The lack of comprehension of fundamental physics on this newsgroup is
astounding, so it's no surprise that a less-known fact has been missed:

A superconductor has zero resistance only at DC. The resistance at RF
depends, among other things, the frequency and the material's
temperature. Because the resistivity of copper drops dramatically at
cryogenic temperatures, it can be difficult to make a superconductor
with resistance as low as copper at the same temperature.

Very small superconducting antennas have been demonstrated, but they
still have a very large near field which sustains loss by coupling to
nearby objects, and a large reactance which necessitates potentially
lossy matching networks.

Roy Lewallen, W7EL

On Mon, 30 Aug 2010 14:22:11 -0700, Roy Lewallen
wrote:

The lack of comprehension of fundamental physics on this newsgroup is
astounding, so it's no surprise that a less-known fact has been missed:

A superconductor has zero resistance only at DC. The resistance at RF
depends, among other things, the frequency and the material's
temperature. Because the resistivity of copper drops dramatically at
cryogenic temperatures, it can be difficult to make a superconductor
with resistance as low as copper at the same temperature.

Zero resistance is not strictly a function of direct current. It is
simply the most often reported experimental characteristic in the
popular press. Impracticality of the additional RF characteristic
(which I presume in this forum to be confined to UHF and below) is
unwarranted in materials research at this point, but EHF/IR and above
results are frequently reported in association with other research -
plasmonics and phonon/electron interaction.

The resistivity of copper falls with temperature, true, but we
encounter diminishing returns as we approach absolute zero: the drop
fails to follow through to the expected final zero resistance. This
was an experimental dissappointment decades ago. Silver and gold are
rarely chosen for their electrical properties in the nano-dimension -
chilled or otherwise (although gold is suitable, gold is far more
useful in association with thiols). In fact, what are typically poor
conductors exhibit less low temperature resistance than copper (cold
or warm). I won't go into that list, it is enough to consider that
such "wires" would be confined to thin film depositions on a flexible
tape substrate - pretty exotic.

Going further, it isn't even necessary to drive temperatures to the
basement for improved conduction. Carbon nanotubes are exemplars of
high conductivity (several orders of magnitude better than what we
consider good metals) at room temperature where a carbon macrotube
would be called a resistor. Conductivity and superconductivity
research has long ago left the realm of temperature and has entered
the realm of crystal alignment.

However, even this academic. Carbon Nanotube construction at a scale
to compete with standard copper wire is off by a scale of a million to
billions (of dollars, much less practicability).

73's
Richard Clark, KB7QHC

Richard Clark wrote:

Going further, it isn't even necessary to drive temperatures to the
basement for improved conduction. Carbon nanotubes are exemplars of
high conductivity (several orders of magnitude better than what we
consider good metals) at room temperature where a carbon macrotube
would be called a resistor. Conductivity and superconductivity
research has long ago left the realm of temperature and has entered
the realm of crystal alignment.

However, even this academic. Carbon Nanotube construction at a scale
to compete with standard copper wire is off by a scale of a million to
billions (of dollars, much less practicability).

This may have changed also, I'm no expert in superconductors (though I
do play one on TV) Don't the high temperature superconductors have
issues with current capacity, and does this translate into problems with
impedance?

- 73 de Mike N3LI -

On Wed, 01 Sep 2010 09:54:25 -0400, Michael Coslo
wrote:

Richard Clark wrote:

Going further, it isn't even necessary to drive temperatures to the
basement for improved conduction. Carbon nanotubes are exemplars of
high conductivity (several orders of magnitude better than what we
consider good metals) at room temperature where a carbon macrotube
would be called a resistor. Conductivity and superconductivity
research has long ago left the realm of temperature and has entered
the realm of crystal alignment.

However, even this academic. Carbon Nanotube construction at a scale
to compete with standard copper wire is off by a scale of a million to
billions (of dollars, much less practicability).

This may have changed also, I'm no expert in superconductors (though I
do play one on TV) Don't the high temperature superconductors have
issues with current capacity, and does this translate into problems with
impedance?

Hi Mike,

High temperature is a relative thing (being it is measured in the 10s
of Kelvins for high temperature superconductivity).

However, Impedance? In the convetional application here in this
forum, it is a remote consideration for research. Afterall, nothing
has changed about the usual characterisitics of conduction,
inductance, or capacitance except for conduction's magnitude/density.

Aside from the conventional discussion here, researchers do tons of
work in the realm of superconductivity that employs radiation. That
body of research is called Plasmonics and Excitonics. Phononics
doesn't strictly apply because it is, by definition, high temperature.

Most of the research into subresonant structures is done in the
nanoscale. What is discussed here as possibilities in that same
regard is sheer nonsense. However, there have been glimmers of
nanoscale research reaching out into the macro dimension.

I've posted such items from Boeing's skunk works on negative
refractive index material research. It is something that could be
modeled in NEC - but only at a vastly expansive scale with hours of
computer time to run.

I am going to broach a taboo and see if an attachment of a split-ring
resonator would be supported.

73's
Richard Clark, KB7QHC