I came across this in a recent ECN Daily email. I have heard of other purported means of harvesting "free" energy, but of course Heinlein was spot on with TANSTAAFL.
I wonder if there is enough power in the electromagnetic field anywhere to achieve anything even close to the claims for this device, which supposedly can harvest perhaps 5 W-H of energy to fully charge a typical cellphone battery in 90 minutes. And if so, what would be the effects on the health of life forms in such a field, and the operation of other electronic equipment.
People are concerned about the health effects of EMF near power lines, but perhaps they should be very afraid of the energy in WIFI hotspots. Assuming an antenna of 100 cm^2, the charger would need to be in a field of about
300W/sq meter. And 2.4 GHz. Probably about the same as a microwave oven with the door open.I found that the exposure limit is about 50W/sq meter.
I tried to find the power density inside a microwave oven, and came across this:
My rough estimate, assuming a 1000W oven, with an inside surface area of
0.5 sq meter, is 2kW/sq meter.According to this website, WIFI transmitters produce an energy density of about 0.04 mW/cm^2 or 4mW/sq meter at a distance of one meter. Even if you could capture half of the radiated energy (250mW), using an antenna perhaps sized and shaped like an umbrella, it would still take 40 hours to charge the battery.
But watch the presentation in the top link. Gotta love the Oz!
Paul