A piezoelectric actuator includes a suspension plate, an outer frame, at least one bracket and a piezoelectric ceramic plate. The suspension plate is a square structure. The length of the suspension plate is in a range between 7.5 mm and 12 mm, and the suspension plate is permitted to undergo a curvy vibration from a middle portion to a periphery portion. The outer frame is arranged around the suspension plate. The at least one bracket is connected between the suspension plate and the outer frame for elastically supporting the suspension plate. The piezoelectric ceramic plate is a square structure and has a length not larger than a length of the suspension plate. The piezoelectric ceramic plate is attached on a first surface of the suspension plate. When a voltage is applied to the piezoelectric ceramic plate, the suspension plate is driven to undergo the curvy vibration.