Rotation speed detector

A rotation speed detector comprising:

• a non-magnetic base material to be attached to a rotating body;
• a first magnetic pole having an arcuate strip shape and provided on the base material such that an outer peripheral side serves as an N pole and an inner peripheral side serves as an S pole;
• a second magnetic pole having an arcuate strip shape and provided on the base material such that an outer peripheral side serves as the S pole and an inner peripheral side serves as the N pole;
• and
• a power generation element including, a magnetic wire configured to cause a large Barkhausen effect, and a pickup coil configured to detect magnetization reversal of the magnetic wire, wherein
• the power generation element is arranged to face the first magnetic pole and the second magnetic pole so that a longitudinal direction of the magnetic wire is provided along a radial direction of the first magnetic pole and the second magnetic pole, and
• a non-magnetic gap is provided between the first magnetic pole and the second magnetic pole, wherein
• each of the first magnetic pole and the second magnetic pole includes a plurality of bar magnets, and
• an installation interval of the plurality of bar magnets included in the first magnetic pole and the second magnetic pole is equal to or less than a half of a half bandwidth, wherein
• the half bandwidth is a dimension in a direction parallel to a surface of the base material on which the first magnetic pole and the second magnetic pole are provided and orthogonal to a longitudinal direction of the bar magnet and is a dimension of a range in which a magnetic field generated by the bar magnet is equal to or more than a half of a peak.