An improved nondestructive inspection method uses terahertz energy for density and thickness mapping in dielectric, ceramic, and composite materials.

This non-contact, single-sided terahertz electromagnetic measurement and imaging method characterizes micro-structural (e.g., spatially-lateral density) and thickness variation in dielectric (insulating) materials. This method was demonstrated for space shuttle external tank sprayed-on foam insulation and has been designed for use as an inspection method for current and future NASA thermal protection systems and other dielectric material inspection applications where no contact can be made with the sample due to fragility and it is impractical to use ultrasonic methods (the latter methods require the sample under test to be immersed in liquid).