US4476459A
Expired / Lapsed
US
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Theft detection method and apparatus in which the decay of a resonant circuit is detected
Assignee: Sentry Technology Corp
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Filing: 1981-10-23
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Granted: 1984-10-09
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Expires: 2001-10-23
Abstract
Abstract In an electronic theft detection apparatus the passage of a resonant circuit wafer 16 through an interrogation zone formed by transmitter and receiving antennas (30, 90) (32, 92) is detected by generating sharp pulses of electromagnetic energy to cause the resonant circuit wafer to resonate for a duration following each pulse. A receiver is provided with a switch (54), signal accumulators or filters (56 and 58) and a comparator (60) to sense the decay of the signal from the resonating wafer and to activate an alarm (36) when that decay occurs at a predetermined value.
Inventors
- 👤 Michael N. Cooper
- 👤 Peter A. Pokalsky
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-23 23:14
CPC Classifications
G; G08; G08B; G08B13/00; G08B13/22; G08B13/24; G08B13/2402; G08B13/2405; G08B13/2414; G08B13/2465; G08B13/2468; G08B13/2471; G08B13/2474; G08B13/2477; G08B13/2488
Claims Analysis
Total Claims: 33
Claim 1
Independent Claim
86 words
Apparatus for detecting, in an interrogation zone, an article of merchandise on which is fastened a wafer containing a resonant electrical circuit, said apparatus comprising: means for generating interrogation signals in the form of short pulses of electromagnetic field energy in said interrogation zone, said pulses being separated by intervals, means for detecting electromagnetic energy in said interrogation zone during the interval following each pulse, and means for actuating an alarm in response to a predetermined amount of variation of electromagnetic energy detected during said intervals.
Claim 2
Dependent Claim
86 words
Apparatus for detecting, in an interrogation zone, an article of merchandise on which is fastened a wafer containing a resonant electrical circuit, said apparatus comprising: means for generating interrogation signals in the form of short pulses of electromagnetic field energy in said interrogation zone, said pulses being separated by intervals, means for detecting electromagnetic energy in said interrogation zone during the interval following each pulse, and means for actuating an alarm in response to a predetermined amount of variation of electromagnetic energy detected during said intervals.
Claim 3
Dependent Claim
32 words
Apparatus according to claim 1 wherein said means for actuating an alarm comprises means responsive to the variation of detected electromagnetic field energy which occurs after a predetermined time following each pulse.
Claim 4
Dependent Claim
25 words
Apparatus according to claim 2 wherein said predetermined time is sufficient to permit transients in said generating and detecting means to subside following each pulse.
Claim 5
Dependent Claim
31 words
Apparatus according to claim 2 wherein said predetermined time is sufficient to permit electrical responses from objects other than resonant electrical circuits in said interrogation zone to subside following each pulse.
Claim 6
Dependent Claim
27 words
Apparatus according to claim 1 wherein said means for actuating an alarm comprises means for comparing the amplitudes of signals generated during different segments within each interval.
Claim 7
Dependent Claim
43 words
Apparatus according to claim 5 wherein said time segments occur after a predetermined time following each pulse to permit transients in said generating and detecting means and responses from objects other than resonant circuits in said interrogation zone to subside following each pulse.
Claim 8
Dependent Claim
47 words
Apparatus according to claim 1 wherein said means for actuating an alarm comprises means for directing signals corresponding to the detected electromagnetic field energy into different signal accumulators during different time segments in each interval and means for comparing the amplitudes of the signals in said accumulators.
Claim 9
Dependent Claim
14 words
Apparatus according to claim 7 wherein said means for directing signals includes a switch.
Claim 10
Dependent Claim
22 words
Apparatus according to claim 8 wherein said switch is operated by a timing clock which operates said means for generating interrogation signals.
Claim 11
Dependent Claim
22 words
Apparatus according to claim 9 wherein said timing clock and switch are arranged to provide two such time segments in each interval.
Claim 12
Dependent Claim
23 words
Apparatus according to claim 10 wherein said timing clock and switch are arranged such that said two time segments are adjacent each other.
Claim 13
Dependent Claim
26 words
Apparatus according to claim 7 wherein each signal accumulator is connected and arranged to accumulate detected signals during corresponding time segments in a plurality of intervals.
Claim 14
Dependent Claim
52 words
Apparatus according to claim 12 wherein said means for comparing the amplitudes of the signals in each accumulator is set to produce an output when the difference in the detected signals accumulated in said accumulators corresponds to the difference produced in several successive intervals by a resonant circuit within said interrogation zone.
Claim 15
Dependent Claim
47 words
Apparatus according to claim 1 wherein said means for detecting electromagnetic energy in said interrogation zone includes a gate, said gate being controlled by said means for generating interrogation signals to prevent said means for detecting electromagnetic energy from operating for a predetermined time following each pulse.
Claim 16
Dependent Claim
23 words
Apparatus according to claim 14 wherein said predetermined time is sufficient to permit electrical transients within said transmitting and detecting means to subside.
