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.
Temperature effect on the asymmetric giant magnetoimpedance in amorphous materials
The asymmetric giant magnetoimpedance (GMI) curve has been measured under the rotating field as a function of temperature in a Co-based amorphous ribbon (Co/sub 66/Fe/sub 4/B/sub 15/Si/sub 15/). The magnetic softness in the amorphous phase is enhanced at temperature between 370 and 415 K. The bias-field caused by the hard magnetic phase is nearly constant up to 350 K and then rapidly decreases with temperature. The field angle of 95/spl deg/ from the ribbon axis for maximum impedance increases to 97/spl deg/ at a temperature of 440 K, indicating little change of anisotropy configurations with temperature.
Active profiling and polishing for efficient control of material removal from large precision surfaces with moderate asphericity
We present the development of an active fabrication technology for controlling material removal on large precision surfaces of moderate departure from a sphere. The underlying philosophy was established as an efficient solution to the challenging problem of fabricating secondary mirrors of up to nominally 2.5 m in diameter for modern 8 m class telescopes and beyond. The facility described comprises a CNC profiler, two contact profilometers, and a full size active polisher. The trial work-piece was a convex surface of 830 mm in diameter on a zero-expansion ceramic (`Cervit') blank – a 1/3 scale hyperbolic mirror for a proposed 2.5 m diameter f/7 secondary mirror for the 8 m Gemini telescope. Using software error-correction from profilometric metrology data, a factor of 2 improvement in generating the convex aspheric profile was achieved. An active loose-abrasive polishing process is also described, in which a full-size tool is configured to deliver variable, edgeless, sub-diameter removal-footprints. Real-time monitoring of process variables is described, and approximately 10% convergence in each polishing pass is reported.