# What is Fresnel zone diffraction?

## What is Fresnel zone diffraction?

It is used to calculate the diffraction pattern created by waves passing through an aperture or around an object, when viewed from relatively close to the object. In contrast the diffraction pattern in the far field region is given by the Fraunhofer diffraction equation.

Why does Fresnel diffraction occur?

Fresnel diffraction occurs when either the distance from the source to the obstruction or the distance from the obstruction to the screen is comparable to the size of the obstruction. � These comparable distances and sizes lead to unique diffractive behavior.

### How is zone plate construction?

Unlike lenses or curved mirrors, zone plates use diffraction instead of refraction or reflection. A zone plate consists of a set of concentric rings, known as Fresnel zones, which alternate between being opaque and transparent. Light hitting the zone plate will diffract around the opaque zones.

What is half period?

According to Fresnel’s the entire wave front can be divided into a large number of parts of zones which are known as Fresnel’s half period zones (HPZ’s). i.e. For large number of HPZ, the amplitude of light at point P due to whole wave front is half the amplitude due to first HPZ.

#### Which zone of Fresnel has strongest?

Zone 1
The Fresnel zone is a 3-D cylindrical ellipse shape (like a cigar or sausage) and is made up of multiple zones, Zone 1 being the strongest area for signal strength, Zone 2 being the weaker, Zone 3 being weaker still and so on.

Why is Fresnel zone important?

The Fresnel Zone is the area around the visual line-of-sight that radio waves spread out into after they leave the antenna. You want a clear line of sight to maintain signal strength, especially for 2.4 GHz wireless systems. This is because 2.4 GHz waves are absorbed by water, like the water found in trees.

## What is Huygens principle?

7. Huygens’ principle states that every point on a wave front may be considered as a source of secondary waves. The word interference is used to describe the superposition of two waves, whereas diffraction is interference produced by several waves.

What type of wavefront is needed for Fresnel diffraction?

The diffraction pattern does not change. Explanation: In Fresnel Diffraction, the interference takes place between the light waves reaching a point from different parts of the same wavefront. Thus, the incident wavefront is spherical or cylindrical.

### What are half period zones?

That is why the zone are called fresnel’s half period zone. The area of the first circle (radius = r1) is called ‘first half period zone’. The annular area between first and second circle is known as a second half period zone and so on. Thus, the annular area between (n-1)nt and nth circle is the nth half period zone.

What is difference between zone plate and convex lens?

➢ A convex lens has only one focus while a zone plate has a number of foci. amplitude from successive zones will help each other and the intensity of the image approaches that for an equivalent lens.