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.
Studies on root enamel (2). Enamel pearls. A review of their morphology, localization, nomenclature, occurrence, classification, histogenesis and incidence.
Enamel pearls are one of a number of different enamel structures that can be found on the roots of deciduous and permanent teeth. They have a distinct predilection for the furcation areas of molar teeth, particularly the maxillary third and second molars. They can consist primarily of enamel, but in most instances, a core of dentin is contained within them. On rare occasions, even pulpal tissues can be found. Enamel pearls usually occur singularly, but up to 4 enamel pearls have been observed on the same tooth. Depending on the study, enamel pearls on permanent molar teeth have an incidence rate of between 1.1%-9.7% with distinct differences among racial and national groups. The incidence of enamel pearls increases greatly in histological studies, suggesting that they are often obscured by a covering of cementum.