Improved complementary split-ring resonator for nondestructive testing of materials

This paper presents the design and applications of an improved complementary split-ring resonator (CSRR) sensor for nondestructive testing of dielectric samples in the S-band (2-4 GHz). Two sensors are presented here, first sensor is designed by loading the microstrip line with a single CSRR unit cell and the second sensor is designed by loading the line with a pair of identical CSRRs unit cell. The later shows the higher sensitivity towards the loss tangent of the material under test and hence appears to be more appropriate for the characterization of low loss dielectric samples and small impurity detection. Numerical models are developed for both the sensors to calculate the complex permittivity of sample. The sensors are designed and numerically tested using a 3-D full wave electromagnetic simulator, the Computer Simulation Technology Microwave Studio (CST-MWS). The determined complex permittivity results of various reference samples from both the sensors show good agreement with reference data and the results also illustrate that the microstrip line sensor loaded with double CSRRs unit cell is more sensitive and accurate than the microstrip line sensor loaded with single CSRR unit cell.