Research on the Model and the Location Method of Ship Shaft-Rate Magnetic Field Based on Rotating Magnetic Dipole

In this paper, the ship’s rotating propeller is a considered as rotating magnetic dipole. The shaft-rate magnetic field is modeled, and an inversion calculation is utilized to realize the magnetic target localization. The low frequency of the shaft-rate magnetic field provides long propagation distance, high stability, and low interference by sea conditions and other noises. The magnetic field signal has an important role in target and location detection. In the developed model, the magnetic moment of the rotating magnetic dipole is decomposed into three orthogonal magnetic moments indicated by $m_{p},m_{f}$ and $m_{l}$ . The mentioned moments can be obtained through a three-component integration of the measured magnetic field of the rotating dipole at a point. The relation between the eigenvectors of these orthogonal magnetic moments and the coordinates of the observation position is employed to obtain the coordinates and the magnetic target position. In the simulation, the relative and absolute errors of the location method are analyzed, while the measurement noise confines the positioning distance. Finally, the rotating magnetic field of 80 points is measured, and the feasibility of the rotating magnetic model is verified. Besides, the relative mean error of 80 points is equal to 3.7%, demonstrating the feasibility of the location method. However, due to some experiment limitations, including the measurement distance, measurement error, and the experimental equipment sensitivity, the maximum relative error is obtained as 7.4% which is higher than its theoretical value.