Abstract:  This paper derives the amplitude relationship between the incident and reflected waves of ultrasonic longitudinal waves at the interface of different media based on the wave equation. The amplitude is related to the acoustic impedance of the two media and the incident angle. Using COMSOL, an ultrasonic longitudinal wave detection model is established to perform finite element simulations of the longitudinal wave propagation characteristics at the interface, and experiments are designed for verification. In the case of no grazing incidence, when an ultrasonic longitudinal wave is incident from a high-impedance (dense) medium to a low-impedance (sparse) medium, An abrupt phase shift of π occurs at the interface relative to the incident wave, resulting in a half-wave loss phenomenon. Conversely, when the interface is between two media with similar impedances, the reflected wave and the incident wave are in phase with no half-wave loss. This paper discusses the half-wave loss phenomenon of ultrasonic longitudinal waves at different media interfaces from theoretical, simulation, and experimental perspectives, providing significant theoretical support and experimental evidence for the application of ultrasonic longitudinal waves in non-destructive testing. It also offers a valuable supplement to relevant textbooks and teaching cases in industrial applications.

Key words: ultrasonic longitudinal wave, half-wave loss, finite element simulation