Passive wirelessly requestable sensors for magnetic field measurements

A direction-sensitive micro-magnetic field sensor is developed using the gi ant magneto-impedance (GMI) effect in a 30-mu m diameter amorphous FeCoSiBN d wire. Consisting of a micro-sized zero-magnetostrictive amorphous wire of about 70-mu m length, the GMI sensor was connected to a self-oscillating C olpitts oscillator circuit by laser welding. It shows a high sensitivity wi th a resolution of 100 nT for DC fields, quick response, and a high tempera ture stability. Reproducible measurements of a surface-flux distribution of mechanically 100 mu m structured magnetic bar codes were carried out. Surf ace Acoustic Wave (SAW) devices are shown as passive, radio-requestable sen sor devices, A new type employs the electrical load of the SAW device by th e impedance of conventional sensors. In order to develop a wirelessly inter rogable magnetic field sensor, the combination of the GMI sensors and SAW t ransponders is discussed and the results are shown. (C) 2000 Elsevier Scien ce S.A. All rights reserved.