Electricity: measuring and testing – Magnetic – Magnetometers
Patent
1984-05-15
1986-07-29
Strecker, Gerard R.
Electricity: measuring and testing
Magnetic
Magnetometers
250227, 350375, 324 96, 356345, G01R 33032, G01B 902, G02F 129
Patent
active
046032967
ABSTRACT:
A fiber optic magnetometer for detecting DC magnetic fields includes a first optical fiber having a magnetostrictive jacket thereon which defines a sensing arm, and a second fiber defining a reference arm. A first AC magnetic field of frequency .omega..sub.o and a second AC field of frequency .omega..sub.s are imposed on the magnetostrictive jacket so as to cause a time varying optical path length change, having .omega..sub.o, (.omega..sub.o +.omega..sub.s), and (.omega..sub.o -.omega..sub.s) components in the sensing arm fiber. This induces a corresponding time varying phase shift, also having the above components, in light transmitted through the sensing arm fiber which is detected by a phase detector. The phase detector produces a signal proportional to the phase shift, this signal being passed to a lock-in amplifier set to amplify at .omega..sub.o. .omega..sub.s is sufficiently small such that the lock-in amplifier filters all components other than the .omega..sub.o, (.omega..sub.o +.omega..sub.s), and (.omega..sub.o -.omega..sub.s) components. The sum of these components changes in magnitude upon exposure of the magnetostrictive jacket to a DC field, thereby indicating the presence of a DC field. The lock-in amplifier output is plotted on an oscilloscope versus the second AC field of frequency .omega..sub.s to give a loop which shifts in position when the device is exposed to an external DC field.
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Koo Kee P.
Sigel, Jr. George H.
Beers Robert F.
Edmonds Warren S.
Sharp William R.
Sheinbein Sol
Strecker Gerard R.
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