THE SCIENCE OF ULTRASOUND
Figure 1. Pregnant woman having an ultrasound.
Figure 2. Wavelength.
Figure 3. Echo of microwaves.
Figure 4. Bat echolocation.
Figure 5. Submarine sonar.
Figure 6. Ultrasound in animals.
Figure 7. Game of Marco Polo.
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 various animals (see Figure 2).
Using ultrasound depends on an echo or reflection (see Figure 3):
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.
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
Disadvantages in Medicine
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:
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
If it took 1 second for a bat to detect the ultrasound, how far away is the prey? (See Figure 4)
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? (See Figure 5.)
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:
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.
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
See Figure 6.
Can you work out which of the following are true or false?
Answers are at the bottom of this page.
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 (see Figure 7).
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