Distance Sensors Utilizing a Current-Exciting Large Barkhausen Effect in Twisted Amorphous Magnetostrictive Wires

A distance sensor which uses the large Barkhausen effect in amorphous wires magnetized by a current is described. A helical anisotropy is created in an Fe77.5Si7.5B15 amorphous wire (cold-drawn and then tension-annealed) by applying torsion, and consequently the wire can be magnetized by the circumferential magnetic field created by the wire current. This type of distance sensor does not require a long exciting solenoid coil, and its construction is simple. The characteristics of the sensor are controlled by the number of turns used to apply the torsion. The smallest deviation from linearity, ¿=0.4%/FS for a 1000 mm long wire, was obtained when the torsion was 10 turns/m. Domain wall motion in a twisted amorphous wire was also analyzed. The domain wall velocity increases linearly with the wire current, and its mobility decreases with increasing torsion.