RIFD question___

Hi everyone, I have a question for you.... I'm doing some tests with RFID , and everything is ok ... but I would like to use a much larger antenna type 45cm x 30 cm to detect a very small tag ( like the one in the picture), do you think it is possible?
What should I pay attention to?

grazie :raised_back_of_hand:

Since that works like an air core transformer, you should pay attention to the amount of energy being induced into the ID tag. If you cannot tune any antenna to the matching frequency, then no amount of antenna size will help.

Here's a 41x32 cm reader. Is that big enough?

Here's one that's 44.5x44.5 cm. Is that too big?

It all depends on the frequency of the tag. Tuning is essential, normally you read that the antenna should be tuned to the resonant frequency of the tag, but if you do get it spot on then the range will be zero.
You need to tune it just off resonance to one side or the other. As it gets further from the resonant the range increases until you get to a flattish peak, then it slowly declines.

The side matters also. This is because if you mount the coil on something conductive the tuning will change and one side (I can’t remember which way round it is) will get a better range for none conductive coil mounting.

I was once employed to design RFID readers so I had to do a lot of tests on them and work out how they could be tuned on the factory floor.

Hi Paul, thank you so much for your reply, first of all happy new year! :confetti_ball:
Unfortunately I'm not very knowledgeable on this topic, so should I have the ability to tune the antenna frequency according to the tag?
What tools or what calculations should I do?
What characteristics should I ask the supplier of the tags?
thanks again! :pray:

Hi Johnwasser :wave:, thank you very much for your reply, and happy new year to you too! :confetti_ball:
Sorry but I missed maybe one important thing about the need for such a large antenna.
I should have the possibility to make it in this manners ( see photo) , that is I should apply it on the outside or the inside of a wooden frame and make this frame ( with the dimensions of 45x30 cm or so) become the antenna.
Yes I know ... something a bit strange ... :grinning:

Hi Mike :wave:, thanks to you too for the reply!
what you are telling me, makes me realize that it is not so simple ( at least for me) ...I have to understand well how to do and tune.
I think I also need tools a little special to understand the tuning ... not enough tester!
As I replied to Paul, I need to figure out how to "tune", what and how I need to pay attention to, and do some testing...lots of testing ....
Can you point me in the direction of how to get started?
Is this something that is doable in your opinion?

thanks again to all :pray:

What you need to know is what sort of reader / tag you have. There are three main types.

  1. 125 KHz
  2. 13.5 MHz
  3. UHF tags with a frequency in the GHz range.

The simplest to work with is the 125KHz tags.

To tune an antenna you have to add a capacitor or two to it in parallel with the antenna, you can add them in parallel so they will add up. The capacitors have to be high voltage because you can get over 200V on a coil in resonance.

You measure the voltage across the coil with an oscilloscope and apply a signal to it using a signal generator. You change the signal generator’s frequency and when the voltage across the coil peaks to a maximum, that is the resonant frequency of the coil / antenna. You then change the capacitance across the coil and measure again, and repeat this until you get the right resonant frequency. I used to use a capacitor substitution box for the capacitor I was working with.

So it is an easy procedure if you have all the test gear.

The 13.5MHz are a bit more tricky because the reader transmits on one frequency and receives on one quarter of that frequency. And UHF tags need advanced test equipment that will work at those frequencies, these are very expensive.

ok, first of all I have to buy an oscilloscope, because otherwise all the info you wrote me I can not verify ...
just to explain even better.....( see picture) .
This is what I need to do only bigger .
The board they use in this picture( taken from internet) seems to me to fit arduino right?

And also a signal generator.
You still haven't said what sort of RFID reader you have, can you post a link to where you got it from.

like this ........Unfortunately or fortunately, I have to use as small a tag as possible.

Is the 41x32 large enough for the inside dimension of your wooden frame? Is the 44.5x44.5 small enough for the outside dimension of your wooden frame?

Since you are dealing with induced voltages, the "antenna" coil needs to be as close to the same physical size as the little blue button. Then it needs to be tuned using the procedure you have been given.

This is a pity because the coil in the photograph will not tune to 13.5MHz because it has too many turns on it. adding capacitors only reduces the resonant frequency it does not increase it.

I need to attach the antenna (in red) to the attached frame , but leave the whole inside part ( in blue) free to pass through.
The passage will be made by that tiny tag ...
For this reason, the antenna I have to figure out how to do, because surely I will not find one that suits my needs ...

ok, so I need to figure out how to create ( and therefore the number of turns ) the antenna.
I think I can find a nano tag but with different features , because maybe the antenna with that size requires special features right?

Is your tag going to pass through that frame?
What is the tag attached to?

What is a nano tag?

You can get RFID tags that are designed for injecting into animals, like when you have your dog or cat tagged. But the range is very small.

yes, I call the tag nano only because it is very small, not because it has a particular definition....
I have to apply the tag on the tip of a device that after a certain time approaches the frame and rests on the blue "sheet".
I just have to signal with a led, when this device is leaning. Obviously it never rests on the same point inside the antenna.
This is my "strange" application ... :slightly_smiling_face:

Well you are not giving much away there.

You know that you can only read tags of this type if there is only one of them in the field?

yes, it will be always and only one (the same one) that will approach and will go away...slow movement.