Fiber optic magnetic field sensing transducer having a resonant structure

Abstract

Abstract A magnetic field sensing transducer which converts magnetic field intensity into a magnetostrictive strain and transfers that strain to an optical fiber employs a thin wall, hollow, cylindrical shell around which is wound a ribbon of an amorphous metallic magnetostrictive material. In another embodiment, the entire shell is formed by turns of the ribbon of magnetostrictive material. The optical fiber is coiled around the magnetostrictive cylinder formed by the wound ribbon and at both its ends, the optical fiber is affixed to the shell. The shell is covered at both its ends by caps and forms a thin wall resonator having three normal axisymmetric modes of vibration. The torsional vibratory mode is here of no interest because it does not appreciably couple to the optical fiber. Any one of the other two axisymmetric modes of vibration can be made dominant by selection of the appropriate length to radius ratio of the cylindrical shell. That property enables the transducer to be tuned to maximize its response to the applied dither field. The transducer is supported by a rod that extends centrally from the end caps. Strains induced by a magnetic field cause a modification in the phase of the light propagating through the optical fiber.

Inventors

• 👤 Marc D. Mermelstein

Bibliographic Details