On parametric source aperture factors

TLDR: In this paper, the authors discussed the importance of the aperture size in determining the off-axis behavior of a spherically spreading, conical primary beam of finite initial aperture.

Abstract: It is well known that the beam pattern of a parametric acoustic source whose difference frequency is generated largely within the nearfield of the primary beam includes a multiplicative aperture factor that can be important at large angles when ka≳1 (k is the difference frequency wave number, a is the aperture radius). Not so well known, however, is the fact that the same aperture factor arises in the case of a spherically spreading, conical primary beam of finite initial aperture. The importance of the aperture size in determining the off‐axis behavior of parametric sources is discussed.Subject Classification: [43]25.35; [43]20.30; [43]30.75.