[HN Gopher] What are terahertz waves useful for?
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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.
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