Abstract
A simple method for the visualization of ultrasonic fields is described, which requires no special material except conventional photographic paper and developer. A transducer was set in a tank filled with a dilute solution of photographic developer. A sheet of photographic paper previously exposed to light uniformly was supported in the liquid and irradiated ultrasonically. After 1 minute or so, the darkened diffracion pattern appeared gradually on the paper. Then, the paper was fixed in the usual manner. The pattern obtained by using the circular piston-like source consists of concentric circles, the radii and the number of these circles varying regularly with the distrance between the paper and the transducer. The appearance of these diffraction patterns can be explained by applying the method of the Fresnel's zones, known in physical optics, to sound diffraction problems. A detailed theoretical calculation of the sound field near the source will be described in the next paper.
