What primarily determines the behavior of a pulse at a boundary?

The behavior of a pulse at a boundary is primarily determined by the angle of incidence. This concept relates to how sound waves interact with different media at their boundaries. When an ultrasound pulse reaches a boundary at a certain angle, it can either reflect or refract based on that angle. The angle of incidence plays a significant role in determining the proportion of the wave that is reflected back into the original medium versus the amount that transmits into the second medium, according to Snell's Law.

If the angle is perpendicular to the interface, the behavior of the pulse can be quite different compared to an oblique angle. For instance, at a 90-degree incidence, the majority of the wave will transmit, while at oblique angles, there can be significant reflection and refraction occurring. Additionally, the mismatch of acoustic impedance between the two media also affects how the sound waves behave at the boundary, which is indirectly influenced by the angle of incidence.

While factors such as frequency and the type of media are also important in determining how sound propagates and interacts at boundaries, the angle of incidence is the primary factor that dictates the reflection and transmission characteristics of the pulse at a given interface.