Distance Sensors Utilizing Large Barkhausen Effect of Amorphous Wires

New distance sensors are described which utilize the large Barkhausen effect of amorphous magnetostrictive wires. Only one domain wall propagates in the direction of the wire axis under a driving magnetic field H when the condition H* ≫ H ≫ H0 is satisfied throughout the length of the wire, where H* is the critical field for nucleation of reverse domains, and H0 is the critical field for domain wall displacement. A distance sensor with a nonlinearity of less than 0.7% full-scale throughout a length of 1000 mm was fabricated using a cold-drawn and then heat-treated Fe77.5Si7.5B15 amorphous wire of diameter 30 ¿m and length 1400 mm, in which the wall velocity vw = 2Ms(H-H0)/ß is controlled by increasing H*.