[HN Gopher] What are terahertz waves useful for? ___________________________________________________________________ What are terahertz waves useful for? Author : prostoalex Score : 40 points Date : 2022-03-31 14:18 UTC (2 days ago) (HTM) web link (www.popsci.com) (TXT) w3m dump (www.popsci.com) | aeonik wrote: | I wish they wouldn't call it Terhertz waves. The article states | that we haven't been able to harness THz waves, but the author | shows a visual diagram clearly showing that visible light falls | completely in the Terhertz range, even making up 39% if the | entire THz spectrum. | | Far Infrared is much more specific. If THz is really that desired | on the title, calling it low band THz would probably be better. | fsh wrote: | They are referring to the ITU "Terahertz" band which is defined | to range from 300 GHz to 3 THz: | https://en.wikipedia.org/wiki/Radio_spectrum#ITU | SigmundA wrote: | Yes I almost thought it was an April fools joke article like | dihydrogen oxide dangers. | danielmittleman wrote: | 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. | willis936 wrote: | Engineers and physicists have long referred to low THz RF as | such and not with optical terms. | | Also, there are many low THz applications but nature doesn't | make it easy to work with. | | https://en.wikipedia.org/wiki/Terahertz_gap | sydthrowaway wrote: | Is it possible to make an antenna that radiates teraherrz | radiation? | danielmittleman wrote: | 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). | sydthrowaway wrote: | Will it look like a beam of light? | ddingus wrote: | Not to us, and that's the interesting bit in this EM range. | | 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. | danielmittleman wrote: | 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. | WJW wrote: | Sure, why not? THz wavelengths are between 3 mm and 30 mm which | is not very large for an antenna but not anywhere near the | limit of what we can make these days. | danielmittleman wrote: | 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. | LWIRVoltage wrote: | So, i'm just an enthusiast/geek who owns Long Wave Thermal | Cameras- and while the article wasn't the clearest to me,- | | 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... | danielmittleman wrote: | I like your enthusiasm. | marcodiego wrote: | [deleted] | hamandcheese wrote: | > Light-producing technologies like lasers, which are right at | home in infrared, don't work with terahertz waves either. | | What about red, green, blue lasers? | jasonwatkinspdx wrote: | Those are yet higher wavelengths. Terahertz is 10e12 hz, | visible light starts around 4.5e14 hz. | Terretta wrote: | I don't understand the "Electromagnetic Spectrum Infographic" | that purports to illustrate a continuum from sound to light where | what's changing is frequency, and says "radio spectrum" has | "perceptible sounds". | | 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"_ | cookiengineer wrote: | I mean, it's popsci.com...what did you expect? /s | | 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. | danielmittleman wrote: | 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. | cookiengineer wrote: | Touche, you're right. I should've worded that differently | in the moment. | | 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. | danielmittleman wrote: | 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... | jasonwatkinspdx wrote: | Big yikes on that second link. Everything there should be taken | with a whole dump truck of salt. | Terretta wrote: | I was told by media Russia's already putting it to use! | | 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. | fsh wrote: | Or more likely: People trained to be paranoid being | paranoid. | mardifoufs wrote: | Yeah if you go on the home page of that article you get this: | | 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. | heavyset_go wrote: | Credible sources and studies on "The Hum" have different | conclusions than what the second link is purporting to be true. | Some of them are cited on Wikipedia's entry for "The Hum"[1]. | | [1] https://en.wikipedia.org/wiki/The_Hum | Terretta wrote: | > _different conclusions_ | | 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. | danielmittleman wrote: | 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. | jameshart wrote: | The diagram of the EM spectrum at the top has a very | confusing section on the left where ranges of frequencies are | labeled 'infrasound', 'perceptible sound' and 'ultrasound'. | They have nothing to do with the ability of the corresponding | radio waves to be modulated to transmit sound signals, but | are literally just marking off the frequencies that | correspond to those ranges in sound waves, over a diagram of | EM frequencies. | danielmittleman wrote: | 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. | tinus_hn wrote: | The low frequencies carry less data so perhaps they mean that | the low frequencies cannot be used to transmit perceptible | sound. | danielmittleman wrote: | 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. | tinus_hn wrote: | I presume most people here are aware that sound waves are | different from electromagnetic waves. | | 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. | ddingus wrote: | Am, modulated at 10 to 20Khz would sound GREAT! We just | don't do that. Typical bandwidth is 5 to 8Khz these days. | Earlier AM broadcasts were wider, out to 10+Khz. | | 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. | danielmittleman wrote: | 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. | FooBarWidget wrote: | I don't understand the problem the article mentions. It says we | can't produce terahertz waves while showing an infographic | showing that visible light _are_ terahertz waves... | danielmittleman wrote: | 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. ___________________________________________________________________ (page generated 2022-04-02 23:00 UTC)