Highest Wireless Power: Inductively Coupled Or RF?

Abstract

Embedded microsensors are the critical components for the Internet of Things (IoT) as they provide interfaces between the physical and the digital worlds. Unfortunately, these microsensors' tiny batteries cannot sustain their operation for long. Ambient energy sources, such as light or motion, are not always available, so transmitting power wirelessly is often the only option to recharge their onboard batteries. This paper discusses and compares two of the most popular wireless power transfer technologies: inductively coupled and RF, in terms of their highest output power over distance. As an example, a 125 kHz, coil-based inductively coupled power transfer system is compared with a 2.45 GHz, antenna-based RF power transfer system. When closely coupled, the inductively coupled receiver outputs higher power density with a normalized transmitter. As the distance grows, the power density of the inductively coupled receiver decays 3 times faster than the RF. So past 3.5 times of the transmitter's length, the RF's power density beats the inductively coupled.