Worlds of David Darling > Children's
Encyclopedia of Science > Ultrasound For Kids
THE SCIENCE OF ULTRASOUND
What is Ultrasound?
Sound is caused by tiny, fast
movements called vibrations, and it travels in waves from its source
to a receiver (e.g., from vibrating vocal cords to our ears). A sound wave
involves the transfer of energy through a medium (solid, liquid, or gas).
The sound vibrations can very in size (amplitude) and in rate (frequency).
The greater the amplitude the louder the sound, and the higher the frequency
the higher the sound (higher the pitch). If a dog barks loudly, the sound
vibrations will have a greater amplitude and lower frequency than the sound
made when a mouse squeaks.
Humans can hear frequencies of 15 hertz to 20,000 hertz
(number of vibrations per second).
Sound waves of more than 20,000 hertz are known as ULTRASONIC
and cannot usually be heard by humans. However, we can use ultrasound in
medicine, in ship navigation, and in industry. Ultrasound is also used by
Using ultrasound depends on an echo (or reflection):
- An ultrasonic wave is produced and released by an electrical device.
- The ultrasonic wave hits a solid surface.
- The ultrasonic wave is reflected off the surface and bounces back
(like an echo in an empty cave).
- The ultrasonic wave is picked up from a receiver.
- This is repeated to get the object's shape and direction from the
Uses of Ultrasound
To examine unborn (fetuses). Ultrasound can be used to examine the number,
sex, movement, and heart beat of a fetus in the mother's womb, the stage
of the pregnancy, and whether there are any major physical abnormalities
with the fetus.
As therapy for muscle pain (can accelerate wound healing).
Breaking down particles
To clean teeth (used by dentists to remove plaque without damage or pain.
To navigate under water. Submarines and boats use SONAR (sound navigation
and ranging) to detect objects underwater.
As quality control. Ultrasound can be used to detect cracks in metal and
plastic that is made in factories. This is because the ultrasonic waves
reflect off cracks more than the metal or plastic.
To heat liquids (dry corn milling plants enhance ethanol production using
heat produced by ultrasound).
Breaking down particles
To clean jewelry, lenses, and clothes. Objects are placed in an ultrasound
bath, in which ultrasound is passed through water and creates bubbles that
remove the dirt. Ultrasonic washing machines are currently under development.
Advantages and Disadvantages of Ultrasound
Advantages in Medicine
- It is non-invasive (can be used without equipment entering the body).
- It is relatively inexpensive.
- It is a quick procedure.
- No harmful effects have been detected yet.
- It is good for examining soft tissues (eye, heart, blood vessels).
- If a problem with the fetus is detected, the parents can prepare emotionally
- Ultrasound can be absorbed into the bone and can accelerate fracture
Disadvantages in Medicine
- The picture it produces doesn't give as much detail as an X-ray.
- It can't be used to examine areas that contain gas (lungs, digestive
- It does not pass through bone.
- More research is required to determine whether long term exposure
- It can sometimes be wrong in its detection of physical abnormalities.
- It can affect fetal brain development in mice (no such evidence for
Ultrasound for sex determination has led to parents choosing abortion in
some countries, such as China and India, where male offspring are more highly
Can we "cure" human disabilities with ultrasound?
Could we use ultrasound systems to help blind people "see"? This is related
to the use of robotic machinery for human function, as researched by Professor
Kevin Warwick of Reading University, England. In 1998, he had a chip implanted
directly into the nerves of his
arm; this chip was also connected to an ultrasound detector and computer.
Professor Warwick was able to sense things moving even when blindfolded,
as moving objects were detected by the ultrasound detector, which would
then send signals to the implanted chip. The chip in Professor Warwick's
arm would send the signal to his brain.
Calculating Distance With Ultrasound
How can ultrasound be used to detect objects in air and water?
