A Miniaturized CSRR Loaded Wide-Beamwidth Circularly Polarized Implantable Antenna for Subcutaneous Real-Time Glucose Monitoring

Abstract

A single-fed miniaturized wide-beamwidth circularly polarized implantable antenna, operating in the Industrial, Scientific, and Medical band (2.40–2.48 GHz), is designed and experimentally verified for subcutaneous real-time glucose monitoring applications. The proposed antenna features a very good miniaturization with the dimensions of ${\mathbf 8.5 \times 8.5 \times 1.27 \; \text{mm}^{3}}$ by employing four C-shaped slots and a complementary split-ring resonator (CSRR). Meanwhile, by adjusting the slits of CSRR, circular polarization is realized. The simulation results in a three-layer phantom demonstrate that the impedance bandwidth is 12.2% (2.32–2.62 GHz) with a peak gain of −17 dBi, and the 3-dB axial-ratio bandwidth is 2.4% (2.42–2.48 GHz) with a wide beamwidth of around 140°. An in vitro test was carried out in a pork slab, and the measured impedance bandwidth is 13% (2.31–2.63 GHz) with ${\boldsymbol S_{11} , confirming the simulated results. The specific absorption rate distribution has been evaluated for the consideration of health safety, and the calculated link margin shows that the reliable communication can be guaranteed within 10 m in free space.