T-Ray Scanner to Protect Airports, Detect Cancer

Scientists at the U.S. Department of Energy’s Argonne National Laboratory, in collaboration with colleagues in Turkey and Japan, have created a compact device that may serve as a basis for developing a portable, battery-operated source of terahertz radiation, known as T-rays. T-rays are a non-ionizing sub millimeter form of radiation, meaning they lack the energy needed to remove an electron from an atom, and therefore do not harmfully effect people exposed to them. Despite the fact that they cannot penetrate metal or water, T-rays have the capability to penetrate a wide variety of non-conducting materials, such as clothing, paper, cardboard, wood, plastic and ceramics. These qualities make terahertz radiation scanning one of the most promising new scanning technologies for security and medical applications.
 The international research team who developed the compact terahertz-radiation superconducting source (Credit: Argonne National Laboratory/ George Joch).
The international research team
who developed the compact
terahertz-radiation
superconducting source
(Credit: Argonne National Laboratory
/ George Joch).

The new T-ray sources created at Argonne use high-temperature superconducting crystals grown in Japan. The crystals are composed of stacks of so-called Josephson junctions, exhibiting a unique electrical property: when an external voltage is applied to the crystal, an alternating current flows back and forth across the junctions at a frequency proportional to the strength of the voltage. This phenomenon is known as the Josephson Effect. The alternating currents produce electromagnetic fields whose frequency is tuned by the applied voltage. It’s enough to apply a voltage of 2 millivolts per junction to the crystals to induce electromagnetic fields of frequencies in the terahertz range.

Since the junctions within the crystals are so small in size (1/10,000 the width of a human hair), the scientists stacked approximately 1,000 of them in order to generate a sufficiently powerful signal. The real challenge was finding a way to make them all radiate in phase, so that they do not cancel each other out. In order to synchronize the signal, Argonne physicist Alexei Koshelev suggested that the stacks of junctions be shaped into resonant cavities. When the width of the cavities was precisely tuned to the frequencies set by the voltage, the natural resonance of the structure synchronized the oscillations and amplified the T-ray output, in a method similar to the production of light in a laser. 

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Schematic of the terahertz-source, which was fabricated on the top of an atomically layered superconducting crystal. The applied current excites the fundamental cavity mode (solid half-wave) on the width w of the mesa, and high-frequency electromagnetic radiation is emitted from the side faces (red waves)
Schematic of the terahertz-source,
which was fabricated on the top of
an atomically layered superconducting crystal
(Credit: Argonne National Laboratory)

The researchers are currently working on improving the extraction efficiency. Getting the signal up to 1 milliwatt will be considered a great success that will enable the creation of a new generation of scanners. In the meantime, T-rays capable of penetrating the human body by almost half a centimeter are already helping doctors to better detect and treat certain types of cancer, such as skin and breast cancer.

In 2006, TFOT covered a new technology for detecting the deadly explosive TATP. More recently, TFOT covered the development of new sensors that can detect structural defects

More information about T-rays and their potential applications can be found on the Argonne National Laboratory website.