Research On Time-domain Airborne Electromagnetic Transmitter

At present,China's proven mineral resources are being nearly exhausted,but desert,forest,mountain,Gobi and other people less accessible areas cannot be explored due to lack of effective resource exploration method.Therefore,we need to find a detection equipment that can explore such areas.The airborne time-domain electromagnetic measurement system is suitable for detecting complex geological structures due to its better characteristics of flexibility,terrain adaptability and detection depth.However,the research on airborne time-domain electromagnetic measurement system of China is lagging far behind the advanced countries,and the high-power electromagnetic transmitter is the key to the system.This thesis mainly studied design of airborne time-domain electromagnetic transmitter,which important for promoting the development of aviation transient electromagnetic technology in China.In this thesis,the energy-feedback double clamping technique is proposed to realize emission current rising edge and falling edge symmetrical characteristic.And analyzed the transmitter circuit working principle,established circuit complex frequency filed model,analyzed the relation of emission current and storage capacitor voltage.Furthermore,the transmitting pulse energy loss is analyzed and the energy loss of capacitor after the single pulse is calculated.Aiming at the problem emission current peak drop caused by energy consumption,designed boost circuit to supplement energy for capacitor in transmitting off period.We have written the transmitter software control program in complex programmable logic controller.Combining with sampling and driver circuit designed complete transmitter control system,which can control the IGBT orderly on-off.In order to reduce switching loss and ensure power devices safety,a circuit for suppressing the peak voltage of power tube at the moment of switching off is designed.Analyzed overshoot and oscillation phenomenon during the late period of the emission current turn-off.Based on the principle of damping absorption making the turn-off period response becomes critical damping response.Equations calculating the critical damping resistance are derived from the self-inductance,internal resistance,and the distributed capacitance of the transmitting coil,accordingly.Designed a device to precisely match the damping resistance,which can improve emission current quality.Used hardware monitoring circuit combined with software control program,proposed the whole machine fault protection scheme to ensure the transmitter and personnel safety.The test platform was built and tested the transmitter.Actual measurement transmitter's emission current is bipolar trapezoidal pulse with frequency of 8Hz and duty cycle of 0.5.The peak current is 306 A and falling-edge time is less than 1.5ms,the overall results meet the design requirements.