Waveguide
The frequency of the wave also affects the size of a waveguide. Each waveguide has a cutoff wavelength that is determined by its size. It can not be used for waves that have a greater wavelength than its cutoff value. For example, an optical fiber that guides light can not be used for microwaves because they have a much larger wavelength. Some naturally occurring structures can also act as waveguides. The SOFAR channel layer in the ocean can guide the sound of whale song across very large distances.