How do NFC antennas work?
NFC antennas are planar coils that operate at 13.56 MHz, where the wavelength is about 22 m, so they couple to each other through the magnetic near field like a loosely coupled transformer rather than radiating. Each coil is resonated with a capacitor at f = 1/(2π√(LC)), and practical reading distances are a few centimeters.[1][2]
How is an NFC coil designed?
The designer chooses coil area (larger area increases coupling and range), number of turns (sets inductance, often around 1–3 µH for reader coils), trace width and spacing, then adds a matching network that resonates the coil and transforms its impedance to the NFC controller’s output. Quality factor is set to balance energy transfer against the bandwidth needed for data modulation.[1]
Why are ferrite sheets used in phones?
A metal battery or chassis behind the coil supports eddy currents that oppose the coil’s field and detune it. A thin ferrite sheet between coil and metal guides the flux, restoring inductance and coupling.[1]
What determines NFC range?
Coupling coefficient falls rapidly with distance relative to coil size; reader field strength, tag sensitivity, coil alignment and nearby metal dominate. Standards such as ISO/IEC 14443 define field strengths and test assemblies for proximity cards.[2]
Frequently asked questions
Is NFC radiation?
Essentially near-field magnetic coupling; radiated far fields are tiny because the coil is electrically small.
Can NFC work through metal?
Not directly; slots in metal or ferrite and coil placement around metal are used.
Is wireless charging similar?
Qi charging also uses inductive coupling, at lower frequencies around 100–200 kHz.
See also
References
Online sources accessed October 21, 2026; printed works cited by edition. See all sources.
- “RFID Handbook, 3rd ed.”. K. Finkenzeller, Wiley. 2010.
- “ISO/IEC 14443: Cards and security devices for personal identification — Contactless proximity objects”. ISO/IEC. current edition.