| Underground drilling equipment collected lots of data while drilling, whichneed to be transmitted to the ground in real-time. Electromagnetic inductiontransmission system is an effective method of achieving high-speed datatransmission. A data transmission system based on electromagnetic induction wasestablished in our laboratory, Frequency shift keying (FSK) was used in the systemto modulate carrier wave according to digital signal. Modulated signal traveled innon-contact way by the electromagnetic induction between the coils of the dill pipejoints.Many progress had been made in the system, while problem still remained to besolved.1. The received signal will be affected if the coupler in contact with water,while the received signal may be affected, sometimes do not, if the signal wireinsulated.2. The resonance frequency of the channel of magnetic induction willchange to the increase of the number of drill pipe underground, we want to achievefrequency tuning circuit.In this paper, work has been done to solve these remaining problems. Firstly, acircuit model of the coupler is established, and the principle of the data transmissionsystem based on electromagnetic induction is described, Using the COMSOLmulti-physics coupling analysis software simulated the electromagnetic field of thecoupler, obtained the magnetic field distribution and signal transmission frequencycharacteristics, For single-section coupler, the simulation results matches well withthe measured results.A modem circuit is designed based on AD9832and NE564. To solve theproblem of the circuit will not work when the resonance frequency of thetransmission channel changed, the frequency tuning circuit and the bidirectional datatransmission circuit established, the bidirectional data transmission circuit ishalf-duplex communication.Finally, the transmission system was tested in the laboratory. In the experiment,the signal travelled through20couplers without relay, the rate reached115.2kbps. |
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