Sub-Terahertz Antenna Array Packaged in Bio-Compatible Polymer for Fully-Passive Subdermal Sensing

Sub-terahertz (sub-THz) systems are ideal for implants that require continuous high-resolution sensing and wireless communications for diagnostics. There is also a need for these systems to be small, cost-effective, and of bio-compatible material. Here, we present an antenna array that is capable of sub-THz operation (0.063-0.212THz) and is small in size with a $\mathbf{5\times 5}$ configuration $\mathbf{(2.85{mm}\times 2.85{mm})}$, or a $\mathbf{3\times 3}$ array $\mathbf{(1.7mm\times 1.7mm)}$. Furthermore, the antenna uses a low-cost polymer as substrate and superstrate. This ensures efficient high frequency operation and bio-compatible packaging while maintaining a profile of 0.38mm. The array has dual-linear polarization and achieves a 3.4:1 contiguous impedance bandwidth at broadside with a voltage standing wave ratio (VSWR) $\mathbf{< 2}$ across the entire band under a 0.07mm epidermis layer. Similarly, the antenna achieves a 3.2:1 bandwidth with VSWR $\mathbf{< 2}$ for a 0.015mm layer of stratum corneum. Full-wave simulation of the array demonstrates $\mathbf{>70 \%}$ efficiency across the entire band for both conditions. A 60dB polarization purity is also achieved.