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Microwave and Millimeter Wave High-resolution Imaging of Voids in a Rubber Composite Sheet

This paper shows the efficacy of using wideband microwave and millimeter wave synthetic aperture radar (SAR) imaging techniques to inspect rubber composite samples containing manufactured anomalies (voids with different shapes and sizes). A relatively wide range of frequencies (12.4 to 75 GHz) was examined utilizing multiple discrete bands. This type of wideband SAR imaging renders images with high spatial resolution, in addition to having a relatively fine depth (that is, long range) resolution. The manufactured discontinuity within the material is “seen” by the probe from multiple locations along the scan path as the composite is raster scanned. The data are then combined in the SAR algorithm, which results in images with high spatial resolution. The results clearly showed the efficacy and utility of high-resolution millimeter wave imaging even for a relatively thin rubber composite product. Overall, and considering the spatial and depth resolutions and the details produced by the images, the best results for voids were obtained at the Ka-band (26.5 to 40 GHz), although they were clearly detected at other frequency bands as well. A comparison was made with single-frequency images showing the advantages that can be gained with wideband SAR imaging technique. This paper presents the foundation of the technique along with the results of these experiments.

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