RFID - pointer to a good introduction ?

I only have general knowledge of RFID and have never implemented it.

I now need to incorporate it into a product and was hoping someone could
point me to a relevant practical introduction. Emphasis on practical.

I'm going to need to do something very similar to the sensors used in
supermarkets etc. So hopefully I'm not trying to be too clever.

In my case I want to be able to sense it as far away as possible while
still maintaining a very small physical size for both sides (battery/mains powered I could do either)
Something up to 6 feet away as someone is walking past the sensor if possible.

Is this a reasonable goal for current technology with a low cost/small form factor design?

If so I'd also welcome specific product suggestions.

Thanks as always

jack

There are RF and microwave sensors capable to detect a person walking around up to 30 or more feet.
But if you need to detect a person moving around over 6 feet, the lowest-cost solution is to use a PIR detector. Those are generally used in security systems and passively detect any warm object radiating a wide-bandwidth infrared.
I can recommend a PIR sensor; I have used some for years and they are easily available, some even combined with spot-lights or replacing wall switches.

Thanks - but I need an RFID solution.
It's not so much walking around as proximity I need.

jack

If you need a RFID solution, then I think you should select a "low-frequency" version; this can give you the response over more than "6 feet" distance with a reasonable power. Also, you can install the interrogator antenna as a loop on ground (or above), so RFIDs can be activated within the area of that loop.

6 feet distance would be in reach of an ISO/IEC 15693 application (13.56 MHz, vincinity cards). But considerable reader power is needed for the range. A standard tag could have e.g. an ID1 (credit card) form factor. You didn't however give a clear specification of the intended application and it's constraints yet.

P.S.: Finkenzeller, The RFID Handbook, also available as pdf in previous versions, is a good introduction.

Sorry guys I missed the responses here:

I like the ground loop idea that could work well in some circumstances
I think.

Also I'll check out the PDF as suggested (I've been sidetracked from this
speculative idea to do real work for a short time!)

I expect it's already in use although not for my specific purposes.
The application is to monitor objects moving around a building transfering
a small amount of data as a reader is passed without the tag/card having to be "swiped". Positioning of the card on the object should not be relevant and
it should be readable directly through a range of materials at speeds up to about 3 mph maximum for the objects passing. Data rates as high as possible but just a few bytes transfered is acceptable.

If the reader electronics could be battery powered and physically very small
that would be ideal - a larger antenna would be OK in most cases though.

If I could make a portable version that would be icing for the cake.
If cheap modules exist to build a prototype I could do it that way to start.
Any suggestions there may be useful but I need to get the final product price
right down low.

I need to make time for some reading I think.

jack