From the abstract:

> Here, we demonstrate a covert communications method in which photon emission is rapidly electrically modulated both above and below the level of a passive blackbody at the emitter temperature. The time-averaged emission can be designed to be identical to the thermal background, realizing communications with zero optical signature for detectors with bandwidth lower than the modulation frequency

It sounds like maybe they're modulating the emissivity of a diode up and down so that over time, its IR spectrum looks like black body radiation. Only someone looking at the intensity of the thermal radiation coming from the diode at really fast timescales (kilohertz or megahertz) would notice that there was a signal being transmitted.

So all an eavesdropper has to do is setup the right equipment then? I guess it is only invisible until the technology becomes more widely available.

> But if someone doesn’t even know the data is being transferred, then it’s really very hard for them to hack into it. If you can send information secretly then it definitely helps to prevent it being acquired by people you don’t want to access it.

Very strange framing. Symmetric cryptography has been "unhackable" for a while now, for all intents and purposes. The real advantage is surely that nobody notices you're transmitting data at all?

Electronic warfare is not about listening, but just seeing the location of the emitter. If you had someone with a different thermal camera/ camera with SWIR, you might see that something is just not right.

So this negative-light technology is quite interesting in that it's stealth, but it has to come a long way to reach the ubiquity of UWB. I'm curious if and how such technology could be used in space though. Happy to hear more!

One of the most plaguing questions I have is that it's very odd that specialists are so quite about the wide-spread integration of UWB chips in all modern phones and the accompanying "possible" surveillance nightmare. As a government it'd be total horror to be fully penetrated by an adversary like this. If you find otherwise please share the paper here, there's a lot of literature about UWB, OAM, beam-forming, antenna-design and related technology that, when put together easily make someone doubting it at least more inclined to be more open.

My work back then was sold to military by one of my professors behind my back, and after confronting the professor about it he laughed it off telling me it's normal and okay. I refused to publish about it, as I was finding it difficult to find a positive usage scenario, plus he was profiting of off my work that I needed for a grade financially outside of university and of course of no intention of integrating my work. To add salt to that wound he instructed me to change my applied-science paper to be more of a guide for a few select PhDs who'd receive the financial grants, making my work a footnote at best. I have no words. Later I learnt by a friend working on his Dr. degree how he got betrayed by his Dr Father. He was working on a science-backed improvement for a factory, after telling his Dr. Father he found that he patented the technology and sold it to the factory. When he found out, he heard a similar story to mine, where his Dr. Father basically told him, "lesson-learnt, better me than someone else". He finished his degree and kept his profile-low for years after that to not cause conflict.. quite sad.

My initial plan was to provide IPS to the campus with a few-cm accuracy and gesture recognition through walls as a cool gimmick with future work focusing on accessibility scenarios.

But with current devices it's possible to use the UWB chips in distributed mesh (similar to find-my) to create an ultra-high-resolution 3D-feed with city-wide, real-time and through-wall sensing at mm-accuracy. I'm not even factoring in resolution upgrades using AI.

Cook me, if you want, this was genuine scientific work taking months of work back in 2015 to be able to build, but being backstabbed by your professor was quite unreal to find out. Later I got similar signals from friends at Fraunhofer and Max-Planck. Just listening to their work stories made clear they were fooled doing science, when they in tandem were quite frankly building military reconnaissance technology, but distributed in small disconnect groups of low-paid scientists (PhD/Dr/MSc).

For a contrived example, imagine I'm in a warzone:

- Secure = Enemies can't read my messages. Good. But they can still triangulate my position.

- Covert = Enemies don't know I exist

The big claim in general appears to be that the signal is not obvious because it averages out to normal background radiation noise. The article doesn't communicate this well though.

The bit that you quoted, I think that's just a random sentence that looks dumb out of context. I don't think it means anything special.

Modulating the infrared emission by cooling and heating a body is slow, so the transmission rate is low and it is also easy to detect, because any infrared detector will show pulsed infrared light.

The whole point of the article is that they have found a method for modulating the infrared emission that is much faster than cooling and heating, so because the modulation frequency is so high any normal infrared detector will not see anything, it would just detect the normal infrared emission that corresponds with the ambient temperature.

They exploit a phenomenon that exists in infrared LEDs made for a low frequency (high wavelength), which when biased forward emit infrared light, like any LED, but when biased backward the reverse happens, i.e. their infrared emission is lower than it should be for a black body at ambient temperature, because a part of the thermally emitted photons are reabsorbed by the semiconductor, generating electron-hole pairs that are separated by the electric field, being thus prevented to recombine and emit again a photon.

Because the increases and decreases in infrared luminosity are done by changing the bias voltage of a LED, they can be done orders of magnitude faster than by cooling and heating.

I do not know whether this proposed application in steganography would ever be worthwhile, but this is certainly a very cool development.

The device presented in the parent article would be undetectable by any classic detectors.

However, if such a method would ever become widely used in reality, it would not be difficult to make detectors for it. So it could have a window of opportunity, between the first development of spying devices based on it and the development of countermeasures.