This paper describes a noncontact, single-sided terahertz electromagnetic measurement and imaging technique that simultaneously characterizes microstructural (for example, spatially lateral density) and thickness variation in dielectric (insulating) materials. The technique was demonstrated for two materials — space shuttle external tank spray-on foam insulation and a silicon nitride ceramic. It is believed that this technique can be used for current and future NASA thermal protection systems and other dielectric material testing applications, where microstructural and thickness variation require precision mapping. Scaling up to more complex shapes, such as cylindrical structures and structures with beveled regions, would appear to be feasible.

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