# NFC Antenna Design to radiate strong field strength

1. ## NFC Antenna Design to radiate strong field strength

Hello Everyone,

I have to design a NFC antenna in which it needs to radiate a strong field strength (H) from 1 A/m to 7.5 A/m. I have these following questions:

1) What equation I can use to calculate the magnetic field (H) based on coil's field strength?

2) What electrical current magnitude necessary to get this strong field strength (H)?

3) Also, I have copper (Cu) to build the antenna. So is there any equation to calculate the diameter of the wire?

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2. ## Re: NFC Antenna Design to radiate strong field strength

I am not exactly "expert" in this field, but I would try a few protoypes based on PCB design. The good starting point will be AN2866 application note from ST Microelectronics "How to design a 13.56 MHz customized antenna for ST25 NFC / RFID Tags" - it explaint theory and practiocal approach. When it will come to actual design of the coil, take a look at two free softwarte packades - coil32 and Saturn PCB Design Tool. As for inexpensice and fast turn around for PCB prototypes I always use www.easyeda.com - you will have PCB in your hands in a matter of week for the fraction of what you would pay elsewhere. By the end what you are looking for PCB similar to this: https://www.quora.com/Is-it-practica...ntenna-for-NFC

And this is a "cheap man" gadget to test your PCB design : https://www.smartcardfocus.us/shop/i.../p/index.shtml

Just my 10 cents.

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3. ## Re: NFC Antenna Design to radiate strong field strength

The field strength of a circular coil can be easily calculated using Biot-Savart's law. See https://www.edaboard.com/showthread....smitter-design.
The axial field strength calculates as follows

H = 1/2 * (I*a²)/((r² + a²)^1.5), a coil radius, r axial distance

For spiral antennas, add field of individual circular coils or use calculator tools.

NFC antennas are usually operated in (series) resonance to achieve high current with relative small driver voltage. Many manufacturer application notes are describing typical designs.

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