Numerical Optimization of the Tube-Cored Induction Magnetometer Weight Under Specific Noise Constraints

The aim of this paper is to achieve the minimum weight for the induction magnetometer (IM) with specific noise constraints. First, a tube magnetic core was used to decrease the weight and achieve a similar magnetic concentrating performance as the rod one. The parameters, including the coil resistance, the inductance, the apparent permeability with different coil-to-core length ratios, and the noise equivalent magnetic induction, were evaluated theoretically. A chopping pre-amplifier circuit was used to suppress the <inline-formula> <tex-math notation="LaTeX">$1/f$ </tex-math></inline-formula> noise in low frequencies. Finally, the optimization problem proposed from the practical applications was solved using the penalty function method (interior point method). To verify the theoretical analysis, the optimal IM was manufactured and tested. The experimental results showed 3.1 pT/<inline-formula> <tex-math notation="LaTeX">$\surd $ </tex-math></inline-formula>Hz at 1 Hz, noise floor 22 fT/<inline-formula> <tex-math notation="LaTeX">$\surd $ </tex-math></inline-formula>Hz, and total weight 0.52 kg, which were well coincided with the theoretical calculation. Moreover, the relationships among the noise constraints and the coil weight were also discussed.