Unit 3: Week 1

Question 1

What is sound and how do we interpret it?

Answer 1

Sound is vibrations.

Vibrations in the air cause the air in your ear to vibrate the same frequency against the ear drum which is picked up by the ossicles and cochlea (small hairlike projections on cells) to vibrate at the same frequency and then picked up by neves and interperated as sound.

Question 2

What are ultrasounds and what are their range?

Answer 2

They are are frequency sounds waves that are above the human range of hearing (20hz-20khz)- sound waves above 20,000hz (20khz)

Question 3

What are piezoelectric crystals?

Answer 3

They are a material which generate electricity when mechanical stress is applied to it because the structure which is usually perfectly balance electrical charge gets distrupted

Question 4

What is the process of generating an ultrasound?

Answer 4

1. The PC has an AC applied across it causing it to vibrate and produce ultrasounds
2. The US go to the target and are reflected back towards the probe
3. When the US reaches the probe the vibrations cause mechanical stress to be applied to the PC causing it to produce AC
4. The large back blocking chamber get rid of unwanted sound waves to improve resolution
5. The US transducers process the AC as sound waves based of frequency and time between signals to calculate depth and speed

Question 5

Why is energy lost?

Answer 5

This is due to acoustic impedance- the resistance a material has towards sounds waves (US) passing through it.- the resistance towards vibrations passing through. This depends on density, elasticity, texture or the normal speed of sound.

Between two materials some energy is lost in the boundary which is the difference in acoustic impedance between two materials. The less of a difference, the less boundary you have, the less US wave is reflected

lose energy at boundary interactions (eg reflection and absorption) and acoustic impedance