A Time-Domain Electromagnetic Transmitter with Great Power and Large Current by Using a Closed-Loop Phase Shifting Control Strategy

A time-domain electromagnetic transmitter（TDET） with great power and large current was designed by using a closed-loop phase shifting control strategy. A clamping voltage source circuit was applied in this system to improve the falling edge of emission current and shorten the turn-off time. The simulated results showed that this TDET exhibited the advantages including a large current, strong capability for rapid turn-off, stably output voltage, preferably dynamic performance, a widely adjustable range in transmitting voltage, accurate measurement precision.

Snubber Circuit for Marine Controlled-Source Electromagnetic Transmitter

A high-power marine controlled-source electromagnetic transmitter(HP-MCSET)transmits a highfrequency conversion current on the sea floor.Some problems exist when the direct-current to alternating-current(DC-AC)launch bridge(LB)is used in the marine controlled-source electromagnetic transmitter(MCSET).There is a high voltage peak in the LB when the insulated gate bipolar transistor(IGBT)is turned on and off.In some cases,the voltage stress of the IGBT can be exceeded,which may cause IGBT damage.Because the rise of the current steepness is relatively low and the output voltage has a voltage peak in the LB,a snubber circuit is added to the IGBT to suppress the voltage peak to improve the output current and voltage waveform.The suppression of the voltage peaks is analyzed and compared for several groups of snubber circuits.To meet the performance requirements of the MCSET,the optimal snubber circuit is selected to effectively suppress the voltage peaks at an output current of 1 kA.This method is verified by using a 70 kW MCSET and the experimental waveforms are provided.The simulation of the inductance obstruction load in seawater is necessary to determine the conditions for actual marine environment experiments.

A transparent electromagnetic-shielding film based on one-dimensional metal–dielectric periodic structures

In this study, we designed and fabricated optical materials consisting of alternating ITO and Ag layers. This approach is considered to be a promising way to obtain a light-weight, ultrathin and transparent shielding medium, which not only transmits visible light but also inhibits the transmission of microwaves, despite the fact that the total thickness of the Ag film is much larger than the skin depth in the visible range and less than that in the microwave region. Theoretical results suggest that a high dielectric/metal thickness ratio can enhance the broadband and improve the transmittance in the optical range. Accordingly, the central wavelength was found to be red-shifted with increasing dielectric/metal thickness ratio. A physical mechanism behind the controlling transmission of visible light is also proposed. Meanwhile, the electromagnetic shielding effectiveness of the prepared structures was found to exceed 40 dB in the range from 0.1 GHz to 18 GHz, even reaching up to 70 dB at 0.1 GHz, which is far higher than that of a single ITO film of the same thickness.