Piezos in health care
Examples are dental scalers, ultrasonic scanners and ultrasonic instruments.
The piezo in the ultrasonic dental scalers operates as a transducer by rapidly changing size when excited by an electrical signal. The scaler vibrates against the tooth, creating sound waves that break apart the hard calculus on the tooth structure. Water also flows out of the scaler and combined with the vibration, this produces millions of tiny air bubbles that collapse with enormous energy resulting the cell walls of bacteria in the plaque to break up.
Piezo scalers usually operate in the low ultrasonic range, typically 24-36 kHz, with peak powers reaching up to 25 W. The tool can be adapted to several tasks from cleaning to extraction, simply by changing the tip and power level.
The ultrasound scanner sends out a pulse of ultrasound through a transducer at a frequency typically in the range 3 to 5 MHz for usual systems. The transducer is placed on the abdomen of the pregnant woman and the pulse of ultrasound is send through the tissue and into the womb. The sound is reflected by structures including muscles, internal organs etc. The reflected sound is captured by several individual piezo elements, then analyzed and results displayed on a screen as an image of the baby inside. The most common systems utilize a linear sensor, providing a “slice” image. Using beamforming techniques, it is possible to determine where the reflected sound comes from and thereby locate the structures in the plane.
Ultrasonic surgery instruments
Ultrasonic instruments vibrate typically at 55 kHz, creating a wave of mechanical energy. This ultrasonic energy is transferred from a blade to tissue molecules, which begin to vibrate in response. The vibration improves the cutting and leads to a better coagulation of the tissue, thereby reducing bleeding. The reaction to the vibrations depends on the density of the objective (tissue, bone etc.) and the frequency of oscillation. As an example, bone reacts most to frequencies in the low ultrasonic range (20-25 kHz).