Ultrasound is the sound itself — vibration above the range of human hearing, roughly above 20 kHz. Ultrasonic is the adjective describing anything using or relating to it. You have an ultrasound scan performed by an ultrasonic device.
The core difference
- ultrasound — noun: sound above the upper limit of human hearing, and by extension the medical scan that uses it.
- ultrasonic — adjective: operating at or relating to those frequencies.
The grammar is most of the answer
An ultrasonic cleaner uses ultrasound. An ultrasonic sensor emits ultrasound. The noun names the phenomenon; the adjective describes the equipment. Where speakers hesitate is that ultrasound has also become a noun for the procedure — you go for an ultrasound — which makes it look like the two words compete when they do not.
Where the boundary sits
Human hearing tops out around 20 kHz in young adults and declines with age, so the threshold is a convention rather than a physical edge. Dogs hear to roughly 45 kHz, bats well beyond 100 kHz. A dog whistle is an ultrasonic device only from a human point of view.
What it is used for
- Imaging — medical scanning, which works by timing echoes from tissue boundaries.
- Cleaning — ultrasonic baths create microscopic cavitation bubbles that lift contamination from surfaces.
- Ranging — parking sensors and rangefinders time the return of a pulse.
- Welding — ultrasonic vibration fuses plastics and thin metals without a heat source.
Infrasound, at the other end
Below the range of hearing, roughly under 20 Hz, is infrasound. It travels much further than audible sound, which is why elephants and whales use it over long distances, and why volcanoes and large explosions are detectable from thousands of miles away.
Supersonic is a different thing entirely
A common mix-up. Supersonic means faster than the speed of sound, and describes motion. Ultrasonic means above the frequency of hearing, and describes vibration. A supersonic aircraft is not making ultrasonic noise.
Frequently asked questions
What is the difference between ultrasonic and ultrasound?
Ultrasound is the noun — sound above human hearing. Ultrasonic is the adjective for devices that use it. An ultrasonic scanner produces an ultrasound image.
Is ultrasonic the same as supersonic?
No. Ultrasonic means above the frequency of human hearing. Supersonic means faster than the speed of sound. One is about pitch, the other about speed.
Where does ultrasound begin?
Conventionally around 20 kHz, the upper limit of young adult hearing. It is a convention rather than a physical boundary — many animals hear well above it.