Experimental Investigations on Enhanced GPR Detection Assisted by Broadband Metasurfaces

Attenuation within the material under test (MUT) and reflection loss at interfaces of different MUT layers make subsurface targets especially nonmetallic objects difficult to detect. Increasing the penetrable depth by depositing an impedance matching layer is a standard solution to effectively enhance the electromagnetic (EM) transmission from air into the lossy MUT. However, the trade-off between the working bandwidth and thickness of such a layer is generally difficult, especially by the traditional quarter-wave transformer solution. In this article, we utilize the novel metasurface approach, and design a broadband metasurface for the detection of a nonmetallic inclusion inside a highly lossy foam brick. Such a metasurface has a wide relative bandwidth (~44%) and a small electrical thickness ( ${\sim }\lambda /9$ ). Both the numerical simulation and ground penetrating radar (GPR) experimental results show enhanced transmission over a broader frequency range compared to traditional narrowband metasurface designs. On-site GPR validations successfully demonstrate that the air pipe that is hardly detectable by the narrowband metasurface can be distinguished with the aid of the overlaid broadband metasurface. The proposed broadband metasurface of small thickness showcases its potentials in the integration with future GPR systems.