But it is a new signal originating from the 3D object. They even convert Bluetooth to Wifi signals with this technique. Read about comment of mine for source.
"We 3D print a cup anemometer as shown in Fig. 2 to measure wind speeds. The entire setup is sufficiently light that even wind speeds as low as 2.3 m/s will cause it to spin. The hub of the anemometer is attached to backscatter gear that encodes an alternating sequence of zero one bits. When the hub spins, the backscatter gear pushes against the spring switch. The switch makes contact with the antenna and generates the backscatter signal. Wind speed can be inferred from the rate at which bit transitions occur."
That's a totally different project than the one this submission is about, using totally different technology. The 3d-printing one is modulating things in the range of few Hz, you're not making packets with that.
They could do it with a radio signal of a clean sine wave and through the 3D object they could convert the sine wave into wifi. Just like they could take a bluetooth wave and make a wifi signal. The big advantage to this is they can just take a Wifi and use it to do the same thing. No need for new hardware.
They are similar in a very high-level view, but that's exactly what's causing the confusion here. Yes, the video you link is about a project that is actually generating Wifi signal. The article discussed here is not, and it's IMHO irresponsible by (what I assume was) the PR department of the university to present them as doing the same. Take a few minutes and compare the papers (printed Wifi http://printedwifi.cs.washington.edu/printedwifi.pdf and Hitchhike https://web.stanford.edu/~pyzhang/papers/sensys16_back_comm.... or interscatter http://interscatter.cs.washington.edu/files/interscatter.pdf), the principles used are very different. The 3D printed objects only switch an antenna which attentuates (=modulates the signal strength of) Wifi signals with a few Hz frequency at max, HitchHike and interscatter involving electronics completely transform the signal at HF level, retransmitting full packets at a different frequency.
They are both "backscatter" in that they change an existing signal and thus require less energy than if they generated it themselves, but that's about it when it comes to similarities.
They both must have single side modulation for anything to work. If not than Wifi and FM and AM would never work since everything would confuse the receiver.
I thought maybe I am missing something, but I see that the objects are encoded with bit and transmits.
Printed Wifi Paper
"PRINTED MAGLINK
At a high level, by varying the magnetic properties of the material used within a single print job, we can embed multiple sequences of bits across the object. We consider the 3D printed object that modulates the magnetic field as the transmitter and the smartphone as the receiver.
Maybe it is the word modulates that is the issue?
Modulate Definition - In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the carrier signal, with a modulating signal that typically contains information to be transmitted. Most radio systems in the 20th century used frequency modulation (FM) or amplitude modulation (AM) to make the carrier carry the radio broadcast. https://en.wikipedia.org/wiki/Modulation
> I thought maybe I am missing something, but I see that the objects are encoded with bit and transmits.
I think you're confusing three or four different projects at this point, whose only common property is that they operate on the energy of an incoming 2.4GHz signal (the "backscatter" thing).
The project that is the topic of discussion in this whole HN thread is the one that uses a 3D-printed plastic mechanism that changes the way an antenna (incidentally, 3D-printed too, out of a filament that mixes copper and plastic) reflects an incoming signal. There is a binary pattern, but it's encoded in the cog-like thing in the mechanism.
It's pretty much like sending light signals with a mirror, except it's reflecting radio waves. The way they use technical terms in this article (and the original paper) is problematic, and I believe your confusion in this subthread is a perfect example of why the abuse of "Wi-Fi" references is a problem.
No read the paper once. I did and I learned a ton and than I commented. When people don't read the material and assumptions are made is how you get into these arguments.
