What are the formulas for transmission lines?

For non-normal incidence (at an angle), a phenomenon known as mode conversion occurs. Longitudinal waves (P-waves) are converted to transverse waves (S-waves) and vice versa. In this case, the expressions for the reflection and transmission coefficients are found by applying appropriate boundary conditions to the wave equation, a topic beyond the scope of this article. The resulting formulas, first determined at the beginning of the 20th century, are known as the Zoeppritz equations.