Cornu's spiral in the Fresnel regime studied using ultrasound: A phase study

TL;DR

This study uses ultrasound to experimentally visualize Cornu's spiral in the Fresnel diffraction regime, verifying Babinet's principle and phase behaviors predicted by classical diffraction theories.

Contribution

It introduces a simple ultrasound-based phase measurement technique to demonstrate Cornu's spiral and verify diffraction principles with straight-edged objects.

Findings

Ultrasound phase measurement visualizes Cornu's spiral.

Babinet's principle is experimentally verified.

Observed phase delays match theoretical predictions.

Abstract

A simple experimental technique for measuring the phase and amplitude of diffracting ultrasound wave [A. Hitachi and M. Takata, Am. J. Phys. 78, 678 (2010)] has been applied to diffracting objects with straight edges as a demonstration of the Cornu spiral. Babinet's principle is studied observing the ultrasound field behind a slit and a complementary strip obstacle and is verified directly by comparing vectors (phasors) in the complex plane. The phase of the diffracted wave observed in the geometrical shadow of the straight screen has the form of a cylindrical wave originating at the edge of the straight screen as the boundary diffraction wave proposed by Young. In addition, the incident wave has a phase delay of pi/4 behind the wave passing through on the center line of the slit, the plane of symmetry, has been observed as predicted by Huygens-Fresnel diffraction theory.