Research On Long-distance Through-the-Earth Communication System

Through-the-Earth Communication(TEC)plays an important role in downhole resource exploration and safety by providing a stable and reliable connection between the surface and the subsurface.But with the increase in the depth of resource extraction,traditional TEC systems are constrained by the large size of low-frequency antennas,low radiation efficiency and slow transmission rates,so it is difficult to meet the needs of deep mining.In conjunction with above questions,this thesis focuses on the problems of mechanical antenal through-the-earth communication(MA-TEC)system with a single transmitter and low radiation efficiency,and the electromagnetic measurement while drilling through-the-earth communication(EM-MWD-TEC)system with limited transmission distance and rate,then develops the TEC system respectively.The specific research content and innovation points are as follows.(1)To design a multi-mechanical antenna(MMA)array beamforming technique and implement a multi-mechanical antenna communication system to address the problems of monolithic transmitter defects and low radiation efficiency in MA-TEC systems.Specifically,the spatial magnetic field distribution model of MMA array based on a three-phase induction motor is established by studying the theory of ultra-low frequency multi-mechanical antenna electromagnetic radiation in a multiple-input single-output(MISO)scenario.Based on the simulation results,a multi-motor synchronous control technique was designed and a multi-mechanical antenna communication system was built.It is verified that under single-hop transmission and FSK signal modulation,the transmission power of the system is increased by 6 d Bm compared to a single antenna by using a binary antenna array,and the transmission distance can reach 50 m.(2)The design of a multi-relay transmission protocol and the implementation of a drilling relay cooperative transmission communication system for EM-MWD-TEC systems with limited transmission distances and rates.Specifically,the relationship between the frequency of the drill pipe signal and the received power is obtained by building a transceiver experiment platform,and the system communication function module is designed based on FPGA,a multi-relay transmission protocol has also been designed based on the frame structure in order to improve the reliability of multi-relay transmission.Then the corresponding hardware circuit modules were designed on the transmitter and receiver sides,and the prototype was built and tested.The results show that the system can correctly send and receive signals within 8 m,and the transmission rate can reach 4 kbps.Finally the integrated PCB design of the system is completed based on the hardware module to further improve the practical application of the system.