U.S. patent number 3,740,742 [Application Number 05/142,132] was granted by the patent office on 1973-06-19 for method and apparatus for actuating an electric circuit.
Invention is credited to Joseph W. Griffith, Thomas F. Thompson.
United States Patent |
3,740,742 |
Thompson , et al. |
June 19, 1973 |
METHOD AND APPARATUS FOR ACTUATING AN ELECTRIC CIRCUIT
Abstract
A field of electrostatic, electromagnetic or high frequency
radiant energy is provided on a predetermined intermittent cycle in
a confined space through which persons are directed. A tuned
resonant circuit, concealed on merchandise being carried through
the space, is activated by the energy field. During the time
interval when the energy field is cut off, the decaying electric
signal from the tuned resonant circuit is radiated to a receiver.
The received electric signal functions to activate an alarm.
Inventors: |
Thompson; Thomas F. (Eugene,
OR), Griffith; Joseph W. (Portland, OR) |
Family
ID: |
22498659 |
Appl.
No.: |
05/142,132 |
Filed: |
May 11, 1971 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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879080 |
Nov 24, 1969 |
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797053 |
Feb 6, 1969 |
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Current U.S.
Class: |
340/572.3;
324/67; 334/39; 340/572.5 |
Current CPC
Class: |
G08B
13/2471 (20130101); G08B 13/2477 (20130101); G08B
13/2414 (20130101) |
Current International
Class: |
G08B
13/24 (20060101); G08b 013/24 () |
Field of
Search: |
;340/280,258D,258B,258C,408,224,152T ;325/29,8 ;128/2.1A
;343/6.8R |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Yusko; Donald J.
Assistant Examiner: Swann, III; Glen R.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATION
This application is a continuation-in-part of the earlier filed
application Ser. No. 879,080 filed Nov. 24, 1969 and now abandoned
which, in turn, was a continuation-in-part of the earlier filed
application Ser. No. 797,053, filed Feb. 6, 1969 and now abandoned.
Claims
Having now described our invention and the manner in which it may
be used, we claim:
1. Apparatus for activating an electric circuit, comprising
a. resonant electrical energy absorbing and radiating means tuned
to a predetermined frequency and operable upon cut-off of an
electric energy field in which it is located to radiate a decaying
electric signal at its tuned frequency,
b. a radio frequency transmitter and a source of intermittent
electric potential connected to the transmitter for intermittently
activating the latter for producing an intermittent electric energy
field in a predetermined space through which the energy absorbing
and radiating means may pass, the transmitter being characterized
by having no residual stored energy after a time, following cut-off
of the energy field, less than the decay time of the decaying
signal,
c. electric signal detector means responsive only to said decaying
electric signal to produce an electric output signal, the detector
means being characterized by having no residual stored energy after
a time, following cut-off of the energy field, less than the decay
time of said decaying signal, and
d. means for connecting said output signal to an electric circuit
to be activated.
2. The apparatus of claim 1 wherein the resonant electrical energy
absorbing and radiating means comprises a passive LC tuned resonant
circuit.
3. The apparatus of claim 2 wherein the tuned resonant circuit is
confined between sheets of dielectric material forming a flat
laminated tag.
4. The apparatus of claim 2 wherein the tuned resonant circuit
comprises two inductively coupled tuned resonant circuits, one
tuned to the frequency of the detector means and the other tuned to
a different frequency, and wherein the transmitter produces a radio
frequency signal tuned to the same frequency as said other tuned
circuit.
5. The apparatus of claim 1 for activating an electric circuit for
detecting stolen merchandise, wherein the resonant electrical
energy absorbing and radiating means is attached to the
merchandise.
6. The apparatus of claim 1 wherein the radio frequency transmitter
includes an oscillator having a reference electrode controlled by
low impedance resonant means tuned to a predetermined frequency,
and energy absorbing means is associated with the resonant means
for reducing its effective Q.
7. The apparatus of claim 6 wherein the resonant means comprises a
series tuned LC circuit, and the energy absorbing means comprises
resistance means arranged in shunt with the inductance of said LC
circuit.
8. The apparatus of claim 1 including electric timing signal means
interconnecting the radio frequency transmitter and the detector
means and operable to render the detector means incapable of
producing said output electric signal when the transmitter is
turned on.
9. The apparatus of claim 1 wherein the radio frequency transmitter
is tuned to the same frequency as the energy absorbing and
radiating means, and the apparatus includes timer means
synchronizing the transmitter and detector means for activating the
detector means only during the time said transmitter is cut
off.
10. The apparatus of claim 1 wherein the electric signal detector
means includes an amplifier having a reference electrode controlled
by low impedance resonant means tuned to the frequency of the
decaying signal of the resonant electrical energy absorbing and
radiating means, and energy absorbing means is associated with the
resonant means for reducing its effective Q.
11. The apparatus of claim 10 wherein the resonant means comprises
a series tuned LC circuit, and the energy absorbing means comprises
resistance means arranged in shunt with the inductance of said LC
circuit.
12. The apparatus of claim 1 wherein the radio frequency
transmitter has a cut-off time equal to about one-half cycle of the
resonant frequency of the energy absorbing and radiating means.
