rfid wider surface

Hello Everyone,

here it is yet another post on rfid and arduino, I apologize if this was discussed before but I was definitely not able to find a solution so far. I should design a rfid table for books in my installation. The problem is I'd like to have a wide surface as a rfid reader, like a table or a desk. Example: people lay a book on the table (might be not right over the typical small antenna spot) and the "table" reads the tag hidden in the back cover of the book. What's the best solution in this case? Is it possible to make a large coil, to hide right below the table surface? how large maximum? Do I need more power than 5v for a bigger size? I did not find any tutorial to custom design a custom rfid antenna, I've read about 60 cm large ones (Grumpy Mike made it, he's a master here) but I was not able to find any deeper explanation and the tutorials online are quite complicated and full of formulas. Other solution? to use multiple antennas? In this case I should connect more antennas to the same arduino I guess and if I'd prefer to avoid. Also bar code or IR is not prefereable.

Tank you for any help or suggestion.


Usually the problem is to make the antenna smaller not bigger. The wave length of the short distance RFID tags used commonly in price tags and the like is about 22m so an ideal antenna is about this size. Usually an even division of it. If you take a fourth (5.5m) and do a double round, you get a square of about 70cm width and height.

The problem is that antenna design is more of an art than an engineering discipline. The mass of formulas you found shows that it's not an easy task to do it right and it's kind of a miracle to do it good. I'm definitely not a specialist in this area but you can replace the antenna in all RFID readers I've seen yet. I guess your project is feasible but you maybe have to try a lot of antennas till you get a working one.

Thanks for your answer, pylon. You mean if I use the low frequency tags, I make a 70 cm double round square with copper tape and I work around with it along with capacitors for the tuning I could come to a solution? hm... I'm afraid I am making it too easy...

I found something like this in a previous message in the forum: whatever inductance the coil has, add a parallel capacitor to tune the resonance to 125KHz following the formula 125KHz=1/2pi*sqr(LC) is this a possible way? There are inductance java calculators online so that I can try with different sizes and number of loops... One more thing: is the size if the antenna to be in relation with the size of the transponders?



Do you use 125kHz tags? What I meant were 13.56MHz tags which are commonly used for price tags. The lower frequencies are a bit more complex because the wave length is in the kilometer range. I guess you could divide that down somehow but making a bigger antenna for these devices is definitely something for a specialist in that area.

hm... The fact is I don't know yet what to use. 13.56 MHz is probably also better because of its longer range. Still confused about the antenna though. I think I'll buy some transponders, start with experiments and see what happens. In the meantime if anybody can provide videos or tutorials on how to design a DIY (wide) antenna for 13.56MHz that would be much appreciated. Of course I will post mine, if I'll ever come to a solution. And again thanks pylon for your hints.