Ultrasounds are waves with a frequency higher than 20,000 Hz (ie, cycles per second). A large number of ultrasonic frequencies used in everyday life—such as those used in car alarms and other antitheft systems—are not perceptible to the human ear. Humans perceive frequencies between 20 and 20,000 Hz. Ultrasound is therefore inaudible to humans but audible to certain animals such as dogs, bats, and dolphins. Developed in the 1950s, ultrasound technology is now widely used in the fields of medicine, dentistry, metallurgy, and aviation, and by the navy. It is also used for fishing, cleaning, and remote controls (eg, automatic gates).
The ultrasonic wave displaces itself in a medium and transmits its energy to the particles encountered. Ultrasonic vibrations are waves that are (1) displaced in a longitudinal direction, (2) displaced in a medium, and (3) reflected and absorbed at the interface of the different surfaces encountered (Van Der Weijden 2007).
Different mechanisms of ultrasonic wave production
Three vibrational systems have been developed for the different ultrasonic devices.
Magnetostrictive systems
A ferromagnetic bar and a copper spiral thread in the handpiece generate vibrations ranging from 18,000 to 45,000 Hz. These devices produce an elliptic movement of the tip resembling a hammering motion.
Sonic systems
An air turbine in the handpiece generates vibrations ranging from 2,500 to 16,000 Hz. These devices produce an elliptic or circular movement of the tip resembling hammering and abrasion motions.
Piezoelectric systems
Piezoelectric instruments are widely used in dentistry, and their effects are becoming better understood.
The physicists Pierre and Jacques Curie (younger and elder brother, respectively), in collaboration with Gabriel Lippmann, discovered the piezoelectric effect as early as 1890. According to these French researc/>
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