Abstract: The invention provides a method for magnetic imaging of an object. The method comprises monitoring a magnetic field of sources in the object at a plurality of magnetic detectors to obtain a corresponding plurality of sensor outputs, monitoring a position of the object while monitoring the magnetic field of the sources, modeling the magnetic field of the sources in the object as a gradient of a scalar potential, the scalar potential comprising a sum of spherical harmonic functions each multiplied by a corresponding coefficient, and, compensating for the position of the object by applying a transformation to the plurality of sensor outputs, the transformation including, at least in part, a spherical harmonic translation transformation.

Abstract: The invention provides a method of compensating for crosstalk between electromagnetic sensors in an array, each sensor having a flux transformer with a current therein which does not vary smoothly with an applied magnetic field, each sensor configured to produce an output signal comprising a stepwise varying component and a finely varying component. The method comprises, for each sensor to be compensated, applying a crosstalk compensation function to the output signal of the sensor to be compensated, the crosstalk compensation function based at least in part on at least one of the stepwise and the finely varying components of at least one other of the sensors in the array.

Abstract: A method for locating an object relative to an array of magnetic sensors in an environment in which there is present a noise signal having a fundamental frequency fNOISE, includes generating one or more magnetic signals by means of one or more magnetic emitters mounted at known locations on the object during an integration time T. The one or more magnetic signals have one or more frequencies. The one or more magnetic signals and the noise signal are detected at six or more magnetic detectors. Relative amplitudes of the magnetic signals are determined. The one or more frequencies of the magnetic signals are substantially equal to frequencies at which a power spectrum of the detected noise signal has zeros.