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A Fresnel lens (/ ˈ f r eɪ n ɛ l,-n əl / FRAY-nel, -nəl; / ˈ f r ɛ n ɛ l,-əl / FREN-el, -əl; or / f r eɪ ˈ n ɛ l / fray-NEL [1]) is a type of composite compact lens which reduces the amount of material required compared to a conventional lens by dividing the lens into a set of concentric annular sections.
Unlike lenses or curved mirrors, zone plates use diffraction instead of refraction or reflection. Based on analysis by French physicist Augustin-Jean Fresnel, they are sometimes called Fresnel zone plates in his honor. The zone plate's focusing ability is an extension of the Arago spot phenomenon caused by diffraction from an opaque disc. [2]
Fresnel zone: D is the distance between the transmitter and the receiver; r is the radius of the first Fresnel zone (n=1) at point P. P is d1 away from the transmitter, and d2 away from the receiver. The concept of Fresnel zone clearance may be used to analyze interference by obstacles near the path of a radio beam.
Zoned lens - Microwave lenses, especially short wavelength designs, tend to be excessively thick. This increases weight, bulk, and power losses in dielectric lenses. To reduce thickness, lenses are often made with a zoned geometry, similar to a Fresnel lens. The lens is cut down to a uniform thickness in concentric annular (circular) steps ...
Variables used in the Fresnel equations. In the diagram on the right, an incident plane wave in the direction of the ray IO strikes the interface between two media of refractive indices n 1 and n 2 at point O. Part of the wave is reflected in the direction OR, and part refracted in the direction OT.
This means the lens's F-number value is fixed to the overall designed focal ratio of the optical system (the diameter of the primary mirror divided into the focal length). The inability to stop down the lens results in the catadioptric lens having a short depth of field.
A lens with a different shape forms the answer to Mrs. Miniver's problem, on finding a lens with half the area of the union of the two circles. Lenses are used to define beta skeletons, geometric graphs defined on a set of points by connecting pairs of points by an edge whenever a lens determined by the two points is empty.
The formulae and algorithms for predicting the radiation pattern of an offset Fresnel lens antenna are presented in, [8] where some experimental results are also reported. Although a simple Fresnel lens antenna has low efficiency, it serves as a very attractive indoor candidate when a large window or an electrically transparent wall is available.