Communications: radio wave antennas – Antennas – High frequency type loops
Patent
1998-06-15
2000-11-21
Wong, Don
Communications: radio wave antennas
Antennas
High frequency type loops
340825, 34082554, 340572, H04B 700, G08B 1324
Patent
active
061509868
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a transponder, in particular an antenna system for a transponder and activation or driver circuits incorporated in the transponder for issuing information carrying electromagnetic waves on the antenna system.
2. Description of the Prior Art
Electronic systems for identification of domestic animals utilize electronic units attached to the animals, usually in the shape of transponders that lack an energy source of their own. Such transponders obtain induced electric energy from receiving suitable electromagnetic energy that is emitted by antennas or coils located at those positions where an identification is desired, such as at the entrance of a feeding place or a milking station. After receiving induced energy the transponder issues a radio frequency signal that is captured by an antenna which can be the same antenna by means of which the energy was induced or at least is arranged in parallel therewith. The identification signal can then be used for e.g. only counting the number of animals, controlling amounts of delivered food, guiding a milking animal to the correct stall, etc.
Transponders are generally used for identification of movable objects, for example and primarily of bovine animals. A transponder comprises conventionally a receiving and transmitting antenna, a storage means for storing energy transferred wirelessly to the transponder and control circuits. A transponder is associated with at least one usually fixed or stationary reading station that comprises an antenna loop having one or more turns located at some position, in the direct neighbourhood of which the movable object is sometimes located or passes, such as for example directly through the antenna loop of the reading station. The antenna of the transponder is in a similar way made as a coil having a multitude of turns, the coil being substantially flat. The antenna of the transponder and the antenna in the reading station cooperate in principally the same way as the two windings of a transformer having an air core. By suitable arrangements it can often be achieved that these two coils at least sometimes will be located approximately in parallel with each other, when the movable object is staying close to or passes the stationary reading station, but this can be difficult to achieve in a secure manner, e.g. for the case where the reading station comprises loops located at each side of a passage through which the movable objects pass. Thus, it would be advantageous that the antenna system comprising the two antennas could be arranged for arbitrary mutual directions of the magnetic field of the stationary antenna in the reading station and the antenna of the transponder.
U.S. Pat. Nos. 4,247,758 and 4,798,175 and the published European patent applications EP-A1 0 494 764 and EP-A2 0 496 610 disclose typical examples of prior transponder systems and antennas designed therefor.
In U.S. Pat. No. 4,274,089 it is disclosed how an interrogation system for theft protection responders can be designed to have two transmission antennas, each one of which being a flat coil and which are located perpendicularly to each other. These antenna coils are made having only one terminal and thus they have one end open. They are supplied with electrical energy alternatingly so that always only one antenna is active. A separate receiving antenna is used. By the arrangement comprising antenna coils arranged perpendicularly to each other the station is less sensitive to the orientation of the antenna of a responder attached to some object that passes the interrogation station.
This previously known design having two antenna elements arranged perpendicularly to each other can of course also be modified for use in reading stations for transponders, as appears from the published European patent application EP-A1 0 496 609. Here two vertical antenna coils that are perpendicular to each other are provided surrounding the path along which a transponder passes. U.S. Pat. No. 5,258,7
REFERENCES:
patent: 4247758 (1981-01-01), Rodrain
patent: 4274089 (1981-06-01), Giles
patent: 4798175 (1989-01-01), Townsend et al.
patent: 5191349 (1993-03-01), Dinsmore et al.
patent: 5258766 (1993-11-01), Murdoch
patent: 5281941 (1994-01-01), Bernstein
patent: 5592182 (1997-01-01), Yao et al.
patent: 5699048 (1997-12-01), Galloway
Andersson Lars
Sandberg Ola
Alfa Laval Agri AB
Clinger James
Wong Don
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