Piezo buzzer is an electronic trwnsductr used for produce sounds. The buzzer had an outer case with two pins. Inside the buzzer it has piezo element, cosiscon of a ceramic disc surrounded by metal disc.
The working principle is, whenever an electric potential is applied across a piezoelectric material, a pressure variation is generated. These pressure variation, push and pull the internal crystals in the piezo diec. The continuous push and pull operations generates a sound wave.
When we apply AC Voltage it deforms and produce sounds as proportional with Frequency of AC signal.