Synchronized Re-Entrant Flux Reversal of Multiple FeSiB Amorphous Wires Having the Larger Output

Magnetostrictive Fe-Si-B amorphous wires fabricated by in-rotating-water quenching technique exhibit jitter-free and stable Barkhausen discontinuities (BHD) at a critical field (H*) less than earth field. The BHD generates pulse voltage in a sense coil located near the wires. So, the amorphous wire can be used as a pulse-voltage generating element in an application of electrical surveillance system. The minimum length of the amorphous wire as a pulse voltage generator depends on its demagnetizing effect. When the as-quenched amorphous wire with 120μm diameter is shortened less than 7cm, the demagnetizing field becomes over the H* and characteristic of re-entrant flux reversal is destroyed. Effort was made with success to fabricate a small size pulse-voltage generator using multiple die-drawn 4cm long amorphous wires with 65 and 95μm diameter. The die-drawn wires were annealed first in a longitudinal applied field to relax mechanical stress and to induce the magnetic anisotropy. The 3cm long annealed wire exhibit the sheared magnetization curve with the small flux steps of the BHD owing to the enhanced demagnetizing effect. To control the demagnetizing field of the annealed wire, small pieces of amorphous ribbons were contacted to the wire ends. It was observed that the amorphous ribbons coupled magnetically with the annealed wire and worked as a flux keeper. It was found that demagnetizing field of the amorphous wire decreased markedly and the BHD of a bundle of 3 wires synchronized after optimization of the size and anisotropy of the amorphous ribbons. Domain observation revealed that synchronized re-entrant flux reversal of multiple wires was triggered with the BHD of one of three wires and propagated to the other two wires through the amorphous ribbon flux keeper. As a result, a pulse voltage generator consisting of 4cm long three wires with 95μm diameter and flux keeper generated the output pulse voltage 6 times as large as that of a single wire.