Since the invention of the first implantable pacemaker in 1958, wireless implantable microelectronic devices (IMDs) have been significantly improved by going through many generations. They have made it possible to treat a wide range of ailments and disabilities from bradycardia and chronic back pain to epilepsy and deafness. IMDs have the potential to alleviate more challenging types of disabilities such as blindness and paralysis. These devices need to transmit and receive information wirelessly across the skin barrier as breaching the skin with interconnect wires would be a source of morbidity for the patient and significantly increases the risk of infection.

IMDs can be divided in autonomous and sensory devices which, in turn, results in different requirements for the wireless telemetry system. Autonomous devices such as pacemakers, cardioverters, and deep-brain stimulators usually have a small number of stimulating sites (<5), low stimulus pulse rates (<500/s), and low power requirements. The anatomical location of implantation for most autonomous devices in the body allows them to be large enough to contain an energy source that would last for several years. Their autonomous operation limits the need to communicate with the external world to only occasional adjustments and interrogations, which can take place at low data rates. On the other hand, in sensory prosthetic devices—those that interface with the central nervous system (CNS) to restore a sensory function such as hearing or vision—the quality of perception enhances with the number of stimulating sites/electrodes and the rate of stimulation. These latter devices may stimulate the neural tissue by means of tens to hundreds of stimulating channels and, consequently, they generally require considerably more power and communication bandwidth than autonomous devices. Future visual prostheses might even go beyond one thousand sites to better provide the most important visual functions to the blind such as mobility without a cane, face recognition, and reading. Thus, sensory prosthetic devices usually require an inductive link between two (or more) magnetically couple coils for the transmission of power and data to the implanted device.