U.S. patent number 4,308,530 [Application Number 05/904,416] was granted by the patent office on 1981-12-29 for detection system forming wide gates with superior spatial selectivity.
This patent grant is currently assigned to N.V. Nederlandsche Apparatenfabriek NEDAP. Invention is credited to Tallienco W. H. Fockens, Harm J. Kip.
United States Patent |
4,308,530 |
Kip , et al. |
December 29, 1981 |
Detection system forming wide gates with superior spatial
selectivity
Abstract
A detection system comprises at least one gate including
transmitter means for forming a magnetic field and receiver means
for receiving a signal transmitted by a detecting wafer provided
with an oscillating circuit, wherein each gate comprises at least
two spatial detection zones.
Inventors: |
Kip; Harm J. (Lichtenvoorde,
NL), Fockens; Tallienco W. H. (Eibergen; both of,
NL) |
Assignee: |
N.V. Nederlandsche Apparatenfabriek
NEDAP (Groenlo, NL)
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Family
ID: |
19828910 |
Appl.
No.: |
05/904,416 |
Filed: |
May 10, 1978 |
Foreign Application Priority Data
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Jul 19, 1977 [NL] |
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7708012 |
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Current U.S.
Class: |
340/572.2;
340/572.5; 340/572.7 |
Current CPC
Class: |
G08B
13/2417 (20130101); G08B 13/2474 (20130101); G08B
13/2422 (20130101) |
Current International
Class: |
G08B
13/24 (20060101); G08B 013/24 () |
Field of
Search: |
;340/572,551
;343/6.8R,6.8LC |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2101879 |
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Jul 1972 |
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DE |
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6804325 |
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Oct 1968 |
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NL |
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1254571 |
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Nov 1971 |
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GB |
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Primary Examiner: Swann, III; Glen R.
Attorney, Agent or Firm: Fleit & Jacobson
Claims
We claim:
1. A detection system comprising at least one gate including:
transmitter means for transmitting a first signal,
detection wafer means for receiving said first signal and
responsive thereto for retransmitting said first signal to provide
a second signal, and
receiver means for receiving said second signal retransmitted by
said detection wafer means, said detection wafer means including an
oscillating circuit;
wherein each said at least one gate comprises at least two spatial
detection zones directly adjoining one another with no barrier
therebetween.
2. A detection system according to claim 1, wherein each said at
least one gate has a left-hand sidewall incorporating a first
transmitter coil, and a right-hand sidewall incorporating a second
transmitter coil, and comprising transceiver coils provided in two
adjacent zones in at least one substantially horizontal plane
between said left-hand sidewall and said right-hand sidewall.
3. A detection system according to claim 1, wherein each said at
least one gate has a left-hand sidewall incorporating a first
transceiver coil, and a right-hand sidewall incorporating a second
transceiver coil, and comprising transmitter coils provided in two
adjacent zones in at least one substantially horizontal plane
between the sidewalls.
4. A detection system according to claim 1, wherein each said at
least one gate comprises at least three transmitter coils disposed
in alternation with transceiver coils in at least one substantially
horizontal plane.
5. A system according to claim 1, wherein each said at least one
gate comprises a left-hand sidewall incorporating a first
transmitter coil and a first transceiver coil, and a right-hand
sidewall incorporating a second transmitter coil and a second
transceiver coil, each of said transceiver coils being connected to
a corresponding receiver.
6. A system according to claim 4, wherein all transmitter coils are
connected to a single first transmitter, adjacent transceiver coils
being connected through different coding devices for effecting
coding to a second transmitter, and each of said transceiver coils
being connected to a separate receiver capable of recognizing the
coding effected by the coding device.
7. A system according to claim 5, further comprising means for
comparing, one with the other, the intensity of signals received by
adjacent ones of said transceiver coils.
8. A system according to any one of claims 2 through 4, wherein the
coils lying in the at least one substantially horizontal plane are
situated in off-set relationship to one another in adjacent
zones.
9. A system according to any one of claims 2 through 4, wherein
each said at least one gate has a substantially horizontal bottom
plane and a substantially horizontal ceiling plane, there being at
least one coil in each of said substantially horizontal bottom and
ceiling planes.
10. A system according to claim 9, wherein the coils in the
substantially horizontal bottom plain are disposed in off-set
relationship to the coils in the substantially horizontal ceiling
plane.
11. A system according to claim 5, further comprising an
electrically conductive screen disposed on one side of at least one
of said left-hand and right-hand sidewalls.
12. A system according to claim 1, wherein each said at least one
gate comprises a left-hand, vertically directed arrangement of
transmitter and transceiver coils and a right-hand, vertically
directed arrangement of transmitter and transceiver coils so as to
form two detection fields in the intermediate area.
