Chapter 9 Flashcards
At the starting point, the beam width is exactly the same as the ______.
transducer diameter
what 5 terms describe the shape of the sound beam?
focus, near zone, focal length (near zone length), far zone, focal zone
______ is the location where the beam is the narrowest
focal point
For a disc-shaped crystal, the width of the sound beam at the focus is ______ the width of the beam as it leaves the transducer
one-half
the ______ is the region from the transducer to the focus
near zone, near field, or fresnel zone
at the end of the near zone, the beam narrows to only ______ the width of the active element, the focus is located at the end of this zone
one-half
______ is the distance from the transducer to the focus
focal length, focal depth, or near zone length
______ is the region that starts at the focus and extends deeper, the beam diverges and spreads out
far field, Fraunhofer zone, or far zone
when the beam is two near zone lengths from the transducer, the beam is again the same as the ______
active element
the ______ is a region around the focus where the beam is relatively narrow
focal zone
reflections arising from the focal zone create images that are more ______ than those from other depths
accurate
Half of the focal zone is in the ______ field, the other half is in the ______ field
near, far
when the beam is deeper than 2 near zone lengths the beams diameter is ______ than the transducers diameter.
wider
the ______ marks the end of the near zone and also marks the beginning of the far zone
focus
adjustable focus systems are called ______
phased array
what 2 factors determine the focal depth in a fixed focus transducer
transducer diameter, frequency of the sound
transducer diameter and focal depth are ______ related
directly
frequency and focal depth are ______ related
directly
smaller diameter PZT and lower frequency has a ______ focus
shallow
larger diameter PZT and higher frequency has a ______focus
deep
what is the equation for focal depth
focal depth= (diameter (mm)2 x frequency (MHz)) / 6 or diameter (mm)2 /( 4 x wavelength (mm))
Deeper than the focus, the sound beam spreads out, or ______
diverges
______ describes the gradual spread of the ultrasound beam in the far field
beam divergence
what two factors determine beam divergence?
transducer diameter and frequency of the sound
crystal diameter and beam divergence are ______ related
inversely
large diameter crystals and a higher frequency improve ______ resolution in the far field
lateral
Larger diameter and higher frequency produce ______ divergence in the far field
less
smaller diameter and lower frequency produce ______ divergence in the far field
more
frequency and beam divergence are ______ related
inversely
what is the equation for divergence angle?
sin divergence angle = 1.85 / (diameter (mm) x frequency (MHz)) or 1.2 x wavelength / diameter
sounds waves produced by very small sources diverge in a ______ shape
V
the V-shaped waves are known as ______
spherical waves, diffraction patterns, or Huygen’s wavelets
the small sources of sound producing the V-shaped wavelets are known as ______
Huygens sources
______ states that a large active element may be thought of as millions of tiny, distinct sound sources
Huygen’s principle
the hourglass shape produced by a large crystal is the result of ______ of the many Huygen’s sound wavelets emitted from these numerous sound sources
interference
the shape of an imaging transducers emitted sound beam based upon ______ and ______ wavelets interfering with each other
in-phase and out-of-phase
