Through-transmission ultrasound detection across liquid–liquid interfaces

An investigation of through-transmission ultrasound across extended liquid–liquid interfaces is presented, where aperture-level phase cancellation produces apparent sensitivity loss. The results demonstrate a practical understanding of ultrasound wave propagation on the oil–water interface for process monitoring in industrial vessels. A numerical model using a matrix formulation of the mesh-free method of fundamental solutions (MFS) is constructed and validated against finite-element method (FEM) simulations and benchtop measurements. Phase cancellation at the phase-sensitive receiving aperture is quantified and exploited to produce a signature for detecting liquid–liquid interfaces. The formulation uses boundary collocation to represent the interface, capturing interference-driven energy redistribution and viscous losses. An energy-weighted line-source excitation preserves power consistency across the aperture. The model reproduces the measured dependence of transmission on beam depth and interface height and supports the parametric study through reusable system matrices.