Near-field microwave identification and quantitative evaluation of liquid ingress in honeycomb sandwich structures

Honeycomb sandwich structures are susceptible to liquid ingress, which causes a serious degradation of performance. Herein, a near-field microwave nondestructive detection technique was proposed to detect, identify, and quantitatively evaluate liquid ingress in honeycomb sandwich structures. Based on the microwave reflection spectrums, liquids of different polarity properties were identified. The amplitude of reflection microwaves was found nearly linear with respect to the height of the intruding liquids in the near field of the coaxial adapter probe. A simple characteristic peak method (CPM) based on line scans was presented and applied to quantify the size of liquid ingress region, and it turned out to be quite accurate with relative errors less than 0.5%. In summary, the near-field microwave testing technique proposed in this study is effective to detect, identify, and quantify liquid ingress in honeycomb sandwich structures.