Performance of an Implanted Electrically Coupled Loop Antenna inside Human Body

Implanted antennas are widely used in hyperthermia and biomedical applications. The antenna needs to be extremely small while maintaining a permissible Specific Absorption Rate (SAR) and being able to cope with the detuning effects due to the dielectric properties of human body tissues. Most of the proposed antennas for implanted applications are electric field antennas such as Planner Inverted-F Antennas (PIFA) and micro-strip patch antennas. By minimizing the size of an electric field antenna, the near zone electric field will increase, resulting in higher SAR. This work is devoted to design a miniaturized magnetic field antenna to overcome the above limitations. The proposed electrically coupled loop antenna (ECLA) has high magnetic field and low electric field in the near zone and therefore, has a small SAR and is less sensitive to detuning effects. ECLA is designed at the Medical Implanted Communication Service (MICS) band with dimensions of (5 x 5 x 3 mm(3)). ECLA has been simulated inside one-layer human body model, three-layer spherical human head model, human head and human body. From the simulation results, ECLA inside the human body has a 5 MHz-3 dB bandwidth, 14 dB gain, and radiation efficiency of 0.525%. The 1 g average SAR inside the human body for 10 mW input power is about 1 W/kg which is 7 times lower than the SAR for a patch antenna of the same size with the same accepted power.