| Time-domain airborne electromagnetic method is a high-speed and effective geological survey method,which uses a helicopter or fixed wing aircraft as a carrier,equipped with electromagnetic transmission system and receiving system.Due to the fact that the airborne electromagnetic survey can be used for high-altitude reconnaissance to overcome the difficulties brought about by the terrain,it is widely used in geological survey,mineral resources exploration,environmental assessment,etc.At present,the international time domain aeronautical electromagnetic emission system has four kinds of emission current waveforms,including square wave,trapezoidal wave,half sine wave and triangular wave.But the transmission system can only transmit one current waveform,can't take into the advantages of other emission waveforms,To solve this problem,The transmitter circuit studied in this paper can transmit bipolar half sine wave and bipolar triangular wave,which has the advantages of two kinds of emission waveforms.This paper mainly refers to emission current parameters of the international advanced airborne electromagnetic emission system,this parameter is used as the emission current parameter standard to design the double waveform emission circuit.The design of the transmitter circuit structure mainly includes four parts,including triangular wave transmitter circuit,half sine wave transmitter circuit,isolation circuit,the transmission coil.The triangular wave transmitting circuit and the half sine wave transmitting circuit share a transmitting coil,In order to avoid the mutual influence between the two circuits,an isolation circuit is added between the transmitting coil and the transmitting circuit.The half sine wave transmitting circuit utilizes the series resonant principle,the resonant capacitor in the circuit resonates with the transmitting coil to produce a sine wave,the half-sine wave transmitter circuit requires a relatively low supply voltage,in order to be compatible with this design,the triangular wave transmitter circuit added a boost circuit,the boost circuit charges the storage capacitor to raise its voltage,because the capacitance is large,the power of the triangular wave firing circuit is small,fully charged energy storage capacitor can be regarded as high voltage constant voltage high power supply,using this power supply to power the transmitter coil,it can produce the triangular wave with a high linearity and symmetry.In order to ensure the safe and stable operation of the transmitting circuit,the transmit circuit adds the protection circuit and the eliminating overshoot circuit.this paper first uses Simulink software of Matlab to simulate the transmission circuit to verify its feasibility,then,actually build circuit and test the whole circuit,according to the test results,this paper improves and optimizes the circuit parameters to make the transmission current waveform quality higher.This paper describes the process and problem of designing the transmitting circuit,in this paper,the parameters of the whole emission current are tested.test results have reached the design requirements,the actual measured half sine wave current peak is 2000 A,the maximum output magnetic moment is 648000 Am2,the pulse width is 4ms,triangular wave current peak is 200 A,the maximum output magnetic moment is 64800 Am2,the pulse width is 1.95 ms,the overall transmission frequency is 12.5Hz,the firing frequency can be adjusted.In the aeronautical simulation laboratory for the suspension experiment,the transmitter circuit and the receiver were debugged online,The receiving system collects an on-time signal,its noise amplitude is comparable to that of the magnetic field waveform attenuation curve received by the bipolar trapezoidal CHTEM-I system in the Hami field flight experiment in Xinjiang,so the dual-waveform launch system can be on-time acquisition.Finally,this paper summarizes the experimental work,and gives some suggestions for the next step for the shortcomings of the transmitter circuit and the system. |
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