Ch 9: Sound Beams Flashcards
This is the location where the beam is the narrowest.
focus or focal point
The width of the sound beam at the focus is ___ the width of the beam as it leaves the transducer.
one half
This is the region from the transducer to the focus.
near zone, near field, Fresnel zone
This is the distance from the transducer to the focus.
focal depth, near zone length
This is the region that starts at the focus and extends deeper.
far field, Fraunhofer zone
When the beam is two near zone lengths from the transducer, the beam is ___ as the active element.
the same size
At depths more than two near zone lengths, te beam is ___ than the active element.
wider
This is a region around the focus where the beam is relatively narrow.
focal zone
Adjustable focus systems are called…
phased array.
What characteristics of a fixed focus transducer determine the focal depth?
- transducer diameter
- frequency of sound
How does transducer diameter affect the focal depth?
The larger the diameter, the deeper the focus.
Transducer diameter and focal depth are ___ related.
directly
How does frequency affect focal depth?
The higher the frequency, the deeper the focus.
Frequency and focal depth are ___ related.
directly
This describe the gradual spread of the u/s beam in the far field.
beam divergence
What characteristics of a transducer determine the spread of the beam in the far field?
- transducer diameter
- frequency of the sound
How does transducer diameter affect beam divergence in the far field?
The smaller the diameter, the larger the spread of the far field.
Crystal diameter and beam divergence are ___ related.
inversely
___ diameter crystals improve lateral resolution in the far field.
Larger
How does frequency alter beam divergence in the far field?
The lower the frequency, the larger the spread of the far field.
Frequency and beam divergence are ___ related.
inversely
___ frequency sound improves lateral resolution in the far field.
Higher
Sound waves produced by small sources diverge in the shape of a ‘V’ called…
Huygens’ wavelets, spherical waves, diffraction paterns
The small sources of sound producing Huygens’ wavelets are known as…
Huygens’ sources.
___ describes why ‘V’ shaped wavelets form an hourglass-shaped beam.
Huygens’ Principle