Claim 17
Dependent Claim
30 words
Apparatus according to claim 14 wherein said predetermined time is sufficient to permit electrical responses from other objects in said interrogation zone, not carrying a resonant electrical circuit, to subside.
Claim 18
Dependent Claim
77 words
Apparatus according to claim 1 wherein said means for generating an alarm comprises a pair of signal accumulators and an electrical switch arranged to receive detected signals from the detecting means, said electrical switch being connected to be switched by said means for generating electrical signals to direct said detected signals into one of said accumulators during a first time segment in each interval and into the other accumulator during a second time segment in each interval.
Claim 19
Dependent Claim
54 words
Apparatus according to claim 17 wherein said means for generating interrogation signals comprises a clock for generating a continuous series of pulses, a counter for producing said pulses sequentially on different output terminals, an interrogation pulse generator connected to one of said terminals, and said electrical switch being connected to others of said terminals.
Claim 20
Dependent Claim
45 words
Apparatus according to claim 18 wherein said means for detecting electromagnetic energy includes a gate connected to be opened in response to signals from a further terminal of said counter to prevent operation of said detecting means for a predetermined time following each interrogation pulse.
Claim 21
Dependent Claim
39 words
Apparatus according to claim 1 wherein said means for generating interrogation signals and said means for detecting electromagnetic energy comprise antenna means arranged on a counter top on which articles of merchandise are prepared for delivery to a customer.
Claim 22
Dependent Claim
35 words
Apparatus according to claim 20 wherein said antenna means comprises a transmitter antenna forming part of said means for generating interrogation signals and a receiver antenna forming part of said means for detecting electromagnetic energy.
Claim 23
Dependent Claim
20 words
Apparatus according to claim 21 wherein said receiver antenna is in the form of two loops wound in opposite directions.
Claim 24
Dependent Claim
44 words
Apparatus according to claim 1 wherein said means for generating interrogation signals and said means for detecting electromagnetic energy comprise antenna means arranged along an exit from a protected area in which articles of merchandise on which wafers containing a resonant circuit are fastened.
Claim 25
Independent Claim
84 words
A method for detecting, in an interrogation zone, an article of merchandise on which is fastened a wafer containing a resonant electrical circuit, said method comprising the steps of: generating interrogation signals in the form of short pulses of electromagnetic field energy in said interrogation zone, said pulses being separated by intervals, detecting electromagnetic energy is said interrogation zone during the interval following each pulse, and actuating an alarm in response to a predetermined amount of variation of electromagnetic energy detected during said intervals.
Claim 26
Independent Claim
84 words
A method for detecting, in an interrogation zone, an article of merchandise on which is fastened a wafer containing a resonant electrical circuit, said method comprising the steps of: generating interrogation signals in the form of short pulses of electromagnetic field energy in said interrogation zone, said pulses being separated by intervals, detecting electromagnetic energy is said interrogation zone during the interval following each pulse, and actuating an alarm in response to a predetermined amount of variation of electromagnetic energy detected during said intervals.
Claim 27
Dependent Claim
57 words
A method according to claim 24 wherein the step of actuating an alarm is carried out by accumulating separately signals corresponding to the detected electromagnetic field energy which occur during different time segments in each interval, comparing the amplitudes of the separately accumulated signals and actuating said alarm when a predetermined difference exists between the compared amplitudes.
Claim 28
Dependent Claim
37 words
A method according to claim 24 wherein the step of actuating an alarm is carried out in response to a predetermined amount of variation of electromagnetic energy detected after a predetermined amount of time following each pulse.
Claim 29
Dependent Claim
27 words
A method according to claim 26 wherein said predetermined amount of time is sufficient to permit electrical transients produced in the generating and detecting steps to subside.
Claim 30
Dependent Claim
33 words
A method according to claim 26 wherein said predetermined amount of time is sufficient to permit electrical responses from other objects in said interrogation zone, not carrying a resonant electrical circuit, to subside.
Claim 31
Dependent Claim
22 words
A method according to claim 24 wherein signals occuring in corresponding time segments in a plurality of intervals are accumulated and compared.
Claim 32
Dependent Claim
18 words
A method according to claim 24 wherein signals occuring in two time segments in each interval are compared.
Claim 33
Dependent Claim
15 words
A method according to claim 30 wherein said two time segments are adjacent each other.
References Cited (Backward Citations)
US2812427A
Cited
US2899546A
Cited
US2958781A
Cited
US3117277A
Cited
US3373425A
Cited
FR2033401A1
Cited
US3740742A
Cited
US3810172A
Cited
US3919704A
Cited
US3836842A
Cited
US3911534A
Cited
US4135184A
Cited
US4242671A
Cited
US4215342A
Cited
US4321586A
Cited
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| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
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| 3.5 Years (Year 4) | 1987-10-09 | 1988-04-09 | 1988-10-09 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1991-10-09 | 1992-04-09 | 1992-10-09 | $3760.00 | Window Closed / Lapsed |
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