13. A system according to claim 12, wherein the left-hand
transmitter and transceiver coils and the right-hand transmitter
and transceiver coils are each combined to form respective single
coils to which two transmission frequencies are supplied for
transmission and which are also connected to a receiver.
14. A system according to claim 12, further comprising an
electrically conductive screen disposed on that side of the
transmitter and transceiver coils remote from the detection
zone.
15. A system according to claim 12, wherein each said transmitter
coil is connected to a corresponding first transmitter, each said
transceiver coil being connected to a corresponding receiver.
16. A system according to claim 12, wherein a transmission signal
is supplied to each said transceiver coil via a coding device of
its own, and each transceiver coil is connected to a separate
receiver capable of recognizing the coding.
17. A system according to claim 15, further comprising comparator
means for comparing the intensities of the signals received by the
transceiver coils of said at least one gate.
18. A system according to claim 1, wherein the oscillating circuit
of the detection wafer means has a reasonance range and a resonance
frequency coinciding essentially with a first frequency (f.sub.1)
transmitted in a given detection zone; a second frequency (f.sub.2)
simultaneously transmitted in each detection zone being in the
vicinity of the first frequency (f.sub.1) and well within the
resonance range of the oscillating circuit; a non-linear element
being connected to the oscillating circuit, said non-linear element
being capable of forming a third frequency (f.sub.3) also within
the reasonance range of the oscillating circuit, but on the other
side of the first frequency (f.sub.1) from the second frequency
(f.sub.2).
19. A system according to claim 18, wherein the non-linear element
is a semiconductor diode.
20. A system according to any one of claims 18 and 19, wherein the
second frequency (f.sub.2) is higher than the first frequency
(f.sub.1), and the third frequency (f.sub.3) formed by the
non-linear element being equal to twice the first frequency
(f.sub.1) minus the second frequency (f.sub.2).
21. A system according to any one of claims 18 and 19, wherein the
oscillating circuit comprises a coil and a capacitor.
22. A system according to any one of claims 18 and 19, wherein the
oscillating circuit and the non-linear element form an integrated
circuit embedded in the detection wafer means.
23. A system according to claim 13, further comprising an
electrically conductive screen disposed on that side, remote from
the detection zone, of each of the respective single coils.
24. A system according to claim 13, wherein each said respective
single coil is connected to a corresponding first transmitter and
to a corresponding receiver.
25. A system according to claim 13, wherein a transmission signal
is supplied to each of said respective single coils via a coding
device of its own, and each of said respective single coils is
connected to a separate receiver capable of recognizing the
coding.
26. A system according to claim 25, further comprising comparator
means for comparing the intensities of the signals received by the
respective single coils.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a detection system that can be used for
detecting and possibly identifying persons, cattle or goods moving
through a pre-determined zone. Such a system normally comprises a
number of gates provided with means for generating a magnetic
field, and each forming a detection zone for detecting wafers
having electrical oscillating circuits embedded therein. The wafers
are carried by the persons to be detected or are attached to the
goods to be detected or the cattle to be detected.
2. Description of Prior Art
A disadvantage of prior systems is that, for example, when they are
used as anti-theft systems for shops, but also with other
applications, the gates should be rather narrow for effective,
spatially determined detection. In prior systems, use is made of
gates approximately 1 m wide. If wider gates were used, it would be
possible for two or more persons to move through the gate at the
same time. If one of these persons carries an article provided with
a wafer with an oscillating circuit; it is almost impossible to
determine which person is carrying the safeguarded article, in
other words, the spatial selectivity of the prior systems is poor.
Furthermore, relatively narrow gates form obstacles in passageways,
such as entries and exits of shops, which may be objectionable in
connection with fire regulations.
SUMMARY OF INVENTION
It is an object of the present invention to overcome these
disadvantages.
According to the present invention, therefore, there is provided a
detection system comprising at least one gate including
transmission means for forming a magnetic field and receiving means
for receiving a signal transmitted by a detection wafer provided
with an oscillating circuit, characterized in that each gate
comprises at least two spatial detection zones.
BRIEF DESCRIPTION OF DRAWINGS
Some embodiments of the invention will now be described, by way of
example, with reference to the accompanying drawings. In said
drawings,
FIG. 1 is a diagrammatic illustration of a detection system to
which the present invention relates;
FIG. 2 shows some frequency spectrums in illustration of the system
shown in FIG. 1;
FIG. 3 shows a first embodiment of a system according to the
present invention;
FIG. 4 shows an extension of the system shown in FIG. 3;
FIG. 5 shows the configuration of the magnetic fields in the system
of FIG. 4;
FIG. 6 shows a different embodiment of a system according to the
present invention;
FIG. 7 shows the configuration of the magnetic fields in the system
shown in FIG. 6;
FIG. 8 shows still another embodiment of a gate of a system
according to the present invention; and
FIG. 9 shows a variation of the first embodiment of FIG. 3; and
FIG. 10 shows a variation of the embodiment of FIG. 8.
