A German student has built an electromagnetic harvester that recharges an AA battery by soaking up ambient, environmental radiation. These harvesters can gather free electricity from just about anything, including overhead power lines, coffee machines, refrigerators, or even the emissions from your WiFi router or smartphone.
In essence, every electrical device gives off electromagnetic radiation — and if that radiation passes across a coil of wire, an electrical current is produced.
The efficiency of wireless charging, however, strongly depends on the range and orientation of the transmitter, and how well the coil is tuned to the transmitter’s frequency.
One question does remain, though: How much ambient, wasted electromagnetic radiation is actually available?