13. Apparatus for activating an electric circuit, comprising:
a. a loop of electrically conductive material forming a passive LC
circuit, a portion of the loop comprising a material of lower
melting point capable of being melted under the influence of a
current density field, the LC circuit being tuned to a
predetermined frequency and operable upon cut-off of an electric
energy field in which it is located to radiate a decaying electric
signal at its tuned frequency,
b. electric field generating means for producing an intermittent
electric energy field in a predetermined space through which the LC
tuned resonant circuit may pass, the generating means being
characterized by having no residual stored energy after a time,
following cut-off of the energy field, less than the decay time of
said decaying signal,
c. electric signal detector means responsive only to said decaying
electric signal to produce an electric output signal, the detector
means being characterized by having a residual stored energy after
a time, following cut-off of the energy field, less than the decay
time of said decaying signal, and
d. means for connecting said output signal to an electric circuit
to be activated.
14. The apparatus of claim 13 wherein the lower melting material
divides the loop into a closed loop portion and an open loop
portion which defines the LC circuit.
15. The apparatus of claim 13 including means producing a current
density field capable of melting said material of lower melting
point.
16. Apparatus for activating an electric circuit, comprising:
a. resonant electrical energy absorbing and radiating means tuned
to a predetermined frequency and operable upon cut-off of an
electric energy field in which it is located to radiate a decaying
electric signal at its tuned frequency,
b. electric field generating means comprising a pair of spaced
electrostatic plates and a source of intermittent electric
potential connected to the plates for intermittently charging the
plates in opposite polarities, for producing an intermittent
electric energy field in a predetermined space through which the
energy absorbing and radiating means may pass, the generating means
being characterized by having no residual stored energy after a
time, following cut-off of the energy field, less than the decay
time of said decaying signal,
c. electric signal detector means responsive only to said decaying
electric signal to produce an electric output signal, the detector
means being characterized by having no residual stored energy after
a time, following cut-off of the energy field, less than the decay
time of said decaying signal, and
d. means for connecting said output signal to an electric circuit
to be activated.
17. The apparatus of claim 16 including electric shorting switch
means connected across the plates and operable to interconnect the
plates when the latter are not being charged, whereby to accelerate
discharge of the plates and collapsing of the electrostatic
field.
18. Apparatus of activating an electric circuit, comprising:
a. resonant electrical energy absorbing a radiating means tuned to
a predetermined frequency and operable upon cut-off of an electric
energy field in which it is located to radiate a decaying electric
signal at its tuned frequency,
b. electric field generating means for producing an intermittent
electrostatic field in a predetermined space through which the
energy absorbing and radiating means may pass, the electrostatic
field having a collapse time of about one-half cycle of the
resonant frequency of the energy absorbing and radiating means, the
generating means being characterized by having no residual stored
energy after a time, following cut-off of the energy field, less
than the decay time of said decaying signal,
c. electric signal detector means responsive only to said decaying
electric signal to produce an electric output signal, the detector
means being characterized by having no residual stored energy after
a time, following cut-off of the energy field, less than the decay
time of said decaying signal,
d. means for activating the detector means only during the time
said field is cut off, and
e. means for connecting said output signal to an electric circuit
to be activated.
19. Apparatus for activating an electric circuit, comprising:
a. resonant electrical energy absorbing and radiating means tuned
to a predetermined frequency and operable upon cut-off of an
electric energy field in which it is located to radiate a decaying
electric signal at its tuned frequency,
b. electric field generating means comprising a pair of spaced
electromagnetic coils and a source of intermittent electric
potential connected to the coils for intermittently energizing said
coils, for producing an intermittent electric energy field in a
predetermined space through which the energy absorbing and
radiating means may pass, the generating means being characterized
by having no residual stored energy after a time, following cut off
of the energy field, less than the decay time of said decaying
signal,
c. electric signal detector means responsive only to said decaying
electric signal to produce an electric output signal, the detector
means being characterized by having no residual stored energy after
a time, following cut-off of the energy field, less than the decay
time of said decaying signal, and
d. means for connecting output signal to an electric circuit to be
activated.
20. The method of actuating an electric circuit for detecting
stolen merchandise, comprising:
a. producing an intermittent electric energy field in a
predetermined space through which customers are required to
pass,
b. attaching to said merchandise for introduction into said space a
resonant electrical energy absorbing and radiating device tuned to
a predetermined frequency and operable upon cut-off of said field
to radiate a decaying electric signal at its tuned frequency,
c. cutting off said energy field in a time less than the decay time
of said decaying electric signal,
d. detecting only said decaying electric signal to produce an
output electric signal,
e. utilizing said output electric signal to actuate an electric
circuit, and
f. subjecting the energy absorbing and radiating device to a
radiant energy field sufficient to destroy its resonating
characteristics prior to passage of the merchandise through said
space, when said merchandise has been purchased by a customer.
Description
BACKGROUND OF THE INVENTION
This invention relates to the actuation of electric circuits, and
more particularly to a novel method and apparatus for actuating an
electric circuit from a remote position. Specially, this invention
relates to a method and apparatus for detecting stolen
merchandise.
Various methods and devices have been employed heretofore to effect
actuation of an electric circuit from a remote position. Among
these is the method and apparatus disclosed in applicant's earlier
U.S. Pat. No. 2,774,060 over which the present invention represents
an improvement. The method and apparatus of applicant's earlier
patent has many functions, including the detection of stolen
merchandise, and involves the use of a tuned resonant circuit
which, when placed in the field of an oscillator causes the
oscillator to produce a change in potential which may be utilized
to actuate an electric circuit.
