Research On Improvement For Quality Of Current Waveform Of Time-domain Electromagnetic Transmitter

For latest decades,Electromagnetic detection has been widely used in modern construction applications,it has become one of the most important methods of geophysical exploration.In time-domain electromagnetic detection,the quality of the transmitting current waveform directly influences the receiving data,thus,has great effect on the later data processing.In order to improve the quality of the transmitting current,this thesis mainly completed the following work:(1)The thesis analyzes the development of electromagnetic detection technology and the electromagnetic transmitter from worldwide,comparison is made for the advantages and disadvantages of domestic and foreign electromagnetic transmitters,and the relationship between the quality of transmitting current and the TEM response is studied.Hence,the necessity of transmit waveform improvement under an optimized power supply system is pointed out.(2)In this thesis,a model of the conducting EMI of time-domain electromagnetic transmitter is proposed and analyzed.This model is built to find the influence of the EMI that may bring to the transmitter current.And to improve the quality of the transmitter current,in this paper,several methods were proposed to deal with the EMI within the TEM transmitter circuit.(3)This paper proposes a unipolar current pulse circuit that generates fast and highly linear rising-edge and falling-edge current pulse with low voltage power supply.This current pulse enables high quality data in the pulse turn-off stage as well as in the pulse turn-on stage.(4)In order to test the effect of the proposed unipolar current pulse circuit.A detection experiment is conducted,during which both the rising edge and the falling edge of the transmitter current are used to collect the second field data.In the end,the contours of apparent resistivity section of the detection experiment proves the effectivity of the proposed unipolar current pulse circuit.