Sunday, December 19, 2010

Wireless at the speed of plasma

BEFORE you leave for work in the morning, your smartphone downloads the latest episode of a television series. Your drive to work is easy in spite of fog, thanks to in-car radar and the intelligent transport software that automatically guides you around traffic jams, allowing you to arrive in time for a presentation in which high-definition video is streamed flawlessly to your tablet computer in real time.

This vision of the future may not be far off, thanks to a new type of antenna that makes use of plasma consisting of only electrons. It could revolutionise high-speed wireless communications, miniature radar and even energy weapons.

Existing directional antennas that transmit high-frequency radio waves require expensive materials or precise manufacturing. But the new antenna, called Plasma Silicon Antenna, or PSiAN, relies on existing low-cost manufacturing techniques developed for silicon chips. It has been developed by Plasma Antennas of Winchester, UK.

PSiAN consists of thousands of diodes on a silicon chip. When activated, each diode generates a cloud of electrons - the plasma - about 0.1 millimetres across. At a high enough electron density, each cloud reflects high-frequency radio waves like a mirror. By selectively activating diodes, the shape of the reflecting area can be changed to focus and steer a beam of radio waves. This "beam-forming" capability makes the antennas crucial to ultrafast wireless applications, because they can focus a stream of high-frequency radio waves that would quickly dissipate using normal antennas.

"Beam-forming antennas are the key for enabling next-generation, high-data-rate indoor wireless applications," says Anmol Sheth, at Intel Labs in Seattle. "Without beam-forming antennas it would be difficult to scale to the levels of density of wireless devices we expect to have in future homes."

There are two types of plasma antenna: semiconductor or solid-state antennas, such as PSiAN, and gas antennas. Both could fit the bill, but solid-state antennas are favoured as they are more compact and have no moving parts.

That makes them attractive for use in a new generation of ultrafast Wi-Fi, known as Wi-Gig. Existing Wi-Fi tops out at 54 megabits of data per second, whereas the Wi-Gig standard is expected to go up to between 1 and 7 gigabits per second - fast enough to download a television programme in seconds. Wi-Gig requires higher radio wave frequencies, though: 60 gigahertz rather than the 2.4 GHz used by Wi-Fi. Signals at these frequencies disperse rapidly unless they are tightly focused, which is where PSiAN comes in.

Ian Russell, business development director at Plasma Antennas, says that PSiAN is small enough to fit inside a cellphone. "Higher frequencies mean shorter wavelengths and hence smaller antennas," he says. "The antenna actually becomes cheaper at the smaller scales because you need less silicon."

The antennas shouldn't raise any health issues, as they are covered by existing safety standards. The narrow beam means there is less "overspill" of radiation than with existing omnidirectional antennas.

As well as speeding up Wi-Fi, plasma antennas could also allow cars to come with low-cost miniature radar systems to help drivers avoid collisions. Their millimetre wavelengths could be used to "see" through fog or rain, and another set of antennas could listen for real-time updates on traffic and road conditions.
The US military is also interested in solid-state plasma antennas, for use in a more advanced version of their so-called "pain beam", a weapon called the Active Denial System. The ADS heats a person's skin painfully with a beam of 64 GHz radio waves. But the current design involves a 2-metre-wide, mechanically steered antenna mounted on a large truck. Switching to a small, lightweight plasma antenna would allow multiple narrow beams to selectively target several individuals at once.

Ted Anderson of Haleakala R&D, based in Brookfield, Massachusetts, has been involved in the development of gas plasma antennas for many years. He points out that although the solid-state version is compact, it is limited to high frequencies, making certain applications tricky. For instance, indoor Wi-Gig routers operating at 60 GHz wouldn't be able to penetrate walls. The signal would instead have to be reflected off surfaces to reach every room in a house.

"Semiconductor plasma antennas will work at only high frequencies, between 1 GHz and 100 GHz," says Anderson. "Theoretically, we see no upper or lower bound to ionised gas antennas in the radio frequency spectrum."

Russell says that PSiAN could be commercially available within two years. At present, getting movies and high-quality images on and off our smartphones almost certainly means hooking them into a computer. But as the demand for such content increases, the only way to break the wire is going to be an ultrafast wireless connection. When it comes, it may very well be in the form of plasma.

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