What are terahertz waves useful for?
popsci.com
popsci.com
Which ones of these things are not like the other ones?
Conventionally, sound waves are a vibration traveling through an object and cannot travel through a vacuum, while light is* a wave of oscillating electromagnetic fields that can travel fine through a vacuum.
In more detail: https://socratic.org/questions/how-are-sound-waves-different...
OK, there’s this on “Sensation of Hearing in Electromagnetic Fields” but not at these frequencies:
“The "hearing" of electromagnetic waves is an established fact. It appears that this takes place by direct stimulation of the nervous system, perhaps in the brain, thus bypassing the ear and much of the associated hearing system. It is a possible, perhaps the most probable, explanation of the reports of hearing meteors and auroras” — https://www.bibliotecapleyades.net/scalar_tech/the_hum/ingal...
So, not so much “hear” as “perceive” perhaps. But I doubt this is what the graphic is suggesting either.
I fear grade school kids reading this PopSci issue could be mislead for a while about why they can hear the radio.
* for interesting values of “is”
Yeah, the article confuses a lot of physics and doesn't make sense from a wavelength standpoint. Of course, light has similar properties than electromagnetic waves, but sound definitely doesn't have anything to do other than it can be described with wavelengths.
If you approach the terahertz spectrum, however, resonance is getting a little complicated because it can hit the natural vibrations of molecules. I guess that's what the author was trying to write about in terms of potential medical/scanning applications.
As moving molecules physically in order to create terahertz frequencies seems unfeasible (as of now, u know, because lack of vacuum to make it possible), the only possibility is to generate electromagnetic frequencies and/or light based emissions.
Electromagnetic frequencies for transmission on that scale get complicated real fast though, due to interference and basically everything making it worse, from humidity to infrared waves until basically all longer molecules.
Finding a molecule to use this as a transmission medium in something like a chip as a circuit is a whole other question.
Overall I think the article tries to make "this is ohmagerd" point without understanding the basic physical interactions, laws and properties.
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.
I was trying to come from the perspective of the author, where he tries to argue about difference of appliances through technological means. E.g. using a laser for communication vs using a wifi like transmitter setup.
Both are EM waves but the practicality of the environment with degradation and radiation and the medium that are common for us (gases in the air) make the approach of how to reach the target vibration (in the sense of targeting a specific antenna length on a specific wavelength) harder when trying to use the sub infrared spectrum.
As I wanted to say, I think finding the right material and medium will be a huge challenge in this regard.
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...
That's why I was assuming that higher frequencies than the Ku Band will likely lead to more signal degradation on the way.
I also don't have any calculations or plots in my head for the minima and maxima, so I could be totally wrong about this :D
120Ghz is quite amazing as an achievement though. They probably used a wider band and multiple channels, I would assume?
edit: looked up a little on K (18-27Ghz) and Ka band (26.5-40Ghz), but both seem to be still unfeasible for long range communications.
umm, Ka band is rather popular for satellite communications (very long range by most standards!). Yes things like L band are great for propagation and penetration, but the fundamental motivation for going to higher frequencies is that they can carry more data. This is the same reason you don't get music on AM radio--there's not enough bandwidth for good sound quality.
https://foreignpolicy.com/2020/12/05/us-diplomats-havana-syn...
https://www.foxnews.com/world/us-officials-were-targeted-acr...
Sonic attacks? Radio waves? Either way, gives ‘em a headache.
https://www.bibliotecapleyades.net/esp_gaia.htm#Additional_I...
Its something about the Gaia theory, which makes even the electromagnetic hearing stuff look sane in comparison.
Those seem to be wildly different phenomena. The “hearing radar” mentioned frequencies of 1, 3, and 10 GHz(!?!?), while “The Hum” is between 32 Hz and 80 Hz, modulated from 0.5 to 2 Hz.
My including the link was not suggesting the thing reported was true, rather, it was the only thing I quickly found suggesting anyone hearing electromagnetic frequencies of any kind.
In the hum, most thinking is either physical noise, or resonance. That said, one paper linked from Wikipedia does have this:
“Analysis of the largely anecdotal data that are available at the present time suggests that the most probable explanation is that some people have the capability to interpret radio transmissions at certain wavelengths as sound. It is well established in the scientific literature that people can hear electromagnetic energy at certain frequencies and peak power levels.” — https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.51...
However, while this could validate both phenomena as being perceivable by some, I do not think this is why Pop-Sci made their chart as they did. I stand by my objection.
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.
To transmit audio you have to encode it into electromagnetic radiation, transmit it and then decode it to reconstruct the audio.
You might have noticed that the audio transmitted on lower frequencies or longer wavelength sounds worse. AM (medium wave) sounds pretty bad, long wave sounds even worse. Even lower and you can’t make out speech anymore, it’s no longer possible to usefully transmit sound.
I had an AM Stereo modulator for a while that did 10Khz and on the better radios was quite good. Commercial AM, with a few rare exceptions, isn't a good representation of what one can get at those frequencies. Nor are the radios sold today. They are frankly, terrible!! Get any older AM radio, 80's era and older and it's quite the difference.
Shortwave is modulated at about 3.5Khz, and is enough for speech and the gist of other material.
