Mechanism insights for impedance matching in split-ring resonator topologies under bio-medical scenarios

The utilization of microwave radiation has gained increasing importance in various biological applications. However, a significant challenge remains in the interaction between the microwaves and the human skin, primarily due to the impedance mismatch. Recently, the employment of split-ring resonator (SRR) topologies has become increasingly prevalent for addressing such a problem. Despite this, most existing literatures lack a comprehensive understanding of the underlying mechanisms. In this study, we follow Babinet's principle and numerically study the dispersion relations of a single-split-ring resonator (S-SRR) and its complementary topology, single-complementary-split-ring resonator (S-CSRR). We focus on conducting the impedance analysis, along with far-field and near-field excitation characterizations. The results indicate that S-CSRR ensures an improved impedance matching, thereby significantly enhancing microwave power flow within the bio-tissue. A 2 × 2 array of S-CSRR is experimentally examined for validation. We demonstrate that the S-CSRR array enhances the total specific absorption rate (SAR) of a deeply-implanted-tumor-phantom by a factor of 1.95. Our work may provide a broader understanding towards impedance matching, which may facilitate the design of more efficient diagnostic tools in bio-medical field.