Abstract
A simple design for the orthogonal fluxgate (OFG) mechanism in the fundamental mode is presented with detailed descriptions of the circuit. To avoid complexity in the circuit, an offset common to the fundamental mode is largely suppressed by using a U-shaped wire core and using a large dc bias current at the cost of increased power consumption. The remaining offset can be nulled at the final stage by a simple subtraction. The circuit presented in this paper consists of a logic inverter gate IC for a sinusoidal oscillator, two operational amplifiers, and a modulator/demodulator IC (AD630), as well as a U-shaped sensor head made of thin magnetic wire or thin magnetic ribbon. A magnetometer we developed with this design provided resolution of 10 pT/ √Hz for frequencies greater than 1 Hz.
