NFC MATRIX-M24SR and SMD antenna

[evelair]

Dear Community,

i'm looking for a solution for NFC antenna of range ~10mm and M24SRxx-Y. The space on double layer PCB (1.6mm) is limited to max. +/- 20mm x 8mm, tag should be read by a mobile app.

Does anyone experienced / has a reference design for such requirements ? 

I have found a MATRIX-M24SR - Matrix of multiple antenna for M24SR - Documentation purpose only - STMicroelectronics - there is a SMD coil antenna which can fit, but I'm afraid that it will not couple well with mobile antenna, which probably is much bigger. 

Does anoyone tested this antenna design on bench, what is a reading distance and performance ?

Thanks for help and regards !

[Henry Crane]

Hello,

you can use any 4.7uH SMD coil assuming it is not shielded.

Read range will depend on coil diameter (use the largest as possible) and smartphone (because of its internal NFC antenna size and implementation) but we obseved between 1 and 2.5cm with the M24SR antenna you mentionned above.

For a PCB antenna, based on the folllowing data:

- antenna dimension: 20mmx8mm

- layer=2

- FR4 thickness between layers: 1.6mm

the following antenna design may be considered:

- on top: 20x8mm, 10 turns, track width=0.15mm, track spacing=0.15mm

- on bottom: 20x8mm, 9 turns, track width=0.15mm, track spacing=0.15mm

- an additional parallel tuning capacitance to adjust resonant frequency

this design is provided as is and has not been tested by ST.

Please read the AN5605 Application note "Design of a 13.56 MHz double-layer antenna" for recommendations and more details on how to implement, tune and validate  a double layer antenna based our eDesign suite NFC antenna calculation tool.

feel free to contact us for more informations

Henry Crane NFC/RFID technical support team.