ULTRASOUND = Sound with a higher frequency than we can hear.
They are made by converting electrical oscillations into mechanical vibrations with a frequency of over 20,000 Hz.
Ultrasound waves get partially reflected at a boundary between media.
- This is partial reflection.
- So, you can point a pulse of ultrasound at any object - whenever there are boundaries between one substance and another, some of the ultrasound gets reflected back.
- This can be used to measure how far away the boundary is.
Oscilloscope traces can be used to find boundaries.
s = v x t
s = Distance in metres, m. v = Speed in metres per second, m/s. t = Time in seconds, s.
1. Breaking down kidney stones.
Ultrasound beams concentrate high-energy waves at the kidney stones, turning them into small patticles which can be passed out in the urine.
2. Pre-natal scanning of a fetus.
US waves can pass through the body and bounce between the baby's skin and another boundary to give a video image of the fetus.
MEDICAL IMAGING - SAFE?
- US waves are non-ionising, so are safe.
- X-Rays are ionising, so can cause cancer.
- CT Scans expose patients to a high dose of radiation.
- US images are fuzzy and would be hard to use to diagnose conditions.
- X-Rays produce clear images but only of bones and metal.
- CT Scans produce detailed images and can be used to diagnose conditions and in the planning of complicated surgery.