Patent US2730379A successfully refreshed from Google Patents.
US3820103A
Expired / Lapsed
US
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System for detecting an object within a magnetic field
Assignee: STOP LOSS Inc
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Filing: 1972-12-15
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Granted: 1974-06-25
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Expires: 1992-12-15
Abstract
Abstract The specification discloses a system for detecting a marker secured to an object when the object is positioned within an interrogation zone having a magentic field periodically varying at a predetermined fundamental frequency. The magnetic field is generated by a coil unit including a plurality of loops of rigid hollow metal pipe which is electrically resonated by capacitors and energized by an electrical signal having a frequency equal to the resonant frequency of the electrical circuit. Phase-lock loop circuitry is provided to maintain the drive to the pipe loops at a frequency equal to the resonant frequency of the pipes, irregardless of variance in the load imposed in the magnetic field generated by the pipes. The transmitting pipe loops are also driven by electrical signals of less than full wave, such that the generated magentic field has improved distortion characteristics. The marker of the invention generates detectable signals containing harmonics of the fundamental frequency of the alternating magnetic field. Detection circuitry is provided to detect the harmonic signals generated by the marker. The detection circuit is gated in synchronism with the less than full wave driving signal applied to the transmitting coil. A dropout circuit is provided to disconnect the transmitting circuitry in case a heavy load is imposed upon the magnetic field.
Inventors
- 👤 E Fearon
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-23 08:09
CPC Classifications
G; G08; G08B; G08B13/00; G08B13/22; G08B13/24; G08B13/2402; G08B13/2405; G08B13/2408; G08B13/2428; G08B13/2431; G08B13/2437; G08B13/2465; G08B13/2468; G08B13/2474; G08B13/2477
Claims Analysis
Total Claims: 15
Claim 1
Independent Claim
163 words
In a system for detecting a ferromagnetic marker within a magnetic field interrogation zone, the combination comprising: coil means placed adjacent said interrogation zone and having a relatively high Q, electrical circuitry connected to said coil means for applying a chopped sinusoidal electrical signal to drive said coil means to generate an alternating magnetic field in said interrogation zone, said chopped signal comprising a plurality of spacedapart periodic pulses of the same polarity and of less than one half wave configuration, such that said coil is not continuously driven by said electrical signal but wherein a continuous magnetic field having improved distortion characteristics is provided due to the relatively high Q of said coil, means for detecting a predetermined harmonic signal generated by said marker in response to said continuous magnetic field in said interrogation zone, means for gating said detecting means in synchronism with said alternating electrical signal, and means for initiating an alarm indication upon the detection of said harmonic signal.
Claim 2
Dependent Claim
163 words
In a system for detecting a ferromagnetic marker within a magnetic field interrogation zone, the combination comprising: coil means placed adjacent said interrogation zone and having a relatively high Q, electrical circuitry connected to said coil means for applying a chopped sinusoidal electrical signal to drive said coil means to generate an alternating magnetic field in said interrogation zone, said chopped signal comprising a plurality of spacedapart periodic pulses of the same polarity and of less than one half wave configuration, such that said coil is not continuously driven by said electrical signal but wherein a continuous magnetic field having improved distortion characteristics is provided due to the relatively high Q of said coil, means for detecting a predetermined harmonic signal generated by said marker in response to said continuous magnetic field in said interrogation zone, means for gating said detecting means in synchronism with said alternating electrical signal, and means for initiating an alarm indication upon the detection of said harmonic signal.
Claim 3
Dependent Claim
105 words
In a system for detecting a ferromagnetic marker in an interrogation zone, the combination comprising: coil means for being disposed adjacent said interrogation zone, electrical driving circuitry for applying alternating electrical signals to said coil means to cause the generation of a magnetic field in said interrogation zone, said electrical signals having a fundamental frequency substantially equal to the resonant frequency of said coil means, and phase-lock loop means connected between said coil means and said electrical driving circuitry for varying said fundamental frequency to maintain said coil means in resonance irrespective of variations in the loading of the magnetic field in said interrogation zone.
