# Confused about smart card wavelengths and antennas

The tap-to-pay cards. These are also called contactless cards, right? And also smart cards?

The interrogator frequency is 13.56 MHz, correct? The reply (subcarrier) frequency is .969 MHz to 3.013 MHz, correct? That's what ISO/IEc 18000-3 says.

Using $$\\nu\lambda = c \$$, we can calculate the wavelength.

Frequency (MHz) wavelength (m)
.969 310.
3.013 99.
13.56 22.12

Per Wikipedia, the picture of a chip on a Canadian penny makes them look like they're about 3mm square.

Now, various articles and web sites indicate that for a dipole antenna, the antenna has to be about 1/2 the wavelength. But that means the chip is waaaay too small, by a factor of around 33000.

What am I missing? Yeah, I know that the dipole isn't the only antenna configuration, and I get that other configs respond differently, but 4.5 orders of magnitude????

I guess what I'm asking is about how the near field works vs. "normal" antennas.

• They work via magnetic coupling much like a transformer. The main reason is so the card can harvest the energy from the field in order to operate. Sep 14, 2021 at 7:39