The present invention provides an electromagnetic tracking system that includes
a field generator and a field sensor arranged to generate and detect, respectively,
an electromagnetic field. Both the transmitter and receiver coils are connected
to signal conditioning and processing circuitry to provide outputs indicative of
the coil signals. A processor operates on the signals to determine the coordinates
of the sensing assembly relative to the generator assembly. The signal processor
produces ratiometric outputs, and applies a mutual inductance model to solve for
position/orientation coordinates. In some embodiments, a disturber in the form
of a conductive ring or a sheath is disposed about an interfering piece of equipment
to moderate and standardize disturbances due to eddy currents.