Akira Matsushita

Annealing And Torsion Stress Effect On Magnetic Anisotropy And Magnetostriction Of Vicalloy Fine Wire

A twisted semi-hard magnetic wire of Vicalloy with composition of Fe/sub 41/Co/sub 48/V/sub 11/ revealed remarkable uniaxial magnetic anisotropy along central axis direction of the wire and showed a difference in coercivity between outer shell and inner core of the wire. Also the wire remained the large torsion stress enough to generate the large Barkhausen jump. The magnitude of the jump depends strongly on the magnetic characteristics, such as magnetic anisotropy and magnetostriction constants, which may be varied with change of annealing treatment and torsion stress. In this study, the causes of large Barkhausen jump induced due to the stress remained by dice drawing process was investigated. As a result, it was found that the pulse voltage induced in the wire was in proportion to logarithmic two power of reduction.

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. >

Generation of large Barkhausen jump with bilayered thin film

A pulse voltage of half-amplitude width of approximately 20 /spl mu/s was induced in a detecting coil wound around a wire by large Barkhausen effect, when torsional stress and AC external magnetic field were applied to Fe-Co-V fine wires. Effective characteristics of the pulse voltage, the pulse amplitude and the pulse width were found not depend on frequency of external magnetic field. Based on this phenomenon, a unique magnetic sensor was developed for a flow meter. In this study, the bilayered thin films with several different coercive forces and residual stresses were fabricated in order to simulate the Barkhausen effect in the thin film. As a result we observed a large Barkhausen jump in the bilayered film having the upper layer in tension and the lower layer in compression. The induced pulse voltages are not dependent on the external magnetic field frequency.

Dependence of large Barkhausen jump on length of a vicalloy fine wire with torsion stress

This paper concerns a magnetic sensor using a vicalloy wire with uniaxial anisotropy and torsion stress. In the magnetic sensor using a compound magnetic wire, the relationship between wire length, magnetization state and the output voltage based on the large Barkhausen jump was investigated. When the specimen wire was short, magnetizations of soft and hard layers were stable only when in anti-parallel due to the demagnetizing field. This result indicated that a large output voltage might be obtained when the ratio of length to diameter of the wire was more than 100. Consequently, a pulse voltage V/sub p/ as high as 2 mV/turn was obtained in the wire even with diameter as fine as 0.1 mm and length as small as 10 mm.

Induced pulse voltage in twisted Vicalloy wire with compound magnetic effect

When a Vicalloy wire (40wt%Fe-50Co-10V) is twisted, the coercivity reduces due to large stress. The pulse-inducing characteristics and domain wall propagation are investigated utilizing this effect on such compound magnetic wire. We find that the generating point of inverse nucleation varies according to the strength of set field Hs and the demagnetizing field near the end of the wire, when the entire compound magnetic wire is excited by an asymmetrical field. Moreover, we find that the velocity of domain wall propagation in the smaller coercivity layer to be 400-500 (m/s) at Hs=16-25 Oe.

Frequency dependence of output voltage generated from bundled compound magnetic wires

The output voltage generated from bundles of twisted Vicalloy wires was studied. When the magnetically soft layers of the wires were reversed by an applied external magnetic field, a pulse voltage, owing to a large Barkhausen jump, was induced in a search coil wound around the wires. The output did not depend on the exciting frequency of the applied field for the bundled wires with n (number of bundled wires) <5. The frequency dependence for n=10 was attributed to the demagnetizing field in the thicker shape of the bundle. The bundled wires of n=25 exhibited dispersed peaks in output waveform due to a self-biasing effect, which was advantageous for obtaining a rectangular output waveform.

Power generating device using compound magnetic wire

A new method of generating power using compound magnetic wires is proposed. The coercive force of twisted Vicalloy (40Fe–50Co–10 V) wire is about 20 Oe in the outer shell near the surface and 60 Oe in the inner core. By applying an external magnetic field to the wire, a pulse voltage, owing to a large Barkhausen jump, is induced in a search coil wound around the wire. The voltage of 4 V for 1.2 ms was obtained with a bundle of 150 compound magnetic wires and a 2000 turn search coil.

Bias magnetic effect using compound magnetic wire sensor in AC magnetic field

A magnetic sensor which consists of a compound magnetic wire and search coil has a novel performance to induce the detection voltage independent of changing rate of AC external field frequency in every one cycle. The detection voltage is changed by the previous magnetized state of the compound magnetic wire. This paper reports the effect of a DC bias magnetic field which is applied with an AC magnetic field to make an asymmetric field. To make a compound wire a previous magnetized state, the demagnetized wire is magnetized by various orienting DC field H/sub 0/. When a symmetric AC field Hex and DC bias field Hb are applied to the wire, the wire is magnetized by an asymmetric magnetic field, which consists of a reset field Hr=Hex+Hb and a set field Hs=Hex-Hb. According to the relationship among the critical field Hp, H/sub 0/ and Hb, Hp is independent of the previous magnetized state of wire at Hb of 25 Oe or larger, and the pulse voltage is always induced at a fixed Hp. This phenomenon is very stable and reproducible.