At some point, the difference between a "wifi receiver" and "RF receivers, including wifi" is splitting hairs, yeah?
Like, I understand that wifi is a specific protocol that uses a spectrum shared by lots of other devices, and that without the ability to generate more complex signals it won't actually be "wifi" but if a standard wifi radio can receive these signals and be made to understand them, wants the point of the pedantry?
If I get a box talking RS232 to a host with wifi, I can claim it talks to "signal receivers including wifi". It's not speaking wifi. The host is speaking wifi. Using that specific awkward wording was a big tell to me.
I mean, it's very cool stuff, but it's not things without electronics speaking wifi.
I haven't read the paper yet, so I can't speak to the specifics beyond what they included in the web page and their powerpoint.
The website says "Our goal is to 3D print wireless sensors, input widgets and objects that can communicate with smartphones and other Wi-Fi devices, without the need for batteries or electronics."
Now, based on my understanding of how wifi works, they would need direct control of the radio, and to write a custom driver in order for the data their devices produce to be readable by a smartphone.
It wouldn't technically happen over wifi, but to an end user the difference wouldn't matter.
There's a wifi transmitter, and wifi receiver, and between them, the sensor.
The sensor modulates the wifi signal passing between the wifi devices.
The differences between the unmodulated signal and the modulated signal are decoded by a device at the receiving end.
They go in to the details in section 3.2 of the paper.