Metal foil heralds Terahertz radio

Researchers claim that a sheet of perforated foil could usher in a new age of communications using Terahertz waves.

The holes in a sheet of foil can filter and control terahertz waves, leading to components in signalling equipment that could go much faster than current point-to-point equipment which operates around 5Ghz, according to Ajay Nahata, a professor of electrical and computer engineering at the University of Utah.

TeraHertz signalling, uses frequencies between microwaves and infra-red - from 100 GigaHertz to 10 TeraHertz. Because they oscillate 1,000 times faster, THz signals could in theory - given adequate electronics - carry data 1,000 times faster than current WiFi or WiMax.

Higher frequencies tend to have a shorter range, however, which has been a problem with efforts to commercialise the 60GHz band, but this is not insuperable.

There are "water windows" - frequency bands where the radiation is not absorbed by water vapour in the atmosphere and so could be used to carry information - says Dr Don Arnone, chief executive officer of TeraView, a UK company that spun out of Toshiba to exploit THz radiation. "We looked at using THz for communications ten years ago, but came to the conclusion that the basic technology is not available."

It has long been known that holes in a conductor can selectively affect radiation. The conductor converts the signal into a surface wave, and the holes then set up interference which regenerates an electromagnetic wave. Till now, researchers have assumed that the holes should be a regular, periodic array, but Nahata and his team have proved that the effect works with an irregular array, according to a paper in Nature (requires payment) and an article on Technology Review.

Non-periodic arrays will give researchers more flexibility to use foils to create improved filters for specific frequencies, says Nahata.

Commercial Terahertz companies aren't pouncing on the discovery, however. "Filters could be an important component, but we also need compact sources and detectors, before point-to-point or last mile THz communication is feasible from a technological point of view," said Dr Arnone. "Some other innovation will be be required."

Meanwhile, TeraView is happy to exploit THz in imaging applications, where Dr Arnone says there is more immediate demand, albeit in very specialised areas. TeraView is developing imaging systems for pharmaceutical companies, that can analyse the distribution of chemicals within a slow-release tablet, to ensure that a drug is dispensed properly. The technology also has the potential to locate non-metallic weapons carried by airline passengers, or to locate and identify concealed explosives that would be invisible to X-rays.