What Is the Piezoelectric Effect?

The piezoelectric effect is a unique property of certain crystals where they will generate an electric field or current if subjected to physical stress. The same effect can also be observed in reverse, where an imposed electric field on the crystal will put stress on its structure. The piezoelectric effect is essential to transducers, which are electrical components used in a wide variety of sensor and circuitry applications. Despite the versatility of the phenomenon for applications in electro-mechanical devices, it was discovered in 1880, but did not find widespread use until about half of a century later. Types of crystalline 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, who is famous for winning the 1903 Nobel Prize in physics for research into radiation with his wife Marie, is credited with discovering the piezoelectric effect with his brother Jacques Curie in 1880. The brothers did not at the time discover the inverse piezoelectric effect, however, where electricity deforms crystals. Gabriel Lippmann, a Franco-Luxembourgish physicist, is credited with the inverse effect discovery the following year, which led to his invention of the Lippmann electrometer in 1883, a device at the heart of the operation of the first experimental electrocardiography (ECG) machine.

Piezoelectric effects have the unique property of often developing thousands of volts of electrical energy potential difference with very low current levels. This makes even tiny piezoelectric crystals useful objects for generating sparks in ignition equipment such as gas ovens. Other common uses for piezoelectric crystals include to control precise movements in microscopes, printers, and electronic clocks.

The process whereby the piezoelectric effect takes place is based on the fundamental structure of a crystal lattice. Crystals generally have a charge balance where negative and positive charges precisely cancel each other out along the rigid planes of the crystal lattice. When this charge balance is disrupted by applying physical stress to a crystal, the energy is transferred by electric charge carriers, creating a current in the crystal. With the converse piezoelectric effect, applying 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 has been widely monopolized and used in everything from quartz clocks to water heater igniters, portable grills, and even some handheld lighters. In computer printers, the miniscule crystals are used at the nozzles of inkjets to block the flow of ink. When a current is applied to them, they deform, allowing ink to flow onto paper in carefully-controlled volumes to produce text and images.

The piezoelectric effect can also be used to generate sound for miniature speakers in watches, and in sonic transducers to measure distances between objects such as for stud finders in the construction trade. Ultrasonic transducers are also based on piezoelectric crystals as well as many microphones. As of 2011, they use crystals made out 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 most advanced forms of technology to capitalize on the piezoelectric effect as of 2011 is that of the scanning tunneling microscope (STM) that is used to visually examine the structure of atoms and small molecules. The STM is a fundamental tool in the field of nanotechnology. Piezoelectric crystals used in STMs are capable of generating measurable motion on the scale of just a few nanometers or billionths of a meter.