Ultrasound
Ultrasound is a type of sound with a frequency higher than humans can hear. This frequency, the upper limit of human hearing, is approximately 20,000 hertz (20 kilohertz).
Hearing ultrasound
Some animals, such as dogs, dolphins, bats, and mice, are able to hear sounds which have a frequency higher than upper-limit of the human ear. This makes them able to hear ultrasounds. Children can hear some high-pitched sounds that older adults cannot hear, as in humans the upper limit pitch of hearing gets lower as a person gets older. This frequency limit is caused by the middle ear that acts as a low-pass filter. If ultrasound is fed directly into the skull bone and reaches the cochlea without passing through the middle ear, much higher frequencies (up to about 200 kHz) can be heard. This effect (sometimes called ultrasonic hearing) was first discovered by divers exposed to a high-frequency (ca. 50 kHz) sonar signal.
Medical ultrasonography is commonly used during pregnancy. Ultrasound is generally thought of as a "safe test" because it does not use destructive ionizing radiation like x-rays.
Ultrasonic cleaning
Ultrasonic cleaners are sometimes mistakenly called supersonic cleaners. They are used at frequencies from 20 to 40 kHz for jewellery, lenses and other optical parts, watches, dental instruments, surgical instruments and industrial parts. An ultrasonic cleaner works by the energy released from the collapse of millions of tiny (microscopic) bubbles near the dirty surface. The bubbles are formed by cavitation and collapse, forming small jets directed at the surface.
Ultrasound Media
Aparelho de ultrassom
Galton whistle, one of the first devices to produce ultrasound
Approximate frequency ranges corresponding to ultrasound, with rough guide of some applications
Bats use ultrasounds to navigate in the darkness.
A dog whistle, which emits sound in the ultrasonic range, used to train dogs and other animals
Principle of flaw detection with ultrasound. A void in the solid material reflects some energy back to the transducer, which is detected and displayed.
Non-destructive testing of a swing shaft showing spline cracking
Principle of an active sonar
Sonogram of a fetus at 14 weeks (profile)
