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Physics 2 > Transducer Construction > Flashcards

Transducer Construction Flashcards

1
Q

in US, we convert _____ energy to _____ and then _____ energy back to _____

A

electrical
acoustic
acoustic
electrical

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2
Q

piezoelectric crystal or element
signal conversion device

A

transducer

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3
Q

piezoelectric material

A

crystal

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4
Q

element is another name for

A

piezoelectric material

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5
Q

scan- head is another name for

A

transducer

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6
Q

another name for transducer including the housing and internal circuitry

A

transducer assembly

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7
Q

housing

A

contains all probe components

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8
Q

backing material

A

mixture of metal, plastic, or epoxy bonded to the back of the crystal

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9
Q

crystal

A

ceramic element that has piezoelectric properties

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10
Q

matching layer

A

used to reduce sound reflection from the skin and enhance sound transmission

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11
Q

contains all probe components

A

housing

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12
Q

mixture of metal, plastic, or epoxy bonded to the back of the crystal

A

backing material

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13
Q

ceramic element that has piezoelectric properties

A

crystal

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14
Q

used to reduce sound reflection from the skin and enhance sound transmission

A

matching layer

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15
Q

electric shield

A

blocks electricity from interfering

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16
Q

insulator ring

A

prevents sound from coming out of the side

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17
Q

what is PZT

A

lead zirconate titanate
man-made ceramics in replacement of the crystal

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18
Q

what is PVFD

A

polyvinylidene fluoride
man-made polymer in replacement of the crystal

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19
Q

natural material used as the crystal

A

quartz
tourmaline
Rochelle salt

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20
Q

the piezoelectric effect (____) occurs when a mechanical pressure _____ the crystal which changes the _____ of the electric _____ producing a small electrical voltage

A

direct
deforms
orientation
dipoles

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21
Q

the piezoelectric effect (direct) occurs when a ______ pressure deforms the crystal which changes the orientation of the electric dipoles producing a small ____ _____

A

mechanical
electrical voltage

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22
Q

the reverse (_____) effect is where an electrical voltage changes the ______ of the ____ causing the crystal to ____ and _____

A

indirect
orientation
dipoles
expand
contract

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23
Q

what is the reverse piezoelectric effect

A

Electricity sent to Crystal causing them to vibrate (producing ultrasound)

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24
Q

what is the piezoelectric effect

A

Applying pressure waves to crystal causes electrical pulses (voltage)

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25
Q

what are electricity dipoles

A

essentially the molecules within the crystal and they have a positive charge at one end and a negative charge at the other end

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26
Q

like any other dipolar material, it can be influenced by an _____ or _____ ___

A

electrical
magnetic
field

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27
Q

what is better, when the dipoles are at random alignment or if they are in the same alignment and why

A

in the same alignment
the vibration is inefficient when an electrical current is applies if random but improves lots when in alignment

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28
Q

in early probes the crystal was ___ shaped and could vibrate in a ____ mode or in a ____ mode

A

disc
thickness
radial

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29
Q

the probes we use today have a different shaped crystal and can vibrate in three modes: ____, _____, ____
which one(s) are desirable

A

thickness
length
width

desirable: thickness

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30
Q

when a substance is ___ beyond its ____ ____, the ___ between the molecules _____

A

heated
Currie temperature
bonds
weaken

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31
Q

if the substance is subjected to an electrical field, then the dipoles will ____ accordingly, then the substance is ___, and the bonds ____

A

align
cooled
strengthen

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32
Q

the Currie temp for PZT is

A

350 celsius (not Fahrenheit like an oven)

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33
Q

why aren’t probes autoclaved (2)

A

reheating them could potentially depolarize the dipoles
plastic housing would melt

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34
Q

the crystal determines what _____ a probe can emit

A

frequencies

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35
Q

4 types of frequency

A

resonant
driving
operating
harmonic

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36
Q

resonant frequency (what, determined by, AKA)

A

one at which the crystal likes to ring at
determined by crystal material and thickness
AKA fundamental frequency

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37
Q

driving frequency (determined, voltage altered =?)

A

determined by the AC voltage sent to the crystal
voltage altered= crystal can be forced to ring at a different f than the resonant (fundamental) frequency

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38
Q

operating frequency

A

one that you are using to scan
same as driving f

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39
Q

2nd harmonic frequency

A

two times the driving/operating f
higher f = higher res

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40
Q

frequency of the crystal relates to the ______ and ____ of the crystal

A

propagation speed of sound
thickness

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41
Q

thicker = _____
thinner= _____

A

lower f
higher f

42
Q

the thickness of the crystal which determines its resonance frequency is equal to _____

A

1/2 wavelength

43
Q

double the thickness of the crystal = ____ the frequency

A

half

44
Q

halve the thickness of the crystal = ____ the frequency

A

double

45
Q

when calculating the crystal thickness it is important to use the ______ in the crystal as a constant

A

speed of sound

46
Q

4000 m/sec = _____ mm/us

A

4

47
Q

what is the backing material typically made of

A

epoxy resin and metal powder (tungsten)

48
Q

backing material AKA

A

damping block

49
Q

the purpose of the backing material (2)

A

reduce the SPL which will improve axial resolution
absorb sound so that reflections don’t occur from behind the crystal

50
Q

what is axial resolution

A

along the ling of the beam
think of the example where long SPL makes two dots look like a line whereas short SPL makes two dots look like two dots

