US3873908A
Expired / Lapsed
US
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Self-oscillating optically pumped magnetometer having automatic phase correction
Assignee: CAE Electronics Ltd
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Filing: 1973-12-17
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Granted: 1975-03-25
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Expires: 1993-12-17
Abstract
Abstract In a dual cell optically pumped cross coupled self-oscillating magnetometer, orientation dependent phase shift, i.e., heading errors, are reduced by phase modulating the self-oscillating frequency to produce a corresponding amplitude modulation in the Zeeman resonance of each of the two cells. This amplitude modulation of the Zeeman resonance is a function of the corresponding slope of the respective overlapping Zeeman resonance lines at the self-oscillating frequency. The two Zeeman resonance amplitude modulation signals are compared to derive a difference error signal which is utilized for adjusting the phase shift of the self-oscillating frequency to correspond to an overlap frequency of the two Zeeman resonance lines wherein both Zeeman lines have the same slope, thereby automatically minimizing heading errors.
Inventors
- 👤 Byron A Young
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-31 05:23
CPC Classifications
G; G01; G01R; G01R33/00; G01R33/20; G01R33/24; G01R33/26
Claims Analysis
Total Claims: 10
Claim 1
Independent Claim
341 words
In an optically pumped magnetometer: means having first and second optical absorption volumes, each containing an assemblage of quantum systems which may precess in a unidirectional magnetic field at a rate which is determined by the intensity of said field; means for directing optical radiation to said absorption volumes with such spectral characteristics as to be differentially absorbed with respect to the magnetic sub-levels of said quantum systems, whereby the intensity of the optical radiation received from each volume is intensity modulated at a frequency which depends on said precession rate; means for converting the intensity modulation of the radiation received from said absorption volumes into alternating electrical signals; means for cross-coupling the alternating electrical signal derived from each absorption volume to the other absorption volume in the form of an alternating magnetic field which produces forced precession of said quantum systems, thereby effecting self-sustained oscillation of said electrical signals at a frequency determined by the intensity of said unidirectional magnetic field and at a frequency corresponding to an overlap of the envelopes of the resonance lines of said first and second quantum systems, each of said resonance lines corresponding to slightly different center frequency precessional rates in each of said volumes; and phase control means for causing said overlap frequency of oscillation to occur at a frequency corresponding to substantially equal slope for the envelopes of each of said overlapping resonance lines, said phase control means including, means for modulating the phase of said selfoscillating frequency at a modulation frequency to effectuate a corresponding amplitude modulation in each of said first and second alternating electrical signals derived from each of said absorption volumes, means for comparing said amplitude modulation signals to derive an error signal proportional to the difference in slope of the first and second resonance lines at the self-oscillating frequency, and means for shifting the phase of said self-oscillating signal in response to said error signal to cause said self-oscillation frequency to occur at a frequency corresponding to equal slopes of said first and second resonance line envelopes.
Claim 2
Dependent Claim
341 words
In an optically pumped magnetometer: means having first and second optical absorption volumes, each containing an assemblage of quantum systems which may precess in a unidirectional magnetic field at a rate which is determined by the intensity of said field; means for directing optical radiation to said absorption volumes with such spectral characteristics as to be differentially absorbed with respect to the magnetic sub-levels of said quantum systems, whereby the intensity of the optical radiation received from each volume is intensity modulated at a frequency which depends on said precession rate; means for converting the intensity modulation of the radiation received from said absorption volumes into alternating electrical signals; means for cross-coupling the alternating electrical signal derived from each absorption volume to the other absorption volume in the form of an alternating magnetic field which produces forced precession of said quantum systems, thereby effecting self-sustained oscillation of said electrical signals at a frequency determined by the intensity of said unidirectional magnetic field and at a frequency corresponding to an overlap of the envelopes of the resonance lines of said first and second quantum systems, each of said resonance lines corresponding to slightly different center frequency precessional rates in each of said volumes; and phase control means for causing said overlap frequency of oscillation to occur at a frequency corresponding to substantially equal slope for the envelopes of each of said overlapping resonance lines, said phase control means including, means for modulating the phase of said selfoscillating frequency at a modulation frequency to effectuate a corresponding amplitude modulation in each of said first and second alternating electrical signals derived from each of said absorption volumes, means for comparing said amplitude modulation signals to derive an error signal proportional to the difference in slope of the first and second resonance lines at the self-oscillating frequency, and means for shifting the phase of said self-oscillating signal in response to said error signal to cause said self-oscillation frequency to occur at a frequency corresponding to equal slopes of said first and second resonance line envelopes.
