Laser Welding Process and Packaging for Magnetic Field Sensors
A manufacturing process for the production of miniaturized magnetic field sensors based on the GMI-effect (giant magnetoimpedance) in a thin wire of an amorphous Fe78Si7B15 alloy connected to Cu wires by laser welding is described. Due to the strong inclination of the amorphous structure to recrystallization already at a temperature far below the melting point a thermally optimized welding process is decisive for the success of the manufacturing process. The thermal load in the GMIwire in terms of the temporal temperature distribution caused by the laser welding process has been studied using transient thermal simulation. The length of the wire ends in the vicinity of the welding points in which recrystallization is believed to destroy the GMI effect is estimated. The results show that the length of the remaining active part of the GMI wire can be controlled by the energy and duration of the laser pulse and to a certain extent by the thermal properties of the substrate material. This study should help to understand the influence of welding parameters on the sensitivity of the sensor. The results of the thermal investigation are discussed with respect to the sensitivity of our GMI-sensor prototypes obtained from magnetic field measurements.
Large nonlinear magnetoimpedance in amorphous Co80.89Fe4.38Si8.69B1.52Nb4.52 fibers
Fourier analysis of the nonlinear response of the impedance signal of amorphous Co80.89Fe4.38Si8.69B1.52Nb4.52 fibers is presented. The harmonic components of the voltage signal present a strong asymmetry. A strong variation (around 1400%) of the second-harmonic signal (V2 f) as a function of the applied magnetic field is observed. Nonlinear effects and the asymmetric behavior in harmonics can be associated with the anisotropies induced during the fabrication process. These results can lead to improvement of the performance of future magnetoimpedance sensors.
Magneto-impedance in sputtered amorphous films for micro magnetic sensor
The magneto-impedance (MI) effect in RF sputtered (CoFe)/sub 80/B/sub 20/ zero-magnetostrictive amorphous films are presented. The relation between annealing conditions and MI characteristics was investigated. Impedance Z monotonously decreased with increasing applied field Hex when a high frequency sinusoidal current was applied to the sample annealed in a rotational field. In case of the samples having transverse anisotropy, Z sharply increases with Hex for the region Hex<Hk (anisotropy field). MI ratio (/spl Delta/|Zl/lZ/sub 0/l/Oe) of 8%/Oe was obtained for the sample annealed in a dc field (or applying dc current) after annealing in the rotational field. The Colpitts oscillator type field sensor was constructed using the film element. A direction sensing utilizing the terrestrial field was carried out using the MI-colpitts sensor.