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SPI Chapter 9

Sound Beams

QuestiosAnswer
What is the shape of a sound beam? at the start it is the same as the transducer, the beam narrows progressively until it reaches its smallest diameter. After that the beam expands
What 5 regions consist the anatomy of a sound beam? focus, near zone, focal length, far zone, and focal zone
What is focus or (focal point)? the narrowest part of the beam
What is the near zone (near field or Fresnel zone)? the region closest to the transducer
What is focal length (focal depth, near zone length)? the distance from the transducer to the focus
What is far zone (far field or Fraunhofer zone)? far zone from transducer
What is focal zone? where the beam is relatively narrow
What are adjustable focus systems called? phased array
What are two factors that determine the focal depth? transducer diameter and frequency of sound
What is the transducer diameter directly related to? focal depth
What is the frequency directly related to? focal depth
What does higher frequency sound create? a deeper focus
What does a very small diameter obtain? high frequency crystals
What is focal depth formula? focal depth (mm) = diameter (mm)^2 x frequency (MHz)/6 or focal depth (mm) = diameter (mm)^2/4 x wavelength (mm)
What is beam divergence? gradual spread of ultrasound beam in the far field
What 2 characteristics determine beam divergence? transducer diameter and frequency of sound
What is the crystal diameter inversely related to? beam divergence
What do larger diameter crystals improve? lateral resolution in the far field
What is the frequency inversely related? beam divergence
What does higher frequency improves lateral resolution in the far field
What is the formula that describes the effect of transducer diameter and frequency on beam divergence? sin divergence angle = 1.85/diameter (mm) x frequency (MHz) or sin divergence angle = 1.2 x wavelength/diameter
When is the V-shaped wave created? is created when the sound is about the size of the sound's wavelength
What are other synonyms of V-shaped waves? spherical waves, diffraction patterns, or Huygens' wavelets
What explains a sound beam created by a disc-shaped crystal is hourglass shaped? Huygens' Principle
Created by: Lazacha
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