Abstract: A sonar projector having a pair of opposed oscillating pistons driven by an electromagnetic assembly is provided with reduced weight and high power by forming the electromagnetic assembly with a permanent magnet structure consisting of two coaxial longitudinally juxtaposed members each having permanent magnets radially poled oppositely to the permanent magnets of the other coaxial member, each of the permanent magnets of one coaxial member forming a series magnetic circuit with one of the permanent magnets of the other coaxial member. As a result of this arrangement, the amount of iron required for pole pieces of the electromagnetic assembly is reduced without reducing power. Furthermore, the size or volume is also reduced as compared to an equivalent projector.

Abstract: A sonar projector having a pair of opposed oscillating pistons driven by an electromagnetic assembly is rendered capable of operating at reduced resonant frequency by providing liquid mass loading for the pistons. The mass loading is achieved by utilizing a structure which constricts a body of liquid on one side of the piston. The constricted liquid may be sea water or liquid sealed within the body of the unit. In accordance with a further aspect of the invention, a seal assembly is provided for the moving pistons which not only provides a sealing function but which also acts to radially center the pistons and to provide an axially directed restoring force thereto during piston oscillation. The electromagnetic assembly, in accordance with still a further aspect of the invention, is formed with a permanent magnet structure arranged in a cylindrical configuration with the opposed pistons on opposite axial ends thereof to reduce magnetic leakage losses.

Abstract: A sonar projector having a pair of opposed oscillating pistons driven by an electromagnetic assembly is rendered capable of operating at reduced resonant frequency by providing liquid mass loading for the pistons. The mass loading is achieved by utilizing a structure which constricts a body of liquid on one side of the piston. The constricted liquid may be sea water or a liquid sealed within the body of the unit. In accordance with a further aspect of the invention, a seal assembly is provided for the moving pistons which not only provides a sealing function but which also acts to radially center the pistons and to provide an axially directed restoring force thereto during piston oscillation. The electromagnetic assembly, in accordance with still a further aspect of the invention, is formed with a permanent magnet structure arranged in a cylindrical configuration with the opposed pistons on opposite axial ends thereof to reduce magnetic leakage losses.