How Piezoelectric Speakers Work?

Piezoelectric materials change shape when exposed to electric fields. Learn how we can use them to create sound.

Atomic Theory

 

An atom has a center nucleus that is made of neutral charges called neutrons, and positive charges called protons. Moving around the nucleus are negative charges called electrons. 

Opposite charges attract, so electrons are attracted to the protons in the nucleus. At the same time, similar charges repel, so too many electrons in one area tend to push one or more electrons to leave.

Electrons are in constant motion around an atom.

Piezoelectric Effect

Certain materials will generate a measurable potential difference when they are made to expand or shrink in a particular direction.  

Increasing or decreasing the space between the atoms by squeezing, hitting, or bending the crystal can cause the electrons to redistribute themselves and cause electrons to leave the crystal, or create room for electrons to enter the crystal. A physical force on the crystal creates the electromotive force that moves charges around a circuit.

The opposite is true as well: Applying an electric field to a piezoelectric crystal leads to the addition or removal of electrons, and this in turn causes the crystal to deform and thereby generate a small physical force.

 

Representation of a compressed (left) and stretched (right) crystalline structure.

How Piezoelectric Speakers Move

The piezoelectric effect can be employed in the construction of thin-form-factor speakers that are valuable alternatives to traditional electrodynamic speakers in space-constrained applications. These devices are referred to as both piezoelectric speakers and ceramic speakers.

Apply an electric field to a piezoelectric material and it will change size. The piezoelectric material will shrink or grow as charges are introduced or removed, but the base material will not.  

This causes elastic deformation of the material toward or away from a direction that is perpendicular to the surface of the speaker. As soon as the electric field is removed from the piezoelectric material, it will return to its original shape.

As the speaker flexes and strikes air molecules, it causes a chain reaction of collisions that eventually reaches your ear. If enough air molecules strike your ear, the nerve cells send a signal to your brain that you interpret as sound.

How Disturbances Travel

An unimaginable number of atoms and molecules surround us and are in constant motion. These particles move in straight lines until they hit other atoms and their direction changes. A single particle will never move far before a collision, but the effects of the collision can travel great distances as new particles collide with their neighbors.  

Imagine adding a single drop of food coloring to the center of a swimming pool. The particles of food coloring might take minutes or hours to reach the edge, but the waves generated by the drop would be at the pools edge in seconds.

Air particles strike our bodies constantly and randomly all the time. When the collisions stop being less constant and less random, and start being more regular and patterned, we are hit with more particles at specific times. Certain nerve cells in our ears can detect these increased, patterned collisions and send signals to our brains, and our brain interprets the pattern as sound.