“So far, it’s safe,” says Gian Piero Gallerano, coordinator of Terahertz Bridge. Preliminary results have been encouraging researchers have seen no evidence of irreversible, x-ray-like tissue damage from the doses of t-rays that would be used for bodily imaging. The European Union is sponsoring a program, called Terahertz Bridge, to study just that.
A terahertz camera built by QinetiQ of Farnborough, England, takes eerily invasive pictures of people through their clothes.īut the interaction of t-rays with proteins raises the question of how safe human exposure is. Another is a t-ray chemical sensor, which would take advantage of the fact that other large molecules, such as polymers, also respond to terahertz waves in characteristic ways. One potential application is automated identification of biological warfare agents, such as anthrax. “Life is a terahertz process,” says Chamberlain. T-rays could also identify unknown biological materials, since biomolecules naturally vibrate at terahertz frequencies, and each has a distinct terahertz “fingerprint.” In other words, specific proteins absorb certain characteristic t-ray frequencies, which change their molecular arrangement, or conformation sensors can then monitor this absorption to indicate the identity of the protein.
HUMAN EXPOSURE X RAY 1890S SKIN
In one ambitious effort, TeraView, a Cambridge, England-based startup, has used terahertz imaging to detect skin cancers that elude other imaging technologies-in particular, tumors that form invisibly beneath the surface of the skin. The most near-term application for terahertz technology is in medical imaging. Last year, Qin Hu, an MIT electrical engineer, demonstrated a quantum cascade laser that produces a continuous terahertz beam at a well-defined frequency.Ī cavity shows up clearly as a pink region in a tooth’s terahertz image (right).(Image courtesy of Teraview) Moving the technology into the terahertz range requires exquisitely precise control over the materials. Another approach is something called the “quantum cascade laser,” a neat bit of semiconductor engineering used to produce infrared light. The company is targeting its instrument primarily at observing interactions involving biomolecules for applications such as drug discovery. Changing the energy of the electron beam also changes the terahertz frequency generated, says Vermont Photonics cofounder Michael Mross.
One such system, made by Brattleboro, VT-based Vermont Photonics, works by sending an electron beam across the microscopically rippled surface of a conductor, such as aluminum the beam causes electrons in the conductor to move up and down the undulations, a motion that shakes loose t-rays. In the past year, however, several research projects have made substantial progress in developing devices that produce t-rays within a narrow frequency band-a requirement for precise chemical sensing and medical imaging. The terahertz sources now on the market tend to emit many frequencies at once, limiting their utility. “You’re never sure whether to use electronics-based or optics-based” technology, says Martyn Chamberlain of the University of Leeds in England, a leading terahertz researcher. They’re higher than microwaves but lower than infrared light. Terahertz frequencies are tough to produce and detect.
And since t-rays penetrate paper and clothing, a terahertz camera could detect hidden weapons. Potential applications range from detecting tumors to finding plastic explosives. Thanks to this power, “terahertz imaging is getting hotter and hotter,” says Xi-Cheng Zhang, a terahertz pioneer at Rensselaer Polytechnic Institute. And different compounds respond to terahertz radiation differently, meaning a terahertz-based imaging system can discern a hidden object’s chemical composition. But t-rays are believed to be less harmful than x-rays. These so-called t-rays can, like x-rays, see through most materials. Just as x-ray technology came along in the 1890s-allowing doctors to peer beneath flesh to see bones and organs-another promising imaging technology is now emerging from an underused chunk of the electromagnetic spectrum: the terahertz frequencies.
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