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Changing energy from one form to another, such as solar radiation from sunlight to dc voltage, can help meet the growing global demands for energy in the years ahead. In the near term, it is also a practical means of providing power for remote sensors and other electronic devices that must be “set and forget” as part of Internet of Things (IoT) applications. Even when such devices are in standby mode, awaiting a signal, they consume energy and require a power source.
With this goal in mind, French researchers sought an alternative to a single omnidirectional antenna for collecting what RF energy was present in a room, such as in a home or factory setting. They developed a system that combines six parasitic element antennas (PEAs) and RF-to-dc converter circuits to transform RF energy into dc voltage.
Given the growing number of wireless devices, from smartphones, tablets, and other mobile devices connected to a small cell, base station, or Wi-Fi gateway, the amount of “discarded” RF/microwave EM radiation is enormous and readily available for scavenging and reuse. Many RF-to-dc conversion circuits have been developed for this purpose, but they have been hampered by the limited efficiency of their antennas, otherwise known as “rectennas.”
The researchers focused on boosting the efficiency of an RF-to-dc home-automation system by improving the performance of an array of six rectennas within a room. Their solution was to take a cellular approach to energy harvesting within the room, combining printed-circuit-board (PCB) rectennas with RF-to-dc-conversion circuits on the same circuit board, about the size of a credit card.
Developed for use at 2.45 GHz, the compact energy-harvesting system was designed, manufactured, and tested, and found to be capable of providing enough energy to maintain additional circuits, such as an RF switch. The researchers performed simulations and computed that the system would deliver different amounts of energy based on room size; for example, 1723 and 880 mV, respectively, for rooms measuring 5 × 5 m and 10 × 10 m.
See “Multidirectional Receiving System for RF to dc Conversion Signal,” IEEE Antennas & Propagation Magazine, Vol. 58, No. 3, June 2016, p. 22.