Method and apparatus for detection using magnetic gradient tensor

摘要

Locating and characterising a magnetised body involves moving a magnetic gradienttensor sensor relative to the magnetised body along a profile, or allowing themagnetised body to move along a profile past the sensor. Magnetic gradient tensormeasurements are obtained at points along the profile. A rotational invariantcalculated from the eigenvalues of the magnetic gradient tensor measurementsis then used to locate and/or characterise the body. The rotational invariantcan 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 invariantis modelled and sufficient measurements obtained to over-determine parametersof the model. A system of linear equations resulting from a model of the gradienttensor elements is then solved using the determined values of parameters.