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Wireless Networking Hardware

Using the Terahertz Spectrum for Wireless Communication 134

Posted by CowboyNeal from the kicking-it-up-a-notch dept.
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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Using the Terahertz Spectrum for Wireless Communication More

Using the Terahertz Spectrum for Wireless Communication

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  • I work on radiotelescopes that work at several hundreds of gigahertz, and the technology used there is rather exotic. There is also the slight problem of water absorption of the signal - our telescope at 10,500 ft (3200m) altitude has trouble getting a clear shot to space due to the atmosphere, so communication would have to be rather short-haul as in LAN.

    • 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: (Score:1, Insightful)

      by FMota91 ( 1050752 )
      Well, if Internet speeds keep getting better (which I'm sure they will), this could be used to make a faster Wi-Fi router. It shouldn't be too difficult in a few years. Amirite?

      Admittedly, I don't know if I am.

      • Well, if Internet speeds keep getting better (which I'm sure they will), this could be used to make a faster Wi-Fi router. It shouldn't be too difficult in a few years. Amirite?

        First off, there's no such thing as a 'Wi-Fi router'. At least not in the technical sense. My guess is some marketing genius decided that was a good name for an AP/Router combo.

        Anyway... this tech looks like it would be fairly poor as an omni-directional access point. While you can fit more data on a frequency that high, it'

    • 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.
    • Ok so this would only be effective in a LAN type of situation but just as a question, wouldn't this free up some frequencies in the long run? Also does anyone have any idea on the possible ranges for point to point vs point to multi point? I'm thinking if the cost of these things goes down (a lot) and a point to point connection can get out to about a mile then point to multi point ought to cover a block, then we may have a future with these things on top of telephone poles. The distance for wimax is typica
    • LAN? Fuck, I'd be happy if I had terahertz communication two inches from my CPU to my memory. And terahertz memory. And a terahertz CPU.

    • 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.

    • High rates of atmospheric absorption mean that Mother Nature is making your network cellular for you. This would be great technology for meshes, because the node three hops away simply can't interfere with you. Sub-mile ranges are also entirely useful for point-to-point links in dense areas. If you had a meeting in Bangkok with someone a mile away, you'd really prefer a broadband video conference over driving a mile in Bangkok traffic.

    • 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?

  • Geek into English. (Score:1, Interesting)

    by Anonymous Coward
    "Resonantly enhanced light transmission through periodic subwavelength aperture arrays perforated in metallic films1 has generated significant interest because of potential applications in near-field microscopy, photolithography, displays, and thermal emission2. The enhanced transmission was originally explained by a mechanism where surface plasmon polaritons (collective electronic excitations in the metal surface) mediate light transmission through the grating1, 3. In this picture, structural periodicity i

    • 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]
        • You shouldn't file this under "Geek to English" though.

      • Re: (Score:2, Interesting)

        by cats-paw ( 34890 )
        "Sounds really interesting. I wonder if any of this applies to antenna design at average RF."

        yes it does.

        Fractal antenna design is old news at this point.

        You get a modest reduction in antenna design, but it really excels at giving you a broadband design. So it's particularly handy for UWB.

    • 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.

  • 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.

    • Re:ridiculously expensive (Score:5, Funny)

      by markov_chain ( 202465 ) on Thursday March 29, 2007 @10:17PM (#18538955)
      Pshaw, that's nothing. I work with high end audio equipment, and let me tell you, a Hi-Fi 3 foot cable can easily cost several thousand dollars. The 40GHz cable would never be enough, as some people can still hear frequencies in that range.

    • Re: (Score:3, Informative)

      by John Miles ( 108215 )
      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.

      Depends on how precise you want to be. Conducting and measuring signals in that region of the spectrum with low-loss gear can be tough. Generating and receiving them isn't, necessarily. Not many people realize that some of the very first wireless communications experiments were done in the 60 GHz range, two years before Marconi [nrao.edu].
      • Precision is key for distance, this stuff already doesn't carry that far.
        • Not to mention the regulatory hurdles associated with spark gaps...
          • I'm not that smart, just a little familiar with 802.16. Are you saying that the cost of common electronics would need to go up in order to support this?

      • Re: (Score:2)

        by tengwar ( 600847 )
        Just RTFA'd - that's definitely Real Physics. I'm impressed.

    • Re: (Score:1, Informative)

      by Anonymous Coward
      Terahertz signals can be generated using microwave vacuum tubes (BWOs and Gyrotrons) and transmitted through waveguides, so cables aren't really necessary. Reception might be more of an issue, although that's not something I know much about. There is or at least has been work on terahertz generation at the University of Utah as well.
      • Since TFA is all about work done on metamaterial filters for terahertz radiation done at the University of Utah, I think you can probably assume that there's still work going on there.
    • At the same time won't the cost of lower frequency hardware go down a little bit with a new premium around?

