Terahertz Imaging

Recently, electromagnetic radiation in the terahertz frequency range, best known as Terahertz radiation (hereafter abbreviated as THz), has emerged as one of the most promising measurement techniques for a variety of applications in science and engineering.  THz, residing at a relatively unexplored region between the microwave and infrared, roughly 0.1-10THz, is one of the last frontiers in the electromagnetic spectrum.  Unlike X-ray, THz causes no known harm to the human body and the materials being examined.  THz can penetrate many common gases, non-polar liquids, and non-metallic solids including air, plastics, gasoline, paper, plant material, clothing, fatty tissue, and composites.  Because they lie in a frequency region in which molecular resonances dominate, the absorption spectra of THz exhibit distinct signatures for substances such as water vapor, polar plastics, certain gases, DNA, crystalline solids, biofuel, and explosives.  These advantages make THz a particularly attractive characterization tool in the areas of automotive, aviation, food, energy, materials, pharmaceuticals, medical diagnosis, forensics, defense, and homeland security.  In fact, THz’s ability to penetrate thick foam-like materials has made it the de facto technique to inspect the foam insulation structures of NASA’s space shuttle fleet, the application that brought this technology to the interest of CNDE.

For the past five years, under the support of NASA, the Air Force, and the Army, CNDE has expanded its state-of-the-art modeling and processing capabilities further into THz technology.  Significant progress had been made in addressing the inspection problem of the space shuttle’s external tank foam insulation as well as in providing assistance to Air Force Research Laboratory’s THz development.  Elsewhere at ISU, faculty and researchers from various science and engineering disciplines have also quickly recognized the potential of THz technology.  Driven by these needs, the acquisition of THz systems for imaging and spectroscopy was realized in 2008 via a major funding boost from the National Science Foundation’s Major Research Instrumentation program, and a new $0.5M THz research facility was established.  With this new THz facility, a number of applications in physics, chemistry and engineering have been extensively studied, including the detection of chemical contamination in drinking water pipe systems, solvation of ionic liquids, fundamental studies of multiphase combustion and flow processes, and nondestructive evaluation of composite materials.  The growing potential of THz has been further explored in inspecting many other advanced materials such as ceramic tiles and high-molecular weight fiber polymers used in military personal protection applications.  It is evident that we have extended THz application opportunities well into the full spectrum of science and engineering disciplines with significant benefits in both research and education to the entire ISU community.

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