Patent ID: 7285958

Claim:
A method of locating one or more markers, comprising: generating a series of electromagnetic pulses by generating a transmit signal with resonant frequencies from at least one marker and applying the transmit signal to an electronic marker, wherein the generation of the transmit signal includes: determining a marker or more active markers; determining a marker transmit signal to activate the one or more active markers from a frequency, field strength, and phase, wherein the marker transmit signal is phase shifted to provide a delay phase of substantially zero at the end of the electromagnetic pulse; summing the marker transmit signal to form a digital transmit signal; and converting the digital transmit signal to form the transmit signal; receiving signals as a function of time between application of the pulses; averaging the signals over a predetermined number of pulses to obtain an average decay signal; initially determining a frequency, field strength, and phase for responses from the one or more markers; accurately determining the frequency, field strength, and phase by successive elimination of a contribution from each of the one or more markers; and refining the electromagnetic pulses in order to provide resonant frequencies for each of the one or more markers.