A magnetic sensor is disclosed in which a ferromagnetic runner (e.g., a permalloy runner) can be located relative to a target. A coil structure is generally wound about the ferromagnetic runner, such that when a magnetic field changes direction along an axial length of the ferromagnetic runner, a voltage is induced in the coil structure that is proportional to a time range of change of a magnetic flux density, due to the sudden internal magnetization reversal of the runner. Additionally, an interfacing circuit can be provided in which the ferromagnetic runner and the coil structure are integrated with the interfacing circuit to thereby produce a magnetic sensor for magnetically sensing the target. The magnetic sensor is highly sensitive and can operate without electrical current or upon a negligible electrical current.
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