Polarization Reconfigurable Planar Inverted-F Antenna for Implantable Telemetry Applications

Abstract

A polarization reconfigurable implantable planar inverted-F antenna (PIFA), operating at 2.45–GHz ISM band, is introduced for monitoring and biotelemetry purposes. The proposed implantable antenna featuring with the reconfigurability of two polarizations is effective to overcome the polarization mismatch and multi-path reflection in an indoor environment. By using two groups of PIN diodes as radio frequency (RF) switches along <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$x$ </tex-math></inline-formula> -direction and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$y$ </tex-math></inline-formula> -direction respectively, two orthogonal linear polarizations can be switched to avoid communication link failure. The proposed antenna is based on a planar inverted-F antenna structure and the implantable environment of human body to develop. The antenna exhibits a good stability of an impedance bandwidth with the reflection coefficient ≤−10 dB in the environment of a human phantom. The simulated results in simple muscle-layer phantom, multi-layer phantom and 3D realistic human voxel model demonstrates the good robustness of the proposed antenna in the complex implantable environment. An in-vitro test was carried out in body tissue simulant liquid to validate our proposed design. A sleeve balun was fabricated and incorporated into the semirigid coax cable in order to eliminate the unwanted effect of the long cable during the measurement. The experimental results agree with simulation and show an overlapped impedance bandwidth of 9.1% from 2.3 GHz to 2.52 GHz in different reconfigurable states. The radiation performances, evaluation of Specific Absorption Rate (SAR), and link characteristics in different propagation scenarios are also discussed. This proposed antenna technology is suitable for implantable telemetry applications.