Complementary Split-Ring Resonator With Improved Dielectric Spatial Resolution

Abstract

A nondestructive complementary split ring resonator (CSRR), working in the 0.5 to 6 GHz frequency range, is presented in this work. Three CSRR designs, on the same 5 mm by 5 mm footprint, with different internal dimensions were designed, fabricated, and measured. The results demonstrate a large shift in resonant frequency, up to 2.544 GHz, over a broad relative permittivity range from 1 to 80, and a large penetration depth, up to 7 mm, into the material under test. Secondly, this work presents a deconvolution-based method to increase the spatial resolution of the presented sensors compared to other sensing structures and algorithms. A conformal mapping function relating the resonant frequency to the relative permittivity was fitted through measurements and the point spread function (PSF) was derived from a known dielectric permittivity distribution. Experimental results demonstrated that the extracted PSF was able to reconstruct the dielectric distribution in six different scenarios. Additionally, a spatial resolution of 2 mm has been established according to the Rayleigh criterion, and objects smaller than the size of the sensor have been reconstructed as well. Objects with a different permittivity values can be distinguished as well. The reconstructed images of the objects have a good signal-to-clutter ratio up to 12.0%, which results from a smooth recovered background, and no spatial offset was present between the original and reconstructed objects.