Piezoelectricity Basics & FAQs

by Jessie Wong / Monday, 14 October 2013 / Published in Ultrasonic Technology

What causes piezoelectricity

Piezoelectricity is formed when the only ion in the cage of atoms is deformed or put under electric field. There are atomic structures that contain a cage that has atoms. Among the many atoms in this cage, there is one ion that is semi-mobile. This ion has a stable state. However, the state of the sole ion becomes unstable when pressure or electric field is applied to it. When the state of the ion changes, piezoelectricity is formed.

Definition of electric field

When there are electric charges, there is an electric field. It is the electric field that connects electric charges. It surrounds electric charges and it is through the electric field that electric charges interact. When a particle that has very little amount of charge is put beside another particle with a high amount of charge, the charge of the first particle increases because of the electric field.

Definition of pyroelectric effect

The electrical polarization in some materials is prone to change when temperature is changed. The change in temperature causes voltage to occur between electrodes of the materials. This is called pyroelectric effect.

Definition of damping

When an object vibrates, it loses some of its elastic energy. The lost elastic energy is due to the friction caused by external forces or the heat inside the object. The proneness of a vibrating object to do this is called damping.

Definition of elastic modulus

Elastic modulus is also known as Young’s modulus. It defines how stiff a material is. The formula to compute Young’s modulus is Y = (L/A) * (F/delta L). Y is Young’s modulus. L is the length of the object while A is the cross section of the object. F is the force applied to the object.

In situations where piezoelectricity is used, Young’s modulus is used to get the value of stiffness of the object subjected to piezoelectricity.

The meaning of strain

To strain an object is to apply stress on that object. There is a formula to measure the amount of strain applied on an object. For example, when a stick that has a length represented by L is strained to elongate it, the length of the elongated stick becomes represented by L + delta L. To get the amount of strain being experienced by the stick, delta L is divided by the original length L.

Definition of tensile strength

At some point, an object subjected to stress will break. To know the point where the object breaks due to stress, tensile strength is computed. It is measured using the formula Newton/ m2 or psi.

Are piezoceramic actuators effective when the level of temperature is very low

Temperature does not really affect the capacity of piezoceramic actuators to produce piezoelectricity. And so, these actuators will work even when the level of temperature is very low. Piezoelectricity occurs due to the application of electric field. Temperature has no effect on electric fields. Moreover, a drop in temperature does not cause piezo coupling to drop.

The poling and depoling of piezoceramics

Piezoceramics are capable of producing piezoelectricity. But these materials do not release piezoelectricity just for being piezoceramics. In order for them to produce piezoelectricity, an electric field has to be applied to them. The application of electric field causes the micro-dipoles of piezoceramics to align themselves. The alignment is known as poling. The electric field may also be applied in the opposite direction. When the level of electric field applied is low, piezoceramics are not really affected. When medium level electric field is applied, the polarization is slightly affected. When the electric field applied has a high level, depoling happens.