Although apparatus of the type disclosed in applicant's earlier
patent is quite effective for the purposes intended, its
effectiveness is somewhat limited by the shielding effects of
extraneous objects placed in proximity to the tuned circuit,
thereby limiting the effective range of operation of the
apparatus.
Other methods and devices of the class described are generally
characterized by being operable with a multiplicity of magnetic or
electrically conductive objects of various shapes and sizes.
Although such methods and apparatus may find utility in the
actuation of certain types of electric circuits, they are of no
value for the purpose of detecting stolen merchandise.
SUMMARY OF THE INVENTION
In its basic concept the present invention involves the activation
of a tuned electric energy absorbing and radiating device by an
intermittently generated field of electrostatic, electromagnetic or
radio frequency radiant energy, whereby when the energy field is
cut off the decaying electric signal from the tuned device is
radiated to a receiver. The receiver electric signal functions to
activate an electric circuit.
It is by virtue of the foregoing basic concept that the principal
objective of the present invention is achieved, namely to overcome
the disadvantages of prior methods and apparatus as described
hereinbefore.
Another important object of the present invention is to provide
apparatus of the class described in which the tuned device is a
passive tuned resonant LC circuit in which means is provided for
disabling the tuned resonant circuit after it has served its
purpose.
A further important object of this invention is the provision of a
novel tuned resonant circuit construction for use with the method
and apparatus.
The foregoing and other objects and advantages of the present
invention will appear from the following detailed description,
taken in connection with the accompanying drawings of the preferred
embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic electrical diagram, partly in block form,
illustrating the method and one form of apparatus of the present
invention.
FIG. 2 is a graphic representation of a plurality of waveforms of
electric signals illustrating the operation of the apparatus of
FIG. 1.
FIG. 3 is a plan view of a merchandise tag having concealed
therein, and illustrated by broken lines, a tuned resonant circuit
embodying features of the present invention.
FIG. 4 is a fragmentary sectional view on a magnified scale taken
on the line 4--4 in FIG. 3.
FIG. 5 is a schematic representation of means for disabling the
tuned resonant circuit illustrated in FIGS. 3 and 4.
FIG. 6 is a schematic electrical diagram, partly in block form,
illustrating the method and a second form of apparatus of the
present invention.
FIG. 7 is a graphic representation of a plurality of waveforms of
electric signals illustrating the operation of the apparatus of
FIG. 6.
FIG. 8 is a schematic electrical diagram, partly in block form,
illustrating the method and a third form of apparatus of the
present invention.
FIG. 9 is a schematic electrical diagram, partly in block form,
illustrating a still further modified form of apparatus embodying
the features of this invention.
FIG. 10 is a plan view of an identification card having
incorporated therewith means by which to activate the apparatus
shown in FIG. 9.
FIG. 11 is a schematic diagram of another form of tuned resonant
circuit concealed in a tag illustrated by broken lines and
embodying features of this invention.
FIGS. 12 and 13 are schematic representations of further modified
forms of tuned resonant circuits embodying features of this
invention.
FIG. 14 is a schematic electrical diagram, partly in block form,
illustrating a still further modified form of apparatus embodying
the features of this invention.
FIG. 15 is a schematic electrical diagram in block form
illustrating a modification of the receiving component of the
apparatus of FIG. 14.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring first to FIG. 1 of the drawings there is illustrated a
pair of electrically conductive plates 10 and 12. These plates are
separated a distance sufficient to define a space between them
operable to receive at least one energy absorbing and radiating
device, such as tuned resonant circuit 14. Thus, the plates may be
spaced apart on opposite sides of a conveyor on which merchandise
may travel. The spacing between plates alternatively may define an
aisle in a department store or the like through which the customers
must pass. As a still further alternative, the plates may be
positioned adjacent the opposite walls of a room, whereby to
activate all of the tuned resonant circuits carried by articles of
merchandise contained in the room.
One of the plates 10 is connected to the positive terminal of a
source 16 of direct current. The negative terminal of the source is
connected to the plate of the switching tube 18, the cathode of
which is grounded. The control grid of the tube is connected
through the capacitor 20 to the output of the clipper circuit 22,
many types of which are well known in the art. The input of the
clipper circuit is connected across the secondary winding 24 of the
transformer 26. One end of this secondary winding is connected to
ground. The primary winding 28 is connected to a source of
alternating current, conveniently the 60 cycle, 110 volt
conventional household source.
The other electrostatic plate 12 is connected to the negative
terminal of the source 30 of direct current. The positive terminal
of the supply source is connected to the cathode of the switching
tube 32, the plate of which is connected to ground. The control
grid of the tube is connected through the capacitor 34 to the
output of the clipper circuit 36 the input of which is connected
across the ungrounded secondary winding 38 of the transformer
26.
The positive electrostatic plate 10 also is connected to the plate
of the switching tube 40. The negative plate 12 is connected
through the adjustable potentiometer 42 to the cathode of the
switching tube 40. This cathode also is connected to one terminal
of the source 44 of direct current. The other terminal of the
supply source and the control grid of the switching tube 40 are
connected through the capacitor 46 to the output of the clipper
circuit 48. Although one clipper circuit may be sufficient, it is
preferred that two or more clipper circuits be employed to provide
the desired signal waveform described hereinafter. Thus, the input
of the clipper circuit 48 is connected to the output of the
associated clipper circuit 50 the input of which is connected
across the secondary winding 52 of the transformer 26. The grounded
end of this winding is the same as that of winding 24.
