Characterization of LF Band Underground Wireless Communication Using Principal Component Analysis Method

The low-frequency (LF) wireless system is considered suitable for underground communication owing to its lower path loss in the earth medium compared to MHz-band frequencies.In this study, to establish a wireless link with electronic devices inside bedrock, we investigated the nearfield strength distribution using a prototype consisting of a circular loop antenna and a coil operated at a frequency of 255 kHz.The loop antenna angles were varied in three actual tunnel construction site environments with different rock compositions.Using the principle component analysis (PCA) method to analyze the distance pass loss characteristics, we found that the plots are distributed according to the position of the null direction and there were regions where the null directions were than expected.