DETAILED DESCRIPTION
Referring to the drawings, the system shown in FIG. 1 comprises a
first transmitter I and a second transmitter II. The first
transmitter transmits a signal having a frequency f.sub.1, and the
second transmitter transmits a signal having a frequency f.sub.2.
Both signals can be received by a detection wafer W. Wafer W
comprises a resonance circuit with a coil L, a capacitor C, and a
non-linear element D, which for example may be a diode.
Furthermore the system comprises a receiver R, capable of actuating
an alarm device upon the receipt of a signal having a predetermined
frequency. In order that the chance of a false alarm may be
limited, one of the transmitted signals may be modulated, for
example, in amplitude, and the signal received may be checked for
the condition that it comprises this modulation before the alarm
device is actuated. Thus FIG. 1 shows a modulator M, which is
connected to transmitter II and to a modulation checking device MC,
to which the output signal from receiver R is also supplied. The
output of the modulation checking device is connected to an alarm
device.
In illustration of the operation of the system of FIG. 1, FIG. 2
shows some frequency spectrums. Part A of FIG. 2 shows the relative
positions of frequencies f.sub.1 and f.sub.2, transmitted by
transmitters I and II, respectively. FIG. 2A also shows that the
amplitude of the signals of frequency f.sub.1 is larger than that
of the signals having frequency f.sub.2.
Part B of FIG. 2 shows the resonance curve of the oscillation
circuit in detection wafers W. The resonance frequency is f.sub.1,
but the location of f.sub.2 is such that the attenuation of the
resonance circuit at f.sub.2 is not yet very large.
Part C of FIG. 2 shows the frequencies re-transmitted by the
detection wafers W when these are in the field of transmitters I
and II. In addition to frequencies f.sub.1 and f.sub.2, a third
frequency f.sub.3 is transmitted, given by f.sub.3 =2f.sub.1
-f.sub.2. Frequency f.sub.3 is formed as a result of the nonlinear
element D. Frequencies f.sub.1 and f.sub.2 have been so selected
that the amplitude curve of the oscillation circuit at f.sub.3 has
not yet decreased very much relative to the value at f.sub.1.
Part D of FIG. 2, finally, shows the frequency response curve of
receiver R. The frequency response curve shows that the receiver is
only responsive to signals having frequency f.sub.3 or a frequency
that is very slightly different from f.sub.3.
The system described above requires coils for the formation of
magnetic fields to which a detection wafer can react. For each
frequency a separate coil may be used, so that a gate has three
coils, i.e. two transmitter coils and one receiver coil. It is also
possible, however, to use coils combined for two or even three
signals. In prior systems a gate often comprises one horizontal
coil, e.g. in the bottom of the gate, and one or more vertical
coils. The width of the gate is here dictated by the dimensions of
the horizontal coil. If, however, the horizontal coil is made very
wide, there is no longer any spatial selectivity whatsoever.
In order to overcome this disadvantage, according to the present
invention a plurality of side-by-side coils are used in each
gate.
FIG. 3 shows a first embodiment of a detection system according to
the present invention. A transmitter I energizes an associated
transmitter coil CI. Transmitter coil CI is accommodated in the
sidewall 30 of a gate P. Installed in the bottom 31 of gate P is a
coil CII, which is energized by a second transmitter II. In this
example, coil CII also serves as a receiver coil, for which purpose
it is coupled to a receiver R. Connected between coil CII, on the
one hand, and transmitter II as well as receiver R is a terminating
set D, which in a suitable manner separates transmission signals
and reception signals. Lying next to coil CII in the bottom of the
gate is a second coil CII'. This coil CII' is connected to a
separate receiver R'. Furthermore a vertical transmitter coil CI'
is accommodated in the other sidewall 32 of the gate. Coils CI' and
CII' may be energized by transmitters I and II, respectively, or by
separate transmitters. In this way two detection fields are
generated within the gate. If a detection wafer W is over coil CII,
an alarm signal will be given by receiver R, and if a detection
wafer W is over coil CII', an alarm signal will be given by
receiver R'.
It is clear that a gate constructed in this way can be twice as
wide as a conventional gate.
It is noted that the vertical coils could be used as transceiver
coils and the horizontal ones as transmitter coils.
FIG. 4 shows diagrammatically in what way a plurality of gates as
shown in FIG. 3 can be arranged in side-by-side relationship. Arrow
40 indicates the direction of movement of the detection wafers; in
the case of an anti-theft system for shops, this is the direction
of travel of customers leaving the shop.
