London RF survey for radiative ambient RF energy harvesters and efficient DC-load inductive power transfer

This paper presents experimental results of energy harvesters working from ambient RF sources and an efficient inductive power transfer (IPT) system. A city-wide RF spectral survey was undertaken outside all of the 270 London Underground stations. Results from this unique survey demonstrate that DTV, GSM900, GSM1800 and 3G are the highest contributors. As a result, single and multiband rectennas were fabricated for these frequencies. Based on the spectral survey and the harvesters' performance, it is expected that more than 220 of the surveyed locations are suitable for ambient RF energy harvesting. Finally, experimental results from a high frequency IPT system with a semi-resonant Class-E driver, capable of transmitting 105 W with a dc-to-load efficiency above 77% across a distance of 30 cm, are presented.