1) Power from mains to antenna, which is made of copper
2) Antenna resonates at a frequency of 6.4MHz, emitting electromagnetic waves
3) 'Tails' of energy from antenna 'tunnel' up to 5m (16.4ft)
4) Electricity picked up by laptop's antenna, which must also be resonating at 6.4MHz. Energy used to re-charge device
5) Energy not transferred to laptop re-absorbed by source antenna. People/other objects not affected as not resonating at 6.4MHz
I have tried to find more details about what Soljacic means by 'tails' of energy 'tunneling' between the coils, but have so far found nothing. The text of the paper he was going to present is not online yet. Soljacic claims that the system can work with up to 50% efficiency, which is good enough for small applications such as delivering power to peripherals on and around the desktop. The system he describes is designed to provide power within a 5 meter radius, but he also claims that similar systems could work both at nanoscale and at the scale of a factory floor.
Of course, all of this remains to be proven, since as far as I can tell no-one has actually built a system yet. It's all just theoretical results. Also, it is not clear whether there will be any significant side-effects, either for living things or for other electronics. I eagerly look forward to further developments. Interestingly, what inspired this bit of research was Soljacic's repeated irritation with forgetting to plug his cellphone into its recharger.
Addendum:
I finally located a preprint of Soljacic's paper on arxiv.
4 comments:
The article says, “Any energy not diverted into a gadget or appliance is simply reabsorbed. “ It’s been a long time since I did any reading on this kind of topic. Do you know if this means that there would be no energy at all radiated and thus no chance of producing noise or interference with nearby devices? If flickering tails of radiation emerge from the device seeking a similarly tuned circuit it sounds to me like there is some radiation which could affect nearby devices. Maybe this is so localized as to be of insignificant concern but it still sounds to me like there is some continuous energy drain when the device is on even if no other device is receiving energy. While this might not be significant for a device designed to charge your cell phone it could be more substantial if the device is suppose to power your space heater or recharge your electric car.
Several of the articles I ran across quoted Soljacic as saying that he expected to be achieve about a 50% efficiency rate. That is, only 50% of the power would be transmitted. The rest would presumably be lost in radiative and other losses.
I finally located a preprint of the paper on arxiv.
Gotta go decipher it....
Fifty percent loss is pretty fatal for most applications. One would have to have a very essential need without better alternatives to use this kind of device given that your cost of power would double. Maybe one could use this technique to charge a pacemaker battery or the battery in an implanted IV pump where direct access is inconvenient to say the least.
While a 50% loss would definitely be a bad thing for, say, an arc welder, for myself I would gladly pay a few pennies more on my electric bill simply to be done with the tangle of little wires that connect clunky transformer 'warts'. And I somehow suspect that these little, heavy, ugly masses of plastic, iron and copper are not exactly paragons of electrical efficiency, either. I can envision a reasonable compromise solution for the desktop computer:
-a single big conventional cord that connects the main box to the wall
-a Soljacic-type wireless power system for all of the peripherals: keyboard, mouse, speakers, printer, etc.
-possibly one more conventional power cable to the monitor in case your 52" screen will draw more power than you are willing to waste wirelessly
Of course, I am presuming that all of the signal-type wires are replaced by Bluetooth or some such.
Soljacic et al. said in their paper that their work was strictly preliminary. They expected that some basic experimentation and engineering could improve matters. I could see that a slight bit of directionality might be better than a perfectly uniform field. For example, it would be better if the oscillating magnetic field only went toward the front of the computer box, and not back into the wall where it definitely would be wasted.
Regardless of any of that, I just want to play with one. I looked at the paper for a bit, but it is clear that my EE theory is now rusty enough that building a simple model might well require an inordinate amount of fooling around. Thus prudence tells me to wait until someone else builds one. In the meantime, I'll just dream.
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