# A Split Ring Resonator-Based Metamaterial for Microwave Impedance Matching with Biological Tissue
## 5 Conclusions  
A metamaterial lens based on SRR has been designed to be employed as a lens to be put on an SIW cavity-backed patch antenna in order to improve the impedance matching of the antenna when loaded with human tissue and to enhance the focusing of the electromagnetic field into the biological tissue to be treated. A prototype has been fabricated employing the standard, low cost PCB technology and has been characterized by using a Network Analyzer. The simulated scattering parameter modulus of the antenna loaded with the biological tissue with and without metamaterial lens is \(|S_{11}|=-37\) dB and \(|S_{11}|=-14\) dB at the \(f=11\) GHz frequency, respectively. The measured minimum of the scattering parameter modulus \(|S_{11}|=-42\) dB has been measured at the \(f=10.6\) GHz frequency. The experimental results are in good agreement the simulations. The impedance matching improvement has been proved. The electromagnetic field distributions simulated have highlighted the focusing capability of the metamaterial lens. The antenna measurement in the anechoic chamber has confirmed that this kind of SRR lens can find actual application to focus the electromagnetic field of microwave applicators used in dermatology for the thermal therapy of skin cancer. Conceptualization, Investigation and Methodology, V.P., A.M.L., F.P. ; Writing--Original Draft Preparation, V.P., F.P. ; Review and Editing, V.P., A.M.L., F.P. ; Supervision, F.P. All authors have read and agreed to the published version of the manuscript. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Ref/** & **Antenna/Frequency** & **Metamaterial** & **Biological Tissue** & **Results** \\ \hline
[19] & Line source extended & Flat left-handed & & \(T_{\text{max}}=44.7\,^{\circ}\)C at 0.71 cm below the skin surface \\
2009 & infinitely/2.45 GHz & metamaterial (LHM) & Superficial tumor & \(42\,^{\circ}\)C HZD of 1 cm \(\times 1.2\) cm \\  & & & (LHM) & Electromagnetic field source & \(43.44\) Vcm\({}^{-1}\) \\ \hline
[36] & Dipole & Flat left-handed & & \(T_{\text{max}}=46\,^{\circ}\)C at 7.5 cm from the border of the LHM lens \\
2011 & antenna/4.15 GHz & metamaterial (LHM) & & Input power \(P=8\) W \\ \hline
[18] & Multiple line source & Flat left-handed & & \\
2012 & extended infinitely/2.45 GHz & metamaterial (LHM) & Superficial tumor & \(42\,^{\circ}\)C HZD of 6.2 cm \(\times 1.3\) cm \\ \hline
[20] & Zero-order resonator & Zero-order resonator (ZOR) & Superficial tumor & \(50\%\) SAR zone of 6 cm \(\times 24\) cm \\
2014 & antenna/434 MHz & metamaterial & & \\ \hline
[37] & Multiple microwave & Flat left-handed & & \(42\,^{\circ}\)C HZD of \\
2015 & sources/6 GHz & metamaterial (LHM) & Breast tissue & \(1.13\) cm \(\times 0.89\) cm \(\times 0.61\) cm, two \\  & & & & LHM lens \\  & & & & \(42\,^{\circ}\)C HZD of \\  & & & & \(0.87\) cm \(\times 0.87\) cm \(\times 0.61\) cm, four \\  & & & & LHM lens \\ \hline
[38] & Microstrip & Electromagnetic & & Peak \(\text{SAR}_{1\,\text{g}}=25\,\text{mWg}^{-1}\) \\
2016 & antenna/2.45 GHz & band gap (EBG) & Breast tissue & Peak \(\text{SAR}_{10\,\text{g}}=4.54\,\text{mWg}^{-1}\) \\  & & & & Input power \(P=1\) W \\ \hline
[39] & Coaxial & Left-handed & & \(50\%\) SAR zone of \\
2017 & antenna/2.45 GHz & metamaterial (LHM) & Superficial tumor & \(1.81\) cm \(\times 0.32\) cm \\ \hline  & & & & \(\text{Peak}\,\text{SAR}_{1\,\text{g}}=51.1\,\text{mWg}^{-1}\) \\ This work & SIW cavity backed patch & Split ring resonator & & \(\text{Peak}\,\text{SAR}_{10\,\text{g}}=14.2\,\text{mWg}^{-1}\) \\  & antenna/Ku-band & (SRR) & Superficial tumor & \(42\,^{\circ}\)C HZD of \\  & & & & \(1.4\) cm \(\times 1.3\) cm \(\times 0.4\) cm \\  & & & & Input power \(P=1\) W at \\  & & & & \(f=11\) GHz \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Comparison with other microwave applicators for cancer therapy. **Funding:** This research received no external funding.