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Using the Terahertz Spectrum for Wireless Communication
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."
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.
The determined Real Programmer can write Fortran programs in any language.
10 years? Anyone?
"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 is perceived to be crucial in forming the transmission resonances. Here we demonstrate experimentally that, in contrast to the conventional view, sharp transmission resonances can be obtained from aperiodic aperture arrays. Terahertz transmission resonances are observed from several arrays in metallic films that exhibit unusual local n-fold rotational symmetries, where n = 10, 12, 18, 40 and 120. This is accomplished by using quasicrystals with long-range order, as well as a new type of 'quasicrystal approximates' in which the long-range order is somewhat relaxed. We find that strong transmission resonances also form in these aperiodic structures, at frequencies that closely match the discrete Fourier transform vectors in the aperture array structure factor. The shape of these resonances arises from Fano interference4 of the discrete resonances and the non-resonant transmission band continuum related to the individual holes5. Our approach expands potential design parameters for aperture arrays that are aperiodic but contain discrete Fourier transform vectors, and opens new avenues for optoelectronic devices."
Alright, how many here can translate that into english?
Why use Terahertz when theres Petahertz?
We normally call those frequencies microwave. Microwave transmission is nothing new?
We at slashdot are scientists, specialists and kernel hackers. Your FUD will be found out.
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.
The scientific community needs to come up with a name for this part of the band between radio and infrared. Some sort of name that symbolizes that the wavelength is small. Perhaps we can all agree that these wavelengths, shorter than radio waves, could be called "microwaves".
What do you guys think?
Integrated circuits are cheap. We aren't talking about putting watts of energy into the ether here.
Sure you have lots of bandwidth, but frequencies that high must have totally crap penetration. if it's truly line of sight it's totally useless indoors, and probably nearly as bad out.
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:
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.
I want gamma ray wireless.
What?
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 only designed as a replacement for RS232 wires, not networking. Speeds could be pushed higher than anything in the UHF spectrum, as evidenced by fiber optics.
Slashdot gets worse every day... Pipedot: News for nerds, without the corporate slant
Hmm, just use wideband CW with Morse Code like the old spark transmitters. That works just fine at any frequency.
Excuse me, but please get off my Pennisetum Clandestinum, eh!
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?
Do it yourself, because no one else will do it yourself. [beta blockade 10-17 Feb]
Nonetheless, a question: does anyone know offhand how much power these devices require?
Something in the jigawatt range, mayhaps?
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 books and tons of publications in IEEE transactions, etc. in this area.
I did etched FSS filters for 375 GHz around 1982, and the concept was already pubslished in books by then.
Old stuff. Too many scientists, too much money, too little brain.
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 thought we conquered radio waves in the 50s and everything since then has just been 'computing speed'. I think this is pretty interesting.
It will be cool to see what new forms of cancer and mental disease equipment broadcasting in this spectrum doesn't cause.
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WRONG frequency!
Ace
Yea great job on the informative side of that post there guy...
o mmunication
For those that don't know about it (I didn't know about it until a couple of weeks ago:
"Free Space Optics (FSO) is a line-of-sight wireless technology, which enables secure, high speed bandwidth connections using optical laser communication"
http://en.wikipedia.org/wiki/Free-space_optical_c
Here's to the crazy ones
I was under the impression that the teraHertz bands include the visible light portion of the electromagnetic spectrum. Are we going to start actually seeing the network traffic as coherent light? (Read: Lasers!)
There are active experiments in radio communications on the visible light bands. Last time I checked, the distance record was pushing 200 km.
... 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
lots of other THz articles if you chop back the URL to PubLib/
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 non-problem. Again.
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 your friend can accurately clock.
You may want to consider a "return to zero" phase or a "return to zero inverted" phase (NRZ/NRZI) to help you clock the signal for repeated bits at less accurate clock rates.
The problem with quotes on the internet, is that nobody bothers to check their veracity. -- Abraham Lincoln
So now your wireless network can take voyeur porn for you... http://en.wikipedia.org/wiki/Terahertz_imaging#The oretical_and_technological_uses_under_development/
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.
"The other thing about terahertz waves is that they behave quasi-optically, being focused by teflon lenses and blocked by cardboard"
n cy_planning/spectrum_plan/arsp-wc.pdf
It is blocked by card board people! why would you want to use it as a LAN? ok maybe if you wanted comms between two pc's sitting right next to each other or some thing but if you are thinking of using it like you do 2.4GHz think again. cubical walls would block the signal! it would be great speed and licensing wise if it where practical but it just isn't.
also if any one wants a PDF of the RF Spectrum here is the link for the Australian Communications Authority (ACMA) one http://www.acma.gov.au/acmainterwr/radcomm/freque
cheers
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 frequency between HF and light have properties between HF and light. For example VHF and UHF (used for over the air TV, fire and police radios and so on) these waves travel in a mostly straight line but can be bend somewhat, some times.
Once you get to microwaves they act even more like light. They need a line of sight and are easy to block.
These terraherz waves would act even more like light then microwaves. They are almost infrared and so act almost like infrared So even if you could build it this would be useless for many applications. Possibly it would open up NEW applications such as extreme high speed communications between objects that are almost touching each other but not wifi that covers an area or goes through solid objects.
Forget about terrahertz carriers. I want communication at the frequency of gravity.