A system for enabling the acquisition from outside the body of a patient of data pertaining to a medical device implanted therein. A characterization tag is secured to the medical device prior to the implantation thereof. The characterization tag is powered by energy absorbed through the mutual inductive coupling of circuitry in the characterization tag with an alternating magnetic field generated outside the body of the patient. That circuitry in the characterization tag is selectively loaded and unloaded in a predetermined sequence of loading conditions that correspond to data about the implanted medical device. The alternating magnetic field is generated in a characterization probe, moveable external to the body of the patient. The probe includes electrical circuitry for sensing variations in the amount of energy absorbed from the field by the characterization tag. The characterization tag is secured to the exterior of the medical device by a biocompatible potting material in a characterization tag recess or, if the medical device is assembled from a plurality of constituent parts, by permanently capturing the characterization tag between a pair of these parts. Two single fluid reservoir access ports, a double fluid reservoir access port, a septum-less access port, and prosthetic hip joint are disclosed employing the system.