# Scalp-Implanted Ultra-Wideband Circularly Polarized MIMO Antenna for Biotelemetry Systems
## 4 Conclusions  
This paper introduces a miniaturized two-unit implantable ultra-wideband CP MIMO antenna with two individually excited radiating patches: antenna-1 operates with LHCP and antenna-2 with RHCP, achieving polarization diversity at 2.45 GHz. The radiating patches are separated by 0.4 mm and are mounted on a shared ground plane, with the entire antenna measuring 0.065 \(\times\) 0.057 \(\times\) 0.0042 \(\lambda_{0}\)\({}^{3}\). The designed MIMO antenna functions within the 2.45 GHz ISM band, which has an FBW of 28.16% (2.14-2.83 GHz) and a 3 dB ARBW of 16.3% (2.23-2.63 GHz).  
By analyzing the results obtained in a seven-layer homogeneous human head model, a real human head model, and minced pork, this MIMO antenna was determined to be effective. Additionally, the antenna's low SAR permits operation with an input power of 24.27 mW when considering 10 g of tissue. This setup allows for data transmission rates  
Figure 11: SAR over 10 g of tissue at 2450 MHz when both ports are powered with 1 W in a real human head.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Parameters** & [11] & [16] & [17] & [18] & [35] & [36] & **This Work** \\ \hline Size (mm\({}^{3}\)) & 13.04 & 360 & 3375 & 9.01 & 434.6 & 280 & 28.448 \\ Frequency (GHz) & 0.433 & 2.45 & 2.45, 5.8 & 0.915 & 2.45 & 2.4 & 2.45 \\ Tissue & Skin & Five-layer & Skin–fat–n muscle & Rim–fat–muscle & Skin–fat–muscle & Seven-layer head model \\ Isolation (dB) & 26 & 26.3 & 37/32 & 29.7 & 15.9 & 37 & 27.5 \\ ECC & 0.1 & 0.1 & 0.1 & 0.0025 & - & 0.1 \\ FBW (\%) & 33.9 & 0.151 & 36/26 & 10.5 & 18.64 & 8.5 & 28.16 \\ Polarization & LP & LP & CP & CP & LP & LP & CP \\ ARBW (\%) & - & - & 36/8.33 & 10.35 & - & - & 16.3 \\ Polarization & - & - & No & Yes & - & - & Yes \\ diversity & & & & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 3: Comparative evaluation of the proposed implantable MIMO antenna with existing implantable MIMO designs.  
of up to 78 Mbps across a distance of 9.6 m. Furthermore, the antenna exhibits significant independence between the MIMO units, with excellent performance in terms of ECC, DG, and CC. Therefore, this antenna is well suited for biomedical IMDs that require high data transfer rates.  
Methodology, Z.S. and Y.S.; software, Y.S. and Z.S.; validation, Y.S., X.Z. and Y.W.; formal analysis, X.Z., Y.W. and Y.S.; writing--original draft preparation, Y.S.; writing--review and editing, Z.S.; supervision, Z.S.; project administration, Z.S.; funding acquisition, Z.S. All authors have read and agreed to the published version of the manuscript.  
This research was funded in part by the Xinjiang Uygur Autonomous Region Natural Science Foundation General Project, under Grant 2022D01C424; in part by the Tianchi Talent Project in Xinjiang Uygur Autonomous Region, under Grant 510523005137; in part by the National Natural Science Foundation of China, under Grant 62261052; and in part by the Xinjiang University Youth Doctoral Research Launch Project, under Grant 620321063.  
Not applicable.  
The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author(s).  
We thank the Institute of Micro, Nano, and Radio Frequency at the Hebei University of Technology for providing experimental equipment.  
The authors declare no conflicts of interest.