II-Piezoelectric materials
  • Piezoelectric effect
The piezoelectric effect describes the relation between a mechanical stress and an electrical voltage in solids. It is reversible: an applied mechanical stress will generate a voltage and an applied voltage will change the shape of the solid by a small amount (up to a 4% change in volume). In physics, the piezoelectric effect can be described as the the link between electrostatics and mechanics.

external image piezoeffect.jpg

  • Brief history
The piezoelectric effect was discovered in 1880 by the Jacques and Pierre Curie brothers. They found out that when a mechanical stress was applied on crystals such as tourmaline, tourmaline, topaz, quartz, Rochelle salt and cane sugar, electrical charges appeared, and this voltage was proportional to the stress.
First applications were piezoelectric ultrasonic transducers and soon swinging quartz for standards of frequency (quartz clocks).
An everyday life application example is your car's airbag sensor. The material detects the intensity of the shock and sends an electricla signal which triggers the airbag.

  • Applications
Air bag sensor, air flow sensor, audible alarms, fuel atomiser, keyless door entry, seat belt buzzers, knock sensors.
Disc drives, inkjet printers.
Cigarette lighters, depth finders, fish finders, humidifiers, jewellery cleaners, musical instruments, speakers, telephones.
Disposable patient monitors, foetal heart monitors, ultrasonic imaging.
Depth sounders, guidance systems, hydrophones, sonar.
  • Structure of the piezoelectric material