Instrumentation

Question 1

What is the purpose of the backing block?

Answer 1

defines Q value and bandwidth; absorbs energy

Question 2

What is the purpose of the matching layer?

Answer 2

Improves acoustic matching, maximizes pressure entering the tissue

Minimize acoustic
impedance
mismatch between
PZT and Tissue

Question 3

Properties of piezro-electric crystals

Answer 3

• applied voltage induces crystal contraction/expansion
• contraction/expansion produces pressure pulse
• applied pressure induce voltage change
• transmitter and receiver

Question 4

How does the size of the transducer affect penetration depth and convergence angle?

Answer 4

as d increases:
- penetration depth increases
((d^2)f) / 4v
- convergence angle decreases
v / (df)

Question 5

How does the frequency affect penetration depth and convergence angle?

Answer 5

as f increases:
- penetration depth increases
- convergence angle decreases

Question 6

Describe the Fresnel zone of the transducer beam

Answer 6

• “near field”
• constant beam width
• extends to distance: r^2 / (lamda * (d^2)*f)

Question 7

Describe the Fraunhoffer zone of the transducer beam

Answer 7

• “far field”
• divergent beam width
• extends to distance: lamda / (2r * (d^2)*f)