  In-vivo sensing, diagnosis and treatment of diseases is having a great
attention lately. With advanced computational systems, the processing of the
biological data as well as the prediction of diagnosis is becoming more
promising. However, the implementation of these systems inside the human body
has a major challenge; modeling the communication channel. To overcome this
problem, researchers are investigating the main factors that define the
characteristics of the communication channel between nano-devices. In this
work, we summarize the elements that contribute to the path loss encountered by
an EM wave traveling in water, skin or epidermis. Then, the impact of
nano-antenna directivity on the EM propagating wave is studied along with the
frequency and the communication distance. The simulation results show that the
nano-antenna directivity seems to have minor contributions 5 to 7 dB on the
total path loss inside the human body with respect to the distance 2 to 30 dB
and frequency 10 to 15 dB.
