How to read NFC tags Simultaneously?

Question

I look for a solution for a problem in my project.

The idea of the project is to create a smart library which help us to know where every book located in every period of time.

Picture :

The idea is to make a scanner which pass over the shelf and scans the books every 30 minutes.

I thought to implement that project with NFC tags and NFC scanner, but I found that there are limitations of distance between one tag to another.

Another problem is that I want to read radius of tags and not tag after tag (like QR code for example) because I don't know in which position the book will be on the shelf.

Picture of the problem:

The questions are

1. If the limit of NFC tags distance is more or fewer millimeters

2. If there is another cheap solution for reading some objects which are located in distance of 5-10 centimeter from some scanner

Answer 1

In my brief and recent experience of this kind of thing, the answer is yes it is possible, but all the solutions I found were expensive. First of all, unlike the low frequency rfid tags, high frequency tags with anticollision are fairly expensive. Next, the readers for these high frequency tags are fairly expensive. Long range readers for these kinds of tags do exist, but they are extremely expensive, on the order of hundreds of dollars each. That sort of answers the question you did ask.

The question you didn't ask, but probably the one you want the answer to (How do I cheaply implement my entire smart library) is a bit more difficult. Certainly, webcams are cheap, and you could put one on each shelf, facing it's opposite shelf. Using a bit of image processing, you should be able to (fairly easily?) identify each book on the shelf from the spine, in any orientation. The processing requirements of this would, I think, not be huge; A raspberry pi zero could probably do it. This solution is likely to be the cheapest one that does exactly what you want, and is probably the best too. It's not the simplest, because you have to figure out exactly how to set up the image processing, and probably scan each book, but you would have had to do some operation to each book (install a tag) anyway, so this isn't that much more effort.

If you wanted to, you could stick with the webcams, but use QR codes instead. The processing for these is simpler, but then you have big qr codes on each book, which doesnt look great.

Answer 2

Instead of using NFC tags on each individual book (which may add up in $), you could try a barcode of some sort. This way you wouldn't have the problem of the scanner proximity to the book and the cost of printing a tag for each book would be negligible.

Answer 3

NFC tags are powered by the NFC reader using magnetic coupling (so called near field). You need to research the use of much smaller loop antennas which will control the distance over which you can power the transponder NFC tags. There was a great answer here from Sigrlami, though this was asked around increasing detection distances.

NXP have great information on NFC antenna design here.

The major problem you may have is that you need to be able to cope with variable distance to the NGC tag, depending on the thickness of the book. If you assume that the NFC tag is attached to the center of the book close to the spine, then you may have to deal with book returned to the shelf back to front (longer distance to tag. If you place the NFC tag in the facial center of the cover, then the reading distance becomes greater.

It may be worth considering using a much smaller diameter antenna with a Ferrite backing and Ferrite side shields (or even a small Ferrite E core) for the Reader antenna/transformer, This will allow you to distort the Reader field to provide a more constrained/directional magnetic field. There are some details in the NXP document that may help you as they discuss Ferrite backplanes.