Time-Reversal SAR Imaging for Nondestructive Testing of Circular and Cylindrical Multilayered Dielectric Structures

In this paper, a synthetic aperture radar (SAR) approach, for imaging internal structures of generally lossy layered dielectric cylindrical objects, is presented. This method which properly accounts for different transmission and refraction paths at each boundary between different layers produces a properly focused image of embedded targets. This approach is also capable of addressing imaging needs for asymmetrical multilayered cylindrical bodies. Consequently, this approach overcomes the limitation associated with the conventional methodology, in which free-space propagation is assumed. The calculation method of angular sampling criterion for circular and cylindrical SARs (i.e., circumferential and in height) is also presented. Electromagnetic simulations are performed on a three-layer cylindrical object, symmetrical and asymmetrical, with embedded targets to validate the approach. In addition, representative measurements are conducted at X-band (8.2-12.4 GHz), demonstrating the effectiveness of the approach for practical nondestructive evaluation applications.