Transducer Construction Flashcards
1
Q
in US, we convert _____ energy to _____ and then _____ energy back to _____
A
electrical
acoustic
acoustic
electrical
2
Q
piezoelectric crystal or element
signal conversion device
A
transducer
3
Q
piezoelectric material
A
crystal
4
Q
element is another name for
A
piezoelectric material
5
Q
scan- head is another name for
A
transducer
6
Q
another name for transducer including the housing and internal circuitry
A
transducer assembly
7
Q
housing
A
contains all probe components
8
Q
backing material
A
mixture of metal, plastic, or epoxy bonded to the back of the crystal
9
Q
crystal
A
ceramic element that has piezoelectric properties
10
Q
matching layer
A
used to reduce sound reflection from the skin and enhance sound transmission
11
Q
contains all probe components
A
housing
12
Q
mixture of metal, plastic, or epoxy bonded to the back of the crystal
A
backing material
13
Q
ceramic element that has piezoelectric properties
A
crystal
14
Q
used to reduce sound reflection from the skin and enhance sound transmission
A
matching layer
15
Q
electric shield
A
blocks electricity from interfering
16
Q
insulator ring
A
prevents sound from coming out of the side
17
Q
what is PZT
A
lead zirconate titanate
man-made ceramics in replacement of the crystal
18
Q
what is PVFD
A
polyvinylidene fluoride
man-made polymer in replacement of the crystal
19
Q
natural material used as the crystal
A
quartz
tourmaline
Rochelle salt
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
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
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
23
Q
what is the reverse piezoelectric effect
A
Electricity sent to Crystal causing them to vibrate (producing ultrasound)
24
Q
what is the piezoelectric effect
A
Applying pressure waves to crystal causes electrical pulses (voltage)
25
what are electricity dipoles
essentially the molecules within the crystal and they have a positive charge at one end and a negative charge at the other end
26
like any other dipolar material, it can be influenced by an _____ or _____ ___
electrical
magnetic
field
27
what is better, when the dipoles are at random alignment or if they are in the same alignment and why
in the same alignment
the vibration is inefficient when an electrical current is applies if random but improves lots when in alignment
28
in early probes the crystal was ___ shaped and could vibrate in a ____ mode or in a ____ mode
disc
thickness
radial
29
the probes we use today have a different shaped crystal and can vibrate in three modes: ____, _____, ____
which one(s) are desirable
thickness
length
width
desirable: thickness
30
when a substance is ___ beyond its ____ ____, the ___ between the molecules _____
heated
Currie temperature
bonds
weaken
31
if the substance is subjected to an electrical field, then the dipoles will ____ accordingly, then the substance is ___, and the bonds ____
align
cooled
strengthen
32
the Currie temp for PZT is
350 celsius (not Fahrenheit like an oven)
33
why aren't probes autoclaved (2)
reheating them could potentially depolarize the dipoles
plastic housing would melt
34
the crystal determines what _____ a probe can emit
frequencies
35
4 types of frequency
resonant
driving
operating
harmonic
36
resonant frequency (what, determined by, AKA)
one at which the crystal likes to ring at
determined by crystal material and thickness
AKA fundamental frequency
37
driving frequency (determined, voltage altered =?)
