Voids or porosity in carbon fiber reinforced plastics (CFRP) caused by improper curing, moisture in the prepreg and other reasons can degrade the mechanical properties of the composite components [1–3]. Voids caused by trapped air in the layup process or volatile gas released in the curing process tend to occur at the interface between the plies of unidirectional prepregs and are usually elongated along the adjacent fiber directions [4]. On the other hand, voids in woven composites tend to be more spherical. Matrix dominated strengths such as transverse tensile and interlaminar shear strengths are affected the most by the presence of porosity. Quantitative nondestructive evaluation (QNDE) methods for the detection and characterization of porosity in composites are therefore highly desirable.