The secondary winding 54 of the transformer 26 is connected across
the input of the clipper circuit 56 the output of which is
connected to the radio frequency receiver 58 to effect activation
of the latter. For example, the clipper output may be connected to
provide bias voltage for the first r.f. stage of the receiver. The
receiver antenna 60 functions to receive a corresponding radio
frequency signal from a tuned resonant circuit 14, as described
hereinafter, whereby to activate an alarm L or other electric load
connected to an appropriate output of the receiver. For example,
the load may be in an electric circuit controlled by a relay, the
coil of which is connected through a rectifier to the output of the
i.f. stage of the receiver.
Although the resonant circuit 14 may be provided in a variety of
forms well known in the art, the construction illustrated in FIGS.
3 and 4 is preferred. In this construction the resonant circuit is
concealed between laminated sheets 62 and 64 of paper, or other
electrically non-conductive material, as follows: On the inside
face of one sheet 62 there is formed an open loop 66 of
electrically conductive metal such as copper, silver, etc. This may
be provided by the well known technique of printed circuitry. On
the inner side of the other sheet 64 there is similarly formed an
arcuate segment 68 of the electrically conductive material. This
segment is positioned on the sheet so that when the latter is
superimposed over the first mentioned sheet 62, the arcuate segment
68 overlaps one end portion of the open loop 66. Interposed between
these overlapped portions is a film 70 of electrical insulation
material. This may be provided in the form of a small plate bonded
to one of the overlapping portions, or it may be in the form of a
liquid material, such as thermoplastic resin, painted or otherwise
deposited over the surface of one of the overlapping portions.
The arcuate segment 68 of electrically conductive material may be
of sufficient length to overlap the opposite end of the open loop
66 to provide electrical conductivity therebetween when the two
sheets are bonded together in superimposed relation. However, in
the embodiment illustrated, the arcuate segment terminates short of
the opposite end of the loop and electrical connection is provided
by a length of lead or other electrically conductive fusible
material 72. This length of fusible material preferably is of small
cross section, such as a thread, and it may be formed as an
extension of the arcuate segment, as illustrated, or as an
extension of the opposite end of the open loop. In either case it
functions as a fusible electrical connection between the arcuate
segment and the end of the open loop opposite the overlapped
portions.
The fusible connection serves the additional function of enabling
the destruction of the tuned resonant circuit after it has served
its purpose. Thus, referring to FIG. 5, when it is desired to
destroy the tuned circuit it is placed in the field of the output
coil 74 of an oscillator 76 which provides sufficient current to
melt the fusible connection.
The L-C tuned circuit 14 is designed to provide a Q factor of
sufficient magnitude as to effect appropriate activation of the
receiver output circuit. Although the Q factor may vary over a
considerable range, depending in part upon the sensitivity of the
receiver, a Q factor of about 80 is satisfactory. Improvement of
the Q factor of the tuned circuit may be achieved by depositing
particles 78 (FIG. 3) of polyiron or other suitable material within
the loop 66 prior to bonding the two sheets 62 and 64 together.
Having formed the segments 66 and 68 of the tuned circuit on the
inner surfaces of the sheets, the latter are bonded together in
superimposed relation, by means of a suitable adhesive, with the
overlapped portions properly oriented and with the insulating layer
70 between them. The completed tag is thin and flexible and may be
used in the manner of a conventional price tag upon which
appropriate pricing information may be printed.
The dimensions of the tuned circuit, and hence of the confining
tag, may be varied over a considerable range, as desired. For
example, the tuned circuit may be designed to have a resonant
frequency of 10 megacycles, whereby the diameter of the loop will
be about one-half inch. This may provide a tag of about
three-quarters inch square.
The resonant frequency of the tuned circuit also may be selected
from a wide range of radio frequencies most suitable for the use
intended. The lower the frequency the larger the dimensions of the
tuned circuit becomes but the lesser are the shielding effects
imposed by extraneous objects. Thus, very low or very high radio
frequencies may be employed for certain uses. For use with
merchandise price tags a frequency of about 10 megacycles is quite
satisfactory, although other frequencies may be employed.
In the operation of the apparatus illustrated in FIG. 1 let it be
assumed that the electrostatic plates 10 and 12 are positioned on
opposite sides of an aisle, downstream of a cashier's counter to
which customers are directed. The receiver antenna 60 also is
positioned downstream from the cashier's counter. Let it also be
assumed that each piece of merchandise in the store has attached to
it one of the tags concealing a tuned resonant circuit 14. The tag
may be concealed within the merchandise, or it may take the form of
a price tag attached in a visible place to the merchandise.
As a customer passes through the aisle and completes his purchases
with the cashier, the cashier either removes the tag from each
piece of merchandise, or subjects the tuned circuit 14 to
destruction by placing it in the field of the oscillator coil 74.
Conveniently, this coil may be placed under the surface of the
cashier's counter so that the tuned circuit will be destroyed
merely by placing the merchandise on the counter. In either case
the customer then may exit along the aisle between the
electrostatic plates 10 and 12 and past the receiver antenna 60
without incident.
