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In the field of acoustics, a parametric array is a nonlinear transduction mechanism that generates narrow, nearly side lobe-free beams of low frequency sound, through the mixing and interaction of high frequency sound waves, effectively overcoming the diffraction limit (a kind of spatial 'uncertainty principle') associated with linear acoustics. The main side lobe-free beam of low frequency sound is created as a result of nonlinear mixing of two high frequency sound beams at their difference frequency. Parametric arrays can be formed in water, air,〔(Experimental study of a saturated parametric array in air )〕 and earth materials/rock.〔(Finite amplitude wave studies in earth materials )〕〔(Parametric Beam Formation in Rock )〕 == History == Priority for discovery and explanation of the parametric array owes to Peter J. Westervelt,〔(Professor Peter Westervelt and the parametric array )〕 winner of the Lord Rayleigh Medal〔(Institute of Acoustics - Medals & Awards Programme )〕 (currently Professor Emeritus at Brown University), although important experimental work was contemporaneously underway in the former Soviet Union.〔 According to Muir (p. 554 ) and Albers (), 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. According to Albers (), he (Westervelt) there first observed an accidental generation of low frequency sound ''in air'' by Captain H.J. Round (British pioneer of the superheterodyne receiver) via the parametric array mechanism. The phenomenon of the parametric array,seen first experimentally by Westervelt in the 1950s, was later explained theoretically in 1960, at a meeting of the Acoustical Society of America. A few years after this, a full paper () was published as an extension of Westervelt's classic work on the nonlinear Scattering of Sound by Sound, as described in (). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Parametric array」の詳細全文を読む スポンサード リンク
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