Patent ID: 7360459

Claim:
A rotation sensor for use with first and second shafts arranged for relative rotation, comprising: a first rotor mounted to the first shaft, and having a magnetic material section and a conductive material section alternatively arranged along a circumference of the first rotor; a stationary core having a stationary core body; a second rotor disposed between the first rotor and the stationary core, mounted to the second shaft, and having a metal member corresponding to the conductive section of the first rotor; an exciting coil accommodated in the stationary core body, operable when supplied with an AC current, and having inductance thereof varying with a change in a relative rotation angle of the first and second rotors; and a circumferential groove formed inside said stationary core body of the stationary core, the circumferential groove being configured so as to allow magnetic lines produced by the AC current supplied exciting coil to avoid passing therethrough.