Microonde evanescenti generate per diffrazione

Riassunto

È stata verificata sperimentalmente la presenza di onde evanescenti nella diffrazione, valendosi di onde centimetriche e di reticoli a striscie metalliche. La costante di attenuazione trovata è quella prevista dalla teoria.

Summary

A direct experimental proof has been given, concerning the existence of surface waves generated by diffraction. Microwaves of 32 mm wavelength have been used. The diffraction screen was a grating made out of metal strips. The period of the grating was so chosen that all the diffracted waves, excepting the central one, were surface waves attenuated along the direction perpendicular to the grating. One of the first order waves was transformed into an ordinary wave by refraction on a paraffin prism, according to Fig. 1, and could be revealed by means of a receiver. Plotting the logarithm of the power carried by the wave as a function of the distance of the prism from the grating, a straight line has been obtained (Fig. 2), whose angular coefficient equals the attenuation constant of the surface wave, as predicted by theory.