Things we need to remember:
The time it takes to detect an object by ultrasound is equal to the time
it takes for the ultrasound wave to be emitted, bounce off an object and
return to the detector. So, we need to halve this time when using the equation
- Distance traveled (d) = speed (s) × time (t)
- Speed of sound in air = approximately 334 meters per second
- Speed of sound in water = approximately 1530 meters per second
Ultrasound and bats
If it took 1 second for a bat to detect the ultrasound, how far away is
d = s × t
= 334 meters per second × 1 second
= 334 meters in total
We need to divide this by 2 to get the distance from bat to prey only.
So, 330/2 = 165 meters.
Ultrasound and ships
An iceberg is 3,000 meters from a submarine. The submarine emits ultrasound.
How long will it take for the submarine to detect the iceberg?
d = s × t
t = d/s
d = 2 × 3000 m (the ultrasound wave has to go to the iceberg
= 6000 meters
t = d/s
= 3.92 seconds
Medical Ultrasound Debate
The use of ultrasound in medicine has both its advantages and disadvantages,
which results in some debate over its use. Here are a few things you might
want to consider:
- How useful is ultrasound in medicine?
- Is the relatively small risk of damage to the fetus through ultrasound
scanning worth it for the information gained?
- Would you want to know the sex of the baby or whether it had any physical
- Should we use ultrasound to help humans who are blind (i.e., to help
them "see" objects)?
Some tips for running a debate
Using a physical continuum. E.g., read aloud a controversial
statement; individuals who agree completely with the statement should then
stand at one side of the room and those that disagree completely should
stand at the other. Those that aren't so sure how they feel should stand
somewhere in the space between depending on what views they do have on the
topic. Once all of the group is standing somewhere, ask whether anyone wishes
to share why they are standing at a particular point.
- Provide the debaters with resources on this page on this topic
- Lay out the ground rules of the debate before the debate begins
- Ensure participants stick to the chosen topic
- Try to involve the whole group in the discussion by:
Use a ballot box. Each individual anonymously writes down
their views on the topic on a piece of paper, which is then put into a ballot
box. One at a time, the pieces of paper are picked from the box and read
aloud. The group discusses each one in turn.
Animal Sounds and Ultrasound
Can you work out which of the following are true or false?
Answers are at the bottom of this page.
- Non-toxic moths can fool bats by mimicking the toxic, ultrasound-producing
- Most bats emit ultrasound through their noses, but some also do it
using their mouths.
- Dogs can hear "silent whistles," which humans use to create ultrasound.
- Bats navigate using ultrasound; they produce and detect the ultrasonic
- Some crickets produce ultrasound by rubbing their wings together.
- Ultrasound is useful for detecting pregnancy in animals.
- Tiger moths can emit ultrasound with their wings.
- All crickets emit ultrasound.
- Bats have large ears to detect ultrasound echoes that are reflected
off their prey.
- Some frogs in America keep quiet when they detect ultrasound from
bats which prey on them.
- Studies show that dolphins, whales, and sharks use ultrasound to navigate.
- Studies show sloths and gorillas use ultrasound to warn others of
- Humans can hear the ultrasound emitted by bats.
- Ultrasound echoes can be detected by sinuses in the lower jaw of the
- Tiger moths hear ultrasound from bats and warn them of their bad taste
by emitting ultrasound.
- The male mouse emits ultrasound when looking for a mate.
The game of Marco Polo
Marco Polo is a bit like the game "tig" but the person being "it" keeps
his or her eyes closed.
To begin, select a player to be "it"; this person must try to tig/tag another
player, who then becomes "it" and attempts to tig someone else, and so on.
The player who is "it" must keep his or her eyes closed at all times (or
be blindfolded), so needs to depend on sound to find the other players (who
are moving around the room). To help him/her to find the other players,
he/she can shout "Marco," after which all the other players must shout back
Before and after playing the game, you could consider how useful ultrasound
might be for the player who is "it".
Animals and Ultrasound True or False Answers
- False. The ultrasound is made in the larynx (voicebox) and usually
emitted through the mouth of the bat, although some bats also emit through
- False. Most crickets do not emit ultrasound.
- False. Tiger moths emit ultrasound using a pair of organs called "tymbals".
- False. No study has shown sharks use ultrasound to navigate.
- False. No study has shown gorillas use ultrasound for warning others.
- False. Humans cannot hear ultrasound.