book study questions Test3 Flashcards
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?
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
Is pulse length directly or inversely related to pulse duration?
directly
Is Q-factor directly or inversely related to bandwidth?
inversely
Is pulse duration directly or inversely related to bandwidth?
inversely
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.
less than
Describe an imaging transducer:
low sensitivity
low Q
wide bandwidth
damped
Shorter duration events (such as dampened pulses) are more likely to be wide bandwidth.
True
What occurs when a PZT crystal’s temp is elevated above the Curie point?
the PZT is depolarized
the crystal’s piezoelectric properties are lost and the transducer is ruined
The acoustic impedance of the matching layer is approx the same as the acoustic impedance of skin
False
impedance of matching layer is greater than that of the skin
Imaging transducers are usually of high rather than low bandwidth
True
A very high Q factor transducer is used more often in diagnostic imaging transducers than a low Q factor
False
Imaging transducers are low-Q
A pulse with a long pulse duration is likely to have a narrow bandwith
True
The damping material in a transducer increases the sensitivity
False
damping reduces sensitivity
The damping material in a transducer increases the pulse length
False
damping shortens pulse length
The damping material in a transducer decreases the pulse duration
True
The damping material in a transducer improves the system’s lateral resolution
False
damping does not affect lateral resolution
The damping material in a transducer improves the system’s longitudinal resolution
True
The damping material in a transducer decreases the bandwidth
False
damping increases bandwidth
The damping material in a transducer decreases the quality factor
True
If the frequency of the electrical excitation voltage of a pulsed wave transducer is 6MHz, then the operating frequency of the transducer is 6MHz
False
pulsed wave transducers-frequency of sound is not determined by the elcetrical signal
If the pulse repetition frequency of a transducer is increased, then the frequency of sound produced by the transducer remains the same
True
The diameter of the active element of a transducer helps to determine the frequency of the sound that the transducer creates
False
If the frequency of the electrical excitation voltage of a continuous wave transducer is 6MHz, then the operating frequency of the transducer is 6MHz
True
they are identical with continuous wave transducers
Two piezoelectric crystals are made from the same material
The thicker crystal will make a pulsed transducer with a higher frequency
False
thicker active elements create sound with lower frequency, not higher
Two piezoelectric crystals are made from the same material
the thicker crystal will make a continuous wave transducer with a lower frequency
False
continuous wave transducer-active element thickness does not determine the sound beam’s frequency
The normal propagation speed in piezoelectric material is about 3-5 times greater than that in soft tissue
True
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?
The impedance of the matching layer should be something in between the active element and the skin
What will produce sound with the lowest frequency?
Sound with the lowest frequency is produced by a thick active element with a low speed
Which type of transducer has a greater Q-factor:
therapeutic or imaging?
Therapeutic
Which type of transducer has a greater bandwidth:
continuous wave or imaging?
Imaging has a wider bandwith
Which type of transducer has more backing material:
therapeutic or imaging?
Imaging transducers
In an imaging transducer, what is the purpose of attaching the backing material to the PZT?
improve the image quality
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?
6MHz
bandwidth is the range of frequencies
8MHz-2MHz=6MHz
What is the main frequency of a transducer that has a resonant frequency of 5MHz?
the resonant, main, or center frequency is 5MHz
What is the Q-factor of a transducer with a resonant frequency of 5MHz and a bandwidth of 6MHz?
0.8
Q-factor is resonant frequency/bandwidth
5MHz/6MHz=0.8
bandwidth has no units
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?
probe with a 6mm probe has a shallower focus
a pair of 9mm diameter probes are identical except for frequency, which is 3MHz and 6MHz
which beam will have a shallower focus?
3MHz beam has a shallower focus
what type of beam would create the deepest focus?
probe with the largest diameter and highest frequency gives it the deepest focus
what type of probe would create the shallowest focus?
probe with the smallest diameter and lowest frequency will have the shallowest focus
active element diameter and near zone length are directly related
true
transducer frequency and near zone length are inversely related
false
frequency and near zone length are directly related
wavelength and near zone length are inversely related
true
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?
probe with a 10mm active element has a less divergent beam
larger diameter, higher frequency= less divergent
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?
3MHz beam is more divergent
smaller diameter, lower frequency= more divergent
transducer frequency and beam divergence are inversely related
true
active element diameter and beam divergence are inversely related
true
the frequency of a transducer does not change
if the diameter of the new piezoelectric crystal increases, what happens to the near zone length?
increases
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?
decreases
the frequency of a transducer does not change
if the diameter of the new piezoelectric crystal increases, what happens to the wavelength?
no change
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?
increases
what is the shape of a sound beam created by a tiny piece of PZT?
V-shaped
what explains why a sound beam created by a disc-shaped crystal is hourglass shaped?
Huygens’ Principle
what is the deepest location in a sound beam?
the end of the Fraunhofer zone