FIG. 5 diagrammatically shows the configuration of the magnetic
fields generated. The fields of coils CI and CI' are designated by
H.sub.1, and the fields of coils CII and CII' are designated by
H.sub.2.
Although the combined transceiver coils CII and CII' are all shown
to be lying in the floor of a gate in the accompanying drawings,
these transceiver coils may just as well be mounted in the ceiling
of a gate. A combination of coils in the ceiling and coils in the
floor is also possible. Such a combination is recommended if good
detection is necessary at different levels. Furthermore, the
transceiver coils may be placed in off-set relationship.
FIG. 6 shows a different embodiment of the inventive idea. All
coils are here disposed in one horizontal plane, including those
exclusively serving as transmitting coils. All transmitting coils
CI, forming a magnetic field H.sub.1 with a frequency f.sub.1, can
be connected to one single transmitter. All coils CII, serving both
to generate a magnetic field H.sub.2 with a frequency f.sub.2 and
to detect a signal with a frequency f.sub.3 generated by a
detection wafer W, can also be connected to one single transmitter.
Coils CII should, however, be connected each to a separate
receiver. In this manner any given number of detection units d can
be formed side by side, without vertical partitions being
required.
FIG. 7 shows the configuration of the magnetic fields formed by
coils CI and CII for two detection units. Two coils CI together
form a magnetic field, the field lines of which entirely enclose
the intermediate coil CII. In this configuration the magnetic
coupling between coils CI, on the one hand, and coil CII, on the
other, is minimal.
In this configuration of the transmitter coils and the transceiver
coils, too, the coils may be mounted in the floor, in the ceiling,
or both, and if desired in off-set relationship in the direction of
travel. It is noted that, in all embodiments described, means may
be provided for comparing the intensity of signals received by
adjacent receiving coils, in order that, in boundary cases, the
position of the detection wafer may be determined more
accurately.
For the same purpose, it is possible for the signals supplied to
adjacent transceiver coils to be given a different code, for
example, by means of amplitude modulation, and for the receivers
concerned to be provided with detectors for the codes
concerned.
All of the above-described embodiments of the invention employ two
or more horizontal coils. This may be objectionable under certain
circumstances, owing to spurious signals being generated by piping
and wiring mounted in the floor or ceiling of the building, or the
reinforcement of a concrete building.
A first possibility of overcoming this drawback consists in the use
of electrically conductive screens between the coils concerned and
the spurious sources in the surroundings. Such screens are
effective to spatially confine and separate the detection field and
the spurious field.
A second possibility of overcoming the drawback outlined above is
to use vertical coils only, between which two detection zones lie
next to each other. If desired, this solution may be combined with
the use of electrically conductive screens for partitioning the
fields of adjacent gates.
This arrangement is shown in FIG. 8.
FIG. 8 shows two pillars 80 and 81, each accommodating a pair of
coils CI, CII and CI', CII', respectively, located one within the
other. Similar to the embodiments described earlier, coils CI and
CI' are connected to transmitter I and I', respectively, and coils
CII and CII' are connected to transmitters II and II',
respectively. Coils CII and CII' further serve as receiving coils
for the signal transmitted by a detection wafer, for which purpose
they are connected via terminating sets D and D', respectively,
receivers R and R', respectively. In order to ensure good spatial
selectivity, a comparator circuit V is used for comparing the
intensity of the signals received by receivers R and R' to
determine whether the detection wafer is on the left or the right
in the gate.
Furthermore there are shown electrically conductive screens 83 and
84, which confine the fields generated to the space defined between
pillars 80 and 81. In this way a plurality of gates can be placed
side by side without the occurrence of any cross-effects.
It is also possible to use only one coil in each pillar, to which
both transmission signals are supplied via a multiplex device, and
which also serves as a receiving coil.
FIG. 9 shows a variation of the first embodiment of FIG. 3.
Specifically, in FIG. 9, the transmitter coils CI and CI' are
connected to a single first transmitter I, with adjacent
transceiver coils CII and CII' being connected through different
coding devices D and D' (for effecting coding) to a second
transmitter II, each of the transceiver coils CII and CII' being
connected to a separate receiver R and R', respectively, capable of
recognizing the coding effected by the coding device.
FIG. 10 shows a variation of the embodiment of FIG. 8. As seen in
FIG. 10, left-hand transmitter and transceiver coils (CI and CII,
respectively, in FIG. 8) and right-hand transmitter and transceiver
coils (CI' and CII', respectively, in FIG. 8) are combined to form
respective single coils C and C' (FIG. 10), to which two
transmission frequencies are supplied by separate transmitters I
and II, respectively. Moreover, the coils C and C' are connected to
corresponding receivers R and R', respectively.
Various modifications of the embodiments described will readily
occur to those skilled in the art without departing from the scope
of the present invention.
* * * * *