Abstract

This paper presents a novel microwave assisted nondestructive evaluation system for industrial applications. The technique provides rapid, on-line, non-intrusive, non-destructive, and volumetric monitoring of adhesively bonded polymer materials. When a microwave signal of a given frequency is launched into a metallic cavity which is fully or partially filled with a material, the microwaves reflect back and forth between cavity walls and travel through the material many times until a final standing wave condition is established. Material property variables such as physical geometry, chemical and physical properties, internal or surface defects, and dielectric properties can contribute to its unique output characterisation. The established reflected and the input signals form a ratio, which can be monitored and plotted as a function of the frequency. The signal ratio versus frequency curve is called the microwave reflective spectrum. The spectrum generated can be used as a signature curve for assessing bond quality during processing. This way, the same material under the same processing environment provides a common characteristic curve, which can be traced. Therefore, the quality of adhesively bonded products can be detected by the intrinsic spectrum signals generated.

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