Technological Challenges and Theoretical Limits of Energy Harvesting by Electromagnetic Fields at Microwave Frequencies and Beyond

Modern life is more and more based on the massive use of small, heterogeneous, and interconnected electronic devices dedicated to different functions, such as mobile phones, smart electrical appliances, smart car sensors, wireless sensor networks, and actuators, just to cite some of them. In this complex context, where the devices are geographically distributed and, in most of the cases, are in motion, one of the issues is to make them self-powered. Energy harvesting (EH) from different fonts seems to be promising to this scope, but still deserves technological challenges and suffers from theoretical limits.

The Special Issue is dedicated to EH from electromagnetic sources. Many anthropic sources (e.g., radio and TV towers, cellular base stations, radar, mobile phones, and wifi routers) radiate electromagnetic waves in a wide frequency range. As a matter of fact, the advent of new generation communication systems entails the increasing presence in the environment of radiations at frequencies even higher than 60 GHz. Although such sources are designed for communication purposes, in principle, their radiated energy can be exploited for powering low-consumption devices. Also, dedicated sources, specifically designed for powering purposes, can be considered (in this case, the local laws currently in force for health safety dictate limitations on the radiated power and licenced frequency band must be observed).

Concerning EH from electromagnetic sources, both anthropic and dedicated, one of the main difficulties is related to the low level of available power density at the single node. Transfer efficiency mainly depends on several factors that contribute to the so-called link power budget: the kind of radiating source (frequency band, transmitted power, antenna gain and polarization, and beamforming) and the propagation channel (free space, urban environment, indoor, and outdoor) provide the density power level at the nodes. The efficient extraction of such a power at the node location relies on the receiving antenna and on its matching network. Then, rectifying the circuit and receiver architecture plays a crucial role in energy transformation and storage. All of these factors need to be understood and optimized to achieve a level of power sufficient to supply a single device. This Issue welcomes works concerning miniaturization, broadband devices, self-adaptive antennas, and matching circuits. It is also worth investigating the possibility of designing hybrid systems, based on the simultaneous and synergic use of different physical sources, such as vibrations, in addition to the electromagnetic one.

Progress beyond the state of the art is in the investigation and optimization of all these key aspects.

Prof. Dr. Adriana Brancaccio
Guest Editor

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• Energy harvesting
• Wireless power transfer
• Wireless sensor networks
• Radiowave propagation
• Matching network
• Rectennas
• Multiband rectennas
• Low power devices
• RF measurements