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Fiber-optic magnetic field gradiometer for first, second and higher order derivatives

  • US 4,814,706 A
  • Filed: 03/18/1988
  • Issued: 03/21/1989
  • Est. Priority Date: 03/06/1987
  • Status: Expired due to Term
First Claim
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1. A magnetic field gradiometer comprising:

  • at least a first, second and third magnetic transducer;

    at least three optical fibers, one fiber wrapped around each of said magnetic transducers wherein said fibers define at least three optical paths;

    a laser means coupled to said fibers to provide laser light within said fibers wherein the laser light travels along the optical paths defined by said fibers;

    an applied magnetic field generating means for immersing each of said magnetic transducers in an applied magnetic field having an AC and a DC component; and

    first means operative when said fibers are subjected to an external magnetic field to be measured for detecting a change in the length Δ

    L1,2 of the optical paths defined by said fibers between said first and second magnetic transducers and the change in length Δ

    L2,3 of the optical paths defined by the fibers between the second and third magnetic transducers, and second means for detecting a total length change Δ

    LT proportional to |Δ

    L1,2 - Δ

    L2,3 | of said fibers wherein said total change in length Δ

    LT of the optical paths provides an indication of the second derivative of said external magnetic field.

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