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Using the Terahertz Spectrum for Wireless Communication

Posted by CowboyNeal on Thu Mar 29, 2007 09:53 PM
from the kicking-it-up-a-notch dept.
Wireless Networking Hardware
holy_calamity writes "A first step to allowing wireless data transfer over a currently unused part of the electromagnetic spectrum is reported in New Scientist. Terahertz radiation exists between radio and infrared. A new filter created at the University of Utah can filter out particular frequencies, a prerequisite for using it for data. The abstract of the paper in the journal Nature is freely available."
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    • Didn't Nikola Tesla study/invent devices which work in this frequency spectrum?

      I know that not all of his inventions were made public and that much of his writing was confiscated upon his death, but does anyone have any leads on this?

  • ridiculously expensive (Score:5, Informative)

    by evwah (954864) on Thursday March 29 2007, @10:06PM (#18538865)
    I regularly work with equipment that produces signals up to 50 GHz and let me tell you... components get much higher in cost the higher in frequency they go. a 3 foot 40GHz cable can cost hundreds of dollars and a 100GHz connector can cost a thousand dollars or more on its own. I imagine that producing and transmitting signals in the terahertz range is not economically viable for most companies.

  • Not strictly true (Score:4, Informative)

    by femto (459605) on Thursday March 29 2007, @10:28PM (#18539045) Homepage

    ... a prerequisite for using it for data

    It's not strictly true that you need to have bandpass filters to transmit information. There are other ways to select individual users without frequency division multiplexing. For example:

    • Do it in the time domain (ultra wideband) using narrow pulses. Each user transmits at a different time.
    • Use a spreading sequence to spread the signal so it takes up the entire band, with no need for a narrow filter (CDMA). Each user has a different sequence.
    • Use multiple antennas to do space encoding. Users are separated in space, not frequency.

    The gotcha is that you need some way of sampling the band. One way is to to use a bandpass filter, mixer and slow sampler. Another is to directly sample (using RTDs???) or in the case of UWB just detect pulses. Bandpass filters are the conventional way of doing it, but not the only way.

    • Re: (Score:3, Informative)

      by NixieBunny (859050)
      Bandpass filters are not typically used with the astronomical receivers I'm familiar with. They use a local oscillator operating a few gigahertz above or below the interesting signal and just mix it down to microwave. The usual receiver sees the imagefrequency as well as the desired frequency, but the latest generation uses a sideband-separating mixer with hybrid couplers at RF and IF ports to allow separate reception of upper and lower sidebands. The group I work in was the first to apply such receivers to
  • The New Scientist article is talking about comms, but the Nature abstract actually doesn't have a single word in it with that regards. It only talks about completely different uses. From the abstract:

    "Resonantly enhanced light transmission through periodic subwavelength aperture arrays perforated in metallic films has generated significant interest because of potential applications in near-field microscopy, photolithography, displays, and thermal emission."

    No comms there at all.

  • Another example of how the tabloids (Nature & Science) publish things that have been known for ages... There seems to be a trend that you can get anything published there, since the peer review is done by totally clueless physicists who do not know anything about the state of the art.

    The concept of making filters by cutting holes in a sheet of metal has been known for ages. Using periodic (or in this case quasiperiodic) metallic patterns is called Frequency Selective Surfaces (FSS). There are numerous b
  • Watch them put together their first prototype crystal radio with their new 'filter' and find an entire cosmos of alien phone calls, television broadcasts and quasar's giving off travel-instructions to nearby ships.

    Some people here have said, this is very old news and the article is the equivalent of saying, 'one day railroad lines will cover this great country of ours' -- but seriously, how many average people - like myself, are aware that we're still not using the full EM spectrum available to us. I thoug
  • ... been doin' teraherz for years - it's just "in fashion" now.

    Publication with some terahertz images of concealed weapons on people (towards the article end):

    http://stl.uml.edu/PubLib/DickinsonDSS2006.pdf [uml.edu]

    lots of other THz articles if you chop back the URL to PubLib/
  • I helps if one looks at these things with a certain perspective.
    • First, is there a problem that needs solving? Are we really that short of spectrum?
    • Secondly, if this is so great, why hasnt it been done already?
    • Next, did anybody do a literature search to see if it has been done?
    • Next, is this the most economical way to do this?

    Otherwise, we end up with wildly expensive proposed solutions using already tried and rejected technology that violates basic laws of physics, scale, or economics, to attack a n

  • At about 430 terahertz with direct line of sight over a distance of over a mile in some cases. Much longer if you're transmitting through a vacuum.

    It can be very fast, but you can build your own slower version simply.

    1. Take a red flashlight.
    2. Stand on a hill.
    3. Have a neighbor stand on another hill.
    4. shine light at neighbor.
    5. Cover the light with your hand, which produces a bitwise "0"
    6. Uncover the light, which produces a bitwise "1"
    7. Repeat, encoding your signal in binary at whatever rate yo

    • Re:It might just take a while (Score:5, Informative)

      by Anonymous Coward on Thursday March 29 2007, @10:06PM (#18538877)
      ...so communication would have to be rather short-haul as in LAN.

      Perhaps TFA should have mentioned that.
       
      Wait...

    • Re:It might just take a while (Score:5, Insightful)

      by evilviper (135110) on Thursday March 29 2007, @10:18PM (#18538961) Journal

      There is also the slight problem of water absorption of the signal [...] so communication would have to be rather short-haul as in LAN.

