METHOD AND APPARATUS FOR DETECTION USING MAGNETIC GRADIENT TENSOR

摘要

Locating and characterising a magnetised body involves moving a magneticgradient tensor sensor relative to themagnetised body along a profile, or allowing the magnetised body to move alonga profile past the sensor. Magnetic gradient tensormeasurements are obtained at points along the profile. A rotational invariantcalculated from the eigenvalues of the magnetic gradienttensor measurements is then used to locate and/or characterise the body. Therotational invariant can be the scaled moment of a pointdipole representation of the magnetised body, or one third of the square rootof the scaled moment. The rotational invariant ismodelled and sufficient measurements obtained to over-determine parameters ofthe model. A system of linear equations resultingfrom a model of the gradient tensor elements is then solved using thedetermined values of parameters.