Fat in the Abdomen Area as a Propagation Medium in WBAN Applications

Abstract

This paper presents a study on the fat in the abdomen area as a propagation medium in wearable and implant communications systems. Propagation via subcutaneous and visceral fat is considered separately. Simulations and measurements are done for both female and male bodies with the on-body antennas designed for in-body communications. Propagation paths are calculated and compared with the simulated and measured impulse responses. Furthermore, we analyze simulated 2D power flow figures, which illustrate the propagation inside the different tissues. It is shown that the signal propagates through the fat layer with minor losses compared to the other tissues of the studied cases. The signal propagates through the fat tissue from the abdomen area to the backside of person with 60 dB power loss. Additionally, the calculated fat layer propagation paths match well with the peaks of the simulated and measured impulse responses. The information about the fat as propagation medium is useful when designing the wireless and wired medical and health monitoring devices.

WBAN Channel Characteristics Between Capsule Endoscope and Receiving Directive UWB On-Body Antennas

“…When studying power flow (at 4 GHz) from the capsule towards the on-body antenna, it is noted that power flow is strongest through the central line of the abdomen and outer fat layer and less power can be seen in the muscle layers. This is evident from the results presented in [18], [20], [33], [34], which discuss about the fat as propagation medium.…”

“…The path goes between the abdominal muscle elements and via the inner fat between the intestine elements. As explained in [18], [20], [33], [34], fat is a good propagation medium inside the human body due to its dielectric properties. Propagation paths through the fat layer enables that even deeper capsule locations in the small intestine can be achieved with reasonable losses.…”

WBAN Radio Channel Characteristics Between the Endoscope Capsule and on-Body Antenna

“…2) The layer model mainly takes account the simple direct propagation through the tissues whereas the voxel model includes the impact of more complex indirect propagation paths, e.g. through the fat layer, as explained in [7], [8]…”

“…9 a-b, respectively. Evidently, the path loss is lowest as the capsule is located in the middle of the SI (case a), since the distance between the capsule and the on-body antenna is smallest and since the part of the signal may travel without passing the muscle layer, as explained in [7] and [8]. Instead, the path loss difference between the cases b and c is surprisingly small in the frequency range of interest, although "c" is clearly further from the on-body antenna than in the case "b".…”

“…Since there are no remarkable differences in the antennas' radiation patterns toward point "b" and "c", as presented in [18], the reason for this phenomenon can be found from the propagation paths. For the point "c", there is a propagation path option through the fat layer, in which the losses are minor, as explained in [7], [8], [12], [13]. Instead, for the point "b", most of the signal needs to travel through the small intestine tissue, in which the losses are high.…”