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I'm not sure why they say these are RFID-enabled; all the tags they show are BTLE. The difference being that BTLE devices are active transmitters (they have a

by daeken 12y ago

I'm not sure why they say these are RFID-enabled; all the tags they show are BTLE. The difference being that BTLE devices are active transmitters (they have a battery), and RFID tags are passive, having their energy provided via radio waves or magnetic coupling. The problem with RFID is that past a few feet, you need a lot of energy to power them (it falls off with the inverse-square law), which your phone just won't (and shouldn't) put out. So RFID is dead in the water for this sort of thing, but BTLE solutions abound and are quite cheap, despite that they need to have a battery.

TTPrograms 12y ago
IIRC RFID actually falls off with R^4 because the power gets transmitted to the RFID tag and then it's reduced by the same factor again when it transmits back.
- daeken 12y ago
  The power is obviously lost on the way back, but this doesn't actually factor into the distance you can read from, practically speaking. If you can get power to the device, you can use a super high-gain antenna to receive its transmission. Same thing goes with NFC chips; the one I have implanted can only be powered feasibly from about 10 inches away (physically impossible beyond about half a meter, due to flesh and the fact that it's magnetic coupling), but if something else powers it, you can read it from an exceptionally large distance.
  - TTPrograms 12y ago
    Well, yeah, by the same logic you could could power it with a high gain antenna as well and boost your distance. The falloff is still 1/R^4 without a third power source, you've just multiplied it by a constant.
    - Dylan16807 12y ago
      The limiting factor is (afaik) getting enough energy into the tag to run its components. If you were working with much higher distances and powers then the transmission strength of the tag might matter, but in this case it's basically a one-way transmission problem. compare O(n^2 + .0001 n^4) where n is 5
  - wglb 12y ago
    Implanted?

by daeken 12y ago

TTPrograms 12y ago

IIRC RFID actually falls off with R^4 because the power gets transmitted to the RFID tag and then it's reduced by the same factor again when it transmits back.

daeken 12y ago
The power is obviously lost on the way back, but this doesn't actually factor into the distance you can read from, practically speaking. If you can get power to the device, you can use a super high-gain antenna to receive its transmission. Same thing goes with NFC chips; the one I have implanted can only be powered feasibly from about 10 inches away (physically impossible beyond about half a meter, due to flesh and the fact that it's magnetic coupling), but if something else powers it, you can read it from an exceptionally large distance.
- TTPrograms 12y ago
  Well, yeah, by the same logic you could could power it with a high gain antenna as well and boost your distance. The falloff is still 1/R^4 without a third power source, you've just multiplied it by a constant.
  - Dylan16807 12y ago
    The limiting factor is (afaik) getting enough energy into the tag to run its components. If you were working with much higher distances and powers then the transmission strength of the tag might matter, but in this case it's basically a one-way transmission problem. compare O(n^2 + .0001 n^4) where n is 5
- wglb 12y ago
  Implanted?