Far infrared for wireless and security

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study has shown how far-infrared light, the last unexploited part of the electromagnetic spectrum, could be harnessed to build much faster wireless communications and to detect concealed explosives and biological weapons.

’We found a way to manipulate a form of infrared radiation that is not now used for communications so that, in the future, it may be possible to use it for high-speed, short-range communication between computers and other devices,’ said Ajay Nahata, an associate professor of electrical and computer engineering.

The study also showed the feasibility of building devices that emit and detect specific frequencies of far-infrared light, also known as terahertz radiation, to spot chemical or biological warfare agents such as anthrax bacteria. They could also make images of packages or people to find concealed weapons and plastic explosives.

The Utah researchers shined far-infrared radiation through holes punched in a thin steel foil or film, and found almost all of the radiation passed through the film if the holes were arranged in semi-regular patterns known as ‘quasicrystals’ or ‘quasicrystal approximates.’

Until now, such efficient transmission of far-infrared light was achieved only when crystal patterns were used, but unwanted frequencies also were transmitted. In the new study, the researchers could select the wavelength of far-infrared light transmitted through the holes and, by tilting the films, they could switch the transmission on and off.

That means high-frequency terahertz signals can be switched on and off to carry digital data, and that it someday may be possible to build superfast switches to carry terahertz data at terahertz speeds.

Near-infrared radiation and some visible light now are used for fibre optic phone and data lines. But terahertz or far-infrared radiation – on the spectrum between microwaves and mid-infrared radiation – is not currently used for communication.

’Terahertz is a new region of the spectrum for communications because the rest of the spectrum is crowded with communication and broadcasting signals,' said Nahata.

Nahata said terahertz technology has two main uses for homeland security. ‘Vibrational spectroscopy’ uses emitters and detectors of terahertz radiation to detect materials, such as anthrax or other biological or chemical weapons, that resonate at a terahertz frequency when exposed to far-infrared light.

Early terahertz devices emit numerous frequencies. The new study shows perforated films can serve as filters so future terahertz devices can use desired frequencies to zero in on specific chemical or biological weapons or concealed guns and explosives.

Another method uses a terahertz emitter and a camera. ‘Since plastics and clothing are transparent to terahertz wavelengths, metal reflects terahertz, and certain chemicals – such as plastic explosives – strongly absorb terahertz radiation at specific frequencies, this approach is being pursued for package inspection and whole-body imaging to look for concealed weapons or explosives,’ Nahata said.