Wireless Complex Permittivity Measurement Using Resonant Scatterers and a Radar Approach

In this article, a method to characterize complex permittivity of dielectric is presented. The backscattered signal from a resonant scatterer placed in contact with the dielectric is used to estimate the dielectric properties. The proposed method was tested in simulation and validated in practice using different dielectric samples and different dielectric thicknesses. This method is wireless, nondestructive, with no restriction on the sample thickness and is done using a vector network analyzer (VNA) and an antenna. Discussions on the geometry of the resonator as well as the calibration step is proposed to improve the sensing capability of the approach. Monte-Carlo (MC) simulation has been performed to define a confidence interval for the values extracted with the proposed approach in the range 1–3.5 for permittivity and 0–0.2 for
$\tan \delta $
with an SNR of 20 dB. For example, a permittivity
$\varepsilon _{r} = 3.54 \pm 0.06$
and
$\tan \delta = 0.0024 \pm 0.003$
has been measured for Rogers RO4003C and
$\varepsilon _{r} = 2.31 \pm 0.05$
and
$\tan \delta = 0.004 \pm 0.002$
for Duroid RT5880 with different thicknesses. It is also shown in simulation that the approach is compatible with materials having loss tangents up to 0.5, and real permittivity up to 10.