What is ultrasound?

Sound wave is a vibration that is transmitted through a medium, such as air, water, and metals. Ultrasound is sound waves with frequencies higher than the upper audible limit of human hearing. This limit varies from person to person and is approximately 20 KHz (20,000 hertz) in healthy young adults.

The Ranges of Sound Frequencies Sensed by Humans and Other Species

The upper frequency limit in humans is due to limitations of the middle ear. Children can hear some high-pitched sounds that older adults cannot hear, because in humans the upper limit pitch of hearing tends to decrease with age. US researchers also discovered that ultrasound examinations during pregnancy expose the fetus to a sound as loud as that made by a subway train coming into a station.

Bats use a variety of ultrasonic ranging (echolocation) techniques to detect their prey. They can detect frequencies from 10 KHz to 120 kHz, possibly up to 200 kHz.

Bottlenose dolphins produce sounds in the range 7 KHz to 15 kHz which are continuously variable in pitch. In addition, they produce short burst from 20 KHz to 170 kHz, presumably for better echolocation.

The Application of Ultrasonic Devices and Their Frequencies

Ultrasound is used in many different fields. Ultrasound devices operate with frequencies from 20 kHz up to several gigahertz, and are used to detect objects, measure distances and flow rates. Ultrasound imaging or ablation is often used in medicine. In the nondestructive testing of products and structures, ultrasound is used to detect invisible flaws. Industrially, ultrasound can be used for cleaning, mixing, and accelerating chemical processes.