Giant Magneto-Impedance

Schematic of NiFe plated BeCu wire cross section MRSEC has recently demonstrated a novel magnetic field sensor that is capable of measuring fields smaller than one millionth of the earth's magnetic field. This development was undertaken in collaboration with scientists from the Eastman Kodak Company. The device is very simple and economical. It consists of a wire, five thousandths of an inch in diameter, on which is electroplated a very thin magnetic film. When a high frequency alternating current is passed through the wire, it was found that the resistive component of the electrical impedance changes enormously in the presence of very small magnetic fields. For example, the earth's tiny magnetic field changes the resistance by more than 100 percent! Since resistance can be measured very accurately, this leads to extraordinary sensitivity. The phenomenon has been labeled GMI, which stands for Giant Magneto-Impedance. Among the numerous potential applications of GMI are read heads for ultra-high density magnetic information storage, brain wave mapping, military sensors, and tachometers.
Schematic of NiFe plated BeCu wire cross-section. The magnetic easy axis is indicated. A current generates a magnetic field of 0.03 Oe/mA at the surface.
Resistance and reactance of a NiFe plated wire as a function of an axially applied magnetic field for a drive current frequency of f = 1 MhZ and amplitude I rms = 60 mA

The resistance and reactance of a NiFe plated wire as a function of an axially applied magnetic field for a drive current frequency of f = 1 MHz and amplitude Irms = 60 mA.