What is Piezoelectricity?
A definition of piezoelectricity – piezo being Greek for “subjected to pressure” – is the generation of the electrical polarisation of a material as a response to mechanical strain. This phenomenon is known as direct effect or generator effect and is applied fundamentally in the manufacture of sensors (mobile phone vibrators, lighters, etc.). In these cases piezoelectric materials, also used in actuators, undergo an inverse or motor effect, i.e. a mechanical deformation due to the application of an electrical signal.
Thus, piezoelectricity means electricity resulting from pressure. The piezoelectric effect was discovered in 1880 by the Jacques and Pierre Curie brothers. It is the phenomenon in which electrical voltage is produced from mechanical stress when pressure is applied to an object. A mechanical stress induces a negative charge on the expanded side and a positive charge on the compressed side. Once the pressure is relieved, electrical current flows across the material. Piezoelectricity is found in useful applications such as the production and detection of sound, generation of high voltages, electronic frequency generation, microbalances, and ultra fine focusing of optical assemblies. It is also the basis of a number of scientific instrumental techniques with atomic resolution and everyday uses such as acting as the ignition source for cigarette lighters.
Polymer-based piezoelectric materials
Polyvinylidene Difluoride (PVDF).
Currently, the Polymer-based piezoelectric materials are object of great interest as they enable their use in new applications in sectors such as transport and aeronautics, amongst others. At present, probably the only piezoelectric polymer that exists on the market is Polyvinylidene Difluoride (PVDF). This semi-crystalline polymer is characterised by having very good piezoelectric properties, but only to 90 ºC. Thus the interest in synthesising new piezoelectric polymers capable of maintaining their properties at greater temperatures.
Over the last four decades zirconium or lead titanate ceramics have been mainly used as piezoelectric materials, amongst other reasons because of their high elastic modularity, their high dielectric constant and their low dielectric and elastic losses. However, and although they have also been used successfully in many other applications, ceramic piezoelectric materials have some important drawbacks: limited deformation, fragility and a high mass density that limit their use in sectors such as aeronautics or electrical-electronics. These limitations can be overcome in specific applications using polymeric piezoelectric materials instead of ceramic ones.