      Which is EXACTLY what TFA said...

      But hey, what do I know, your post is a +5, so it must be somehow insightful, not 100% redundant.

    • Re:It might just take a while (Score:4, Informative)

      by FuzzyDaddy (584528) on Friday March 30 2007, @08:09AM (#18542105) Journal
      http://www.gigabeam.com/technology.cfm [gigabeam.com] has a nice plot of atmospheric absorption versus wavelength. For reference, 100 dB/Km = 3 dB/30 meters - or 50% signal strength loss per 30 meters, not counting the 1/r^2 factor.

      Also, generating and modulating signals, with current technology, is done by firing very expensive lasers at very customized pieces of semiconductor materials. As for receivers, NixieBunny would know better then me what the current technology cost and noise figures would be.

      All of which to say, this is an interesting article, but it's about 1% of the way towards communications in this band.

      Don't get me wrong - this is a cool paper, looks like good work, and this might have some very interesting technological applications. But the perpetual question of "what is it good for?" that every reporter asks (it's got to be a law or something) about every scientific advance misses the point. We don't know what it's good for, but it expands our knowledge of the world, and that can only help us.

      Using it for something is the job of the next genius. These guys did enough by getting it to work. Someone else will have to figure out what it's good for.

    • Re: (Score:2, Informative)

      by evwah (954864)
      micrwave frequencies are usually considered to be the upper end of the radio frequency spectrum... the former being about 1G-300GHz, and the later covering 3Hz-300GHz.

      • Re:Hmm, (Score:5, Informative)

        by NixieBunny (859050) on Thursday March 29 2007, @10:17PM (#18538951) Homepage
        The microwave spectrum really ends at about 30 GHz, with the frequencies from 30G-300GHz called millimeter wave, and those from 300 GHz up called submillimeter. Terahertz technology is quite in its infancy. There was a terahertz conference last week, so the office I work in was pretty well cleared out. (I work on spectrometers that use what we consider low frequencies, The other thing about terahertz waves is that they behave quasi-optically, being focused by teflon lenses and blocked by cardboard. So it's not a radio band that one would use for cellphones.

    • Re:Geek into English. (Score:5, Informative)

      by rhythmx (744978) * on Thursday March 29 2007, @10:12PM (#18538925) Homepage Journal
      Basically it says that putting the holes in a fractal pattern give much better results than holes in more 'normal' pattern. The rest is Calculus explaining how they can generate patterns that are really good at transmitting a certain frequency.

      Sounds really interesting. I wonder if any of this applies to antenna design at average RF.

      • Re: (Score:3, Informative)

        by mdsolar (1045926)
        In a way this is a pretty standard result. One can reduce the ringing in a Fourrier transform by including non-periodic sampling. What is provacative is the implication that there is some flaw in the surface plasmon interpretaion. Namely, they point to straight interference as being important rather than the constrained response of the surface electons.
        --
        Get solar: http://mdsolar.blogspot.com/2007/01/slashdot-user s -selling-solar.html [blogspot.com]

    • Re: (Score:2, Funny)

      by Anonymous Coward
      This is trivial. At Starfleet Academy, surface plasmon polaritons and Fano interference in quasicrystals were on our freshman exams in the first week. Even WESLEY got it right, and he was the dumbest one in our class. Well, except for that guy, George Bush VIII. I don't know how he got in, except his father was like the king of some country named Texas or something. All he ever did was exotic drugs, until the day he blew his testicles off in chem lab. Thank goodness for modern transplant technology.

    • Re: (Score:2, Insightful)

      by Short Circuit (52384) *

      Once you get close to the frequency of infrared light... Why not just make the jump, and go with light instead?

      Perhaps because there aren't many known ways to tune the frequency of visible-spectrum EM emissions at rates which make using that part of the spectrum in that manner effective?

      Terahertz research would seem to me to be a step in that direction, by bringing existing EM modulation techniques closer to that spectrum.

      And, in the end, we're not going to want to stop there. We're going to eventually want to extend application of understood techniques to the UV bands and beyond.

      It may not be effective for commun

      • Perhaps because there aren't many known ways to tune the frequency of visible-spectrum EM emissions at rates which make using that part of the spectrum in that manner effective?

        I'm not sure what point you're trying to make here. "Tuning" is absolutely not necessary. Simple off/on digital communications work at very high speeds with fiber optics in the visible light spectrum right now.

    • Once you get close to the frequency of infrared light... Why not just make the jump, and go with light instead?

      Ummmm. In case you didn't know, people have been using light for years. Ever heard of semaphore?

      • High-speed digital communications bear little resemblance with low-speed manual signaling.

        That said, I'm not sure why you got a Flamebait mod.

        • That said, I'm not sure why you got a Flamebait mod.

          Probably because there are no "-1 I don't get it" or "-1 That joke was really lame" options.

    • Re: (Score:3, Informative)

      by Mad Bad Rabbit (539142)

      Once you get close to the frequency of infrared light... Why not just make the jump, and go with light instead? They're both going to be line-of-sight anyhow, with anything that blocks light very likely also blocks THz rf.

      Actually no; terahertz rays [wikipedia.org] can go through wood, sheetrock, masonry, etc. (but not metal or water).

    • oh no.. not petahertz... then we'll have those animal rights crazies demanding we let it go..

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