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Advanced Imaging Magazine

Updated: July 8th, 2008 05:26 PM CDT

Terahertz Waves

Terahertz Imaging Faces Some Challenges, but New Developments Offer Great Promise
Sample of Metamaterial
Los Almos
The sample of metamaterial fabricated at Los Alamos used in the demonstration of active THz metamaterial devices.
Terahertz Metamaterial
Los Almos
The detailed structure of the terahertz metamaterial developed at Los Almos.
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By Keith Reid

If it's in the spectrum somebody will find a use for it. Such is the case with terahertz waves, that occupy the space between microwaves and the infrared optical band (from 30 microns to 1 mm). These "T-rays" provide some exciting capabilities, but there are currently some notable challenges.

T-rays can pass though thin layers of non-metallic substances like clothing, wood, plastic and ceramics and can penetrate up to several centimeters of flesh at some frequencies while reflecting back. Because they are non-ionizing, there is no real risk to living subjects like you find with X-rays. They provide images comparable to backscatter X-rays, and with known transmission/reflection spectra a variety of materials can be easily identified including many common explosives and drugs.

"There are other techniques like X-rays and millimeter waves where you can image through clothing, but what terahertz allows you to do is when you see something suspect you can then go to that pixel in the image and you can pull out the spectral fingerprints that terahertz spectrum and you can actually use that to identify what the object is," said Dr. Don Arnone, CEO of Teraview (U.K.), a company that has taken an early lead in providing fieldable terahertz technology. "For example, a piece of polyethylene and the leather in a wallet have very different spectral signatures compared to Cemtex or TNT, etc. so it's a combination of imaging through many common objects allied with the ability that once you actually detect an object in an image you can in some cases identify what it is by comparing its spectrum to a library of spectra."

Typical applications for this technology include security screening, semiconductor inspection, 2D and 3D imaging, food inspection, pharmaceutical inspection, medical diagnosis in areas like skin cancer and various dental applications.

However, as noted, there are limitations. T-rays cannot penetrate metal, and are heavily absorbed by water. While they can penetrate fog, clouds and soil the moisture present in all three currently limit the effective range, as is generally the case in the atmosphere. Also, there exists a shortage of engineered, fieldable hardware that will allow terahertz imaging to occur at practical speeds relative to many application goals.

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