No internal power supply. The antenna is designed to both collect power from the incoming signal and to transmit the response.
Have their own power source, but it only powers the microchip and does not power the antenna. The RF energy is reflected back like a passive tag.
Have their own internal power sources.


10 cm (4 in) up to a few meters
Increased range over passive tags due to the higher power receive circuits
Practical ranges of hundreds of meters

Other information

Low-frequency passive tags are normally inductively coupled and need a lot of coils in the antenna. At 13.56 MHz, a high frequency tag, a lot less coils can produce ranges of tens of centimeters. There are also ultra-high frequency antennas.



Hardware (with links)

In 2006, Hitachi developed a passive device called the u-Chip (with the u being a greek mu) which can transmit a 128 bit unique ID and has a maximum read range of 30 cm (1 foot). In 2007, Hitachi unveiled a smaller chip that can be read from as far away as a few hundred meters.

Alternative uses of RFID (if the cost for the range we want is too great)

I don't like the thought of this since it defeats the purpose of the self-contained small device to go in our pocket, but instead of putting the RFID reader on the device, put the reader in the bookbag so it needs a much shorter range (and thus we can get it cheaper and it might be able to be smaller) and that can be used to see if we have anything and transmit a bluetooth signal to our device letting it know what it reads.

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