Charging your phone with ambient electromagnetic radiation ? they can?t be serious!

Iphone charging

Apparently Nokia claimed that by 2013 it will be possible to charge your cell phone from the ambient electromagnetic radiation (AER) emitted by Wi-Fi transmitters, mobile phone antennas and TV masts. This sounds amazing! Who wouldn’t want a phone that never needs to be charged? But, when making the sums I can’t see how they’re going to pull this one off.

Most cell phones consume about 2W of peak power during a conversation that works on a +- 20% duty cycle. This means that to talk for one minute your phone needs about 6.6 mW-h of battery power.

Typically the signal levels of radio, TV and cell phones are quite low unless you stand right in front of the base station antenna. I just spoke to a friend of mine who is an expert on base station safety and compliance. Their company has done over 65 000 measurements for Vodacom (a large service provider in South Africa) and most of their measurements show that the total signal strength in public areas is more than 10 000 times below the ICNIRP safety compliance standard. Thus the maximum AER power in most places is less than 1 mW/m2.

If we assume the surface of the antenna is the same size as the phone (+- 40 cm2) and receives all the power that hits the antenna (i.e. 100% absorption, no loss) it will receive 0.4% of 1 mW which is equal to 4 uW.

This means you have to charge your phone for 1650 hours (almost 70 days) to be able to talk for one minute!

Here’s another interesting blog article, http://boingboing.net/2010/01/12/rcas-wifi-power-harv.html where they determined that it would take 34.5 years to charge a Blackberry when holding it 5 feet from a Wi-Fi router.

Author: Robert Kellerman

One Response to “Charging your phone with ambient electromagnetic radiation ? they can?t be serious!”

  1. Only 1,650 hrs for 1 minute! I love it!

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