1. A method comprising: producing a first magnetic field in the vicinity of an object such that a current is induced in the object, the object having an orientation relative to a direction of propagation of the first magnetic field; sensing quadrature and in-phase data representing a second magnetic field produced by the current induced in the object; fitting the sensed data to a two-dimensional signature to a model of an object; generating, from the fitted data, a parameter that is independent of the orientation of the object relative to the first magnetic field; extracting a feature of the object from the parameter; and determining whether the object is an object of interest based on the feature.