In physics, Babinet's principle[1] states that the diffraction pattern from an opaque body is identical to that from a hole of the same size and shape except for the overall forward beam intensity.
In places where the undisturbed beam would not have reached, this means that the radiation patterns caused by B and B' must be opposite in phase, but equal in amplitude.
For instance, the size of red blood cells can be found by comparing their diffraction pattern with an array of small holes.
The principle is most often used in optics but it is also true for other forms of electromagnetic radiation and is, in fact, a general theorem[citation needed] of diffraction in wave mechanics.
Babinet's principle finds most use in its ability to detect equivalence in size and shape.
The slit can be made either by using a laser printer or photocopier to print onto clear plastic film or by using a pin to draw a line on a piece of glass that has been smoked over a candle flame.
A consequence of the principle states that where Zmetal and Zslot are input impedances of the metal and slot radiating pieces, and