Aaltomuunnos

Aaltomuunnos, in physics and engineering, refers to the transformation of a wave from one propagation mode to another when it encounters an interface between media with different properties. This phenomenon occurs whenever boundary conditions at the interface couple different wave types, leading to reflected and transmitted waves that may belong to different modes than the incident wave. Common examples include elastic waves in solids, where P-waves and S-waves convert at boundaries, and light in anisotropic or layered media, where polarization or mode content can change upon refraction or transmission.

In seismology, a sharp boundary between geological layers can generate P-to-S, S-to-P, SH to SV conversions, depending on incidence angle and material properties like density and elastic moduli. The amplitudes of the generated modes are described by equations such as the Zoeppritz equations, and mode conversions are a major source of information in seismic imaging.

In optics, birefringent crystals or stratified media can produce polarization-mode conversion; ordinary and extraordinary rays in anisotropic crystals travel at different speeds, leading to transformation of polarization state. In guided-wave and plasmonic systems, mode coupling occurs when the waveguide or surface supports multiple modes, allowing energy transfer between them.

The extent and efficiency of aaltomuunnos depend on impedance contrasts, incidence angle, frequency (dispersion), surface roughness, and anisotropy. It is exploited in seismic exploration, nondestructive testing, optical modulators, and waveguide design. The term in Finnish literally translates to wave transformation or wave-mode conversion.