AIn the field of [[acoustics]], a '''parametric array''' is a nonlinear [[transducer|transduction]] mechanism that generates narrow, nearly sidelobe[[side lobe]]-free beams of low frequency sound, through the mixing and interaction of high frequency [[sound wave]]s, effectively overcoming the [[diffraction limit]] (a kind of spatial 'uncertainty principle') associated with linear acoustics.<ref>{{cite book| last=Beyer| first=Robert T| title=Nonlinear Acoustics| chapter=Preface to the Original Edition| url=http://asa.aip.org/books/nonlinear.html#Preface1}}</ref> Parametric arrays can be formed in water,<ref name=nonlinear-underwater-acoustics-book>{{cite book| last1=Novikov| first1=B. K.| last2=Rudenko| first=O. V.| last3=Timoshenko| first3=V. I.| others= Translated by Robert T. Beyer| title=Nonlinear Underwater Acoustics| url=http://asa.aip.org/books/nonuw.html}}</ref> air,<ref>[http://dx.doi.org/10.1121/1.384959 Experimental study of a saturated parametric array in air]</ref> and earth materials/rock.<ref>[http://dx.doi.org/10.1121/1.403453 Finite amplitude wave studies in earth materials]</ref><ref>[http://www.lanl.gov/orgs/ees/ees11/geophysics/nonlinear/pubs/parabeam.html Parametric Beam Formation in Rock]</ref>
