danielmittleman

We have been (reluctantly) using the term "6G" in grant proposals for several years now. It's not that new, actually.

Actually, here's a fun fact: the audio "chirp" that you have heard in association with black hole mergers is not slowed down. The measurement is a gravitational wave, of course, not a sound wave. But when it is played as a sound wave, that's real speed, not slowed. This is actually mostly determined by the frequencies at which the gravitational wave detectors (LIGO and VIRGO) are sensitive, which happen to coincide with acoustic frequencies that your ears can hear.

True, but the article is all about electromagnetism, not acoustics. I'm sure the author of the article was not the same person as the person who made the graphics. They probably ought to have communicated with each other a bit more clearly.

The atmospheric transmission's dependence on frequency is complicated. There are water vapor resonances above 100 GHz which one would want to avoid. There is frequency-dependent scattering from droplets, and there is a continuum background from water vapor dimers that rises with frequency. It is a very non-trivial situation. Having said that... the 2008 Olympics demonstration had a broadcast range of about 1 km, and people have demonstrated ranges up to several km at higher frequencies, even close to 300 GHz. So although it will never be as good as the range one can obtain at lower frequencies, there's a lot one can do.

Well, actually it's much easier at lower frequencies. After all, your cell phone operates at around 2.5 GHz (if it is a 4G phone).

But yes, there are huge challenges involved in using higher frequencies for communications. We will eventually use 120 GHz, and then probably 290 GHz, for comms, but it will be a while. The technical challenges are... not trivial.

You might be interested to know that the Japanese television broadcasts of the 2008 Olympic games in Beijing made use of a wireless link operating at 120 GHz. It was really just a demonstration of feasibility, not a fully deployed system. But still, pretty fantastic. And that was 14 years ago...

Your eyes cannot see THz radiation, so no. It's invisible to the human eye. Like microwaves.

But yes, it is possible to produce a beam.

Also: to be fair, the challenge in finding efficient sources is really only one of the challenges. Not even the biggest one.

That question of the sound quality is actually a question of the bandwidth used to encode the transmission. It is naturally easier to access a broader bandwidth if the frequency is higher. But there is a point of diminishing returns. You don't get improved audio quality if you use more bandwidth than the original acoustic signal requires. So, yes, AM is not as good as FM... but a THz signal would be no better than an FM signal in transmitting an acoustic signal.

Yea, that's confusing, despite not being wrong. It is a juxtaposition of two completely distinct phenomena on one graphic, which is confusing, for sure. But the whole article is about EM waves, not sound waves.

Sigh.

I like your enthusiasm.

By now, it has become standard terminology in the research community to use the phrase "terahertz radiation" to mean EM waves between 0.1-10 THz (although some people prefer 0.3-30 THz, and there are also other options out there). There is no uniform and universally agreed-upon definition. But the bottom line is this: the term is never used to refer to infrared (e.g., 100 THz) or visible light (e.g., 500 THz).

This part of the spectrum has previously been lumped into the "far infrared", and sometimes called "submillimeter waves", and in the old old days was called "mega-mega cycles". The reason that there is so much confusion about the terminology to describe this spectral range is that it lies outside of the purview of both optics people and RF engineers. It is the "in between" region, which until recently was unfamiliar to most scientists. So there has been a lot of borrowing terms from different communities going on, and these communities have often not coordinated with each other. It's a bit of a mess, but we live with it.

To be clear: there is NOTHING at all about sound in this article. The spectrum does not show a continuum from sound to light. It shows the electromagnetic spectrum, which does not contain any sound waves at all. One can encode acoustic information on an EM wave (that is how radios work), but the transmitted signal (from the radio tower to your radio receiver) is an EM wave, not a sound wave. The receiver converts the EM wave to the appropriate sound wave by decoding the information that was encoded into the EM wave, and using that information to drive a speaker.

Sound waves are pressure variations in the air. Thus they require air in order to propagate.

Electromagnetic waves are oscillations of an electric field (and also a magnetic field). These fields exist independent of air (or any other medium), so they can propagate in completely empty space.

These are two completely distinct phenomena. They both involve waves, but that's about all they have in common.

No that's not it. There is NOTHING about sound in that article. It is ALL about electromagnetic waves, which are NOT sound waves.

Sound waves are pressure variations in the air. Electromagnetic waves do not require air. They are oscillations of an electric field, which can propagate in empty space. Completely different wave phenomena.

The article has nothing at all to do with sound.

Of course, you can send acoustic information on an electromagnetic wave. That's how radio works. But it's not the sound wave that is transmitted by the radio station - it is the EM wave, with information about the sound wave encoded into it.

Yes. We do it all the time. In some sense, the tricky part is not the antenna itself. It's the electronics that you use to drive it. Electronics can be fast enough to drive an antenna at a few GHz, which is why it is easy to generate microwaves: just hook up some fast electronics to a microwave antenna. But there are few (if any) electronics fast enough to drive an antenna at these high frequencies (like 1 THz).

It does not say that we can't produce terahertz. It says that there are no consumer products that make use of terahertz, because (among other reasons) producing it is more challenging than, say, producing microwaves. That statement is correct.

When people say "terahertz radiation", they do NOT mean visible light. They are referring to radiation between (roughly) 0.1-10 THz, which is much lower frequency than visible light.

Light IS an electromagnetic wave, so to say it has similar properties to EM waves is kind of like saying that pizza has similar properties to food.

Also not sure what you mean by "needs a vacuum to make it possible" seeing as we generate terahertz radiation in air all the time, using a variety of techniques that use off-the-shelf commercial products.

As far as I can tell, the article doesn't say very much that is outright false, although for sure he glosses over some fairly complex concepts with very little detail in a few cases. His statement about "a few dozen meters" of propagation range is outright false, but other than that he more or less got the facts right.

There's a lot of misinformation in the comments posted here. Maybe this bit of information will help. The phrase "terahertz radiation" refers specifically to the band of the electromagnetic spectrum lying between 0.1 THz and 10 THz. The boundaries are arbitrary, and not well agreed upon. Some people say 0.3-30 THz, instead. But the basic idea is the same: it is the realm of the spectrum that lies between the region of microwaves and the region of infrared. It has historically also been called "far infrared" and "submillimeter waves" (submillimeter refers to the wavelength). When people say "terahertz radiation", they are NOT referring to visible light (which has a frequency of hundreds of terahertz).

My evaluation of the text of this article is that it is mostly accurate, although sometimes some concepts are skimmed over a bit quickly. There is one blatantly false comment about the propagation distance for terahertz radiation in air being limited to "a few dozen meters" - that's just plain false. But other than that, everything he wrote is reasonable.