Fresnel number [SEP] named after
Fresnel number
The Fresnel number ("F"), named after the physicist Augustin-Jean Fresnel, is a dimensionless number occurring in optics, in particular in scalar diffraction theory.
For an electromagnetic wave passing through an aperture and hitting a screen, the Fresnel number "F" is defined as
where 
The Fresnel number is a useful concept in physical optics. Conceptually, it is the number of half-period zones in the wavefront amplitude, counted from the center to the edge of the aperture,
Fraunhofer distance
The Fraunhofer distance, named after Joseph von Fraunhofer, is the value of:
where D is the largest dimension of the radiator (in the case of a magnetic loop antenna, the diameter) and formula_2 is the wavelength of the radio wave. This distance provides the limit between the near and far field.
See also.
- Fresnel number
- Fresnel diffraction and Fraunhofer diffraction
- Antenna measurement