This paper discusses harvesting of low-power density incident plane waves for electronic devices in environments where it is difficult or impossible to change batteries and where the exact locations of the energy sources are not known. As the incident power densities vary over time and space, distributed arrays of antennas with optimized power-management circuits are introduced to increase harvested power and efficiency. Scaling in array size, power, dc load, frequency, and gain is discussed through three example arrays: a dual industrial-scientific-medical band Yagi-Uda array with a low-power startup circuit; a narrowband 1.96-GHz dual-polarized patch rectenna array with a reconfigurable dc output network designed for harvesting base-station power; and a broadband dual-polarized 2-18-GHz array with multi-tone performance. The efficiency of rectification and power management is investigated for incident power densities in the 1-100-W/cm range.

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This paper introduces a new capacitive wireless power transfer approach with the potential to significantly enhance power transfer density in large air-gap applications. This enhancement is achieved through the use of multiple phase-shifted capacitive plates that reduce fringing fields in areas where field levels must be limited for safety reasons. The effectiveness of the proposed approach is evaluated using an analytical framework and validated using finite-element and circuit simulations. It is shown that a 6.78-MHz eight plate-pair system based on the proposed approach reduces fringing fields by a factor of five relative to a two plate-pair system while retaining the same power transfer density.Index Terms -Wireless power transfer, capacitive power transfer, modular architecture.

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