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Is it theoretically possible to engineer manufacture a RFID tag that works within the Bluetooth wavelength range allowing a standard booth-tooth device (a phone for example) to power and pick up data from this specially designed passive tag.

I understand there are bluetooth tags but these have batteries and are not passive nor are they necessarily cheap or small.

I am a novice when it comes to electronics (chemical engineering background) but would like to understand more. If you worked with an actual RFID manufacturer, could you design a passive tag that natively was powered and passed a very small amount of data to a bluetooth device? Data would only need to be transmitted 5-12 inches, keeping the power requirements and footprint small.

I appreciate any feedback! Hopefully my question makes sense!

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  • \$\begingroup\$ No, since the Bluetooth transciever in the phone isn't designed to read the kind of modulation that a passive tag produces. \$\endgroup\$
    – Dave Tweed
    May 1, 2014 at 14:38
  • \$\begingroup\$ Could you hypothetically design a passive tag that gives off a different "modulation", one that the bluetooth transceiver would recognize? The answer is probably no but thought I would ask! \$\endgroup\$
    – user41183
    May 1, 2014 at 14:46
  • \$\begingroup\$ To work within the Bluetooth protocol, the tag would have to first receive a packet and also store enough energy so that it could subsequently create and transmit a reply packet. While possible in the most hypothetical sense, I really don't see it being practical in any sense. \$\endgroup\$
    – Dave Tweed
    May 1, 2014 at 15:01
  • \$\begingroup\$ I believe your need is for a smart-phone that could be used with RFID tags. Can modern day phones read some RFID tags? \$\endgroup\$
    – Kári Gunnarsson
    Sep 23, 2014 at 9:24
  • \$\begingroup\$ @KáriGunnarsson I've converted your post to a comment, as it's more appropriate (it's not an actual answer). Note that the question is a bit old, you may or may not get an answer from the poster. \$\endgroup\$
    – clabacchio
    Sep 23, 2014 at 9:31

1 Answer 1

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It's all about power.

Passive RFID tags work by transmitting power from the transmitter to the tag (typically three orders of magnitude more than the data signal), and then communicating with the tag at various frequencies (13.56 MHz, 433 MHz, and 900 MHz band being the most common). The transceivers on these chips operate in the hundreds of µW range (probably 1 mW at the most).

As you mentioned, there are Bluetooth RFID tags (as well as WiFi), but they require active tags (a separate power source). You cannot use passive tags with Bluetooth (even if they were redesigned to work at 2.4 GHz), primarily because of the power requirements Bluetooth requires to transmit, in the hundreds of mW (Bluegiga's WT11 module uses an average of 72 mA while transmitting at its lowest power setting).

Near-field RFID tags, like those an employee might swipe at a door, usually use an inductive loop for power, and operate at the lower RFID frequency (13.56 MHz), since the RF antenna and inductive loop can be combined into one antenna (in fact I've designed one myself). These obviously operate at higher power.

Assuming you could power a Bluetooth transceiver using an inductive loop over a couple of inches, what's the point? A passive near-field RFID tag can cost as low as 5¢, while a Bluetooth module may cost several dollars. It is a complete waste to use a Bluetooth module, which is designed to operate over range of 100m, at a near-field range of an inch or so.

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  • \$\begingroup\$ Surely there isn't anything fundamentally stopping you building an inductive-powered bluetooth device? The power required would be orders of magnitude greater than RFID and so would require a corresponding increase in coils at both sides. Essentially a wireless charging system coupled with a bluetooth tag. The loops would have to basically touch though, and given that whatever you ended up with would require a custom reader device it's not clear why you'd bother. \$\endgroup\$
    – LeoR
    May 1, 2014 at 16:28
  • \$\begingroup\$ I've added my reply to my answer, since it's too long for a comment. \$\endgroup\$
    – tcrosley
    May 1, 2014 at 17:10
  • \$\begingroup\$ @tcrosely, is reading distance really one inch only for a passive Bluetooth tag with a loop?? \$\endgroup\$
    – user50907
    Aug 7, 2014 at 16:31

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