ultrasonics

Ultrasonics refers to the study and practical use of acoustic waves whose frequencies exceed the upper limit of human hearing, typically above 20 kilohertz. The field covers the generation, propagation, detection, and control of ultrasonic waves in solids, liquids, and gases, and their application in science, engineering, medicine, and industry.

Ultrasonic waves are usually generated by piezoelectric or magnetostrictive transducers, driven by electrical signals. They are detected when returning echoes produce electrical signals in the same or a nearby transducer. Common configurations include pulse-echo, where a short burst is sent and echoes are received, and continuous-wave methods for range and velocity measurements.

Medical imaging typically uses frequencies from about 2 to 18 megahertz, balancing resolution and penetration. Industrial nondestructive testing often uses 0.5 to 20 megahertz, selected for material type and thickness. Higher frequencies yield finer detail but shallower reach; lower frequencies penetrate deeper but resolve less clearly.

Applications include medicine, where ultrasonography is used for diagnostic imaging, obstetrics, and cardiology; therapeutic uses include high-intensity focused ultrasound for tissue ablation and lithotripsy. In industry, ultrasonics underpin nondestructive testing of welds and metals, material characterization, and cleaning or processing through cavitation. Ultrasonic cleaning uses cavitation to dislodge contaminants. In marine and underwater acoustics, sonar systems use ultrasonic waves for navigation, detection, and communication. Dental ultrasonic scalers employ high-frequency vibrations to disrupt deposits.

Technologies include phased arrays and 3D/4D imaging; advances in materials and electronics have expanded miniaturization and sensitivity. Safety guidelines address potential thermal and mechanical effects; exposure is kept within recommended limits in diagnostic contexts.

Ultrasonics emerged from the discovery of the piezoelectric effect in the 19th century and the early development of sonar in the 20th, with rapid growth during and after World War II.