4 ms·

"Inductively coupled rather than RF coupled"? What's the difference?

jacquesm 12y ago
He means coupled using a magnetic field (like a transformer) rather than using an electric field (like a transmitter). They're related, to make things more complicated, see Maxwell. http://galileoandeinstein.physics.virginia.edu/more_stuff/Maxwell_Eq.html http://galileoandeinstein.physics.virginia.edu/more_stuff/Ma...
- simcop2387 12y ago
  That's exactly it. I couldn't think of the correct way to put it earlier and kept thinking of it like an open core transformer rather than an antenna.
- quietplatypus 12y ago
  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
- pgcudahy 12y ago
  It won't be catastrophic but it could affect them. Most pacemakers have a mode that if you put a magnet on them they revert to pacing at 60 beats per minute (VVI mode) like a metronome rather than more advanced adaptive modes (like DDD mode). That's how if a doctor suspects it's malfunctioning due to bad sensing they can get it into a basic mode. I've done it in the ER when a pacer was freaking out and going way too fast due to bad sensing.
- dogma1138 12y ago
  pacemakers act up near high voltage power lines and transformers. Most modern PM's are actually much more resistant to RF induction than one from strong magnetic fields mainly due to the saturation of the RF spectrum over the past 2 or so decades coupled with a decline in high voltage power in populated areas (they are underground as well as farther from residential areas these days). That said I have no idea if the field those things generate is strong enough to create any issue with PM's or similar devices (like the "jump start" internal defibrillator some people are getting these days). I would think that these devices are quite safe, especially considering that you see wireless charging station in courtesy area's in lobbies and other public places without any warning signs.
  - aramas 12y ago
    Actually, the health risks of wireless charging is still unknown without longitudinal studies. Are you sure you want this kind of devices at home where your kids can access it easily?
    - dogma1138 12y ago
      I wasn't talking about long term health risks like cellphones give you brain cancer and WiFi makes you blind. But there are guidelines for certifying consumer electronics compatibility with medical devices is on that list.

He means coupled using a magnetic field (like a transformer) rather than using an electric field (like a transmitter). They're related, to make things more complicated, see Maxwell. http://galileoandeinstein.physics.virginia.edu/more_stuff/Maxwell_Eq.html http://galileoandeinstein.physics.virginia.edu/more_stuff/Ma...

simcop2387 12y ago
That's exactly it. I couldn't think of the correct way to put it earlier and kept thinking of it like an open core transformer rather than an antenna.
quietplatypus 12y ago
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
pgcudahy 12y ago
It won't be catastrophic but it could affect them. Most pacemakers have a mode that if you put a magnet on them they revert to pacing at 60 beats per minute (VVI mode) like a metronome rather than more advanced adaptive modes (like DDD mode). That's how if a doctor suspects it's malfunctioning due to bad sensing they can get it into a basic mode. I've done it in the ER when a pacer was freaking out and going way too fast due to bad sensing.
dogma1138 12y ago
pacemakers act up near high voltage power lines and transformers. Most modern PM's are actually much more resistant to RF induction than one from strong magnetic fields mainly due to the saturation of the RF spectrum over the past 2 or so decades coupled with a decline in high voltage power in populated areas (they are underground as well as farther from residential areas these days). That said I have no idea if the field those things generate is strong enough to create any issue with PM's or similar devices (like the "jump start" internal defibrillator some people are getting these days). I would think that these devices are quite safe, especially considering that you see wireless charging station in courtesy area's in lobbies and other public places without any warning signs.
- aramas 12y ago
  Actually, the health risks of wireless charging is still unknown without longitudinal studies. Are you sure you want this kind of devices at home where your kids can access it easily?
  - dogma1138 12y ago
    I wasn't talking about long term health risks like cellphones give you brain cancer and WiFi makes you blind. But there are guidelines for certifying consumer electronics compatibility with medical devices is on that list.