 Parametric arrays can be formed in water, air, and earth materials/rock.Priority for discovery and explanation of the parametric array owes to Peter J. Westervelt, winner of the Lord Rayleigh Medal (currently Professor Emeritus at Brown University), although important experimental work was contemporaneously underway in the former Soviet Union.According to Muir [16, p. 554] and Albers [17], the concept for the parametric array occurred to Dr. Westervelt while he was stationed at the London, England, branch office of the Office of Naval Research in 1951.