On Tue, Jun 09, 2009 at 02:40:29PM -0700, Gary wrote: > > Imagine if you could harvest enough juice to run a low power AP... > > Tuesday, June 09, 2009 > Wireless Power Harvesting for Cell Phones > > Nokia hopes to create a device that could harvest enough power to keep a > cell phone topped up. ... > Rouvala says that his group is working towards a prototype that could > harvest up to 50 milliwatts of power--enough to slowly recharge a phone > that is switched off. He says current prototypes can harvest 3 to 5 > milliwatts.
There is just not enough radio power in most places. Assuming a transportable harvesting array 20 inches on a side, and 20% efficiency (VERY difficult for broadband), that imply a radio field of 1 watt per square meter. That might work if you were in a balloon floating a few hundred meters from the Sylvan TV transmitters directly in the center of the beak, but not miles away. That much energy would probably swamp the receiver of an access point, even though the AP is tuned to a very different frequency. Note also that rectifying radio energy splatters harmonics all over the place - unless the circuit is tuned, which they are claiming they are not. You can make very high power tuned beams - radars do this. Inside a box, this is called a microwave oven, and is not very healthy in the beam. There are FCC limits to how much concentrated radio energy you can splatter around, and engineers work hard to not splatter it. For comparison, 50mW is what you can collect with a 10% efficient, 1 inch square solar cell on a sunny day, or a 10 inch square cell on a darkly cloudy day. An access point needs about 5 watts when moving data. Keith -- Keith Lofstrom [email protected] Voice (503)-520-1993 KLIC --- Keith Lofstrom Integrated Circuits --- "Your Ideas in Silicon" Design Contracting in Bipolar and CMOS - Analog, Digital, and Scan ICs --~--~---------~--~----~------------~-------~--~----~ The Personal Telco Project - http://www.personaltelco.net/ Donate to PTP: http://www.personaltelco.net/donate Archives: http://news.gmane.org/gmane.network.wireless.portland.general/ Etiquette: http://www.personaltelco.net/index.cgi/MailingListEtiquette List information: http://lists.personaltelco.net To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] -~----------~----~----~----~------~----~------~--~---
