Separate Power and Reader for RFID

Hello,

I'm working on a design, and I was wondering if the following is possible:

I have an RFID reader that is too far from the tag. I would like to be able to power the tag and amplify the signal enough that it reaches the RFID reader.

I know that RFID readers power the tag when they come close enough on contact. In this case putting the tag closer to the reader is not an option for what I want to do. The distance of the tag to reader maybe 1-6 feet.

Questions:
1. If the RFID tag is not powered by the reader, will the reader still read the tag?
2. Do all RFID readers have the ability to read LF, HF and UHF tags?
3. If what I want to do is possible, is there any reference example antenna design I can take a look at?

Thanks in advance!
Amir

Standard 125 kHz with passive tags can do maybe 2 feet, but the antenna size increase with increasing distance.

The are tags that get power only from the magnetic field and sends the response as a radio signal. They can handle a longer distance, but I don't know the maximum.
There is a problem with this if you have more than one reader. A response from a tag can be received by more than one reader. This is not always acceptable.

1. If the RFID tag is not powered by the reader, will the reader still read the tag?

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No. The way they work is the reader pulses power bursts (typically every 100mS) at the card resonant frequency. The tag picks up the power burst in it's own antenna coil and uses it to power the internal processor. It then adjusts it's loading on the reader to signal back the codes. If the tag has no power it will do nothing at all, all its power requirement is sourced from the pulsed signals sent by the reader.

2. Do all RFID readers have the ability to read LF, HF and UHF tags?

Click to expand...

No. There may be some dual frequency ones around but in general they work on one of the standard RFID frequencies only and also only decode one of the RFID data protocols.

3. If what I want to do is possible, is there any reference example antenna design I can take a look at?

Click to expand...

A long range antenna would be cumbersome (maybe several metres diameter). You can increase the transmitted range by increasing the power level but bear in mind the complications of detecting the different loading on the transmitter as the power gets higher. As pointed out, you also run the risk of reading multiple devices if you increase the range. Even short range RFID pulses more than 100V across the transmit antenna so safety issues come into play as well.

Brian.