Witricity

MIT has been doing some work recently on power transmission by using resonant transformers. That is, both the primary and secondary are resonant at the same frequency. The claim is that they will get increased efficiency, and that the primary and secondary can be at some distance.
They have coined the term 'Witricity' to describe this.

Apparently they powered a 60w bulb at some distance via this method. However, their main focus seems to be remotely powering devices such as laptops.

I have some doubts as to the ultimate efficiencies that they may realize. Of course, a lot of media are predicting some truly amazing results, but I remain skeptical.

I will agree that you can direct an EM field using a solenoid or Helmholtz coil arrangement. The field strength in these cases is well documented.

Making the primary resonant can also make it easier to drive. However, I don't understand why they apparently chose 10MHz as their frequency.
(Or so the media says)

Where I see things breaking down is on the receiving end. A resonant receiver will indeed provide good coupling to the source --AS LONG AS IT'S LIGHTLY LOADED. As soon as you try to draw significant power from the secondary, you pretty much remove the benefits of resonance.

Think of coupling sound energy into a tuning fork. Doesn't matter what the source of the sound is, just that it's at the proper frequency. The tuning fork will resonate wonderfully. Now try to use that energy to drive some mechanical contrivance. The tuning fork will no longer be free to move at resonance, and it will not really provide any benefit.

I also predict that there will be problems with detuning by environmental elemets. In the 60w light bulb demo, someone apparently put a piece of wood in the middle of the field, and it had no effect. Not too surprising. Results might have been a little different if there was a piece of metal in the area.

I also think that they are a little naive on the health impact, but this is a physics forum, so I won't go into that.

I would be glad to be proven wrong about this subject, but I don't think that I will be. They may be able to make some low current remote charging devices, but I think that there will be severe limits on what can be accomplished.

ford2go

Somewhere in the bowels of this forum amongst all the dead threads, decaying flesh, and fossilised Scottish rock samples there is a thread where this was discussed before, I for one agree with you, as soon as you load your tuned circuit the Q factor will decompose faster than an Aberdonian's ...... well you know what I mean.

I am not sure that the health impacts you mention will be a problem 10Mhz is pretty low, I have worked with powers of up to 25KW at 30Mhz with noooo noooo nooo f=1/2pi sqr(lc) noo problems.

Unless you are referring to Inductive heating which can bee effective from Kilohertz upwards.

Was there a particular article you can link to, so I can have a butchers?

Even though I know little about electrical mechanics, I agree with you; your argument seems to make sense.

How do you tune a transformer?