Impulse response analysis of an ultrasonic human body channel

Ultrasounds have been successfully and safely employed in underwater communications and for health diagnosis in the last 60 years because of their good performance in environments with high water concentration. Recently it has been proposed also to employ them for supporting intra-body communications; however exploitation of ultrasounds inside the body calls for a deep understanding of their features and a full characterization of the impulse response inside these challenging channels. In this paper we provide a complete experimental characterization of the impulse response inside a human body communication channel, composed for more than 65–70% of water. To this purpose we developed a testbed which employs a human phantom of ballistic gel to emulate the human body propagation features and performed a set of measurements to fully discuss the channel behavior as a function of different parameters such as the employed frequency, the channel composition and the distance. Our results show that, it is possible to clearly identify the three main components generated by multipath propagation inside the human phantom, i.e. the direct, lateral and reflected waves. Also, it is possible to observe that the excess delay which measures the time elapsed between the first and the last arriving waves, increases approximately as 10 μs per cm. Our analysis provides interesting has strong implications on the design of communication protocols for intra-body scenarios.