Babinet’s principle in the Fresnel regime studied using ultrasound

Abstract

The diffraction of ultrasound by a circular disk and an aperture of the same size have been investigated as a demonstration of Babinet"s principle in the Fresnel regime. The amplitude and the phase of diffracted ultrasonic waves have been measured and a graphical treatment of the results is performed. The results verify Babinet"s principle. It is also found that the incident wave is indeed /2 behind the phase of the wave passing through on the central axis of a circular aperture. This paradox has previously been regarded as a defect of Fresnel"s theory.