A bipolar pulsed current excitation ERT system with 10 kΩ high-load capability for real-time gas–liquid two-phase flow imaging in underwater ramjet engine ducts

This article presents a dedicated electrical resistance tomography (ERT) system for real-time visualization of gas–liquid two-phase flow patterns in the working ducts of underwater ramjet engines. To overcome the bottlenecks of limited load capacity and low imaging speed in conventional sinusoidal-excited ERT, a bipolar-pulsed-current excitation scheme controlled by a field-programmable gate array (FPGA) is proposed. A high-load constant-current source is constructed using LM334 combined with J310 FET, extending the measurable impedance to 10 kΩ, which is five times higher than traditional systems. Based on Maxwell’s equations, a sensitivity-field mathematical model is established to reveal the mapping relationship between the conductivity distribution and the boundary voltage. The hardware architecture eliminates low-pass filters and phase-sensitive demodulation modules, enabling direct DC-component voltage sampling. Calibration experiments with a 10 kΩ precision resistor show that the relative measurement error is below 5% in 5–20 kHz. Channel consistency tests yield maximum absolute relative deviations of 4.57% for pure water and 5.72% for brine, verifying robustness against moderate conductivity variations. The system achieves 51 frames per second (fps) imaging speed using a linear back-projection algorithm. The proposed system can be directly applied to the online monitoring of gas–liquid two-phase flow in underwater propulsion ducts, filling the gap in high-speed ERT for high-impedance, high-interference underwater environments.