
{"publication_number": "US-6373240-B1", "abstract": "a method for tracking an object , including producing an unperturbed energy field at a plurality of predetermined frequencies in the vicinity of the object and determining a characteristic of a perturbing energy field induced responsive to the unperturbed field , due to introduction of an article , responsive to the unperturbed field , into the vicinity of the object . the method further includes receiving a plurality of resultant signals responsive to the unperturbed and perturbing energy fields generated at a location of the object after introduction of the article , determining an optimal frequency for the unperturbed energy field from amongst the plurality of predetermined frequencies responsive to a parameter of the resultant signals , and determining spatial coordinates of the object responsive to the resultant signal at the optimal frequency .", "application_number": "US-70297300-A", "description": "reference is now made to fig2 which schematically illustrates a system 10 for tracking a probe 20 , such as a catheter for medical use , according to a preferred embodiment of the present invention . the operation of systems generally similar to system 10 are described in detail in the above - mentioned u . s . patent application ser . no . 09 / 173 , 763 , u . s . pat . no . 5 , 391 , 199 , and pct patent publication wo / 96 / 05768 , whose disclosures are assigned to the assignee of the present invention , and which are incorporated herein by reference . system 10 comprises a plurality of radiator coils 22 , 24 and 26 . these coils generate respective magnetic fields h , h and { right arrow over ( h )