Is the squiggly line an antenna?

I thought so at first, but since this card is metal I’m assuming it has something to do with adding the chip during manufacturing.

Edit: from the other comment, it likely breaks up continuity of the metal card so NFC energy flows into the antenna instead of being absorbed by the metal card itself

It connects the chip to the NFC antenna that runs around the rest of the card.

Interesting.
What does it do when you shine the light on the card numbers?

lol

Well, the card numbers become illuminated

So metal

The account starts reporting unexpected transactions.

Electrical Engineer here. Pretty sure the slit is to break up the metal in the card so it won't interfere with NFC.

If you look at an NFC antenna, it's a big coil of wire. It's energized by an oscillating magnetic field that passes through it. Faraday's Law dictates that when a magnetic field oscillates, an electric field will form around it. This electric field generates a current in the antenna that powers the NFC chip.

In a metal card, the current will flow in the card instead and draw energy away from the NFC chip. This slit blocks that current flow so that the current flows in the antenna instead.

Peak mildly interesting, bravo

Doing that can reveal a whole bunch of interesting patterns. I was repairing something on a circuit board once and was trying to figure out the wiring. Trying to get more light, I shone my phone's flashlight at it. At some point I suddenly realized that the circuit board lets a bit of light through. I realized that, at least for some of the board, I could shine a flashlight onto the other side and see pretty exactly how the circuit was laid out. It also looked really, really cool.

Any reason it's a staircase instead of just a simple. Straight line?

It's an antenna & it needs to be a certain length - making it a bit gay just adds enough pizazz (length) and it's the ez thing to do from a designers pov.

Oh, no, the metal ones do in fact use the metal as an antenna?? Can't really tell (but I would guess not).

yt/wyj7r_C51UU&t=115, yt/P5aszRLpa3Y

I though it was like this:

So the pattern of the cut is maybe structural (harder to bend with the plastic inside it bcs it's longer?) or just perhaps a CNC simplification.

I believe that minimizes capacitance. My question is why diagonal at all. Maybe it helps with adhesion during the manufacturing process?

Capacitance between turns, specifically. Provides e-field shielding too.

Fascinating.

I recently took an x-ray of a card, might be interesting to some of you as well:

Ooh, very cool!

Are the two different pictures different wavelengths, or do you just have two seperate sensors? (I have no idea how this works, just a highschool level understanding of x-rays.)

Pics or it didn't happen/j