Measurement and characterization of the path loss for ear-to-ear wireless communication

The path loss of the ear-to-ear wireless communication channel has been measured for the frequencies 1 GHz, 1.6 GHz, 2.6 GHz and 3.6 GHz. The accuracy of the PL measurements was estimated to be 5 dB. Several parameters that could affect the path loss have been investigated. The parameters were chosen to cover all the possible locations and orientations of the antennas near the head. We came to the conclusion that small variations in the locations of the antennas do not affect the path loss of the ear-to-ear channel while the operating frequencies have a large impact on the path loss. The path loss increases as the frequency increases. We measured the path loss PL at 1 GHz to approximately 33 dB for the tangential magnetic dipole and 45 dB for the normal magnetic dipole. These measurements show the importance of the orientation with respect to the surface of the head. We were able to gain 12 dB for the same antenna just by choosing different orientation. The significance of the feeding cables was demonstrated in the measurements with bow-tie dipoles (ant. 4 and 5), where the measurements show smaller path loss than for the low frequency cases. By using numerical simulations we were able to estimate the cable effect on the measurements.