Electrically small antenna design: from mobile phones to implanted sensors

In this review, intended to introduce the convened session on electrically small antennas, we describe the evolution of electrically small antennas from the early nineties, when the boom of mobile phones triggered an intense research activity on the, to our days, where virtually everything has a wireless connection. A special emphasis will be set on antennas for wearables and implants, as in those cases the strategies and limitations derived for electrically small antennas radiating into free space do not hold anymore. We will present the design strategies based on fundamental limitations and the special care that should be taken to measure and simulate such antennas.