Worlds of David Darling > Children's Encyclopedia of Science > Ultrasound For Kids


THE SCIENCE OF ULTRASOUND



pregnant woman having an ultrasound

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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).

wavelength
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 various animals.

echo of microwaves
Using ultrasound depends on an echo (or reflection):
  1. An ultrasonic wave is produced and released by an electrical device.
  2. The ultrasonic wave hits a solid surface.
  3. The ultrasonic wave is reflected off the surface and bounces back (like an echo in an empty cave).
  4. The ultrasonic wave is picked up from a receiver.
  5. This is repeated to get the object's shape and direction from the ultrasound device.

Uses of Ultrasound


In Medicine


Detection

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.


Heat production

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.


In Industry


Detection

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.


Heat production

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 and practically.

  • Ultrasound can be absorbed into the bone and can accelerate fracture healing.

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 system).

  • It does not pass through bone.

  • More research is required to determine whether long term exposure is harmful.

  • It can sometimes be wrong in its detection of physical abnormalities.

  • It can affect fetal brain development in mice (no such evidence for humans).

Abortion

Ultrasound for sex determination has led to parents choosing abortion in some countries, such as China and India, where male offspring are more highly values.


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:
  • 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
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 above.


Ultrasound and bats

bat and prey
If it took 1 second for a bat to detect the ultrasound, how far away is the prey?

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

submarine and iceberg
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 and back)
    = 6000 meters

t = d/s
    = 6000/1530
    = 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 abnormalities?
  • Should we use ultrasound to help humans who are blind (i.e., to help them "see" objects)?

Some tips for running a debate

  • 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:
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.

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



ultrasound in animals


Can you work out which of the following are true or false?
  1. Non-toxic moths can fool bats by mimicking the toxic, ultrasound-producing moths.
  2. Most bats emit ultrasound through their noses, but some also do it using their mouths.
  3. Dogs can hear "silent whistles," which humans use to create ultrasound.
  4. Bats navigate using ultrasound; they produce and detect the ultrasonic waves.
  5. Some crickets produce ultrasound by rubbing their wings together.
  6. Ultrasound is useful for detecting pregnancy in animals.
  7. Tiger moths can emit ultrasound with their wings.
  8. All crickets emit ultrasound.
  9. Bats have large ears to detect ultrasound echoes that are reflected off their prey.
  10. Some frogs in America keep quiet when they detect ultrasound from bats which prey on them.
  11. Studies show that dolphins, whales, and sharks use ultrasound to navigate.
  12. Studies show sloths and gorillas use ultrasound to warn others of danger.
  13. Humans can hear the ultrasound emitted by bats.
  14. Ultrasound echoes can be detected by sinuses in the lower jaw of the dolphin.
  15. Tiger moths hear ultrasound from bats and warn them of their bad taste by emitting ultrasound.
  16. The male mouse emits ultrasound when looking for a mate.
Answers are at the bottom of this page.


The game of Marco Polo



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 "Polo."

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

  1. True.
  2. False. The ultrasound is made in the larynx (voicebox) and usually emitted through the mouth of the bat, although some bats also emit through their nose.
  3. True.
  4. True.
  5. True.
  6. True.
  7. False. Most crickets do not emit ultrasound.
  8. False. Tiger moths emit ultrasound using a pair of organs called "tymbals".
  9. True.
  10. True.
  11. False. No study has shown sharks use ultrasound to navigate.
  12. False. No study has shown gorillas use ultrasound for warning others.
  13. False. Humans cannot hear ultrasound.
  14. True.
  15. True.
  16. True.