Wireless sensor networks (WSN) have gained increasing recognition and constitute an integral part of modern day high-speed wireless communication. In general, a WSN comprises a large number of static sensor nodes with low processing and limited power capabilities that often communicate over short-range radio links. With the widespread use of wireless sensors, the management of their energy resources has become a topic of great interest. The sensor nodes usually rely on conventional batteries for their power supply. However, replacing batteries periodically for a large number of sensors is a cumbersome process and requires a considerable amount of time, thereby affecting the working of the sensor networks.

Recently, wireless energy harvesting has emerged as an appealing solution to energize low-powered wireless autonomous devices, such as wearable devices, Internet of Things (IoT), and sensor nodes in modern wireless systems. Energy harvesting is the process that captures energy from ambient natural sources and converts them to electricity to energize these low-power devices. The energy harvesting approach is a green and sustainable solution and can operate for years without human intervention, as compared to conventional battery sources. Among the different ambient sources, harvesting energy from radio frequency (RF) signals has emerged as a promising and convenient solution to power energy-constrained wireless systems. However, harvesting energy from ambient RF sources for wireless sensor networks involves many challenges and requires attention from researchers. For example, the limited capability of energy harvesting systems to capture ambient RF power along with a low RF-to-DC conversion efficiency acts as a major obstacle in the development of practical harvesting systems.

This Special Issue aims to take advantage of the opportunity provided by this topic for the development of energy efficient future wireless sensor networks and wireless devices, and to satisfy the demand for new theories and contributions in the development of state-of-the-art wireless energy harvesting devices. We welcome contributions on state-of-art energy harvesting architectures for potential applications in future 5G/millimeter-wave/3D wireless technologies, as well as those with applications in future wireless communications, IoT, and smart city wireless systems.

Potential topics include but are not limited to the following:

• Millimeter-wave wireless harvesting system designs
• Modeling and characterization of antennas for harvesting applications
• Designing high efficiency and low-powered rectifier circuits
• Higher order harmonic attenuating bandpass filter designs
• Semiconductor devices for energy harvesting and power transfer applications
• New design topologies for high performance rectenna systems
• Multi-layered strategies for the design of energy harvesting system
• Miniaturized array configurations and beam-steering topologies for high gain and efficient rectenna systems
• Flexible and wearable rectenna system for light-weight and portable wireless sensor networks
• Compact metamaterial/metasurface designs for performance enhancement of rectenna systems
• Multichannel selection strategies and energy harvesting in cognitive radio systems
• Evolutionary algorithms for the optimization of rectenna designs and performance efficiencies
• 3D-based wireless energy harvesting/power transfer systems