The piezoelectric effect is a property of certain crystals that generates an electric field or current when subjected to physical stress. It is essential to transducers and has various applications, including generating sparks in ignition equipment and controlling precise motion in microscopes and printers. The effect occurs due to the disruption of charge equilibrium in the crystal lattice. The inverse piezoelectric effect, where electricity warps crystals, was discovered by Gabriel Lippmann. The effect is used in various technologies, including ultrasound transducers and the tunneling microscope.
The piezoelectric effect is a unique property of some crystals where they will generate an electric field or current when subjected to physical stress. The same effect can also be observed in reverse, where an electric field imposed on the crystal will strain its structure. The piezoelectric effect is essential to transducers, which are electrical components used in a wide variety of sensor and circuit applications. Despite the phenomenon’s versatility for applications in electromechanical devices, it was discovered in 1880, but did not find widespread use until about half a century later. The types of crystal structures that exhibit the piezoelectric effect include quartz, topaz, and Rochelle salt, which is a type of potassium salt with the chemical formula of KNaC4H4O6 4H2O.
Pierre Curie, famous for winning the 1903 Nobel Prize in Physics for research on radiation with his wife Marie, is credited with discovering the piezoelectric effect with his brother Jacques Curie in 1880. The brothers at the time they did not discover the inverse piezoelectric effect, however, where electricity warps crystals. Gabriel Lippmann, a French-Luxembourg physicist, is credited with discovering the reverse effect the following year, which led to his invention of the Lippmann electrometer in 1883, a device central to the operation of the first experimental electrocardiography (ECG) machine .
Piezoelectric effects have the unique property of often developing thousands of volts of potential difference of electrical energy at very low current levels. This also makes tiny piezoelectric crystals useful objects for generating sparks in ignition equipment such as gas furnaces. Other common uses for piezoelectric crystals include controlling precise motion in microscopes, printers, and electronic clocks.
The process by which the piezoelectric effect occurs is based on the fundamental structure of a crystal lattice. Crystals generally have a charge equilibrium in which negative and positive charges cancel each other along the rigid planes of the crystal lattice. When this balance of charge is disrupted by applying physical stress to a crystal, energy is transferred by electric charge carriers, creating a current in the crystal. With the inverse piezoelectric effect, the application of an external electric field to the crystal will unbalance the neutral charge state, which results in mechanical stress and slight readjustment of the lattice structure.
As of 2011, the piezoelectric effect was largely monopolized and used in everything from quartz watches to water heater lighters, portable grills, and even some portable lighters. In computer printers, tiny crystals are used on inkjet printer nozzles to block the flow of ink. When a current is applied, they deform, allowing ink to flow onto the paper in carefully controlled volumes to produce text and images.
The piezoelectric effect can also be used to generate sound for miniature speakers in clocks and in sonic transducers to measure distances between objects such as for stud finders in construction. Ultrasound transducers are also based on piezoelectric crystals and many microphones. As of 2011, they use crystals made of barium titanate, lead titanate, or lead zirconate, which produce lower voltages than Rochelle salt, which was the standard crystal in early forms of these technologies.
One of the more advanced forms of technology to exploit the piezoelectric effect as of 2011 is that of the tunneling microscope (STM) which is used to visually examine the structure of atoms and small molecules. The STM is a fundamental tool in the field of nanotechnology. The piezoelectric crystals used in STMs are capable of generating measurable movement on the scale of a few nanometers or billionths of a metre.
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