ultrasonic

Ultrasonic refers to sound waves with frequencies above the upper limit of human hearing, typically above about 20 kHz. The term covers both the waves themselves and devices designed to generate and receive them. In practice, ultrasonic systems operate from tens of kilohertz to hundreds of megahertz, with many medical and industrial applications using the kilohertz to low megahertz range.

Propagation and characteristics of ultrasonic waves depend on the medium. The speed of sound is higher in liquids and solids than in air; for example, about 343 m/s in air and around 1480 m/s in water. Wavelength is the ratio of speed to frequency, so higher frequencies produce shorter wavelengths and finer resolution but greater attenuation. Attenuation increases with frequency, limiting penetration depth in tissues or materials.

Generation and detection are typically achieved with transducers. Piezoelectric materials convert electrical energy into mechanical vibration to produce ultrasonic waves and also detect echoes. Magnetostrictive transducers use magnetic fields to induce vibration. In water, underwater acoustics use hydrophones to receive signals. Signal processing and imaging techniques are applied to interpret the received echoes.

Applications are diverse. Medical imaging uses diagnostic ultrasound to visualize soft tissues, while high-intensity focused ultrasound can treat tissues noninvasively. In nondestructive testing, ultrasonics detect flaws in metals and composites. Ultrasonic cleaning uses cavitation in liquids to remove contaminants. Ultrasonic welding, drilling, and material processing exploit high-frequency vibrations for bonding or shaping.

Safety considerations include potential tissue heating and cavitation effects. Exposure limits and proper training help minimize risks in medical, industrial, and research settings.