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 . 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 &# 39 ; s magnetic field changes this frequency , thus providing information about large metallic masses hidden under the earth &# 39 ; s surface or underwater .