3 ms·

C'mon, is not _fundamentally_ different, since both techniques use EM energy. And guess what, where is the RF in RFID comes from?? In order to harvest power fr

by ccozan 11y ago

C'mon, is not _fundamentally_ different, since both techniques use EM energy. And guess what, where is the RF in RFID comes from?? In order to harvest power from EM (RF) you need a nantenna, a micro rectifying antenna, aka [1]. [1] https://en.wikipedia.org/wiki/Rectenna https://en.wikipedia.org/wiki/Rectenna

deleted 11y ago
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jacquesm 11y ago
Wifi does not use magnetic resonant coupling. To expand on that, the difference is (in laymans terms) 'radio waves' versus 'magnetic fields'. The difference being that in WiFi the magnetic field component is not relevant and in NFC technologies such as RFID it is the main component (the hint is whether the main active component is a coil or an antenna). There is a close relationship between the two fields governed by Maxwells equations.
- JoeAltmaier 11y ago
  In fact they are the same - one is the derivative of the other. So the RFID scanner emits a radio wave; the RFID chip magnetically couples to it to provide a small charge; enough to run the RFID circuitry for a few milliseconds.
  - jacquesm 11y ago
    At the frequencies and distances at which WiFi normally operates the magnetic component is all but invisible, it's mostly a matter of electric fields. At lower frequencies the electromagnetic field portion becomes dominant. This is one reason why the 'antenna' inside one of those old fashioned AM receivers is actually a coil with a ferrite core (and conveniently internal to the device), and an FM radio (the A/F have to do with the modulation, not specifically with the frequency but the bands are between 455 and 1600 KHz vs 88-108 MHz) typically uses a rod antenna. Now you could make an FM radio with a coil for its antenna or an AM radio using a rod but neither would be very efficient. So it's the small distance and low frequency of RFID technology that drive the choice for magnetic coupling, whereas the high frequency and longer distances of WiFi make the choice for antennas. AM radio, with its low frequency and enormous power output allows magnetic pick-up at very large distances from the point of origin, this is also why it is not 'line-of-sight' but WiFi is line-of-sight (yes, you can bounce radio waves off objects (such as the moon or the Heavyside layer) but that's another subject entirely). The higher the frequency of operation the more you'll be looking at properties resembling those of light (which is also a form of electromagnetic radiation).

by ccozan 11y ago

deleted 11y ago

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jacquesm 11y ago

Wifi does not use magnetic resonant coupling. To expand on that, the difference is (in laymans terms) 'radio waves' versus 'magnetic fields'. The difference being that in WiFi the magnetic field component is not relevant and in NFC technologies such as RFID it is the main component (the hint is whether the main active component is a coil or an antenna). There is a close relationship between the two fields governed by Maxwells equations.

JoeAltmaier 11y ago
In fact they are the same - one is the derivative of the other. So the RFID scanner emits a radio wave; the RFID chip magnetically couples to it to provide a small charge; enough to run the RFID circuitry for a few milliseconds.
- jacquesm 11y ago
  At the frequencies and distances at which WiFi normally operates the magnetic component is all but invisible, it's mostly a matter of electric fields. At lower frequencies the electromagnetic field portion becomes dominant. This is one reason why the 'antenna' inside one of those old fashioned AM receivers is actually a coil with a ferrite core (and conveniently internal to the device), and an FM radio (the A/F have to do with the modulation, not specifically with the frequency but the bands are between 455 and 1600 KHz vs 88-108 MHz) typically uses a rod antenna. Now you could make an FM radio with a coil for its antenna or an AM radio using a rod but neither would be very efficient. So it's the small distance and low frequency of RFID technology that drive the choice for magnetic coupling, whereas the high frequency and longer distances of WiFi make the choice for antennas. AM radio, with its low frequency and enormous power output allows magnetic pick-up at very large distances from the point of origin, this is also why it is not 'line-of-sight' but WiFi is line-of-sight (yes, you can bounce radio waves off objects (such as the moon or the Heavyside layer) but that's another subject entirely). The higher the frequency of operation the more you'll be looking at properties resembling those of light (which is also a form of electromagnetic radiation).