Complex amplitude of the primary wave
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).
|Complex amplitude at a distance r0 (dimensionless)
|Complex amplitude at source (m)
|Distance from the source (m)