* Astronomy

A new antenna made of plasma (a gas heated to the point that the electrons are ripped free of atoms and molecules) works just like conventional metal antennas, except that it vanishes when you turn it off.
That's important on the battlefield and in other applications where antennas need to be kept out of sight. In addition, unlike metal antennas, the electrical characteristics of a plasma antenna can be rapidly adjusted to counteract signal jamming attempts.

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An antenna, developed by Gerard Borg and his colleagues at the Australian National University (ANU) in Canberra, replaces the metal in a standard aerial with a plasma confined inside a gadget similar to a large fluorescent strip light.
Borg revealed the technology at a mid-November plasma physics meeting of the American Physical Society in Seattle. The plasma is formed by a radio wave which is shot into a shock-resistant dielectric tube containing a noble gas by a single metal electrode at the base of the antenna. This wave moves up the antenna, stripping electrons from the gas molecules as it goes, ionising them to form a plasma. The free electrons allow the plasma to act like a metal, which has many free electrons drifting inside it.
And just like a metal antenna, those electrons can be forced to oscillate to create the electromagnetic waves that transmit a radio signal. When the antenna is in receive mode, incoming radio waves cause the electrons to oscillate in the same fashion.
The most striking aspect is that when the electrode at the base of the plasma antenna is turned off, the gas inside instantly becomes neutral, so the antenna is as invisible to radar as air.

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