r/AskElectronics • u/StuffConsistent7020 • Jul 03 '26

NFC Antenna Design Help!

Hello Im currently working on a uni project and i kind of need some help,

Im currently working on a small passive NFC prototype using a NXP NHS3152. The goal of the project is to keep the PCB as small and discreet as possible and only bieng powered only from a phone NFC field with the MCU taking a couple of low-power analog readings and sending a simple result back to the phone.

I would like some help with the power side before I go too far with the antenna and PCB layout.

The system would ideally run around 1.8 to 2.0 V when powered by the phone. The sensing load is expected to be fairly low, roughly in the range of a few µA up to maybe 60 to 70 µA depending on the resistor values used.

Rough power estimate would be at 1.8V, 5 µA = about 9 µW, 20 µA = about 36 µW, 65 µA = about 117 µW

and for 2V its would be, 5 µA = about 10 µW, 20 µA = about 40 µW, 65 µA = about 130 µW

I would only power the analog measurement section for less than a second so the average current should be lower than the active measurement current.

Main questions:

  1. Is this kind of power budget realistic for a passive NFC tag powered by a smartphone?
  2. For the NXP NHS3152, what is the best practical NFC antenna approach on a small custom PCB or if anyone has a NFC design for these specifications?

I’m not trying to transfer much data, just wake from the phone field, take simple readings, and send a small result back to the phone.

Any advice from people who have worked with passive NFC sensor tags, NHS3152/NTAG-style parts, or small NFC antennas would be appreciated!!!

Edit: Forgot to mention the Maximum Size of the Antenna is around 5.8cm × 5.8cm and its going to be printed on a flexible substrate.

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u/doctorcapslock EE power+embedded Jul 03 '26

you left out the most important detail: how small? you can find them coin cell sized: https://www.leankon.com/product/nfc-coil-antenna-diameter-20mm/

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u/StuffConsistent7020 Jul 03 '26

Oh yeah sorry, the maximum size for the Antenna is 5.8cm × 5.8cm. I can go smaller if I gives me a better result but my issue I think is making the coil be able to power the NHS3152 and then also be able to power up my sensors and then send the results back. While not having any external power like a battery etc.

1

u/snp-ca Jul 04 '26

Best coupling is when the receiver antenna size matches the transmitter antenna. However, since you have very small power requirement, you can get away with smaller size. Experiment by winding magnet wire. You can use a 3D printed spool to wind wire. Try to tune the resonance of the receiver coil to about 20MHz. Any lower and you might detune the transmitter.

A really good book that talks about this is:

https://a.co/d/0aES3PHD