Biomedical implants such as cochlear implants, retinal implants, brain implants, cardiac pacemakers, implanted defibrillators, and electronic pills require information to be wirelessly communicated from outside the body to inside the body and vice versa. Wired links from an external electronic unit to an implanted unit inside the body are prone to infection in the long term and are thus unlikely to meet approval by regulatory agencies such as the Food and Drug Administration (FDA). Thus, wireless communication is essential in such implants. in Chapter 16, we discussed how to wirelessly transmit power to such implants via an RF inductive near-field link. Near-field communication is important when the distance of communication, often 1 mm to 10 mm across the skin of the patient, is considerably less than the RF carrier wavelength. In contrast, in far-field communication systems used in most traditional radios, the communication distance is significantly in excess of the carrier wavelength. The relationship between near-field and far-field communication is discussed in quantitative depth in Chapter 17 on antennas and RF energy harvesting.

In this chapter, we shall first focus on how to communicate data via ultra-low-power near-field RF telemetry in such implants.