Noise is the primary reason we do not use those wavelengths. Power requirements go up too, if the signal is to reach max distance. There is a compromise in play, bandwidth vs propagation.
Finally, we also use an emphasis curve where higher order frequencies pack a real punch, with lower ones getting a less due to how sensitive we are to noise at various audio frequencies. Higher pitch noise stands right out, with our peak sensitivity around 3.5Khz.
We can, if desired, transmit a pretty great audio signal at the Khz frequency range. We just don't, because a narrow bandwidth is a better use of the spectrum.
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.
Sigh.
I also shared the same information as your 2nd (aside: sound doesn't require air, as bone conduction headphones or scuba diving demonstrate, does require "not vacuum") and 3rd paragraph, and made the same point as in your close.
So I agree with you, which is why I objected to the graphic.
Except that a portion of the spectrum graphic is labeled “perceptible sound.” That’s what the OP is referencing.
Perhaps the illustrator is pointing out that the frequency range of these EM waves coincides with frequency range of audible sounds? Or perhaps they’re confused. Either way, there’s no mistaking that the graphic is labeled with the words “perceptible sound.”
There are lots of uses for terahertz waves, if they become cheap to generate and sense. Lots of things could use high-definition short-range radar. Right now, experimental radars are pushing 300GHz.[1] Most commercial stuff is below 100GHz.
That's because human ear is very good at hearing small changes in frequencies. E.g. first movies vere silent not because they couldn't play the audio, but because they couldn't synchronize between the video and audio.
Human eye is very forgiving to uneven or hickking-up video playback, but not the ear.
I count no less than SEVENTEEN OTHER external sites trying to inject resources. Must be a new high score.
Far Infrared is much more specific. If THz is really that desired on the title, calling it low band THz would probably be better.
Also, there are many low THz applications but nature doesn't make it easy to work with.
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.
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.
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.
What about red, green, blue lasers?
Actually. No joke there.
The joke will be that if they go forward and try and make a case for using terahertz waves from your phone to 3D map your environment. If you think the knee jerk to 5G is bad, hold on to your tin foil.
All em waves, whether light, UV, radio, gamma, etc- can be measured in frequency - so yes, I see why one person is confused- but no, it's just measuring them all in THZ waves instead of nanometers or HZ, but the scale of the spectrum gets big, so they chose that one arbitrarily it seems./
And yes, the graphic mentioning sound- I am not sure what that chosen graphic is actually getting at...I suppose it's more about frequency.
Regarding the Terahertz part of the spectrum- it's neat, in that it's really the area after far infrared, well, blending from that- into Microwave.
So, it's got a longer wavelength, than far infrared, and can penetrate further into materials in general(except some materials which are opaque, of course )- and less energy..../
I find it neat because the deeper you go into the spectrum from an imaging standpoint(something they don't talk about here)- you start to see some unique effects- Example; in a thermal image, people glow because they emit, mostly in the LWIR thermal band(not MWIR, though they glow there too) - as you go deeper and deeper ,they don't emit as much, but they still do- meanwhile, the penetration against waver vapor, gets better and better the deeper you go- so ultimately, you could build imagers that see even farther through bad weather, but still give a unique view of the world with it's own unique properties. We're actually talking about superman-level vision, i suppose.
There's a LOT of other uses for accessing more of the spectrum, but the terahertz, and passive millimeter wave- and further, isn't used in as many applications as it could be yet, due to some problems that have never been bothered to really have been addressed, like the increasing wavelength(not insurmountable) and the chips and sensors required to access those bands...
Example: Driverless cars with access to sensors across more of the spectrum, from long wave infrared ,to longer- would allow passively seeing through rain and fog and obscurants to a better and better degree- and while active sensors are good, passive ones 100% won't interfere with anything else.
Medical imaging- how many conditions of the human body cna be seen, if you just keep going up and down the scale in the right wavelength? Thermal imaging already sees MANY medical conditions on people (I can also confirm this having seen...things like Reynaulds Syndrome on people , just walking around with my thermal cameras in public to my surprise(It was said people who noticed it and pointed it out to me when looking at my thermal cameras) ) - Xray wavelengths don't necessarily see everything - there's a whole lot of spectrum aside fromthem
I leave any fellow geeks who love seeing this stuff, with these images from around the web- To give an idea of what the world looks like as you go further in the spectrum.
http://www.vision4thefuture.org/s4_resources/2_passive.htm [throwing in an Image of the world Further down the spectrum at the passive millimeter-wave area, to be exact, 90 GHZ) https://www.researchgate.net/figure/Photographs-and-correspo...
[Radio Wave imaging of satellites in the sky at 10-12 ghz , couldn't resist throwing this one in- sadly it appears No ground level imaging has been done in these bands, but it would take effort to set up a radio-wave imager, it'd also be a bit large and unwieldy- though still useful} https://www.orbiter-forum.com/threads/the-amateur-radio-astr...
It will be more light like than microwaves are, but less light like than light is.
And what we can learn from using that range is still new ground because it's hard to make devices that emit RF in those ranges.
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.
Heres a quick example: [1] http://www.aowireless.com/about-us/wireless-partners/wireles...