Ultrasound

Sound below 20 Hz is called infrasound; sound above 20 kHz is called ultrasound. These are still sound waves, even though their frequencies lie outside the normal human hearing range.

Ultrasound is sound with a frequency greater than 20 000 Hz.

Ultrasound is sound too high in frequency for people to hear. When an ultrasound pulse reaches a boundary between materials, part can reflect as an echo while part continues through. A transmitter sends out the pulse and a receiver detects the returning echo.

Ultrasound is sound at frequencies too high for people to hear. A probe sends short ultrasound pulses into the body and detects returning echoes. At a boundary between different tissues, part of a pulse is reflected while part continues deeper.