Ultrasound
Sound above 20 kHz is used in medicine and industry.
About this topic
Ultrasound is sound with frequency above 20 kHz, beyond human hearing. Pulses reflect from boundaries between tissues, and the echo times build an image, as in prenatal scans. It is safe because it is non-ionising.
Other uses include sonar, cleaning jewellery and instruments, breaking up kidney stones, and detecting cracks in metal. Typical medical frequencies are 1 to 15 MHz, and a gel on the skin removes air that would otherwise reflect nearly all the sound. Higher frequencies give finer detail but do not penetrate as deeply. Bats use frequencies up to about 100 kHz, and dolphins even higher.
Worked example: if an echo from a tissue boundary returns after 0.00013 s and sound travels at 1540 m/s in soft tissue, the round trip is 0.2 m, so the boundary is 10 cm deep. A scanner repeats this thousands of times, building a picture from the delays and strengths of the echoes.
Doppler ultrasound adds the ability to observe blood flow and the fetal heartbeat. Industrial systems measure thickness and find flaws in welds, and ultrasonic cleaners shake dirt loose. A misconception is that ultrasound uses radiation like X-rays; it uses mechanical sound waves, so it avoids ionising damage, although high-power beams can heat tissue.
Key ideas
- Imaging uses echoes
- Bats navigate with it
- Cleaning and sonar
Quick check
Use cases: where Ultrasound helps
- Homework: review the key idea behind Ultrasound before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Ultrasound without notes.
- Visual learning: play with the interactive lab to see how Ultrasound changes when you adjust its inputs.
- Teaching a friend: explain Ultrasound in your own words, then compare your version with the key ideas.
The same laws describe car crashes, sports, satellites and everyday machines.
Frequently asked questions
What is Ultrasound?
Sound above 20 kHz is used in medicine and industry.
What will I learn in Ultrasound?
Imaging uses echoes. Bats navigate with it. Cleaning and sonar.
Is Ultrasound part of Physics?
Yes. It is one of 150 Physics topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Ultrasound lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Ultrasound?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.