Communications: radio wave antennas – Antennas – Including magnetic material
Reexamination Certificate
1998-09-08
2001-06-19
Phan, Tho (Department: 2821)
Communications: radio wave antennas
Antennas
Including magnetic material
C343S742000, C343S787000, C343S867000
Reexamination Certificate
active
06249258
ABSTRACT:
FIELD OF THE INVENTION
The present invention pertains to a transponder array with a transponder arranged on a conductive surface.
BACKGROUND OF THE INVENTION
Transponders, which are able to exchange data with a polling device via alternating electromagnetic fields, are suitable for the contactless polling of information stored on a movable data storage medium. The coupling with the electromagnetic fields is performed, at least on the transponder side, preferably via magnetic dipole antennas, especially air core coils or ferrite antennas.
For example, a device for the recognition of objects, especially motor vehicles, in which flat antennas of a polling station are recessed into the ground with their antenna surfaces in parallel to the road surface, has been known from DE 40 39 690 A1. As for the polling device, the transmitting antenna is designed as a rotating spaced loop, and the receiving antenna as a simple frame. The orientation of transponder antennas arranged on the underbodies of motor vehicles is adjusted to the orientation of the polling antennas or to the strength distribution of their field such that on the transponder side, the coils wound as flat coils on a rectangular parallelepiped have horizontal or vertical antenna surfaces standing vertically one on top of another.
An antenna system for arrangement in the outer surface of an airplane, especially as a direction-finding antenna, is described in GB A 719526. In a first embodiment, a winding is wound on a rod made of a material of high permeability and the rod is inserted into a slot of the outer surface of the airplane. According to another embodiment, rods made of a material of high permeability are inserted in depressions of the metallic surface of the airplane and they face with one end a coil array inserted into a window of the metallic surface. Another direction-finding antenna for airplanes, in which a direction-finding antenna consisting of two crossed air core coils is arranged in the metallic surface of an airplane behind a window covered by a dielectric plate, has been known from GB A 2024522. These prior-art arrays for direction-finding antennas for airplanes require that the metallic surface of the airplane be interrupted at the site of the antenna. In addition, there are restrictions concerning the nature of the material of the metallic surface, which shall not be magnetic.
Besides applications with transponders located in an extensively undisturbed environment, e.g., with transponders carried by persons, transponder arrays on electrically conductive, especially metallic surfaces with nonuniform orientation of the transponders and objects with respect to a polling device are of considerable significance, especially in automatization engineering for the identification of objects.
SUMMARY AND OBJECTS OF THE INVENTION
The basic object of the present invention is to provide advantageous transponder arrays with a transponder antenna arranged on an electrically conductive surface as well as advantageous embodiments of transponders for this.
A transponder array according to the present invention includes a support body formed as a flat body with a small height compared with transverse dimensions of the support body. A coil is wound on the support body with a plurality of coil turns. The coil turns cover a portion of a surface of the support body and are wound around the support body to form a longitudinal axis of the coil oriented substantially in parallel to a plane of the flat body. The coil forms a transponder antenna arranged on an electrically conductive surface with the antenna coil generating a magnetic field having a principal direction forming an angle of less than 45° with the conductive surface and preferably less than 15 degrees.
The principal direction of the magnetic field (director) of the coils is determined in the known manner by the surface normal of the coil surface in the case of flat coils and by the longitudinal axis of the coil in the case of elongated coils.
It is seen that good field coupling and consequently a reliable data exchange are guaranteed with the transponder arrays according to the present invention with an extensive freedom in terms of the arrangement and the orientation of the antennas of the polling device. The present invention takes advantage of the fact that a polling signal emitted by the antenna of the polling device has a nearly disappearing magnetic field component in the direction of the surface normal and, compared with this, a substantially stronger magnetic field component in parallel to the conductive surface in the vicinity of the electrically conductive surface, extensively independently from the orientation of the transmitting antenna of the polling device. The transponder arrays according to the present invention utilize this property of the field by their orientation with respect to the conductive surface and arrangement on this surface in an especially advantageous manner. In the case of the division of the transponder antenna into a plurality of coil sections, e.g., for transmitting and receiving, the orientation applies to all coil sections.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated.
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Bloch Werner
Leuck Lothar-Markus
Muller Michael
Reitmayer Thomas
AEG Identifikationssysteme
McGlew and Tuttle , P.C.
Phan Tho
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