ULTRASOUND

ULTRASOUND

1. Frequency (Hz) is the vibrations per second

   • Humans can hear sound between 20Hz and 20,000 Hz
   • Ultrasound waves have frequencies above about 20,000 Hz (which is why we can't hear them)

2. Ultrasound can be produced by some animals, such as bats, who echolocate and listen to reflections

   • Ultrasounds require particles to move and is not apart of the electromagnetic spectrum

3. REFLECTIONS

   • When ultrasound waves reach a boundary between two media (substances) with different densities, they are partly reflected back
   • A detector placed is able to detect the reflected waves. It can measure the time between an ultrasound wave leaving the source and it reaching the detector. The further away the boundary, the longer the time taken.
   • An ultrasound machine can be used to detect cracks or flaws in materials such as metal. This is used in industry for quality control procedures to check manufactured objects, such as railway tracks and oil pipelines, for damage or defects.

4. Medical uses of ultrasound

   • Medical imaging
     • The body is made of different tissues and ultrasounds will be reflected at the boundry of different tissue
     • These are widely used in pre-natal scanning to check foetal developments and measurements. Computers can combine many ultrasound reflection readings to produce a detailed image.
   • Removing kidney stones
     • Kidney stones are crystals made from substances in urine, and can block the ureter (tube from kidney to bladder), causing severe pain
     • High frequency ultrasound waves focused at a kidney stone cause it to vibrate, breaking it into small enough pieces to pass out in the urine.

5. The distance travelled by an ultrasound wave can be calculated

   • s = v × t
     • v = speed in metres per second, m/s
     • s = distance in metres
     • t = time in seconds, s
   • Remember to half the figure if they ask for the distance to boundary, as this measurement will include the reflection