What is Piezoelectric Effect ?
Appearance of an electric potential across certain faces of a crystal when it is subjected to mechanical pressure The word originates from the greek word "piezein", which means "to press"
Discovered in 1880 by Pierre Curie in quartz crystals.
Conversely, when an electric field is applied to one of the faces of the crystal it undergoes mechanical distortion. Examples --- Quartz, Barium titanate, tourmaline
How does this Work?
The effect is explained by the displacement of ions in crystals that have a nonsymmetrical unit cell.
When the crystal is compressed, the ions in each unit cell are displaced, causing the electric polarization of the unit cell.
Because of the regularity of crystalline structure, these effects accumulate, causing the appearance of an electric potential difference between certain faces of the crystal.
Conversely, When an external electric field is applied to the crystal, the ions in each unit cell are displaced by electrostatic forces, resulting in the mechanical deformation of the whole crystal.
Illustration
Displacement of electrical charge due to the deflection of the lattice in a naturally piezoelectric quartz crystal
The larger circles represent silicon atoms, while the smaller ones represent oxygen.
Quartz crystals is one of the most stable piezoelectric materials.
Artificial Piezoelectric Materials
polycrystalline, piezoceramics are man made materials which are forced to become piezoelectric by applying large electric field.
high charge sensitivity
materials available which operate at 1000 F (540 C)
characteristics vary with temperature
Use of Piezoelectric Crystals
Red indicates the crystal
Arrows indicate the direction of applied force
the compression design features high rigidity, making it useful for implementation in high frequency pressure and force sensors
Grey- test structure.
Red- piezoelectric crystals
Blue- Sensor housing
The black electrode is where the charge from the crystals accumulates before it is conditioned by the yellow, micro-circuit.
pressure sensors utilize a diaphragm to collect pressure, which is simply force applied over an area.