review: Test3 Flashcards
Two crystals made of the same material
the thicker crystal will create pulsed ultrasound with what?
(what’s a thicker crystal going to produce?)
thicker PZT crystal will create pulsed ultrasound with slower speeds and low frequency
what are the characteristics of imaging transducers?
pulses with short duration and length
uses backing material to limit ringing
reduced sensitivity
wide bandwidth or broadband
lower Q-factor
improved axial resolution
what are the characteristics of non-imaging transducers?
creates continuous wave or pulses with long duration and length
no backing material
increased sensitivity
narrow bandwidth
higher Q-factor
cannot even create an image
what is the thickness of the matching layer?
1/4 wavelength thick
what is the thickness of the active element?
1/2 wavelength thick
what happens when PZT exceeds the Curie point?
the crystal’s properties are destroyed (depolarization)
the PZT is depolarized
what is the process called when PZT materials change shape?
piezoelectric effect
what are all the names for lead zirconate titanate?
PZT, ceramic, active element, crystal, piezoelectric, ferroelectric
which component reduces the ringing of the pulse?
backing material (damping element)
if we have a transducer with a main frequency of 6MHz, produces a sound pulsed that has frequencies ranging from 1MHz-6MHz, the bandwidth or range of frequency in this pulse is, what?
5MHz
6MHz-1MHz=5MHz
How do you calcuate a Q-factor?
quality factor=
main frequency/bandwidth
what is the normal propagation speed of piezoelectric material?
the speed of sound in most PZT material ranges from 4-6mm/µs (about 4 times greater than the speed of sound in soft tissue)
which crystal will produce sound with a lower frequency and which will produce sound with a higher frequency?
thinner crystals=higher frequency
thicker crystals=lower frequency
what is the acoustic impedance of the matching layer?
damping material improves the system’s what?
improves axial resolution
if the frequency of the electrical excitation voltage of a pulsed transducer is 6MHz, then the operating frequency is, what?
what is the impedance of an active element in Rayls?
the impedance of a transducer active element is 1,900,000 Rayls
which transducer component has a thin barrier of cork?
acoustic insulator
which transducer component increases the efficiency of sound?
matching layer
what’s the purpose of having backing material?
it reduces the “ringing” of the PZT
factors that affect focal depth:
shallow focus, deep focus
shallow focus- smaller diameter PZT, lower frequency
deep focus- larger diameter PZT, higher frequency
how are frequency and near zone length related?
frequency and near zone length are DIRECTLY related
two transducers have the same diameter
one probe has a higher frequency than the other, which one has the shallow focus? the deeper focus?
higher frequency-deeper focus
lower frequency-shallow focus
with the diameter of the probe and the frequency given, which one will have the least divergence? the most divergence?
less divergence- larger diameter, higher frequency
more divergence- smaller diameter, lower frequency
how is the frequency of sound determined?
speed of sound in the PZT
thickness of the PZT
how is the focal length determined?
transducer diameter
frequency of the sound
how is the spread of the sound beam in the far field determined?
transducer diameter
frequency of the sound
with the transducer’s frequency and diameters, which one has the best lateral resolution?
higher frequency and larger diameter= less divergence
(better lateral resolution)
with measurement of diameter, where is the focal depth?
transducer diameter and focal depth are DIRECTLY related
focal depth(mm)=
diameter(mm)2/4 x wavelength(mm)
if the frequency has not changed and the diameter increases, what will happen to the wavelength?
there is no change to the wavelength
if the frequency has not changed and the diameter increases, what will happen to the near zone length?
it increases
what determines the spread of the beam in the far field?
transducer diameter
frequency of the sound
which one has the shallowest focus?
smallest diameter PZT
lowest frequency
which has the deepest focus?
largest diameter PZT
highest frequency
which one diverges more?
smallest diameter
lowest frequency
which one diverges less?
largest diameter
highest frequency
what is the shape of the sound beam that is created by a tiny piece of PZT? what type of pattern is it?
V-shaped waves
spherical, diffraction patterns
What are the different names for the different fields on the hour glass?
near zone
focal zone
focus
far zone
on the hourglass, where’s the deepest section? most shallow?
deepest- deeper than 2 near zone lengths
most shallow- at the focus
