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Carbon Nanotube antennas

Carbon Nanotube antennas - Physics Forum

Carbon Nanotube antennas - Physics Forum. Discuss and ask physics questions, kinematics and other physics problems.


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Old 09-26-2004, 01:25 PM
W1xyz
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Default Carbon Nanotube antennas



I'm posting this because a few people have emailed pointing me to a discussion
in sci.physics about making nano-antennas for lightwave detection. I don't see
it but I got a fragment in the email, so here goes.

First, photodiodes are considered to be distinct from Hertz antennas.

On prior art: Marks proposed using tuned elements in various configurations but
didn't talk about how to make them. So-called uncooled IR detectors have been
proposed and some have been made of pillars of materials that are scaled to
light wavelngths. Lots of people suggested and wrote about using carbon 60 or
nanotubes as electrical or optical devices. A quick search in uspto.gov will
locate a few of these.

I proposed a way to make them to specific sizes needed for operation at short
wavelengths, such as light wavelengths.

My personally funded research work in the mid 90's was based directly upon
conventional antenna design, and specifically on the monopole or dipole version
as "the basic building block" for practical nano-antennas. I found we could
place and tune wavelength-specific elements on substrates such as silicon and
get them to be "real" antennas. I proposed experiments to uncover the
"velocity factor" - a term borrowed from transmission line engineering after
realizing that the nano-antennas were going to be physically shorter than the
free space wavelength, just as we find with our 80M dipole antennas strung
between the trees. But, the shortening effect is more severe at light
wavelengths - stated simplistically, the inertia of electrons affects these
structures to a greater degree than, say, on a 2M Yagi. (that's about 146 Mhz
for the non-hams)

Using groups of nano-antennas, directivity, gain, steering, phased array,
narrow and broadband operation could be achieved. Additionally, we can attach
the nano-antennas to junctions. The junctions and antennas can be accessed to
switch, modulate, further tune, detect, demodulate, upconvert, downconvert -
all useful.

The nano-antennas are a bit small and hard to wire up, so one handy way to use
them is to look at reradiation - that's what the BC group appears to be doing.
Carbon nanotube antennas can be metallic (linear) or semiconducting
(nonlinear). The addition of a rectifyng junction at an end can render the
structure nonlinear, which makes it a nice reradiating frequency doubler,
tripler, mixer etc. To do this you beam light in and look at what gets
reradiated. The reradiation is polarized, has frequency components that are
related to the tuned operation of the little antennas, and can also have other
information superimposed upon it by modulating the substrate. The antennas are
close together so some band gap effects (cavity tuning effects to the hams) are
also present.

The size of these structures is very small, about 100nm or so, depending upon
wavelength. The junctions are also very small and are fast. That allows us to
switch lightwaves, make logical devices, or mass array memory. There is also
an attraction of oppositely charged nanotubes and a repulsion of those
nanotubes when like-charged. They move and can be used as a sort of
electrostatic switch.

Other interesting stuff can be done at the nano-scale using tuned structures or
arrays of lightwave antennas. It all started with Maxwell, Fourier, Hertz and
Armstrong, and ham radio, of course.

If you want, check out [Only registered users see links. ]

That will bring you to some other work and patents on this technology and
related fun and probably useful electromagnetic devices.

Cheers,

Bob Crowley
w1xyz
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