Some approaches:

http://www.instructables.com/id/Free-energy-generators/

http://www.gtresearchnews.gatech.edu/device-captures-ambient-energy/

http://www.techweekeurope.co.uk/news/scavenging-free-green-power-from-radio-waves-35622

http://www.eurekalert.org/pub_releases/2013-11/du-wdc110713.php

http://www.impactlab.net/2011/12/21/this-magic-box-harvests-spare-electricity-from-your-microwave/

http://www.pratt.duke.edu/news/wireless-device-converts-lost-energy-electric-power

Regards,

Joachim

known as RF energy harvester.

contains of:

i) an antenna,

ii) RF-to-DC rectifier circuit, and

iii) signal conditioning circuit.

electromagnetic wave (RF ) is received by antenna. then the RF signal is converted to DC signal by RF-to-DC rectifier. to stabilized the DC signal, the signal conditioning circuit is used.

Cont'd..

the output DC signal of the RF energy harvester can be used to powering the wireless sensor devices.

I read somethings about your interest. Some groups working on that issue (especially , the aim of use sunlight with others) the Georgia team working on the antenna, if they or smone succeed, that ultra small antenna tech. will initialize respectively for harvesting....