A piezoelectric diaphragm is a device for which a piezoelectric element with electrodes is bonded to a metal plate such as brass or nickel.
Piezoelectric sound components necessary have piezoelectric diaphragms.
This is a simple structure which a piezoelectric ceramic is adhered to a metal plate of brass or nickel-alloy.
When a voltage is applied across the piezoelectric ceramics, it stretches in its plane. When a voltage is applied to piezoelectric diaphragm, as the metal plate does not stretch, it bends as shown in Fig (a).
When the polarity of the applied voltage is reversed, the piezoelectric ceramics shrinks and the metal plate bends toward the opposite side as shown in Fig (b).
When the direction of applied voltage changes alternately, the state of Fig (a) and Fig (b) is repeated as shown in Fig (c), producing sound waves in the air.
You can get higher sound by using the resonance effect when a product is case type.
(1) The peak of sound pressure level of diaphragm
(2) The peak of sound pressure level of amplified in a case
(3) 10 to 20 dB higher sound pressure level by resonance effect
By designing fosc and fcav close each other, you will get 10 to 20 dB higher sound pressure level compared to non-cased diaphragm.
A piezoelectric buzzer has a structure in which a piezoelectric diaphragm and drive circuit are embedded into a case.
A single-frequency sound is generated with the input of a DC voltage into the drive circuit. This has a single tone.
A piezoelectric sounder has a structure in which a piezoelectric diaphragm is embedded into a case.
There is no drive circuit in the product; instead, sound is generated with the input of an external AC voltage. The tone can be changed with the frequency of the AC voltage.
The scale (frequency) of a piezoelectric buzzer is determined for each product. It cannot be changed.
It is possible to change the scale (frequency) according to the frequency of the AC voltage for a piezoelectric sounder. However, the volume varies depending on the frequency.
The volume of a piezoelectric buzzer/sounder can be increased by raising the input voltage. However, please note that the input voltage of the product has a rating.