Question about current and voltage of RFID reader antenna

[Catalyst]

Hello,

A 13.56MHz RFID system utilises inductive coupling (transformer). Therefore, is it right to say that the current in the reader antenna determines the voltage available to the chip on the RFID tag?

Is the current in the reader antenna important or am I looking at this from the wrong perspectice?


Any help is much appreciated



Cat

 

[rautio]

Re: RFID Reader Antenna

Hi Catalyst -- It is certainly right to look at it that way. Check out pg. 16-17 in the attached pdf. There are probably other right ways to look at it too, but the way you have suggested works very well when it comes time to design a real system. There have already been substantial discussions on RFID here and in the EM forum. If you haven't already, you might want to search for RFID threads.

 

[Catalyst]

Re: RFID Reader Antenna

Cheers Rautio

Is there a specific equation that enables me to predict the voltage across the tag coil with a specific reader antenna current (including parameters such as the size of the tag and reader antenna) ?


Cheers


Cat

 

[rautio]

Re: RFID Reader Antenna

I would imagine there is some kind of approximate equation, but it is so easy to analyze it using EM software, that is what I would do. Perhaps someone else has details on closed form approximations.

 

[dika]

Re: RFID Reader Antenna

can u explain in simpler words, cause i'm thinking to extend the range of the reader.
my reader works at 13,56 MHz with a maximum detection range of 6cm.
it has a variable resistor connected with the antenna module. could it be the amplifier??
thanks

 

[PaulHolland]

Re: RFID Reader Antenna

Hi you are looking for more range ?. How much ?. If you need 10cm you can increase the Antenna diameter and the number of turns the coil makes from one to 4 or more. But keep in mind you need to be able to get a resonance at 13.56 MHz. I use an antenna which is 8cm long and 6 cm width. 4 turns and it gives some 10cm range. If you need more you have to swich to a different card technology ISO15... regards, Paul.

 

[dika]

Re: RFID Reader Antenna

Hi you are looking for more range ?. How much ?. If you need 10cm you can increase the Antenna diameter and the number of turns the coil makes from one to 4 or more. But keep in mind you need to be able to get a resonance at 13.56 MHz. I use an antenna which is 8cm long and 6 cm width. 4 turns and it gives some 10cm range. If you need more you have to swich to a different card technology ISO15... regards, Paul.

well 30cm will do fine. i'm trying to design a reader that could read from a door frame (post) to another. like the one in the departement store entrance. for the antenna it could be 1 m tall and 50 cm wide. would it need a amplifier? or just a impendance limiting?
btw my reader (inside M210H) have a built in antenna, and i have tried to connect an external (FM radio) antenna but the reader wouldnt connect to PC. i havent figured the problems yet. maybe u could help me?
thanks

 

[PaulHolland]

Re: RFID Reader Antenna

Hi, This size antenna is possible but works better at 125 KHz RFID. So use this !. Make a frame and take 4 to 8 turns and make an Amp with an IRF510 (look for info on google). One frame can bet Transmitter and the other receiver. good liuck.

BTW: You can buy these antenna's but this that this is not wat you want .

Paul.

 

[dika]

Re: RFID Reader Antenna

Hi, This size antenna is possible but works better at 125 KHz RFID. So use this !. Make a frame and take 4 to 8 turns and make an Amp with an IRF510 (look for info on google). One frame can bet Transmitter and the other receiver. good liuck.

BTW: You can buy these antenna's but this that this is not wat you want .

Paul.

which IRF510 do you recommend (manufacturer)?
could you explain more on this

One frame can bet Transmitter and the other receiver. good liuck.

thanks

 

[PaulHolland]

Re: RFID Reader Antenna

Hi, Brand does not matter. IRF is very good but others also make them. ST has a low cap. input so easy to drive with a 74HC4069. Make sure you tune the coil with a capacitor in serie with the output of the FET. You can also connect parallel to the coil a cap. and connect this on the Drain of the FET to VCC (12 V) if you now make 125 KHz with a microcontroller you can drive the gate through a 4069 ports (place all inverters parallel to get more power). If you do this you should use an oscilloscoop and a normal coil to pick-up the field from your antenna. Now tune the C parallel to your coil untill you get the maximum field from you antenna. This is all you have to do on the TX side. Now duplicate the antenna for the receiver frame and make an receiver with a bandfiltered opamp tuned at 125 KHz with an 50 KHz bandwidth. don't give to much gain to your first OPAMP buit filter first your signal from unwanted signals.

regards,

Paul.

 

[dika]

Re: RFID Reader Antenna

what material do u recommend for the coil?
is it posibble to direct the wave?so i could have a limited field without compromising the maximum distance.
btw can i use the configuration u gave in a 13Mhz reader? coz i already have one, and my goal is improving it without buying a new one.
thanks a lot!

 

[PaulHolland]

Re: RFID Reader Antenna

You can direct the wave by increasing the number of turns, but keep in mind that you can't make a coil to resonate at 13 Mhz with 10 turns at a frame of 1 by 1 meter .. I am sure you can't increase the field for 13 MHz Mifair tag's more than 10 - 15 cm most.. THey need 1.5 - 7 A/m field strength !!!!!!!!..

Paul.