Capacitively Coupled Electrode Antenna: A Practical Solution for Biomedical Implants

A capacitively coupled electrode antenna is proposed for use in medical implants. The antenna involves the conductivity of the biological medium and extends the applied RF electric signal to the conductive biological medium, thus the antenna virtual size increase that results in higher radiation efficiency compared to the similar size physical antennas. The antenna is self-matched or can be easily matched to a 50-ohm source impedance and provides ultra-wideband impedance matching that makes it less sensitive to the variations of the surrounded biological tissues. The proposed antenna occupies a minimal volume, which is a requirement for the implants. The physical structure of the antenna is similar to the contact electrodes but uses a capacitive coupling gap to the medium to increase radiation efficiency and reduce the specific absorption rate (SAR). A sample antenna at 403 MHz is designed and compared to the ideal conventional dipole and loop geometries.