What is Piezoelectric Property?

As seen in the figure, when the electric dipoles in the cylindrical piezoelectric material are exposed to an electric field, the electrical charges that form the dipole in the material will move away from each other or get closer to each other due to the electrostatic forces caused by the electric field. This movement of the dipoles causes a shape change in the material geometry. This phenomenon is known as the reverse piezoelectric effect.

* Electric dipole: It is a system formed by two particles of equal charge size but of different signs and with a certain distance between them.

Piezoelectric property is the ability of a material to change electric field or electric potential as a result of mechanical pressure applied to certain materials. This effect is directly related to the change in polarization density inside the material. If the material is not short-circuited, the stress applied creates a voltage in the material.
If pressure is applied to an asymmetric ionic crystal with continuous cleavage, the distance between the poles decreases, the charge accumulation on its surface increases, so a voltage difference arises between the two ends, and if they are coupled with a conductor, current occurs. Thus, mechanical energy turns into electrical magnitude.
On the other hand, if a voltage is applied between the two ends of the same crystal, (-) charges are drawn towards the (+) electrode, (+) charges towards the (-) electrode, the distance between (-) and (+) charge centers increases, and as a result, the length of the crystal increases. . If the direction of the field changes, the same signed charges repel each other and the crystalline becomes shorter. Thus, the electrical effect turns into mechanical magnitude. This behavior is called piezoelectric property.
Piezo effect from mechanical energy to voltage generation using piezoelectric property; The generation of mechanical vibration from voltage is also called the inverse piezo event. With the help of reverse piezoelectric, a significant shape change can be created in a ceramic material. These features make it possible for a number of special uses such as ultrasonic sound generators and ultrasonic devices for intrusion alarms, automatic door openers and remote control devices.

It is not possible to use the crystals that make up the piezo phenomenon as they are in nature. The cutting surfaces of the crystal with respect to the center must be symmetrical because the cutting shapes of the crystals directly affect the vibration frequency they generate and the voltage they generate.
Some ceramics such as barium titanate, lead zirconate titanate and potassium sodium niobate are also in a structure to show piezoelectric properties. These ceramics are polycrystalline materials and can be produced like normal porcelain ceramics. Piezoelectric properties are then given to these by the application of high DC voltage.
Piezoelectric ceramics are used in electromagnetic converters (transducers) where electrical waves are desired to be converted into mechanical vibrations.
In the working principle of ultrasonic welding machines, vibration is obtained by converting electrical energy into mechanical energy in transducers with reverse piezo effect. Piezoelectric ceramic material (PZT8) with high conversion efficiency and serial production is used in Tnection ultrasonic welding transducers. The piezoelectric material used is lead-zirconium-titanium (PZT), it can change shape up to 0.1% from its original size. Thanks to this feature, it is very useful for creating electronic frequency.