74. ULTRASOUNDS: PIEZOELECTRIC MATERIAL

Question 1

1. What are Transducers made of?

Answer 1

• they are made of a Synthetic Ceramic
• this is known as Piezoceramic

Question 2

2. What are some examples of Piezoceramic materials?

Answer 2

1. Lead-Ziconate-Titanate (PZT)
2. Polyvinylidene Difluoride (PVDF)
3. A composite

Question 3

3. Do the Piezoelectric properties of PZT occur spontaneously?

Answer 3

• NO
• they are created by exposing the material to a strong
  electric field
• this is done while the material is being heated to a
  substantial temperature
• this is called Polarisation

Question 4

4. What is the Curie Temperature (Curie Point)?

Answer 4

• this is the temperature at which PZT is polarised
• it is generally around 360°C

Question 5

5. What happens if the polarised PZT is heated above the Curie Temperature?

Answer 5

• the Crystal Piezoelectric properties are destroyed
• this is known as Depolarisation

Question 6

6. In a Pulse Wave Transducer, what can be said about the speed of sound in PZT and the frequency?

Answer 6

• they are directly related

Question 7

7. What happens when the Speed of Sound in PZT becomes faster?

Answer 7

• the frequency of the sound that is created is higher

Question 8

8. What range does the Speed of Sound in most Piezoelectric materials fall into?

Answer 8

• 4 to 6 mm/µs

Question 9

9. In a pulsed wave, what kind of materials create higher frequency sound pulses?

Answer 9

• thinner active elements

Question 10

10. What is the relation between PZT thickness and Frequency?

Answer 10

• they are inversely proportional

Question 11

11. How would we mathematically calculate the frequency (MHz)?

Answer 11

Question 12

12. What range does the thickness of PZT crystals in Diagnostic Imaging transducers fall into?

Answer 12

• 0.2 to 0.1 mm