Fully Blind Electromagnetic Characterization of Deep Sub-Wavelength (λ/100) Dielectric Slabs With Low Bandwidth Differential Transient Radar Technique at 10 GHz

Transient radar method (TRM) is introduced as a novel non-destructive testing (NDT) technique that is capable of analyzing fully blindly and simultaneously the electromagnetic (EM) properties as well as geometric parameters of deep sub-wavelength thin single layer slabs. This study focuses on the minimum detectable layer thickness by means of TRM, which mainly depends on the experimental setup configuration. In this article, the complex permittivity and thickness of three polyvinyl chloride (PVC) sheets are extracted by means of a differential TRM set-up. The thickness of these PVC sheets was 1 mm,
$500 ~\mu \text{m}$
, and
$300 ~\mu \text{m}$
that corresponded to
$\lambda $
/30,
$\lambda $
/60, and
$\lambda $
/100, respectively (
$\lambda $
is the wavelength in free space). The carrier frequency was 10 GHz and the experiments were done in a bistatic radar setup. A differential TRM structure was used in this experiment. Some error sources, such as switch leakage and non-perpendicular illumination as well as systematic errors are considered as well. The experimentally obtained results are as follows: the thickness of these samples were 1033 ± 12, 535 ± 11, and 302 ±
$9 ~\mu \text{m}$
with 1.18%, 0.94%, and 2.89% relative error, respectively. Additionally, the complex permittivity of these samples was found as (2.73 ± 0.02)–(0.23 ± 0.01)j, (2.70 ± 0.02)–(0.20 ± 0.02)j, and (2.65 ± 0.02)–(0.37 ± 0.01)j, respectively. This novel technique has the potential for deployment in a wide range of applications ranging from the piping, wind energy industry, and automotive to biotechnology, food industry, clinical monitoring, and pharmacy.