Research and Design of a Transmission System for Time-Frequency-Domain Electromagnetic Method

In electromagnetic sounding, the detection areas of time-domain and frequency-domain electromagnetic detection methods cannot be effectively connected, and the detection processes for these two methods must be implemented separately. To combine time-domain and frequency-domain electromagnetic detection methods and simplify the detection process, a time-frequency fusion transmission method is proposed to simultaneously excite the earth to produce transient and steady-state responses. By analyzing the characteristics of the time-domain and frequency-domain excitation current waveforms, a pseudorandom transmission waveform with dead time is designed, and a transmission system for a time-frequency fusion electromagnetic detection method is developed. In this detection mode, the pseudorandom transmission waveform contains several frequencies, and the transient induction field can be received during the dead time. The time-domain and frequency-domain responses can be obtained by the same procedure. At the same time, a self-adaptive pseudoload device is designed and matched with the corresponding control sequence to reduce the influence of dead-time. The experimental results show that the self-adaptive pseudoload transmitter can effectively reduce the current fluctuation, and the time-frequency electromagnetic transmission system can effectively excite the earth to produce transient and steady-state responses. The time-frequency fusion electromagnetic transmission method proposed in this paper can be used in electromagnetic detection instruments to improve the efficiency of electromagnetic sounding.