Cellular thermoplastic polymers, such as poly-propylene (PP), poly-ethylene-therephtalate or cyclo-olefines, can be tailored to obtain a piezoelectric-like behavior. Since ferroelectrets show a similar behavior to piezoelectric materials, they are introduced within this section, but not discussed within the following chapters. PVDF is used for example in transducers of ultrasonic devices up to 24GHz, hydrophones or infrared sensors (Infrared Thermography). In comparison to piezoelectric ceramics it’s less chemical resistant and sensors using PVDF are less sensitive than sensors using PZT. Compared to the piezoelectric ceramics, PVDF is more elastic, has a lower specific weight and thinner piezoelectric components can be built. There are also some partially crystalline polymers like polyvinylidene fluoride (PVDF), which are piezoelectric after having been polarized. Before polycrystalline piezoelectric materials can be used, they need to be polarized, what is described within the next chapter. Hard PZT ceramics are used for high power ultrasound applications such as ultrasound cleaning and sonar. Typical application for soft PZT ceramics are sound generators and receivers (acoustics), sensors (metrology), ultrasonic diagnostics (medicine) and deformation elements (actuation). Soft PZT ceramics are characterized by easier polarization, higher piezoelectric coefficients, higher relative permittivity, higher dielectric losses, higher insulating resistance, higher coupling factors, lower mechanical quality factors and lower resistance against depolarization compared to hard PZT ceramics. Without going into details, their relevant piezoelectric properties are compared in the following part. Depending on the lattice structure, soft and hard PZT ceramics are differed. Adding alloys to the PZT ceramic, the lattice structure can be optimized for better piezoelectric properties. Contrary to PVDF (described below), piezoelectric ceramics are very hard and brittle, therefore not very resistant to high tension stresses, insensitive to chemical influences and moisture. Moreover polycrystalline ceramics are produced synthetically, what allows a more flexible design of their shape. Ĭompared to these, polycrystalline ferroelectric ceramics like barium titanate and lead zirkonate titanate (PZT) (mostly used for sensors and actuators) show a higher electric-mechanical coupling. Typical materials used in applications are natural monocrystalline materials like Rochelle salt (used for microphones, pick-up heads of record players, ultrasonic sensors), turmalin crystals and quartz crystals (used for oscillators, filters, sensors). Two separate effects are differed:Ī) Direct piezoelectric effect (sensor): Applied pressure leads to a mechanical deformation of the piezoelectric material and induces a separation of charges within the material, which can be measured as a difference in electric potential between opposite sides of the solid object.ī) Inverse piezoelectric effect (actuator): Applying a voltage to the surface of the piezoelectric material the solid object changes its shape and dimension (mechanical deformation). The phenomenon of the piezoelectric effect was discovered by Pierre and Jacques Curie in 1880.

Piezoelectric materials (piezein (greek): press, squeeze) are used for engineering applications as actuators and sensors generating and sensing mechanical deformation in materials.

Applications of piezo actuators