Duty Cycle Operation of an Orthogonal Fluxgate

Orthogonal fluxgate employing duty cycle operation is developed and tested. The fluxgate wire core is excited in duty cycle and the output is sampled only once, at a single time instance in each excitation cycle. As a result, the output signal is simultaneously sampled and demodulated back to baseband. The excess magnetic noise and the decrease in sensitivity caused by the discontinuous excitation are avoided by omitting the idle intervals, which contains that noise and does not contain information of the measured external field. By selecting the optimal bandwidth of the antialiasing filter, we gather signal from a controlled number of harmonics adjacent to the fundamental and dramatically improve the equivalent magnetic noise. By operating at a duty cycle of 1/128, the fluxgate excitation power consumption is dramatically reduced by a factor of 120 from 7.7 mW to 64 μW, while the equivalent magnetic noise remains at 6 pT/√Hz at 1 Hz. The proposed approach not only reduces the fluxgate power consumption, but also simplifies the fluxgate output processing by eliminating the need for analog or digital synchronous detection. We show that the power consumption of an orthogonal fluxgate operated in duty cycle can come close to other extremely low-power magnetometers, such as search coil and magnetoelectric sensors but significantly surpass their resolution at low frequencies.