Construction of electromagnetic rotation sensor using compound magnetic wire and measurement at extremely low frequency rotations

A pulse generator device, utilizing the effect of large Barkhausen jumps, is investigated. The device is an assembly of rotating permanent magnets and a magnetic sensing element. The sensing element is a compound magnetic wire around which a search coil is wound. The compound magnetic wire is made by twisting a ferromagnetic wire and is doubly layered. The surface shell part of the wire has lower coercivity compared to the inner core part. Even if the frequency of the external field due to the rotation of permanent magnet becomes nearly zero, we observe the sharp voltage pulse of 2 mV/turn due to a large Barkhausen jump. We demonstrate an impeller type flowmeter as an application of these experimental results, which is able to detect 0.5 l/min, where the rotation speed is so slow that the impeller is stopping due to the friction