Diffraction phenomena in acoustic fields of ultrasonic frequency in air have been photographed by schlieren technique and by shadow methods employing a spark of extremely short duration. Variations of intensity in the field are observed in the immediate vicinity of apertures and obstacles as indicated by theoretical treatment of the problem in a more rigorous manner than that of Kirchhoff.
J. C. HUBBARD, I. F. ZARTMAN, and C. R. LARKIN, "Optical Study of Acoustic Fields Near Diffracting Edges," J. Opt. Soc. Am. 37, 832-834 (1947)