3 ms·
Physics fail. I can't see how they would be allowed to market this?
by bioweek 17y ago
Physics fail. I can't see how they would be allowed to market this?
- Confusion 17y agoKindly demonstrate the alleged 'physics fail'. Harvesting the energy of a dozen wifi and GSM signals 24/7 seems a reasonable way to yield a significant amount of energy. Wait, I'll do the math myself: my accesspoint sends at 100mW. If this harvesting device is 10x10cm and, on average, 1 meter from the accesspoint, it will pick up 0.01/Pi ~ 0.3% of that signal, or 0.3 mW. Let's cut that in three to account for conversion efficiency: 0.1 mW. My phone has a 0.9 Ah battery. At 3.7V, this is 12kJ. With an uptime of 200 hours, this means it sends out 17 mW to the world. So could I use this device to power my phone? Only with 170 close-by accesspoints and after 200 hours would my phone be fully charged. So it indeed sounds pretty bogus. Edit: updated as per commentary below and I grant this probably overestimates the actual working of the device. Evenn on an expo, with a couple of hundred hundred GSM signals in the vicinity, it wouldn't work.
- ableal 17y agoYou're still off by a power of ten in the areas: 10x10cm = 0.01 m2. (Edit: by the way, I think you also plugged in the sphere volume formula - surface is 4.pi.r²). Radius of one meter is a bit close - make that three, and you're off by another order of magnitude - 10 uW harvestable.
- bioweek 17y agoThanks for clarifying. I figured it was obvious.
- Confusion 17y agoStill forgot a factor of 4 while dividing through the area over which the EM radiation has been spread.
- gvb 17y agoSimple solution to the RF energy density problem: pop the phone and "harvester" into your microwave and nuke it on high for 3 hours. Bingo, full charge. Demo: http://www.youtube.com/watch?v=uu-oroNqAbs http://www.youtube.com/watch?v=uu-oroNqAbs