E. Hristoforou

Non-destructive evaluation distribution sensors based on magnetostrictive delay lines

In this paper, we present a non-destructive evaluation sensor able to perform distribution measurements on metallic surfaces. The sensing principle is based on the magnetostrictive delay line (MDL) technique. The pulsed MDL excitation field generates eddy currents on the test surface, which are balanced when no cracks are present. In case of cracks, these eddy currents are summed up around the inhomogeneity, thus causing microstrain generation in the region of the MDL close to the crack. The amplitude and time delay of the detected pulsed voltage signals corresponding to those additional microstrains caused by the eddy currents, are the indication of the size and the position of the defect on the test surface. In this paper, we present the sensing principle as well as the first results in such kind of measurements.

Domain wall propagation in Fe-rich glass covered amorphous wires

Abstract The domain wall velocity in Fe77.5Si7.5B15 glass covered amorphous wires, before and after glass removal was determined. The domain wall axial velocity linearly increases with driving magnetic field. The driving magnetic field is higher for glass covered amorphous wires than for conventional ones having the same composition. The domain wall velocity increases when the diameter of the metallic core decreases and the critical field of reverse domain nucleation decreases with increasing the wire diameter. After glass removal, the nucleation and drive fields decrease.

A new magnetic field sensor based on magnetostrictive delay lines

A magnetic field sensor based on the dependence of the magnetostrictive delay line (MDL) response on its biasing magnetic field is presented in this paper. Such a sensor can be formed in an integrated array measuring the distribution of field along the MDL axis. Experimental results are reported for amorphous FeSiB wire MDLs, showing that high sensitivity and nonhysteresis are two advantages of this type of sensor.

Amorphous Wire Delay Lines Used For Magnetic Field Measurements

In this paper we report some results concerning the dependence of the pulsed voltage output on the exciting magnetic field and on the bias magnetic field applied at the exciting or receiving point, for Fe/sub 77.5/Si/sub 7.5/B/sub 15/ amorphous wires used as delay lines. The obtained results show a strong dependence of the pulsed voltage output on the values of the magnetic fields. Magnetic fields up to about 2000 A/m applied at the receiving point can be detected. Small magnetic fields applied at the exciting point can be detected using small values of the exciting magnetic field. Using this technique magnetic field sensors with high accuracy and sensitivity and absence of hysteresis can be realized. Such sensors can be formed in integrated arrays measuring the distribution of the magnetic field along the magnetostrictive delay line axis.

Torsion and magnetic field measurements using inverse Wiedemann effect in glass-covered amorphous wires

Abstract This paper presents results concerning inverse Wiedemann effect (IWE) dependence on the torsion and d.c. magnetic field applied along the length of the Fe77.5Si7.5B15 glass-covered amorphous wires tested in the as-cast state both before and after glass removal. In the absence of torsion during measurements, the IWE voltage is zero. Increasing the torsion value up to about 55 rad/m increases the value of the induced voltage until it reaches a maximum. In the 0.02–0.03 mT range there is a linear dependence of the IWE voltage on the d.c. magnetic field. The obtained results suggest the possibility of using Fe77.5Si7.5B15 glass-covered amorphous wires as sensing elements for torsion and magnetic field, based on the IWE.

Design and fabrication of mirominiature delay line using thin film technology

Abstract This paper describes the fabrication of a miniaturized magnetostrictive delay line thin film. A monolithic design has been achieved with the coils and the magnetoelastic element contained onto the same silicon substrate. Such a miniaturized device able to be used as a sensor was fabricated by using a multilayer-like technique. The exciting conductor, the receiving coil and the magnetostrictive delay line were fabricated using a conventional photolithographic technique. In order to use conventional magnetostrictive thin films and Fe-metalloid amorphous thin films as active-magnetoelastic elements, the magnetoelastic properties which determine their performance was studied.

On the calibration of position sensors based on magnetic delay lines

Abstract Results on the characteristics of three position sensors based on magnetic delay line techniques are illustrated in this paper. These sensors are based on the linear motion of coils or magnets along the length of a magnetic delay line. The uncertainty of the first sensor has been improved up to 40 μm m−1 by applying bias field along its length, while the second cordless sensor has the worst accuracy of 100 μm m−1. The sensitivity of the third position sensor has been determined to be better than 1 μm, provided that it is firmly shielded against ambient magnetic fields. The simplicity of these arrangements makes them interesting for industrial applications, where corded or cordless linear motion position sensors of relatively low cost are required.

Torsional and tensile stress dependence in amorphous magnetic wires

Abstract In this paper we present results concerning the magnetostrictive delay line (MDL) response for positive magnetostrictive wires as well as the magneto-inductive (MI) response for negative magnetostrictive wires, on the applied torsion and tensile stress. The obtained results show a non-monotonic dependence of the MDL response and a parabolic magneto-inductive response on applied torsion. The tensile stress dependence in MDLs could be fitted by a linear curve for as-cast wires, and by an exponential curve for annealed wires while the MI response could be fitted by a linear curve. Load cells and torque sensors may be realised by using this technique.

Sound velocity in Fe-rich glass covered amorphous wires

Abstract The bias magnetic field ( H ) dependence of the longitudinal sound velocity ( v ) in Fe 77.5 Si 7.5 B 15 glass covered amorphous wires is reported. The amorphous wires were tested in the as-cast state and after dc current annealing between 5 and 20 mA for 10–30 min. For the glass covered amorphous wires tested in the as-cast state the bias magnetic field dependence of the sound velocity was insignificant. For current annealed samples a decrease of the sound velocity for the smaller bias magnetic fields was observed. Increasing the annealing temperature, the bias magnetic field corresponding to the v minimum decreased. For about 600 A/m bias magnetic field, the longitudinal sound velocity reaches saturation.

Inverse Wiedemann Effect in glass-covered amorphous wires

Abstract We present results concerning the Inverse Wiedemann Effect (IWE) in Fe 77.5 Si 7.5 B 15 amorphous glass-covered wires having 10–27 μm and 5–15 μm diameters of the metallic core and thickness of the glass cover, respectively, and also on wires obtained after the glass removal. The dependence of the IWE voltage induced in the pick-up coil on torsion, tensile stress, and frequency of the ac current flowing through the wire are analysed. The amorphous wires were tested in the as-cast state and after heat treatments performed by current annealing technique, with and without applied torsion along the length of the wire. The obtained results show that the IWE voltage strongly depends on the state of amorphous wires (as-cast or annealed). The work was made in order to realise new sensor elements using glass-covered amorphous wires.