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What are ultrasounds?
High frequency sound waves which exceed 20,000Hz.
Why is this high frequency noise not heard by the baby during a pre-natal scan?
The frequency cannot be heard by the human ear as it is in the ultrasound region.
What can an ultrasound be used for?
Pre-natal baby scan, testicular scanning, soft tissue injuries, breakdown of kidney stones.
What are some advantages of ultrasounds?
Can be used on pregnant women as there is no ionising radiation, quick imaging, gives clear image of soft tissue, can see moving parts.
What are some disadvantages of ultrasounds?
Hard to distinguish bone, poor images of tissues which hold air such as the lungs, limited image resolution.
How are ultrasounds produced?
- -Short pulses are sent from the transmitter
- -The sound waves are reflected from tissues of a different density
- -The different densities produce different intensity reflection
- -The transmitter detects a reflection and an image is transported to a camera where a 2D image is created
Why is a coupling gel put on the skin before doing an ultrasound scan?
The gel and the skin have the same acoustic impedance and therefore all of the reflected waves can reach the detector to create a clear image.
What is the formula to work out wave speed, frequency and wave length?
v (velocity)= f (frequency) x λ (wavelength)
What is the frequency of a wave?
The number of waves in a second.
Why do soundwaves travel quicker through denser materials?
The particles are more tightly packed so vibrations are passed on quicker.
What is frequency measured in?
What is velocity measured in?
m/s (metres per second)
What is acoustic impedance?
How badly sound waves are transmitted through a material.
What is intensity reflection coefficient?
How badly sound waves are transmitted across a boundary from one material to another.
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