Claim 4
Dependent Claim
105 words
In a system for detecting a ferromagnetic marker in an interrogation zone, the combination comprising: coil means for being disposed adjacent said interrogation zone, electrical driving circuitry for applying alternating electrical signals to said coil means to cause the generation of a magnetic field in said interrogation zone, said electrical signals having a fundamental frequency substantially equal to the resonant frequency of said coil means, and phase-lock loop means connected between said coil means and said electrical driving circuitry for varying said fundamental frequency to maintain said coil means in resonance irrespective of variations in the loading of the magnetic field in said interrogation zone.
Claim 5
Dependent Claim
54 words
The combination of claim 2 wherein said phase-lock loop comprises: a phase comparator for comparing the voltage appearing on said coil means and a signal representative of current in said coil means, and voltage controlled oscillator means for generating an alternating electrical signal having a frequency dependent upon the output of said comparator means.
Claim 6
Dependent Claim
18 words
The combination of claim 3 wherein said signal representative of current comprises the output of said oscillator means.
Claim 7
Dependent Claim
150 words
A coil unit for detection of objects passing through an interrogation zone comprising: an upright housing for being positioned adjacent said interrogation zone, a plurality of loops of rigid metal pipe having a hollow air-filled interior, said loops being mounted within said upright housing and extending vertically for approximately the height of a person traversing said interrogation zone, a predetermined capacitance mounted in said housing and connected across said loops of rigid metal pipe to tune said loops to a predetermined fundamental frequency, circuitry connected to said loops of rigid metal pipe to generate from said Pipe an alternating magnetic field having said fundamental frequency, said fundamental frequency substantially equal to the resonant frequency of said pipe and said capacitance, and a plurality of coils of wire mounted in said housing in the center of said loops of rigid metal pipe and tuned to receive harmonics of said fundamental frequency.
Claim 8
Dependent Claim
150 words
A coil unit for detection of objects passing through an interrogation zone comprising: an upright housing for being positioned adjacent said interrogation zone, a plurality of loops of rigid metal pipe having a hollow air-filled interior, said loops being mounted within said upright housing and extending vertically for approximately the height of a person traversing said interrogation zone, a predetermined capacitance mounted in said housing and connected across said loops of rigid metal pipe to tune said loops to a predetermined fundamental frequency, circuitry connected to said loops of rigid metal pipe to generate from said Pipe an alternating magnetic field having said fundamental frequency, said fundamental frequency substantially equal to the resonant frequency of said pipe and said capacitance, and a plurality of coils of wire mounted in said housing in the center of said loops of rigid metal pipe and tuned to receive harmonics of said fundamental frequency.
Claim 9
Dependent Claim
13 words
The coil unit of claim 5 wherein said metal pipe comprises copper pipe.
Claim 10
Dependent Claim
19 words
The coil unit of claim 5 wherein said pipe has an interior diameter of at least about one inch.
Claim 11
Dependent Claim
16 words
The coil unit of claim 5 and further comprising three loops of said rigid metal pipe.
Claim 12
Dependent Claim
23 words
The coil unit of claim 5 and further comprising a pair of said coil units disposed on opposite sides of said interrogation zone.
Claim 13
Dependent Claim
25 words
The coil unit of claim 9 wherein said loops of pipe in each of said pair of coil units are connected in an aiding configuration.
Claim 14
Independent Claim
65 words
A system for detecting a ferromagnetic magnetic marker in an interrogation zone comprising: coil means placed adjacent said interrogation zone, electrical circuitry for applying alternating electrical signals to said coil means for generating an alternating magnetic field in said interrogation zone, and means responsive to the presence of unusually large magnetic objects within said magnetic field for disconnecting said electrical circuitry from said coil means.
Claim 15
Independent Claim
65 words
A system for detecting a ferromagnetic magnetic marker in an interrogation zone comprising: coil means placed adjacent said interrogation zone, electrical circuitry for applying alternating electrical signals to said coil means for generating an alternating magnetic field in said interrogation zone, and means responsive to the presence of unusually large magnetic objects within said magnetic field for disconnecting said electrical circuitry from said coil means.
References Cited (Backward Citations)
No citation records indexed.
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1977-06-24 | 1977-12-24 | 1978-06-25 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-06-24 | 1981-12-24 | 1982-06-25 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-06-24 | 1985-12-24 | 1986-06-25 | $7700.00 | Window Closed / Lapsed |