Applied Underwater Acoustics

5.2. Scattering From Point-Like Objects

An object may be said to be perfectly engulfed by an acoustic beam, when all object dimensions are smaller than the first Fresnel zone of the beam. The first Fresnel zone forms the central part, with the same sign of the phase, around the acoustic axis of the diffraction patterns of a beam transmitted by a plane, circular transducer, for instance. Single objects, such as, solid or elastic spheres and other canonically shaped objects, bubbles, single fish, underwater vehicles, and mines may be smaller than the first Fresnel zone and form point-like objects.

5.2.1. Single Objects

5.2.1.1. Rigid and Elastic Spheres

When a rigid sphere with radius, a {unit: m}, is ensonified by a high-frequency plane acoustic wave, ...