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
38
operating frequency
one that you are using to scan
same as driving f
39
2nd harmonic frequency
two times the resonant f
higher f = higher res
40
frequency of the crystal relates to the ______ and ____ of the crystal
propagation speed of sound
thickness
41
thicker = _____
thinner= _____
lower f
higher f
42
the thickness of the crystal which determines its resonance frequency is equal to _____
1/2 wavelength
43
double the thickness of the crystal = ____ the frequency
half
44
halve the thickness of the crystal = ____ the frequency
double
45
when calculating the crystal thickness it is important to use the ______ in the crystal as a constant
speed of sound
46
4000 m/sec = _____ mm/us
4
47
what is the backing material typically made of
epoxy resin and metal powder (tungsten)
48
backing material AKA
damping block
49
the purpose of the backing material (2)
reduce the SPL which will improve axial resolution
absorb sound so that reflections don't occur from behind the crystal
50
what is axial resolution
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
what is a downside to the backing material
it also reduces the amplitude of the wave thus reducing sensitivity
52
what has to be the same for both the crystal and backing material
the Z values
53
as we increase the amount of damping material we will shorten the _______
length of the pulse
54
as we increase the amount of damping material we will _____ the length of the pulse
shorten
55
shorter pulse = better ____ resolution
axial
56
what is needed to accomplish the damping material absorbing sound so that reflections dont occur from behind the crystal
the Z value of the damping material must be comparable to the element
57
typically only ____ cycles per pulse are produced (with backing material)
2-3
58
a short pulse is better for _____ but for ___ a longer pulse is more accurate
resolution
Doppler
59
dynamic damping
an electronic means to suppress the ringing of the crystal
60
reflection occurs when there is a difference in _____ across the interface
Z values
61
the impedance mismatch between the crystal and the skin is quite large and without the matching layer much of the sound would ______
return to the probe before entering the patient
62
the matching layer has a Z value between the ___ and the ____ to help reduce the amount of the ____
crystal
skin
reflection
63
a potential problem with adding a matching layer is the _____
reflections can occur between them and the crystal
64
to solve the problem of reflections occurring between the matching layer and the crystal, the thickness of the matching layer is ____
1/4 wavelength
65
1/4 wavelength helps create ______ of waves that reverberate between the matching layers
destructive interferance
66
why is more than one matching layer typically used
because more than one frequency can come out of the probe
67
many matching layers will accommodate multiple frequencies thus improving the transmission and reception of a wide ___ of frequencies
bandwidth
68
1/4 wavelength = ____ degrees on a sine wave
90
69
what is also a matching layer as it helps transmit the sound into the patient
gel
70
gel has a Z value somewhere between the ____ of the probe and the ___
last matching layer
skin
71
spike voltage uses a _____ (____) to vibrate the crystal
direct current (DC)
72
in spike voltage what is true about the driving/resonant frequency
the driving/operating frequency is always equal to the resonant frequency
73
in spike voltage the ______ frequency is always equal to the _____ frequency
driving/operating
resonant
74
DC current is AKA and why
saw tooth voltage because of its appearance (each spike is one pulse like a saw tooth)
75
in burst voltage, what is true about the driving/operating frequency
the driving frequency of the voltage determines the operating frequency
76
burst voltage uses _____ (____) to vibrate the crystal
alternating current (AC)
77
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
spike
voltage burst
78
in burst voltage, the _____ frequency of the voltage determines the ______ frequency
driving
operating
79
burst voltage (AC) looks like what
a sine wave
80
in burst voltage, the frequency of the voltage determines ...
the frequency of the probe
81
what is the bandwidth
the range of frequencies that are produced by a pulse
82
when we dampen the crystal to _____ the length of the pulse, then a _____ range of frequencies are emitted from the probe
shorten
greater
83
without dampening, a crystal will ring at its _______ frequency and there is a ____ range of frequencies produced
resonant
small
84
what frequency has the highest amplitude when graphing the bandwidth and why
the resonant
crystal thickness/material determine the most efficient f to ring at
85
the shorter the pulse the ____ the bandwidth
wider
86
short pulse is more desirable for better _____
resolution
87
have a wider bandwidth means that we have more options for what _____ frequency we can choose
driving
88
the frequencies that we can drive the probe at are limited by (2)
the size of the bandwidth
attenutation
89
what frequencies are too weak to be used by the system (bandwidth)
any frequencies with less than half the amp of the resonant frequency
90
what is the usable bandwidth referred to as and why
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
increase amount of damping = _____ the pulse and ____ the range of frequencies that are emitted
shorten
increase
92
increase damping = ______ sensitivity, but shorter pulse = _____ resolution
decrease
increased
93
fractional bandwidth equation
FB = bandwidth/frequency
94
a probe with an FB of over ___ percent is considered a ______ design
80
broadband
95
what is quality factor and its equation
the reciprocal of FB
Q= frequency/bandwidth
96
it is desirable to have a ____ Q for 2D scanning, and it gets _____ as we use colour Doppler, pulsed Doppler, and CW doppler respectively
low
higher
97
high fractional bandwidth (FB) = _____ quality factor (Q)
decreased
98
increased Q = _____ FB
decreased
99
to optimize 2D we use ___ damping to ____ the pulse; this ____ resolution by ____ SPL and ____ the bandwidth
more
shorten
increases
reducing
increasing
100
modes requiring more sensitivity will benefit from a _____ bandwidth or ____ Q (CW Doppler)
narrower
higher
