One piezoelectric crystal has been placed between the metal plates (two), and pressure is applied on that material through the metal plates. And because of that force, the electric charges get out of balance within the crystal.
There will be excess positive and negative charges that appear on the opposite side of the face of the crystal.
It is the sensor used within so many different devices to convert the physical parameter into the electrical signal.
It is mainly used to measure the pressure, strain, or even acceleration and then convert it to get it to convert into the electrical charge.
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