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

Abstract

A magnetic field sensing system with a single primary sensor and multiple reference sensors deployed locally and orthogonally, was proposed for downlink signal reception and interference cancelling for Through-theEarth Communication (TEC). This paper mathematically analyzes a design optimization process for a search coil magnetometer (SCM), and applies that process to minimize the bandwidth of the primary SCM for TEC signal reception and the volume of reference SCMs for multiple distributions. The primary SCM achieves a 3-dB bandwidth of 7 Hz, a sensitivity threshold of 120 fT/√Hz, and a volume of 2.32 × 10 −4 m 3 . The entire sensing system volume is as small as 10 −2 m 3. Experiments with interference from industrial frequency harmonics demonstrated an average of 36 dB and 18 dB improvements in signal-to-interference ratio and signal-tointerference plus noise ratio, respectively, using multichannel recursive-least-squares algorithm. Thus, the proposed sensing system can reduce the interference effectively and allows reliable downlink signal reception.

Research on Permanent Magnet-Type Super-Low-Frequency Mechanical Antenna Communication

“…In order to study the factors influencing the variation of coil sensitivity in the International Journal of Antennas and Propagation same structure during communication, the coil sensitivity calculations were normalized with a normalization factor of 1/f. erefore, the normalized formula for coil sensitivity can be organized into equation (20), which has units of T/ �� � Hz √ :…”

“…From equations ( 16) and (20), the relationship between the geometric parameters and sensitivity of the magnetic induction coil can be expressed as follows:…”

“…In the field of magnetic sensor technology today, there are mainly magnetic induction coils, optical pump magnetometers, proton (nucleon) spin-in magnetometers, and superconducting quantum interference magnetometers with resolutions up to the pT level [18,19]. Magnetic induction coils are used in mechanical antenna receiving units because of their simple structure, low power consumption, stable performance, and high resolution [20]. Domestic and international scholars have done a lot of beneficial research for the establishment of an accurate mathematical model for the transmission characteristic analysis of magnetic induction coils in the super-low-frequency domain.…”