Search coil

The search coil magnetometer or induction magnetometer, based on an inductive sensor (also known as inductive loop and inductive coil), is a magnetometer which measures the varying magnetic flux due to Lenz's law. An inductive sensor connected to a conditioning electronic circuit constitutes a search coil magnetometer. It is a vector magnetometer which can measure one or more components of the magnetic field. A classical configuration uses three orthogonal inductive sensors. The search-coil magnetometer can measure magnetic field from mHz up to hundreds of MHz.The inductive sensor is based on Faraday's law of induction. The temporal variation of the Magnetic Flux Φ {displaystyle Phi }   through a N turns circuit will induce a voltage e {displaystyle e}   which follows: When a coil is wound around a ferromagnetic core, that increases the sensitivity of the sensor thanks to the apparent permeability of the ferromagnetic core.A search coil is used to measure eye movement using coils that are embedded into a tightly-fitting contact lens or a rubber ring that adheres to the eye. In animal studies, the search coil may be surgically implanted into the sclera of the eye. Alternating magnetic fields are generated by magnets positioned around the eye. Through electromagnetic induction, electric currents are generated in the search coils. The polarity and amplitude of the current generated varies with the direction and angular displacement of the eye. By measuring these values, the position of the eye can be determined. Search coils can be applied to one or both eyes.