A micromagnetostrictive vibrator using a U-shaped core made of iron-gallium alloy (Galfenol) was investigated. The vibrator consists of a Galfenol core, with a 1 mm2 cross section, a length of 5.8 mm, and a 0.3 mm separation between the prongs of the "U," driving coils, and an iron yoke to close the magnetic loop. The Galfenol vibrator is superior to the PZT type in its high mechanical strength, low drive voltage requirements, and wide temperature operating range, and compared to our previous cylindrical type vibrator has a simpler construction and higher bandwidth. A displacement of 1.2 mu m (220 ppm) was verified for the prototype with a 5.8 mm long Galfenol core; the high magnetostriction >200 ppm is inherited from the stress-annealed Galfenol. The displacement was also maintained under a 21 MPa tensile stress (1.5 kg hanging weight). Incorporation of a Nd-B-Fe magnet into the magnetic circuit successfully shifted the operating point to the linear portion of the magnetostrictive curves. This biasing effect is useful in reducing the drive voltage.
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