3 ms·

Wouldn't the RF coupled version use a magnetic field as well, because the electric field is osciollating? Seems like the difference is in how spatially localiz

Wouldn't the RF coupled version use a magnetic field as well, because the electric field is osciollating? Seems like the difference is in how spatially localized the two are, and % magnetic power vs electric. Presumably though there is probably some way to drive (or receive) the wireless charger in a dangerous way so you can microwave things from a distance :p

beambot 12y ago
In "magnetic coupling", the bulk of the power transfer occurs due to strong mutual coupling between the antennas (eg. a transformer). For electromagnetic, the waves are propagating (oscillating electric and magnetic moving through space) and the coupling between receiver and transmitter is weak (ie. loading the receiver has no effect on the transmitter). Both are governed by Maxwell's Equations. Sometimes you'll hear these referred to as "near field" and "far field" -- though those definitions are nebulous in terms of modeling the coupling.
- madengr 12y ago
  There is still strong mutual coupling in the near field if the coils are mutually resonant. The magnetic systems uses a ferrite core to concentrate the field, and these need to be well aligned to achieve high efficiency. These are ferrite based: http://www.digikey.com/product-search/en/inductors-coils-chokes/wireless-charging-coils/197928?k=wireless%20power%20coil http://www.digikey.com/product-search/en/inductors-coils-cho... The near field systems rely on both coils being within about one radius of one another, and the coils are typically self resonant, but the smaller you make the coil, the higher it's self resonance, thus it's efficiency is lower. That's the issue with resonant near field coupling, the small devices like phones limit the coil size, and efficiency. Near field demo: https://www.youtube.com/watch?v=4GransrkXd4 https://www.youtube.com/watch?v=4GransrkXd4

beambot 12y ago

In "magnetic coupling", the bulk of the power transfer occurs due to strong mutual coupling between the antennas (eg. a transformer). For electromagnetic, the waves are propagating (oscillating electric and magnetic moving through space) and the coupling between receiver and transmitter is weak (ie. loading the receiver has no effect on the transmitter). Both are governed by Maxwell's Equations. Sometimes you'll hear these referred to as "near field" and "far field" -- though those definitions are nebulous in terms of modeling the coupling.

madengr 12y ago
There is still strong mutual coupling in the near field if the coils are mutually resonant. The magnetic systems uses a ferrite core to concentrate the field, and these need to be well aligned to achieve high efficiency. These are ferrite based: http://www.digikey.com/product-search/en/inductors-coils-chokes/wireless-charging-coils/197928?k=wireless%20power%20coil http://www.digikey.com/product-search/en/inductors-coils-cho... The near field systems rely on both coils being within about one radius of one another, and the coils are typically self resonant, but the smaller you make the coil, the higher it's self resonance, thus it's efficiency is lower. That's the issue with resonant near field coupling, the small devices like phones limit the coil size, and efficiency. Near field demo: https://www.youtube.com/watch?v=4GransrkXd4 https://www.youtube.com/watch?v=4GransrkXd4