A piezoelectric actuator includes a square suspension plate, an outer frame, a plurality of brackets and a square piezoelectric ceramic plate. The outer frame is arranged around the suspension plate. A second surface of the outer frame and a second surface of the suspension plate are coplanar with each other. Each of the plurality of brackets has two ends, a first end is perpendicular to and connected with the suspension plate, and a second end is perpendicular to and connected with the outer frame for elastically supporting the suspension plate. Each bracket has a length in a range between 1.22 mm and 1.45 mm and a width in a range between 0.2 mm and 0.6 mm. A length of the piezoelectric ceramic plate is not larger than a length of the suspension plate. The piezoelectric ceramic plate is attached on a first surface of the suspension plate.