Assume now that a person has concealed an article of merchandise
with the intent of stealing it. Having completed his purchase of
other articles at the cashier counter, he proceeds to exit from the
aisle by passing between the plates 10 and 12 and by the receiver
antenna 60. The apparatus then operates as follows:
The electrostatic plates 10 and 12 are charged positively and
negatively, respectively, as indicated in FIG. 1, on an
intermittent time cycle determined by the frequency of the
alternating current supply to the primary winding 28 of the
transformer. The waveform 80 (FIG. 2) illustrates the in-phase
outputs of the clipper circuits 22 and 36, and when the voltage
reaches the level indicated by the dash line 82 the switching tubes
18 and 32 are caused to conduct. Such conduction functions to
complete the electric circuits of the direct current supply sources
16 and 30, whereby to apply the corresponding charges to the plates
10 and 12. The time interval T.sub.1 of conduction of the switching
tubes is governed by the frequency of the alternating current
supply at the primary winding, and this conveniently may be 60
cycles per second as mentioned hereinbefore.
The waveform 84 represents the output of the final clipper unit 48.
This waveform is in phase opposition to waveform 80 by virtue of
the opposed ground connections of windings 24 and 52. When the
potential reaches the level indicated by the dash line 86 the
switching tube 40 is caused to conduct. Conduction of this tube
functions to provide an electrical short between the plates 10 and
12, thereby accelerating their discharge and collapse of the
electrostatic field. The potentiometer 42 is adjusted to provide
complete collapse of the electrostatic field in the time interval
T.sub.2 between cutoff of conduction of the switching tubes 18, 32
and the attainment of maximum conduction of the switching tube 40.
This time interval is chosen to represent one-half cycle of the
resonant frequency of the tuned circuit 14.
The waveform 88 represents the output of the clipper 56. This
waveform is in phase with waveform 84. When the potential reaches
the level indicated by the dash line 90 the receiver 58 is
activated. The time interval T.sub.3 between conduction of the
switching tube 40 and activation of the receiver provides
sufficient time delay to insure against reception by the receiver
of false signals due to collapsing of the electrostatic field and
to insure reception by the receiver only of the signal radiated by
the tuned circuit 14.
The damped waveform 92 represents the decaying radio frequency
signal radiated by the tuned circuit. The decay of this signal
commences upon complete collapse of the electrostatic field and,
depending upon the Q factor of the tuned circuit, continues for a
time T.sub.4 following activation of the receiver. The decaying
signal following activation of the receiver activates the output
circuit of the receiver to provide an electric signal to activate
the alarm L. The alarm may be in the form of a lamp, a buzzer, a
camera actuator and/or any other device suitable for the purpose
intended.
Referring now to the embodiment illustrated in FIG. 6: The pair of
electrostatic plates 10 and 12 previously described are replaced by
electrically conductive coils 100 and 102 to provide an
electromagnetic field between them. In the preferred embodiment
illustrated, each of the coils of the pair consists of two or more
coils connected together in parallel to provide a very low Q
factor.
In manner similar to the electrostatic plates, the pair of coils
are spaced apart to define between them a space in which one or
more tuned resonant circuits 14 may be placed for excitation on an
intermittent cycle.
The coils are connected at one end to ground and at the other end
to one terminal of a source 104 of direct current. The other
terminal of the supply source is connected to the plate of the
switching tube 106. The control grid of the tube is connected
through the capacitor 108 to the output of the clipper circuit 110.
The input of the clipper unit is connected across the secondary
winding 112 of the transformer 114 the primary winding 116 of which
is connected to a suitable source of alternating current as, for
example, conventional 60 cycle household current.
The other secondary winding 118 of the transformer is connected
across the input of the clipper circuit 120 the output of which is
connected to the receiver 122 for activating the latter on an
intermittent cycle, 180.degree. out of the phase with activation of
the switching tube 106. As in the embodiment previously described,
this is achieved by grounding the secondary windings 112 and 118 at
opposite ends, as illustrated. The antenna 124 of the receiver
functions to receive the signal radiated by the tuned resonant
circuit 14 to effect activation of an alarm L.
Referring now to FIG. 7, the waveform 130 represents the output of
the clipper circuit 110. When the potential reaches the level
indicated by the dash line 132, the switching tube 106 is caused to
conduct, thereby completing the electric circuit of the direct
current supply 104 and energizing the coils 100 and 102 for the
time interval T.sub.5 of conduction. The waveform 134 represents
the output of the clipper circuit 120. When the potential reaches
the level indicated by the dash line 136, the receiver 122 is
activated for the time interval T.sub.6. The interval T.sub.7 of
time between cutoff of conduction of the switching tube 106 and
activation of the receiver 122 provides sufficient time delay to
insure complete collapse of the electromagnetic field and thus
insure reception by the receiver only of the decaying signal 92
radiated by the tuned circuit 14, as explained hereinbefore.
In the embodiment illustrated in FIG. 8 the electrostatic plates of
FIG. 1 and the electromagnetic coils of FIG. 6 are replaced by
transmitter and receiver antennas 140 and 142, respectively, spaced
apart sufficiently to provide the desired energy field for
activating one or more tuned resonant circuits 14. The transmitting
antenna is associated with a transmitter 144, the input of which is
connected to the output of the clipper circuit 146. The input of
the clipper circuit is connected across the secondary winding 148
of the transformer 150, the primary winding 152 of which is
connected to a suitable source of electric potential, as explained
hereinbefore. The receiving antenna 142 is associated with a
receiver 154 the input of which is connected to the output of the
clipper circuit 156 having its input connected across the secondary
winding 158 of the transformer 150. As in the previous embodiments,
these transformer secondary windings are grounded at opposite ends
so that the output waveforms from the clipper circuits activate the
transmitter and receiver during different portions of the cycle,
substantially in the manner illustrated by the waveforms of FIG. 7.
