# Complex amplitude of the primary wave

## Description

The Huygens–Fresnel principle is a method of analysis applied to problems of wave propagation both in the far-field limit and in near-field diffraction.

If a point source located at a point, is vibrating at a frequency f, the disturbance may be described by a complex variable Uo known as the complex amplitude. The disturbance produces a spherical wave with wavelength λ, and wave number k = 2π/λ. The complex amplitude of the primary wave at an arbitrary point located at some distance from the source is related to the distance λ and the wave number k.

(The wavenumber is the spatial frequency of a wave. It is the number of waves that exist over a specified distance).

## Variables

U_{r0} | Complex amplitude at a distance r0 (dimensionless) |

U_{0} | Complex amplitude at source (m) |

e | e |

i | Imaginary unit |

π | pi |

λ | Wavelength (m) |

r_{0} | Distance from the source (m) |