    • Re: (Score:3, Funny)

      by fahrbot-bot ( 874524 )
      ...a 3 foot 40GHz cable can cost hundreds of dollars and a 100GHz connector can cost a thousand dollars or more on its own...

      So, CAT-5e is out?

    • Re:ridiculously expensive (Score:4, Funny)

      by Erandir ( 578490 ) on Friday March 30, 2007 @01:18AM (#18540091)
      I dunno, apparently many companies are already broadcasting in the 450-750 terahertz range, using something called a "light bulb"...

    • Re: (Score:2, Informative)

      by 91degrees ( 207121 )
      A TV remote uses Terahertz frequencies. The components you need depend on what you're using it for.
      • But that varies its frequency upon temperature constant. There's no other way to modulate other than flashes.
        • It's just an extreme example of how you can use extremely high frequencies cheeply. Obviously they're not particularly useful at this price, but it's cheap...

  • 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

      • Re: (Score:1)

        by femto ( 459605 )
        True. My bad. I was forgetting that the filter in front of the mixer isn't so much to eliminate images due to negative frequencies (when using a complex mixer with I and Q components) as to suppress out-of-band signals that might cause overloading, the non-linearity resulting in yet more images. Make the mixer linear enough and you can mix straight down then filter and sample.
    • Hmm, just use wideband CW with Morse Code like the old spark transmitters. That works just fine at any frequency.
    • You are exactly right. All we have to do is look at the very early days of radio, before the invention of the vacuum tube. They used spark gap transmitters that splattered over the entire RF spectrum. If worked just fine when you could count the number of transmitters in range with the thumbs on one hand.
  • I want gamma ray wireless.
  • 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.

    Light, however, has the distinct advantage of being ridiculously cheap to implement... You could cheaply put 1 (or more) transceivers on every side of every device so that it never has to be reoriented to communicate in any specific direction.

    IrDA isn't very fast, but only because it was

    • 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.
        • Simple on/off signaling is a very low grade form of amplitude modulation, and thus places limitations on the kinds and rate of signaling you can do without bleeding into neighboring frequencies.

          Modulation using FM or QAM allows one to pack a lot more data into a much smaller frequency band, but they require the ability to alter the frequency of the EM radiation.
          • I don't believe frequency overlap is much of an issue with short-distance/line-of-sight (wireless) communications to begin with. It would have to be a very dense open space for many devices to be competing for spectrum.
            • What with the trend to add information capabilities to anything and everything, I wouldn't be surprised if, in 30 years, we had wireless networks insanely dense by today's standards.

              Another thing...Digital amplitude modulation works fine for fiber because fiber has a very high signal-to-noise ratio as a medium, leading to high data integrity. Open does not. FM and QAM offer some protection against this. Listen to the radio during a thunderstorm. Switch between AM and FM, and listen to the noise on each.
      • "tune the frequency of visible-spectrum EM emissions"

        Diffraction gratings.

        Glass prisms.

        Dichroic filters and dichroic mirrors.

        Conventional filters based on the optical properties of various chemicals.

    • Re: (Score:2, Flamebait)

      by Max Littlemore ( 1001285 )

      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).

      • Some controversy surrounds the use of terahertz scanners for routine security checks due to the potential capability to produce detailed images of a subject's body through clothing.
        X-ray vision [wikipedia.org]

        That's what I'm waiting for :)

  • 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.

  • Clueless.... (Score:2, Informative)

    by j_square ( 320800 )
    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

    • Re: (Score:2)

      by zCyl ( 14362 )

      * First, is there a problem that needs solving? Are we really that short of spectrum?

      Yes there is, and yes we could always use more. First, terahertz communication has a much higher theoretical bandwidth than gigahertz communication. Second, it's not currently locked down by regulation and existing use. (2.45 GHz isn't used for wireless because it's ideal. In fact, it's a wavelength quite likely to absorbed by biological tissue. It's used because regulations permit that band to be used.)

      * Secon

  • 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

    • 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.

      How does anyone know this to be true? IIRC the only vacuum that is larger than a mile is MegaMaid, and AFAIK we don't have access to her.

  • Some very basics....

    An 100 watt HF transmitter (HF is from 3.0 to 30.0 Mhz) has world wide range. You can send a signal all the way around the world at those frequencies becaue the ionosphere bounds the waves back to Earth and the Earth bounces them back up. These HF waves will travel trough things like walls, trees and people.

    On the other hand a 100 watt light bulb radiates the same power but it's waves go only in a stight line and can be stopped by a piece of cardboard.

    It turns out the wave with frequen
  • Forget about terrahertz carriers. I want communication at the frequency of gravity.

    • Forget about terrahertz carriers. I want communication at the frequency of gravity.

      Let's see ... I guess the biggest source of gravitational waves in the solar system is Mercury (the planet) on its way around the sun. It circulates the sun once in 88 days, which means the frequency is about 0.13 microhertz. I don't think you get much bandwidth at that frequency :-)

      BTW, it's terahertz (from greek teras, monster), not terrahertz (it has nothing to do with the earth).

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