US3706982A
Expired / Lapsed
US
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Intrusion detection system
Assignee: General Dynamics Corp
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Filing: 1968-07-01
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Granted: 1972-12-19
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Expires: 1988-07-01
Abstract
Abstract An electromagnetic intrusion system is disclosed wherein a sensor having single antenna radiates a sensing field when driven by two independent oscillators having frequencies offset from each other. The oscillators are closely coupled to the antenna and are effected by changes in antenna impedance as results when an object enters the sensing field so that their frequencies deviate. The response of the driving signals from each oscillator and the frequencies thereof are adjusted so that the frequency deviation or pulling of each of the oscillators is out of phase with respect to the other at the selected maximum range, whereas the frequency deviation and therefore sensitivity is dimished in the immediate vicinity of the antenna. The difference frequency is applied to a detection circuit which produces an output in the event of a shift in the differential frequency. The latter circuitry may include a local oscillator, the output of which is mixed with the frequency difference output in two channels. The output of the mixer in one channel is shifted in phase with respect to the output of the mixer in the other channel by 90* at the mixed frequency. A sampling phase detector compares the two channel frequencies and produces an error voltage which varies in polarity depending upon whether the differential frequency is lower or higher than the local oscillator frequency. This error voltage may be used to vary the local oscillator so that no error voltage is produced in the event that an object does not enter the sensing field. Upon entry of an object the error, voltage may be utilized to modulate a transmitter in accordance with a predetermined code representing the sensor. This transmitter may utilize the same antenna, as does the sensor, to transmit a coded signal to a receiving station at which it is demodulated to indicate the particular sensor, out of many, which has detected an object. Inasmuch as each sensor has a separate code, a single receiving channel at a station remote from the sensors may be used to monitor several sensors.
Inventors
- 👤 John B Gehman
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-28 17:25
CPC Classifications
G; G08; G08B; G08B13/00; G08B13/22; G08B13/26
Claims Analysis
Total Claims: 14
Claim 1
Independent Claim
206 words
A sensor system comprising a. an antenna for radiating a sensing field, b. first and second means for generating electromagnetic waves independently coupled to said antenna, the frequency of the waves generated by said first means being offset from the frequency of the waves generated by said second means, to provide a signal having a frequency equal to the frequency differential between the frequencies of said waves which deviates when an object enters said field, c. a source of signals having a frequency about equal to said offset and variable in frequency, d. a first and second frequency translation channel for respectively providing outputs corresponding to the products of (i) said frequency difference signal and said source signal and (ii) said frequency differential signal and said source signal shifted in phase with respect to said source signal, e. means responsive to the phase difference between said outputs for providing an error signal, f. means for varying the frequency of said source in accordance with said error signal in a sense to reduce said error signal, and g. means responsive to the frequency deviation of the output from one of said channels for providing a signal representing the absence or presence of said object in said field.
Claim 2
Dependent Claim
206 words
A sensor system comprising a. an antenna for radiating a sensing field, b. first and second means for generating electromagnetic waves independently coupled to said antenna, the frequency of the waves generated by said first means being offset from the frequency of the waves generated by said second means, to provide a signal having a frequency equal to the frequency differential between the frequencies of said waves which deviates when an object enters said field, c. a source of signals having a frequency about equal to said offset and variable in frequency, d. a first and second frequency translation channel for respectively providing outputs corresponding to the products of (i) said frequency difference signal and said source signal and (ii) said frequency differential signal and said source signal shifted in phase with respect to said source signal, e. means responsive to the phase difference between said outputs for providing an error signal, f. means for varying the frequency of said source in accordance with said error signal in a sense to reduce said error signal, and g. means responsive to the frequency deviation of the output from one of said channels for providing a signal representing the absence or presence of said object in said field.
Claim 3
Dependent Claim
227 words
A sensor system comprising a. an antenna for radiating a sensing field, b. first and second means for generating electromagnetic waves independently coupled to said antenna, the frequency of the waves generated by said first means being offset from the frequency of the waves generated by said second means, to provide a signal having a frequency equal to the frequency difFerential between the frequencies of said waves which deviates when an object enters said field, c. a source of signals having a frequency about equal to said offset and variable in frequency, d. a first and second frequency translation channel for respectively providing outputs corresponding to the products of (i) said frequency differential signal and said source signal and (ii) said frequency differential signal and said source signal shifted in phase with respect to said source signal, e. means responsive to the phase difference between said outputs for providing an error signal, f. means for varying the frequency of said source in accordance with said error signal in a sense to reduce said error signal, g. means coupled to said antenna for applying a signal to said antenna for transmission thereby, and h. means responsive to said error signal for modulating said last named means when said error signal is produced whereby to transmit a signal indicative of the presence of an object in said sensing field.
