Orthogonal fluxgate mechanism operated with dc biased excitation

A mode of operation is presented for an orthogonal fluxgate built with a thin magnetic wire. By adding a proper dc bias to the wire excitation, the new mode is easily established. In this case, the fundamental component of the induced voltage at the sensing coil (secondary voltage) is made sensitive to the axial magnetic field, compared to the second harmonic in a conventional orthogonal fluxgate. The operating principle is explained using a magnetization rotation model. A method is proposed to cancel the offset that is inevitable when the magnetic anisotropy is present in a magnetic wire at an angle to its circumference. Experimental results are shown for a sensor head consisting of a 2-cm-long Co-based amorphous wire 120 μm in diameter with a 220-turn sensing coil. The sensitivity obtained is higher than that obtained using a conventional type of the orthogonal fluxgate built with the same sensor head. It is also demonstrated that the proposed method for canceling the offset works well.