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Re: 'MIT/Wireless power/ 50% asserted (fwd)



---------- Forwarded message ----------
Date: Fri, 08 Jun 2007 09:30:49 -0700
From: Jim Lux <jimlux@xxxxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: 'MIT/Wireless power/ 50% asserted (fwd)

At 05:58 AM 6/8/2007, you wrote:

>---------- Forwarded message ----------
>Date: Fri, 08 Jun 2007 07:06:09 -0400
>From: davep <davep@xxxxxxxx>
>To: Tesla list <tesla@xxxxxxxxxx>
>Subject: 'MIT/Wireless power/ 50% asserted
>
>Just heard radio news.
>50% energy transfer efficiency claimed,
>(Presumably over 'lab scale' distances:
>few meters.)

0.5 m transmit and receive coils, 2m apart.  I think we can fairly 
say that the coils are in each other's "near field"

Hey, if they keep the IR losses low enough in the coils, and make 
sure it's well away from anything else, you could get 50% efficiency 
(e.g. lose 20% in IR losses in tx coil and 20% in rx coil, etc.).

The rest of the field in the space around the coils is just stored 
energy and air is pretty darn close to loss free.


As far as minor details like RF safety, losses in surroundings, the 
need to have both coils oriented properly, etc., ... "We scientists 
have demonstrated the principle, it's up to you engineers to take 
care of the minor practical details. Our work is done. On to the next 
(re)discovery."

Just as a quick back of the envelope...
The 0.5 meter coil has an area of pi*(0.25^2) square meters
They're pulling out 60W(?.. doesn't say if lit to full brilliance).. 
so that implies that the energy density at the receiving coil is (at 
best) 60W/0.4m^2.. 150W/m^2  (about what you get out of middling good 
solar cells in full sunlight).  15mW/cm^2  ...   The RF exposure 
limits run in the "few" milliwatts per square centimeter range, 
depending on frequency.


One might want to compare energy densities with something like an 
induction heating cooktop...