Water-loaded, Compact Ultrawideband Antenna with a Broadside Radiation Characteristic for Brain Signal Monitoring Applications

In this study, a compact, miniaturized, ultrawideband (UWB) implantable antenna system with a broadside radiation characteristic is proposed for brain signal monitoring applications. This antenna is insulated with a de-ionized (DI) water-based insulator. The proposed antenna is designed on a 0.2 mm thick Taconic TRF-43 substrate with a relative permittivity ($\varepsilon _{\mathbf{r}}$) of 4.3 and a loss tangent (${tan }$ $\delta$) of 0.0035. It consists of a modified rectangular slot etched on the ground plane and a tapered stepped microstrip feed line to achieve a wideband frequency response. To reduce the size of the antenna significantly and to further improve impedance matching and the broadside radiation characteristics, high permittivity DI water is used as an insulator. The entire system is composed of $10 \times 9 \times0.7$ mm$^{\mathbf{3}}$ size antenna, batteries, sensors, and electronic components: they are enclosed in a 3D printed biocompatible casing. The system is designed and analyzed using CST and Sim4Life. It is found that the antenna exhibits -10 dB impedance bandwidth of 129% ranging from 3 GHz to 14 GHz with a broadside radiation characteristic. The peak gain is -19 dBi at 3 GHz. Based on the performance attributes, simplicity, compactness, and wideband impedance bandwidth, it is believed that this could be a potential implantable system for modern health and brain monitoring devices.