products - I wonder if
read-only RFID tag.
passive, no bigger than
custom.
reader.
available.
seen so far this would
but for 13.56MHz, an
in series with it due
when commanded to,
limitations ?
from what I've seen
...Jim Thompson
-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et |
RFID manufacturers seem to be a bit cagey about the operating range of their products - I wonder if anyone who has direct experience could help....
I'm looking at an application that needs to read a few tens of bytes from a read-only RFID tag. The choice of tag type and frequency is open at the moment, but needs to be passive, no bigger than a car-alarm keyfob, reasonably cheap and probably off-the-shelf rather than custom. It needs to be writeable in production but not necessarily by the same type of reader.
Problem is that we have limitations on the size of reader antenna, and power available. The antenna needs to fit in a space of about 40 x 40 x 5mm - from what I've seen so far this would suggest that if we go for a 125KHz tag, a ferrite antenna would be appropriate, but for 13.56MHz, an open coil may be possible, but may suffer detuning from stray capacitance. (Are ferrite antennas viable at 13.56MHz ?) Available power is about 7V minimum, but this will have something like 8 ohms in series with it due to other requirements. Overall power draw is not a problem as it will only read when commanded to, which is not very often - the main issue is the series resistance,
So the question is, what sort of range could we expect with the above limitations ?
100mm has been suggested as desirable but I'm skeptical that this is possible from what I've seen from some 125K tags I've played with.
products - I wonder if
read-only RFID tag.
passive, no bigger than
custom.
reader.
available.
seen so far this would
appropriate, but for 13.56MHz, an
in series with it due
read when commanded to,
limitations ?
from what I've seen
My experience with passive 13.56MHz RFID antennas is such that the sender antenna defines the range. Roughly the diameter of the sender antenna. So your proposed antenna will be good for a hand thickness apart.
Note that the power is limited by law, you cannot use this antenna and drive it with 1kW.
The whole looks different when the tag has a battery, then the range is greatly enhanced.
Rene
-- Ing.Buero R.Tschaggelar - http://www.ibrtses.com & commercial newsgroups - http://www.talkto.net
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