Note: Descriptions are shown in the official language in which they were submitted.
~32:~223
This invention relates to an electromagnetic detection
and identification system for identifying vehicles or their -~
occupants by means of an interrogation field generated by a
transmitter/receiver through an antenna coil.
Electromagnetic detection and identification systems for
identifying human beings, animals and goods, including various
systems of the present applicants, are well-known. Such
identification systems can be used, for example, for
permitting or refusing access to premises, for feeding -~
animals, and for monitoring and supervising logistic
processes.
One example of an electromagnetic detection and
identification system is described in Netherlands patent
specification 176404. Such systems operate as follows. An
electromagnetic A.C. field is generated by a
transmitter/receiver. Identification labels, also referred to
as responders, are provided with an electronic circuit
including at least a resonant circuit and a coding device. If
the responder is moved into an electromagnetic A.C. field
generated by the transmitter/receiver ~the interrogation
field), the resonant circuit will start resonating. By means
of the resonant circuit, the responder circuit is capable of
withdrawing electrical energy from the field. This energy is -~
used, after rectification, to provide the coding device with
supply power. The coding device then generates a code which
through the same coil and the same electromagnetic field can
be identified by the transmitter/receiver. Taking into account
the maximum permissible field strength in the various
countries, such identification systems can achieve a detection
distance of about 90 cm. The drawback of the prior systems is
that, for a number of uses, this distance is insufficient. ~ ~
Under certain conditions, detection is even downright --
impossible. In the case, for example, of persons seated in
(metallic) vehicles, such as motorcars, detection is basically
impossible, as the metal construction virtually is a perfect -
electromagnetic screen (Faraday cage). Furthermore, if `~
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identification is possible after all, the detection distance
would be insufficient for the system to function properly in
practice for the identlfication of vehicles.
It is an object of the present invention to overcome the
drawbacks outlined above, and, in general, to provide an
electromagnetic identification system for vehicles, such as
motorcars, which operates reliably.
For this purpose, according to the present invention, a
system of the above-described kind is characterized in that
the vehicles are provided with an opening surrounded by at
least one frame and that, in operation, a responder is
arranged in the vicinity of said frame.
The transmitter/receiver generates an electromagnetic
A.C. field. The field lines generated induce a current along
the metallic parts surrounding vehicle openings, such as
windows When a responder with a resonant circuit is applied
in the vicinity of a vehicle post, the current induced, which
is concentrated in the post, will in turn generate an
electromagnetic field in the resonant circuit. Owing to the
existence of a second field, the electromagnetic field of the -: -
transmitter/receiver will be concentrated.
In accordance with a further elaboration of the present
invention, the form of the electromagnetic field of the
transmitter/receiver is influenced by using a metallic floor
plate, which is positioned in or on the roadway to extend
partly under a vehicle in the longitudinal direction. The
floor plate will cause a portion of the magnetic field lines
of the electromagnetic field generated by the
transmitter/receiver to be concentrated in the direction of
the vehicle. Owing to the above features of the present
invention, the responder is capable of drawing more electrical
power from the more concentrated electromagnetic field to
generate a code, which can be detected, via the same
electromagnetic field, by the transmitter/receiver. Owing to
the more concentrated electromagnetic field, a larger
detection distance can be bridged than the conventional 90 cm.
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Some embodiments of the present invention will now be
described,by way of example, with reference to the
accompanying drawings. In said drawings,
Fig. 1 diagrammatically shows a system according to the
present invention for the identification of motorcars;
Fig. 2 shows a side-elevational view according to the
arrow II of F~g. 1; and
Fig. 3 diagrammatically shows a detail of Fig. 2.
Fig. 1 shows a transmitting antenna 1 with a vehicle 2,
in this case a passenger car. The field lines 3 of
transmitting antenna 1 extend towards vehicle 2. Vehicle 2 is ;
within an electromagnetic field generated through the
transmitting antenna by a transmitter/receiver 10. As a
consequence, an electrical current is generated in the
metallic parts which surround openings, such as windows and
doorways, of vehicle 2. Owing to the presence of the openings,
a concentration of these induced currents is brought about.
Furthermore, a metallic floor plate 9 may be provided, which
promotes that the field formed by antenna 1 is concentrated in
the direction of vehicle 2.
Fig. 2 shows a practical arrangement. Antenna 1 is
arranged next to the vehicle and is dimensioned to match the
dimension of the vehicles to be identified. For example, for
passenger cars the antenna coil may be 4 m long and 1 m high.
As a result of the electromagnetic field generated, a current ~ -
is induced around window 4 in door 5. A floor plate 9 is again
provided to bring about a concentration effect with regard to
the electromagnetic field. The (A.C.) current i induced around -
window opening 4 by the interrogation field generates in turn
an electromagnetic A.C. field, which can serve as an
interrogation field for a responder. A responder placed within ~;
the field generated by the current i around a window post 6 is ~ `~
shown schematically at 7 in Fig. 2. All this is shown in more
detail in Fig. 3.
Fig. 3 shows a responder 7 in the vicinity of post 6. The
current i in post 6 generates an electromagnetic A.C. field 8.
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As the responder 7 is ln the vicinity of the post, the
resonan~ circuit of the responder is coupled
electromagnetically with the electromagnetic field of the
current through the post. When responder 7 is positioned so as
to achieve maximum coupling for this application, the intake
of electrical energy will be relatively high. When used with
vehicles, the responder 7 is preferably arranged in one of the
corners of the window or doorway. In fact, the field is
concentrated in the vicinity of the corner of a window or
doorway, at least in the interior zone of the angle. In Fig.
3, responder 7 is shown to be positioned in the vicinity of
the front bottom corner of the window opening of a passenger
car 2. Alternatively, however, the responder may be positioned
in the vicinity of any of the other corners.
A final feature of importance to the present invention is
that the transmitting antenna should be positioned so that the
current flows optimally through the vehicle posts. To this
effect, the antenna is preferably disposed in a vertical plane
to extend substantially parallel to the side of the vehicles
to be identified.
It is noted that, in view of the above, various
modifications will readily occur to those skilled in the art.
Thus, if the system is designed to identify vehicles, a
responder will be fixed to the vehicle. If, however, the
system is intended for the identification of passengers, the
vehicle could be provided with a holder disposed, in the
manner described, in the field of an induction current, and
adapted to receive a card-shaped or other responder in a pre-
determined position.
These and similar modifications are considered to fall
within the scope of the present invention.