Accordingly, a portion of the decaying signal 92 radiated by the
tuned circuit 14 after the transmitter has been cut off is received
by the receiver to activate an alarm L. It will be understood that
the transmitter and the receiver are designed to operate on the
same frequency as the resonant frequency of the tuned circuit
14.
FIG. 9 illustrates a further modified form of apparatus wherein
three receivers 160, 162 and 164 each are tuned to a different
frequency for association with a correspondingly tuned resonant
circuit 166, 168 and 170, respectively, as is illustrated on the
card 172 in FIG. 10. The outputs of the receivers are connected one
to each of the relay coils 174, 176 and 178, respectively, the
switch contacts 180, 182 and 184 of which are arranged in series in
the electric circuit of a device L to be actuated. Accordingly, it
will be apparent that in order to actuate the device all three
tuned circuits must be present at one instant within the field of
the antennas of the three receivers.
The apparatus of FIG. 9 may be employed for the detection of stolen
merchandise, as well as for many other purposes. For example, it
may be adapted for use in actuating a door lock, such as in private
clubs, defense plants, parking lots and various other places where
privacy or secrecy is to be maintained. For this purpose each
person authorized to enter a restricted area is provided with an
identification card or membership card, such as the card 172
illustrated in FIG. 10. As a matter of additional security, such
cards may be changed from time to time to add or subtract tuned
circuits, or to change the frequency characteristics thereof, in
order to render previously issued cards obsolete. It will be
understood, of course, that the receivers also will be adjusted to
correspond to the frequencies of the tuned circuits in the newly
issued cards.
In the embodiments previously described both the source of electric
energy field and the receiver necessarily must have the
characteristic that once they are turned off they must have no
residual stored energy during the time of radiation of the decaying
signal from the tuned circuit 14 or other energy absorbing and
radiating device. Further, the source of intermittent electrical
energy field must have the characteristic of cutting off in a time
substantially less than the time during which the decaying signal
is being radiated. The embodiments of FIGS. 14 and 15 illustrate
specific apparatus providing these characteristics.
Referring first to FIG. 14, the transistor 220 and transformer 222
represent an oscillator. One winding 224 of the transformer is
connected to the transmitting antenna 226, a second winding 228
connects a source of direct current potential to the collector of
the transistor, and the third winding 230 connects the base of the
transistor to a source 232 of electric timing signals through an
amplifier 234 and bias circuit 236. The timing signals may be
provided by means of a conventional pulse generator, or other well
known form of device providing timing signals, in the manner of the
transformer and clipper arrangement described hereinbefore.
The desired frequency of oscillation of the transmitter is
established by providing a tuned reference electrode. In the
embodiment illustrated this is provided by a low impedance resonant
device 238 in the form of the series arrangement of inductor 240
and capacitor 242 connecting the transistor emitter to ground. The
inductor and/or capacitor are adjustable in order to establish the
desired frequency of transmission providing the intermittent
electric energy field.
Means is provided for insuring that the transmitter will be cutoff
in a time substantially less than the time during which the
decaying signal of the energy absorbing and radiating device 14 is
being radiated. For this purpose, the capacitor 242 or, preferably,
the inductor 240 is shunted by a resistor 244 of an appropriate
value capable of reducing the effective Q of the series tuned
circuit, i.e., reducing the energy storing capability of the
inductor to a very low value. In this regard, at all frequencies
other than that determined by the LC circuit, the impedance of the
emitter circuit is high and therefore it has a high degenerative
capability for all such other frequencies. However, at the
frequency established by the LC circuit, the series impedance is
low and the emitter is essentially at ground potential.
Accordingly, any signal appearing on the base of transistor, by
virtue of the transformer, becomes amplified.
In a typical application, the direct current resistance of the
inductor 240 is, for example about 0.1 ohm, but at a frequency of
for example 150 megacycles it is about 10,000 ohms, and the series
tuned impedance of the LC circuit at the resonant frequency is
about 0.1 ohm. A shunting resistor 244 of about 200 ohms provides
satisfactory results.
Means other than the shunting resistor 244, such as a ferrite bead,
may be associated with the LC circuit for absorbing energy from the
circuit and thereby reducing its effective Q.
The source of intermittent electric energy field may be obtained by
means other than the transmitter previously described. For example,
it may be a pulse transmitter providing a single spike of energy,
or a saturable reactor, or any other type of device providing the
amplification and phase shift requirements for an oscillator.
The LC circuit previously described is but one of many other
suitable forms of series tuned devices capable of use for purposes
of this invention. Crystals, mechanical filters and other low
impedance resonant devices are examples. In any event, the source
of intermittent electric energy field must be characterized by the
absence of residual stored energy when turned off, as previously
explained.
The receiver component of the apparatus illustrated in FIG. 14 is a
selective energy detector synchronized with the operation of the
transmitter by means of timing signals from the timer 232. These
signals are fed through a bias circuit 246 and the winding 248 of
an untuned transformer 250 of a receiving antenna 252, to the base
of amplifier transistor 254. The emitter of the transistor is
connected to ground through a low impedance resonant device 256,
again in the form of the series arrangement of inductor 258 and
capacitor 260, in manner similar to the series tuned LC circuit
previously described, with the inductor being shunted by the
resistor 262. Thus, the low impedance series tuned LC circuit
functions as part of the reference for the receiver amplifier at
all frequencies other than the frequency established by the LC
circuit. At this selected frequency, which is the same as the
frequency of the decaying signal from the energy absorbing and
radiating device, the emitter is held at a particular potential and
therefore any signal of that selected frequency appearing at the
base or control electrode is amplified.
