Physics-Transducers

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1. You are given 5 substances: backing material, PZT, matching layer, gel, and skin, whos impedances have been measured. Unfortunately the labels identifying the impedances of each substance have fallen off these materials. There are 5 labels, indicating impedances of 0.8 Mrayls, 1.9 Mrayls, 1.6 Mrayls, 2.0 Mrayls, and 1.0 Mrayls. If the impedance of the backing material is 1.9 Mrayls, what are the impedances of soft tissue, matching layer, gel and PZT? Why?
• soft tissue: 0.8 Mrayls
• gel: 1.0 Mrayls
• matching layer: 1.6 Mrayls
• PZT: 2.0 Mrayls
• Impedance decreases as it moves from the PZT to the skin
2. Pulse length is __________ related to pulse duration. (directly, inversely)
directly
3. Q-factor is __________ related to bandwidth (directly, inversely)
inversely
4. Pulse duration is __________ related to bandwidth. (directly, inversely)
inversely
5. The sensitivity of transducers that create short duration pulses is likely to be __________ that of transducers that create long pulses. (greater than, less than, equal to)
less than
6. All of the following correctly describe an imaging transducer except:
A. high sensitivity
B. low Q
C. wide bandwidth
D. damped
• A. high sensitivity
• Transducers have low sensitivity
7. True or False.
Shorter duration events (such as dampened pulses) are more likely to be wide bandwidth.
True
8. What occurs when a PZT crystal's temperature is elevated above the Curie point?
the PZT is depolarized
9. True or False.
The acoustic impedance of the matching layer is approximately the same as the acoustic impedance of skin.
• False.
• matching layer is greater than skin impedance
10. True or False.
Imaging transducers are usually of high rather than low bandwidth
• True.
• aka wide bandwidth
11. True or False.
A very high Q factor transducer is used more often in diagnostic imaging transducers than a low Q factor.
• False.
• Imaging transducers are low-Q
12. True or False.
A pulse with a long pulse duration is likely to have a narrow bandwidth.
True.
13. True or False.
The damping material in a transducer increases the sensitivity.
• False.
• damping reduces sensitivity
14. True or False.
The damping material in a transducer increases the pulse length.
• False.
• damping shortens pulse length
15. True or False.
The damping material in a transducer decreases the pulse duration.
True.
16. True or False.
The damping material in a transducer improves the system's lateral resolution.
• False.
• damping does not affect lateral resolution
17. True or False.
The damping material in a transducer imporves the systems lateral resolution.
True.
18. True or False.
The damping material in a transducer decreases the bandwidth.
• False.
• damping increses bandwidth
19. True or False.
The damping material in a transducer decreases quality factor.
True
20. True or False.
If the frequency of the electrical excitation voltage of a pulsed wave transducer is 6 MHz, then the operating frequency of the transducer is 6 MHz.
• False.
• With pulsed wave transducers, the frequency of sound is not determined by the electrical signal.
21. True or False.
If the pulse repetition frequency of a transducer is increased, then the frequency of sound produced in the transducer remains the same.
• True.
• Frequency and PRF are not related.
22. True or False.
The diameter of the active element of a transducer helps to determine the frequency of the sound produced by the transducer.
• False.
• The thickness does
23. True or False.
If the frequency of the electrical excitation voltage of a continuous wave transducer is 6 MHz, then the operating frequency of the transducer is 6 MHz.
true
24. True or False.
Two piezoelectric crystals are made from the same material. The thicker crystal will make a pulsed transducer with a higher frequency.
• False.
• Thicker crystal = lower frequency
25. True or False.
Two piezoelectric crystals are made of the same material. The thicker crystal will make a continuous wave transducer with a lower frequency.
• False.
• with continuous wave, the active element thickness does not determine frequency
26. True or False.
The normal propagation speed in piezoelectric material is about 3 to 5 times greater than is soft tissue.
True.
27. The impedance of a transducer active element is 1,900,000 rayls, and the impedance of the skin is 1,400,000 rayls. What is an acceptable impedance for the matching layer?
A. 1,200,000 rayls
B. 1,400,000 rayls
C. 1,726,000 rayls
D. 1,950,000 rayls
C. 1,726,00 rayls because it is between the two impedances
(this multiple choice question has been scrambled)
28. Which of the following crystals will produce sound with the lowest frequency?
A. thick and high speed
B. thick and low speed
C. thin and with low speed
D. thin and high speed
B. thick and low speed
(this multiple choice question has been scrambled)
29. Which type of transducer has a greater Q-factor: therapeutic or imaging?
therapeutic
30. Which type of transducer has greater bandwidth: continuous wave or imaging?
imaging
31. Which type of transducer has more backing material: therapeudic or imaging?
imaging
32. In an imaging transducer, what is the purpose of attaching the backing material to the PZT?
to improve the image quality
33. A pulsed wave transducer has a resonant frequency of 5 MHz. The lowest frequency in the pulse is 2 MHz and the highest is 8 MHz. What is the bandwidth?
• 6 MHz
• 8 MHz - 2 MHz
34. A pulsed wave transducer has a resonant frequency of 5 MHz. The lowest frequency in the pulse is 2 MHz and the highest is 8 MHz. What is the main frequency?
5 MHz
35. A pulsed wave transducer has a resonant frequency of 5 MHz. The lowest frequency in the pulse is 2 MHz and the highest is 8 MHz. What is the Q-factor?
5/6 = 0.8
 Author: aprilh4485 ID: 115800 Card Set: Physics-Transducers Updated: 2011-11-10 02:10:32 Tags: Sonography Folders: Description: Transducers Show Answers: