http://www.bbc.co.uk/news/science-environment-18072618

16 May 2012 Last updated at 03:00 ET

Milestone for wi-fi with 'T-rays'

RTD terahertz wi-fi deviceThe device will be improved first by adding an
antenna to increase its efficiency

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Researchers in Japan have smashed the record for wireless data transmission
in the terahertz band, an uncharted part of the electro-magnetic spectrum.

The data rate is 20 times higher than the best commonly used wi-fi standard.

As consumers become ever more hungry for high data rates, standard
lower-frequency bands have become crowded.

The research,  <http://dx.doi.org/10.1049/el.2012.0849> published in
Electronics Letters, adds to the idea that this "T-ray" band could offer
huge swathes of bandwidth for data transmission.

The band lies between the microwave and far-infrared regions of the
spectrum, and is currently completely unregulated by telecommunications
agencies.

Despite the name, the band informally makes use of frequencies from about
300 gigahertz (300GHz or about 60 times higher than the current highest
wi-fi standard) to about 3THz, 10 times higher again.

It is used principally for imaging in research contexts, as terahertz waves
penetrate many materials as effectively as X-rays but deposit far less
energy and therefore cause less damage.

Until recently, the technology required both to generate and detect these
"T-rays" has been too bulky, costly or power-hungry to offer a plausible
alternative to existing devices tucked within smartphones or wi-fi routers.

That looks set to change; in November electronic component firm ROHM
<http://www.dailytech.com/ROHM+Demos+15Gbps+Terahertz+Wireless+Chip+Pl...
Gbps+Version/article23346.htm> demonstrated a 1.5Gb/s (1.5 billion bits per
second) transfer rate at a frequency of 300GHz.

Terahertz wi-fi would probably only work within ranges of about 10m, but
could in theory support data rates up to 100Gb/s - close to 15 times higher
than the next-generation 802.11ac wi-fi standard that is under development.

The new work, by researchers from the Tokyo Institute of Technology,
demonstrated 3Gb/s transmission at 542GHz.

At the heart of the team's 1mm-square device is what is known as a resonant
tunnelling diode, or RTD.

Tunnelling diodes have the unusual characteristic that the voltage across
them can sometimes go down as current is increased.

RTDs are designed such that this process makes the diode "resonate", which
in the current work's design means it sprays out waves in the terahertz
band.

The team is now working to improve their proof-of-principle device and
extend its range deeper into the terahertz regime, as well as increasing its
power output.

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