ARDMS SPI Transducer Construction and Function 2 — Questions and Answers
Question 1: Which material property is most important for a transducer backing layer?
- High acoustic impedance and high attenuation (Correct answer)
- Low acoustic impedance and low attenuation
- High acoustic impedance and low attenuation
- Matched acoustic impedance to tissue
Correct answer: High acoustic impedance and high attenuation
The backing layer requires high acoustic impedance to load the crystal and high attenuation to absorb rearward-traveling energy and shorten pulse duration.
Question 2: A transducer's Q factor is defined as the ratio of the operating frequency to the:
- Pulse repetition frequency
- Bandwidth (Correct answer)
- Nyquist frequency
- Frame rate
Correct answer: Bandwidth
Q factor = operating (center) frequency divided by bandwidth; a low Q indicates wide bandwidth and good axial resolution.
Question 3: In a linear array transducer, electronic focusing in the elevation plane is achieved by:
- Time-delay steering of individual elements
- A fixed acoustic lens (Correct answer)
- Variable aperture selection
- Changing the PRF
Correct answer: A fixed acoustic lens
Elevation-plane focusing in a linear array is fixed and accomplished by a curved acoustic lens bonded to the transducer face.
Question 4: What is the primary purpose of the matching layer in a transducer?
- Increase the transducer's center frequency
- Reduce acoustic impedance mismatch between crystal and tissue (Correct answer)
- Protect the piezoelectric element from mechanical damage
- Absorb backward-propagating sound waves
Correct answer: Reduce acoustic impedance mismatch between crystal and tissue
The matching layer minimizes reflection at the crystal-tissue interface by presenting an intermediate acoustic impedance, maximizing energy transmission.
Question 5: Lateral resolution in a single-element focused transducer is BEST at the:
- Near field only
- Far field only
- Focal zone (Correct answer)
- Transducer face
Correct answer: Focal zone
Lateral (azimuthal) resolution is best at the focal zone where the beam is narrowest.
Question 6: Which transducer array configuration uses a convex curved surface to produce a fan-shaped image wider than the footprint?
- Linear sequenced array
- Phased array
- Curvilinear array (Correct answer)
- Annular array
Correct answer: Curvilinear array
A curvilinear (convex) array has elements arranged along a curved surface, producing a trapezoidal or sector image that widens beyond the transducer footprint.
Question 7: The spatial pulse length of a transducer is determined by the number of cycles in a pulse multiplied by the:
- Pulse repetition period
- Propagation speed divided by frequency
- Wavelength
- Both B and C (they are equivalent) (Correct answer)
Correct answer: Both B and C (they are equivalent)
Wavelength equals propagation speed divided by frequency, so spatial pulse length = number of cycles × wavelength = number of cycles × (speed/frequency).
ARDMS SPI Transducer Construction and Function 2
Which material property is most important for a transducer backing layer?