Abstract: A GMI sensor for determining spin rate of a rotating body within an external magnetic field is presented. The sensor comprises an oscillator generating an AC drive signal at an oscillator output terminal. A voltage divider circuit includes a first terminal AC coupled to the oscillator output terminal through a coupling capacitor, and a second terminal electrically connected to a reference ground. The voltage divider circuit further includes a GMI fiber having a GMI junction terminal. The fiber is disposed in fixed relation to the rotating body such that impedance of the fiber is modulated by the external magnetic field to provide a modulated drive signal at the GMI junction terminal. A signal processing circuit is electrically connected to the GMI junction terminal to processes the modulated drive signal and provide an output signal indicative of the spin rate of the rotating body.