A novel bipolar half-sine current transmitter for helicopter transient electromagnetic surveying

As a core component of a Helicopter Transient Electromagnetic (HTEM) system, the current transmitter determines the primary field. In this paper, a novel bipolar half-sine current transmitter is proposed and analyzed in detail. The Non-dominated Sorting Genetic Algorithm II (NSGA-II) and COMSOL electromagnetic simulation software are employed to optimize the parameters and structure of the pulsed current-generating coil to minimize the weight and maximize the dipole moment under a specified power. A two-stage resonant pulsed current source circuit is designed to reduce conduction losses and improve transmission efficiency. The charging resonant circuit and the transmitting resonant circuit alternately operate to generate a bipolar half-sine waveform pulsed current with an adjustable peak value. A damping resistor is used to suppress turn-off overshoot of the pulsed current. A prototype is constructed and tested in a field experiment. The transmitting moments of the HTEM system exceed 1 MAm² at all three base frequencies, with the pulsed current-generating coil consuming 2.8 kW of power and weighing only 229.2 kg. The experimental results closely align with the theoretical calculations. The field exploration results confirm that the proposed current transmitter generates high-quality current waveforms and has high stability, significantly enhancing the HTEM system's detection capability.