Design And Application Of Airborne Electromagnetic Transmitting Coil Device

In recent years,China’s demand for mineral resources has become stronger and stronger.At present,China’s central and western regions are rich in mineral resources and the degree of exploitation is low.However,due to the complex topographic conditions in these regions,the traditional exploration equipment can not work smoothly.Therefore,the development of airborne electromagnetic detection equipment has important strategic significance.Helicopter borne transient electromagnetic(HTEM)system takes helicopter as the carrier.It has the advantages of easy modification and strong terrain adaptability,and has a very broad application prospect.Based on the Beijing Science and technology plan-the key project of deep earth exploration technology: the development of large depth airborne electromagnetic detection system(Z181100005718001),the following work is carried out:(1)The optimal design of transmitting coil based on skin effect and proximity effect.Under the initial conditions of emission current frequency,aircraft load requirements and engineering construction,analyze the skin effect and proximity effect caused by AC,model and simulate the emission coil,obtain the changes of AC resistance of the coil under different structural models,and determine the optimal arrangement of multi turn coil on the premise of meeting the structural stability.Starting from the internal structure of the transmitting coil,the current transition state of the coil connection surface is analyzed.On the premise of stable connection,the structure,length,welding material and processing technology of the copper bar are determined to minimize the coil loss.(2)Design of high frequency transformer of switching power supply based on area product method(AP method).A 10 k Hz,2.8k W high-frequency transformer of switching power supply is designed by AP method for aviation electromagnetic emission system.The winding layout is simulated in ANSYS Maxwell eddy current field to determine the model of cross layout;When calculating the leakage inductance,loss and inductance parameters of the transformer,the external circuit is introduced into the transient field for joint simulation,and a more accurate simulation calculation method is obtained.The experimental prototype is built for testing.The simulation and experimental results show that the designed transformer has stable output,small leakage inductance and high efficiency,and improves the performance of the transmitter.(3)The principle analysis of htem system,the calculation of magnetic induction intensity around the transmitting coil and the structural design of compensation coil.By simplifying Maxwell’s equations,the electromagnetic wave propagates underground in the form of diffusion equation.According to Biot Savart’s law,the magnetic field in the plane where the transmitting coil is located and the longitudinal magnetic field below the plane are analyzed and calculated.Combined with the offset effect of the compensation coil and its influence on the emitted magnetic moment,the optimal concentric compensation coil structure is selected.(4)Joint experiment of circuit and coil.The topology of transmitting coil and full bridge circuit is simplified to RLC series resonant circuit.After the reliability of circuit and coil is verified by modeling and simulation,the designed coil is hoisted and tested in the test base.The peak value of transmitting half sinusoidal current waveform reaches800 A,and the transmitting magnetic moment also meets the requirements of the project,which lays a good foundation for the research and design of transmitting equipment in the future.