Out-of-band radiation: Opportunities for antenna-based RF energy harvesting in wireless devices?

In this paper opportunities for wireless devices to harvest out-of-band RF energy are explored. Emerging multi-standard wireless communications devices such as mobile handsets currently include multiple antennas and multiple transceiver systems. Typical device usage leverages a subset of available antenna and transceiver systems at any given time. Additionally, receiver chains in use typically filter out-of-band energies to improve communications system performance. These out-of-band energies can be collected in multi-antenna and single-antenna systems or simpler devices such as wireless sensor nodes. In this paper, opportunities for harvesting out-of-band energy are investigated. Investigations use both data collected from an extensive measurement campaign spanning 88-2686MHz across 4 mid-sized US cities as well as simulations to provide insights into the opportunities for RF energy harvesting. An architecture is proposed using a 3-port out-of-band RF harvester to enable opportunistic capture of ambient RF energy. The proposed approach is demonstrated via simulation using a planar inverted-F antenna with feed line coupled to a split ring resonator, for harvesting out-of-band energy. Results indicate that potentially significant proportions of ambient energy remain untapped and can be harvested using the proposed approach. This work provides valuable insight into the design space for harvesting out-of-band RF energy.