RF Material Property Characterization

The research team proposes to expand the capabilities of an existing microwave nondestructive evaluation (NDE) system that measures thickness, quantifies dielectric properties (e.g. loss tangent, phase shift, dielectric constant, conductivity), and detects flaws in composite materials. The prototype system has been successfully used on military aircraft sandwich and single layer composite structures in the field. Proposed improvements will allow it to measure thickness and dielectric properties of each individual layer of material while maintaining its ability to detect very small (0.25"diameter, 0.008"thick) flaws. The existing system provides this level of flaw detection, but provides thickness and dielectric properties of the bulk composite. Preliminary results using the new approach show successful measurement of dielectric properties and thicknesses of each individual layer in stacks up to 7 layers. The system requires only inputs of measured NDE data. No base dielectric properties nor target thicknesses need be entered before calculating the answers. The existing equipment is portable (<5 lbs), low power, and allows data mapping and storage. Phase I will use multilayer samples up to 1"thick to demonstrate accurate, quantitative dielectric property and thickness measurement of every individual layer in a composite stack while also detecting small defects.