Claim 4
Dependent Claim
227 words
A sensor system comprising a. an antenna for radiating a sensing field, b. first and second means for generating electromagnetic waves independently coupled to said antenna, the frequency of the waves generated by said first means being offset from the frequency of the waves generated by said second means, to provide a signal having a frequency equal to the frequency difFerential between the frequencies of said waves which deviates when an object enters said field, c. a source of signals having a frequency about equal to said offset and variable in frequency, d. a first and second frequency translation channel for respectively providing outputs corresponding to the products of (i) said frequency differential signal and said source signal and (ii) said frequency differential signal and said source signal shifted in phase with respect to said source signal, e. means responsive to the phase difference between said outputs for providing an error signal, f. means for varying the frequency of said source in accordance with said error signal in a sense to reduce said error signal, g. means coupled to said antenna for applying a signal to said antenna for transmission thereby, and h. means responsive to said error signal for modulating said last named means when said error signal is produced whereby to transmit a signal indicative of the presence of an object in said sensing field.
Claim 5
Dependent Claim
85 words
The invention as set forth in claim 2 wherein said generating means are oscillators each coupled to said antenna and via said antenna to each other, and wherein the input to said channels is connected to at least one of said oscillators to derive said differential frequency signal therefrom, said channels including separate mixers, and means for applying said source signals to said mixer in said first channel and said source signal shifted in phase by about 90* to said mixer in said second channel.
Claim 6
Dependent Claim
71 words
The invention as set forth in claim 3 wherein said phase responsive means includes means responsive to said first channel output for providing pulses at one of said crossovers thereof, and a sample and hold circuit to which said second channel output is applied as one input and said pulses as sampling pulses, and integrator means responsive to the output of said sample and hold circuit for providing said error signal.
Claim 7
Dependent Claim
56 words
The invention as set forth in claim 4 wherein said error signal responsive means includes means for providing an output when the magnitude of said error signal exceeds a predetermined threshold, and a modulating circuit operated by the output of said last-named means for applying a modulating signal having a predetermined characteristic to said transmission means.
Claim 8
Dependent Claim
56 words
The invention as set forth in claim 5 wherein said system includes a plurality of sensors each including an antenna and the system elements, as set forth in claim 5, and wherein the modulating circuits associated with different ones of said antennas includes means for generating different modulating signals each coded to represent its associated sensor.
Claim 9
Dependent Claim
102 words
A sensor system comprising a. an antenna for radiating a sensing field, b. first and second means for generating electromagnetic waves at frequencies offset from each other separately coupled to said antenna, c. a primary processor responsive to a signal having a frequency equal to the differential frequency between the waves radiated by said antenna, and d. a secondary processor responsive to said differential frequency signal for providing an output when the frequency deviation of said signal exceeds a predetermined threshold and said frequency differential varies cyclically through at least one cycle for providing an output representing the detection of an object.
Claim 10
Dependent Claim
102 words
A sensor system comprising a. an antenna for radiating a sensing field, b. first and second means for generating electromagnetic waves at frequencies offset from each other separately coupled to said antenna, c. a primary processor responsive to a signal having a frequency equal to the differential frequency between the waves radiated by said antenna, and d. a secondary processor responsive to said differential frequency signal for providing an output when the frequency deviation of said signal exceeds a predetermined threshold and said frequency differential varies cyclically through at least one cycle for providing an output representing the detection of an object.
Claim 11
Dependent Claim
30 words
The invention as set forth in claim 7 further comprising a. a transmitter coupled to said antenna, and b. means responsive to said secondary processor output for modulating said transmitter.
Claim 12
Dependent Claim
76 words
The invention as set forth in claim 6 wherein said secondary processor comprises a. means responsive to said differential frequency signals for producing a first output when the frequency deviation of said differential signal exceeds a certain threshold, b. counter means for counting each half cycle of deviation of said differential frequency signal, and c. logic means for proviDing said object representing output when said counter registers a predetermined count and said first output is produced.
Claim 13
Dependent Claim
124 words
The invention as set forth in claim 9 including a. means responsive to said differential frequency signal for producing a second output when said differential frequency signal has a frequency deviation exceeding a predetermined threshold lower than said certain threshold, b. means for inhibiting said counter means from counting in the absence of said second output, c. means for resetting said counter a predetermined time period after each of said half cycles is counted, d. means for inhibiting said resetting means for a certain time after the end of said second output, and e. logic means for providing said object representing output when a second predetermined count greater than said first mentioned count is registered in said counter and said second output is produced.
Claim 14
Dependent Claim
132 words
The invention as set forth in claim 2 wherein said modulating means includes a source of signal having predetermined frequency and wherein said system includes a double conversion superheterodyne receiver for receiving the signal transmitted by said transmitting means, said receiving having first and second sources of injection signals, means for mixing the first injection signal with the received transmitted signal to produce a first signal which is the sum of a first intermediate frequency and said predetermined frequency of said source, said second injection signal having a frequency equal to said first intermediate frequency, means for mixing said second injection signal and said first signal to produce a second intermediate frequency signal corresponding to said source signal, and means responsive to said source signal for indicating the detection of an object.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1975-12-19 | 1976-06-19 | 1976-12-19 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1979-12-19 | 1980-06-19 | 1980-12-19 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1983-12-19 | 1984-06-19 | 1984-12-19 | $7700.00 | Window Closed / Lapsed |