The acoustic back-scattering cross sections of short cylinders

Although formulae are available for the acoustic back-scattering cross sections of short cylinders, the computations are very laborious, except in special cases. For this reason, an empirical approach is adopted. Measurements were made on short cylinders immersed in water, using a method previously shown to be accurate. The cylinders had radii between 0.01λ and 0.5λ and lengths from 0.2λ to 10λ and were made from the following elastic materials (of various amplitude reflectivities); rubber (11%), nylon (35.3%), Perspex (36.5%) and copper (93%). These readings are amalgamated with those of prior work and with new calculations. Two particular cases can be applied to the calculation of the echo back-scattered by a fish; (i) the cross section of a perfectly reflecting cylinder and (ii) that of a fishbone cylinder (reflectivity 26%) which is deduced by interpolation since it would have been too difficult to work directly with this material.