Envelope (waves)


![Dispersion relation ω=ω(k) for some waves corresponding to lattice vibrations in GaAs.[6]](/uploads/202502/20/Phonon_dispersion_relations_in_GaAs2841.png)
![Electron probabilities in lowest two quantum states of a 160Ǻ GaAs quantum well in a GaAs-GaAlAs heterostructure as calculated from envelope functions.[8]](/uploads/202502/20/Electron_probabilities_in_GaAs_quantum_well2841.png)
In physics and engineering, the envelope function of an oscillating signal is a smooth curve outlining its extremes. The envelope thus generalizes the concept of a constant amplitude. The figure illustrates a modulated sine wave varying between an upper and a lower envelope. The envelope function may be a function of time, space, angle, or indeed of any variable.