A Flexible Broadband CPW-Fed Circularly Polarized Biomedical Implantable Antenna With Enhanced Axial Ratio Bandwidth

Abstract Implantable antennas have a vital role in biomedical telemetry applications. Therefore, a compact low-profile circularly polarized biomedical implantable antenna operational in industrial, scientific, and medical (ISM) band at 2.45 GHz is reported. The presented antenna is fed by a modified co-planar waveguide (CPW) technique to keep the size of the antenna compact. The radiating monopole consists of a slotted rectangular patch with one slot at an angle of 45 degree and truncated small patch on the left end of the CPW ground plane to make the antenna circularly polarized at the required frequency band. A flexible Roger Duroid RT5880 substrate (εr = 2.2, tanδ = 0.0009) with the standard thickness of 0.254 mm is used to achieve bending abilities. The complete volume of the designed antenna is 21 mm × 13.5 mm × 0.254 mm (0.25 × 0.16 × 0.003 ). The antenna covers the bandwidth from 2.35-2.55 GHz (200 MHz) in free space while from 1.63 GHz to 2.8 GHz (1.17 GHz) inside skin tissue. As the designed antenna is operational in skin tissue with larger bandwidth, the bending analysis along the (x & y)-axis is also analyzed through the simulation. A good agreement between the simulation and measurements of the bended antenna is observed. The measured -10dB impedance bandwidth and the 3dB axial ratio (AR) bandwidth inside skin-mimicking gel are 47.7% and 53.8%, respectively at 2.45 GHz frequency band. Finally, the specific absorption rate (SAR) values are also analyzed through simulations, and it is 0.78 W/kg inside skin over 1 g of mass tissue. The proposed SAR values are less than the limit of the federal communication commission (FCC). This antenna is miniaturized and an ideal applicant for the biomedical implantable applications.