Abstract

This paper presents comprehensive study on fat as propagation medium in abdominal implant communication system at low ultrawideband (UWB) frequency range 3.75—4.25 GHz. The main aim is to investigate how signal propagates through visceral and subcutaneous fat layers and how that information can be exploited in implant communication systems. The study is conducted using different methods: electromagnetic simulations, power flow analysis, propagation path calculations and radio channel measurements with animal meat pieces. Simulations are conducted using layer models and anatomical voxel models having different sizes. Results of channel simulations are verified with propagation path calculations. Power flow analysis on cross-cuts of the voxel models is conducted to investigate how the signal propagates inside the tissues. Furthermore, measurements using different animal meat pieces are performed to evaluate the impact of fat constitution on channel characteristics. It is found that similar tendency on fat propagation is seen in the evaluations with different methods. It is also observed that channel attenuation depends not only on the types and thicknesses of the tissues between transmitter and receiver antennas, but also how the tissues, especially fat, is located between the antennas. Channel attenuation difference between different voxels is maximum 14 dB in the studied antenna locations. Furthermore, propagation channel is evaluated with measurements using pork meat having different fat and muscle constitutions. It is found that antenna location respect to fat layers has clear impact on the channel strength although the fat tissue is not directly above the in-body antenna. The difference is noted to be 3–15 dB especially on the side peaks of channel impulse response. The knowledge on fat as a propagation medium is crucial when designing medical monitoring or implant communication systems. Location of antennas/sensor nodes for the monitoring devices can be established so that propagation through fat layer can be exploited.