Quiz 5 Flashcards
What is the region in an unfocused beam that extends from the transducer surface to an axial distance where the field begins to diverge?
Fresnel zone
What change while make the near zone become longer?
Increased diameter of crystal
Which statement regarding the near field or the far field zones is true?
The near field length increases with increasing frequency
Which change will increase the rate of far field divergence?
Decrease in frequency
For an unfocused transducer, what is the approximate beam width at the focal distance and twice the focal distance, given a crystal diameter of 5mm ?
2.5 mm, 5 mm
The transmitted beam diverges is which zone?
Fraunhofer Zone
True/False
If the number of cycles in the pulse are increased, the axial resolution improves
False
What will happen to the crystal if you heat a transducer above the Curie point?
Becomes depolarized
What is used to make most crystals in modern diagnostic sonographic transducers?
Lead zirconate titanate
Why is the piezoelectric effect employed in diagnostic medical ultrasound?
Generate sound waves from electrical waves
True/False
Intensity is uniform throughout the beam
False
What is the use of the transducer lens?
Used to help focus the beam
What is the use of the transducers matching layers?
Lowers acoustic impedance mismatch between the transducer and patient
What is the use of the transducers piezoelectric effect?
Converts electrical to mechanical energy
What is the use of the transducers backing material?
Used to decrease the SPL, improve AR, increase transducer BW, and decrease transducer sensitivity.
What is the most common natural piezoelectric material?
Quartz
The matching layers are cut to _______ the _______ of the crystal.
1/4 of the wavelength
An advantage to multiple transmit foci per line is improved _____ resolution, however, ______ resolution will degrade.
Lateral, temporal
The velocity of sound waves is primarily dependent on the…
Material in which the sound is being transmitted
One benefit of composit piezoelectric elements over natural elements is:
Acoustic impedance closer to that of soft tissue.
True/False
The crystals in linear sequenced array transducers are fired off in groups to create a longer near zone.
True
True/False:
If a crystal is damaged in a phase array transducer there will be a black line on the screen corresponding to that specific crystal.
False
Huygens principle states that:
Numerous wavelets that are produced form a new wave front using constructive interference.
What primarily determines the operating frequency of an ultrasonic transducer?
Thickness of the crystal