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Fall:Physics > book study questions Test3 > Flashcards

book study questions Test3 Flashcards

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1
Q

You are given 5 substances:

backing material, PZT, matching layer, gel, skin

five impedances of:

0.8 Mrayls, 1.9 Mrayls, 1.6 Mrayls, 2.0 Mrayls, 1.0 Mrayls

If the impedance of the backing material is 1.9 Mrayls, what are the impedances of the other four?

A

The impedance of the active layer is similar to the backing material, so:

backing material-1.9Mrayls

PZT-2.0Mrayls

matching layer-1.6Mrayls

gel-1.0Mrayls

skin-0.8Mrayls

in order of the course of the energy from the PZT through the skin

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2
Q

Is pulse length directly or inversely related to pulse duration?

A

directly

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3
Q

Is Q-factor directly or inversely related to bandwidth?

A

inversely

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4
Q

Is pulse duration directly or inversely related to bandwidth?

A

inversely

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5
Q

The sensitivity of transducers that create short duration pulses is likely to be (greater than, less then, or equal to) that of transducers that create long pulses.

A

less than

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6
Q

Describe an imaging transducer:

A

low sensitivity

low Q

wide bandwidth

damped

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7
Q

Shorter duration events (such as dampened pulses) are more likely to be wide bandwidth.

A

True

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8
Q

What occurs when a PZT crystal’s temp is elevated above the Curie point?

A

the PZT is depolarized

the crystal’s piezoelectric properties are lost and the transducer is ruined

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9
Q

The acoustic impedance of the matching layer is approx the same as the acoustic impedance of skin

A

False

impedance of matching layer is greater than that of the skin

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10
Q

Imaging transducers are usually of high rather than low bandwidth

A

True

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11
Q

A very high Q factor transducer is used more often in diagnostic imaging transducers than a low Q factor

A

False

Imaging transducers are low-Q

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12
Q

A pulse with a long pulse duration is likely to have a narrow bandwith

A

True

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13
Q

The damping material in a transducer increases the sensitivity

A

False

damping reduces sensitivity

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14
Q

The damping material in a transducer increases the pulse length

A

False

damping shortens pulse length

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15
Q

The damping material in a transducer decreases the pulse duration

A

True

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16
Q

The damping material in a transducer improves the system’s lateral resolution

A

False

damping does not affect lateral resolution

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17
Q

The damping material in a transducer improves the system’s longitudinal resolution

A

True

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18
Q

The damping material in a transducer decreases the bandwidth

A

False

damping increases bandwidth

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19
Q

The damping material in a transducer decreases the quality factor

A

True

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20
Q

If the frequency of the electrical excitation voltage of a pulsed wave transducer is 6MHz, then the operating frequency of the transducer is 6MHz

A

False

pulsed wave transducers-frequency of sound is not determined by the elcetrical signal

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21
Q

If the pulse repetition frequency of a transducer is increased, then the frequency of sound produced by the transducer remains the same

A

True

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22
Q

The diameter of the active element of a transducer helps to determine the frequency of the sound that the transducer creates

A

False

23
Q

If the frequency of the electrical excitation voltage of a continuous wave transducer is 6MHz, then the operating frequency of the transducer is 6MHz

A

True

they are identical with continuous wave transducers

24
Q

Two piezoelectric crystals are made from the same material

The thicker crystal will make a pulsed transducer with a higher frequency

A

False

thicker active elements create sound with lower frequency, not higher

25
Q

Two piezoelectric crystals are made from the same material

the thicker crystal will make a continuous wave transducer with a lower frequency

A

False

continuous wave transducer-active element thickness does not determine the sound beam’s frequency

26
Q

The normal propagation speed in piezoelectric material is about 3-5 times greater than that in soft tissue

A

True

27
Q

The impedance of a transducer active element is 1,900,000 Rayls, and the impedance of skin is 1,400,000 Rayls

what is an acceptable impedance for the matching layer?

A

The impedance of the matching layer should be something in between the active element and the skin

28
Q

What will produce sound with the lowest frequency?

A

Sound with the lowest frequency is produced by a thick active element with a low speed

29
Q

Which type of transducer has a greater Q-factor:

therapeutic or imaging?

A

Therapeutic

30
Q

Which type of transducer has a greater bandwidth:

continuous wave or imaging?

A

Imaging has a wider bandwith

31
Q

Which type of transducer has more backing material:

therapeutic or imaging?

A

Imaging transducers

32
Q

In an imaging transducer, what is the purpose of attaching the backing material to the PZT?

A

improve the image quality

33
Q

A pulsed-wave transducer has a resonant frequency of 5MHz

the lowest frequency in the pulse is 2MHz and the highest is 8MHz

what is the bandwidth?

A

6MHz

bandwidth is the range of frequencies

8MHz-2MHz=6MHz

34
Q

What is the main frequency of a transducer that has a resonant frequency of 5MHz?

A

the resonant, main, or center frequency is 5MHz

35
Q

What is the Q-factor of a transducer with a resonant frequency of 5MHz and a bandwidth of 6MHz?

A

0.8

Q-factor is resonant frequency/bandwidth

5MHz/6MHz=0.8

bandwidth has no units

36
Q

A pair of 6MHz probes are identical except for the active element diameter

the active element diameters are 6mm and 10mm

the sound beam of which probe will have a shallower focus?

A

probe with a 6mm probe has a shallower focus

37
Q

a pair of 9mm diameter probes are identical except for frequency, which is 3MHz and 6MHz

which beam will have a shallower focus?

A

3MHz beam has a shallower focus

38
Q

what type of beam would create the deepest focus?

A

probe with the largest diameter and highest frequency gives it the deepest focus

39
Q

what type of probe would create the shallowest focus?

A

probe with the smallest diameter and lowest frequency will have the shallowest focus

40
Q

active element diameter and near zone length are directly related

A

true

41
Q

transducer frequency and near zone length are inversely related

A

false

frequency and near zone length are directly related

42
Q

wavelength and near zone length are inversely related

A

true

43
Q

a pair of 6MHz probes are identical except for the active element diameters, which are 6mm and 10mm

which beam will be more compact in the far field?

A

probe with a 10mm active element has a less divergent beam

larger diameter, higher frequency= less divergent

44
Q

a pair of 9mm diameter probes are identical except for frequencies, whcih are 3MHz and 6MHz

which sound beam will spread out more in the far field?

A

3MHz beam is more divergent

smaller diameter, lower frequency= more divergent

45
Q

transducer frequency and beam divergence are inversely related

A

true

46
Q

active element diameter and beam divergence are inversely related

A

true

47
Q

the frequency of a transducer does not change

if the diameter of the new piezoelectric crystal increases, what happens to the near zone length?

A

increases

48
Q

the frequency of a transducer does not change

if the diameter of the new piezoelectric crystal increases, what happens to the beam diameter in the far zone?

A

decreases

49
Q

the frequency of a transducer does not change

if the diameter of the new piezoelectric crystal increases, what happens to the wavelength?

A

no change

50
Q

the frequency of a transducer does not change

if the diameter of the new piezoelectric crystal increases, what happens to the beam diameter in the near zone?

A

increases

51
Q

what is the shape of a sound beam created by a tiny piece of PZT?

A

V-shaped

52
Q

what explains why a sound beam created by a disc-shaped crystal is hourglass shaped?

A

Huygens’ Principle

53
Q

what is the deepest location in a sound beam?

A

the end of the Fraunhofer zone

Fall:Physics (10 decks)

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