RECENT ADVANCES OF MICRO MAGNETIC SENSORS AND SENSING APPLICATION

Principle and basic performance of micro magnetic sensors such as the Hall element, the magneto-resistance (MR) element, the giant magneto-r esistance (GMR) element, the thin-film fluxgate sensor (FGS), and the magneto-impedance (MI) element are summarized. Their basic properties are compared with each other considering a new sensing target in vario us modern industrial fields. A new micro-sized magnetic field sensor w ith a high sensitivity and a quick response is developed using the MI effect in amorphous wires and thin films. The MI sensor having a micro -sized zero-magnetostrictive amorphous wire head of about 1 mm install ed in self oscillation circuits such as the Colpitts oscillator and a multivibrator circuit shows a high sensitivity with a resolution of 10 (-6) Oe for ac fields and 10(-5) Oe for de fields, quick response with a cut-off frequency of about 1 MHz, and a high temperature stability of less than 0.05%FS degrees C-1 up to 70 degrees C. A very low power consumption and highly stable MI sensor is constructed using a CMOS mu ltivibrator. A stable measurement for a surface-flux distribution arou nd a 2000-pole ring magnet with a diameter of 19 mm for a high density rotary encoder was carried out using the MI sensor. A small pin hole of 100 mm diameter in an iron sheet was detected at non destructive te sting (NDT) using a gradient-field detection type MI sensor cancelling back ground disturbance fields. A sample of clustered magnetite parti cles was magnetically detected using the MI sensor probe in a simulati on of detection of a brain tumor at which an injected sol was induced with the magnetite particles. (C) 1997 Published by Elsevier Science S .A.