Magnetic anomaly detector and method using the microwave giant magnetoimpedence effect

Abstract

A high sensitivity magnetic anomaly detector for geomagnetic exploration comprises a shorted coaxial transmission line having as central conductor an amorphous magnetic wire. A static magnetic field is applied along the transmission line. A transverse electromagnetic wave also propagates along the transmission line and excites a ferromagnetic resonance of the magnetic ions located within the depth of penetration of the circumferential microwave magnetic field into the magnetic wire. The microwave giant magnetoimpedance effect occurring in the magnetic wire changes the magnetic wire impedance as follows: the real part of the impedance peaks and the imaginary part passes through zero at a given frequency (the ferromagnetic resonance frequency). This frequency depends on the saturation magnetization of the magnetic wire and the strength of the static magnetic field. A slight variation of the Earth's magnetic field (a magnetic anomaly) changes this frequency, thus providing information about large metallic masses hidden under the Earth's surface or underwater.