Method and apparatus for detection using magnetic gradient tensor

摘要

Locating and characterising a magnetised body involves moving a magnetic gradient tensor sensor relative to the magnetised body along a profile, or allowing the magnetised body to move along a profile past the sensor. Magnetic gradient tensor measurements are obtained at points along the profile. A rotational invariant calculated from the eigenvalues of the magnetic gradient tensor measurements is then used to locate and/or characterize the body. The rotational invariant can be the scaled moment of a point dipole representation of the magnetised body, or one third of the square root of the scaled moment. The rotational invariant is modelled and sufficient measurements obtained to over-determine parameters of the model. A system of linear equations resulting from a model of the gradient tensor elements is then solved using the determined values of parameters.