Optimized Triple-Junction Insulation Facilitating Low-Delay and Controllable Electrohydraulic Discharge Toward Underwater Acoustics

Underwater pulsed discharges are pivotal for research fields like acoustic wave generation and material processing, where improving energy efficiency and achieving precise parametric control are critical objectives. However, the performance of electrohydraulic discharge load faces challenges including large breakdown delay and jitter, complex multi-physical coupling, etc. Here, an underwater surface load utilizes carbon-foil triple-junction (TJ) points to trigger kV-level discharges and pressure waves. The optimized load offers key advantages: largely-reduced electric breakdown delay and phenomenal reproducibility in repetitive operation. This study systematically investigates the effects of current density, load length, and stored energy on discharge characteristics, acoustic performance, and bubble pulsation. Results show that increasing foil length from 5 mm to 20 mm (at 2 J) elevates the voltage peak from 0.93 kV to 1.37 kV and improves energy deposition efficiency from 1.47 J to 1.85 J. Furthermore, the acoustic performance is highly controllable: peak pressure rises with stored energy, reaching up to 43.1 kPa (corresponding to a sound pressure level of approximately 212.7 dB re 1 μPa @ 20 cm), while the discharge pressure waveform before material failure is closer to a strong shock wave. Additionally, four distinct bubble regimes are identified in varied tests: merged double bubbles, non-merging double bubbles, triple bubbles, and multi-bubbles. These findings may deepen the understanding of underwater discharge physics and demonstrate its advantages in related applications.