Patent ID: 7806122

Claim:
An implantable medical device system comprising: an implantable substance delivery device including: a housing maintaining a reservoir for containing a therapeutic substance, a fill port assembly defining a port chamber having a fill port opening and in fluid communication with the reservoir, a first coil positioned at a known location relative to the fill port opening; and an external locator device for detecting the coil, the external locator device including: a controller, a locator grid including: a plurality of interleaved X-loops electrically coupled to the controller, each of the X-loops defining a major axis that is oriented parallel to a first major axis, at least one Y-loop electrically coupled to the controller and oriented along a second major axis differing from the first major axis; wherein the implantable medical device system is configured such that when the locator grid is spatially proximate the coil, energization of the coil induces a voltage in the at least one Y-loop that is read by the controller, and further wherein the controller is adapted to determine a location of the coil relative to the locator grid based upon the read voltage.