A spherical cap radiator is one of the important parts of an underwater wide-beam imaging system.The back radiation of a traditional spherical cap radiator,which is composed of a vibrating cap and a rigid baffle,is strong and its far-field directivity function may fluctuate in big amplitude in the vicinity of the polar axis.These shortcomings complicate the processing of the reflective waves received for imaging the targets.In this study,the back radiation is weakened by adding an acoustic soft material belt between the vibrating cap and the rigid baffle.And the fluctuation mentioned above is lowered remarkably by dividing the spherical cap radiator into many annuluses and a relatively smaller spherical cap,and by controlling the phase retardations of all elements appropriately.Furthermore,the numerical experiments are carried out by the finite element method(FEM) to prove the validity of the above methods.