51
Q

what is a downside to the backing material

A

it also reduces the amplitude of the wave thus reducing sensitivity

52
Q

what has to be the same for both the crystal and backing material

A

the Z values

53
Q

as we increase the amount of damping material we will shorten the _______

A

length of the pulse

54
Q

as we increase the amount of damping material we will _____ the length of the pulse

A

shorten

55
Q

shorter pulse = better ____ resolution

A

axial

56
Q

what is needed to accomplish the damping material absorbing sound so that reflections dont occur from behind the crystal

A

the Z value of the damping material must be comparable to the element

57
Q

typically only ____ cycles per pulse are produced (with backing material)

A

2-3

58
Q

a short pulse is better for _____ but for ___ doppler a longer pulse is more accurate

A

resolution
Doppler

59
Q

dynamic damping

A

an electronic means to suppress the ringing of the crystal

60
Q

reflection occurs when there is a difference in _____ across the interface

A

Z values

61
Q

the impedance mismatch between the crystal and the skin is quite large and without the matching layer much of the sound would ______

A

return to the probe before entering the patient

62
Q

the matching layer has a X value between the ___ and the ____ to help reduce the amount of the ____

A

crystal
skin
reflection

63
Q

a potential problem with adding a matching layer is the _____

A

reflections can occur between them and the crystal

64
Q

to solve the problem of reflections occurring between the matching layer and the crystal, the thickness of the matching layer is ____

A

1/4 wavelength

65
Q

1/4 wavelength helps create ______ of waves that reverberate between the matching layers

A

destructive interferance

66
Q

why is more than one matching layer typically used

A

because more than one frequency can come out of the probe

67
Q

many matching layers will accommodate multiple frequencies thus improving the transmission and reception of a wide ___ of frequencies

A

bandwidth

68
Q

1/4 wavelength = ____ degrees on a sine wave

A

90

69
Q

what is also a matching layer as it helps transmit the sound into the patient

A

gel

70
Q

gel has a Z value somewhere between the ____ of the probe and the ___

A

last matching layer
skin

71
Q

spike voltage uses a _____ (____) to vibrate the crystal

A

direct current (DC)

72
Q

in spike voltage what is true about the driving/resonant frequency

A

the driving/operating frequency is always equal to the resonant frequency

73
Q

in spike voltage the ______ frequency is always equal to the _____ frequency

A

driving/operating
resonant

74
Q

DC current is AKA and why

A

saw tooth voltage because of its appearance (each spike is one pulse like a saw tooth)

75
Q

in burst voltage, what is true about the driving/operating frequency

A

the driving frequency of the voltage determines the operating frequency

76
Q

burst voltage uses _____ (____) to vibrate the crystal

A

alternating current (AC)

77
Q

In DC, the current from the pulser hits the crystal where one _____ is equal to one pulse
In AC, the current from the pulser hits the crystal where one _____ is equal to one pulse

A

spike
voltage burst

78
Q

in burst voltage, the _____ frequency of the voltage determines the ______ frequency

A

driving
operating

79
Q

burst voltage (AC) looks like what

A

a sine wave

80
Q

in burst voltage, the frequency of the voltage determines …

A

the frequency of the probe

81
Q

what is the bandwidth

A

the range of frequencies that are produced by a pulse

82
Q

when we dampen the crystal to _____ the length of the pulse, then a _____ range of frequencies are emitted from the probe

A

shorten
greater

83
Q

without dampening, a crystal will ring at its _______ frequency and there is a ____ range of frequencies produced

A

resonant
small

84
Q

what frequency has the highest amplitude when graphing the bandwidth and why

A

the resonant
crystal thickness/material determine the most efficient f to ring at

85
Q

the shorter the pulse the ____ the bandwidth

A

wider

86
Q

short pulse is more desirable for better _____

A

resolution

87
Q

have a wider bandwidth means that we have more options for what _____ frequency we can choose

A

driving

88
Q

the frequencies that we can drive the probe at are limited by (2)

A

the size of the bandwidth
attenutation

89
Q

what frequencies are too weak to be used by the system (bandwidth)

A

any frequencies with less than half the resonant frequency

90
Q

what is the usable bandwidth referred to as and why

A

the 6dB bandwidth

6dB is equal to one half the amplitude or 1/4 the intensity of the resonant

(remember 1/2 intensity = 3dB loss so 1/4 = 6dB loss,
also I=amp^2 so I=1/4)

91
Q

increase amount of damping = _____ the pulse and ____ the range of frequencies that are emitted

A

shorten
increase

92
Q

increase damping = ______ sensitivity, but shorter pulse = _____ resolution

A

decrease
increased

93
Q

fractional bandwidth equation

A

FB = bandwidth/frequency

94
Q

a probe with an FB of over ___ percent is considered a ______ design

A

80
broadband

95
Q

what is quality factor and its equation

A

the reciprocal of FB

Q= frequency/bandwidth

96
Q

it is desirable to have a ____ Q for 2D scanning, and it gets _____ as we use colour Doppler, pulsed Doppler, and CW doppler respectively

A

low
higher

97
Q

high fractional bandwidth (FB) = _____ quality factor (Q)

A

decreased

98
Q

increased Q = _____ FB

A

decreased

99
Q

to optimize 2D we use ___ damping to ____ the pulse; this ____ resolution by ____ SPL and ____ the bandwidth

A

more
shorten
increases
reducing
increasing

100
Q

modes requiring more sensitivity will benefit from a _____ bandwidth or ____ Q (CW Doppler)

A

narrower
higher

Physics 2 (3 decks)

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