Thus, the receiver component also is characterized by having no
residual stored energy after a time, following cut-off of the
energy field, substantially less than the decay time of the energy
absorbing and radiating device 14.
The output signal from the receiver component may be utilized in
any manner desired. In the embodiment illustrated, this output
signal is applied to a Schmidt trigger circuit 264, silicone
controlled rectifier, or other suitable device, the output of which
functions to activate an alarm 266.
It will be apparent that the transistors previously described may
be replaced by vacuum tubes, if desired. For example, the plate of
a vacuum tube may be connected through the transformer winding 228
to a source of direct current potential, the control grid may be
connected to the transformer winding 230 through the parallel
arrangement of a capacitor and resistor, and the cathode may be
connected to ground through the series tuned reference device
238.
With reference to the synchronized wave forms illustrated in FIG.
14, it will be understood that while the transmitter is turned on,
by virtue of the positive timing signals 268, the receiver
component is turned off by virtue of the negative timing signals
270. Similarly, after the transmitter has been turned off, during
the interval between adjacent signals 268, the receiver component
is turned on by the positive signals 272 for receiving the decaying
signal radiating from the energy absorbing and radiating
device.
Although the passive tuned resonant LC circuit 14 described
hereinbefore is the preferred form of energy absorbing and
radiating device, because of its simplicity, economy and capability
of being provided in the form of a substantially two dimensional
tag, it will be understood that other forms of energy absorbing and
radiating devices may be employed for applications in which the
foregoing advantages are not required.
In the receiver component illustrated in FIG. 14, there is shown a
capacitor 274 across the antenna transformer winding 248. This
capacitor may be a physical element, or it may represent stray
capacitance. In any event, it is desirable to shunt the winding
with a resistor 276 in order to spoil the Q of the tuned circuit,
in order for the receiver to have no residual stored energy, as
previously explained.
FIG. 15 illustrates a modified form of receiver component for use
in the apparatus of FIG. 14. As in the previous embodiment, the
receiver includes an untuned high impedance amplifier 278 connected
to the receiving antenna 252 and having its reference electrode
connected to ground through a low impedance resonant reference
device 256. However, the output of the amplifier is fed to a
coincidence gate 280, forming a part of the receiver, to which also
is fed the timing signals from the timer 232. These timing signals
function to operate the gate synthronously with the transmitter so
as to select between the transmitter signal from the transmitter
antenna 226 and the decaying signals from the energy absorbing and
radiating device 14. Thus, during the time that the transmitter is
on the timing signals to the coincidence gate disables the latter
so that the transmitter signal received by the receiving antenna
252 and amplified by the amplifier, are not passed through to the
Schmidt trigger 264 to cause activation of the alarm 266. However,
during the time the transmitter is shut off, the timing signals
function to enable the gate 280 to pass through to the Schmidt
trigger the amplified decaying signal received by the receiving
antenna 252 from the energy absorbing and radiating device 14.
As an alternative, through less efficient and therefore less
desirable procedure by which to provide a conventional receiver
with the characteristic of having no residual stored energy, means
such as a diode or other electrically actuated switch may be
arranged to shunt or open a tuned resonant antenna circuit, as by
timing signals, during the period of time that the transmitter is
turned on.
FIG. 11 illustrates another form of tuned resonant circuit usable
with the various forms of apparatus described hereinbefore. In this
embodiment two tuned resonant circuits are arranged to be
inductively coupled to each other and preferably concealed in a tag
200 as in the manner previously described. Each tuned circuit may
be constructed in the manner of the tuned circuit illustrated in
FIGS. 3 and 4. One of the tuned circuits comprises an open loop of
electrically conductive metal forming coil 202 and capacitance 204.
When employed with the apparatus of FIG. 8, it is tuned to the
frequency of the transmitter 144. The other tuned circuit comprises
an open loop forming coil 206 and capacitance 208 and it is tuned
to the frequency of the receiver 154 which, for this purpose, is
different from the frequency of the transmitter. Although these
frequencies may be harmonics, it is preferred that they not be, so
as to insure against possible erroneous activation of the
receiver.
It is well known that when the tuned circuit 202, 204 is activated
to oscillation, the closely coupled circuit 206, 208 will oscillate
at the same frequency as the tuned circuit 202, 204. Then, if the
flux energizing the circuit 202, 204 is cut off, both resonant
circuits 202, 204 and 206, 208 will oscillate with a decaying wave
at their own natural frequencies.
Accordingly, let it be assumed for purpose of explanation that the
transmitter 144 and tuned circuit 202, 204 are tuned to the
frequency of 100 megacycles and that the receiver and tuned circuit
206, 208 are tuned to a frequency of 120 megacycles. Thus, when the
tag 200 is placed in the radiation field of the transmitter antenna
140 and the tuned circuit 202, 204 is excited during the time that
the transmitter 144 is energized, the tuned circuit 206, 208 also
will oscillate at the frequency of 100 megacycles. Then, when the
transmitter 144 is cut off, by operation of the clipper 146, the
tuned circuit 202, 204 will transmit a damped wave at 100
megacycles and the tuned circuit 206,208 will transmit a damped
wave at its natural frequency of 120 megacycles. Since the receiver
154 is tuned to the frequency of 120 megacycles, it will receive
only the damped wave from the tuned circuit 206, 208.
