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U.S. Patent No. 5,483,161
In the electrical and sensitive mechanical arts, a general-purpose magnetic field sensor capable of measuring uniform magnetic fields includes a magneto-optic (Faraday-effect) sensor and a flux concentrator. Both the magneto-optic sensor and the flux concentrator have high magnetic permeability. The magneto-optic material and the flux concentrator creates a magnetic circuit which efficiently concentrates the magnetic field into the magneto-optic sensor, and greatly enhances the measurement sensitivity. The preferred embodiment uses a pair of cylindrical flux concentrators in axial alignment. A sensing beam passes through a central axis hole in the cylindrical flux concentrators. The Faraday effect sensor is co-axially aligned with the holes in the cylindrical flux concentrators. The concentrators and Faraday effect sensor create a continuous flux concentrating magnetic circuit.