|
Microwave Nondestructive Evaluation (NDE) offers an attractive alternative to ultrasonic NDE. Using the free space spot focused antenna system developed by CEEAM, it is possible to perform non-contact, non-destructive evaluation of homogeneous, inhomogeneous, composite and anisotriophic materials as a function of frequency and temperature. Vary little sample preparation is required and the technique presented here leads itself to in situ process monitoring during manufacture and quality control of finished products. The material being evaluated may be planar or nonplanar. Reflection and/or transmission measurements may be used to reconstruct the material property tensors. Although microwaves cannot pass through metals, this technique has been used very successfully to evaluate the surface resistivity/conductivity of thin film metal coatings. Unlike ultrasonic measurements which may be limited by temperature, the free space microwave system has been used successfully temperature up to 1000 degree(s)C. In this respect, the free space microwave NDE system is a far cry from conventional methods such as coaxial and waveguide methods as well as the cavity resonance technique, all of which require sample preparation and hence, cannot be used for in situ inspection. Being a noncontact method this system can be used to characterize both liquids and solids. In this paper, the technique and the system will be described and the results will illustrate the versatility and user friendliness of the free space microwave system. In a comparison paper, we describe how this system can be adapted as a non-destructive point to point inspection system for locating flaws, manufacturing defects, delamination and disbonding, accurate thickness measurements, surface profiling, etc. of materials in sheet form or objects of complex shape.
|
