Limb joint effects on signal transmission in capacitive coupled intra-body communication systems

This paper contributes empirical measurements towards an understanding of signal attenuation in intra-body communication (IBC) systems due to limb posture effects. Recent studies have shown a degradation of transmission signals for IBC transmissions between limb segments, but these degradations have yet to be quantified with respect to relative limb position and within the transmission frequency range from 300 KHz to 200 MHz. We examine the impact of limb position specifically the effect of elbow joint flexion and extension into account using a portable vector network analyzer. The results presented indicate that the signal attenuation is larger in the case of extension, i.e., when the angle between forearm and upper arm increases. The minimum attenuation was 20.64 dB and 24.81 dB for the fix distance of 15 cm between transmitter and receiver electrodes and the joint angle of 45 and 180 degree respectively. It was found that attenuation decreased at an approximately linear rate over 300 KHz to 100 MHz and increased over the frequency range from 100 MHz to 200 MHz for the input signal frequency range from 300 KHz to 200 MHz. It was concluded that the minimum attenuation for the range of flexions and extensions occurred in the range 80-100 MHz. Future work will explore theoretical models to explain the observed results.