Since the receiver 154 receives only the damped wave transmitted by
the tuned circuit 206, 208 and is not activated by the transmitter
144 or tuned circuit 202, 204, it will be apparent that the
receiver may be operated continuously. Accordingly, the clipper
circuit 156 in FIG. 8 may be omitted.
When the tuned resonant circuit of FIG. 11 is employed with the
type of apparatus illustrated in FIGS. 1 and 6, it is necessary
merely that the time of complete collapse of the electromagnetic or
electrostatic field be adjusted, as by a potentiometer 42 in FIG.
1, to one-half cycle of the resonant frequency of the tuned circuit
202, 204. Thus, during the time interval that the energy field is
being radiated, both tuned circuits 202, 204, and 206, 208 resonate
at the frequency of the circuit 202, 204. When the energy field is
cut off, both tuned circuits resonate at their own frequencies and
therefore the damped wave from tuned circuit 206, 208 is radiated
for reception by the receiver, which may be operated
continuously.
In this latter regard, it will be understood that since the tuned
resonant circuit 14 is activated by the apparatus of FIGS. 1 and 6
by adjusting the field collapse time to substantially one-half
cycle of the resonant frequency of the tuned circuit 14, it is
desirable that the associated receiver 58 or 122 be activated only
during the time the field is cut off, in order to insure against
possible false activation of the receiver during collapse of the
field.
FIGS. 12 and 13 illustrate still further forms of tuned resonant
circuits which may be concealed in tags, and which are usable with
the various forms of apparatus described hereinbefore. In FIG. 12 a
printed circuit or other suitable form of electrically conductive
metal is arranged to form a pair of interconnected inductive loops
210 and 212. A length of electrically conductive fusible material
214 bridges the metal between the loops 210 and 212, whereby to
close the loop 210 and to complete the loop 212 which terminates at
its spaced-apart ends in a capacitor 216. Loop 212 and capacitor
216 thus form an L-C circuit which is arranged to resonate at the
same frequency as receiver 58, 122 or 154.
Destruction of the tuned resonant circuit is accomplished by
placing it in a strong magnetic field of, for example, conventional
60 cycle household alternating current. This causes a strong
current to flow in the closed loop 210, resulting in melting of the
fusible link 214. In this regard, since the impedance of the closed
loop 210 at 60 cycles is substantially its direct current
resistance, the current circulating in the loop is much higher, for
a given wattage, than it would be at higher frequencies.
Upon melting of the link 214 the inductance of the open loop 212 is
added to loop 210. The combination of this increased inductance
with the capacitance 216 provides a tuned circuit which resonates
at a lower frequency than previously provided by coil 212 and
capacitor 216. Thus, although the resonant circuit is destroyed
effectively for use with the receivers previously mentioned, it may
be re-used at the lower resonant frequency in association with the
similarly tuned receiver.
If it is desired to have the destroyed circuit re-usable at a
frequency higher than that of coil 212 and capacitor 216, the
arrangement illustrated in FIG. 13 may be provided. In this
embodiment the fusible link 214' is made a part of the capacitor
216. Thus, upon melting of the link the capacitance of the
capacitor 216 is lowered, whereby the resonant frequency of coil
212 and capacitor 216 is increased.
The various forms of apparatus described hereinbefore also may be
employed to control the distribution of articles on a moving
conveyor selectively to branch conveyors. For example, all articles
intended for distribution to one location may be identified by
attachment of tags having tuned circuits of the same resonant
frequency, while other articles intended for distribution to
another location may be identified with tags having tuned circuits
of a different resonant frequency. Separate receivers, each
corresponding in frequency to a different one of the tuned
circuits, thus may function to actuate appropriate equipment to
divert the articles on the main conveyor to the appropriate branch
conveyors. Such an arrangement has many practical forms of use in
commerce and industry. One such use is the selective distribution
of luggage at air terminals.
It will be apparent to those skilled in the art that various
changes may be made in the size, shape, arrangement, number, types
and values of parts described hereinbefore. For example, the number
of stages of clipper circuits may be varied to provide the waveform
characteristics desired. The clipper circuits providing the
substantially square waveforms illustrated may be replaced with
sawtooth generators to provide sawtooth waveforms, or with various
other well known circuits providing other desired waveforms. The
vacuum tube circuitry illustrated may be replaced by transistor
circuitry in well known manner.
Activation of the receiver for reception of the damped signal from
the tuned resonant circuit has been exemplified hereinbefore by
connection of the output of clipper 56 to provide bias voltage for
the first r.f. stage of the receiver. Another procedure is to
connect the clipper output to a shorting tube, in the manner of
shorting tube 40, which is connected across the input resonant
circuit of the receiver. In this case the secondary winding 54 is
grounded at its upper end, in phase opposition to winding 52, and
the receiver is operated continuously but is not activated for
reception of the tuned circuit signal except after collapse of the
electrostatic (FIG. 1), or electromagnetic (FIG. 6) field, or after
cut off of the transmitter (FIG. 8).
The foregoing and other changes may be made without departing from
the spirit of this invention.
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