problems due to excessive voltage or power dissipation and, because of a decrease in tag Q, an inability to sufficiently modulate the tag with the data using the aforementioned detuning approach. Such detuning or modulation problems increase the difficulty of correctly reading the tag.
Accordingly, there is a need for a method of preventing RFID tags from generating fields which disturb or affect other nearby resonant cards or tags. There is further a need for an RFID tag whose operation is not adversely affected by large variations in received power. The present invention fulfills these needs.
BRIEF SUMMARY OF THE INVENTION
Briefly stated, in a first embodiment the present invention is a radio frequency intelligent transponder. The transponder includes an integrated circuit for storing data and an inductor electrically connected to the integrated circuit. The inductor includes a first coil electrically connected to a second coil. A resonant capacitor is electrically connected to the integrated circuit and to at least one of the first and second coils, such that the resonant capacitor and the at least one connected coil have a first predetermined resonant frequency. A switch having a first position and a second position is provided for selectively allowing current to flow through the second coil. When the switch is in the first position, exposure of the transponder to an external field at or near the first resonant frequency induces a voltage in the inductor and causes a first current to flow through the inductor in a first direction, thereby generating a local (near) field. When the switch is in the second position, exposure of the transponder to an external field at or near the first resonant frequency induces a voltage in the inductor and causes a first current to flow through the first coil in a first direction, thereby generating a first local (near) field and a second current to flow through the second coil in a second, opposite direction, thereby generating a second local (near) field. A sum of the first and second local fields approaches zero.
In a second embodiment, the present invention is a radio frequency intelligent transponder comprising an integrated circuit for storing data and an antenna circuit. The antenna circuit comprises a first coil and a resonant capacitor having a predetermined resonant frequency electrically connected to the integrated circuit for providing power to the integrated circuit and for transmitting the data stored in the integrated circuit to a device reader. Exposure of the transponder to an external field at a frequency near the predetermined resonant frequency causes a first current to flow through the antenna circuit in a first direction, thereby producing a first local field which couples the transponder with its environment. The transponder further comprises means for selectively generating a second local field, wherein a sum of the first and second local fields approaches zero, for selectively decoupling the transponder from its environment.
In a third embodiment, the present invention comprises an intelligent resonant tag comprising an integrated circuit for storing data and a first antenna circuit electrically connected to the integrated circuit. Exposure of the first antenna circuit to an electromagnetic field at a first predetermined radio frequency induces a voltage therein, which produces a current flowing in a first direction therethrough, thereby producing a first local field. The induced voltage also provides power to the integrated circuit such that the data stored therein is read therefrom and transmitted at a second predetermined radio frequency. The tag also comprises means for generating a second local field which at least partially cancels the first local field generated by the first antenna circuit.
REFERENCES:
patent: 4019181 (1977-04-01), Olsson et al.
patent: 4196418 (1980-04-01), Kip et al.
patent: 4481428 (1984-11-01), Charlot, Jr.
patent: 4583099 (1986-04-01), Reilly et al.
patent: 4598276 (1986-07-01), Tait
patent: 4600829 (1986-07-01), Walton
patent: 4734680 (1988-03-01), Gehman et al.
patent: 4799059 (1989-01-01), Grindahl et al.
patent: 4951057 (1990-08-01), Nagel
patent: 5061941 (1991-10-01), Lizzi et al.
patent: 5065138 (1991-11-01), Lian et al.
patent: 5072222 (1991-12-01), Fockens
patent: 5084699 (1992-01-01), DeMichele
patent: 5103222 (1992-04-01), Hogen Esch et al.
patent: 5142292 (1992-08-01), Chang
patent: 5153583 (1992-10-01), Murdoch
patent: 5182543 (1993-01-01), Siegel et al.
patent: 5189397 (1993-02-01), Watkins et al.
patent: 5241298 (1993-08-01), Lian et al.
patent: 5287113 (1994-02-01), Meier
patent: 5302901 (1994-04-01), Snelten
patent: 5373303 (19
Akin Gump Strauss Hauer & Feld L.L.P.
Bangachon William
Checkpoint Systems Inc.
Horabik Michael
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