Tunable III-type flextensional transducer

The invention relates to a tunable III-type flextensional transducer which comprises a piezoelectric ceramic crystal stack, a cable base and a shell, the shell comprises a metal front cover plate, a metal rear cover plate, a plurality of bending beams and supporting beams with the same number, the middle part of each bending beam is of an arc-shaped structure and has deformation in the bending direction/back to the bending direction, the supporting beams are in a straight strip shape, and the piezoelectric ceramic crystal stack is connected with the cable base. The multiple bent beams jointly define an hourglass-shaped shell with the middle recessed inwards in the circumferential direction, the hourglass-shaped shell is in a shell shape with the cross section area gradually increased from the middle to the two ends, and the front cover plate and the rear cover plate are located at end openings of the two ends of the shell respectively and matched with the end openings of the two ends of the shell. According t