Piezo buzzers use the inverse piezoelectric principle to create movement of a ceramic disc to produce sound waves. The buzzer includes a built-in oscillating circuit. Piezo buzzers operate over a wide temperature range and create noises ranging from soft and gentle to loud and aggressive.
When piezoelectric materials are under pressure, the pressure causes changes along the surface of the material, these pressure differences result in compression along one surface and strain along the other one. As a result, the positive charges collect on one side of the material, and the negative charges collect on the opposite side. This generator effect converts mechanical energy into electricity. In the reverse piezoelectric effect, used in buzzers, applying an electrical field causes the length of the surface to change and converts electrical energy into mechanical energy that creates sound waves the human ear is able to detect.
Jacques and Pierre Curie discovered the piezoelectric principle in 1880 by observing that certain crystals, when placed under pressure, produce electricity. As they continued researching this principle, they found applying electrical fields to piezoelectric crystals caused them to move. The discovery that ceramic materials, made with barium titanate, exhibit the same changes allowed the use of both the piezoelectric and inverse piezoelectric principles in industrial applications, including the development of the Piezo buzzer.