Move over X-Rays, make way for harmless T-Rays

  • Argonne (IL) - Scientists may have found the solution to long airport screening lines:  T-Rays.  T-Rays are Terahertz electromagnetic (EM) emissions which harmlessly scan for the same basic things X-Rays are used for today.  However, since T-Rays are much of a much lower energy, there are no harmful effects, according to researchers.

    Frequencies around 1 THz have been difficult to achieve without a host of expensive components.  This has prohibited their adoption in wide-use applications like airport screening stations.  A research team at the U.S. Department of Energy's Argonne National Laboratory has now changed that.  They've constructed a small, even battery powered device, which generates THz frequencies easily and accurately.

    T-Rays have similar, but distinctly different, properties to X-Rays.  They cannot penetrate through metal or water, but they can penetrate through common materials like leather, fabric, cardboard, paper and even up to half a centimeter into human flesh, allowing for some interesting medical applications.  Each of these materials or substances give off a specific signal which can be identified by the scanning device.  Whenever something is detected which is questionable, then a normal scan through the X-Ray machine, or a pat-down, would be desirable.  However, for the majority of users in an airport screening station, for example, the intrusion would be far less than it is today.

    How it works
    T-Rays propagate like radio waves or visible light.  People who are exposed to THz radiation will suffer no ill effects, according to Argonne National Labs, because their emission strength is insufficient to ionize atoms.  In X-Rays, it's this ionizing phenomena, which knocks electrons loose, which causes radiation sickness.

    Scientists at Argonne National Labs were able create the new form of T-Rays using high-temperature superconducting crystals grown at the University of Tsukuba (Japan).  The crystals comprise stacks of what are called Josephson junctions.  These exhibit unique electrical properties, ultimately creating the Josephson effect.  When voltage is applied, an alternating current begins to flow back and forth across the junctions at a frequency proportional to the strength of the voltage.  The alternating currents produce EM fields.  When they tune the voltage to around 2 millivolts per junction, they emit frequencies in the THz range.

    Each junction is about 1/10,000th the thickness of a human hair.  It takes layer upon layer of these tiny junctions to produce a signal strong enough to be even remotely useful.  And, while all of the junctions are alternating at the same frequency, during the initial experiments they were not in phase.  The researchers had to figure out a way to get them all in sync, otherwise they'd all be canceling each other out, making the signal useless.

    They turned to a natural side-effect of a resonance cup.  By constructing cavities of a particular shape formed specifically for the frequency targets, when voltage was applied they all emit signals which are in phase.  However, the researchers have since encountered another significant hurdle, one which remains even now.  The energy being generated in the resonance cavities cannot be completely extracted.  Much of it is lost, resulting in a low yield of usable signal strength compared to theoretical signal generation.

    Current data shows usable frequencies between 0.4 and 0.85 THz, and even then at only a very low power of 0.5 microwatts.  The researchers are hoping to get it up to 1 milliwatt (2,000x more powerful).  If they can do that, they claim that a wide-ranging host of low-cost, easily adaptable applications will be possible.  Theoretically, this may be possible with today's design, provided they can extract more of the signal generated in the resonance cavities.

    Lutfi Ozyuzer, Alexei Koshelev, Cihan Kurter, Nachappa (sami) Gopalsami, Qing'An Li, Ken Gray, Wai-Kwong Kwok and Ulrich Welp of Argonne; Masashi Tachiki from the University of Tokyo; Kazuo Kadowaki, Takashi Yamamoto, Hidetoshi Minami and Hayato Yamaguchi from the University of Tsukuba; and Takashi Tachiki from the National Defense Academy of Japan, all worked together to develop this technology.  Funding was provided by DOE's Office of Basic Energy Sciences and by Argonne's Laboratory Directed Research and Development.  The group released a scientific paper, "Emission of Coherent THz Radiation from Superconductors," in the November 23 issue of Science.

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