Claim 3
Dependent Claim
104 words
The apparatus of claim 1 wherein said means for comparing said amplitude modulation signal to derive said error signal includes, means for comparing the amplitudes of said first and second modulation signals to derive a difference output at the modulation frequency with an amplitude determinative of the difference in amplitudes between said first and second modulation signals and a phase determinative of which one of said resonance envelopes at said self-oscillating frequency has the largest slope, and means for comparing said difference output with a sample of said modulation frequency employed to modulate said phase of said self-oscillation frequency to derive said error signal.
Claim 4
Dependent Claim
27 words
The apparatus of claim 1 wherein said modulation freqUency is less than the half power bandwidth of both of said first and second overlapping resonance line envelopes.
Claim 5
Dependent Claim
33 words
The apparatus of claim 2 including means for integrating said error signal, and means for applying said integrated error signal to said phase modulator means for shifting the frequency of said self-oscillating frequency.
Claim 6
Dependent Claim
262 words
In an optically pumped magnetometer: means having first and second optical absorption volumes, each containing an assemblage of quantum systems which may precess in a unidirectional magnetic field at a rate which is determined by the intensity of said field; means for directing optical radiation to said absorption volumes with such spectral characteristics as to be differentially absorbed with respect to the magnetic sub-levels of said quantum systems, whereby the intensity of the optical radiation received from each volume is intensity modulated at a frequency which depends on said precession rate; means for converting the intensity modulation of the radiation received from said absorption volumes into alternating electrical signals; means for cross-coupling the alternating electrical signal derived from each absorption volume to the other absorption volume in the form of an alternating magnetic field which produces forced precession of said quantum systems, thereby effecting self-sustained oscillation of said electrical signals at a frequency determined by the intensity of said unidirectional magnetic field and at a frequency corresponding to an overlap of the envelopes of the resonance lines of said first and second quantum systems, each of said resonance lines corresponding to slightly different center frequency precessional rates in each of said volumes; and phase control means for causing said overlap frequency of oscillation to occur at a frequency corresponding to substantially equal slope for the envelopes of each of said overlapping resonance line by introducing a compensating phase shift into said cross coupling means to cancel phase shifts introduced by physical misalignments or unequal frequency-phase characteristics in said means for cross coupling.
Claim 7
Dependent Claim
262 words
In an optically pumped magnetometer: means having first and second optical absorption volumes, each containing an assemblage of quantum systems which may precess in a unidirectional magnetic field at a rate which is determined by the intensity of said field; means for directing optical radiation to said absorption volumes with such spectral characteristics as to be differentially absorbed with respect to the magnetic sub-levels of said quantum systems, whereby the intensity of the optical radiation received from each volume is intensity modulated at a frequency which depends on said precession rate; means for converting the intensity modulation of the radiation received from said absorption volumes into alternating electrical signals; means for cross-coupling the alternating electrical signal derived from each absorption volume to the other absorption volume in the form of an alternating magnetic field which produces forced precession of said quantum systems, thereby effecting self-sustained oscillation of said electrical signals at a frequency determined by the intensity of said unidirectional magnetic field and at a frequency corresponding to an overlap of the envelopes of the resonance lines of said first and second quantum systems, each of said resonance lines corresponding to slightly different center frequency precessional rates in each of said volumes; and phase control means for causing said overlap frequency of oscillation to occur at a frequency corresponding to substantially equal slope for the envelopes of each of said overlapping resonance line by introducing a compensating phase shift into said cross coupling means to cancel phase shifts introduced by physical misalignments or unequal frequency-phase characteristics in said means for cross coupling.
Claim 8
Dependent Claim
53 words
Method for eliminating heading errors in a self-oscillating cross-coupled two-cell optically-pumped, optically-monitored magnetometer, the improvement comprising determining and inserting a compensating phase shift into the cross coupling loop to cause the overlap frequency of oscillation to occur at a frequency corresponding to substantially equal slope for the envelopes of each overlapping resonance line.
Claim 9
Dependent Claim
53 words
Method for eliminating heading errors in a self-oscillating cross-coupled two-cell optically-pumped, optically-monitored magnetometer, the improvement comprising determining and inserting a compensating phase shift into the cross coupling loop to cause the overlap frequency of oscillation to occur at a frequency corresponding to substantially equal slope for the envelopes of each overlapping resonance line.
Claim 10
Dependent Claim
91 words
The method of claim 6 wherein the step of determining and inserting a compensating phase shift includes: modulating the phase of the self-oscillating frequency; comparing amplitude modulation signal outputs of each cell to derive an error signal proportional to the difference in slope of the first and second resonance lines at the self-oscillating frequency; and shifting the phase of the self-oscillating signal in response to said error signal thereby causing the overlap frequency to occur at a frequency corresponding to substantially equal slope for the envelopes of each overlapping resonance line.
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) | 1978-03-24 | 1978-09-23 | 1979-03-25 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1982-03-24 | 1982-09-23 | 1983-03-25 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1986-03-24 | 1986-09-23 | 1987-03-25 | $7700.00 | Window Closed / Lapsed |