Radiation from Circular Pistons of Elliptical Profile

Abstract

While extensive information is available on flat pistons and on spherical radiators, no data have been given in the literature for the intermediate case of convex circular pistons of elliptical profile. In order to fill this gap, this paper presents information on the radiation loading and on the near and far field of such pistons. For the case of a free piston it is found that at small ka (where 2a is the diameter or major axis) the reactance decreases with increasing thickness (minor axis), while the resistance increases at small ka and decreases at large ka with increasing thickness. In the intermediate ka-region, that is, when the wavelength in the fluid is of the order of magnitude of the dimensions of the piston, the dependence of the impedance on the thickness is more complicated. For the case of a piston in an infinite baffle the behavior of the reactance is similar to that for the free pistons. The resistance however is independent of the thickness in the limit of small ka and decreases with increasing thickness at larger ka. The effect of flexure on the impedance is briefly considered for the case of the free piston.