Tomsk State University. Physical Department.
Laboratory of training physics experiment
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Fresnel  Zones   Обратно  Далее  
. Using microwave technology enables to demonstrate wave phenomena on the big-sized installations. In our laboratory we have created amplitude and phase plates for seven central Fresnel zones calculated on 32 mm long. Additionally, we have elaborated a demonstrational tasks set with the parts of central Fresnel zones which has the radius of 12.67 cm. The experiments can be easily explained with the help of the vibration curve.

Photo 1
Holes and targets symmetric about a line which connects the source and receiver of waves are usually used by performing an ordinary diffraction demonstration. But there is a nonstandard objective when the spherical wave front is blocked with a semicircle-formed target which obstructs a half of central Fresnel zone (photo 1). The zero signal is observed in the point of sight due to its effect.

Photo 2
Photo 3
Photo 4

When closing a quarter of the central zone by the quadrant from plexiglas or paraffin having chosen the thickness to bring a propagation difference equal to a half-wave, we obtain a zero amplitude of reception as well (photo 2).
The target represented on the following figure (photo 3), will not change the reception amplitude of completely open front. When 3/4 parts of the central zone are blocked (photo 4), the amplitude will be doubled.
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