Most commenters here are misunderstanding the paper. This is research on a wireless RF power transfer and low strength magnetic field sensing system for BCI sensors. It is not about BCI sensors itself. This is about wireless power transfer and modulating the reflected signal to broadcast the sensor information. In other words your brain computer interface no longer needs a subdermal battery.

How does this sensor actually detect brain activity? Lots of details about RFid, etc... but not the actual sensor used in the first place.

Also, this should be tagged (PDF)

From the lack of details, I can only assume it detects brain activity with future funding/development.

What do people make out of the fact that this is an MDPI article but from a reputable group?

It's a red flag. Looks cool on the surface, but if it's what it appears, it should be subjected to a more rigorous review.

I am disappointed they didn't measure the effect of wearing a tinfoil hat...