Principle of piezoelectric buzzer: Piezoelectric sounders is mainly composed of multivibrator, piezoceramic element, impedance matcher, resonance box, shell, etc. Some piezoelectric buzzers are also equipped with light-emitting diodes on the shell. Multivibrator consists of transistor or integrated circuit. When the power is turned on (1.5 ~ 15V DC working voltage), the multivibrator vibrates and outputs an audio signal of 100 ~ 500Hz. The impedance matcher pushes the piezo beeper to sound. The piezoelectric buzzer is made of lead zirconate titanate or lead magnesium niobate piezoelectric ceramic materials. Silver electrodes are plated on both sides of the ceramic sheet. After polarization and aging treatment, they are bonded with brass sheet or stainless steel sheet.