Casimir force, antennas, and salt water [Physics]

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From: Sam on 15 Jun 2010 15:46

Casimir force, antennas, and salt water
By Physics Today on May 20, 2010 10:26 AM

http://blogs.physicstoday.org/update/2010/05/casimir-force-antennas-and-sal..html?type=PTFAVE

As famously predicted by Hendrik Casimir in 1948, parallel conductors
in a vacuum will attract each other because the conductors impose
boundary conditions that affect the vacuum energy of the
electromagnetic field (see the article by Steve Lamoreaux in Physics
Today, February 2007, page 40). In general, the Casimir force depends
on the shape of the conductors and its value is notoriously difficult
to calculate, but research groups worldwide have been developing
increasingly applicable computational techniques. Now a team at MIT
has shown how tabletop measurements might provide the key information
needed for the general calculation. The Casimir force may be expressed
as an integral over frequency (ù) of correlation functions that
involve electric and magnetic fields. In principle, those frequency-
dependent correlations can be obtained in a suitably scaled tabletop
experiment from measurements of how an antenna at one point responds
to a current generated at a distant point. In practice, such
measurements won't work because the integrand oscillates wildly with
ù. The integrand becomes well behaved--it decays and doesn't oscillate--
if the integration is performed in the complex plane, but real
antennas respond to real frequencies. The key observation made by the
MIT team is that their mathematical expressions always involve ù in
the combination åù², where å is the permittivity. Thus, the
researchers predict, a force integral with real vacuum permittivity
and complex contour can be calculated from a tractable number of
antenna measurements made at real ù in a medium of complex permittivity
--for example, salt water. (A. W. Rodriguez et al., Proc. Natl. Acad.
Sci. USA, in press, doi:10.1073/pnas.1003894107.)--Steven K. Blau

From: Uncle Al on 15 Jun 2010 17:59

Sam wrote:
>
> Casimir force, antennas, and salt water
> By Physics Today on May 20, 2010 10:26 AM
>
> http://blogs.physicstoday.org/update/2010/05/casimir-force-antennas-and-sal.html?type=PTFAVE
>
> As famously predicted by Hendrik Casimir in 1948, parallel conductors
> in a vacuum will attract each other because the conductors impose
> boundary conditions that affect the vacuum energy of the
> electromagnetic field (see the article by Steve Lamoreaux in Physics
> Today, February 2007, page 40). In general, the Casimir force depends
> on the shape of the conductors and its value is notoriously difficult
> to calculate, but research groups worldwide have been developing
> increasingly applicable computational techniques. Now a team at MIT
> has shown how tabletop measurements might provide the key information
> needed for the general calculation. The Casimir force may be expressed
> as an integral over frequency (�) of correlation functions that
> involve electric and magnetic fields. In principle, those frequency-
> dependent correlations can be obtained in a suitably scaled tabletop
> experiment from measurements of how an antenna at one point responds
> to a current generated at a distant point. In practice, such
> measurements won't work because the integrand oscillates wildly with
> �. The integrand becomes well behaved--it decays and doesn't oscillate--
> if the integration is performed in the complex plane, but real
> antennas respond to real frequencies.

Meta-material antennas?

> The key observation made by the
> MIT team is that their mathematical expressions always involve � in
> the combination ��, where � is the permittivity. Thus, the
> researchers predict, a force integral with real vacuum permittivity
> and complex contour can be calculated from a tractable number of
> antenna measurements made at real � in a medium of complex permittivity
> --for example, salt water. (A. W. Rodriguez et al., Proc. Natl. Acad.
> Sci. USA, in press, doi:10.1073/pnas.1003894107.)--Steven K. Blau

--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz4.htm

From: Uncle Al on 15 Jun 2010 18:03

From: Uncle Al on 15 Jun 2010 18:19

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