US3577068A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Optically pumped magnetic gradiometer
Assignee: Atlantic Richfield Co
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Filing: 1968-08-27
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Granted: 1971-05-04
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Expires: 1988-08-27
Abstract
Abstract Apparatus for determining the gradient of the earth''s magnetic field over a zone. The absorption magnetometer is encircled by a coil of wire coupled to a low frequency oscillator. The turns of the coil are unevenly spaced along the length of the cell and are canted with respect to the cell so that the magnetic field caused by current in the coil is inhomogeneous and offsets the gradient in the earth''s magnetic field. The magnetometer''s radio frequency output signal is amplitude modulated by a signal having the frequency of the oscillator output and having an amplitude proportional to the gradient of the earth''s magnetic field. This modulation signal is amplitude detected and then phase detected using the oscillator output as a reference. The phase detector output is a signal indicative of the earth''s magnetic field gradient.
Inventors
- 👤 Richard C La Force
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-06 04:46
CPC Classifications
G; G01; G01R; G01R33/00; G01R33/20; G01R33/24; G01R33/26
Claims Analysis
Total Claims: 8
Claim 1
Independent Claim
145 words
Apparatus for determining the gradient of the earth''s magnetic field over a zone, said apparatus comprising: a. an optical magnetometer having a longitudinal axis and positioned in said zone and including aligned along said longitudinal axis a source of radiation, a radiation absorption cell adapted for passage therethrough of radiation from said source, and radiation detection means for producing an output proportional to the intensity of radiation impinging thereon; b. means for generating a varying local magnetic field gradient around said magnetometer to cyclically vary the net magnetic field gradient over said zone; and c. circuit means coupled to said radiation detection means for measuring the magnitude of said local magnetic field gradient at the point at which that local magnetic field gradient exactly offsets the earth''s magnetic field gradient over said zone to indicate the gradient of the earth''s magnetic field over said zone.
Claim 2
Dependent Claim
145 words
Apparatus for determining the gradient of the earth''s magnetic field over a zone, said apparatus comprising: a. an optical magnetometer having a longitudinal axis and positioned in said zone and including aligned along said longitudinal axis a source of radiation, a radiation absorption cell adapted for passage therethrough of radiation from said source, and radiation detection means for producing an output proportional to the intensity of radiation impinging thereon; b. means for generating a varying local magnetic field gradient around said magnetometer to cyclically vary the net magnetic field gradient over said zone; and c. circuit means coupled to said radiation detection means for measuring the magnitude of said local magnetic field gradient at the point at which that local magnetic field gradient exactly offsets the earth''s magnetic field gradient over said zone to indicate the gradient of the earth''s magnetic field over said zone.
Claim 3
Dependent Claim
42 words
Apparatus as claimed in claim 1 in which said generating means includes an oscillator providing an output of substantially low frequency coupled to a coil encircling said magnetometer with nonuniformly spaced turns canted with respect to the longitudinal axis of said magnetometer.
Claim 4
Dependent Claim
57 words
Apparatus as claimed in claim 2 in which said circuit means includes means for separating said radiation detection means output into a high frequency component and a low frequency component, said low frequency component having substantially the same frequency as said oscillator output and having an amplitude proportional to the earth''s magnetic field gradient over said zone.
Claim 5
Dependent Claim
29 words
Apparatus as claimed in claim 3 in which said magnetometer includes a coil coupled to said separating means for utilizing said high frequency component to make said magnetometer self-oscillating.
Claim 6
Dependent Claim
26 words
Apparatus as claimed in claim 3 in which said circuit means includes means for phase detecting said low frequency component with respect to said oscillator output.
Claim 7
Dependent Claim
25 words
Apparatus as claimed in claim 5 in which said source of radiation is a helium lamp and said radiation absorption cell is filled with helium.
Claim 8
Dependent Claim
18 words
Apparatus as claimed in claim 5 further comprising means for indicating the output of said phase detecting means.
References Cited (Backward Citations)
US3443209A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1974-05-03 | 1974-11-02 | 1975-05-04 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1978-05-03 | 1978-11-02 | 1979-05-04 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1982-05-03 | 1982-11-02 | 1983-05-04 | $7700.00 | Window Closed / Lapsed |