Transducer Construction Flashcards
in US, we convert _____ energy to _____ and then _____ energy back to _____
electrical
acoustic
acoustic
electrical
piezoelectric crystal or element
signal conversion device
transducer
piezoelectric material
crystal
element is another name for
piezoelectric material
scan- head is another name for
transducer
another name for transducer including the housing and internal circuitry
transducer assembly
housing
contains all probe components
backing material
mixture of metal, plastic, or epoxy bonded to the back of the crystal
crystal
ceramic element that has piezoelectric properties
matching layer
used to reduce sound reflection from the skin and enhance sound transmission
contains all probe components
housing
mixture of metal, plastic, or epoxy bonded to the back of the crystal
backing material
ceramic element that has piezoelectric properties
crystal
used to reduce sound reflection from the skin and enhance sound transmission
matching layer
electric shield
blocks electricity from interfering
insulator ring
prevents sound from coming out of the side
what is PZT
lead zirconate titanate
man-made ceramics in replacement of the crystal
what is PVFD
polyvinylidene fluoride
man-made polymer in replacement of the crystal
natural material used as the crystal
quartz
tourmaline
Rochelle salt
the piezoelectric effect (____) occurs when a mechanical pressure _____ the crystal which changes the _____ of the electric _____ producing a small electrical voltage
direct
deforms
orientation
dipoles
the piezoelectric effect (direct) occurs when a ______ pressure deforms the crystal which changes the orientation of the electric dipoles producing a small ____ _____
mechanical
electrical voltage
the reverse (_____) effect is where an electrical voltage changes the ______ of the ____ causing the crystal to ____ and _____
indirect
orientation
dipoles
expand
contract
what is the reverse piezoelectric effect
Electricity sent to Crystal causing them to vibrate (producing ultrasound)
what is the piezoelectric effect
Applying pressure waves to crystal causes electrical pulses (voltage)
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
like any other dipolar material, it can be influenced by an _____ or _____ ___
electrical
magnetic
field
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
in early probes the crystal was ___ shaped and could vibrate in a ____ mode or in a ____ mode
disc
thickness
radial
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
when a substance is ___ beyond its ____ ____, the ___ between the molecules _____
heated
Currie temperature
bonds
weaken
if the substance is subjected to an electrical field, then the dipoles will ____ accordingly, then the substance is ___, and the bonds ____
align
cooled
strengthen
the Currie temp for PZT is
350 celsius (not Fahrenheit like an oven)
why aren’t probes autoclaved (2)
reheating them could potentially depolarize the dipoles
plastic housing would melt
the crystal determines what _____ a probe can emit
frequencies
4 types of frequency
resonant
driving
operating
harmonic
resonant frequency (what, determined by, AKA)
one at which the crystal likes to ring at
determined by crystal material and thickness
AKA fundamental frequency
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
operating frequency
one that you are using to scan
same as driving f
2nd harmonic frequency
two times the resonant f
higher f = higher res
frequency of the crystal relates to the ______ and ____ of the crystal
propagation speed of sound
thickness
thicker = _____
thinner= _____
lower f
higher f
the thickness of the crystal which determines its resonance frequency is equal to _____
1/2 wavelength
double the thickness of the crystal = ____ the frequency
half
halve the thickness of the crystal = ____ the frequency
double
when calculating the crystal thickness it is important to use the ______ in the crystal as a constant
speed of sound
4000 m/sec = _____ mm/us
4
what is the backing material typically made of
epoxy resin and metal powder (tungsten)
backing material AKA
damping block
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
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
what is a downside to the backing material
it also reduces the amplitude of the wave thus reducing sensitivity
what has to be the same for both the crystal and backing material
the Z values
as we increase the amount of damping material we will shorten the _______
length of the pulse
as we increase the amount of damping material we will _____ the length of the pulse
shorten
shorter pulse = better ____ resolution
axial
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
typically only ____ cycles per pulse are produced (with backing material)
2-3
a short pulse is better for _____ but for ___ a longer pulse is more accurate
resolution
Doppler
dynamic damping
an electronic means to suppress the ringing of the crystal
reflection occurs when there is a difference in _____ across the interface
Z values
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
the matching layer has a Z value between the ___ and the ____ to help reduce the amount of the ____
crystal
skin
reflection
a potential problem with adding a matching layer is the _____
reflections can occur between them and the crystal
to solve the problem of reflections occurring between the matching layer and the crystal, the thickness of the matching layer is ____
1/4 wavelength
1/4 wavelength helps create ______ of waves that reverberate between the matching layers
destructive interferance
why is more than one matching layer typically used
because more than one frequency can come out of the probe
many matching layers will accommodate multiple frequencies thus improving the transmission and reception of a wide ___ of frequencies
bandwidth
1/4 wavelength = ____ degrees on a sine wave
90
what is also a matching layer as it helps transmit the sound into the patient
gel
gel has a Z value somewhere between the ____ of the probe and the ___
last matching layer
skin
spike voltage uses a _____ (____) to vibrate the crystal
direct current (DC)
in spike voltage what is true about the driving/resonant frequency
the driving/operating frequency is always equal to the resonant frequency
in spike voltage the ______ frequency is always equal to the _____ frequency
driving/operating
resonant
DC current is AKA and why
saw tooth voltage because of its appearance (each spike is one pulse like a saw tooth)
in burst voltage, what is true about the driving/operating frequency
the driving frequency of the voltage determines the operating frequency
burst voltage uses _____ (____) to vibrate the crystal
alternating current (AC)
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
in burst voltage, the _____ frequency of the voltage determines the ______ frequency
driving
operating
burst voltage (AC) looks like what
a sine wave
in burst voltage, the frequency of the voltage determines …
the frequency of the probe
what is the bandwidth
the range of frequencies that are produced by a pulse
when we dampen the crystal to _____ the length of the pulse, then a _____ range of frequencies are emitted from the probe
shorten
greater
without dampening, a crystal will ring at its _______ frequency and there is a ____ range of frequencies produced
resonant
small
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
the shorter the pulse the ____ the bandwidth
wider
short pulse is more desirable for better _____
resolution
have a wider bandwidth means that we have more options for what _____ frequency we can choose
driving
the frequencies that we can drive the probe at are limited by (2)
the size of the bandwidth
attenutation
what frequencies are too weak to be used by the system (bandwidth)
any frequencies with less than half the amp of the resonant frequency
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)
increase amount of damping = _____ the pulse and ____ the range of frequencies that are emitted
shorten
increase
increase damping = ______ sensitivity, but shorter pulse = _____ resolution
decrease
increased
fractional bandwidth equation
FB = bandwidth/frequency
a probe with an FB of over ___ percent is considered a ______ design
80
broadband
what is quality factor and its equation
the reciprocal of FB
Q= frequency/bandwidth
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
high fractional bandwidth (FB) = _____ quality factor (Q)
decreased
increased Q = _____ FB
decreased
to optimize 2D we use ___ damping to ____ the pulse; this ____ resolution by ____ SPL and ____ the bandwidth
more
shorten
increases
reducing
increasing
modes requiring more sensitivity will benefit from a _____ bandwidth or ____ Q (CW Doppler)
narrower
higher
