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Introduction to the structure and principle of piezoelectric buzzer

The piezoelectric buzzer is a piezoelectric ceramic piece that is pressed by a high pressure and adhered to a vibrating metal piece. When an AC voltage is applied, mechanical deformation stretches and contracts due to the piezoelectric effect, and this characteristic is used to vibrate the metal piece to make an audible sound.
The piezoelectric buzzer is divided into a feedback buzzer (self-excited) and a non-return buzzer (external excitation). When the feedback buzzer is matched with the positive feedback oscillation circuit, a single tone with the same frequency as the resonant cavity is generated; and the non-returned buzzer can be combined with an external oscillation circuit to select any frequency to emit sound.

The following are the two ways to fix the piezoelectric buzzer:

a. Peripheral support method – the outer edge of the buzzer is fixed in the resonant cavity, generally no feedback buzzer is used, and the buzzer must match the frequency of the resonant cavity to have a higher sound pressure output, and The push signal is generated by the external oscillating circuit to make the buzzer sound.
b. Node Support Method – The buzzer is fixed in a ring structure of the same size as the diameter of the ceramic piece. If the resonant cavity is well designed and matched with the correct frequency feedback buzzer and positive feedback circuit, it will produce a large sound pressure and the correct frequency.

How to check the buzzer? How to better master the buzzer inspection standards and methods?

Buzzer appearance inspection
The surface of the buzzer is uniform and flat with no distortion or warpage. The aluminum shell has no grooves, good riveting, no looseness and gaps. The silver layer is smooth and has no cracking. The lead wire is not damaged, the solder joint is uniform and bright, and there is no tipping, soldering or de-soldering.

Buzzer solderability test
After the positive and negative leads are soldered on the upper tin, the tin surface on the wire should be greater than 90%.

Buzzer silver layer reliability
After the silver layer is subjected to a tensile force of 0.2kg, it shall be free from cracking and falling off.

Buzzer structure size
The size meets the sample requirements, and the height of the buzzer lead solder joint is less than 1.2mm. The thickness of the buzzer is less than 1.8mm (excluding the thickness of the solder joint). Use a vernier caliper to directly measure the height of the solder joint and the thickness of the buzzer.

Buzzer electrical performance
Fix the buzzer in the test fixture, input a signal with a amplitude of 1.5V and a frequency of 2KHZ to the buzzer, and read the dB value from the millivoltmeter, which is the sensitivity of the buzzer. The sensitivity is tested according to the specified test method and the sensitivity should be in the range of -57 ± 2 dB.

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