NIOSH-Sponsored Research in Through-the-Earth Communications for Mines: A Status Report

Design of the Magnetic Field Sensing System for Downlink Signal Reception and Interference Cancelling for Through-the-Earth Communication

“…Another effective method involves placing the reference SCMs locally and orthogonally with the primary receiving SCM. When the transmitting antenna and the primary receiving SCM are oriented in the same direction, the TEC signal transmission is optimized [1]. Thus, the signal components can be maximized in the primary receiving SCM while they are minimized in the reference SCMs.…”

“…The gain of the preamplifier is G, and its output is U o . The induction voltage of the SCM is represented by U s and is calculated as (1) in the frequency domain according to Faraday's law. ,…”

“…Further, the radiation efficiency of the transmitting antennas is very low (lower for portable antennas), and the received signal level tends to be several orders lower than the EMI. Thus, the ability to communicate is mainly dependent on the signal-to-noise ratio (SNR) at the receiving terminals [1].…”

“…Several signal processing techniques have been used to reduce interference, such as an adaptive clipper combined with direct matrix inversion achieving average 4.1 dB improvement [2] for interference at extremely-low frequency (ELF, 3 Hz-30 Hz), and adaptive noise cancelling combined with maximum-likelihood detection, nonlinear processing, and decision-aided feedback achieving 10-to-24 dB improvement [3] for interference at verylow frequency (VLF, 3 kHz-30 kHz). To date, the trappedminer communication and location systems continue to encounter many challenges, of which the key research focuses on digital signal processing and interference cancelling techniques that could be effective at these low frequencies [1].…”

“…Further, sensors such as loop antennas [1,6], air coils, and electrodes [7,8] are unsuitable for placement in underground or underwater terrains, especially during emergencies [9]. This is because air coils or loop antennas need to be large (such as these loop diameters of 3.8, 12.5, 26, and 90 m [1]) to obtain high sensitivity required for receiving weak magneticfield signals, and the receiving terminals of the electrodes need to be separated over a large distance. All these receiving sensors occupy a very large area or volume that is usually unavailable in underground or underwater terrains.…”