Estimation of dipole magnetic moment orientation based on magnetic signature waveform analysis by a magnetic sensor

In this paper, we propose a measurement procedure to estimate the magnetic moment orientation (MMO) of a dipole. Theoretical analysis indicates that magnetic field in each orthogonal direction Bi (i = x, y, z) is found to be a superposition of its three basic elements B-ij (i = x, y, z and j = 1, 2, 3) along certain direction, allowing the obtained dipole signature to be decomposed of 9 basic elements. An orthogonal energy ratio (OER) algorithm is used to infer the MMO by calculating the signal energy distribution along each axis. A standard OER database is developed which provides a reference to be compared with the measured OER. The one having the smallest variance is determined as the estimated MMO. Owing to space symmetric property, it generally introduces 8 possible solutions. Then, a mathematic method is presented to define the common characteristics of the magnetic signature in the 8 octants, which is able to identify the octant of unknown target based on detected Bi field. As a result, the unique MMO can be estimated. The experimental results show good estimation accuracy for the dipole orientation with average error of 3.5 degrees. In particular, the algorithm is independent of changing CPA and velocity, which is demonstrated in simulation and experiment.