Impact of the Variability of the EM Properties of Biological Tissues on UWB Channel Modelling for Implanted Devices

Wireless Body Area Networks are being massively developed nowadays. Wireless capsule endoscope, implanted sensors and wearable devices are a few examples of applications of this kind. Antennas for these networks are designed taking into account the electromagnetic properties of the surrounding biological tissues. However, many authors just consider the typical values rather than the whole range of possible electromagnetic properties. The same occurs when modeling the radio channel between transmitting and receiving side, where the body tissues are the propagation medium itself. In this paper, we aim at presenting how this variability can affect the propagation characteristics of the channel as well as the performance of in-body and on-body antennas in UWB frequencies. To this end, electromagnetic software simulations are carried out using a human CAD model with skin, fat and muscle tissues in the 3.1 – 5.1 GHz band. In addition, the fitting coefficients of a 2-pole Debye equation of the average, maximum and minimum permittivities of these tissues are provided, using the data gathered in a previous measurement campaign. Results showed that the dielectric variability has a great impact on the system losses, especially in the upper simulated frequencies, and that it may affect as well the reflection coefficient of WBAN antennas. However, it is worth mentioning that this variability will not have the same impact regardless the antenna tested, so in their design process researchers should check that they are versatile enough to work with some detuning of the surrounding electromagnetic properties.